Free Power Systems MCQs with Answers

• A. Above 220 kv
• B. Above 11kv
• C. Below 660 v
• D. Below 115 v

Explanation: Solid grounding is generally used on low-voltage systems, where the neutral is directly connected to earth and fault current can be safely…

• A. D.C voltage
• B. A.C voltage
• C. Half A.C voltage
• D. Half D.C voltageGet Study Guides

Explanation: AC voltage can be stepped up or down easily with transformers. High-voltage AC transmission carries the same power at lower current…

• A. 200 V D.C.
• B. 25 kV single phase A.C.
• C. 25 kV two phase A.C.
• D. 25 kV three phase A.C.

Explanation: The standard main-line railway electrification system for long-distance routes is 25 kV, single-phase AC at 50 Hz.

• A. ground fault on a cable
• B. short circuit fault on a cable
• C. both the ground fault and the short-circuit fault
• D. none of the above

Explanation: The Murray loop test uses a healthy conductor and a bridge arrangement to locate low-resistance faults such as earth faults and…

• A. Adjustment of voltage at consumers premises within statutory limits
• B. Control of active and reactive power
• C. Adjustment of short period daily and seasonal voltage variations in accordance with variations of load
• D. All of the above

Explanation: Voltage control keeps consumer voltage within statutory limits, compensates for daily and seasonal load variations, and helps regulate…

• A. overhead telephone wire
• B. earth wire
• C. core wire of ACSR
• D. all of the above

Explanation: Steel provides high mechanical strength, so it is used for overhead telephone wires, earth wires, and the central reinforcing core of ACSR…

• A. Copper
• B. Aluminium
• C. Steel reinforced copper
• D. Steel reinforced aluminium

Explanation: Steel-reinforced aluminium conductors combine aluminium's low weight and good conductivity with steel's mechanical strength, making them…

• A. Increases
• B. Decreases
• C. Remains unaffected

Explanation: In an ungrounded system, a single line-to-ground fault shifts the neutral potential.

• A. transmission line
• B. motor
• C. generator
• D. feeder

Explanation: Transmission-line design must limit I²R losses because these losses waste generated power and reduce transmission efficiency.

• A. connecting lines in parallel
• B. connecting lines in series
• C. using machines of high impedance
• D. reducing the excitation of machines
• E. none of the above

Explanation: Parallel lines reduce the equivalent transfer reactance and increase the maximum power transfer, since Pmax is inversely proportional to…

• A. compensate for line inductive reactance
• B. compensate for line capacitive reactance
• C. improve line voltage
• D. none of the above

Explanation: A series capacitor supplies capacitive reactance in series with the line, thereby cancelling part of the line's inductive reactance.

• A. impedance
• B. directional
• C. non-directional
• D. none of the above

Explanation: An admittance relay, commonly called a mho relay, has a directional characteristic and responds to both impedance magnitude and phase…

• A. 100 microsecond
• B. 50 millisecond
• C. 0.5 sec
• D. 0.1 sec

Explanation: High-voltage air-blast circuit breakers are designed for rapid interruption, typically within about 50 milliseconds at this voltage level.

• A. relay
• B. rewirable fuse
• C. H.R.C. only
• D. all of the above

Explanation: During a fault, the relay detects the abnormal condition and sends a trip signal to the circuit-breaker.

• A. zero sequence currents only
• B. positive sequence currents only
• C. negative and zero sequence currents
• D. zero, negative and positive sequence currents

Explanation: A balanced three-phase set has equal magnitudes separated by 120°, which forms a positive-sequence set only.

• A. no current flow
• B. heavy current flow
• C. voltage drop
• D. voltage rise

Explanation: A short circuit creates a very low-impedance path, so the current rises sharply and may become several times the normal load current.

• A. earth wires
• B. isolators
• C. H.R.C. fuses
• D. reactors

Explanation: Reactors add inductive reactance to the circuit, limiting the rate and magnitude of short-circuit current.

• A. fault occurs on the bus itself
• B. fault occurs on neutral line
• C. two or more faults occur simultaneously
• D. fault occurs with respect to earthing

Explanation: In a single-bus arrangement, every circuit is connected to the same bus, so a bus fault can disconnect or shut down all connected…

• A. distribution transformer
• B. generator transformer of the power plant
• C. auto-transformer of the power plant
• D. station transformer of the power plant

Explanation: Overfluxing protection is especially important for the generator transformer because excessive volts-per-hertz can saturate its magnetic…

• A. constant for all distances
• B. lower than that of if fault occurs away from the relay
• C. higher than that of if fault occurs away from the relay
• D. none of the above

Explanation: Interpreting “VII ratio” as the V/I impedance ratio, a fault nearer the impedance relay gives a shorter line impedance and therefore a…