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
In case of an insulation failure, earthing provides:
A)
A high-resistance path
B)
The easiest path for short-circuit current to flow to the ground
C)
A path to the live wire
D)
An open circuit
Option B is correct: The easiest path for short-circuit current to flow to the ground.
MES Departmental • 2025 • Paper-II
What is the primary purpose of the Insulation Resistance (Megger) test of a Transformer?
A)
To measure copper losses
B)
To check winding insulation health
C)
To determine core losses
D)
To verify turns ratio
Option B is correct: To check winding insulation health.
MES Departmental • 2025 • Paper-II
The unit of capacitance is:
A)
Farad
B)
Farad/m
C)
Farad/m2
D)
Farad/m3
Option A is correct: Farad.
MES Departmental • 2025 • Paper-II
According to Faraday’s Laws of Electromagnetic Induction, an e.m.f. is induced in a conductor whenever it:
A)
lies in a magnetic field
B)
cuts magnetic field
C)
moves parallel to the direction of the magnetic field
D)
lies perpendicular to the magnetic flux
Option B is correct: cuts magnetic field.
MES Departmental • 2025 • Paper-II
In a balanced delta-connected system, the line voltage (VL) is
A)
VL = 0.707 × Vph
B)
VL = 1.732 × Vph
C)
VL = 1.414 × Vph
D)
VL = Vph
Option D is correct: VL = Vph.
MES Departmental • 2025 • Paper-II
What is the benefit of proper grounding for lightning protection?
A)
It attracts more lightning strikes.
B)
It stores the lightning energy.
C)
It provides a low-resistance path for surge current to dissipate into the earth safely.
D)
It creates a magnetic field to deflect strikes
Option C is correct: It provides a low-resistance path for surge current to dissipate into the earth safely..
MES Departmental • 2025 • Paper-II
What is the formula for electric power (P) in a circuit, given current (I) and voltage (V)?
A)
P = V/I
B)
P = I/V
C)
P = V×I
D)
P = V/R
Option C is correct: P = V×I.
MES Departmental • 2025 • Paper-II
Which relay protects the transformer from external short circuits and overloads?
A)
Differential Relay
B)
Buchholz Relay
C)
Overcurrent Relay
D)
Thermal Relay
Option C is correct: Overcurrent Relay.
MES Departmental • 2025 • Paper-II
The common type of storage battery generally used in electric power stations is the:
A)
Nickel-cadmium battery
B)
Zinc-carbon battery
C)
Lead-acid battery
D)
Lithium-ion battery
Option C is correct: Lead-acid battery.
MES Departmental • 2025 • Paper-II
Which power is the actual power that performs useful work in a circuit?
A)
Reactive Power
B)
Active Power
C)
Apparent Power
D)
Absolute Power
Option B is correct: Active Power.
MES Departmental • 2025 • Paper-II
What is the primary protection for Power transformers against internal faults?
A)
Fuse Protection
B)
Overcurrent Relay
C)
Differential Protection (Main) & Gas (Buchholz) Protection
D)
Thermal Relay
Option C is correct: Differential Protection (Main) & Gas (Buchholz) Protection.
MES Departmental • 2025 • Paper-II
Restricted Earth Fault (REF) protection covers faults in:
A)
The entire winding
B)
Part of the winding between neutral and tapping point
C)
Only the HV side
D)
Only the LV side
Option B is correct: Part of the winding between neutral and tapping point.
MES Departmental • 2025 • Paper-II
What is magnetizing inrush current?
A)
Current during heavy load
B)
Current during fault
C)
A transient rush of current (6 to 8 times rated current) when first energized
D)
Current during unloading
Option C is correct: A transient rush of current (6 to 8 times rated current) when first energized.
MES Departmental • 2025 • Paper-II
What is the primary function of an inductor in an AC circuit?
A)
To store energy in a magnetic field
B)
To oppose a change in circuit current
C)
Both (a) and (b)
D)
To convert electrical energy to mechanical energy
Option C is correct: Both (a) and (b).
MES Departmental • 2025 • Paper-II
The primary consideration for a transmission substation site is:
A)
Proximity to residential areas
B)
High population density
C)
Proximity to load centers & transmission line corridors
D)
Close to airports
Option C is correct: Proximity to load centers & transmission line corridors.
MES Departmental • 2025 • Paper-II
A major constraint for substation location is proximity to:
A)
River crossings
B)
Industrial zones
C)
Airports & defense establishments
D)
Agricultural lands
Option C is correct: Airports & defense establishments.
MES Departmental • 2025 • Paper-II
What is the primary instrument used specifically for measuring earth resistance?
A)
Ammeter
B)
Voltmeter
C)
Earth Tester (or Ground Resistance Tester)
D)
Frequency Meter
Option C is correct: Earth Tester (or Ground Resistance Tester).
MES Departmental • 2025 • Paper-II
Which of the following activities is typically part of routine (preventive/scheduled) maintenance of HT/LT ABC lines?
A)
Replacement of worn-out parts
B)
Troubleshooting during a breakdown
C)
Regular inspection for physical damage, wear or sagging of the cable
D)
Re-varnishing of the cable
Option C is correct: Regular inspection for physical damage, wear or sagging of the cable.
MES Departmental • 2025 • Paper-II
When is the efficiency of a transformer maximum?
A)
At no load
B)
When copper loss equals iron loss
C)
At half load
D)
When voltage is maximum
Option B is correct: When copper loss equals iron loss.
MES Departmental • 2025 • Paper-II
Which of the following power semiconductor devices has the highest switching speed?
A)
BJT
B)
IGBT
C)
Power MOSFET
D)
SCR
Option C is correct: Power MOSFET.
MES Departmental • 2025 • Paper-II
In a series connection of resistors, what happens to the current across each resistor?
A)
Increases
B)
Decreases
C)
Remains the same
D)
Initially increases and then decreases
Option C is correct: Remains the same.
MES Departmental • 2025 • Paper-II
How does earthing contribute to system stability?
A)
By introducing resistance in the neutral
B)
By providing a stable reference point (zero potential) for the system
C)
By increasing system impedance
D)
By creating an isolated neutral
Option B is correct: By providing a stable reference point (zero potential) for the system.
MES Departmental • 2025 • Paper-II
In a power triangle, what is the relationship between active power (P), reactive power (Q), and apparent power (S)?
A)
P + Q = S
B)
P² + Q² = S²
C)
P = Q + S
D)
S² + Q² = P
Option B is correct: P² + Q² = S².
MES Departmental • 2025 • Paper-II
What is a common maintenance task for Power Transformers in outdoor substations?
A)
Changing the tank paint every year.
B)
Checking oil level, colour, and moisture content, plus oil testing.
C)
Removing all bushings for cleaning.
D)
Reducing the load to below 50%.
Option B is correct: Checking oil level, colour, and moisture content, plus oil testing..
