Quiz: Electrical Engineering 8 Aug 2020

Quiz: Electrical Engineering
Exam: NLC-GET
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. Which damping is used in moving iron instrument?
(a) Air friction damping
(b) Eddy current damping
(c) Fluid friction damping
(d) Electromagnetic damping

Q2. A voltage and current waveform of an element below.
V(t) = 120 sin (3t + 120°)
I(t) = 20 cos (3t – 60°)
The element is ……?
(a) Pure inductor, L = 2H
(b) Pure capacitor
(c)Resistance of 3 Ω in series with inductor of L = 1 H
(d) Resistance of 3 Ω in series with capacitor of

Q3. The Eddy current loss is proportional to the
(a) Frequency
(b) Square of the frequency
(c) Cube of the frequency
(d)Square root of the frequency

Q4. Electrical fault between two windings of same phase of a generator having double star winding can be detected by the following protection in a generator:
(a) Short circuit protection
(b) Earth fault protection
(c) Inter turn Fault protection
(d) Over voltage protection

Q5. Negative sequence relay is used commonly to protect
(a) An alternator
(b) A transformer
(c) A transmission lines
(d) A bus bars

Q6. In Fig., the supply voltage is ……….


(a) 500 V
(b) 100 V
(c) 200 V
(d) 400 V

Q7. In a parallel a. c. circuit, if the supply frequency is less than the resonant frequency, then the circuit is ………….
(a) inductive
(b) capacitive
(c) resistive
(d) none of the above

Q8. The tendency of charge carriers to move from a region of heavily concentrated charges to region of less concentrated charge is known as.
(a) Depletion current
(b) Drain current
(c) Diffusion current
(d) Saturation current

Q9. The type number of the control system with G(s) H(s) = (K(s+2))/(s(s^2+2s+3)) is
(a) One
(b) Two
(c) Three
(d) Four

Q10. What is the purpose of the address bus?
(a) to provide data to and from the chip
(b) to select a specified chip
(c) to select a location within the memory chip
(d) to select a read/write cycle

SOLUTIONS

S1. Ans.(a)
Sol. In moving iron instrument the damping which is used is Air friction damping, by a vane moving in a sector shaped chamber.

S2. Ans.(a)
Sol. V(t) = 120 cos (3t + 120° – 90°); V(t) = 120 cos (3t + 30°)
I(t) = 20 cos (3t – 60°)
Z=V/I=(120∠30)/(20∠-60)=6∠90⁰=j6
∴Z = j6 Ω, ωL = 6, 3×L=6 i.e. L=2 H

S3. Ans.(b)
Sol. Eddy current loss in a transformer is fixed, and it depends on the core material’s magnetic properties. Eddy current loss is given as:

S4. Ans.(c)
Sol. Inter turn stator winding fault can easily be detected by stator differential protection or stator earth fault protection. Hence, it is not very essential to provide special protection scheme for inter turn faults occurred in stator winding. This type of faults is generated if the insulation between conductor (with distinct potentials) in the same slot is punctured. This type of fault rapidly changes to earth fault.

S5. Ans.(a)
Sol. Negative sequence currents gives rise to another rotating magnetic field in the generator in opposite direction which leads to excessive copper loss and pulsation in electromagnetic torque, which causes mechanical stress on the shaft of the alternator. So negative sequence relay is commonly used to protect alternator.

S6. Ans.(b)
Sol. Since voltage across L is equal to voltage across C, it is a case of series resonance.
∴ Supply voltage = Voltage across R = 100 V

S7. Ans.(a)
Sol. In a parallel a. c. circuit, if the supply frequency is less than the resonant frequency, then the circuit is inductive

S8. Ans.(c)
Sol. In a semiconductor the charge will always have a tendency to move from higher concentrated area to less concentrated area to maintain equilibrium this movement of charges will result in diffusion current.

S9. Ans. (a)
Sol. Pole at origin is one. Type of the system is determined by open loop poles at origin.

S10. Ans.(c)
Sol. Address bus is used to choose a particular location in the memory chip. Data bus is used to provide data to and from the chip. Chip select signals are used to select a particular chip within the memory.

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