Quiz: Electrical Engineering 21 Dec 2020

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

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

Q1. Which of the following equipment is used to limit short-circuit current level in a
substation?
(a) Isolator
(b) Lightning switch
(c) Coupling capacitor
(d) Series reactor

Q2. Low tension cables are generally used up to
(a) 200 V
(b) 500 V
(c) 700 V
(d) 1000 V

Q3. When the length of a cable increases, its capacitance
(a) decreases
(b) increases
(c) remains same
(d) none of above

Q4. A linear circuit is one whose parameters
(a) do not change with voltage and current.
(b) change with change in current.
(c) change with change in voltage.
(d) none of the options.

Q5. A dc shunt generator is delivering 500 A at 220 V. The shunt field current is 10 A.
The armature resistance is 0.01 Ω. The stray power is 5000 W. The efficiency of the
generator is
(a) 91.09 %
(b) 95.82 %
(c) 95.64%
(d) 91.82%

Q6. For the circuit shown below, find the resistance between points P and Q.

(a) 2 Ω
(b) 1 Ω
(c) 3 Ω
(d) 4 Ω

Q7. The mmf produced by interpole is proportional to
(a) field current armature current
(b) armature voltage
(c) armature current
(d) 1/field current

Q8. In 750 μ A is flowing through 11 kΩ of resistance, what is the voltage drop across
the resistor?
(a) 146 V
(b) 8.25 V
(c) 14.6 V
(d) 82.5 V

Q9. A 20 kVA, 2000 V/200 V, 2-windign transformer, when used as an autotransformer,
with constant voltage source of 2000 V, is capable of handling
(a) 20 kVA
(b) 200 kVA
(c) 320 kVA
(d) 260 kVA

Q10. A primary cell has an emf of 1.5 V. When short circuited, it gives a current of 3 A.
The internal resistance of cell is
(a) 4.5 Ω
(b) 0.2 Ω
(c) 0.5 Ω
(d) 2 Ω

SOLUTIONS
S1. Ans.(d)
Sol. In a substation the equipment used to limit short circuit current level is series reactor.
Isolator is used to disconnect the circuit when there is no current in the line.

S2. Ans.(d)
Sol. Voltage is an important factor when designing a cable. Based on the voltage the type of electrical cables varies as,
Low tension cables (LT): It has an operating voltage level of below 1.1 KV.
High tension cables (HT): It has an operating voltage level less than 11 KV.
Super tension cables (ST): It has an operating voltage level up to 33 KV.
Extra super tension cables (EST): It has an operating voltage level more than 33 KV.

S3. Ans.(b)
Sol. Cable capacitance, C=(ε(r ) l)/(41.4 log(10 )⁡〖D/d 〗 )×10^(-9)F; l = length of cable
S4. Ans.(a)
Sol. Linear circuit parameters do not change if the voltage/current in the circuit changes.

S5. Ans.(d)
Sol. Armature current,
I_a=I_sh+I_L
=(10+500) A = 510 A
P_output=500×220
=110000 watt=110 kW
Shunt field copper loss
=220×10=2200 watt=2.2 kW
Armature copper loss
=(510)^2×0.01=2601 watt
=2.601 kW
Stray power loss
=5000 watt = 5kW
Efficiency of the generator is
η =110000/(110000+[2200+2601+5000])×100%
=91.818%=91.82%

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