Quiz: Electrical Engineering 16 Sep 2020

Quiz: Electrical Engineering
Exam: SSC JE
Topic: Miscellaneous

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

Q1. In power transformers, it is found that the iron or core losses practically varies very less, this is because
(a) Constant leakage flux
(b) Constant core flux
(c) Constant load current
(d) Constant leakage and core flux

Q2. Which of the conditions is must be fulfilled for a satisfactory parallel operation of transformers?
(a) Correct polarity
(b) Same pu impedance
(c) Same voltage ratio
(d) Leakage impedance should be inversely proportional to KVA of the transformer

Q3. The qualities aspired to obtain a good permanent magnet is/are
(a) High coercivity
(b) High residual flux
(c) Low coercivity
(d) High residual flux and high coercivity

Q4. The pitch factor, in rotating electrical machinery, is defined as the ratio of resultant EMF of a
(a) Full pitch coil to the phase emf
(b) Chorded coil to that of full pitched coil
(c) Full pitched coil to that of a chorded coil
(d) Chorded coil to the phase emf

Q5. What is the maximum load that can be connected in a circuit containing only lighting points?
(a) 500 watts
(b) 750 watts
(c) 800 watts
(d) 1000 watts

Q6. The iron core in a transformer provides a _____path to the main flux
(a) Low reluctance
(b) High reluctance
(c) Low resistance
(d) High conductivity

Q7. For the network shown in the figure, the value of current in 8Ω resistor is

(a) 408A
(b) 2.4A
(c) 1.5A
(d) 1.2A

Q8. In a D.C. machine, fractional pitch winding is used
(a) to increase the generated voltage
(b) to reduce sparking
(c) to save the copper because of shorter end connections
(d) due to (b) and (c) above

Q9. Why are shunt reactors connected at the receiving end of long transmission line system?
(a) To increase the terminal voltage
(b) To compensate voltage rise caused by capacitive charging at light load
(c) To improve power factor
(d) None of these

Q10. A diesel station supplies the following loads to various consumers:
Industrial consumer = 1500 kW
Commercial load = 750 kW
Domestic power = 100 kW
Domestic light = 450 kW
If the maximum demand on the station is 2500 kW, then diversity factor is
(a) 1.5
(b) 1.92
(c) 2
(d) 1.12

SOLUTIONS
S1. Ans.(b)
Sol. Due to the constant core flux, the iron losses also remain constant.

S2. Ans.(a)
Sol. out of all, polarity must be correct for the connected transformers.

S3. Ans.(d)
Sol. both high residual flux as well as coercivity is desired for a good permanent magnet.

S4. Ans.(b)
Sol. Kp= Resultant EMF of a chorded coil/Resultant EMF of a full pitched coil = cos⁡(ε/2)

S5. Ans.(c)
Sol. The maximum load that can be connected in a circuit containing only lighting points is 800 watts.

S6. Ans.(a)
Sol. The iron core in a transformer provides a low reluctance path to the main flux.

S7. Ans.(b)
Sol.

Here 12ohm and 8-ohm resistors are in series and both are parallel connected to 20ohm resistor.
∴R_eqv=20‖20=10Ω
∴I=48/10=4.8 A
And I8Ω= 4.8×20/(20+20)=2.4 A

S8. Ans.(d)
Sol. Some advantages of short pitch winding are:
Due to shortening span, the copper required is less.
Low copper losses
Improve waveform due to reduction in harmonic
Fractional Pitch winding reduces sparking in DC machines

S9. Ans.(b)
Sol. Shunt Reactor compensation at the receiving end help to reduce the effect of capacitance thus reducing the Ferranti effect.
Shunt Reactor absorbs the excess reactive power during no load or light load condition and thus helps in stabilizing the voltage of Transmission Line.

S10. Ans.(d)
Sol. Diversity Factor = Sum of Individual Maximum Demands / Maximum Demand of the System.
Diversity factor=(1500+750+100+450)/2500=1.12

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