Power Electronics 2 mark Questions from University Question Papers: Set9
Power Electronics 2 mark Questions Frequently asked in University Question Papers
 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.
 Mention the applications of chopper fed dc drives [AU/PED -May-2003]
- Subway cars
- Battery operated vehicles.
 What are the four quadrants of dc drives? [AU/PED -2003]
- Forward motoring mode
- Forward braking mode
- Reverse braking mode
- Reverse motoring mode
 What is chopper? [MKU -2000]
It converts fixed DC voltage into variable dc voltage.
 What are the uses of phase controlled rectifier in dc drives? [AU/EEE - Dec2004]
- Rolling mills
- Paper mills
- Printing presses
- Textile mills
 What are the disadvantages of stator voltage control method? [AU/ME-2005]
- Voltage and current waveforms are highly distorted due to harmonics, which affects the efficiency of the motor.
- Performance is poor under running condition at low speeds.
- Operating efficiency is low as resistance losses are high.
- At low speeds, motor currents are excessive and special arrangements should be provided to limit the excessive currents.
- Maximum torque available from the motor decreases with reduction in stator voltage.
 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
Power Electronics Basic Interview Questions : Set-4
Anna University ME Power Electronics and Drives Previous Year Question Papers: Set-7
Electrical Drives Anna University Previous Year Question Papers with Answers: Set - 6
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