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Past Questions
Which of the following bridges is frequency sensitive?
A)
Wheatstone bridge
B)
Maxwell bridge
C)
Anderson bridge
D)
Wien bridge
A Wien bridge is frequency sensitive because its balance condition depends on the supply frequency. It is commonly used for measuring frequency and in Wien bridge oscillators. In contrast, Wheatstone bridge is used for resistance measurement, Maxwell bridge for inductance measurement, and Anderson bridge is also used for inductance measurement; these are not primarily frequency-sensitive in the same way.
As compared to underground cables, overhead lines are
A)
Much costlier
B)
Save from lightning strokes
C)
Save from weather elements
D)
None ofthese
Overhead lines are generally cheaper than underground cables, so (a) is incorrect. They are more exposed to lightning strokes and weather elements, so (b) and (c) are also incorrect. Therefore, the correct answer is (d) None of these.
The spacing of conductors is determined by
A)
Voltage and span
B)
Current and power
C)
Pole height and weight of conductor
D)
None of these
The spacing of conductors in overhead transmission lines is mainly decided by the operating voltage and the span length. Higher voltage requires greater spacing to prevent flashover, and longer spans affect conductor sag and clearance requirements. Current and power do not directly determine conductor spacing, and pole height and conductor weight influence support design rather than the basic spacing criterion.
What is Marshalling Kiosk in power transformer?
A)
It provides alarms, trips, controls and indications from main transformer
B)
Itis the base on which transformer rail is provided to pull and push transformer
C)
Itis the pressure device that ruptures when temperature inside transformer increases
D)
None of these
A marshalling kiosk is the control and relay panel associated with a power transformer. It collects and houses the transformer’s alarms, trips, indications, metering, and control wiring for monitoring and protection. Option (b) describes a transformer base/rail arrangement, and option (c) refers to a pressure relief device, not a marshalling kiosk.
Direct current is preferred over alternating current for testing of ac transmission lines and cables because:
A)
Heavy charging currents will be drawn and so a large sized transformer is required if tested with ac
B)
Transmission lines and cables should not be tested with de
C)
The transformers required for testing cannot be used for long distances
D)
All the above
Direct current is preferred for testing AC transmission lines and cables because, if AC were used, the line/cable capacitance would draw heavy charging current. This would require a very large testing transformer and make the test impractical. Option (b) is incorrect because AC lines and cables can be tested; DC is preferred only for practical reasons. Option (c) is irrelevant and not a valid reason. Therefore, the correct answer is (a).
Ifthe system voltage is high, Electricity can be transferred
A)
More efficiently
B)
Less efficiently
C)
Same
D)
None ofthese
For a given power, increasing the transmission voltage reduces the current. Since line losses are proportional to I²R, lower current means much lower losses and better voltage regulation. Therefore, electricity can be transferred more efficiently at high voltage. The other options are incorrect because high voltage does not reduce efficiency; it improves it.
Motors are commonly protected by
A)
Isolator
B)
Delay fuse
C)
Rewireable fuse
D)
Oil circuit breaker
Motors draw a high starting current, so they are commonly protected by a delay fuse (time-delay fuse) which can withstand the starting surge without blowing unnecessarily. An isolator is only for disconnection, not protection. A rewireable fuse is less suitable for motor protection because it is not as reliable or precise. An oil circuit breaker is used in higher-power systems, not as the common protection for small motors.
A transmission line is protected by
A)
Distance protection
B)
Inrush protection
C)
Differential relay
D)
None of these
Transmission lines are commonly protected by distance protection because the relay measures the impedance seen from the line end and can distinguish faults at different distances along the line. Differential relays are more commonly used for transformers, generators, and busbars, while inrush protection is associated with transformer magnetizing inrush, not transmission lines. Hence, the correct answer is Distance protection.
The advantage of XLPE cables as compared to PVC is higher resistance to
A)
Temperature and moisture
B)
Acids and termite
C)
Oils and salt
D)
All ofthese
XLPE (cross-linked polyethylene) cables have better insulation properties than PVC cables. They offer higher resistance to heat/temperature, moisture, chemicals such as acids and oils, and also better overall durability against environmental effects like salt and termite attack. Hence, the correct choice is 'All of these'.
The sizing of the generator in power plant is based on:
A)
Current carrying capacity ratings only
B)
Insulation strength ratings only
C)
Both (a) and (b)
D)
None of these
The generator in a power plant is sized considering both the current carrying capacity of its conductors and the insulation strength of its windings. Current carrying capacity ensures the machine can safely handle the electrical load, while insulation strength ensures it can withstand the operating voltage without breakdown. Hence, both factors are important.
The main factors which determine the capacity of Hydro Electric Power Station are:
A)
Location and population
B)
Head and discharge
C)
Forebay and penstoke
D)
Weir and Power Channel
The capacity of a hydro-electric power station mainly depends on the available water head and the rate of water flow (discharge). Power generated is proportional to both head and discharge. The other options are components or site-related features, but they do not determine the station capacity directly.
Plant factor is the ratio of
A)
Average demand to peak load
B)
Minimum power to maximum demand
C)
Minimum load to the total generated capacity
D)
Average load to the total generated capacity
Plant factor (also called plant use factor in some contexts) is defined as the ratio of the average load on a power plant to its installed/total generating capacity over a given period. Hence option (d) is correct. Option (a) describes load factor, not plant factor. Options (b) and (c) do not match the standard definition.
Maximum demand or peak load is the greatest demand that occurs usually for a period of:
A)
5 minutes
B)
15 minutes
C)
30 minutes
D)
60minutes
Maximum demand (peak load) is commonly defined in power systems as the greatest average load over a short specified interval, usually 15 minutes. This is the standard interval used by utilities for demand measurement. Hence, the correct answer is 15 minutes. The other options are not the usual standard interval for maximum demand.
According to their principle of operation, turbine can be broadly classified into:
A)
Pelton and Turgo
B)
Crossflow and Francis
C)
Impulse and Reaction
D)
Mixed flow and Axial Flow
Turbines are broadly classified according to their principle of operation into two main types: impulse turbines and reaction turbines. In an impulse turbine, the entire pressure drop occurs in the nozzle before the fluid strikes the runner. In a reaction turbine, pressure drops both in the fixed and moving blades. The other options are classifications based on specific turbine designs or flow direction, not the basic principle of operation.
Which of the following voltmeters have least power consumption?
A)
Movingiron
B)
Hot-wire
C)
Electrostatic
D)
Induction type
An electrostatic voltmeter draws extremely small current because it works on electrostatic attraction and does not require significant power from the circuit. Hence, its power consumption is the least. Moving-iron, hot-wire, and induction type voltmeters consume more power compared to electrostatic voltmeters.
In steam power plant which of the following components needs more maintenance?
A)
Condenser
B)
Boiler
C)
Turbine
D)
Coal carrying system
In a steam power plant, the coal carrying system needs more maintenance because it involves many moving parts such as conveyors, crushers, feeders, and elevators. These parts are subject to wear, dust, jamming, and frequent mechanical issues. The boiler and turbine also require maintenance, but the coal handling system generally needs the most frequent upkeep among the given options.
Which of the following busbar arrangement is generally employed in distribution system?
A)
One-and-half breaker arrangement
B)
Main and transfer arrangement
C)
Ring main distribution system
D)
Single busbar arrangement system
In distribution systems, the most commonly used busbar arrangement is the single busbar arrangement because it is simple, economical, and suitable for lower-voltage substations and distribution networks. One-and-half breaker and main-and-transfer arrangements are more complex and are generally used in high-voltage transmission substations where reliability is more critical. Ring main distribution system is a distribution network configuration, but the question asks specifically about busbar arrangement, so the correct choice is single busbar arrangement system.
The pH value of the water used in boiler is:
A)
unity
B)
seven
C)
slightly less than seven
D)
slightly more than seven
Boiler water is kept slightly alkaline, i.e., with pH a little above 7, to reduce corrosion and prevent acidic attack on boiler parts. A neutral pH is 7, while values below 7 are acidic and can promote corrosion. Hence, the correct choice is slightly more than seven.
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 (also called a line trap) is used in carrier communication systems. It blocks high-frequency carrier signals from entering unwanted parts of the power network while allowing the power frequency current to pass. CVT is used for voltage measurement and coupling, earth conductor provides grounding, and lightning arrestor protects against overvoltage.
Turbine converts energy in the form of falling water into:
A)
Electrical energy
B)
Potential energy
C)
Mechanical energy
D)
Hydro energy
In a hydroelectric power plant, the turbine receives the kinetic and potential energy of falling water and converts it into mechanical energy in the form of shaft rotation. The generator then converts this mechanical energy into electrical energy. So the turbine does not directly produce electrical energy. Potential energy and hydro energy are not the output form of the turbine.
As the voltage of transmission increases, the volume of conductor
A)
increases
B)
does not change
C)
decreases
D)
increases proportionately
For a given power transfer, increasing the transmission voltage reduces the current. Since conductor size is mainly determined by the current-carrying requirement, a lower current allows a smaller cross-sectional area, so the volume of conductor decreases. Hence, option (c) is correct.
Firm power is
A)
that power which is the maximum available
B)
that power which is the minimum available
C)
that power which will always be available
D)
that power which will never be available
Firm power is the dependable power output that a generating station can supply continuously under normal operating conditions. It is the minimum guaranteed power available at all times, so it is considered the power which will always be available. Option (a) refers to maximum available power, which is not firm power. Option (b) is close in idea but incomplete; firm power is not just the minimum available, but the assured continuous supply. Option (d) is incorrect.
The boundary of the protective zone is determined by the
A)
Location of CT
B)
Sensitivity ofrelay used
C)
Location of PT
D)
None of these
In protective relaying, the protected zone is defined by the locations of the current transformers (CTs). The CTs mark the boundaries of the zone in which the relay can detect faults. Hence, the boundary of the protective zone is determined by the location of CT. PT location does not define the zone boundary, and relay sensitivity affects operation, not the zone boundary.
Electrostatic type instruments are mainly used for measurement of
A)
Heavy currents
B)
Low currents
C)
Low voltages
D)
High voltages
Electrostatic instruments work on the force between charged plates and draw very little current, so they are suitable for measuring very high voltages. They are not preferred for heavy or low current measurement, and low-voltage measurement is usually done by other instruments like moving-coil or moving-iron types. Hence, the correct answer is High voltages.
Which of the following circuit breakers has high reliability and minimum maintenance?
A)
Air blast circuit breaker
B)
Vacuum circuit breaker
C)
Circuit breaker with SF, gas
D)
Oil circuit breaker
A vacuum circuit breaker is known for high reliability and minimum maintenance because the interrupting medium is vacuum, which prevents oxidation, contamination, and arc-related wear. It has a long service life and requires very little upkeep. Air blast and oil circuit breakers need more maintenance, while SF6 breakers are also reliable but the standard answer for minimum maintenance in such questions is vacuum circuit breaker.