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Past Questions — 2025
An ammeter is connected in _______with the circuit element whose current we wish to measure.
A)
series
B)
parallel
C)
series or Parallel
D)
None of the above
1. Definition of Current: Electric current is the flow of charge through a conductor. To measure the total current flowing through a specific circuit element, the measuring device must be placed such that all the electrons passing through that element also pass through the meter.
2. Series Connection: In a series circuit, there is only one path for the current to flow. Therefore, connecting an ammeter in series ensures that the same current flowing through the load also flows through the ammeter.
3. Ideal Ammeter Characteristics: An ideal ammeter has zero internal resistance. This ensures that inserting the meter into the circuit does not change the total resistance of the circuit, thereby not altering the current it is intended to measure.
4. Why other options are incorrect:
- Parallel (b): If an ammeter (which has very low resistance) is connected in parallel, it would create a short circuit, diverting most of the current away from the load and potentially damaging the meter or the circuit.
- Series or Parallel (c): Only series connection is correct for current measurement; parallel is used for voltage measurement (voltmeter).
As per P&E Department SOR 2025, standard span of 11kV line is-
A)
120 m
B)
100 m
C)
140 m
D)
80 m
In the Schedule of Rates (SOR) for the Power & Electricity Department, Government of Mizoram, the standard span length for 11kV distribution lines is typically specified as 100 meters. The 'span' refers to the distance between two consecutive poles. While spans can vary based on terrain (shorter in hilly areas or longer in open plains), the standard baseline used for estimation and budgeting in the SOR is 100 m. Options a (120m), c (140m), and d (80m) do not align with the standard departmental specification for general 11kV line estimation.
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 SI unit of Magnetic Flux is-
A)
Hertz
B)
Weber
C)
Ampere
D)
Candela
Magnetic flux (Φ) is a measure of the total magnetic field which passes through a given area. In the International System of Units (SI), the unit of magnetic flux is the Weber (Wb). One Weber is defined as the flux through a surface that is perpendicular to a magnetic field of one tesla (T) over an area of one square meter (m²).
Analysis of other options:
- a. Hertz (Hz): The SI unit of frequency.
- c. Ampere (A): The SI unit of electric current.
- d. Candela (cd): The SI unit of luminous intensity.
A transformer core is laminated to-
A)
reduce hysteresis loss
B)
reduce eddy current losses
C)
reduce copper losses
D)
reduce all above losses
Step-by-step reasoning:
1. **Understanding Eddy Currents**: When an alternating magnetic flux passes through a conductive core, it induces small circulating currents within the bulk of the core material. These are known as eddy currents.
2. **The Problem**: These currents flow in loops and, due to the electrical resistance of the core material, they generate heat (I²R loss), which leads to energy inefficiency and overheating of the transformer.
3. **The Solution (Lamination)**: To prevent these currents from flowing in large loops, the solid core is replaced by a stack of thin sheets (laminations) insulated from each other by a thin layer of varnish or oxide.
4. **Mechanism**: Lamination increases the effective electrical resistance of the path available for eddy currents, thereby restricting their magnitude and significantly reducing the power loss.
Why other options are incorrect:
- **Option a (Hysteresis loss)**: Hysteresis loss depends on the material's magnetic properties (the area of the B-H loop). It is reduced by using high-permeability materials like Silicon Steel, not by laminating the core.
- **Option c (Copper losses)**: Copper losses (I²R losses) occur in the windings due to the resistance of the conductor. Laminating the core has no effect on the resistance of the copper wires.
- **Option d (All above losses)**: Since lamination specifically targets eddy currents and does not affect hysteresis or copper losses, this option is incorrect.
As per JERC(M&M) Electricity Supply Code Regulation 2013, any of the following documents or its attested copies, shall not be considered as acceptable proof of identity for individual in respect to application of new service connection-
A)
Electoral identity card
B)
Driving Licence
C)
Land Settlement Certificate (LSC)
D)
Ration Card
Under the JERC (M&M) Electricity Supply Code Regulations, when applying for a new service connection, the applicant must provide 'Proof of Identity' (POI) and 'Proof of Ownership/Occupancy' (Proof of Address).
1. Electoral Identity Card, Driving Licence, and Ration Card are standard government-issued documents that verify the identity of an individual (who the person is), making them acceptable as Proof of Identity (POI).
2. A Land Settlement Certificate (LSC) is a document used to prove ownership or legal possession of a piece of land. Therefore, it serves as 'Proof of Ownership' or 'Proof of Address', not as a 'Proof of Identity'.
Since the question asks which document shall NOT be considered as acceptable proof of identity, the Land Settlement Certificate is the correct answer because its purpose is to prove property rights, not personal identity.
In aluminium conductors, steel core is provided to-
A)
compensate for skin effect
B)
neutralise proximity effect
C)
reduce line inductance
D)
increase the tensile strength
The question refers to ACSR (Aluminium Conductor Steel Reinforced) conductors.
1. **Reasoning for the correct option**: Aluminium is an excellent conductor of electricity due to its low weight and cost, but it has relatively low mechanical strength (tensile strength). In long-span transmission lines, the conductor must support its own weight and withstand external loads like wind and ice without excessive sagging or breaking. By placing a core of high-strength galvanized steel at the center, the conductor gains the necessary mechanical strength (tensile strength) to withstand these stresses, while the outer aluminium strands carry the bulk of the electrical current.
2. **Why other options are incorrect**:
- **a. Compensate for skin effect**: Skin effect is a phenomenon where current tends to flow on the outer surface of a conductor. A steel core does not eliminate this; in fact, since the current flows primarily in the outer aluminium layers, the steel core is strategically placed in the center where current density is lowest.
- **b. Neutralise proximity effect**: Proximity effect is caused by the magnetic fields of adjacent conductors. A steel core does not neutralize this effect.
- **c. Reduce line inductance**: Line inductance depends on the spacing between conductors and the radius of the conductor. Adding a steel core does not significantly reduce the overall line inductance of the transmission system.
A SWG is used to measure-
A)
length of the wire
B)
Cross sectional area of the wire
C)
Diameter of the wire
D)
Insulation of the wire
SWG stands for Standard Wire Gauge. It is a standardized system used primarily in the UK and other Commonwealth countries to specify the diameter of electrical wires.
1. How it works: The SWG number is inversely proportional to the diameter; as the gauge number increases, the diameter of the wire decreases.
2. Why option 'c' is correct: The primary purpose of a wire gauge (like SWG or AWG) is to provide a standard reference for the physical thickness (diameter) of the conductor.
3. Why other options are incorrect:
- Option 'a' (length): Length is measured using a measuring tape or ruler, not a gauge.
- Option 'b' (Cross sectional area): While the area can be calculated using the diameter (Area = πr²), the SWG specifically defines the diameter. Area is usually expressed in mm².
- Option 'd' (Insulation): Insulation properties are measured using an insulation resistance tester (Megger), not a wire gauge.
Distribution transformers are usually designed to have maximum efficiency-
A)
at 50% of full load
B)
at 75% of full load
C)
near full load
D)
near no load
Option A is correct: at 50% of full load.
Five capacitors each of 5 µF are connected in series, the equivalent capacitance of the system will be-
A)
5 µF
B)
25 µF
C)
10 µF
D)
1 µF
To find the equivalent capacitance (C_eq) of capacitors connected in series, we use the reciprocal formula: 1/C_eq = 1/C1 + 1/C2 + ... + 1/Cn.
Given:
- Number of capacitors (n) = 5
- Capacitance of each capacitor (C) = 5 µF
Since all capacitors are identical, the formula simplifies to:
1/C_eq = n * (1/C)
1/C_eq = 5 * (1/5 µF)
1/C_eq = 1 µF⁻¹
C_eq = 1 / 1 µF⁻¹ = 1 µF.
Analysis of options:
- Option (a) 5 µF: This would be the result if only one capacitor was present or if they were in parallel and we divided by 5.
- Option (b) 25 µF: This is the result if the capacitors were connected in parallel (C_eq = n * C = 5 * 5 = 25 µF).
- Option (c) 10 µF: This is mathematically incorrect for this configuration.
- Option (d) 1 µF: This is the correct result for 5 identical 5 µF capacitors in series.
The capacity of battery is expressed in terms of-
A)
Ampere
B)
Volt-hour
C)
Ampere-hour
D)
Volt-Ampere hour
The capacity of a battery refers to the total amount of electric charge it can store and deliver over a period of time. Mathematically, Charge (Q) = Current (I) × Time (t). In the context of batteries, the standard unit for this is the Ampere-hour (Ah). For example, a battery with a capacity of 100 Ah can theoretically provide a current of 1 Ampere for 100 hours, or 10 Amperes for 10 hours.
Analysis of other options:
- Option (a) Ampere: This is the unit of electric current, not capacity.
- Option (b) Volt-hour: This is not a standard unit for battery capacity.
- Option (d) Volt-Ampere hour: This is equivalent to Watt-hour (Wh), which measures the total energy stored in the battery, not the charge capacity. While energy is important, 'battery capacity' by standard technical definition refers to the charge capacity in Ah.
Transformer ratings are expressed in terms of-
A)
kVA
B)
kW
C)
kVAr
D)
kWh
Transformer ratings are expressed in kVA (kilo-Volt-Ampere) because the losses in a transformer depend on the current (copper losses) and the voltage (core losses), but not on the phase angle between them (power factor).
1. **Copper Losses (I²R):** These depend on the load current flowing through the windings, regardless of whether the load is resistive, inductive, or capacitive.
2. **Iron/Core Losses:** These depend on the supply voltage and frequency, which remain constant for a given rating.
3. **Power Factor Independence:** Since the manufacturer does not know the power factor of the load that the end-user will connect to the transformer, the rating cannot be expressed in kW (which is real power and depends on the power factor: kW = kVA × cosφ).
Therefore, the apparent power (kVA) is the only universal measure for rating a transformer.
Why other options are incorrect:
- **b. kW (kilo-Watt):** This is real power. It depends on the load power factor, which is unknown at the time of transformer manufacture.
- **c. kVAr (kilo-Volt-Ampere Reactive):** This represents reactive power, which is only a component of the total power and does not represent the full capacity of the transformer.
- **d. kWh (kilo-Watt Hour):** This is a unit of energy consumption over time, not a rating of power capacity.
Highest system voltage in Mizoram is-
A)
220kV
B)
132kV
C)
66kV
D)
None of the above
In the state of Mizoram, the power transmission network is managed by the Power and Electricity Department. The state is integrated with the North Eastern Regional Grid. The highest transmission voltage level currently utilized for the main backbone of the state's transmission system is 132kV. While higher voltages like 220kV or 400kV are used in the National Grid and in neighboring states (like Assam), the internal highest system voltage for distribution and transmission within Mizoram's primary infrastructure is 132kV, which is then stepped down to 66kV, 33kV, and 11kV for local distribution. Therefore, option (b) is the correct answer.
Which of the following device is used to measure power in A.C. circuits?
A)
Ammeter
B)
Wattmeter
C)
Voltmeter
D)
Ohmmeter
Step-by-step reasoning:
1. The question asks for the device used to measure 'power' in an A.C. (Alternating Current) circuit.
2. Power in an A.C. circuit is the product of Voltage (V), Current (I), and the Power Factor (cos φ).
3. A Wattmeter is specifically designed to measure active power (real power) in watts. It typically consists of two coils: a current coil (connected in series) and a pressure/voltage coil (connected in parallel), allowing it to account for the phase difference between voltage and current.
Evaluating other options:
- a. Ammeter: Used to measure electric current (I) in Amperes.
- c. Voltmeter: Used to measure electric potential difference (V) in Volts.
- d. Ohmmeter: Used to measure electrical resistance (R) in Ohms.
Therefore, the correct device for measuring power is the Wattmeter.
The corona is considerably affected by which of the following?
A)
Size of the conductor
B)
Shape of the conductor
C)
Surface condition of the conductor
D)
All of the above
Corona discharge occurs when the electric field intensity at the surface of a conductor exceeds the dielectric strength of the surrounding air. The critical disruptive voltage (the voltage at which corona begins) is influenced by several factors:
1. **Size of the conductor (Option a):** The electric field intensity is inversely proportional to the radius of the conductor. A larger conductor radius reduces the potential gradient at the surface, thereby increasing the critical disruptive voltage and reducing the likelihood of corona.
2. **Shape of the conductor (Option b):** The distribution of the electric field depends on the geometry. Smooth, circular conductors have a uniform field, whereas sharp edges, protrusions, or non-circular shapes create points of high electric field concentration, which trigger corona at lower voltages.
3. **Surface condition of the conductor (Option c):** The presence of scratches, dust, moisture, or oxidation on the conductor surface creates local points of high stress (irregularities), which lower the critical disruptive voltage and enhance corona discharge.
Since all three factors significantly influence the onset and intensity of corona, the correct answer is 'All of the above'.
Which element of hydroelectric power plant prevents the penstock from water hammer phenomenon?
A)
Valves and Gates
B)
Draft tubes
C)
Spillway
D)
Surge Tank
Step-by-step reasoning: 1. Water Hammer Phenomenon: This occurs in a hydroelectric plant when there is a sudden change in the velocity of water flowing through the penstock (e.g., due to a sudden closure of the turbine gates). This creates a high-pressure shock wave that can rupture the penstock pipes. 2. Function of a Surge Tank: A surge tank is a storage reservoir or tank placed between the main reservoir and the turbine. When the turbine gates close suddenly, the excess water rises into the surge tank instead of slamming against the penstock walls, thereby absorbing the pressure surge and protecting the pipeline. 3. Analysis of other options: (a) Valves and Gates are used to control flow but their sudden operation is actually the cause of water hammer. (b) Draft tubes are used to recover kinetic energy from the water exiting the turbine to increase efficiency. (c) Spillways are used to release excess water from the dam reservoir to prevent overtopping, not to protect the penstock from pressure surges.