EE1252 – POWER PLANT ENGINEERING Questions Bank 2014


Anna University, Chennai

Anna_University,_Chennai_logo

EE1252 POWER PLANT ENGINEERING

II YEAR / IV SEM – EEE

QUESTION BANK

UNIT I - THERMAL POWER PLANTS PART A (2 marks)

1. What is a thermodynamic cycle?

2. What are the assumptions made for air standard cycle analysis?

3. Define air standard cycle efficiency.

4. List out the major advantages of high pressure boilers in modern thermal power plants.

5. What is the function of economizer?

6. What are the modern trends in generating steam of high pressure boiler?

7. What are types of fluidized bed boilers?

8. What are all the features of the high-pressure boilers?9. What is cooling tower approach?

10. What the advantages of burning coal are in pulverized from?

PART B (16 marks)

1. Explain the construction and working of Steam power plant with a layout. (16)2. (a) Why are feed water heaters used? (8)

(b) Explain with a sketch the working of a Barometric condenser? (8)

3. (a) Discuss the relative merits of different out plant coal handling. (8) (b) Describe the hydraulic ash handling system. (8)

4. (a) Draw a chart showing operations and devices used in coal handling plant. (8) (b) Describe different types of coal conveyors. (8)

5. What is the importance of thermal power development in the country? Describe its development in the last 10 years. (16)

6. Explain the construction and working of any one High pressure boiler with a layout. (16)

7. Explain the construction and working of any one Fluidised bed boiler with a layout. (16)


UNIT II - HYDRO ELECTRIC POWER PLANTS PART A (2 marks)

1. What is the purpose of surge tank in a hydroelectric power plant?

2. What are the three main factors for power output of hydroelectric plant?

3. Give an example for a low head turbine, a medium head turbine and a high head turbine.

4. What are reaction turbines? Give example.

5. Differentiate the impulse and reaction turbine.

6. Define unit speed of turbine.

7. What is the significance of specific speed of hydraulic turbines?

8. What is the function of surge tank in a hydro electric power plant?

9. What is a draft tube? In which type turbine it is mostly used?

10. Write the function of draft tube in turbine outlet?

PART B (16 marks)

1. Explain the construction and working of Hydel power plant with a layout. (16)

2. What are the various factors to be considered in selecting the site for a hydro electric power plant and sicuss about primary and secondary investigations. (16)

3. Explain the design aspects of a pelton wheel. (16)

4. Describe the classification of turbines. (16)

5. What the components of the Francis turbine and describe briefly. (16)

6. (a) Explain in detail the spillways, baffle piers and drainage gallery. (8)

(b) Explain the various factors to be considerd in the selection of a hydraulic turbine. (8)

7. (a) What is surge tanks and state its purpose. (8)

(b) Differentiate Francis turbine between Kaplan turbines. (8)

8. (a) Explain the terms catchment area, rain fall and run off. (8)

(b) Explain the arrangement of the components of a hydro electric power plant with a neat sketch. (8)


UNIT III - NUCLEAR POWER PLANTS PART A (2 marks)

1. How the nuclear reactors are classified?

2. Give the requirements of chain reaction.

3. What is “half life” of nuclear fuels?

4. What do you understand by moderation?

5. Explain the function of the moderator.

6. Define the term “Breeding”.

7. What factors control the selection of a particular type of a reactor?

8. What are the components pressurized water reactor nuclear power plant?

9. What are the components of supercritical water reactor nuclear power plant?

10. List down the nuclear waste disposal methods.

PART B (16 marks)

1. Explain the construction and working of Nuclear power plant with a layout. (16)

2. (a) What is a chain reaction? How it is controlled. (5) (b) Describe the fast breeder reactor. (6)

(c) What is function of shield? What are the different types of shields? (5)

3. (a) With neat sketch explain the boiling water reactor power plant. (8)

(b) What are the advantages and disadvantages of nuclear power plant? (8)

4. (a) What are the advantages and disadvantages of breeder reactor? (5) (b) What do you mean by fission of nuclear fuel? (5)

(c) Explain briefly about radiation hazards and shielding? (6)

5. (a) What do you understand by thermal shielding? (4) (b) What are the functions of a reflector? (4)

(c) Explain the working and characteristic features of a homogeneous reactor. (8)


UNIT IV - GAS AND DIESEL POWER PLANTS PART A (2 marks)

1. What are the main units in a gas turbine power plant?

2. How the gas turbine blades are cooled?

3. Mention the various processes of the brayton cycle.

4. Define mean effective pressure as applied to gas power cycles.

5. How it is related to indicated power of an I.C. engine?

6. Draw the p-V and T-s diagram of Brayton cycle.

7. Sketch the schematic arrangement of open cycle gas turbine plant and name the components.

8. Discuss the effect of inter colling in a gas turbine plant.

9. What is the principle of operation of simple jet propulsion system?

10. Why is the maximum cycle temperature of gas turbine plant much lower than that of diesel power plant?

11. List out the inherent advantages of the combined power cycle.

PART B (16 marks)

1. Explain the construction and working of Gas turbine power plant with a layout. (16)2. (a) Explain with the help of a block diagram the fuel storage and supply system of diesel power plant. (8)

(b) Explain with the help of a block diagram the water cooling system of diesel power plant. (8)

3. (a) Mention the advantages and disadvantages of a diesel power plant over a gas turbine power plant. (8)

(b) Give a maintenance schedule for Diesel engine power plant. (8)

4. Describe the following systems in brief with respect Diesel Power Plant. (a) Fuel storage and supply system (5)

(b) Exhaust system (5)

(c) Lubrication system (6)

5. (a) Draw a neat layout of a diesel power plant and label all the components. (10) (b) List the advantages of diesel power plant s over other thermal power plants. (6)

6. (a) Explain the cooling system of a Diesel power plant. (8)

(b) What are the different types of engines used in Diesel power plants. (8)

7. With a neat sketch explain the working of a simple constant pressure gas turbine. Mention its advantages and disadvantages. (16)

8. (a) With help of a block diagram explain the main components of a open cycle

gas turbine power plant. (8)

(b) Give the classification of gas turbine power plants. (8)

9. (a) Give the advantages and disadvantages of open cycle gas turbine power plant.

(b) A simple open cycle gas turbine plant works between the pressures of 1 bar and 6 bar and temperatures of 300 K and 1023 K. The calorific value of the fuel used is 42

MJ/kg. Find :

i. airfuel ratio

ii. Thermal efficiency of the plant if the mechanical and generating efficiencies are 95%

and 97% respectively. Assume air flow = 20 kg/s and compression and expansion are isentropic. (8)


UNIT V - NON – CONVENTIONAL POWER GENERATION PART A (2 marks)

1. What is geothermal energy?

2. What are the application of geothermal energy?

3. What are the different geothermal fluids?

4. What are the forms of geothermal energy stored deeply inside the earth?

5. What are the important criteria while selecting the geothermal energy?

6. What are the different types of geothermal energy deposits?

7. What are the different working fluids in binary cycle geothermal power plants?

8. What are the different types of OTEC?

9. What are the working fluids in closed cycle OTEC?

10. What are the components of Tidal power plants?

PART B (16 marks)

1. Explain the construction and working of Geo thermal power plant. (16)

2. What are the different types of geothermal energy system? (16)

3. Explain the working principle of OTEC. (16)

4. What are the different types of Tidal power plants? (16)

5. Explain the Solar thermal central receiver system. (16)

6. What are the different types of ocean thermal energy conversion system? (16)

7. Explain the analysis of a central receiver system. (16

EE1251- ELECTRICAL MACHINES – I Questions Bank 2014


Anna University, Chennai

Anna_University,_Chennai_logo

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

QUESTION BANK

SUBJECT CODE & NAME:EE1251- ELECTRICAL MACHINES – I YEAR / SEM : II / IV

UNIT-I

PART-A

1.What is reluctance?

2.What is stacking factor?

3. What is leakage flux?

4. What is fringing effect?

5. Compare electric and magnetic circuits.

6.What is statically induced emf?

7.What is dynamically induced emf?

8.State the three basic types of rotating electrical machines.

9.State two types of induction motors.

10.What are the different types of induced emfs? Give Examples.

11.What are the types of magnetic losses?

12.Define the term self inductance.

13.Define the term mutual inductance.

14.Define coefficient of coupling.

15. State Lenz’s law.

16. Write equation for energy density for a magnetic circuit.

17. What are the factors on which hysteresis loss depends?

18.What is core loss? What is its significance in electric machines?

19. What is eddy current loss?

20.How are hysteresis and eddy current losses minimized? PART-B

1.(a) Explain about the magnetization curve of Ferro –magnetic material. (8) (b) Derive the relation between mutual inductance and self inductances of two

Magnetically coupled coils (8)

2.(a) Explain AC operation of magnetic circuits. (8)

(b) Explain in detail about hysteresis and eddy current losses. (8)

3.(a) Write in detail about magnetically induced emf &force. and derive the relevant

Expression. (8)

(b) An electromagnetic relay has an exciting coil of 800 turns. The coil has a cross section of 5 cm x 5cm . find

1. coil inductance if the air gap length is 0.5 cm.

2. field energy stored for a coil current of 1.25 A

3. Permeance at air gap (8)

4. Explain in detail about three basic rotating electric machine types (16)

5.(a)Compare magnetic and electric circuit. (8)

(b) An iron rod 1.8 cm diameter is bent to form a ring of mean diameter 25cm and wound with 250 turns of wire . a gap of 1mm exists in between the end faces. calculate the current required to produce a flux of 0.6mWb. take relative permeability of iron as 1200 (8)

6.(a)Explain the two different types of magnetic circuits with neat diagram. (8) (b)When two coils are connected in series, their effective inductance is found to be 10H .When the connections of one coil are reversed , the effective inductance is 6H.If the coefficient of coupling is 0.6, calculate the self inductance of each coil and the mutual inductance. (8)


UNIT-II TRANSFORMERS

PART-A

1.Mention the difference between core and shell type transformers.

2.What is the purpose of laminating the core in a transformer?

3.Give the emf equation of a transformer and define each term.

4.Does transformer draw any current when secondary is open? Why?

5. Define voltage regulation of a transformer.

6.Full load copper loss in a transformer is 1600W. what will be the loss at half load?

7. Define all day efficiency of a transformer.

8. Why transformers are rated in kVA?

9. What are the typical uses of auto transformer?

10. What are the application of step-up & step-down transformer?

11. How transformers are classified according to their construction?

12. Explain on the material used for core construction?

13.How does change in frequency affect the operation of a given Transformer?

14.What is the angle by which no-load current will lag the ideal applied voltage?

15. List the arrangement of stepped core arrangement in a transformer.

16. What is the function of transformer oil in a transformer?

17. Distinguish power transformers & distribution transformers.

18.What are properties of an ideal transformer?

19. Give the condition to be satisfied for parallel operation of transformer.

20.What are different losses occurring in a transformer?

PART-B

1. (a) Explain the principle and operation of auto transformer. (8)

(b)Draw and explain the no load phasor diagram of a single phase transformer

(8)

2. (a)Derive the emf equation of single phase transformer. (8)

(b) A 120kVA, 6000/400V, Y/Y, 3-phase, 50Hz transformer has a iron loss of 1800W. The maximum efficiency occurs at ¾ full loads. Find the efficiency of the transformer

at

(i) Full load and 0.8 pf

(iii) The maximum efficiency at unity pf. (8)

3.A100 kVA, 6.6kV/415V, single phase transformer has an effective impedance of (3+8j) _ referred to HV side. Estimate the full load voltage regulation at 0.8 pf lagging and 0.8 leading pf. (16)

4.(a)Explain the working of auto transformer and prove that when transformation ratio approaches unity, the amount copper used approaches smaller value. (8)

(b)The emf per turn of a single phase, 6.6kV/440V, 50 Hz transformer is

approximately 12V. Calculate the number of turns in the HV and LV windings and the net cross sectional area of the core for a maximum flux density of 1.5T. (8)

5. (a)Obtain the equivalent circuit of a 200/400V,50Hz,single phase transformer from

the following test data:

OC test: 200V,0.7A,70W on LV side

SC test: 15V,10A,85W on HV side (10)

(b)With the help of circuit diagrams, explain any two types of three phase transformer connections (6)

6. Find the all day efficiency of a 500kVA, distribution transformer whose iron loss and

full

load copper loss are 1.5kW and 6kW respectively. In a day it is loaded as follows: Duration(Hi) Output(Po) in kW Power factor(cosØ2)

6 400 0.8

10 300 0.75

4 100 0.8

4 0 - (16)

7. Draw the circuit diagrams for conducting OC and SC tests on a single phase transformer. Also explain how the efficiency and voltage regulation can be estimated

by these tests. (16)

8. What is the sumpner’s test? Draw the circuit diagram to conduct this test and explain its principle. (16)

9.(a) Derive the condition for maximum efficiency in a transformer (8)

(b) A11000/230 V,150 KVA ,1-phase ,50 Hz transformer has core loss of 1.4kW

and F.L cu loss of 1.6 Kw .determine

(i) The kVA load for maximum efficiency and the value of maximum efficiency at unity p.f

(ii) The efficiency at half F.L 0.8 pf leading (8)

10. Explain in detail about parallel operation of single phase transformers. (16)

11. Data of a 500KVA, 3300/400 V ,50 Hz ,single phase transformer is given below. S.C test: 1250 W,100 V –secondary short circuited with full load current in it

O.C test : 1000 W –with normal primary voltage .

Calculate the full load regulation and efficiency at a power factor of 0.8(lag) (16)

12.(a) Derive the equivalent circuit of a single phase two winding transformer. (8) (b) The maximum efficiency of a single phase 250kVA,2000/250 V transformer occurs at 80% of full load and is equal to 97.5% at 0.8 pf .determine the efficiency and regulation on full load at 0.8pf lagging if the impedance of the transformer is 9 percent (8)

13.Explain in detail about tap changing of transformers. (16)


UNIT-III

ELECTROMECHANICAL ENERGY CONVERSION PART-A

1.Write the energy balance equation of a motor.

2.What is the energy conversion medium in a singly-excited magnetic field system?

3.What is the basic feature of an electro magnetic energy conversion devices?

4.Why does the energy storage in a magnetic material occurs mainly in the air gap?

5. What is multiply excited magnetic field system?

6. Give the relation between energy and co-energy for linear system.

7.Give an examples for each of single and multiple excited system

8. Write the applications of singly and doubly fed magnetic systems.

9.Why the field in rotating machines should be quasi-static in nature?

10.What are the causes for irrecoverable energy loss when the flux in the magnetic circuitundergoes a cycle

11.Why the relationship between current & coil flux linkages of electromechanical energy conversion devices are linear

12. With respect to the magnetic field ,in which direction does the force act?PART-B

1. Explain in detail about energy in magnetic system (16)

2. (a) With one example derive the co-energy of a multi excited magnetic field system

(8)

(b) two coupled coils have self and mutual inductance of

L11 = 3+0.5 x ;L22 = 2+0.5x ; L12= L21=0.3x

Over a certain range of linear displacement x. The first coil is excited by a constant current of 15A and the second by a constant current of -8A.

(i)Mechanical work done if x changes from 0.6 to1m

(ii)Energy supplied by each electrical source in part 1 (8)

3.(a) With neat sketch explain the multiple excited magnetic field system in electro mechanical energy conversion systems. Also obtain the expression for field

energy in the system. (8)

(b) Draw and explain the general block diagram of an electromechanical energy conversion device (8)

4. Two coupled coils have self and mutual inductance of L11=2+1/(2x); L22=1+1/(2x): L12= L21=1/(2x). Over a certain range of linear displacement x. The first coil is

excited by a constant current of 20A and the second by a constant current of -10A. (i) Mechanical work done if x changes from 0.5to1m

(ii) Energy supplied by each electrical source in part 1 (iii) Change in field energy in part1

Hence verify that the energy supplied by the sources is equal to the increase in field energy plus the mechanical work done (16)

5. Explain the i-_ characteristics of a magnetic system .also derive expression for co energy density assume the i-_ relationship of the magnetic circuit is linear (16)

6. Consider an attracted armature relay is exited by an electric source.Explain about the mechanical force developed and the mechanical energy output with necessary equations. For linear and non linear cases. (16)


UNIT-IV

BASIC CONCEPTS OF ROTATING MACHINES PART-A

1. Explain the following terms with respect to rotating electrical machines

2. State advantages of short- pitched coils.

3. Define rotating magnetic field

4. Define pitch factor.

5. Give the equation for emf generated in D.C.machine.

6. Define winding factor.

7.What are distributed windings?

8.How is voltage generated in rotating machines?

9. Write the torque equation for round rotor machine.

10.Which type of winding is suitable for ac machines?

PART-B

1. (a) Derive an expression for the generated emf in synchronous machines. (8)

(b) A 50 Hz synchronous salient pole generator is driven at 125 rpm .there are 576 stator slots with two conductors per slot .air gap diameter is 6.1 m and stator length

is 1.2m . sinusoidal flux density has a peak of 1.14T.Calculate the line voltage

induced for star connection. (8)

2. Derive the torque equation of a round rotor machine. Also clearly state what are the assumptions made? (16)

3. Write in detail about the MMF space wave of three phase distributed winding. (16)

4. Explain in detail about construction of synchronous machine (16)

5. Write in detail about magnetic fields in rotating machines. (16)

6. (a) Explain with neat diagram the concept of MMF space wave of single coil (8) (b) A 3-phase ,400 kVA ,50 Hz star connected alternator (synchronous generator) running at 300 rpm is designed to develop 3300 V between terminals .the armature consists of 180 slots ,each slot having one coil side with 8 conductors . Determine the peak value of the fundamental mmf in AT/pole when the machine is delivering full load current. (8)

7. (a) A 3-phase 50 kW ,4-pole ,50 Hz induction motor has a winding (ac) designed for delta connection . the winding has 24 conductors per slot arranged in 60 slots.The

rms value of the line current is 48A. find the fundamental of the mmf wave of phase

–A when the current is passing through its maximum value . what is the speed and peak value of the resultant mmf/pole? (8)

(b) Explain in detail about torque –production process of synchronous

machine(motoring) (8)

8.(a) Explain in detail about torque -production process of synchronous machine(generating) (8)

(b)A 50 Hz ,400v ,4-pole cylindrical synchronous generator has 36slots,two –layer

winding with full pitch coils of 8 turns each. The mean air –gap diameter is

0.16m,axial length 0.12m and a uniform air gap of 2mm. calculate the value of the

resultant AT/pole and the peak air gap flux density . the machine is developing

an electromagnetic torque of 60 Nm as a generator at a torque angle of 260 .what should be the rotor AT/pole? what is the stator AT and the angle it makes with

the resultant AT? Also find the stator current. (8)


UNIT-V

DC MACHINES PART-A

1 Write down the emf equation for d.c.generator.

2. Why the armature core in d.c machines is constructed with laminated steel sheets instead of solid steel sheets?

3. Why commutator is employed in d.c.machines?

4.Distinguish between shunt and series field coil construction.

5.How does d.c. motor differ from d.c. generator in construction?

6.How will you change the direction of rotation of d.c.motor?

7. What is back emf in d.c. motor?

8. What is the function of no-voltage release coil in d.c. motor starter?

9. Enumerate the factors on which speed of a d.c.motor depends.

10. Under What circumstances does a dc shunt generator fails to generate?11. Define critical field resistance of dc shunt generator.

12.Why starter is necessary for a dc motor?

13.What are the conditions to be fulfilled by for a dc shunt generator to build back emf?

14. Define armature reaction .

15. What are the different methods of speed control in dc motor?

16. When you will say the motor is running at base speed?

17. List out the different methods of speed control employed for dc series motors

18.What are the losses occurring in a dc machine?

19. What are the drawbacks of brake test on DC machines?.

20.What is a regenerative test?

PART-B

1.(a)Describe with sketches the construction of a DC machine. (8) (b)Derive the EMF equation of DC generator. (8)

2.Draw and explain the no-load and load characteristics of DC shunt, series and compound generators. (16)

3.Explain the effect of armature reaction in a DC shunt generator. How are its demagnetizing and cross-magnetizing ampere turns calculated? (16)

4.Explain the process of commutation in a DC machine. (16)

5.With a aid of a circuit diagram, describe the procedure for paralleling two DC shunt generators and for transferring the load from one machine to the other. (16)

6.A 4-pole, 50 kW, 250 V, wave wound shunt generator has 400 armature conductors.

Brushes are given a lead of 4 commutator segments. Calculate the demagnetization ampere-turns per pole if shunt field resistance is 50 ohm. Also calculate extra shunt field turns per pole to neutralize the demagnetization. (16)

7.A 4-pole, lap connected DC machine has 540 armature conductors. If the flux per pole is .03 Wb and runs at 1500 RPM, determine the emf generated. If this machine is driven as a shunt generator with same field flux and speed, calculate the line current if the terminal voltage is 400V.Given the RSH=450_ and RA=2 _. (16)

8.Two separately excited DC generators are connected in parallel and supply a load of

200A. The machines have armature circuit resistances of 0.05 _ and 0.1 _ and induced emfs of 425V and 440V respectively. Determine the terminal voltage, current and power output of each machine. The effect of armature reaction is to be neglected. (16)

9.(a) Explain the principle of operation of a DC motor. (8)

(b) A shunt machine , connected to a 200V mains has an armature resistance of

0.15 _ and field resistance is 100 _. Find the ratio of its speed as a generator to its speed as a motor, line current in each case being 75 A. (8)

10 (a) Draw and explain the mechanical characteristics of DC series and shunt motor.

(8)

(b) A 230V, DC shunt motor, takes an armature current at 3.33A at rated voltage and at a no load speed of 1000RPM. The resistances of the armature circuit and field

circuit are 0.3 _ and 160 _ respectively. The line current at full load and rated

voltage is 40A. Calculate, at full load, the speed and the developed torque in case the armature reaction weakens the no load flux by 4%. (8)

11. (a)Describe the working of 3 point starter for DC shunt motor with neat diagram. (8) (b)Explain Ward-Leonard method of speed control in DC motors. (8)

12.(a)Derive an expression for the torque developed in a DC machine. (8)

(b)A 220V, Dc shunt motor with an armature resistance of 0.4 _ and a field resistance of 110 _ drives a load , the torque of which remains constant. The motor draws

from the supply, a line current of 32A when the speed is 450 RPM. If the speed is

to be raised to 700RPM, what change must be effected in the value of the shunt field circuit resistance? Assume that the magnetization characteristics of the motor is a straight line. (8)

13.Explain the different methods used for the speed control of D.C. shunt motor. (16)

14.With the help of neat circuit diagram, explain swinburne’s test and derive the relations for efficiency (both for generator and motor)also state the merits and demerits of this method (16)

15.(a)Explain in detail about circuit model of D.C. machine. (8)

(b) A 440 V D.C shunt motor takes 4A at no load . its armature and field resistances are 0.4 ohms and 220 ohms respectively .estimate the kW output and efficiency when the motor takes 60A on full load. (8)

16.(a) Derive an expression for the torque developed in the armature of a D.C. motor.(8) (b) Determine developed torque and shaft torque of 220V, 4 pole series motor with

800 conductors wave-connected supplying a load of 8.2 kW by taking 45A from

the mains. The flux per pole is 25m/Wb and its armature circuit resistance is

0.6_. (8)

17.With the help of neat circuit diagram, explain Hopkinson’s test and derive the relations for efficiency (both for generator and motor)also state the merits and demerits of this method. (16)

18. (a) Explain in detail about different methods of excitation. (8) (b) Derive the expression for efficiency of D.C. machines. (8)

*********** X ***********

EE1302 TRANSMISSION AND DISTRIBUTION Questions Bank 2014


Anna University, Chennai

Anna_University,_Chennai_logo

SUB CODE: EE1302 SUB NAME: TRANSMISSION AND DISTRIBUTION

UNIT-I

TRANSMISSION SYSTEM - INTRODUCTION PART-A

1. What is meant by power supply system? (2)

2. What is meant by Transmission and Distribution system? (2)

3. What are the different types of Power supply system? (2)

4. What are the various components of power supply system? (2)

5. What are the different types of power plants? (2)

6. What are the different operating voltages used for generation, primary and secondary transmission in AC power supply systems in India? (2)

7. Define feeder, distributor and service mains. (2)

8. List the advantages of high voltage transmission. (2)

9. State Kelvin’s law. (2)

10. What are the limitations of Kelvin’s law? (2)

PART-B

1. (i) Discuss various types of HVDC links. (8)

(ii) List out the main components of a HVDC system. (8)

2. (i) Draw and explain the structure of modern power systems with typical

voltage levels (13)

(ii) What is the highest voltage level available in India? (3)

3. (i) Explain the effect of high voltage on volume of copper and on efficiency. (8)

(ii) Explain why the transmission lines are 3 phase 3-wire circuits while distribution lines are 3 phase 4-wire circuits. (8)

4. (i) Draw the model power system with single line representation. Show its essential constituent sections. (6)

(ii) What are the AC transmission and distribution level voltages we have in

India? (4)

(iii) What are the different kinds of DC links? Draw relevant diagrams. (6)

5. (i) Explain why EHV transmission is preferred? What are the problems

involved in EHV AC transmission? (8)

(ii) With neat schematic, explain the principle of HVDC system operation. (8)

6. Explain about FACTS with neat diagram (16)

7. Explain TCSC and SVS systems (16)

8. Explain with neat diagram about STATCOM and UPFC (16)

9. (i) Compare EHVAC and HVDC transmission (8)

(ii) Explain the applications of HVDC transmission system (8)


UNIT- II TRANSMISSION LINE PARAMETERS PART-A

1. Define Skin effect. (2)

2. What is meant by proximity effect? (2)

3. Differentiate the stranded conductor and bundled conductor. (2)

4. List out the advantages of double circuit lines. (2)

5. Define - Self and mutual – G.M.D. (2)

6. What is meant by inductive interference? (2)

7. What is transposition of conductors? (2)

8. What is ACSR conductor? (2)

9. What is fictitious conductor radius? (2)

10. Define unsymmetrical and symmetrical spacing. (2) PART-B

1. From the fundamentals derive an expression for inductance of a single phase transmission system. (16)

2. Derive an expression for capacitances of a single phase transmission system and discuss the effect of earth on capacitance with suitable equation. (16)

3. Derive an expression for inductance

i) Of a single-phase overhead line. (8)

ii) A conductor is composed of seven identical copper strands

each having a radius r. Find the self-GMD of the conductor. (8)

4. i) Derive an expression for the capacitance between conductors of a

Single phase overhead line. (8)

ii) Find the capacitance between the conductors of a single-phase 10 km long line. The diameter of each conductor is 1.213cm. The spacing between conductors is 1.25m. Also find the capacitance of each conductor

neutral. (8)

5. i) Derive the expression for inductance of a two wire 1Φ transmission line (8)

ii) Derive the expression for capacitance of a 1Φ transmission line (8)

6. i) What are the advantages of bundled conductors? (4) ii) Derive the expression for capacitance of a double circuit line for hexagonal spacing. (8) iii) Why is the concept of self GMD is not applicable for capacitance? (4)

7. i) Explain clearly the skin effect and the proximity effects when referred to overhead lines. (8)

ii) Write a short note on the inductive interference between power and communication lines. (8)

8. i) Derive the expression for the capacitance per phase of the 3 Φ double circuit

line flat vertical spacing with transposition. (8)

ii) A 3 Φ overhead transmission line has its conductors arranged at the corners of an equilateral triangle of 2m side. Calculate the capacitance of each line conductor per km. Given the diameter of each conductor is 1.25cm. (8)

9. Find the capacitance per km per phase of a 3Φ line arrangement in a

horizontal plane spaced 8 metres apart. The height of all conductors above the earth is 13 metres. The diameter of each conductor is 2.6 cm. the line is

completely transposed and takes the effect of ground into account. (16)

10. Discuss the concept of GMR and GMD in the calculation of transmission line inductance. (16)


UNIT-III

MODELLING AND PERFORMANCE OF TRANSMISSION LINES PART-A

1. Classify overhead transmission lines. (2)

2. Define transmission efficiency. (2)

3. List out the methods of representation of medium transmission lines. (2)

4. What is Ferranti effect? (2)

5. Define regulation of power transmission line. (2)

6. What is stringing chart? What are the uses of stringing chart? (2)

7. Define corona. What is local corona? (2)

8. Define sag. (2)

9. What are the methods adopted to reduce corona? (2)

10. What is the use of power circle diagram? (2) PART-B

1. Determine the efficiency and regulation of a 3phase, 100Km, 50 Hz transmission line delivering 20 MW at a power factor of 0.8 lagging and 66 kV to a balanced load. The conductors are of copper, each having resistance

0.1 Ω / Km, 1.5 cm outside dia, spaced equilaterally 2 metres between centres.

Use nominal T method. (16)

2. A three phase 5 km long transmission line, having resistance of 0.5 Ω / km and inductance of 1.76mH/km is delivering power at 0.8 pf lagging. The receiving end voltage is 32kV. If the supply end voltage is 33 kV, 50 Hz, find line current, regulation and efficiency of the transmission line. (16)

3. Derive the expressions for sending end voltage in nominal T method and end

Condenser method. (16)

4. i) What is an equivalent π circuit of long line? Derive expression for

parameters of this circuit in terms of line parameters. (8)

ii) A 50Hz transmission line 300 km long total series impedance of 40+j25 Ω and total shunt admittance of 10-3 mho. The 220 KV with 0.8 lagging power factor. Find the sending end voltage, current, power and power factor using nominal π method. (8)

5. i) Define regulation of a transmission line and derive the approximate expression for the regulation of a short transmission line. (8)

ii) What is corona loss? How do you determine this loss? (8)

6. A 220kV, 3Φ transmission line has an impedance per phase of (40+j200)Ω and an admittance of (0+j0.0015) mho. Determine the sending end voltage and sending end current when the receiving end current is 200 A at 0.95 pf

lagging. Use nominal T method. (16)

7. Determine the efficiency and regulation of a three phase 200 km, 50Hz transmission line delivering 100MW at a pf of 0.8 lagging and 33kV to a balanced load. The conductors are of copper, each having resistance

0.1 Ω/km, and 1.5cm outside dia, spaced equilaterally 2m between centres.

Neglect leakage reactance and use nominal T and π methods. (16)

8. i) Explain the Ferranti effect with a phasor diagram and its causes. (6) ii) Explain the classification of lines based on their length of transmission. (4) iii) What are ABCD constants. (6)


UNIT-IV INSULATORS AND CABLES PART-A

1. What is the purpose of insulator? (2)

2. What is the main purpose of armouring? (2)

3. What is meant by efficiency of an insulator string? (2)

4. List out various types of insulators used for overhead transmission lines. (2)

5. Mention the advantages of the pin type insulator. (2)

6. What are the main causes for failure of insulators? (2)

7. What are the different tests that are conducted on an insulator? (2)

8 What are the methods for improving string efficiency? (2)

9. Write short notes on puncture test. (2)

10. Define impulse ratio. (2) PART-B

1.Discuss any two methods to increase the value of string efficiency, with

suitable sketches. (16)

2.Explain any two methods of grading of cables with necessary diagrams. (16)

3. i) What are different methods to improve string efficiency of an insulator? (8)

ii) In a 3-unit insulator, the joint to tower capacitance is 20% of the capacitance of each unit. By how much should the capacitance of the lowest unit be increased to get a string efficiency of 90%. The remaining two units are left unchanged. (8)

4. i) Derive the expression for insulator resistance, capacitance and electric

stress in a single core cable.Where is the stress maximum and minimum?(8)

ii) A single core 66kv cable working on 3-phase system has a conductor diameter of 2cm and sheath of inside diameter 5.3cm. If two inner sheaths are introduced in such a way that the stress varies between the same maximum and minimum in the three layers find:

a) position of inner sheaths

b) voltage on the linear sheaths

c) maximum and minimum stress (8)

5.i)Draw the schematic diagram of a pin type insulator and explain its function (8)

ii) A 3 phase overhead transmission line is being supported by three disc insulators. The potential across top unit (i.e. near the tower) and the middle unit are 8kV and 11kV respectively. Calculate,

a) The ratio of capacitance between pin and earth to the self capacitance of each unit (4) b) Line Voltage (2) c) String Efficiency (2)

6. i) Describe with the neat sketch, the construction of a 3 core belted type

cable. (8)

ii) A conductor of 1cm diameter passes centrally through porcelain cylinder of

internal diameter 2 cms and external diameter 7cms. The cylinder is surrounded by a tightly fitting metal sheath. The permittivity of porcelain is 5 and the peak voltage gradient in air must not exceed 34kV/cm. Determine

the maximum safe working voltage. (8)

7. i) What are the various properties of insulators? Also briefly explain about suspension type insulators. (8)

ii) Calculate the most economical diameter of a single core cable to be used on

132kV, 3 phase system. Find also the overall diameter of the insulation, if the peak permissible stress does not exceed 60kV/cm. also derive the formula used here. (8)

8. i) Briefly explain about various types of cables used in underground system.(8)

ii) A string of 4 insulator units has a self capacitance equal to 4 times the pin to earth capacitance. Calculate,

a) Voltage distribution as a % of total voltage

b) String efficiency (8)

9. i) Give any six properties of a good insulator. (4) ii) With a neat diagram, explain the strain and stay insulators. (4) iii) A cable is graded with three dielectrics of permittivities 4, 3 and 2. The

maximum permissible potential gradient for all dielectrics is same and equal to 30 kV/cm. The core diameter is 1.5cm and sheath diameter is

5.5cm. (8)

10.i) Explain the constructional features of one LT and HT cable (8)

ii) Compare and contrast overhead lines and underground cables. (8) UNIT-V

SUBSTATION GROUNDING SYSTEM AND DISTRIBUTION SYSTEM PART-A

1. What is substation? (2)

2. What is earth resistance? (2)

3. What are the classifications of substation according to service? (2)

4. What are the types of transformer substations? (2)

5. What are the factors to be considered for busbar design? (2)

6. What is neutral grounding or neutral earthing? (2)

7. What are the equipments used in a transformer substation? (2)

8. What are the different types of bus bar arrangements in substations? (2)

9. What is bus bar? (2)

10. What are the materials mainly used in busbars? (2) PART-B

1. With a neat sketch explain double bus with double breaker and double bus

with single breaker. State their advantages and disadvantages. (16)

(i) Neutral grounding

 

(ii) Resistance grounding.

(16)

3. Explain about the various types of substations

(16)

4. Write short notes on

 

I. Sub mains

(4)

II. Stepped and tapered mains

(12)

2. Explain the following:

5. Explain the substation bus schemes.

(16)

6. Write short notes on

 

i. Busbar arrangement in substation

(8)

ii. Grounding grids

(8)

7. i) Explain the design principles of substation grounding system.

(8)

ii) Explain the equipments in a transformer substation.

EC1307 DIGITAL SIGNAL Questions Bank 2014


Anna University, Chennai

Anna_University,_Chennai_logo

M.A.M SCHOOL OF ENGINEERING, SIRUGANUR, DEPARTMENT OF ELECTRONICS

&COMMUNICATIONENGINEERING

QUESTION BANK

SUBJECT CODE/NAME: EC1307 DIGITAL SIGNAL PROCESSING

YEAR / SEM : III / V

UNIT – I SIGNALS

PART – A (2 MARKS)

1. Define Signal.

2. Define a system.

3. What are the steps involved in digital signal processing?

4. Give some applications of DSP?

5. Write the classifications of DT Signals.

6. What is an Energy and Power signal?

7. What is Discrete Time Systems?

8. Write the Various classifications of Discrete-Time systems.

9. Define linear system

10. Define Static & Dynamic systems

11. Define causal system.

12. Define Shift-Invariant system.

13. Define impulse and unit step signal.

14. What are FIR and IIR systems?

15. What are the basic elements used to construct the block diagram of discrete time system?

16. Define sampling theorem.

17. Check the linearity and stability of g(n),

18. What are the properties of convolution?

19. Give the classification of signals?

20. What are the types of systems?

21. What are even and odd signals?

22. What are the elementary signals and name them?

23. What are the properties of a system?

24. What is an invertible system?

25. Define unit step, ramp and delta functions for

CT.

26. Define random signals.

27. Define Aliasing.

28. Define Nyquist rate.

29. What are the used to avoid aliasing?

30. Define Sampling theorem.

31. What is Nyquist interval?

32. Define symmetric and Anti symmetric signals. How do you prevent aliasing while sampling a CT

signal?

33. What is SISO system and MIMO system?

34. Define Quantization.

1

35. Write down the exponential form of the Fourier series representation of a Periodic signal?

36. Write down the trigonometric form of the Fourier

series representation of a periodic signal?

37. Write short notes on dirichlets conditions for

Fourier series.

38. State Time Shifting property in relation to

Fourier series.

PART – B

1. Explain in detail about the classification of discrete time systems. (16)

2. (a) Describe the different types of discrete time signal representation. (6)

(b) Define energy and power signals. Determine

whether a discrete time unit step signal x(n) =

u(n) is an energy signal or a power signal. (10)

3. (a) Give the various representation of the given discrete time signal

x(n) = {-1,2,1,-2,3} in Graphical, Tabular, Sequence, Functional and Shifted functional. (10)

(b) Give the classification of signals and explain it. (6)

4. (a) Draw and explain the following sequences:

i) Unit sample sequence ii) Unit step sequence iii) Unit ramp sequence

iv) Sinusoidal sequence and v) Real exponential sequence (10)

(b) Determine if the system described by the following equations are causal or noncausal i) y(n) = x(n) + (1 / (x(n-1)) ii) y(n) = x(n2) (6)

5. Determine the values of power and energy of the

following signals. Find whether the signals are power, energy or neither energy nor power signals.

i) x(n) = (1/3)n u(n) ii) x(n) = ej((π/2)n +

(π/4)

iii) x(n) = sin (π/4)n iv) x(n) = e2n u(n) (16)

6. (a) Determine if the following systems are time- invariant or time-variant

i) y(n) = x(n) + x(n-1) ii) y(n) = x(-n) (4)

(b) Determine if the system described by the following input-output equations are linear or non- linear.

i) y(n) = x(n) + (1 / (x(n-1)) ii) y(n) =

x2(n) iii) y(n) = nx(n) (12)

7. Test if the following systems are stable or not. i) y(n) = cos x(n) ii) y(n) = ax(n)

iii) y(n) = x(n) en iv) y(n) = ax(n)

(16)

8. (a) Determine the stability of the system

2

y(n) – (5/2)y(n-1) + y(n-2) = x(n) – x(n1) (8)

(b) Briefly explain about quantization. (8)

9. (a) Explain the principle of operation of analog to digital conversion with a neat diagram. (8)

(b) Explain the significance of Nyquist rate and aliasing during the sampling of continuous time

signals. (8)

10. (a) List the merits and demerits of Digital signal processing. (8)

(b) Write short notes about the applications of

DSP.

11. A discrete time system can be static or dynamic, linear or non-linear, Time variant or time invariant, causal or non causal, stable or unstable. Examine the following system with respect to the properties also.

(i) y(n) = log10[{x(n)}] (ii) y(n) = x(-n-2)

(iii) y(n) = cosh[nx(n) + x(n-1)]

13. Compute the convolution of the following signals x(n) = {1,0,2,5,4} h(n) = {1,-1,1,-1}

↑ ↑

h(n) = {1,0,1} x(n) = {1,-2,-2,3,4}

↑ ↑

14. Find the convolution of the two signals x(n) = 3nu(-n); h(n) = (1/3)n u(n-2) x(n) = (1/3) –n u(-n-1); h(n) = u(n-1)

x(n) = u(n) –u(n-5); h(n) = 2[u(n) – u(n-3)]

15. a) Determine the impulse response of the filter defined by y(n)=x(n)+by(n1)

b) A system has unit sample response h(n) given

by

1) y(n)=cos(x(n))

2) y(n)=x(-n+2)

3) y(n)=x(2n)

4)y(n)=x(n) cos ωn

12. a) i) Determine the response of the causal system y(n)-y(n-1)=x(n)+x(n-1) to inputs x(n)=u(n) and x(n)=2 –n u(n).Test its stability

b) Determine whether each of the following systems defined below is (i) casual (ii) linear (iii) dynamic (iv) time invariant (v) stable

h (n)=-1/δ(n+1)+1/2δ(n)-1-1/4 δ(n-1). Is the system BIBO stable? Is the filter causal? Justify your answer.

16. Check whether the following systems are linear

or not.

a) y(n)=x 2 (n) b) y(n)=n x(n)

17. For each impulse response listed below, determine if the corresponding system is i) causal ii)

stable

1) 2 n u(-n)

2) sin nЛ/2

 

3

3) δ(n)+sin nЛ

4) e 2n u(n-1)

18. Explain with suitable block diagram in detail about the analog to digital

conversion and to reconstruct the analog signal

19. Find the cross correlation of two sequences x(n)={1,2,1,1} y(n)={1,1,2,1}

20. Determine whether the following systems are linear, time invariant

1) y(n)=A x(n)+B

2) y(n)=x(2n)


UNIT – II

DISCRETE TIME SYSTEM ANALYSIS PART – A (2 MARKS)

1. Define Z-transform.

2. What is meant by Region of convergence?

3. What are the properties of ROC?

4. List the properties of z-transform.

5. Explain the linear property of z-transform.

6. Explain the time-shifting property of z-transform.

7. What are the different methods of evaluating inverse z-transform?

8. What are the properties of frequency response

H(eiω) of an LTI system?

9. What is the necessary and sufficient condition on the impulse response of stability?

10. Distinguish between Linear convolution and

circular convolution.

11. How will you obtain linear convolution from circular convolution?

12. What is meant by sectioned convolution?

13. What are the two methods used for the sectional convolution?

14. Distinguish between Overlap add and Overlap save method.

15. Distinguish between DFT and DTFT.

16. Distinguish between Fourier series and Fourier transform.

17. Define DTFT.

18. List the properties of DTFT.

19. Define DFT.

20. Define circularly even sequence.

21. Define circularly odd sequence.

22. State circular convolution.

23. State parseval’s theorem.

24. Find Z transform of x(n)={1,2,3,4}

25. State the convolution property of Z transform.

26. State initial value theorem.

 

4

PART – B

1. (a) Obtain the transfer function and impulse response of the LTI system defined by y(n-2)+5y(n-

1)+6y(n)+x(n) (8)

(b) State and prove convolution property of discrete time Fourier transform. (8)

2. (a) State and prove any tow properties of z- transform. (8)

(b) Find the z-transform and ROC of the causal sequence. (4)

X(n) = {1,0,3,-1,2}

(c) Find the z-transform and ROC of the anticausal sequence (4)

X(n) = {-3,-2,-1,0,1}

3. (a) Determine the z-transform and ROC of the signal

i) x(n) = anu(n) and

ii) x(n) = -bnu(-n-1) (12)

(b) Find the stability of the system whose impulse

response h(n) = (2)nu(n) (4)

4. (a) Determine the z-transform of x(n) = cos ωn

u(n) (6)

(b) State and prove the following properties of z- transform. (10)

i) Time shifting ii) Time reversal iii) Differentiation

iv) Scaling in z-domain

. (a) Determine the inverse z-transform of x(z) = (1+3z-1) / (1+3z-1+2z-2) for z >2 .(8)

(b) Compute the response of the system

y(n) = 0.7y(n-1)-0.12y(n-2)+x(n-1)+x(n-2) to input x(n) = nu(n).Is the system is stable (8)

6. Find the inverse z-transform of x(z) = (z2+z) / (z-

1)(z-3), ROC: z > 3. Using (i) Partial fraction method, (ii) Residue method and (iii) Convolution method. (16)

7. (a) Determine the unit step response of the system

whose difference equation is y(n)-0.7y(n-1)+0.12y(n-

2) = x(n-1)+x(n-2) if y(-1) = y(-2) = 1. (8)

(b) Find the input x(n) of the system, if the impulse response h(n) and the output y(n) as shown below.

(8)

h(n) = {1,2,3,2} y(n) = {1,3,7,10,10,7,2}

8. (a) Determine the convolution sum of two sequences x(n) = {3,2,1,2}, h(n) = {1,2,1,2} (8)

(b) Find the convolution of the signals

x(n) = 1 n = -2,0,1

= 2 n = -1

= 0 elsewhere

h(n) = δ(n)-δ(n-1)+ δ(n-2)- δ(n-3) (8)

9. (a) Determine the output response y(n) if h(n) =

{1,1,1,1}; x(n) = {1,2,3,1} by using i) Linear

5

convolution ii) Circular convolution and iii) Circular convolution with zero padding. (12)

(b) Explain any twp properties of Discrete Fourier

Transform. (4)

10. Using linear convolution find y(n) = x(n)*h(n) for the sequences x(n) = (1,2,-1,2,3,-2, -3,-1,1,1,2,-1) and h(n) = (1,2).Compare the result by solving the

problem using i) Over-lap save method and ii) Overlap – add method. (16)

11. For the sequences given below, find the frequency response, plot magnitude response, phase

response and comment. (16)

i) x(n) = 1 for n = -2,-1,0,1,2

= 0 otherwise

ii) x(n) = 1 for n = 0,1,2,3,4

= 0 otherwise

12. (a) Calculate the frequency response for the LTI

systems representation

i) h(n) = [1/n]n u(n) ii) h(n) = δ(n) – δ(n-

1) (8)

(b) Find the frequency response of the system having impulse response

h(n) = [1/2] { (1/2)n + (-1/4)n } u(n) (8)

13. Determine the frequency response (H(ejω)) for the system and plot magnitude response and phase response. y(n)+[1/4]y(n-1) = x(n)-x(n-1) (16)

14. (a) A discrete – time system has a unit sample response h(n) given by

h(n) = [1/2] δ(n) + δ(n-1) + [1/2] δ(n-2). Find the system frequency response H(ejω); Plot magnitude and Phase response. (12)

(b) Explain any two properties of Discrete Fourier

Series. (4)


UNIT – III

DISCRETE FOURIER TRANSFORM AND COMPUTATION

PART – A (2 MARKS)

1. Why FFT is needed?

2. What is the main advantage of FFT?

3. What is FFT?

4, what is meant by Radix-2 FFT?

5. What is decimation-in-time algorithm?

6. What is decimation in frequency algorithm?

7. What are the differences and similarities between

DIF and DIT algorithm?

8. What is the basic operation of DIT algorithm?

9. What is the basic operation of DIF algorithm?

10. What are the applications of FFT algorithms?

11. Draw the flow graph of a two point DFT for a decimation-in-time decomposition.

12. Draw the flow graph of a two point radix-2 DIF FFT.

 

6

13. Draw the basic butterfly diagram for DIT

algorithm.

14. Draw the basic butterfly diagram for DIF

algorithm.

15. Define DFT of a discrete time sequence.

16. What are the differences and similarities between

DIF and DIT algorithms?

17. Define the properties of convolution.

18. Draw the basic butterfly diagram of radix-2 FFT.

19. State and prove parseval’s relation for DFT.

20. What do you mean by the term “bit reversal” as

applied to FFT

21. What are the advantages of FFT algorithm over direct computation of DFT?

22. The first five DFT coefficients of a sequence x(n)

are x(0) = 20, x(1) = 5+j2, x(2) = 0, x(3)=0.2+j0.4, X(4) = 0. Determine the remaining DFT coefficients.

23. Define Complex Conjugate of DFT property.

24. How many multiplications and additions are

required to compute N-point DFT using radix-2

FFT?

25. What are the applications of FFT algorithms?

26. What are twiddle factors of the DFT?

27. How many additions and multiplications are needed to compute N-point FFT?

28. Calculate the number of multiplications in 64 point DFT using FFT?

29. Find the values of WN, when N=8 and k=2 and also for k=3.

30. What are the differences and similarities between

DIF and DIT algorithms?

PART – B

1. Describe the decimation in time [DIT] radix-2

FFT algorithm to determine N-point DFT. (16)

2. An 8-point discrete time sequence is given by x(n)

= {2,2,2,2,1,1,1,1}. Compute the 8-point DFT of x(n)

using radix-2 FFT algorithm. (16)

3. (a) Compute the 4-point DFT and FFT-DIT for the

sequence x(n) = {1,1,1,3} and What are the basic steps for 8-point FFT-DIT algorithm computation? (12)

(b) What is the advantage of radix-2 FFT algorithm

in comparison with the classical DFT method? (4)

4. (a) Perform circular convolution of the two sequences graphically x1(n) = {2,1,2,1} and x2(n) =

{1,2,3,4} (6)

(b) Find the DFT of a sequence by x(n) =

{1,2,3,4,4,3,21} using DIT algorithm. (10)

5. (a) Explain the decimation in frequency radix-2

FFT algorithm for evaluating N-point DFT of the

7

given sequence. Draw the signal flow graph for N=8. (12)

(b) Find the IDFT of y(k = {1,0,1,0} (4)

6. (a) Find the circular convolution of the sequences x1(n)= {1,2,3} and x2(n) = {4,3,6,1} (8)

(b) Write the properties of DFT and explain. (8)

7. (a) Draw the 8-point flow diagram of radix-2 DIF-

FFT algorithm. (8)

(b) Find the DFT of the sequence x(n) = {2,3,4,5}

using the above algorithm. (8)

8. (a) What are the differences and similarities between DIT and DIF FFT algorithms?(6)

(b) Compute the 8-point IDFT of the sequence

x(k) = {7, -0.707-j0.707, -j,0.707-j0.707, 1,

0.707+j0.707, j, -0.707+j0.707} using DIT

algorithm. (10)

9. (a) Compute the 8-point DFT of the sequence x(n)

= {0.5,0.5,0.5,0.5,0,0,0,0} using radix-2 DIT

algorithm. (8)

(b) Find the IDFT of the sequence

x(k) = {4,1-j2.414,0,1- j0.414,0,1+j.414,0,1+j2.414}

using DIF algorithm. (8)

10. Compute the 8-point DFT of the sequence

x(n) = 1, 0 ≤ n ≤ 7

0, otherwise by using DIT,DIF

algorithms. (16)

11. Find 4-point DFT of the following sequences

(a) x(n)={1,-1,0,0}

(b) x(n)={1,1,-2,-2} (AU DEC 06) (c) x(n)=2n

(d) x(n)=sin(nΠ/2)

12. Find 8-point DFT of the following sequences

(a) x(n)={1,1,1,1,0,0,0,0}

(b) x(n)={1,2,1,2}

13. Determine IDFT of the following (a)X(k)={1,1-j2,-1,1+j2} (b)X(k)={1,0,1,0} (c)X(k)={1,-2-j,0,-2+j}


UNIT – IV

DESIGN OF DIGITAL FILTERS PART – A (2 MARKS)

1. What is FIR Filter?

2. Write the procedure for designing FIR filters

3. Write the characteristics of FIR filter.

4. What are the design techniques available for the designing FIR filter?

5. What are the demerits of FIR filter?

6. What are the possible types of impulse response for linear phase FIR filters?

7. What is GIBBS phenomenon?

8. Write the desirable characteristics of frequency response of window functions.

9. Write the characteristics features of rectangular window.

10. List merits and demerits of rectangular window.

11. List the features of Kaiser Window.

12. What do you understand by linear phase response?

13. What are the two types of filter based on the

impulse response?

14. What are the advantages of Kaiser Window?

15. What is the principle of designing FIR filter using frequency sampling method?

16. What are the properties of FIR filter?

17. What is the need for employing window technique for FIR filter design? (Or) What is window and why it is necessary?

18. What is the necessary and sufficient condition for linear phase characteristic in FIRfilter?

19. Define IIR filter.

20. What are the methods available for designing analog IIR filter?

21. What are the methods available for designing analog IIR filter?

22. Mention the importance of IIR filter:

23. Mention the two properties of Butterworth low pass filter.

24. Write the properties of chebyshev type-I filter:

25. What is aliasing? Why it is absent in bilinear transformation ?

26. How one can design digital filter from analog

filter ?

27. What is bilinear transformation?

28. What is warping effect?

29. Write merits and demerits of bilinear

transformation.

30. What is the main advantage of direct-form II realization when compared to directform I realization?

31. What is the main disadvantage of direct-form realization?

32. What is the advantage of cascade realization?

33. Distinguish IIR and FIR.

34. Compare analog and digital filter.

35. Compare Butterworth and Chebyshev Filter:

36. Compare impulse invariant and bilinear technique

37. What are the different types of structures for

realization of IIR systems?

38. Write a short note on prewarping.

PART – B

1. Describe the impulse invariance and bilinear transformation methods used for designing digital IIR filters. (16)

9

2. (a) Obtain the cascade and parallel realization of the system described by

y(n) = -0.1y(n-1)+0.2y(n-2)+3x(n)+3.6x(n-

1)+0.6x(n-2) (10)

(b) Discuss about any three window functions used in the design of FIR filters. (6)

3. Determine the direct form II and parallel form

realization for the following system.

y(n) = -0.1y(n-1)+0.72y(n-2)+0.7x(n)-

0.252x(n-2) (16)

4. An analog filter has a transfer function H(s) = (10 /

s2+7s+10). Design a digital filter

equivalent to this impulse invariant method. (16)

5. For the given specifications design an analog

Butterworth filter,

0.9 ≤ H(jΩ) ≤ 1 for 0 ≤ Ω ≤ 0.2π

H(jΩ) ≤ 0.2 for 0.4π ≤ Ω π (16)

6. Design a digital Butterworth filter satisfying the constraints

0.707 ≤ H(ejω) ≤ 1 for 0 ≤ ω ≤ π/2

H(ejω) ≤ 0.2 for 3π ≤ ω ≤ π

With T = 1 sec using Bilinear transformation. (16)

7. Design a chebyshev filter for the following specification using impulse invariance method. 0.8 ≤

H(ejω) ≤ 1 for 0 ≤ ω ≤ 0.2π

H(ejω) ≤ 0.2 for 0.6π ≤ ω ≤

8. (a) Write the expressions for the Hamming, Hanning, Bartlett and Kaiser windows.(6)

(b) Explain the design of FIR filters using windows.

(10)

9. Design an ideal high pass filter with

Hd(ejω) = 1 for π/4 ≤ ω ≤ π

= 0 for ω ≤ π/4

Using Hanning window for N=11. (16)

10. Design an ideal high pass filter with

Hd(ejω) = 1 for π/4 ≤ ω ≤ π

= 0 for ω ≤ π/4

Using Hamming window for N=11. (16)

11. Using a rectangular window technique design a lowpass filter with pass band gain of unity, cutoff frequency of 1000 Hz and working at a sampling frequency of 5kHZ. The length of the impulse response should be 7. (16)

12. Design an ideal Hilbert transformer having frequency response

H(ejω) = j for -π ≤ ω ≤ 0

= -j for 0 ≤ ω ≤ π

Using blackman window for N=11.Plot the frequency response. (16)

π (16)

10


UNIT – V PROGRAMMABLE DSP CHIPS PART – A (2 MARKS)

1. What are the classifications of digital signal processors?

2. What are the factors that influence the selection of

DSPs?

3. What are the applications of PDSPs?

4. Mention the different addressing modes in

TMS320C54x processor.

5. What is meant by pipelining?

6. Give the digital signal processing application with the TMS 320 family.

7. What are the desirable features of DSP Processors?

8. What are the different types of DSP Architecture?

9. State the features of TMS3205C5x series of DSP

processors.

10. Define Parallel logic unit?

11. Define scaling shifter?

12. Define ARAU in TMS320C5X processor?

13. What are the Interrupts available in TMS320C5X

processors?

14. What are the three quantization errors due to finite word length registers in digital filters?

15. What do you understand by input quantization error?

16. What is co-efficient quantization error?

17. What is product quantization error? (or) What is product round-off error in DSP?

18. What are the different methods of quantization?

19. Define Truncation and Rounding.

20. What is the effect of quantization on pole locations?

21. Which realization is less sensitive to the process of quantization?

22. What is meant by quantization step size?

23. What are the two kinds of limit cycle behavior in

DSP?

24. Define “Dead band” of the filter.

25. Explain briefly the need for scaling in the digital filter implementation.

26. Why rounding is preferred to truncation in realizing digital filter?

PART – B

1. Describe in detail the architectural aspects of TMS320C54 digital signal processor using an illustrative block diagram. (16)

2. Explain the various addressing modes and salient

features of TMS320C54X. (16)

3. (a) Describe the function of on-chip peripherals of

TMS320C54 processor. (12)

11

(b) What are the different buses of TMS320C54 and their functions? (4)

4. Describe the errors introduced by quantization.

Explain the impact of quantization of filter coefficients on the location of poles. (16)

5. Write a brief note on:

i) Input quantization (8)

ii) Limit cycles (8)

6. Discuss in detail the various quantization effects in the design of digital filters. (16)

7. Find the effect of co-efficient quantization on pole

locations of the given second order IIR system, when it is realized in direct form I and in cascade form. Assume a word length of 4 bits through truncation. (16)

H(z) = 1 / (1 – 0.9 z-1 + 0.2 z-1)

12

EE2301-POWER ELECTRONICS Questions Bank 2014


Anna University, Chennai

Anna_University,_Chennai_logo 

M.A.M. SCHOOL OF ENGINEERING

SIRUGANUR, TRICHY – 621 105

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING EE2301-POWER ELECTRONICS

UNIT-I POWER SEMICONDUCTOR DEVICES PART-A

1. What are the different methods to turn on the thyristor?

2. Define latching current.

3. Define holding current.

4. What is a snubber circuit?

5. Why IGBT is very popular nowadays?

6. What is the difference between power diode and signal diode?

7. What is Thyristor? Mention some of them.

8. What are the advantages of GTO over SCR?

9. What losses occur in a thyristor during working conditions?

10.IGBT is a voltage controlled device. Why?

11.Power MOSFET is a voltage controlled device. Why?

12.Power BJT is a current controlled device. Why?

13.What are the different types of power MOSFET?

14.How can a thyristor turned off?

15. What losses occur in a thyristor during working conditions?

16.Define circuit turn off time.

17.Why circuit turn off time should be greater than the thyristor turn-off time?

18.What is the turn-off time for converter grade SCRs and inverter grade

SCRs?

19.What are the classifications of Power semiconductor devices?

20.Define Hard-firing or over driving.

21.Define forward Break over Voltage.

22.Define Reverse Break over voltage.

23.What is forced commutation?

24.What is meant by Secondary breakdown?

25.What are the advantages of TRIAC?

26.What are the disadvantages of TRIAC?

27.Compare Power MOSFET’s with BJT’s.

28. In TRIAC’s which of the modes the sensitivity of gate is high.

29.Define the term pinch off voltage of MOSFET.

30.What are the basic features of power MOSFET?

31.Distinguish between holding current and latching current of SCR.

32.What is commutation? What are the two main types of commutation?

33.Draw the V-I characteristics of SCR and mark the holding current and latching current in the characteristics.

34.Why MOSFET’s are not preferred for high frequency application?

35.What are the advantages of IGBT over MOSFET?

36.What are the classification of power Diodes?

37.What is reverse recovery time of Diodes?

38.What are the difference between SCR and TRIAC.

39.Define Spread Time.

40.What is the turn-off time for converter and inverter grade SCRs?

PART-B

1. Draw the two transistor model of SCR and derive an expression for anode

current.

2. Explain the Construction, principle of operation and static characteristics of

SCR

3. Describe the various methods of thyristor turn on.

4. Explain basic structure, characteristics and operation of MOSFET’s.

5.Explian detail in Structure, characteristics of TRIAC.

6.Explin detail in Construction of BJT and that characteristics.

7. Explain basic structures, characteristics and operation of IGBT’s.

8.Explin detail in GTO.

9. What are the types of special semiconductor devices? And Explain in detail.

10.Describe any one driver circuit and snubber circuit for MOSFET.

11.Explain the switching performance of BJT with relevant waveforms indicating clearly the turn-on, turn off times and their components.

12. Describe turn on characteristics of IGBT with neat waveforms.

13.What is commutation? What are the two types of commutation?

14. What are the different Modes of operation of TRIAC?

15.Sketch the transfer and switching characteristics of IGBT.

16. write short notes on i) snubber circuit for BJT

ii) Commutation circuit of SCR.


UNIT II

PHASE-CONTROLLED CONVERTERS

1. What is meant by phase controlled rectifier?

2. What is the function of freewheeling diodes in controlled rectifier?

3. What are the advantages of freewheeling diodes in a controlled in a controlled rectifier?

4. What is meant by delay angle?

5. What are the advantages of single phase bridge converter over single phase mid-point converter?

6. What is commutation angle or overlap angle?

7. What are the different methods of firing circuits for line commutated converter?

8. Give an expression for average voltage of single phase semiconverters.

9. What is meant by input power factor in controlled rectifier?

10.What are the advantages of six pulse converter?

11.What are the general classification of rectifier circuits?

12. What is meant by uncontrolled rectifier?

13.What are the different types of controlled rectifier?

14.What is meant by half controlled rectifier?

15.what is meant by full converter?

16.List various applications of controlled converters?

17.What are the two configuration of single phase two pulse controlled rectifier?

18.Give an expression for average output voltage of single phase full converter.

19. What is the inversion mode of rectifiers?

20.What are the advantages of single phase bridge converter over single phase mid-point converter?

21.What are the performance factors of line-commutated converters?

22.Define voltage ripple factor?

23. When does the line commutated converter act as a line commutated inverter?

24. How is power factor of semi converter better then that of full converter?

25.Draw the half controlled single phase converter circuit.

26.Draw a half wave AC to DC converter circuit and plot the output waveform for a = 90 . Assume resistance load.

27.Define harmonic factor or THD of the input current.

28. Define displacement factor.

29.What is three phase controlled rectifier?

30. What are the advantages of three phase controlled rectifier?

31.What are the classifications of three phase controlled rectifier?

32.Write down the expression for average output voltage of three phase half controlled rectifier?

33. Write down the expression for average output voltage of three phase full converter?

34.What are the effects of source impedance in the controlled rectifiers?

35. What is meant by continuous current operation of thyristor converter?

1. of fully controlled converter with resistive load and derive the expressions for various parameters.

2. Discuss operation of a single phase full wave controlled rectifier feeding RL load. What is the effect of adding a freewheeling diode on the performance of the converter.

3. Describe the working of 1 ф fully controlled bridge converter in the Rectifying mode and inversion mode. And derive the expressions for average output voltage and rms output voltage.

4. Describe the principle of operation of two pulse midpoint converter with

resistive load and also derive the average load voltage.

5. Explain the operation of full wave mid point converter with RL load.

6. With neat sketch, describe the function of single phase half controlled bridge rectifier with resistive load. what will the waveforms observed?

7. With neat sketch, describe the function of single phase half controlled bridge rectifier with resistive load and inductive load. what will the waveforms observed?

8. Derive the expressions for average output voltage and rms output voltage

of 1 ф semi converter.

9. With neat sketch, describe the function of single phase half controlled bridge rectifier with RLE load free-wheeling load. what will the waveforms observed?

10. Describe the operation three phase half wave controlled rectifier with

resistive load with continuous and discontinuous mode of operation.

11.Describe the operation and waveform of three phase half wave controlled rectifier with RL load.

12.Describe the operation and waveform of three phase half controlled

Bridge rectifier.

13. Describe the working of 3 ф fully controlled bridge converter in the Rectifying mode and inversion mode. And derive the expressions for average output voltage and rms output voltage.

14. Describe the working of Dual converter.

15. Explain the effect of source inductance on the performance of single phase fully controlled converter.

16.Explain the effect of source inductance on the performance of single phase fully controlled converter.

17.A single phase semi converter is operated from 120V 50Hz ac supply.

The load current with an average value Idc is continuous and ripple free firing angle a = p/3. Determine.i) Displacement factor

ii) Harmonic factor of input current

iii) Input power factor

18.write a note on battery charger

19.Describe the effect of source inductance on the performance of a single phase full converter indicating clearly the conduction of various thyristors during one cycle. Derive the expression for its output voltage.

20.Explain the working of a three phase full converter with ‘R’ load for the firing angles of 60˚, 90 and 150˚.


UNIT III

DC TO DC CONVERTERS PART A

1. What is meant by dc chopper?

2. What are the applications of dc chopper?

3. What is meant by step-up and step-down chopper?

4. Write down the expression for average output voltage for step down

chopper.

5. Write down the expression for average output voltage for step up chopper.

6. What is meant by duty-cycle?

7. What are the two types of control strategies?

8. What is meant by TRC?

9. What are the two types of TRC?

10.What is meant by FM control in a dc chopper?

11.What are the advantages of dc chopper?

12.What are the classification of dc converters depending upon the directions of current and voltage?

13.What is meant by PWM control in dc chopper?

14.What are the disadvantages of frequency modulation scheme over the pulse width modulation scheme?

15.Define switched mode regulator.

16.What are the basic topologies of switching regulators?

17.What is meant by buck regulators?

18.What are the advantages and disadvantages of buck converter?

19.Define boost converter?

20.What are the applications of boost converter?

21.What are the advantages and disadvantages of boost converters?

22.Define Buck-Boost Converter.

23.What are the advantages and disadvantages of buck-boost regulator?

24.What is cuk converter?

25.Give the advantages and disadvantages of cuk regulator.

26.What are the different control techniques used in choppers?

27.Draw the circuit of cuk converter.

28.What are the classifications of chopper?

29.Why forced commutation used in chopper circuits?

30.What is meant by SMPS?

31.What is current limit control of a DC chopper?

32.What is the need for a filter at the output of a step up DC converter?

33.What is two quadrant DC chopper?

34.What is a resonant converter?

35. What the effects of chopping frequency on filter sizes?

36.What are advantages of resonant converters?

37.What is meant by zero voltage switching of resonant converters?

38.Sketch the diagram of a basic step up chopper.

39.Differentiate between constant frequency and variable frequency control strategies of varying the duty cycle of DC choppers.

40.What are the differences between Buck-Boost and Cuk converters?

PART B

1. Describe the principle of step-up chopper. Derive an expression for the average output voltage in terms of input dc voltage & duty cycle.

2. Describe the working of four quadrant chopper.

3. Explain the working of current commutated chopper with aid of circuit diagram and necessary waveforms. Derive an expression for its output voltage.

4. Explain the working of voltage commutated chopper with aid of circuit diagram and necessary waveforms. Derive an expression for its output voltage.

5. Discuss the principle of operation of DC-DC step down chopper with suitable waveform. Derive an expression for its average DC output voltage.

6. A step-down dc chopper has a resistive load of R= 15Ω and input voltage Edc= 200V.when the chopper remains ON, its voltage drop is 2.5 for a duty cycle of 0.5. calculate i) Average and r.m.s value of output voltage.

ii) Power delivered to the load .

7. Draw the circuit of CUK regulator and explain its working principle with necessary waveform in detail.

8.A step –up chopper has input voltage of 200V and output voltage of 600V. if the non-conducting time of thyristors chopper is 200ms, compute the pulse width of output voltage . in case pulse width is halved for constant frequency operation, find the new output voltage.

9. Explain the various modes of operation of boost DC-DC converter with necessary waveforms.

10.Explain the working of buck-boost converter with sketch and waveforms and also drive the expression for Is.

11. With neat sketch and output voltage waveforms, explain the working of full bridge SMPS.

12. Explain the operation of BUCK converter in detail.

13. Explain the operation of BOOST converter in detail.

14. Explain the control strategies of chopper.

15. Explain the concept f resonant switching.


UNIT IV INVERTERS PART-A

1. What is meant by inverter?

2. What are the applications of an inverter?

3. What are the main classification of inverter?

4. Why thyristors are not preferred for inverters?

5. Give two advantages of CSI.

6. What is meant a series inverter?

7. What is meant a parallel inverter?

8. What are the applications of a series inverter?

9. What is meant by McMurray inverter?

10. What are the applications of a CSI?

11. What is meant by PWM control?

12. What are the advantages of PWM control?

13. What is VSI?

14.What is CSI?

15. Why thyristors are not preferred for inverters?

16. How the output frequency is varied in the case of an inverters?

17. What are the different methods of forced commutation employed in inverter circuits?

18. What is the main drawback of single phase half bridge inverter?

19. What is the need for voltage control in an inverter?

20. List different methods of controlling the output voltage of inverters.

21. What are the difference types of PWM inverter?

22. What is meant by McMurray inverter?

23. What are the disadvantages of harmonic present in the inverter system?

24. What are the techniques for harmonic reduction?

25. List out the applications of CSI.

26. Difference between VSI and CSI.

27. What are the performance parameters of inverters?

28. What is a PWM inverter?

29. List the advantages of Multiple PWM over single PWM technique.

30. What are the advantages of current source inverter over voltage source inverter?

31. Mention the difference between sinusoidal and modified sinusoidal PWM

techniques.

32. What are the advantages of PWM inverter?

33. Define the term inverter gain?

34. Define modulation index of PWM.

35. List the assumptions that are made in modified McMurray half bridge inverter.

36. What is purpose of connecting diode in antiparallel with thyristors in inverter?

37. What is 60 PWM?

38. What is Space vector PWM?

39. Compare sinusoidal PWM and space vector PWM?40. What are the advantages of SVPWM?

PART B

1. Describe the operation of series inverter with aid of diagrams. Describe an expression for output frequency, current and voltages. What are the disadvantages of basic series inverter?

2. State different methods of voltage control inverters. Describe about PWM

control in inverter.

3. Explain the operation of 3 ф bridge inverter for 180 degree mode of operation

with aid of relevant phase and line voltage waveforms.

4. Explain the working of a single phase full bridge inverter with relevant circuit and waveforms.

5. What is PWM? List the various PWM technique and Explain any one of them.

6. Explain the harmonic reduction by transformer connections and stepped wave inverters.

7. Describe the operation of single phase auto sequential commutated current source inverter with power circuit and waveforms.

8. Explain the operation of 3 ф bridge inverter for 120 degree mode of operation with aid of relevant phase and line voltage waveforms.

9. Describe the different modes of operation of serious resonant inverter unidirectional switch with neat circuit diagram and waveforms.

10. Explain sinusoidal Pulse width modulation technique in detail.

11. Explain Space vector Pulse width modulation technique in detail.

12. Explain the operation of single phase capacitor commutated CSI with R load and necessary waveforms.

13.A single phase full bridge inverter feeds power at 50Hz to RLC load with

R=5 ohms L=0.3H and C=50mF. the DC input voltage is 220V DC. Find i) an expression for load current up to 5th harmonics

ii) Power absorbed by the load and the fundamental power. iii) the RMS and peak currents of each thyristors.

iv) conduction time of thyristors and diodes, if only fundamental components were considered.


UNIT V AC VOLTAGE CONTROLLER PART-A

1. What does ac voltage controller mean?

2. What are the applications of ac voltage controllers?

3. What are the advantages of ac voltage controllers?

4. What are the disadvantages of ac voltage controllers?

5. What are the two methods of control in ac voltage controllers?

6. What is the difference between ON-OFF control and phase control?

7. What is meant by cyclo-converter?

8. What are the two types of cyclo-converters?

9. What is meant by step-up cyclo-converters?

10. What is meant by step-down cyclo-converters?

11. What are the applications of cyclo-converter?

12.What are the effects of load inductance on the performance of ac voltage

controllers?

13. What do you meant by integral cycle control?

14.Write the output R.M.S. voltage for single phase AC voltage controller with resistance load.

15.What is Matrix converter?

16.What are the advantages of Matrix converter?

17.What are the disadvantages of Matrix converter?

18. What are the applications of Matrix converter?

19. Draw the circuit diagram of matrix converter.

20. A step down cycloconverter does not need forced commutation-justify.

PART-B

1. Explain the operation of multistage control of AC voltage controllers with

neat diagram.

2. Explain the operation of 1ф AC voltage controller with RL load.

3. Explain the operation of 1ф sinusoidal AC voltage controller.

4. For a 1 ф voltage controller, feeding a resistive load, draw the waveforms of source voltage, gating signals, output voltage and voltage across the SCR. Describe the working with reference to waveforms drawn.

5. Describe three-phase to three phase cycloconverter with relevant circuit

arrangement using 18 thyristors.

6. Explain the principle of single phase to single phase step-down cycloconverter with power circuit and waveforms.

7. Discuss the working of a 3 phase to single phase cycloconverter with neat voltage and current waveforms.

8. Discuss the working of 2 stage sequence control of AC voltage controller.

9.A single-phase full wave AC voltage controllers feeds of R=20 ohms, with an input voltage of 230V,50Hz. Firing angle for both the thyristors is 45˚ calculate

i) R.M.S. value of output voltage. ii) Load power and input p.f.

iii) Average and R.M.S. current of thyristors

10. A six-pulse cycloconverter, fed from 3-phase,400V, 50Hz source, is delivering a load current of 40A to a 1-phase resistive load. The source has an inductance of 1.2mH per phase. Calculate the R.M.S. value of load voltage for firing angle delays of i) 0 and ii) 30˚.

Electrical Machines – II Two Marks Questions With Answers 2014


Anna University, Chennai

Anna_University,_Chennai_logo

 

M.A.M SCHOOL OF ENGINEERING, SIRUGANUR, TRICHY

Department of Electrical and Electronics Engineering

Sub: Electrical Machines – II

2 Marks questions with answer

UNIT-I

1. Why a 3-phase synchronous motor will always run at synchronous speed?

Because of the magnetic coupling between the stator poles and rotor poles the motor runs exactly at synchronous speed.

2. What are the two classification synchronous machines?

The classification synchronous machines are:

i. Cylindrical rotor type ii. Salient pole rotor type

3. What are the essential features of synchronous machine?

i. The rotor speed is synchronous with stator rotating field. ii. Varying its field current can easily vary the speed.

iii. It is used for constant speed operation.

4. Mention the methods of starting of 3-phase synchronous motor. a. A D.C motor coupled to the synchronous motor shaft.

b. A small induction motor coupled to its shaft.(pony method)

c. Using damper windings –started as a squirrel cage induction motor.

5. What are the principal advantages of rotating field system type of construction of synchronous machines?

· Form Stationary connection between external circuit and system of conditions enable the machine to handle large amount of volt-ampere as high as 500 MVA.

· The relatively small amount of power required for field system can be easily supplied to the rotating field system via slip rings and brushes.

· More space is available in the stator part of the machine for providing more insulation to the system of conductors.

· Insulation to stationary system of conductors is not subjected to mechanical stresses due to centrifugal action.

· Stationary system of conductors can easily be braced to prevent deformation.

· It is easy to provide cooling arrangement.

6. Write down the equation for frequency of emf induced in an alternator.

F = PN / 120 Hertz

Where P = No. Of poles

N = Speed in rpm.

7. What are the advantages of salient pole type of construction used for synchronous machines?

v They allow better ventilation.

v The pole faces are so shaped radial air gap length increases from the pole center to the pole tips so that flux distribution in the air gap is sinusoidal in shape which will help to

generate sinusoidal emf.

v Due the variable reluctance, the machine develops additional reluctance power, which is independent of excitation.

8. Why do cylindrical rotor alternators operate with steam turbines?

Steam turbines are found to operate at fairly good efficiency only at high speeds. The high-speed operation of rotor tends to increase mechanical losses, so the rotors should have

smooth external surface. Hence smooth cylindrical type rotors with less diameter and large axial length are used for synchronous generators driven by steam turbines with either 2 or 4 poles.

9. Which type of synchronous generators are used in Hydroelectric plants and why?

As the speed of operation is low, for hydro turbines used in hydroelectric plants, salient pole type synchronous generators are used. These allow better ventilation and also have other advantages

over smooth cylindrical type rotor.

10. What is the relation between electrical degree and mechanical degree?

Electrical degree θe and mechanical degree are related to one another by the number of poles P, the electrical machine has, as given by the following equation.

θe = (P/2) θm

11. What is the meaning of electrical degree?

Electrical degree is used to account the angle between two points in rotating electrical machines. Since all electrical machines operate with the help of magnetic fields, the electrical degree is

accounted with reference to the polarity of magnetic fields. 180 electrical degrees is accounted as

the angle between adjacent North and South poles

12. Why short-pitch winding is preferred over full pitch winding? Advantages: -

· Waveform of the emf can be approximately made to a sine wave and distorting harmonics can be reduced or totally eliminated.

· Conductor material, copper is saved in the back and front-end connections due to less coil span.

· Fractional slot winding with fractional number of slots/phase can be used which in turn reduces the tooth ripples.

· Mechanical strength of the coil is increased.

13. Write down the formula for distribution factor.

Kd = sin (mβ/2)

or

Kdn = sin (mnβ/2)

msin(β/2)

 

msin(nβ/2)

where

m - number of slots/pole/phase

β - angle between adjacent slots in electrical degree n - order of harmonics.

14. Define winding factor.

The winding factor Kw is defined as the ratio of phasor addition of emf induced in all the coils belonging to each phase winding of their arithmetic addition.

15. Why are alternators rated in kVA and not in kW?

The continuous power rating of any machine is generally defined as the power the machine or apparatus can deliver for a continuous period so that the losses incurred in the machine gives rise to a steady temperature rise not exceeding the limit prescribed by the insulation class.

Apart from the constant loss the variable loss incurred in alternators is the copper loss, occurring in the 3-phase winding, which depends on I2R, the square of the current delivered by the generator. is directly related to apparent power delivered by the generator,Thus the alternators have only their apparent power in VA/kVA/MVA as their power rating.

16. What are the causes of changes in voltage of alternators when loaded?

· Voltage variation due to the resistance of the winding R.

· Voltage variation due to the leakage reactance of the winding X1.

· Voltage variation due to the armature reaction.

17. What is meant by armature reaction in alternators?

The interaction between flux set up by the current carrying armature conductors and the main field flux is defined as the armature reaction.

18. What do you mean by synchronous reactance?

It is the sum of the leakage reactance X1 and armature reactance Xa

Xs = X1 + Xa

19. What is effective resistant [Reff]?

The apparent increase in resistance of the conductor when an alternating current is flowing

through it is known as effective resistance.

20. What is synchronous impedance?

The complex addition of resistance R and synchronous reactance jXs is synchronous impedance

Zs.

Zs = (R+jXs) = Zs∟θ

Where θ = tan –1(Xs/R)

|Zs| = √(R2+jXs2)

21. What is meant by load angle of an alternator?

The phase angle introduced between the induced emf phasor E and terminal voltage phasor V during the load condition of an alternator is called load angle. The load angle increases

with increase in load. It is positive during generator operation and negative during motor

operation.

22. Define the term voltage regulation of alternator.

It is defined as the change in terminal voltage from no load-to-load condition expressed as a function or terminal voltage at load condition, the speed and excitation conditions remaining

same.

% Regulation = (E-V)/V x 100

23. What is the necessity for predetermination of voltage regulation?

Most of the alternators are manufactured with large power rating and large voltage ratings. Conduction load test is not possible for such alternators. Hence other indirect methods of

testing are used and the performance can be predetermined at any desired load currents and power

factors.

24. Why is the synchronous impedance method of estimating voltage regulation is considered as pessimistic method?

Compared to other methods, the value of voltage regulation obtained by this method is always higher than the actual value and therefore is called pessimistic method.

25. Why is the MMF method of estimating the voltage regulation is considered as the optimization method?

Compared to EMF method, MMF method involves more number of complex calculation steps. Further the OCC is referred twice and SCC is referred once while predetermining the voltage regulation for each load condition. Reference of OCC takes core saturation effect. As this method requires more effort, the final result is very close to the actual value. Hence this method is called the optimistic method.

Possible 16 Mark questions:

1. Describle with neat sketches the constructional details of a salient pole type alternator.

2.Draw a neat sketch showing the various parts of a synchronous machine. State the type of synchronous generator used in nuclear power stations.

3.Discuss briefly the load charactertics of alternator for different power factor.

4.Explain any one method of predetermining the regulation of an alternator.

5.Explain why the potier reactance is slightly higher than leakages reactance.

6.Explain dark lamp method of synchronizing an alternator with the bus bar.

7.Explain Blondel’s two-reaction theory,

8.Explain how will you determine the d and q axes reactance of a synchronous machine in your laboratory.

9.Derive an expression for synchronizing power.

10.For a salient pole synchronous machine, derive an expression for power developed as a function of load angle.

11.Explain the operating principle of three-phase alternator.

12.Explain the constructional details of a three-phase alternator, which is used for slow speed operation.

13.State requirements for paralleling alternators.

14.Derive the equation of induced emf for an alternator.

UNIT-II

1. What does hunting of synchronous motor mean?

When the load applied to the synchronous motor is suddenly increased or decreased, the rotor oscillates about its synchronous position with respect to the stator field. This action is called hunting.

2. What could be the reasons if a 3-phase synchronous motor fails to start?

It is usually due to the following reasons a. Voltage may be too low.

b. Too much starting load.

c. Open circuit in one phase or short circuit. d. Field excitation may be excessive

3. What is synchronous condenser?

An over-excited synchronous motor under no load ,used for the improvement of power factor is called as synchronous condenser because, like a capacitor it takes a leading current.

4. Write the applications of synchronous motor.

a. Used for power factor improvement in sub-stations and in industries. b. Used in industries for power applications.

c. Used for constant speed drives such as motor-generator set, pumps and compressors.

5. What is an inverted 'V' curve?

For a constant load, if the power factor is plotted against various values of field exciting current, the curve formed is inverted V Shape and called as inverted 'V' curve.

Also draw draws the graph.

6. A synchronous motor starts as usual but fails to develop its full torque. What could it be due to?

a. Exciter voltage may be too low.

b. Field spool may be reversed.

c. There may be either open-circuit or short-circuit in the field.

7. What are the two types of 3-phase induction motor?

a. Squirrel cage induction motor. b. Slip ring induction motor.

8. Write the two extra features of slip ring induction motors. a. Rotor is having 3-phase winding.

b. Extra resistance can be added in the rotor circuit by connecting through the help of three slip rings for improving the power factor, increasing Starting Torque, limiting the

starting current.

9. Can we add extra resistance in series with squirrel cage rotor? State the reason?

We cannot add extra resistance in series with the rotor because all the copper bars of the rotor are short circuited in both the sides by copper end rings to have a closed circuit.

10. Why an induction motor is called rotating transformer?

The rotor receives electrical power in exactly the same way as the secondary of a two winding transformer receiving its power from primary. That is why an induction motor can

be called as a rotating transformer i.e., in which primary winding is stationary but the secondary is free to rotate.

11. Why an induction motor will never run at its synchronous speed?

If it runs at synchronous speed then there would be no related speed between the two, hence no rotor emf, no rotor current so no rotor torques to maintain rotation. That is why the rotor runs at its synchronous speed.

12. Define SCR?

Short circuit ratio (SCR) is defined as the ratio of field current required to produce rated voltage on open-circuit to field current required to produce rated armature current with the

terminals shorted, while the machine runs at synchronous speed.

13. Why is open circuit charactertics called magnetic charactertic?

The OCC is called magnetic charactertic because it gives the variation of space component of flux in air gap and mmf / pole of magnetic circuit.

14. What are the losses determined from SCC?

i. Copper loss

ii. Mechanical loss

15. What are stray load losses?

Stray load loss is the sum of load core loss and loss due to the additional conductor resistance offered to the ac.

16. What is synchronizing?

The operation of connecting an alternator in parallel with another alternator or with common bus bars is known as synchronizing.

17. What is a synchroscope?

Synchroscope is an instrument, which shows the phase relationship of emf of the incoming alternator. It also indicates whether the incoming alternator is running slow or fast.

18. What is direct axis?

The mmf wave is height when it is aligned with the field pole axis called the direct axis or d

axis.

19. What is quadrature axis?

The permeance offered to a mmf wave is lower when it is oriented 90o

To the field pole axis called the quadrature axis or q axis.

20. What are the two curves required for POTIER method?

i. No load curve.

ii. Full load zero power factor curve called wattless load charactertic.

21. What are the three methods of determining voltage regulation?

i. Synchronous impedance method or EMF method. ii. The ampere-turn or MMF method.

iii. Zero power factor or potier method.

22. When does a synchronous motor get over excited?

If the field excitation of the motor is increased, the field flux will become strong and Eb will increase. As a result Eb will exceed V and the motor will be called an over excited motor.

23. Define pullout torque?

The pullout torque is the torque, beyond which the synchronous link between field poles and resultant flux wave is severed and the machine falls out-of-slip.

24. What is the main advantage of POTIER method?

The voltage regulation calculated by potier’s method is quite accurate.

25. What is meant by the subtransient period?

The initial period of decay of the short circuit current is called the subtransient, in which the current decay is governed mainly by the damper winding constant.

26. What is fractional pitch winding?

When a winding is made with coil span less than full pitch, the winding is called as fractional pitch winding.

Possible 16 mark questions:

1. Explain why a synchronous motor does not have starting torque.

2. Explain one method of starting a synchronous motor.

3. Why does the power factor of industrial installation tend to be low? How can it be improved?

4. Does the change in excitation affect the p.f of the synchronous motor?

5. An over excited synchronous motor is called a synchronous condenser. Explain.

6. Mention some specific applications of synchronous motor.

7. Explain what happens when the load on a synchronous motor is changed.

8. What is meant by constant power circle for synchronous motor?

9. What is meant by hunting in a synchronous motor? Why is it undesirable? What is done to minimize it?

10. Explain V-curves and inverted V-curves.

11. Draw the power angle diagram of a synchronous machine.

12. Explain briefly the principle of operation of three-phase synchronous motor.

13. Describe the effect of varying the excitation on the armature current and power factor of a synchronous motor when input power to the motor is maintained constant.

UNIT-III

1. What are types of 3- phase induction motor?

i. Squirrel cage induction motor ii. Slip ring induction motor

2. Why the rotor slots of a 3-phase induction motor are skewed?

The rotor slots of a three -phase induction motor are skewed

i. to make the motor run quietly by reducing the magnetic hum ii. to reduce the locking tendency of the rotor

3. Why the induction motor is called asynchronous motor?

Since the induction motor runs always at a speed lesser than synchronous speed, it is called asynchronous motor.

4. What are slip rings?

The slip rings are made of copper alloys and are fixed around the shaft insulating it. Through these slip rings and brushes the rotor winding can be connected to external circuits.

5. State the difference between slip ring rotor and cage rotor of an induction motor?

Slip ring rotor has 3-phase windings. Three ends of which are stared and the other three ends are brought up and connected to 3 slip rings mounted in the shaft. Extra

resistance can be added in the rotor circuit. Squirrel cage rotor has short-circuited copper bars.

Extra resistance can’t be added as slip ring rotor.

6. Write an expression for the slip of an induction motor.

Percentage slip = (Ns -Nr) / Ns * 100.

7. What is cogging of an induction motor?

When the number of stator and rotor teeth’s is equal or integral multiple of rotor teeth

,they have a tendency to align themselves exactly to minimum reluctance position. Thus the rotor may refuse to accelerate. This phenomenon is known as cogging.

8. Explain why the no load current of an induction motor is much higher than that of an equivalent transformer.

In induction motor, due to the presence of the air gap, the magnetizing current that is required to set up the flux is much higher. The working component of the current has to meet the hysteresis

loss, eddy current loss, friction and windage losses. Hence the no load current of induction motor is higher.

9. State the effect of rotor resistance on starting torque?

Starting torque increases with increase in value of rotor resistance.

10. What are the advantages of cage motor?

Ø Since the rotor has very low resistance, the copper loss is low and efficiency is high

Ø On the account of simple construction of rotor, it is mechanically robust.

Ø Initial cost is less.

Ø Maintenance cost is less.

Ø Simple stating arrangement

11. Give the conditions for maximum torque for 3-phase induction motor?

The rotor resistance and rotor reactance should be equal for developing maximum torque i.e. R2 = s X2 where s is the slip –under running conditions.

R2 = X2 under starting conditions

12. What is reason for inserting additional resistance in rotor circuit of a slip ring induction

motor?

Introduction of additional resistance in the rotor circuit will increase the starting torque as well as running torque. Also it limits the starting current, improves the power factor.

13. List out the methods of speed control of cage type 3-phase induction motor?

a) By changing supply frequency

b) By changing the number of poles

c) By operating two motors in cascade

14. Mention different types of speed control of slip ring induction motor?

a) By changing supply frequency

b) By changing the number of stator poles c) By rotor rheostat control

d) By operating two motors in cascade

15. What are the advantages of 3-phase induction motor?

a) It was very simple and extremely rugged, almost unbreakable construction b) Its cost is very low and it is very reliable

c) It has been suffiently high efficiency .No brushes are needed and hence

frictional losses are reduced

d) It requires minimum of maintenance.

16. What does crawling of induction motor mean?

Squirrel cage type, sometimes exhibit a tendency to run stably at speeds as low as

1/7 the of their synchronous speed, because of the harmonics this phenomenon is known as crawling

17. State the application of an induction generator?

a) Used in windmill for generating electric power.

b) Used in regenerative breaking places like traction.

18. Name the two windings of a single-phase induction motor.

I. Running winding ii. Starting winding.

19. What are the various methods available for making a single-phase motor self-starting?

I. By splitting the single phase into 2 phases ii. By providing shading coil in the poles.

20. What is the function of capacitor in a single-phase induction motor?

I. To make more phase difference between the starting and running winding. ii. To improve the power factor and to get more torque.

21. Give the names of three different types of single-phase motor.

I. Split phase motor

ii. Shaded pole motor.

iii. Single phase series motor. iv. Repulsion motor.

22. What is the use of shading ring in a pole motor?

The shading coil causes the flux in the shaded portion to lag behind the flux in unshaded portion of pole. This gives in effect a rotation of flux across the pole face and under the influence of this moving flux a stating torque is developed.

23. State any four use of single-phase induction motor.

Fans, Wet grinders, Vacuum cleaners, small pumps, compressors, drills

24. Why is the efficiency of a 3-phase induction motor less than of a transformer?

In induction motor, there is a mechanical loss due to the rotation of the rotor. Hence the efficiency of an induction motor is less than that of the transformer.

25. What are the types of starters?

Stator rheostat, Autotransformer and Star to Delta switch

Rotor resistance starter.

Possible 16 Mark Questions:

1. Develop the equivalent circuit for 3-phase induction motor? Apr: 2003 Ans: 4.26 A

2. Explain the different speed control methods of squirrel cage induction motor. Apr: 2003 Ans:

4.65 A

3. Describe the principle of operation of synchronous induction motor. Apr: 2003 Ans: 4.61 A

4. Explain any one method of speed control of three- phase induction motor. Ans: 4.65 A

5. Draw the slip-torque charactertics for a three-phase induction motor and explain. Apr: 1999

Ans: 4.17 A

6. Explain how a rotating magnetic field is produced in a three-phase induction motor. Apr: 1999

Ans: 4.5 A

7. Draw and explain the equivalent circuit of a three-phase induction motor. Apr: 2000 Ans:

4.23 A

8. Describe with a neat diagram, the principle of operation of induction generator Oct: 2000 Ans: 4.69 A

9. Draw and explain the torque/slip curves of a three-phase induction motor for different values of

rotor resistance. Oct: 2000 Ans: 4.23 A

10. Starting from the first principles, develop the equivalent circuit of a 3- phase induction motor. Apr: 2001 Ans: 4.26 A

11. Explain the procedure of drawing the circle diagram of an induction

motor. How are the performance charactertics obtained from it? Apr: 2001 Ans: 4.29 A

12. Explain the operation of induction generator. Oct: 2001

Ans: 4.69 A


UNIT-IV

1.What are the types of starters?

Stator rheostat, Autotransformer Star to Delta starter and rotor resistance starter.

2. List out the methods of speed control of cage type 3-phase induction motor?

a) By changing supply frequency

b) By changing the number of poles

c) By operating two motors in cascade

3.Mention different types of speed control of slip ring induction motor?

e) By changing supply frequency

f) By changing the number of stator poles g) By rotor rheostat control

h) By operating two motors in cascade

4.State the advantages of capacitor start run motor over capacitor start motor. Running torque is more; Power factor during running is more.

5.What is Universal motor?

A Universal motor is defined as a motor, which may be operated either on direct current or single-phase ac supply.

6.state some application of universal motor.

Used for sewing machines, table fans, Vaccum cleaners, hair driers, blowers etc

7.Explain why single-phase induction motor is not self-starting one.

When the motor is fed from a single phase supply its stator winding produces an alternating or pulsating flux, which develops no torque which is explained in Double revolving field theory..

8.What type of motor is used for ceiling fan?

Capacitor start and capacitor run single-phase motor is used for ceiling fans.

9.what is the type of induction motor used in wet grinders?

Capacitor start capacitor run single-phase induction motor.

10.what kind of motor is used in mixie?

Single-phase ac series motor is used in mixie.

11.what is the application of shaded pole induction motor?

Because of its small starting torque, it is generally used for small fans, toys, instruments, hair driers, ventilators, electric clock etc.

12. In which direction does a shaded pole motor run?

The rotor starts rotation in the direction from unshaded part to the shaded part.

13.why single-phase induction motor has low power factor?

The current through the running winding lags behind the supply voltage by a very large angle. Therefore power factor is very low.

14.Diffrentiate between “capacitor start “and “capacitor start capacitor run “induction motor?

In capacitor start motor, capacitor is connected in series with the starting winding. But it will be disconnected fro m the supply, when the motor picks up its speed. But in capacitor start

capacitor run motor the above starting winding and capacitor are not disconnected, but always connected in the supply .so it has high starting and running torque.

15. State the application of an induction generator?

v Used in windmill for generating electric power.

v Used in regenerative breaking places like traction.

16.What do you mean by residual EMF in a generator.

The EMF induced in the armature conductor only due to the residual flux in the field poles is known as residual EMF

17.State the effect of rotor resistance on starting torque?

Starting torque increases with increase in value of rotor resistance.

18.How can varying supply frequency control speed?

We know that

Ns = 120f

P

From the equation it is clear that by varying frequency speed can be varied it is vary rarely.

19.How is speed control achieved by changing the number of stator poles?

Here change in stator poles is achieved by having two or more independent stator windings in the same slot. Each winding gives different number of poles and different speeds. At a time only one winding is used and other is closed.

20.What are the main disadvantages of rotor rheostatic control?

Ø The speed can be decreased by increasing the rotor resistance, but increases I2R loss and hence decreases efficiency.

Ø Speed depends on load also and so used for small periods only.

21.What are the methods of speed control preferred for large motors?

Ø Kramer system

Ø Scherbius system

22.What is an induction regulator?

An induction regulator is used to obtain the constant voltage at the feeder end. Varying the range between the magnetic axes of the primary and secondary windings controls the voltage; it

may be a single phase. Rotor is moved usually by a maximum of 180 degree.

23.Define-Slip frequency.

The relation motion of the stator flux and the rotor conductors induces the voltage of frequency Sf called slip frequency.

24.Define- Asynchronous torque.

When stator and rotor fields are stationary with respect to each other, a steady torque is produced and rotation is maintained. Such a torque existing at any mechanical speed other than

synchronous speed is called as an asynchronous torque.

25.What is the main use of squirrel cage winding in synchronous motor starting?

When a squirrel cage winding called the amortissuer or damper winding is inserted in the rotor pole faces, the rotor comes up to the synchronous speed by induction motor action with the field winding unexcited.

26.What is breakdown torque?

From the torque verses slip charactertics, we can infer that as the torque increases, slip increases upto a maximum torque developed is called a breakdown torque.

27.What is the function of rotary converter? Where it is used?

Rotary converter converts low slip ac power. It is used in Kramer system, which is for the speed control of three-phase induction motor.

28.What are the advantages of Kramer system of speed control?

Any speed with in the working range can be obtained

When rotary converter is overexcited, it will take leading current, compensates with the lagging current drawn by the motor, thus improving power factor.

29.Write the expression for concatenated speed of the set.

Cumulative mode (Nsc) = 120f

Pa + Pb

Differential mode (Nsc) = 120f

Pa – Pb

Pa – no of poles of motor A Pb – no of poles of motor B

16 Marks Questions:

1.Develop the equivalent circuit for 3-phase induction motor.

APR/MAY 2003 Ans: Page- 4.23A & 289B

2.Explain the different speed control methods of squirrel cage induction motor. APR/MAY 2003 Ans: Page- 4.65A & 378B

3.Explain the methods of starting of induction motor. NOV/DEC 2003

Ans: Page- 4.45A & 368B

4.Explain the charactertics features of alternator on load.

NOV/DEC 2003 Ans: Page- 2.17A

5.Explanin what is crawling and cogging. NOV/DEC 2003

Ans: Page- 4.64A & 302B

6.Describle Kramer system of speed control for 3-phase induction motor with a neat diagram. NOV/DEC 2003 Ans: Page- 389B

7.Explain in detail autotransformer method of starting a squirrel cage induction motor. Ans: Page- 4.48A & 371B

8.How adding an external resistance in the rotor circuit controls the

speed? APR/MAY 2004 Ans: Page- 4.65A & 375B

9.Briefly explain the V/F control of an induction motor. NOV/DEC 2004

Ans: Page- 379B

10.Explain the working of following starters with help of neat circuit diagram.

Stator resistance starter Star- Delta starter Direct On Line Starter Rotor resistance Starter

Autotransformer Starter Ans: Page- 4.45A & 368B

11.Explain the pole amplitude modulation method.

Ans: Page- 4.69A & 383B

12.Explain the supply voltage method. Why this method rarely used in practice. NOV/DEC 2004 Ans: Page- 4.67A & 380B


Unit -V

1. Name the two winding of single phase induction motor?

Running and starting winding.

2. What are methods available for making single phase induction motor a self starting?

By slitting the single phase, by providing shading coil in the poles.

3. What is the function of capacitor in single phase induction motor?

To make phase difference between starting and running winding, to improve PF and to get more torque.

4. State any 4 use of single phase induction motor?

Fans, wet grinders, vacuum cleaner, small pumps, compressors, drills. Explain

5. Why single phase induction motor is not a self starting one?

When motor fed supply from single phase, its stator winding produces an alternating

flux, which doesn’t develops any torque.

6. What kind of motors used in ceiling fan and wet grinders?

Ceiling fan # Capacitor start and capacitor run single phase induction motor, wet grinders# Capacitor start capacitor run single phase induction motor.

7. What is the application of shaded pole induction motor?

Because of its small starting torque, it is generally used for small toys, instruments, hair driers, ventilators.etc.

8. In which direction a shaded pole motor runs?

The rotor starts rotation in the direction from unshaded part to the shaded part.

9. Why single phase induction motor have low PF?

The current through the running winding lags behind the supply voltage by large angle so only single phase induction motor have low PF.

10. Differentiate between “capacitor start” & “Capacitor start capacitor run” single phase

induction motor?

Capacitor start – capacitor is connected series with starting winding, but it will be disconnected from supply when motor pick up its speed. Capacitor start capacitor run# starting winding and capacitor will not be disconnected from supply even though motor pickup its speed.

11. What are the principal advantages of rotating field type construction?

Relatively small amount of power required for field system can easily supplied to rotating system using slip rings and brushes, more space is available in the stator part of the machine to provide more insulation, it is easy to provide cooling system, stationary system of conductors can easily be braced to prevent deformation.

12. Why an induction motor never runs at its synchronous speed?

If it runs at sy.speed then there would be no relative speed between the two, hence no rotor emf, so no rotor current, then no rotor torque to maintain rotation.

13. What are the advantages of cage motor?

Since the rotor has low resistance, the copper loss is low and efficiency is very high. On account of simple construction of rotor it is mechanically robust, initial cost is less; maintenance cost is less, simple starting arrangement.

14. Why an induction motor is called as rotating transformer?

The rotor receives same electrical power in exactly the same way as the secondary of a two winding transformer receiving its power from primary. That is why induction motor is called as rotating transformer.

15. What is the use of shading coil in the shaded pole motor?

In shaded pole motors the necessary phase –splitting is produced by induction. These motors have salient poles on stator and a squirrel cage type rotor. The poles are shaded ie each pole carries a copper band one of its unequally divided part is called shading band. When single phase ac supply is given to the stator winding due to shading provided to the poles a rotating magnetic field is generated.

16. Why capacitor –start induction motors advantageous?

In capacitor start induction motors capacitor is connected in series with the auxiliary winding. When speed of the motor approaches to 75 to80%of the synchronous speed the starting winding gets disconnected due to the operation of the centrifugal switch. The capacitor remains in the circuit only at start. The starting torque is proportional to phase angle ά and hence such motors produce very high starting torque.

17. List out 4 applications of shaded pole induction motor?

Shaded pole motors have very low starting torque, low power factor and low efficiency. The motors are commonly used for small fans, toy motors, advertising displays, film projectors, record players, gramophones, hair dryers , photocopying machines etc

18. What are the drawbacks of the presence of the backward rotating field in a single phase induction motor?

Due to cutting of flux, emf gets induced in the rotor which circulates rotor current .the rotor current produces rotor flux. This flux interacts with forward component φf to produce a

torque in one particular direction say anticlockwise direction. While rotor flux interacts with backward component φb to produce a torque in the clockwise direction. So if anti clock wise torque is positive then clockwise torque is negative thus net torque experienced by the rotor is zero at start.

19. Why is hysteresis motor free from mechanical and magnetic vibrations?

The stator of hysteresis motor carries main and auxiliary windings to produce rotating magnetic field or of shaded pole type also. The rotor is smooth cylindrical type made up of hard magnetic material. The torque in this motor is constant at all speeds it runs at synchronous speed. There is not relative motion between stator and rotor field so the torque due to eddy current vanishes. Only hysteresis torque is present which keeps rotor running at synchronous speeds .the high retentivity ensures continuous magnetic locking between stator and rotor. Hence it is free from magnetic vibrations

20. What types of motor is used in computer drives and wet grinders?

For computer drives permanent magnet dc motors are used while in wet grinder’s

universal motor may be used.

21. Give two advantages and two applications of stepper motor.

Advantages:

*These motors are compatible with digital equipments and are flexible in operation.

*The dynamic response is fast

Applications:

Stepper motors are widely used in computer peripherals such as serial printers tape drives, floppy disk drivers. They are also used in control of machine tools. Robotics.

22. List some applications of linear induction motor?

They are used in machine tool industry and in robotics .They are used in trains operated on magnetic levitation , reciprocating compressors can also be driven by linear motors

23. What are the specific characteristic features of the repulsion motor?

Repulsion motors give excellent performance characteristics. A very high starting torque of about 300 to350% of full load can be obtained with starting currents of about 3 to 4 times the full load current. Thus it has got very good operating characteristics. The speed of the motor changes with load .with compensated type of repulsion motor the motor runs with improved power factor as the quadrature drop in the field winding is neutralized. Also the leakage between armature and field is reduced which gives better regulation.

24. Discuss characteristics of single phase series motor

* To reduce the eddy current losses, yoke and pole core construction is laminated

*The power factor can be improved by reducing the number of turns. But this reduces the field flux.

But this reduction in flux increases the speed and reducing the torque. To keep the torque same it is necessary to increase the armature turns proportionately. This increases the armature inductance.

25. What are the demerits of repulsion motor?

*very expensive

*speed changes with load

* on no load speed is very high causing sparking at brushes*low power factor on no load

26. List four applications of reluctance motors?

This motor is used in signaling devices, control apparatus, automatic regulators, recording instruments, clocks and all kinds of timing devices, teleprinters, gramophones 27. What is a universal motor?

There are small capacity series motors which can be operated on dc supply or single phase ac supply of same voltage with similar characteristics called universal motors. The construction of this motor is similar to that of ac series motor

16 Mark questions:

1.Explain the operation of a single-phase induction motor using double revolving field theory. APR/MAY 2003 Ans: page 5.2A&401B

2.Describe the constructional features and operating charactertics of single- phase shaded pole motor. APR/MAY 2003 Ans: page 5.8A&408B

3.Explain the construction and principle of working of stepper motor. APR/MAY 2003 Ans: page 5.21A&432B

4.Explain the principle of operation and applications of reluctances motor. APR/MAY 2003 Ans: page 5.18A&451B

5.Explain the principle of operation and constructional details of linear induction motor. APR/MAY 2003 Ans: page 5.31A&452B

6.List some applications of linear induction motor. APR/MAY 2003

Ans: page457B

7.Write brief notes on hysteresis motor. APR/MAY 2003

Ans: page 5.20A&442B

8.Write brief notes on A.C.series motor. APR/MAY 2003

Ans: page 5.16A&445B

9.Explain the methods of making single-phase induction motor self-starting.

NOV/DEC 2003 Ans: page 5.4A & 404B

10.Explain write is crawling and cogging? NOV/DEC 2003

Ans: page 4.61A & 302B

11.Write short notes on linear induction motor. NOV/DEC 2003

Ans: page 5.31A &452 B

12.Write notes on permanent magnet DC motor. NOV/DEC 2003

Ans: page 5.27A &454 B

13Write a brief notes on shaded pole motor. NOV/DEC 2003

Ans: page 5.8A&408B

14.Explain the speed control of universal motor. OCT 2000 Ans: page 446B

15.What is a universal motor? Draw its phasor diagram and discuss its operation. Bring out the effects of various emf induced in the armature. APR 2001 Ans: page 446B