EE2303 Transmission & Distribution–Important Questions–2012 Edition

Anna University
Department of Electrical & Electronics Engineering


Department : B.E EEE
Semester : V
Year : 3rd yr
Regulation : 2008
Subject Code : EE2303

Subject Name : Transmission & Distribution

Content : EE2303 Transmission & Distribution 16marks (Part B) Important Questions - 2012 Edition.


UNIT-1

1. i, compare power transmission using over head line and under ground cable. [8 MARKS]

ii, Draw a simple model of UPFC ? . [8 MARKS]

2. What are the advantages of high transmission voltage for the transmission of electrical power?

3. A50KM long transmission line supplies a load of 5 MVA at 0.8 power factor lagging at 33KV.The efficiency of transmission is 90% calculate the volune of Al conductor reqired for the line when three phase 3 wire system is used .The specific resistance of AL IS 2.85*10-8 ohm-m. [16 MARKS]

4. Explain the detail types of FACTS controllers. [16 MARKS]

5. Derive expressions for sag and tension in a power conductor strung between to supports at equal highs taking into account the wind and ice loading also. [16 MARKS]

6. i) Derive the expressions for sag and conductor length under bad weather conditions. Assume Shape of overhead line is a parabola. [8 MARKS]

ii) An overhead line has a span of 300m. The conductor diameter is 1.953cm and the conductor weight is 0.844kg/m. Calculate the vertical sag when a wind pressure is

736 N/sq.m of projected area acts on conductor. The breaking strength of conductor is

77990N and the conductor should not exceed half the breaking strength. [8 MARKS]

7. Draw and explain the structure of modern power systems with typical voltage levels. What is the highest VDH level available in India? [13 + 3 MARKS]

8. i) List out the main components of a HVDC system. [8 MARKS]

ii) Discuss various types of HVDC links. Mentions any one HDVC link available in

Indian with rating ?[8 MARKS]

9. i) Explain the different types of HVDC links and state the advantages of HVDC

transmission over AC transmission. . [8 MARKS]

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


UNIT-2

1. From the fundamentals derive an expression for inductance of a single phase transmission system.[16 MARKS]

2. Derive expression for the inductance of three phase line with conductors untransposed. What is the significance of imaginary term in the expression for inductance ?hence derive the expression for inductance for a completely transposed line.[16 MARKS]

3. Derive for expression for the capacitance of unsymmetrical and symmetrically spaced three Phase line compare the results

4. Derive an expression for capacitances of a single phase transmission system and discuss the effect of earth on capacitance with suitable equation. [16 MARKS]

5. Derive an expression for inductance

i) of a single-phase overhead line. . [8 MARKS]

ii) A conductor is composed of seven identical copper strands each having a radius r. Find the Self-GMD of the conductor. . [8 MARKS]

6. i Derive an expression for the capacitance between conductors of a single-phase overhead line. [8 MARKS]

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 MARKS]

7. Derive an expression for inductance of a 3-phase transmission line with unsymmetrical spacing? [16 MARKS]

8. Drive an expression for capacitance of a 3-phase transmission line with equilateral spacing? [16 MARKS]


UNIT-3

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 O / Km, 1.5 cm outside dia, spaced equilaterally 2 metres between centres. Use nominal T method. [16 MARKS]

2. A three phase 5 km long transmission line, having resistance of 0.5 O / 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 MARKS]

3. i) Show that the real power transferred is dependent on the power angle and the reactive power transferred is dependent on the voltage drop in the line. [8 MARKS]

ii) The constants of a 3-phase lines are A=0.9 2? and B=140 70? O / phase. The lines delivers 60 MVA at 132 kV and 0.8 pf lagging. Draw circle diagrams and find.

4. Explain

i. sending end voltage and power angle. [4 MARKS]

ii. The maximum power, which the line can deliver with the above values of sending end and

receiving end voltages. [4 MARKS]

iii. Sending end power and power factor. [4 MARKS]

iv. Line losses. [4 MARKS]

5. i) What is an equivalent ? circuit of long line? Derive expression for parameters of this circuit in terms of line parameters. [8 MARKS]

ii) A 50Hz transmission line 300 km long total series impedance of 40+j25 O 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 ? Method. [8 MARKS]

6. A short 3-phase transmission line has a series line impedance per phase of (20+j50) ohm. Them line delivers a load of 50 MW at 0.7 pf tag . Determine the regulation of the line and the A,B,C,D parameter of the line. If the same load is delivered at 0.7 pf load . determine the regulation of the line. system voltage 220KV? [16 MARKS]

7. The A,B,C,D constant of a 3- phase transmission line are A=D=0.963+j0.016,B=33.5+j138 ohm ,C=(-0.9280+j901.223) X 10-6 mho. The load at the receiving end is 40 MW at 220 KV with power factor of 0.86 lagging .Find the magnitude of the sending and voltage ,current, power line efficiency and the voltage regulation. Assume the magnitude of the sending and voltage remains constat ? [


UNIT-4

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

2. Explain any two methods of grading of cables with necessary diagrams. [16 MARKS]

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

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 MARKS]

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 MARKS]

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 a such a way that the stress varies between the same maximum and minimum in the three layers find:

1.position of inner sheaths

2.Voltage on the linear sheaths

3.Maximum and minimum stress

5. Elaborate the various methods to improve the string efficiency? [16 MARKS]

6. What is grading of cable? Describe teo methods? [16 MARKS]


UNIT-5

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

breaker. State their advantages and disadvantages. [16 MARKS]

2. Explain the following: (i) Neutral grounding

(ii) Resistance grounding. [16 MARKS]

4.i)Explain different types Tariff. [8 MARKS]

ii) Why a consumer having low power factor is changed at high rates. [8 MARKS]

5. Describe any four type of substation bus schemes?6 Discribe and compare the radial and ring main distribution system. What is the role of interconnectors in distribution systems? [16 MARKS]