MES Departmental • 2025 • Paper-II
What is the fundamental principle of a Percentage Differential Relay used in transformers?
A)
Measures the voltage drop across the line.
B)
Senses changes in ambient temperature.
C)
Operates based on the frequency of the system
D)
Compares currents entering and leaving the protected zone.
Option D is correct: Compares currents entering and leaving the protected zone..
MES Departmental • 2025 • Paper-II
At higher operating voltages, which of the following additional losses becomes significant?
A)
Ohmic loss
B)
Leakage current loss
C)
Corona loss
D)
Eddy current loss
Option C is correct: Corona loss.
MES Departmental • 2025 • Paper-II
The function of a conservator in a power transformer is to:
A)
protect against internal faults.
B)
cool the transformer oil.
C)
provide physical support to the core.
D)
take care of the expansion and contraction of transformer oil due to temperature variation.
Option D is correct: take care of the expansion and contraction of transformer oil due to temperature variation..
MES Departmental • 2025 • Paper-II
If you double the voltage in a circuit while keeping the resistance constant, what happens to the power?
A)
It becomes half
B)
It stays the same
C)
It quadruples
D)
It doubles
Option C is correct: It quadruples.
MES Departmental • 2025 • Paper-II
By controlling the firing angle of the thyristors in a thyristor bridge, you can control the:
A)
Input AC frequency
B)
Average DC output voltage
C)
Transformer turns ratio
D)
Peak Inverse Voltage (PIV)
Option B is correct: Average DC output voltage.
MES Departmental • 2025 • Paper-II
If you increase the distance ‘a’ between the four test pins in a Wenner test setup, what practical change occurs?
A)
You measure soil resistivity at a deeper layer of the earth.
B)
The measured test voltage increases dramatically.
C)
You measure only the dry top soil layer.
D)
The meter automatically runs out of scale range.
Option A is correct: You measure soil resistivity at a deeper layer of the earth..
MES Departmental • 2025 • Paper-II
What is the fundamental property of an inductor in alternating current (AC) networks?
A)
It dissipates electrical energy as heat.
B)
It causes the current to lead the voltage by 90 degrees.
C)
It produces an opposition to current flow known as inductive reactance.
D)
It consumes real power permanently.
Option C is correct: It produces an opposition to current flow known as inductive reactance..
MES Departmental • 2025 • Paper-II
In a standard symmetrical three-phase system, what is the phase difference between each phase voltage?
A)
90°
B)
180°
C)
120°
D)
360°
Option C is correct: 120°.
MES Departmental • 2025 • Paper-II
When two resistances are connected in parallel?
A)
the current through each must be the same.
B)
the voltage across each must be the same.
C)
their combined resistance value equals the sum of the individual values.
D)
each must have the same resistance value
Option B is correct: the voltage across each must be the same..
MES Departmental • 2025 • Paper-II
How is a power transformer protected from indirect lightning strikes or induced overvoltages?
A)
By using overhead ground wires (shield wires)
B)
By using overcurrent relays
C)
By using Differential protection
D)
By using conservator tanks
Option A is correct: By using overhead ground wires (shield wires).
MES Departmental • 2025 • Paper-II
Before energizing a power transformer for the first time during commissioning, what does a “BDV test” evaluate?
A)
Bulk Density Verification of the transformer core steel
B)
Balanced Direct Voltage of the control batteries
C)
Bushing Displacement Vector alignment
D)
Breakdown Voltage of the transformer insulating oil
Option D is correct: Breakdown Voltage of the transformer insulating oil.
MES Departmental • 2025 • Paper-II
The specific resistance of a wire depends upon:
A)
its length
B)
its cross-sectional area
C)
its dimension
D)
its material
Option D is correct: its material.
MES Departmental • 2025 • Paper-II
A constant voltage is applied between two ends of a uniform metallic wire. Some heat is developed. If both length and radius of wire are halved, the heat developed in the same duration is:
A)
half
B)
twice
C)
one-third
D)
one-fourth
Option A is correct: half.
MES Departmental • 2025 • Paper-II
Why is a Magnetic Balance Test conducted on a three-phase transformer during pre-commissioning?
A)
To calculate the total copper losses at full load
B)
To check for inter-turn shorts, core unbalance, or physical displacement of the windings
C)
To evaluate the speed of the cooling fan motors
D)
To measure the insulation resistance of the neutral bushing
Option B is correct: To check for inter-turn shorts, core unbalance, or physical displacement of the windings.
MES Departmental • 2025 • Paper-II
To reduce the transmission line losses for a given amount of transmitted power (P) and distance, the transmission voltage (V) must be:
A)
reduced
B)
kept constant
C)
increased
D)
made zero
Option C is correct: increased.
MES Departmental • 2025 • Paper-II
Why is AC predominantly preferred over DC for long-distance power transmission?
A)
AC can be easily stepped up and down using transformers, minimizing energy loss
B)
AC travels much faster than DC
C)
AC power lines require thinner conductors
D)
DC cannot be transmitted over cables
Option A is correct: AC can be easily stepped up and down using transformers, minimizing energy loss.
MES Departmental • 2025 • Paper-II
Which of the following electrical network components utilizes Faraday’s law and Lenz’s law to function?
A)
Resistor
B)
Capacitor
C)
Inductor
D)
Diode
Option C is correct: Inductor.
MES Departmental • 2025 • Paper-II
What is the most common cause of premature failure of pin insulators on 11kV lines?
A)
Accumulation of dust, salt, or industrial pollution causing leakage currents and flashovers
B)
Over-voltage in the system
C)
High ambient temperature in the summer
D)
High frequency AC transmission
Option A is correct: Accumulation of dust, salt, or industrial pollution causing leakage currents and flashovers.
MES Departmental • 2025 • Paper-II
If two sinusoidal waves are given by v1 = V1 (sint) and v2 = V2 sin(t – 30°), then:
A)
v1 leads v2 by 30°
B)
v2 leads v1 by 30°
C)
Both are in phase
D)
Both are out of phase by 180°
Option A is correct: v1 leads v2 by 30°.
MES Departmental • 2025 • Paper-II
Is it dangerous to leave the secondary of a PT open-circuited?
A)
Yes, it will produce a high voltage and cause a flashover
B)
Yes, it will damage the primary winding
C)
No, a PT is a voltage source and is designed to operate with an open secondary (no load)
D)
No, it will only damage the core
Option C is correct: No, a PT is a voltage source and is designed to operate with an open secondary (no load).
MES Departmental • 2025 • Paper-II
What is the standard minimum ground clearance required for Low Tension (LT) and medium voltage lines crossing a street?
A)
4.5 meters
B)
5.8 meters
C)
6.1 meters
D)
7.2 meters
Option B is correct: 5.8 meters.
MES Departmental • 2025 • Paper-II
If a 6-pole alternator is driven by a prime mover at 1000RPM, what is the frequency of the generated EMF?
A)
60Hz
B)
25Hz
C)
50Hz
D)
100Hz
Option C is correct: 50Hz.
MES Departmental • 2025 • Paper-II
How is an ammeter connected in a panel wiring circuit?
A)
In parallel with the load
B)
In series with the load
C)
Across the voltage transformer
D)
Through a high resistance multiplier
Option B is correct: In series with the load.
MES Departmental • 2025 • Paper-II
How is the primary winding of a Potential Transformer (PT/CVT) connected to the line?
A)
In series with the load
B)
In parallel (across the phase and neutral or phase to phase)
C)
In delta connection only
D)
Through a current limiting resistor
Option B is correct: In parallel (across the phase and neutral or phase to phase).
MES Departmental • 2025 • Paper-II
Kirchhoff’s voltage law deals with:
A)
conservation of energy
B)
conservation of charge
C)
conservation of momentum
D)
conservation of angular momentum
Option A is correct: conservation of energy.
