# Power Electronics 2 mark Questions from University Question Papers: Set9

### Power Electronics 2 mark Questions Frequently asked in University Question Papers

[1] What do you understand by constant torque drive and constant power drive? [AU/PED-May 2003]

Constant Torque Drive
In armature voltage control methods, armature current and field flux ( or field current) are kept constant so as to meet the torque demand.
So the armature voltage control method is also called constant torque drive because motor torque T = KaΦIa remains constant.

Constant Power Drive
Above rated speed can be obtained by varying the field current or field flex and by keeping motor voltage V and Ia constant.
As flux decreases, speed increases so that motor back EMF (Eb) remains almost constant.
So field control method is also called constant power drive because power P = EIa remains constant.

[2] Mention the applications of chopper fed dc drives [AU/PED -May-2003]

1. Subway cars
2. Cranes
3. Traction
4. Battery operated vehicles.

[3] What are the four quadrants of dc drives? [AU/PED -2003]

1. Forward motoring mode
2. Forward braking mode
3. Reverse braking mode
4. Reverse motoring mode

[4] What is chopper? [MKU -2000]

It converts fixed DC voltage into variable dc voltage.

[5] What are the uses of phase controlled rectifier in dc drives? [AU/EEE - Dec2004]

1. Rolling mills
2. Hoists
3. Paper mills
4. Printing presses
5. Textile mills

[6] What are the disadvantages of stator voltage control method? [AU/ME-2005]

1. Voltage and current waveforms are highly distorted due to harmonics, which affects the efficiency of the motor.
2. Performance is poor under running condition at low speeds.
3. Operating efficiency is low as resistance losses are high.
4. At low speeds, motor currents are excessive and special arrangements should be provided to limit the excessive currents.
5. Maximum torque available from the motor decreases with reduction in stator voltage.

[7] What is meant by duty cycle in a chopper circuit? [MKU - 2000]

The duty cycle is defined as the ratio of ON time of the chopper to total time period of the chopper.
α = TON/T

#### Related Posts:

Thanks for reading... Please subscribe to get new posts to your mail id...