DSSSB-JE/AE’21 EE: Daily Practices Quiz 30-Dec-2021

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DSSSB-JE/AE’21 QUIZ: ELECTRICAL ENGG.

DSSSB-JE/AE’21 EE: Daily Practices Quiz 30-Dec-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 06 min

Q1. Under which of the following conditions hunting of synchronous motor is likely to occur?
(a) Small and constant load
(b) Over-excitation
(c) Periodic variation of load
(d) Over loading for long periods

Q2. If a coil of resistance R and inductance L, its time constant is given by
(a) LR
(b) 1/LR
(c) R/L
(d) L/R

Q3. A 125 V DC motor is rated at 10 KW. What is the current rating for the motor?
(a) 4.6 A
(b) 46.2 A
(c) 80 A
(d) 8 A

Q4. The circuit whose properties are same in either direction is known as
(a) Bilateral circuit
(b) Unilateral circuit
(c) Reversible circuit
(d) Irreversible circuit

Q5. Bundled conductors are mainly used in high voltage overhead transmission line to
(a) Reduce transmission line losses
(b) Increase mechanical strength of the line
(c) Reduce corona
(d) Reduce sag

Q6. A device having characteristics very close to that of an ideal voltage source is
(a) Vacuum diode
(b) Transistor
(c) FET
(d) Zener diode

SOLUTIONS

S1. Ans.(c)
Sol. Hunting is the phenomenon that occurs in synchronous motor due to varying load or frequency.
Causes of Hunting in Synchronous Motor:
Sudden change in load.
Sudden change in field current.
A load containing harmonic torque.
Fault in supply system.

S2. Ans.(d)
Sol. The time constant for an RL circuit is defined by τ = L/R.
The time constant in a capacitor circuit is the product of the resistance and capacitance. T = RC.

S3. Ans.(c)
Sol. I_rated=P/V=(10×10^3)/125=80 A

S4. Ans.(a)
Sol.
Unilateral Circuits:
In unilateral circuits, when the circuit property changes at the same time direction of supply voltage or current also are changed. The diode rectifier is the main example of the unilateral circuit because it doesn’t perform the rectification in both directions of supply.
Bilateral Circuits:
In bilateral circuits, when the circuit property didn’t change, but the change in the direction of supply voltage or current takes place. The transmission line is the main example of the bilateral circuit because if you give power supply from any direction, the circuit properties remain constant.

S5. Ans.(c)
Sol. By using bundled conductors, the self GMD or GMR of the conductors is increased.
Corona loss α (V-V_0 )^2
V_0 is approximately directly proportional to the size of the conductor, hence larger the size of the conductor larger will be the critical disruptive voltage and smaller will be the factor (V-V_0 )^2 and hence, smaller will be the corona loss.

S6. Ans.(d)
Sol. Zener diode is used as a Shunt voltage regulator for regulating voltage across small loads. The breakdown voltage of Zener diodes will be constant for a wide range of current. Zener diode is connected parallel to the load to make it reverse bias and once the Zener diode exceeds knee voltage, the voltage across the load will become constant.