250+ TOP MCQs on Electrical Drive Systems and Components – Sequence Operations and Protection & Answers

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Electric Drives Question Bank on “Electrical Drive Systems and Components – Sequence Operations and Protection”.

1. Relay is an electromechanical switch.
A. True
B. False

Answer: A
Clarification: Relay is an electromechanical switch. It uses electrical signals as input and mechanical operation as an output.

2. Mho relay is used in the medium transmission line.
A. True
B. False

Answer: B
Clarification: Mho relay is an inherent directional relay. It is used in the long transmission line. It is less affected by power surges.

3. Full form of LED is _____________
A. Light Emitting Diode
B. Light Emission Digital
C. Light Energy Diode
D. Light Energy Digital

Answer: A
Clarification: The full form of LED is a light-emitting diode. It converts light energy into electrical energy. It works in the reverse bias region.

4. Inter turn fault can be detected by using __________
A. Oil circuit breaker
B. Split phase relay
C. SF6 circuit breaker
D. Vertical breaker

Answer: B
Clarification: Inter turn fault mainly occurs in the winding of the rotor side of the alternator. They can be detected by using the split-phase relaying technique.

5. Calculate the value of the fault impedance if the fault voltage is 2 V and fault current is 4 A.
A. .5 ohm
B. .2 ohm
C. .4 ohm
D. .6 ohm

Answer: A
Clarification: The value of the fault impedance is the ratio of fault voltage and fault current. It is expressed in ohms. Z=V/I=2/4=.5 ohm.

6. Reactance relay is used in _______
A. Medium line
B. Short transmission line
C. Lossless line
D. Long transmission line

Answer: B
Clarification: Reactance relay is used in a short transmission line. Reactance relay is independent of the resistance value. It protects the short transmission line from any fault.

7. Load interrupter operated at ________
A. No-load
B. Full load
C. Half of the full load
D. One-fourth of the full load

Answer: B
Clarification: Load interrupter is used to avoid overloading conditions. It separates the under-stressed area from the line. It operates at full load.

8. Calculate the maximum frequency for ASCI using the data: R=1 kΩ, C=1 μF.
A. 250 Hz
B. 280 Hz
C. 300 Hz
D. 320 Hz

Answer: A
Clarification: The minimum time period for ASCI is a 4×R×C=4×1×1×.001=4 msec. The total time is the sum of charging and discharging time. The maximum frequency is 1÷f=250 Hz.

9. Calculate the PIV for the Full-wave bridge rectifier if the peak value of the supply voltage is 50.
A. 72.5 V
B. 72.8 V
C. 70.7 V
D. 76.1 V

Answer: C
Clarification: The peak inverse voltage for the Full-wave bridge rectifier is Vm = √2×230=70.7 V. The peak inverse is the maximum negative voltage across the thyristor.

10. In single-phase, RLE load, calculate the Peak inverse voltage using the data: (Vs)r.m.s = 9 V, f = 50 Hz, E = 40 V.
A. 52.2 V
B. 52.7 V
C. 59.7 V
D. 52.9 V

Answer: B
Clarification: In a single phase, RLE load the peak inverse voltage across the thyristor VT = Vm+E = 52.7 V.