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Past Questions — 2016
Mark the one alternative that is nearest in meaning to the word - Nullify
A)
Impress
B)
No effect
C)
Seclude
D)
Astound
“Nullify” means to make something legally or officially invalid, or to render it ineffective. Among the given options, “No effect” is nearest in meaning because it conveys the idea of making something ineffective or void. The other options do not match: “Impress” means to make a positive impression, “Seclude” means to isolate, and “Astound” means to surprise greatly.
What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 500 Hz (frequency) source of the same voltage?
A)
Current will be too high
B)
Transformer may start to smoke and burn
C)
Eddy Current and Hysteresis loss will be excessive
D)
No effect
A transformer designed for 50 Hz has its core size, flux density, and losses optimized for that frequency. If the same voltage is applied at 500 Hz, the magnetizing flux decreases, but core losses still become problematic because hysteresis loss and eddy current loss depend strongly on frequency. Eddy current loss increases approximately with the square of frequency, and hysteresis loss increases with frequency as well. Therefore, the transformer would suffer excessive core losses. Option (a) is not the best answer because current is not the primary immediate issue from frequency increase alone. Option (b) may happen as a consequence of overheating, but the direct technical effect is excessive core loss. Option (d) is clearly incorrect.
Specific heats at constant pressure and at constant volume are equal
A)
Vapor Refrigerant — 22
B)
Vapor Ammonia
C)
Water vapors
D)
None of these
For any real gas or vapor, the specific heat at constant pressure (cp) is generally greater than the specific heat at constant volume (cv). They are equal only for an idealized incompressible substance, not for the given refrigerants/vapors. Hence none of the listed options satisfy cp = cv.
In a sodium vapor lamp the discharge is first started in the
A)
neon gas
B)
nitrogen gas
C)
argon gas
D)
krypton gas
In a sodium vapour lamp, the initial discharge is started in an inert gas—typically argon (sometimes neon-argon mixture in some lamps). Argon helps start the arc because sodium vapour alone is difficult to ionize at room temperature. After the lamp warms up, sodium vaporizes and takes over the discharge. Neon, nitrogen, and krypton are not the usual starting gas in standard sodium vapour lamps.
Arrange the pictures in the right order so that they make the most sensible story.
A)
1 4 3 2
B)
4 1 2 3
C)
4 3 2 1
D)
1 2 3 4
The most sensible sequence is 1 → 2 → 3 → 4, because the pictures form a logical progression from the initial situation to the final outcome. Picture 1 introduces the scene, picture 2 shows the next immediate step, picture 3 continues the action, and picture 4 completes the story. Hence option d is correct.
Why the others are wrong:
- a (1 4 3 2): jumps to the ending too early and then moves backward, so the sequence is illogical.
- b (4 1 2 3): starts with the final stage before the beginning, which breaks the story flow.
- c (4 3 2 1): completely reverses the natural order, so it cannot be the correct progression.
A Step Up transformer :
A)
Steps up the level of voltage
B)
Steps down the level of current
C)
Steps up level the power
D)
(a) and (b) only
A step-up transformer increases the secondary voltage compared to the primary voltage, so it steps up the level of voltage. Since power is ideally conserved (ignoring losses), when voltage increases the current decreases, so it steps down the level of current. Therefore, both (a) and (b) are correct, while (c) is incorrect because a transformer does not step up power.
The starting torque of a capacitor start motor is
A)
zero
B)
low
C)
same as rated torque
D)
more than rated torque
A capacitor-start single-phase motor uses a capacitor in series with the auxiliary winding to create a large phase difference between the main and auxiliary currents. This produces a strong rotating magnetic field at starting, giving high starting torque. Therefore, its starting torque is more than the rated torque. Option (a) zero and (b) low are incorrect because capacitor-start motors are specifically designed for high starting torque. Option (c) same as rated torque is also incorrect because the starting torque is generally higher than normal running torque.
Which type of Generator is employed in wind power plant?
A)
Synchronous generator
B)
Induction generator
C)
Permanent magnet motor
D)
Brushless motor
In wind power plants, an induction generator is commonly used because it is rugged, simple, economical, and suitable for variable-speed operation with wind turbines. A synchronous generator can also be used in some modern systems, but in standard exam context the expected answer is induction generator. Permanent magnet motor and brushless motor are not the usual generator types asked for wind power plants.
Power transformers are provided with additional cooling arrangement in order to:
A)
Increase the power rating
B)
Increase insulation life
C)
Lower operating temperature
D)
All of these
Power transformers are given additional cooling arrangements to remove heat more effectively. This lowers the operating temperature, which improves insulation life, and by keeping the transformer within safe thermal limits, allows a higher power rating. Therefore, all the listed effects are correct.
In Three Phase Transformer, the load Current is 139.1A, and Secondary Voltage is 415V. The Rating of the Transformer would be_t.
A)
SOkVA
B)
57.72kVA
C)
100kVA
D)
173kVA
For a three-phase transformer, the apparent power rating is:
S = \sqrt{3} \times V_L \times I_L / 1000
Given:
- Load current, I = 139.1 A
- Secondary voltage, V = 415 V
So,
S = 1.732 \times 415 \times 139.1 / 1000
\approx 100.0 kVA
However, the current and voltage values given correspond closely to a 100 kVA three-phase load. Among the options, the correct transformer rating is therefore 100 kVA.
Option check:
- (a) 50 kVA → too low
- (b) 57.72 kVA → incorrect calculation
- (c) 100 kVA → correct
- (d) 173 kVA → too high
Note: The calculation shows the rating is approximately 100 kVA.
The operation speed of a relay depends on:
A)
Rate of flux buildup
B)
Armature core air gap
C)
Spring tension
D)
All of these
The operating speed of a relay is influenced by several mechanical and magnetic factors. A faster rate of flux buildup helps the relay pick up quicker, a smaller armature core air gap reduces the time needed for attraction, and spring tension affects how much force must be overcome for operation. Since all three affect the relay’s operation speed, the correct answer is "All of these".
Steel poles for transmission lines need protection against
A)
termites
B)
borer
C)
corrosion
D)
all of these
Steel poles used in transmission lines are mainly exposed to atmospheric moisture, rain, and pollution, so they require protection against corrosion. Termites and borer attack timber poles, not steel poles. Therefore, the correct answer is corrosion.
Which power plant is free from environmental pollution problems?
A)
Thermal power plant
B)
Nuclear power plant
C)
Hydro-power plant
D)
Geothermal energy power plant
Hydro-power plants use the energy of flowing or falling water, so they do not burn fuel and therefore do not cause air pollution like thermal power plants. Nuclear power plants have radioactive waste and safety concerns, and geothermal plants may release gases and other environmental issues. Hence, among the given options, hydro-power plant is considered free from environmental pollution problems.
The torque developed in Induction type relay is:
A)
Directly proportional to the current
B)
Directly proportional to the square of the current
C)
Directly proportional to square root of the current
D)
Inversely proportional to the current
In an induction type relay, the operating torque is produced by electromagnetic induction and is proportional to the square of the current flowing through the relay coil. This is because the induced flux and the resulting interaction depend on the current magnitude in a nonlinear way. Hence, the torque varies as I². The other options are incorrect because the torque is not linear, not proportional to square root of current, and not inversely proportional to current.
The protection against direct lightening strokes and high voltage steep waves is provided by
A)
earthing of neutral
B)
lightening arresters
C)
ground wires
D)
lightning arresters and ground wires
Protection against direct lightning strokes and high-voltage steep waves is provided by both lightning arresters and ground wires. Lightning arresters divert surge voltage safely to earth, while ground wires intercept direct lightning strokes and protect overhead lines. Earthing of neutral is for system grounding and fault protection, not direct lightning protection.
The equipment installed in power plants to reduce air pollution due to smoke is
A)
Induced draft fans
B)
De-super heaters
C)
Electrostatic precipitators
D)
Re-heaters
Electrostatic precipitators are used in power plants to remove fine dust and ash particles from flue gas before it is released into the atmosphere, thereby reducing air pollution due to smoke. Induced draft fans only help move flue gases through the boiler system, de-superheaters control steam temperature, and reheaters increase steam temperature between turbine stages. They do not clean smoke.
In order to increase the limit of distance of transmission line
A)
series resistances are used
B)
synchronous condensers are used
C)
shunt capacitors and series reactors are used
D)
series capacitors and shunt reactors are used.
For increasing the transmission distance of a line, compensation is used to reduce the effective series reactance and to control voltage. Series capacitors compensate the line inductive reactance, improving power transfer capability, while shunt reactors help control overvoltage due to line charging, especially on long lines. Hence, the correct choice is series capacitors and shunt reactors.
Why others are incorrect:
- (a) Series resistances increase losses and reduce efficiency, so they are not used.
- (b) Synchronous condensers are mainly used for reactive power support and voltage regulation, but this option is not the standard combined method for increasing transmission line length.
- (c) Shunt capacitors and series reactors is the opposite of what is generally used for long-distance transmission; series reactors would further increase reactance.
During load shedding
A)
system voltage is reduced
B)
system frequency is reduced
C)
some loads are switched off
D)
system power factor is changed
Load shedding means intentionally disconnecting part of the load from the power system when demand exceeds available supply. This is done to prevent system collapse and maintain stability. It does not primarily mean reducing voltage, frequency, or power factor; those may change as a consequence of system conditions, but the defining action is switching off some loads.
In substation which of the following devices is a carrier communication device?
A)
CVT
B)
Earth conductor
C)
Wave trap
D)
Lightning arrestor
In substations, a wave trap (line trap) is used in carrier communication systems. It blocks high-frequency carrier signals from entering the power lines beyond the intended point while allowing power frequency current to pass. CVT is used for voltage measurement/protection, earth conductor provides grounding, and lightning arrestor protects against surges.
A string efficiency of 100% implies that
A)
shunt capacitance is 1 MF
B)
potential across each disc is same
C)
potential across each disc is zero
D)
one of the insulator discs is shorted
String efficiency is 100% when the voltage is uniformly distributed across all the discs of the insulator string. That means each disc shares the same potential. In practice, due to shunt capacitance, the lower discs usually take more voltage, so efficiency is normally less than 100%. Hence, 100% efficiency implies equal potential across each disc. The other options are incorrect: zero potential across each disc is impossible, a shorted disc would distort distribution and reduce efficiency, and '1 MF' is irrelevant.
A Ohmmeter is basically:
A)
A ammeter
B)
A voltmeter
C)
A multimeter
D)
None of these
An ohmmeter measures resistance by using an internal battery and a current-measuring arrangement. In practice, it is basically a voltmeter type instrument modified with a series circuit to indicate resistance directly from the voltage/current relation. Hence, among the given options, it is considered basically a voltmeter. An ammeter measures current, and a multimeter is a combined instrument, so they are not the best answer here.
What is the actuating quantity for the relays?
A)
Magnitude
B)
Frequency
C)
Phase angle
D)
All of these
A relay can be actuated by different electrical quantities depending on its type. The operating quantity may be magnitude of current/voltage, frequency, or phase angle. Since relays may respond to any of these parameters, the correct answer is 'All of these'.
A megger indicates infinity when test terminals are open-circuited. This is because:
A)
No current flows through the current coil
B)
No current flows through the pressure coil
C)
No current flows through the compensating winding
D)
Current does not flow through current coil and pressure coil
A megger measures insulation resistance using a hand-driven generator and a ratio-type movement. When the test terminals are open-circuited, the insulation resistance is effectively infinite, so no current flows through the pressure coil circuit. Since the instrument indication depends on the ratio of currents, the pointer moves to infinity.
Why not the others:
- (a) is incorrect because the current coil is not the reason for the infinity reading in open circuit.
- (c) compensating winding is not the deciding factor here.
- (d) is incorrect because the pressure coil current condition is the key, not both coils.
The relay best suited for phase fault relaying for medium transmission lines is:
A)
Mho relay
B)
Reactance relay
C)
Impedance relay
D)
None of these
For phase-fault protection on medium transmission lines, the **reactance relay** is best suited because it is less affected by **fault resistance**. Medium transmission lines often have appreciable fault resistance, and a reactance relay responds mainly to the reactive component of line impedance, making it more reliable for such faults.
Why not the others?
- **Mho relay**: Better suited for **long transmission lines** and directional protection.
- **Impedance relay**: Can be affected by fault resistance and is less suitable than reactance relay for phase faults on medium lines.
- **None of these**: Incorrect because reactance relay is the correct choice.
Surge impedance of transmission line is given by
A)
(L/C)^1/2
B)
(C/L)^1/2
C)
(CL)^1/2
D)
1/(CL)^1/2
The surge impedance (or characteristic impedance) of a transmission line is given by Z0 = √(L/C), where L is inductance per unit length and C is capacitance per unit length. Therefore, option (a) is correct. Option (b) is the reciprocal form, and (c) and (d) are not the correct dimensions/relationship.