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Past Questions — 2015
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.
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 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.
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.
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.
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.
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.
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 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'.
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.
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.
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.
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).
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.
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.
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.
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.
The sag produced in the conductor of a transmission wire depends on
A)
Weight of the conductor per unit length
B)
Tension in the conductor
C)
Length of the conductor
D)
All of these
Sag in an overhead transmission conductor depends on the conductor’s weight per unit length, the tension applied in the conductor, and the span length. For a given span, sag increases with weight and length, and decreases as tension increases. Therefore, all the listed factors affect sag.
Which of the following is not main item of overhead line?
A)
Conductor
B)
Supports
C)
Insulator
D)
Resistor
An overhead transmission line mainly consists of conductors, supports (poles/towers), and insulators. A resistor is not a main component of an overhead line; it is an electrical element used in circuits, not a structural part of transmission lines.
Stones are provided in the substation
A)
To avoid fire accident by draining oil from transformer ifit leaks
B)
To avoid growing of weeds and plants
C)
To provide insulation
D)
None of these
In substations, a layer of stones (gravel) is laid on the ground mainly for fire safety. If transformer oil leaks, the stones help drain and spread the oil, reducing the chance of ignition and fire spread. They also help reduce weed growth, but the primary purpose in this question is fire prevention. Hence, option (a) is correct.
An inverse transducer is a device which converts
A)
Electrical energy into light energy
B)
Electrical energy into thermal energy
C)
Electrical quantity into a non-electrical quantity
D)
Electrical quantity into mechanical quantity
An inverse transducer performs the reverse function of a normal transducer. While a transducer generally converts a non-electrical quantity into an electrical quantity, an inverse transducer converts an electrical quantity into a non-electrical output. In instrumentation, the common example is conversion of electrical signals into mechanical motion. Hence, option (d) is correct. Option (c) is too general, while (a) and (b) are specific forms not defining the inverse transducer in general.
The arcing contacts in a circuit breaker are made of
A)
Copper tungsten alloy
B)
Alluminium alloy
C)
Electrolytic copper
D)
Porcelain
Arcing contacts in a circuit breaker must withstand very high temperature and severe arc erosion. Copper tungsten alloy is commonly used because it has a high melting point, good arc-resisting property, and adequate conductivity. Aluminium alloy is not suitable for arcing contacts, electrolytic copper is used for good conductivity but not for arc resistance, and porcelain is an insulating material, not a contact material.
Large internal faults in power transformer are protected by
A)
Mho and Ohm relay
B)
Earth fault relay
C)
Temperature relay
D)
Differential relay
Large internal faults in a power transformer are detected by a differential relay, which compares the current entering and leaving the transformer. Under normal conditions, these currents are equal, but during an internal fault there is a difference, so the relay operates. Mho and Ohm relays are mainly used for transmission line protection, earth fault relays are for ground faults, and temperature relays protect against overheating rather than internal electrical faults.
The percentage regulation of a line is determined by
A)
Quantum of current carried
B)
Quantity of power transferred
C)
Sending and receiving end voltages
D)
Allofthese
Voltage regulation of a transmission line is defined as the change in receiving-end voltage when the load changes from no-load to full-load, with the sending-end voltage kept constant. Hence, it is determined using the sending-end and receiving-end voltages. The current carried and power transferred may affect the voltage drop, but they are not the direct definition of regulation. Therefore, the correct option is (c).
Burden of the protective relay is the power
A)
Required to operate the circuit breaker
B)
Absorbed by the circuit of relay
C)
Developed by the relay circuit
D)
None of these
In protective relays, the term 'burden' means the power consumed or absorbed by the relay circuit from the current transformer (CT) or voltage transformer (VT). It is not the power required to operate the circuit breaker, nor power developed by the relay. Therefore, the correct answer is 'Absorbed by the circuit of relay'.