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Past Questions — 2015
The size of Gas Insulated Substation is significantly small compared to conventional substation because:
A)
High electronegative property of SF, gas
B)
High dielectric property of SF, gas
C)
High Insulation property of SF, gas
D)
All ofthese
Gas Insulated Substations (GIS) use SF6 gas, which has excellent insulating and dielectric properties and is highly electronegative. Because of this, the electrical clearances required between live parts can be much smaller than in conventional air-insulated substations. Hence the substation size becomes significantly smaller. Therefore, all the given properties contribute to the compact size.
A thermal protection switch can protect against
A)
Short-circuit
B)
Over voltage
C)
Overload
D)
Temperature
A thermal protection switch operates based on heat/temperature rise. It trips when the temperature exceeds a safe limit, so it protects against overheating. Short-circuit is protected by fuses or circuit breakers, overvoltage by surge protection devices, and overload is usually handled by overload relays, though thermal devices may indirectly respond to overload by sensing the resulting heat.
Overfluxing protection is recommended for
A)
Distribution transformer
B)
Station transformer of the power plant
C)
Auto-transformer of the power plant
D)
Generator transformer of the power plant
Overfluxing means excessive volts-per-hertz (V/f) in a transformer, which can drive the core into saturation and cause overheating. This protection is especially important for the generator transformer (GSU) in a power plant because it is directly exposed to generator voltage/frequency variations and can experience overexcitation during system disturbances. Distribution transformers are generally protected by simpler schemes, while overfluxing protection is specifically recommended for large power-plant transformers, particularly generator transformers. Hence, the correct answer is generator transformer of the power plant.
Which of the following factors is not considered for selection of conductor size?
A)
Current-carrying capacity
B)
Allowable voltage drop
C)
Maximum sag
D)
Breaking strength
The size of a conductor is selected mainly based on electrical and mechanical operating requirements such as current-carrying capacity, allowable voltage drop, and permissible sag. Breaking strength is a property related to the mechanical strength of the conductor material, but it is not a direct criterion for selecting conductor size. Hence, the correct answer is breaking strength.
The transducer which requires an external power and their output is measure of some variations such as resistance, inductance, capacitance, etc. are called
A)
Self generating transducer
B)
Primary sensor
C)
Active transducer
D)
Passive transducer
A transducer that needs an external power source and whose output depends on changes in electrical parameters like resistance, inductance, or capacitance is called a passive transducer. These devices do not generate their own electrical signal; they only modulate the supplied power. Self-generating or active transducers produce output without external power, so options (a) and (c) are incorrect. A primary sensor is not the correct classification here.
Minimum ground clearance along street for high voltage is
A)
15 feet
B)
17 feet
C)
19 feet
D)
21 feet
For high-voltage overhead lines along streets, the minimum ground clearance is 17 feet. This is the standard prescribed clearance for HV conductors over streets. Hence, option (b) is correct. The other options do not match the usual statutory clearance requirement.
Micro-Hydro-Electric Scheme is generally with a total installed capacity upto:
A)
10kW
B)
100kW
C)
1000kW
D)
10000kW
A micro-hydro-electric scheme is generally classified as having a total installed capacity up to 1000 kW (1 MW). Hence option (c) is correct. Options (a) 10 kW and (b) 100 kW are too small for the usual micro-hydro classification, while (d) 10000 kW is much higher and falls into a larger small-hydro category.
Which of the following instruments have least torque/weight ratio?
A)
Dynamometer type
B)
PMMC
C)
Attraction type moving iron
D)
Repulsion type moving iron
The torque/weight ratio is least for the dynamometer type instrument because it produces comparatively low operating torque for its size and weight. PMMC instruments have high torque/weight ratio, and moving iron instruments (attraction and repulsion types) generally have better torque than dynamometer type. Hence, among the given options, dynamometer type has the least torque/weight ratio.
Sub-Stations transform from high to low or the reverse.
A)
Voltage
B)
Current
C)
Power
D)
Allofthem
A sub-station is used to transform electrical voltage levels, either stepping up or stepping down through transformers. Current changes accordingly as a result of the voltage transformation, but the primary function is voltage transformation. Power is ideally conserved except for losses, so it is not the direct quantity transformed. Therefore, the correct answer is Voltage.
Measurement range of a voltmeter can be extended by using
A)
High current resistance
B)
High series resistance
C)
Low shunt resistance
D)
Low series resistance
A voltmeter measures potential difference and is connected in parallel. To extend its measurement range, a large resistance is added in series with the meter movement so that only a small current flows even at higher voltages. This is called a multiplier or high series resistance. A shunt resistance is used to extend the range of an ammeter, not a voltmeter.
Which of the following is not the method generally used for protection against lightning?
A)
Earthing
B)
Overhead earth wire
C)
Circuit Breaker
D)
Surge suppressor
Lightning protection in power systems generally uses earthing, overhead earth wires (shield wires), and surge suppressors/arresters to divert or absorb the lightning surge safely. A circuit breaker is used for switching and interrupting fault currents, not as a direct lightning protection method. Hence, the option not generally used for protection against lightning is Circuit Breaker.
The size of the feeder is determined primarily by
A)
the current it is required to carry
B)
the percent variation of voltage in the feeder
C)
the voltage across the feeder
D)
the distance of transmission
A feeder is a conductor that carries power from the substation to distribution points. Its size is determined primarily by the current it must carry, because the conductor must be able to safely handle the load current without excessive heating. Voltage drop is more critical for distributors, not feeders. Hence, option (a) is correct.
The most serious result of major uncleared fault is
A)
Fire
B)
Insulation Breakdown
C)
Over Voltage
D)
Over Current
A major uncleared fault causes very high fault current and severe heating in conductors, equipment, and surrounding materials. The most serious practical result is often fire due to thermal damage and arcing. Insulation breakdown, overvoltage, and overcurrent are effects or conditions associated with faults, but fire is the gravest consequence among the given options.
Potentiometer is an instrument of
A)
Indicating
B)
Comparison
C)
Calibrating
D)
Recording
A potentiometer measures an unknown voltage by comparing it with a known standard voltage under a null condition. Since it works on the principle of comparison rather than direct indication, it is called an instrument of comparison. It is not primarily an indicating, recording, or calibrating instrument, though it can be used in calibration work.
Pin insulators are manufactured for voltages upto
A)
11kV
B)
33kV
C)
66kV
D)
132kV
Pin insulators are generally used on distribution lines up to 33 kV. Beyond this voltage, the pin-type insulator becomes bulky and uneconomical, so suspension or other types of insulators are preferred. Therefore, the correct answer is 33 kV.
The ‘sheath’ is used in cable to
A)
provide strength to the cable
B)
provide proper insulation
C)
prevent the moisture from entering the cable
D)
avoid chances ofrust on strands
In a power cable, the sheath is the outer protective covering. Its main function is to protect the cable from moisture, water, and other external damage. It does not provide the main mechanical strength, which is the job of the armouring; insulation is provided by the insulating material around the conductor; and rust prevention of strands is not the primary function of the sheath. Therefore, the correct answer is to prevent moisture from entering the cable.
Which of the following equipment(s) is/are not indoor equipment of Sub-Station?
A)
Control Panel
B)
Standby generator sets
C)
Low voltage d.c switchgear
D)
None of these
Indoor sub-station equipment includes control panels, low-voltage d.c. switchgear, and auxiliary equipment such as standby generator sets when housed inside the station building. Since all the listed items can be indoor equipment, none of them is excluded. Therefore, the correct answer is 'None of these'.
The instrument which is cheapest for dc measurement is
A)
Movingiron
B)
PMMC
C)
Hot-wire
D)
Electro-dynamo
For DC measurement, the cheapest instrument among the given options is the moving iron instrument. It is rugged, simple in construction, and generally less expensive than PMMC instruments. PMMC is more accurate for DC but costlier. Hot-wire instruments are mainly used for both AC and DC but are not the cheapest. Electro-dynamo (electrodynamometer) instruments are more complex and expensive.
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