Quiz: Electrical Engineering 11 July 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 is used to neutralize the Ferranti effect in the medium and long transmission lines?
(a) Shunt capacitor
(b) Series resistor
(c) Series capacitor
(d) Shunt reactor

Q2. Which is the top most conductor in high voltage transmission?
(a) Line conductor
(b) Earth wire
(c) Return conductor
(d) Phase conductor

Q3. In Ferranti effect the:
(a) Sending end voltage is equal to the receiving end voltage
(b) Sending end voltage is less than the receiving end voltage
(c) Sending end voltage is greater than the receiving end voltage
(d) None of the above

Q4. Which of the following statement is TRUE about the resistance of a conductor?
(a)The resistance of a conductor does not depend upon the length
(b)The resistance of a conductor does not depend upon the material
(c)The resistance of a conductor does not depend upon the temperature
(d)The resistance of a conductor does not depend upon the pressure

Q5. The critical temperature at which high ferromagnetic materials lose their magnetism is called
(a)Curie Point
(b)Hysteresis
(c)Transition temperature
(d)Standard temperature

Q6. The percentage reactance (% X) of a circuit is defined as
(a)The percentage of total phase voltage leading total load current
(b)The percentage of total phase voltage dropped in the circuit when full load current is flowing
(c)The percentage of total phase voltage lagging total load current
(d)The percentage of total phase voltage dropped in the circuit for no load condition

Q7. In order to obtain higher efficiency for 3-phase induction motors, its slip should be:
(a)Low
(b)1
(c)High
(d)Very high

Q8. In the induction motors the torque is directly proportional to the
(a)Higher slip values
(b)Voltage slip
(c)Lower slip values
(d)None of the above

Q9. A moving coil permanent magnet instrument can be used as………by using a low resistance shunt.
(a)Ammeter
(b)Voltmeter
(c)Flux-meter
(d)Ballistic galvanometer

Q10. Hay’s bridge is suitable for the measurement of which one of the following?
(a) Inductance with Q<10.
(b) Inductance with Q>10.
(c) Capacitance with high dissipating factors.
(d) Capacitance with low dissipating factors.

Solutions:

S1. Ans.(d)
Sol. Ferranti effect: – Receiving end voltage (V_R) > Sending end voltage (V_S) ie V_R > V_S and this is due to no-load or light load condition.
Ferranti effect can be neutralized by using shunt reactor.

S2. Ans.(b)
Sol. The top most wire in high voltage transmission line is “Earth wire” which provides protection against lightning.

S3. Ans.(b)
Sol. in Ferranti effect, V_S<V_R i.e., Receiving end voltage is greater than sending end voltage. It occurs during no-load or light load condition.
Ferranti effect can be neutralized by planting shunt rectors’ at receiving end of the lines.

S4. Ans.(d)
Sol. The resistance R offered by a conductor depends on the following factors:
Length of material
Cross-section area
Nature of material
Temperature

S5. Ans.(a)
Sol. The Curie temperature (T_C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties.
If a ferromagnetic material has a temperature under its Curie temperature, then the material has a net spontaneous magnetization, which means that the material becomes ferromagnetic, or magnetic. If a ferromagnetic material has a temperature over its Curie temperature, then the material becomes paramagnetic or does not become a magnet.

S6. Ans.(b)
Sol. Percentage reactance: It is the percentage of the total phase-voltage dropped in the circuit when full-load current is flowing.
% X= IX/V×100.
Where
I = full-load current
V = phase voltage
X = reactance in ohms per phase

S7. Ans.(a)
Sol. for 3-phase induction motor, in order to obtain higher efficiency its slip should be low. i.e. rotor speed should be approx. equivalent to synchronous speed. (N≃N_S) .
Rotor efficiency =N_R/N_S . So, if rotor speed is approx. equal to synchronous speed, then efficiency will be maximum. i.e. slip should be low.

S8. Ans.(c)
Sol. for lower slip values, torque in an induction motor is directly proportional to it.
For lower slip values, T ⍺ SLIP(S)
For higher slip values, T ⍺1/SLIP.

S9. Ans.(a)
Sol. A PMMC instrument can be used as Ammeter by using low resistance shunt.

S10. Ans.(b)
Sol. Hay bridge is suited for the measurement of high-Q inductors having Q more than 10.
bridges used for measurement of inductance:
Anderson bridge (Q<1).
Maxwell bridge (1<Q<10).
Hay bridge (Q>10).

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