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Past Questions
Temporary connection shall be granted for a maximum period of _______ at a time.
A)
30 days
B)
3 months
C)
6 months
D)
45 days
In the context of electrical supply regulations (specifically those adopted by state electricity departments and based on standard utility guidelines), a 'Temporary Connection' is provided for short-term requirements such as construction sites, festivals, or temporary exhibitions. According to the standard regulations governing the supply of electricity, a temporary connection is typically granted for a maximum period of 6 months at a time. If the requirement extends beyond this period, the consumer is usually required to apply for an extension or convert the connection into a permanent one. Therefore, option (c) is the correct regulatory limit.
The All day (energy) efficiency is the term related to-
A)
Power Transformer
B)
Distribution transformer
C)
Current transformer
D)
Voltage transformer
1. Understanding Efficiency: Standard efficiency of a transformer is calculated at a specific load (e.g., full load) for a short duration. However, transformers in a power system operate under varying loads throughout a 24-hour period.
2. All-Day Efficiency: This is defined as the ratio of energy output (kWh) to the energy input (kWh) over a full day (24 hours). It accounts for both the copper losses (which vary with the square of the load) and the iron/core losses (which are constant as long as the transformer is energized).
3. Distribution Transformers: These transformers are designed to supply end-users. They are energized 24/7 but are rarely loaded to their full capacity; they typically operate at low loads for most of the day and peak loads for only a few hours. Therefore, calculating efficiency based on a single load point is misleading. All-day efficiency is the critical metric for distribution transformers to ensure core losses are minimized.
4. Power Transformers: These are typically used in transmission substations and operate at a nearly constant load. For these, standard efficiency at full load is a sufficient measure.
5. Instrument Transformers (CT/VT): Current and Voltage transformers are used for metering and protection; their performance is measured by accuracy classes and ratio errors, not by energy efficiency.
In the Electricity Act, 2003, there are _______ Sections.
A)
203
B)
190
C)
185
D)
196
The Electricity Act, 2003 is the primary legislation governing the power sector in India. It was enacted to consolidate the laws relating to generation, transmission, distribution, trading, and use of electricity. The Act is structured into several chapters containing a total of 203 sections. These sections cover various aspects including the establishment of the Central Electricity Regulatory Commission (CERC), State Electricity Regulatory Commissions (SERCs), the Appellate Tribunal for Electricity (APTEL), and the licensing and regulation of electricity supply. Therefore, option (a) is the correct answer.
Which of the following materials is not used for transmission and distribution of electrical power?
A)
Copper
B)
Aluminium
C)
Steel
D)
Tungsten
To determine the correct material, we must evaluate the properties required for electrical transmission and distribution: high electrical conductivity, mechanical strength, and cost-effectiveness.
1. **Copper (a):** Has excellent electrical conductivity. While expensive, it is widely used in distribution lines and underground cables.
2. **Aluminium (b):** Has good conductivity and is much lighter and cheaper than copper. It is the primary material used for overhead transmission lines (often as ACSR - Aluminium Conductor Steel Reinforced).
3. **Steel (c):** While steel has higher resistance than copper or aluminium, it is used as the core in ACSR conductors to provide the necessary mechanical tensile strength to support the span of the lines.
4. **Tungsten (d):** Tungsten has a very high melting point and is primarily used for filaments in incandescent lamps and electrodes in welding. It is brittle, expensive, and has significantly lower conductivity compared to copper and aluminium, making it entirely unsuitable for the long-distance transmission and distribution of power.
Therefore, Tungsten is the material not used for transmission and distribution.
AT&C Loss stands for-
A)
Aggregate Transmission & Consumption Loss
B)
Aggregate Technical & Commercial Loss
C)
Average Technical & Consumption Loss
D)
Actual Technical & Control Loss
AT&C loss is a key performance indicator used by power utilities to measure the efficiency of the electricity distribution system. It is the sum of two main components:
1. Technical Losses: These are inherent physical losses occurring due to the resistance of conductors, transformers, and other equipment (I²R losses).
2. Commercial Losses: These are non-technical losses resulting from electricity theft, meter tampering, billing errors, and non-payment of bills.
Therefore, 'Aggregate Technical & Commercial Loss' is the correct term.
- Option (a) is incorrect because 'Consumption' is not the term used; consumption is what is billed, not the loss itself.
- Option (c) is incorrect because 'Average' is not the standard term (it is an aggregate sum) and 'Consumption' is incorrect.
- Option (d) is incorrect because 'Actual' and 'Control' are not the standard industry terms for this metric.
During charging, the specific gravity of the electrolyte of a Lead Acid Battery-
A)
decrease
B)
increase
C)
remain same
D)
None of the above
In a Lead-Acid battery, the electrolyte consists of sulfuric acid (H2SO4) and water. During the discharge process, the sulfuric acid reacts with the lead plates to form lead sulfate (PbSO4), which precipitates onto the plates. This removes sulfate ions from the electrolyte, increasing the water concentration and thereby decreasing the specific gravity. Conversely, during charging, the chemical reaction is reversed: the lead sulfate is converted back into lead and lead dioxide, and sulfate ions (SO4^2-) are released back into the electrolyte. This increases the concentration of sulfuric acid in the solution, which directly leads to an increase in the specific gravity of the electrolyte. Therefore, measuring the specific gravity using a hydrometer is a standard method to determine the state of charge (SoC) of a lead-acid battery.
Hertz is SI unit of-
A)
Current
B)
Voltage
C)
Frequency
D)
Power
Step-by-step reasoning:
1. Definition: Frequency is defined as the number of cycles of a periodic waveform (such as an alternating current or a sound wave) that occur per second.
2. SI Unit: The International System of Units (SI) defines the unit of frequency as the Hertz (Hz), named after Heinrich Hertz. One Hertz is equal to one cycle per second (1 Hz = 1/s).
3. Evaluating other options:
- Current: The SI unit of electric current is the Ampere (A).
- Voltage: The SI unit of electric potential difference (voltage) is the Volt (V).
- Power: The SI unit of power is the Watt (W).
Therefore, Hertz is specifically the unit used to measure frequency.
In a LT 3-ph, 5 wire system, the 5th wire is used for-
A)
Earthing
B)
Spare
C)
Street light
D)
Communication
In a Low Tension (LT) 3-phase distribution system, a '3-phase, 4-wire' system typically consists of three phase conductors (R, Y, B) and one neutral conductor. When a '5th wire' is added to the system, it is specifically designated as the Earth Continuity Conductor (ECC) or the grounding wire. This 5th wire is used for earthing to provide a low-impedance path for fault currents, ensuring the safety of personnel and equipment by preventing the chassis of electrical appliances from becoming energized during an insulation failure.
Breakdown of options:
- a. Earthing: Correct. The 5th wire is the safety earth wire.
- b. Spare: Incorrect. Distribution systems are designed for specific functional requirements; wires are not installed as 'spares'.
- c. Street light: Incorrect. Street lights are connected as loads to the existing phase and neutral wires, not via a dedicated 5th system wire.
- d. Communication: Incorrect. Communication lines (like telephone or internet) are separate infrastructure and are not part of the LT power distribution wiring system.
Trash racks are located-
A)
near tailrace
B)
at the entrance of turbine
C)
inside penstock
D)
intake
Step-by-step reasoning: 1. Definition: A trash rack is a screen or grating made of metal bars designed to prevent large debris (such as logs, branches, leaves, and plastic) from entering the water conveyance system of a hydroelectric plant. 2. Location: To protect the entire downstream system—including the penstock and the turbine—the trash rack must be placed at the very beginning of the water path, which is the intake structure. 3. Analysis of options: (a) Tailrace is where water exits the plant; placing a rack here would be useless for protecting the machinery. (b) Placing a rack at the turbine entrance is too late, as debris would have already damaged the penstock. (c) Inside the penstock is impractical and would cause massive pressure drops and blockages that are difficult to clear. (d) The intake is the correct location to filter water before it enters the penstock. Therefore, option d is the correct answer.
A CRO is used to measure-
A)
Voltage
B)
Frequency
C)
Phase
D)
All of the above
A Cathode Ray Oscilloscope (CRO) is a versatile electronic instrument used to visualize and analyze electrical signals.
1. **Voltage (Option a):** The CRO measures voltage by plotting the signal on the vertical (Y) axis. By using the 'Volts/Div' knob and counting the vertical divisions of the waveform, the peak-to-peak and RMS voltages can be calculated.
2. **Frequency (Option b):** The CRO measures the time period (T) of a signal by plotting it on the horizontal (X) axis. By using the 'Time/Div' knob and measuring the distance of one complete cycle, the frequency can be calculated using the formula f = 1/T.
3. **Phase (Option c):** By using the dual-trace mode (Lissajous figures or time-shift method), a CRO can compare two different waveforms to determine the phase difference between them.
Since a CRO can perform all these measurements, the correct option is 'All of the above'.
The chemical used in breather is-
A)
asbestos fiber
B)
silica sand
C)
sodium chloride
D)
silica gel
In a transformer, the oil expands and contracts due to temperature changes. When the oil contracts, air from the atmosphere is drawn into the conservator tank. This air contains moisture, which can degrade the dielectric strength of the transformer oil. To prevent this, the air is passed through a 'breather' containing silica gel. Silica gel is a highly hygroscopic substance (a desiccant) that absorbs moisture from the air before it enters the tank. Fresh silica gel is typically blue in color and turns pink when it becomes saturated with moisture, indicating that it needs to be replaced or reactivated.
Why other options are incorrect:
- a. Asbestos fiber: Used for thermal insulation or fireproofing, not for moisture absorption.
- b. Silica sand: While it contains silica, it does not have the porous structure or chemical properties required to act as an effective desiccant.
- c. Sodium chloride: This is common table salt; it is not used as a desiccant in transformer breathers.
Which conductor is commonly used as a neutral conductor in LT distribution line?
A)
Weasel
B)
Gnat
C)
Ant
D)
Grasshopper
In ACSR (Aluminum Conductor Steel Reinforced) conductor nomenclature, conductors are named after animals or insects, and their sizes are categorized by their cross-sectional area.
1. **Ant Conductor**: This is a small-sized ACSR conductor commonly used as a neutral conductor in Low Tension (LT) distribution lines because the neutral conductor typically carries less current than the phase conductors under balanced loads and does not require the same current-carrying capacity as the main phases.
2. **Weasel, Gnat, and Grasshopper**: While these are also names of ACSR conductors, they differ in size and application. For instance, 'Dog' or 'Rabbit' are larger conductors used for higher voltage transmission or main distribution phases. In the specific context of standard LT distribution practices in many power utilities (including those following traditional ACSR naming conventions), the 'Ant' conductor is the standard choice for the neutral wire due to its appropriate gauge and cost-effectiveness for that specific role.
Generally grounding is provided for-
A)
only for the safety of the equipment
B)
only for the safety of the operating personnel
C)
both (a) and (b)
D)
none of the above
Grounding (or earthing) is a fundamental safety practice in electrical engineering designed to achieve two primary objectives:
1. Safety of Operating Personnel: By providing a low-resistance path to the earth, grounding ensures that if a fault occurs (such as a phase-to-frame fault), the leakage current is diverted to the ground rather than passing through a human body. This prevents electric shocks and fatalities.
2. Safety of Equipment: Grounding helps in stabilizing the voltage during normal operation and provides a path for fault currents to flow, which triggers protective devices (like circuit breakers or fuses) to trip quickly. This prevents the equipment from overheating or sustaining permanent damage due to overvoltage or sustained fault conditions.
Since grounding serves both the protection of people and the protection of the hardware, option (c) is the correct choice.
Iron loss in the transformer can be determined by-
A)
Short Circuit Test
B)
Open Circuit Test
C)
Both a) and b)
D)
None of the above
In a transformer, total losses are divided into Iron losses (Core losses) and Copper losses.
1. **Iron Loss (Core Loss):** This consists of Hysteresis and Eddy current losses. These losses depend on the magnetic flux density, which is determined by the applied voltage. In an Open Circuit (OC) test, the rated voltage is applied to one winding (usually the Low Voltage side) while the other winding remains open. Since the secondary is open, the current drawn is very small (no-load current), making the copper losses negligible. Therefore, the power measured by the wattmeter during an OC test represents the Iron loss of the transformer.
2. **Copper Loss:** This is the $I^2R$ loss occurring in the windings. This is determined by the Short Circuit (SC) test, where the rated current is passed through the winding while the voltage is kept very low, making the iron losses negligible.
Therefore, the Open Circuit Test is specifically used to determine the iron loss.
Pin type insulators are generally not used for voltages beyond-
A)
1.1 kV
B)
11 kV
C)
22 kV
D)
33 kV
Pin type insulators are designed to support the conductor on the cross-arm of the pole. As the voltage level increases, the size of the insulator must increase to maintain the necessary creepage distance and prevent flashover. For voltages up to 33 kV, pin insulators are practically feasible. However, beyond 33 kV, the size and weight of a pin insulator become prohibitively large and expensive, making them mechanically unstable. Therefore, for voltages above 33 kV, suspension-type insulators (strings of porcelain discs) are used instead, as they provide better flexibility and can be easily scaled by adding more discs to handle higher voltages. Thus, pin type insulators are generally not used for voltages beyond 33 kV.
As per JERC(M&M) Electricity Supply Code Regulation 2013, Supply of LT Single Phase category shall be upto a contracted load of _______ kW.
A)
10
B)
6
C)
8
D)
4
According to the JERC (M&M) Electricity Supply Code Regulations 2013, the guidelines for the supply of electricity specify the limits for single-phase and three-phase connections to ensure grid stability and prevent phase imbalance. For Low Tension (LT) supply, the Single Phase category is permitted for consumers with a contracted load up to 6 kW. If the contracted load exceeds 6 kW, the consumer is required to be provided with a Three Phase connection to distribute the load evenly across the phases of the distribution system. Therefore, option (b) 6 is the correct limit.
The voltage of the single phase supply to residential consumers is-
A)
110 V
B)
210 V
C)
230 V
D)
400 V
In the Indian electrical power system (which governs the Government of Mizoram's electricity department), the standard nominal voltage for single-phase residential supply is 230 V AC at a frequency of 50 Hz.
Step-by-step analysis of options:
1. Option (a) 110 V: This is the standard voltage used in North American countries (USA, Canada), not in India.
2. Option (b) 210 V: This is not a standard nominal voltage for residential distribution.
3. Option (c) 230 V: This is the correct standard nominal voltage for single-phase supply in India, as per the Bureau of Indian Standards (BIS) and the Central Electricity Authority (CEA) guidelines.
4. Option (d) 400 V: This is the standard nominal line-to-line voltage for a three-phase supply in India, not the single-phase supply provided to residential consumers.
Pelton turbines are used for-
A)
medium head applications
B)
low head applications
C)
in steam power plants
D)
for high head applications
A Pelton turbine is an impulse turbine where the entire available head is converted into kinetic energy via a nozzle before the water hits the buckets on the runner. Because it relies on high-velocity jets of water to generate power, it is most efficient and typically used in 'high head' scenarios (usually above 300 meters).
Analysis of other options:
- Option (a) and (b): Medium and low head applications typically utilize Reaction Turbines, such as Francis turbines (medium head) or Kaplan turbines (low head), which utilize both pressure and kinetic energy.
- Option (c): Pelton turbines are hydraulic turbines used for hydroelectric power, not for steam power plants (which use steam turbines).
The power factor of industrial loads is generally-
A)
unity
B)
lagging
C)
leading
D)
zero
Industrial loads are predominantly composed of inductive loads. The most common equipment in industrial settings includes induction motors, transformers, and solenoid valves. In an inductive circuit, the current lags behind the voltage due to the magnetic field requirements of the coils. Since the majority of the power consumed in industries is used to drive motors (which are inductive), the overall power factor of an industrial load is generally 'lagging'.
Analysis of other options:
- Unity (a): This occurs when the load is purely resistive (e.g., heaters), which is rare for an entire industrial plant.
- Leading (c): This occurs when the load is predominantly capacitive (e.g., large capacitor banks), which is usually only seen during power factor correction or in specific electronic loads.
- Zero (d): This would imply a purely reactive circuit with no real power consumption, which is not possible for a functional industrial load.
Cells are connected in series in order to-
A)
increase the voltage rating
B)
increase the current rating
C)
increase life of the cell
D)
None of the above
In electrical circuits, when cells (voltage sources) are connected in series, the total voltage of the battery is the algebraic sum of the individual voltages of each cell. For example, if three cells of 1.5V each are connected in series, the total voltage becomes 1.5V + 1.5V + 1.5V = 4.5V.
Analysis of options:
- Option (a) is correct because series connection increases the total electromotive force (EMF) or voltage rating.
- Option (b) is incorrect because to increase the current rating (capacity/Ah), cells must be connected in parallel. In a series connection, the current remains the same as that of a single cell.
- Option (c) is incorrect because connecting cells in series does not inherently increase the chemical life or cycle life of an individual cell; in fact, if one cell fails or is weaker, it can lead to uneven discharge and potentially shorten the overall battery pack's reliability.
- Option (d) is incorrect as option (a) is the standard electrical principle.
Which of the following does not change in a transformer?
A)
Current
B)
Voltage
C)
Frequency
D)
All of the above
A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.
1. **Voltage (Option b):** The primary purpose of a transformer is to change the voltage level. Depending on the turns ratio (N2/N1), it can be a 'step-up' transformer (increasing voltage) or a 'step-down' transformer (decreasing voltage).
2. **Current (Option a):** According to the principle of conservation of energy (assuming an ideal transformer where Power In = Power Out, i.e., V1*I1 = V2*I2), if the voltage is increased, the current must decrease proportionally, and vice versa. Therefore, current changes.
3. **Frequency (Option c):** The frequency of the alternating current is determined by the source (the generator). Since a transformer does not have any rotating parts or active power electronics to modify the timing of the AC cycle, the frequency of the output voltage is identical to the frequency of the input voltage.
Therefore, frequency remains constant in a transformer.
Meggar is an instrument used for-
A)
measuring current
B)
measuring voltage
C)
measuring power
D)
testing insulation
A Megger (short for Mega-ohmmeter) is a specialized instrument used to measure very high electrical resistance, typically in the range of Mega-ohms (MΩ). Its primary application is to test the insulation resistance of electrical equipment such as cables, motor windings, and transformers. It works by applying a high DC voltage to the insulation and measuring the resulting leakage current to determine the resistance.
Why other options are incorrect:
- Option (a): Current is measured using an Ammeter.
- Option (b): Voltage is measured using a Voltmeter.
- Option (c): Power is measured using a Wattmeter.
A Voltmeter is connected in _______ with the circuit component across which Potential difference is to be measured.
A)
series
B)
parallel
C)
series or Parallel
D)
None of the above
1. Definition of Potential Difference: Potential difference (voltage) is the difference in electrical potential between two distinct points in an electrical circuit. To measure this difference, a device must be connected to both points simultaneously.
2. Voltmeter Characteristics: An ideal voltmeter has infinite internal resistance, and a practical voltmeter has very high internal resistance. This ensures that it does not draw significant current from the circuit, which would otherwise alter the voltage it is trying to measure.
3. Connection Method: To measure the voltage across a component, the voltmeter must be connected in parallel. This allows the voltmeter to experience the same potential difference as the component.
4. Why other options are incorrect:
- (a) Series: If a voltmeter were connected in series, its high resistance would drastically reduce the total current flowing through the circuit, effectively acting as an open circuit and preventing the circuit from functioning normally.
- (c) Series or Parallel: A voltmeter cannot be used in series for voltage measurement purposes due to the reasons mentioned above.
- (d) None of the above: Option (b) is the standard and correct electrical engineering practice.
Which of the following distribution systems is more reliable?
A)
Radial system
B)
Tree system
C)
Ring main system
D)
All are equally reliable
Reliability in a distribution system refers to the ability to maintain power supply to consumers even in the event of a fault in a section of the network.
1. **Radial System (Option a):** In this system, power flows from a single source to the consumers along a single path. If a fault occurs at any point in the line, all consumers downstream of that fault lose power. This makes it the least reliable system.
2. **Tree System (Option b):** This is essentially an extension of the radial system where the main feeder branches off into several sub-feeders. While it covers more area, it still lacks redundancy; a fault on a main branch disconnects all subsequent branches.
3. **Ring Main System (Option c):** In this system, the distribution transformer is fed by a loop (ring) of conductors. Every distribution point is fed from two directions. If a fault occurs in any section of the ring, that specific section can be isolated, and power can still reach all consumers via the alternative path of the ring. This redundancy significantly increases the reliability of the power supply.
Therefore, the Ring Main system is the most reliable among the given options.
In a tap changing transformer, the tappings are provided on-
A)
primary winding
B)
secondary winding
C)
high voltage winding
D)
any of the above
In a tap changing transformer, tappings are provided to regulate the output voltage by changing the turns ratio. While theoretically, tappings could be placed on either winding, in practical engineering and industrial applications, they are almost always provided on the High Voltage (HV) winding for the following reasons: 1. Current Magnitude: The current in the HV winding is significantly lower than in the Low Voltage (LV) winding. Since the tap changer is a mechanical switch, lower current reduces the risk of arcing and wear and tear on the contacts. 2. Cost and Complexity: Implementing a tap changer on a high-current LV winding would require much heavier and more expensive switchgear to handle the high current. 3. Efficiency: Small changes in the number of turns on the HV side produce the desired voltage regulation more effectively. Therefore, while 'any of the above' might seem logically possible in a lab setting, the standard technical answer for power systems is the high voltage winding.