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Browse complete papersWhich of the following is not a common cause of internal faults in a transformer?
Winding short circuits
Core heating
Overloading
Insulation breakdown
Correct answer
Winding short circuits
Which of the following types of faults is the most common in a power system?
Three-phase faults
Phase-to-phase faults
Single line-to-ground faults
Double line-to-ground faults
Correct answer
Three-phase faults
In a substation, which of the following protection schemes provides the fastest and most reliable protection for a fault within a transformer’s winding?
Differential protection
Earth fault relays
Overcurrent relays
Distance relays
Correct answer
Differential protection
What does the term ’attenuation’ mean in the context of a coaxial cable?
The speed at which a signal travels through the cable
The ability of the cable to resist external interference
The amount of power the cable can safely handle
The loss of signal strength over a certain length of cable
Correct answer
The speed at which a signal travels through the cable
A coaxial cable has a velocity factor (VF) of 0. 78. What length of this cable is required to have a total propagation delay of 500 ns? Assume the speed of light c=\(3 \times 10^8\) m/s.
117 m
100 m
150 m
125 m
Correct answer
117 m
What happens to the load angle (\(\delta\)) of an alternator connected to a busbar when its real power output is increased?
The load angle becomes zero
The load angle decreases
The load angle increases
The load angle remains constant
Correct answer
The load angle becomes zero
In a servomotor, the controller compares the commanded position to the actual position from the encoder to generate an error signal. This is a fundamental concept of:
Feedback control
Motor braking
Open-loop control
Torque control
Correct answer
Feedback control
The induced EMF in a coil is directly proportional to the rate of change of magnetic flux linkage. This is a statement of:
Lenz’s Law
Ampere’s Law
Faraday’s Law of Induction
Ohm’s Law
Correct answer
Lenz’s Law
According to Lenz’s Law, the direction of the induced current in a conductor is such that it:
Opposes the change in magnetic flux that produced it
Is always in the same direction as the magnetic field
Aids the change in magnetic flux
Creates a magnetic field that is perpendicular to the conductor
Correct answer
Opposes the change in magnetic flux that produced it
Two alternators are operating in parallel and sharing a total load of \(500 \text{ kW}\). Alternator 1 has a droop characteristic of \(4 \text{ Hz/MW}\) and Alternator 2 has a droop of \(6 \text{ Hz/MW}\). The no-load frequency of both is \(50 \text{ Hz}\). What is the load shared by Alternator 1?
\(250 \text{ kW}\)
\(300 \text{ kW}\)
\(200 \text{ kW}\)
\(400 \text{ kW}\)
Correct answer
\(250 \text{ kW}\)