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Classification of Electric Drive Based on Power Supply

Classification of Electric Drive:

Main classification of electric drives are :

1. DC drives and

2. AC drives

DC drives :

A dc motor speed can be controlled by using a power converter. Here motor is coupled with load.

AC drives:

An AC motor speed can be controlled by power converter. Here motor is coupled to the load.

The main purpose is to vary the motor speed.

Comparison between DC and AC drives:

DC drives AC drives

1. Power circuit and control circuit is simple

2. Frequent Maintenance.

3. Commulator makes bulky , costly and heavy.

4. Speed and design rating are limited due to commutation.

5. This is used in certain location

6. Fast response and wide speed range smooth achieved by conventional and solid state control

7. Poor PF, harmonic distortion of the current.

8. Power / weight ratio is small.

1. Power and Control circuit is

complex.

2. Less Maintenance.

3. Problems are not there, particularly squirrel cage motor.

4. Ratings have no upper limits.

5. Used in all location

6. In solid state control speed range is wide and conventional method it is stepped and limited.

7. For Regenerative drives the line pf is poor, for non-regenerative drives the line PF is better.

8. Power / weight ratio is large.

Solid State Drives – Parts of Electric Drives

Parts of Electric Drives:

1. Electrical motors and load

2. Power modulator

3. Source

4. Control unit

5. Sensing unit.

Electric Motors:

Most commonly used electric drives are

DC motos – Shunt , Series. Compound and permanent magnet.

Induction Motors – Squirel cage , wound rotor and linear

Synchronous motor - Wound field and permanent magnet

Brushless Dc motors , stepper motors, and switched reluctance motors can be used.

Power Modulator

It can classified as

1. Controlled rectifier (AC to DC converters)

2. Inverters (DC to AC converters)

3. AC voltage controllers (AC to AC converters)

4. DC choppers (DC to DC converters)

5. Cyclo converters (Frequency conversion)

Electrical Source:

Single Phase and Three Phase , 50Hz readily available in most locations.

Very low power drives fed from single phase source. Rest of the drives from three phase source.

Low and medium power motor are fet from 400v supply.

Higher rating , motors are fed from 3.3kv , 6.6 kv , 11kv.

Some drives are power from a battery , battery voltage may be 24v, 48v and 110v.

Sensing unit :

1. Speed sensing is required for implementation of closed loop speed control schemes.

2. Speed sensing by tachometers , high speed accuracies required digital tachometers are used.

3. Current sensing methods are

· Use of current sensor employing hall effect.

· Involves the use of a non-inductive resistance shunt in conjunction with an isolation amplifier which has an arrangement for an amplification and isolation bet power and control units.

Control Units :

· Control for power modulator is provided in the control unit.

· When semi conductor converts are used, the control unit will consist of firing circuits, which employ linear and digit integrated circuits and transistor and a up when sophisticated control is required.

Power Modulator and Simple Electric Drive

Block Diagram of a simple electric drive:

· System employed for motion control are called Drives.
· Drives employed electric motors are known as “Electric Drives”
· Load is usually a machinery designed to accomplish a given task eg: fans, pumps, robots, trains and drills.

Power Modulator:
· Modulates the flow of power from the source to the motor in such a manner that the motor will modulate the speed – torque characteristics required by the load.
· During transient operation , such as starting , breaking and speed reversal , it restricts source and motor currents within permissible values.
· Converts electrical energy of the source in the form of suitable to the motor.
· Select the mode of operation of the motor (i.e) Motoring or Braking.

Classification of Electric Drive with Advantage and Disadvantage

Classification of Electric Drive

Generally classified into 3 categories:

I. Group drive

II. Individual Drive

III. Multimotor Drive

Group Drive :

If several group of mechanisms or machines are organized on one shaft and driven or actuated by one motor, the system is called a group drive or shaft drive.

Advantage :

Most Economical

Disadvantage:

1. Any Fault that occurs in the driving motor renders all the driving equipment idle.

2. Efficiency low because of losses occurring in the energy transmitting mechanisms (Power loss)

3. Not safe to operate.

4. Noise level at the working spot is high.

5. Flexibility.

Single motor drives a no of machines through belt form common shaft.

Individual Drive:

1. If a single motor is used to drive or actuate a given mechanism and it does all the jobs connected with this load , the drive is called individual drive.

2. All the operations connected with operating a lathe may be performed by a single motor.

3. Each motor is driven by its own separated motor with the help of gears , pulleys etc.

Disadvantage:

Power loss occurs.

Multi Motor Drive:

· Each operation of the mechanism is taken care of by a separate drive motor.

· The System contains several individual drives each of which is used to operate its own mechanism.

· Separate motors are provided for actuating different parts of the driven mechanism.

Advantage :

1. Each Machine is driven by a separated motor it can be run and stopped as desired.

2. Machines not required can be shut down and also replaced with a minimum of dislocation.

3. There is a flexibility in the installation of different machine’s.

4. In the case of motor fault, only its connected machine will stop where as others will continue working undisturbed.

5. Absence of belts and line shafts greatly reduces the risk of a accidents to the operating personnel.

Disadvantage:

Initial high cost.

TANCET 2013 - Entrance Exam Dates and Timings

Anna University Chennai had announced the TANCET 2013 Entrance Exam Dates and Timings. The Exam will be held on 6th April for M.B.A and M.C.A , for others its on 7th April. The Timings are as follows :

M.B.A

Date : 6/4/2013 (Saturday)

Time : 10am to 12pm

M.C.A

Date : 6/4/2013 (Saturday)

Time : 2.30pm to 4.30pm

M.E/M.Tech/M.Arch/M.Plan

Date : 7/4/2013(Sunday)

Time : 10am to 12pm

All the Best...!!

University of Madras - Nov 2012 Exam Results (PG)

University of Madras PG Examination Result will be announced tomorrow (28th Jan 2013). Result will be announced for PG Courses : M.B.A , M.C.A , M.Sc, M.Com , and M.A examination held on Nov 2012.

Result will be announced on the following website :

www.unom.ac.in

www.examresults.net

- All the Best !!

Anna University - Mathematics 1 - Previous Year Question Paper Collection

Mathematics 1 Anna University Previous Year Question Paper.

Download Links :

Vidyarthiplus (V+) have a collections of Mathematics 1 Previous Year Question Paper from 2004 to 2012.

Students can download the Question Paper from the Below links :

Semester 1 Question Paper Collection

Sem 1 Previous Year Question Paper Index

* More Question Paper will be Updated Soon !!

CA Final Exam Results Nov 2012

CA Final Exam Results Nov 2012

CA Final Exam Results for November 2012 is to be announced on third week of January 2013. On behalf of Institute of Chartered Accountants of India the CA Final Exam was held on November 2012. The Results for the CA Nov 2012 Final Exam Results expected to be announced on January 2013 - said by ICAI President Narendra Shah.

Last year the CA Final Exam Results are announced on January, as the same this year to be expected to be announced on January.

Result Link : http://caresults.nic.in/

Expected Result announcing Date : 21st Jan 2013

All the Best..!!

Anna University Nov / Dec 2012 Exam Results

Anna University

Anna University affiliated colleges Nov / Dec 2012 Exam Results for Chennai ,Coimbatore , Tiruchi , Tirunelveli and Madurai are expected to be announced within a week for semester 3,5 and 7.

V+ is proud to say that we have released the May / June 2012 Exam Results first in net via Anna University Exam Cell Category. We assure this time Nov / Dec 2012 will be released first on V+ Exam Results.

Anna University Exam Cell : http://www.vidyarthiplus.com/vp/Forum-Anna-University-Exam-Cell

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