UPPCL EE : Power electronics Quiz 5 for AE & JE Exams Exams

Question 1

A large dc motor is required to control the speed of the blower from a 3-phase ac source. The suitable ac to dc converter is, 3-phase

Question 2

Consider the following statements regarding ac drives:
1) For the same kW rating, ac motors are 20% to 40% light weight as compared to dc motors.
2) The ac motors are more expensive as compared to same kW rating dc motors.
3) The ac motors have low maintenance as compared to dc motors.
Which of the above statements are correct?

Question 3

Purpose of snubber circuit is to limit which of the following?

Question 4

Statement (I): A switched-mode dc power supply has high efficiency and light weight.
Statement (II): A switched-mode dc power supply uses a dc to dc switching converter switched at high frequency.

Question 5

The operation of an inverter fed induction motor can be shifted from motoring to regenerative braking by

Question 6

Statement I: Power transformer core is made of soft magnetic material like silicon steel.

Statement II: In regenerative braking power is feed back from motor to the source.

Question 7

Match List-i (Controller) with List-ii (Type of load) and select the correct answer using the code given below the lists:
List-i
A- Chopper controlled resistance in the rotor circuit of an induction motor
B- Sub-synchronous converter-cascade in the rotor circuit of an induction motor
C- 3-phase a.c. voltage controller
D- Cycloconverter
List-ii
1. Very low speed, high-power reversible drive
2. Centrifuges in sugar industry
3. Blowers and compressors
4. Loads requiring good starting performance

Question 8

Which of the following statements about static drives are true ?

1. Static Scherbius drives: The speed can be controlled below and above synchronous speeds.

2. Static frames drive offers speed control above synchronous speed only.

3. A speed torque characteristic of static Kramer drive is similar to separately excited dc motor with armature voltage control.

Question 9

A three-phase semi-converter feeds the armature of a separately excited dc motor supplying a non-zero load torque. For steady state operation the motor current is found to assume zero value at certain instances of time. At such instances the armature voltage

Question 10

In cyclo converter, which of following is true?