Quiz: Electrical Engineering 29 Aug 2020

Quiz: Electrical Engineering
Exam: SSC -JE
Topic: Miscellaneous

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

Q1. In a transmission system the feeder supplies power to
(a)Generating stations
(b) Service mains
(c)Distributors
(d)All of the above

Q2. Feeder is designed mainly from the point of view of
(a)Its current carrying capacity
(b)Voltage drop in it
(c)Operating voltage
(d) Operating frequency

Q3. Distributors are designed from the point of view of
(a)Its current carrying capacity
(b)Operating voltage
(c)Voltage drop in it
(d)Operating frequency

Q4. Which of the following is/are active element?
(a)Current source
(b)Voltage source
(c)Both voltage source and current source
(d)None of the above

Q5. Superposition theorem is not applicable for
(a)Current calculations
(b)Voltage calculations
(c)Power calculations
(d)None of the above

Q6. The speed-torque regimes in a DC motor and the control methods suitable for the same are given, respectively, in Group-II and Group-I
Group-I                           Group-II
P. Field control                 1. Below base speed
Q. Armature control         2. Above base speed
3. Above base torque
4. below base torque
The match between the control method and the speed-torque regime is as follows:
Code:
P      Q
(a) 1       3
(b) 2       1
(c) 2        3
(d) 1       4

Q7. Two capacitance, C1 = 150 ± 2.4µF and C2 = 120 ± 1.5 µF are connected in parallel. What is the limiting error of the resultant capacitance C (in µF)?
(a)0.9 µF
(b)2.4 µF
(c)1.5 µF
(d) 3.9 µF

Q8. A 0 – 200 V voltmeter has a guaranteed accuracy of 1% of full-scale reading. The voltage measured by this instrument is 50 V. What is the limiting error?
(a)1 %
(b)2 %
(c)3 %
(d) 4 %

Q9. Which of the following is done in speed control of DC motor by field flux control?
(a)Inserting an additional resistance in the armature circuit
(b)Inserting an additional resistance in the field circuit
(c)Inserting resistance to armature circuit and field circuit
(d)Any of the above

Q10. The acceptable value of grounding resistance to domestic application is
(a)0.1 Ω
(b)1 Ω
(c)10 Ω
(d)100 Ω

SOLUTIONS
S1. Ans.(c)
Sol. In a transmission system the feeder supplies power to distributors.

S2. Ans.(a)
Sol. Feeders are the conductors which connect the substations or generating stations to the areas to be fed by these stations. Generally, from feeders no tapping is taken to the consumer, so current loading in the feeder remains the same throughout the conductors. so, feeders are designed based on the current carrying capacity.

S3. Ans.(c)
Sol. Distributors are the conductors from which numerous tapping are taken for providing power supply to the consumers. Therefore, the current loading on the distributors varies along the length. So, distributors are designed from the point of voltage drop in it.

S4. Ans.(c)
Sol. Active elements are capable of delivering energy independently for long or infinite time.
Both voltage source and current source are active elements and they can change energy level of a circuit.

S5. Ans.(c)
Sol. Superposition theorem is only applicable for linear quantities. Whereas power is a non-linear quantity. i.e. P=I^2 R
So, superposition theorem is not applicable for power calculations.

S6. Ans.(b)
Sol. For below base speed we use armature control method and for above base speed we use field control method.

S7. Ans.(d)
Sol. Equivalent capacitance of the given parallel combination is C = C1 + C2. So, limiting error of C is (2.4 + 1.5) = 3.9 µF

S8. Ans.(d)
Sol. limiting error=(full scale reading)/(measured value)×accuracy at full scale
∴ limiting error=200/50×1=4 %

S9. Ans.(b)
Sol. By inserting a resistance cause to reduce field current and hence the flux is also reduced. The reduction in flux will result in an increase in speed. Because of saturation of iron, the flux cannot increase beyond its normal value. So, the motor runs at a speed higher than normal speed.

S10. Ans.(b)
Sol. The acceptable value of grounding resistance to domestic application is nearly equal to 1 Ω.

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