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Past Questions — 2015
Which of the following is digital transducer?
A)
Encoder
B)
Thermistor
C)
LVDT
D)
Strain gauge
A digital transducer gives output in digital form. An encoder converts mechanical position or motion into a digital code, so it is a digital transducer. Thermistor, LVDT, and strain gauge are analog transducers because they produce continuous output changes.
The term used for conveyance of electric power at extra-high voltages from generating stations to the grid sub-stations is:
A)
Transformation
B)
Transmission
C)
Generation
D)
Distribution
Electric power conveyed at extra-high voltages from generating stations to grid substations is called transmission. Transmission is used for bulk transfer of power over long distances at high voltage to reduce losses. Generation means producing electricity, transformation means changing voltage levels using transformers, and distribution refers to supplying power from substations to consumers at lower voltages.
PVC stands for
A)
Polyethylene Vinyl Cable
B)
Poly Vacuum Cable
C)
Poly Vinyl Chloride
D)
Polythene Vacuum Chloride
PVC is the standard abbreviation for Poly Vinyl Chloride, a widely used plastic insulation material in electrical cables. The other options are incorrect because they expand PVC into non-standard or meaningless terms.
A Sub-station is a part of an electrical
A)
Generation
B)
Transmission
C)
Distribution
D)
Allofthese
A sub-station is an important part of the power system and can be used in generation, transmission, and distribution networks. It may step up voltage at generating stations, step down voltage in transmission systems, or distribute power to consumers. Hence, it is part of all these sections.
The machine which converts mechanical energy into electrical energy is:
A)
Governor
B)
Generator
C)
Turbine
D)
Power House
A generator converts mechanical energy into electrical energy by electromagnetic induction. A governor controls speed, a turbine converts fluid energy into mechanical energy, and a power house is the building/facility where power generation equipment is installed.
Load curve are plotted between
A)
Time and Demand
B)
Current and Load
C)
Power and Voltage
D)
Load and Voltage
A load curve is a graph showing how the electrical load (demand) varies with time. Hence it is plotted between time on the x-axis and demand/load on the y-axis. The other options do not represent the standard definition of a load curve.
Where more than one multicore cable is laid in the same trench, a desirable horizontal inter-axial spacing is
A)
less than 0.1m
B)
0.1 to 0.2m
C)
0.25 to 0.4m
D)
more than 0.4m
When more than one multicore cable is laid in the same trench, a horizontal inter-axial spacing of about 0.1 to 0.2 m is considered desirable. This spacing helps reduce mutual heating and allows safer cable operation. Spacing less than 0.1 m is too close, while 0.25 m or more is generally larger than the usual desirable range for this arrangement.
Hydrogen cooling employed in large thermal power plant alternator:
A)
Increases the insulation life
B)
Decreases the insulation life
C)
Does not effect the insulation life
D)
None of these
Hydrogen is used as a cooling medium in large alternators because it has high thermal conductivity, low density, and low windage losses. Better cooling keeps the machine temperature lower, and lower operating temperature reduces thermal stress on insulation. Hence, hydrogen cooling increases insulation life. Options (b) and (c) are incorrect because insulation life is strongly affected by temperature.
Sub-Stations can be classified based on the following:
A)
Voltage level & Configuration
B)
Applications & Structure
C)
Insulation & Switching
D)
Allofthese
Sub-stations are commonly classified on multiple bases, including voltage level, configuration, application, structure, insulation, and switching arrangement. Since all the listed bases are valid classification methods, the correct answer is 'All of these'. Options (a), (b), and (c) each mention only part of the full classification, so they are incomplete.
Post insulators are used for
A)
Supporting bus bars in switchgear
B)
Insulating guard wires
C)
High-voltage suspension lines
D)
Insulating stay wires
Post insulators are rigid insulators used to support and isolate bus bars and other live parts in switchgear and substations. They are not used for guard wires, suspension lines, or stay wires. Suspension lines use suspension insulators, and stay wires use stay insulators.
In order to improve the power factor the following device is employed in the substation
A)
Synchronous Condenser
B)
Synchronous Reactor
C)
Series Capacitors
D)
None of these
A synchronous condenser is used in substations to improve power factor by supplying reactive power (VARs) to the system. It operates as an over-excited synchronous machine and helps compensate inductive loads. A synchronous reactor is used to absorb reactive power, so it does not improve power factor. Series capacitors are mainly used for transmission line compensation, not as the standard substation device for power factor improvement.
Which of the following factors is not the cause of breakdown at normal voltage?
A)
Detorioration of insulation
B)
Accidental short circuiting by tree branches
C)
Surges caused by lightning
D)
Damage perching of birds
Breakdown at normal voltage is usually caused by external or accidental factors such as tree branches short-circuiting lines, lightning surges, or bird perching causing flashover. Deterioration of insulation is generally a gradual internal aging problem and is not a direct cause of breakdown at normal operating voltage.
A conductor made up of a number of wires twisted together is
A)
Bunched conductor
B)
Shaped conductor
C)
Multi-core conductor
D)
Stranded conductor
A conductor made up of a number of wires twisted together is called a stranded conductor. This construction improves flexibility and is commonly used in power and electrical applications. A bunched conductor is a type of stranded arrangement but the standard term for wires twisted together is stranded conductor. Shaped conductor refers to a conductor with a specific cross-sectional shape, and multi-core conductor means several insulated conductors combined in one cable.
Hydrogen cooling is employed in:
A)
Turbo Generators only
B)
Water wheel Generators only
C)
Can be used in both turbo generators and water wheel generators
D)
None of these
Hydrogen cooling is used in large turbo generators because hydrogen has high thermal conductivity, low density, and low windage losses, making it ideal for cooling high-speed rotating machines. Water wheel generators (hydro generators) are generally air-cooled or water-cooled by other arrangements, not hydrogen-cooled. Therefore, the correct answer is Turbo Generators only.
Number of disc insulators needed to form strings for 33 kV (tension or dead ending assembly) is
A)
2
B)
3
C)
6
D)
12
For a 33 kV line, the usual suspension or tension string uses 3 disc insulators. In standard transmission-line practice, 11 kV generally needs 1 disc, 33 kV needs 3 discs, 66 kV needs 4 discs, and 132 kV needs 8 discs (approximate standard values). Hence, for 33 kV dead-ending/tension assembly, the correct answer is 3.
Demand factor is
A)
Minimum power demand to maximum power demand
B)
Average power demand to total connected load of the system
C)
Maximum power demand to total connected load of the system
D)
Average power demand to maximum power demand
Demand factor is defined as the ratio of maximum demand to the total connected load. It indicates how much of the connected load is actually used at the time of peak demand. Therefore, option (c) is correct. Option (a) is incorrect because it describes a ratio involving minimum demand, which is not the definition of demand factor. Option (b) is the load factor-related idea, not demand factor. Option (d) is also incorrect because average demand divided by maximum demand is not demand factor.
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.
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.
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.
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.
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.
Earth resistance of service connection should not exceed
A)
1.0ohms
B)
2.0 Ohms
C)
3.5 Ohms
D)
5.0 Ohms
For a service connection, the earth resistance is required to be kept low for safety and proper fault current dissipation. The standard value commonly specified in such exam questions is not more than 2 ohms. Hence option (b) is correct. The other values are either too low to be the usual prescribed limit in this context or too high to ensure safe earthing.
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.
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.
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.