← Junior Engineer
Past Questions — 2016
If the height of transmission towers is increased, which of the following parameters is likely to change?
A)
Resistance
B)
Inductance
C)
Capacitance
D)
None of these
When the height of transmission towers is increased, the conductors are placed farther from the ground and generally the spacing with earth changes. The capacitance of a transmission line depends on the geometry of the conductors and their distance from the ground/each other, so it changes with tower height. Resistance depends on the conductor material and size, not tower height. Inductance is mainly affected by conductor spacing and arrangement, but the standard expected answer here is capacitance because increasing tower height directly changes the line-to-ground capacitance.
On what factor does the operating speed of the relay depend upon?
A)
Rate of flux built up
B)
Armature core air gap
C)
Spring tension
D)
All of these
The operating speed of a relay depends on multiple mechanical and magnetic factors. The rate at which flux builds up affects how quickly the relay coil develops enough force to operate. The armature air gap influences the magnetic pull and travel time, and spring tension affects the force that must be overcome before the relay closes. Since all three factors contribute, the correct answer is "All of these".
Which of the following is usually not the generating voltage?
A)
6.6kV
B)
9.9KV
C)
11kV
D)
13.2kV
Generating voltages in power stations are commonly standard values such as 6.6 kV, 11 kV, and sometimes 13.2 kV. 9.9 kV is not a usual standard generating voltage. Therefore, the correct answer is 9.9 kV.
A load curve is a plot of
A)
Load versus generation capacity
B)
Load versus current
C)
Load versus time
D)
Load versus cost of power
A load curve is the graph of electrical load demand against time. It shows how the load varies over a day, week, month, or year. The other options are incorrect because a load curve does not plot load against generation capacity, current, or cost of power.
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 (ESPs) are installed in power plants to remove fine particulate matter like fly ash and smoke from flue gases, thereby reducing air pollution. Induced draft fans only help move flue gases through the system, de-superheaters control steam temperature, and reheaters raise the temperature of steam between turbine stages; none of these are pollution-control devices.
A thermo-couple instrument can be used for the measurement of
A)
Direct current only
B)
Alternating current only
C)
Both direct current and alternating current
D)
dc/ac voltage only
A thermo-couple instrument works on the heating effect of current. Since heating is proportional to the square of current, it is independent of current direction. Therefore, it can measure both DC and AC currents. Hence, option (c) is correct. Options (a) and (b) are wrong because the instrument is not limited to only one type of current, and (d) is incorrect because a thermo-couple instrument is primarily used for current measurement, not voltage measurement.
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
To increase the transmission distance of a line, its effective reactance and voltage drop must be reduced, and voltage regulation improved. Series capacitors compensate for the inductive reactance of the line, while shunt reactors help control overvoltage due to line capacitance, especially in long transmission lines. Hence, series capacitors and shunt reactors are used. Option (a) is wrong because series resistance increases losses. Option (b) synchronous condensers can improve power factor and voltage support, but they are not the standard answer for increasing transmission distance. Option (c) is incorrect because shunt capacitors are generally used to improve power factor, not series reactors.
Power plants using coal work closely on known which of the following cycle?
A)
Otto cycle
B)
Binary vapor cycle
C)
Brayton cycle
D)
Rankine cycle
Coal-based thermal power plants work on the Rankine cycle. In these plants, water is converted into steam in a boiler, the steam expands in a turbine to produce work, and then it is condensed and pumped back to the boiler. This closed steam cycle is the Rankine cycle. Otto cycle is for spark-ignition engines, Brayton cycle is for gas turbines, and binary vapor cycle is used in some special power plants but not the standard coal-fired plant cycle.
Any winding of a power transformer develops short circuit owing to:
A)
Loose connections
B)
Insulation failure
C)
Impulse voltage
D)
Mechanical vibration
A short circuit in any winding of a power transformer occurs when the insulation between turns, layers, or windings breaks down. This insulation failure allows current to bypass the intended path and create a short circuit. Loose connections, impulse voltage, and mechanical vibration may contribute to transformer problems, but the direct cause of a winding short circuit is insulation failure.
If the voltage across the units in a two unit suspension insulator is 60% and 40% respectively of the line voltage, the ratio of capacitance of the insulator to that of its capacitance to earth will be
A)
0.5
B)
0.50
C)
0.65
D)
0.75
For a 2-unit suspension insulator, let the ratio of capacitance between the insulator units and earth be k. The voltage distribution depends on this ratio. When the first and second units take 60% and 40% of the line voltage respectively, the known result for a two-disc string is that the capacitance ratio comes out to 0.5. Hence, the ratio of capacitance of the insulator to its capacitance to earth is 0.5. The other values do not match the standard voltage distribution relation for a two-unit string.
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 generate electricity using flowing or falling water, so they do not burn fuel and produce smoke, ash, or harmful gaseous emissions during operation. Thermal power plants cause air pollution by burning coal/oil/gas. Nuclear power plants are not free from environmental issues because of radioactive waste and safety concerns. Geothermal plants may release small amounts of gases and can have site-related environmental impacts. Hence, the best answer is hydro-power plant.
Which component connects the substation to the area where power is to be distributed?
A)
Distributors
B)
Service mains
C)
Feeders
D)
All of these
In a distribution system, feeders carry power from the substation to the distribution area. Distributors then supply power to consumers, and service mains connect the distributor to the consumer’s premises. Therefore, the component that connects the substation to the area where power is to be distributed is the feeder.
Which of the following devices is employed in substation to limit the short circuit current in the power system?
A)
Shunt condenser
B)
Reactor
C)
Series capacitor
D)
Shunt capacitor
A reactor is an inductive device connected in series in a power system to limit short-circuit current by adding inductive reactance and thereby restricting fault current. Shunt condenser, series capacitor, and shunt capacitor are used mainly for power factor correction, voltage improvement, or transmission efficiency, not for limiting fault current.
Advantage of passive instrument is
A)
It does not need power supply
B)
Cheap
C)
Sensitive
D)
Accurate
A passive instrument does not require an external power source to operate; it draws the necessary energy from the quantity being measured. That is its main advantage. Option (b) may sometimes be true, but it is not the defining advantage. Options (c) and (d) are not generally guaranteed characteristics of passive instruments.
Best protection is provided by HRC fuses in case of
A)
Open circuits
B)
Short circuits
C)
Overloads
D)
None of these
HRC (High Rupturing Capacity) fuses are designed to safely interrupt very high fault currents, especially during short circuits. They can break heavy fault current quickly without exploding or causing much damage. They are not the best choice for open circuits, and overload protection is generally handled by other protective devices like relays or MCBs, though fuses can also respond to overloads to some extent.
In a system if the base load is the same as the maximum demand, the load factor will be
A)
1
B)
Zero
C)
Infinity
D)
1 percent
Load factor = Average load / Maximum demand. If the base load is the same as the maximum demand, then the load remains constant at that value throughout the period, so average load = maximum demand. Hence load factor = 1. The other options are incorrect because zero would mean no load, infinity is impossible here, and 1 percent is just 0.01, not the required value.
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 defined as the ratio of the voltage across the whole string to n times the voltage across the most highly stressed unit. If string efficiency is 100%, it means all discs share the voltage equally, so the potential across each disc is the same. Option (a) is unrelated, (c) is impossible in normal operation, and (d) would reduce efficiency, not make it 100%.
Guy wire is used to
A)
Support the pole
B)
Provide protection against surges
C)
Provide emergency earth route
D)
Protect conductors against short circuiting
A guy wire (stay wire) is used to provide mechanical support and balance to an overhead line pole or mast, especially when the pole is subjected to lateral tension from conductors. It helps keep the pole upright. It is not used for surge protection, earthing, or preventing short circuits between conductors.
For the measurement of high pressure with high accuracy the device used is
A)
Manganin wire pressure
B)
Ionization gauge
C)
Dead weight gauge
D)
Bourdon tubes
For measuring high pressure with high accuracy, a dead weight gauge is used because it is a primary standard instrument. It balances the unknown pressure against calibrated weights acting on a known piston area, giving very accurate pressure measurement. Bourdon tubes are common but less accurate, manganin wire pressure gauges are used for very high pressures, and ionization gauges are meant for very low pressures (vacuum), not high pressure.
Thermal relays are used for the protection of motors against over-current owing to:
A)
Short circuit
B)
Heavy loads
C)
Earth fault
D)
All of these
Thermal relays protect motors against sustained over-current caused by overload or heavy load conditions. They work on the heating effect of current and trip when the motor draws excessive current for too long. They are not meant for instantaneous protection against short circuit or earth fault; those are usually handled by fuses, circuit breakers, or earth-fault relays.
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 for carrier communication. It blocks high-frequency carrier signals from entering the power transformer and other equipment while allowing power frequency current to pass.
- CVT (Capacitive Voltage Transformer) is used for voltage measurement and can also be used for coupling, but it is not the carrier communication device itself here.
- Earth conductor is for grounding and safety.
- Lightning arrestor protects equipment from overvoltage surges.
Therefore, the correct answer is Wave trap.
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 principle of electrostatic attraction/repulsion between charged plates. The force produced is proportional to the square of the applied voltage, so they are most suitable for measuring high voltages. They draw negligible current, making them unsuitable for current measurement. Hence, the correct answer is high voltages.
Transmission efficiency increases as
A)
voltage and power factor both increase
B)
voltage and power factor both decrease
C)
voltage increases but power factor decreases
D)
voltage decreases but power factor increases
Transmission efficiency is improved by reducing line current for a given power transfer. Since current I = P / (V × power factor), increasing either the transmission voltage or the power factor reduces current, which reduces I²R losses in the line. Therefore, when both voltage and power factor increase, transmission efficiency increases. The other options either reduce voltage or power factor, which increases current and losses.
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 relaying on medium transmission lines, the **mho relay** is best suited because it is inherently **directional** and performs well for **longer transmission lines**, but it is also widely used on medium lines due to its good stability on power swings and reduced effect of arc resistance compared with simple impedance relay. The **reactance relay** is more suitable where arc resistance is significant, but it is generally more prone to unwanted operation under load conditions. The **impedance relay** is non-directional and less suitable for transmission line protection because it cannot distinguish fault direction by itself. Hence, the best choice is **mho relay**.
A lightning arrester connected between the line and earth in a power system
A)
Protects the terminal equipment against travelling surges
B)
Protects the terminal equipment against lightning strokes
C)
Suppresses the high frequency oscillations in the line
D)
Reflects back the travelling waves approaching it
A lightning arrester is connected between the line and earth to divert surge current safely to ground when an overvoltage occurs. Its main function is to protect terminal equipment from travelling surges, including those caused by lightning. Option (b) is too narrow because the arrester does not directly protect against only lightning strokes; it protects against the surges produced by them. Option (c) is incorrect because suppressing high-frequency oscillations is not the primary function of a lightning arrester. Option (d) is incorrect because the arrester does not reflect waves; it provides a low-impedance path to earth during surges.