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Past Questions — 2025
The overall average per unit subsidized tariff in the prevailing Tariff is:
A)
Rs. 8.05
B)
Rs. 7.82
C)
Rs. 7.10
D)
Rs. 6.82
The overall average per unit subsidized tariff in the prevailing tariff is Rs. 7.82, so option **b** is correct. The other options are incorrect because they do not match the computed/quoted average tariff value: **a (Rs. 8.05)** is higher than the prevailing average, **c (Rs. 7.10)** is lower, and **d (Rs. 6.82)** is also lower. Hence, the correct answer is **b**.
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, an instrument must be connected to both points simultaneously.
2. Connection Method: To measure the voltage across a component without altering the current flowing through that component, a voltmeter must be connected in parallel. This allows the voltmeter to experience the same potential difference as the component.
3. Ideal Characteristics: An ideal voltmeter has infinite internal resistance. By connecting it in parallel, it ensures that negligible current flows through the meter, preventing it from loading the circuit or changing the voltage it is intended to measure.
4. Why other options are incorrect:
- (a) Series: If a voltmeter were connected in series, its high resistance would drastically reduce the total current in the circuit, effectively acting as an open circuit and preventing the device under test from functioning.
- (c) Series or Parallel: A voltmeter cannot be used in series for voltage measurement as it would disrupt the circuit operation.
Transformer oil must be free from:
A)
odour
B)
gases
C)
sulphur
D)
moisture
Transformer oil serves two primary purposes: insulation and cooling. Moisture is the most critical contaminant because it significantly reduces the dielectric strength (breakdown voltage) of the oil. The presence of water molecules allows for the formation of conductive paths, which can lead to internal arcing and catastrophic failure of the transformer. While gases (like dissolved hydrogen or methane) are indicators of faults, and sulphur can cause corrosion, moisture is the fundamental impurity that must be strictly removed during the oil filtration and degassing process to ensure the operational safety and longevity of the insulation system. Therefore, transformer oil must be absolutely free from moisture.
Under the Electricity Act, 2003, who is a ‘consumer’?
A)
A person using electricity for residential purposes
B)
A person who purchases electricity for any purpose
C)
A bulk purchaser of electricity
D)
Anyone using power from the grid
According to Section 2(15) of the Electricity Act, 2003, a 'consumer' is defined as any person including a distributor who purchases or hires electricity for any purpose.
- Option (a) is incorrect because it is too narrow; residential use is only one type of consumption.
- Option (c) is incorrect because while a bulk purchaser is a consumer, the definition of 'consumer' is broader and encompasses all purchasers regardless of volume.
- Option (d) is incorrect because 'using power from the grid' is a general description, whereas the legal definition specifically hinges on the act of 'purchasing' or 'hiring' electricity.
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)
PAN Card
C)
Registered General Power of Attorney
D)
Ration Card
According to the JERC (Joint Electricity Regulatory Commission) Electricity Supply Code Regulations, when applying for a new service connection, the applicant must provide valid Proof of Identity (POI) and Proof of Ownership/Occupancy.
1. Electoral Identity Card, PAN Card, and Passport are universally accepted as primary government-issued photo identity proofs because they verify the identity of the individual.
2. A Registered General Power of Attorney is accepted as a legal document to establish the authority of an individual to apply on behalf of the owner.
3. A Ration Card is primarily a document for the distribution of essential commodities and serves as a proof of residence/address in some contexts, but it is NOT considered a valid 'Proof of Identity' (POI) for the purpose of establishing the legal identity of an individual in formal electricity connection applications, as it often lacks standardized biometric or secure identity verification compared to the other options listed.
The efficiency of a transformer will be maximum when:
A)
copper losses = hysteresis losses
B)
eddy current losses = copper losses
C)
hysteresis losses>eddy current losses
D)
copper losses = iron losses
In a transformer, total losses consist of two main components:
1. Iron Losses (Core Losses): These include hysteresis and eddy current losses. They are considered constant losses because they depend on the supply voltage and frequency, not the load.
2. Copper Losses (Ohmic Losses): These occur in the windings due to resistance and are variable losses, as they vary with the square of the load current (I²R).
Mathematically, Efficiency (η) = (Output Power) / (Output Power + Constant Losses + Variable Losses).
To find the maximum efficiency, we differentiate the efficiency expression with respect to the load current and set it to zero. This calculus derivation proves that maximum efficiency occurs when the variable losses (copper losses) are exactly equal to the constant losses (iron losses).
Analysis of options:
- Option (a) and (b) are incorrect because they only compare one part of the iron loss to copper loss, rather than the total iron loss.
- Option (c) is a general statement about the composition of iron losses and does not determine the point of maximum efficiency.
- Option (d) correctly identifies the condition: Copper Losses = Iron Losses.
Transformer oil used in transformer provides:
A)
insulation and cooling
B)
cooling and lubrication
C)
lubrication and insulation
D)
insulation, cooling and lubrication
Transformer oil (mineral oil) serves two primary functions in a power transformer:
1. **Insulation**: It acts as a dielectric medium between the windings and the grounded tank, as well as between the turns of the windings, preventing electrical arcing and short circuits.
2. **Cooling**: It acts as a heat transfer medium. As the transformer operates, heat is generated in the core and windings due to hysteresis, eddy currents, and I2R losses. The oil absorbs this heat and carries it away via convection to the radiator or cooling fins, where it is dissipated into the surrounding air or water.
Regarding the other options: Lubrication is not a requirement for the internal components of a transformer because there are no moving mechanical parts (like gears or pistons) within the tank that require lubrication. Therefore, options b, c, and d are incorrect.
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
1. Efficiency of a transformer is maximum when the variable losses (copper losses) are equal to the constant losses (iron/core losses).
2. Power transformers are typically designed for maximum efficiency near full load because they operate at a relatively constant load.
3. Distribution transformers, however, are connected to the grid to supply end-users. The load on these transformers varies significantly throughout the day (peaking during evening hours and dropping significantly at night).
4. Since the average load of a distribution transformer is much lower than its rated full-load capacity, they are specifically designed to achieve maximum efficiency at a lower loading point—typically between 50% and 75% of full load—to minimize overall energy losses over a 24-hour cycle.
5. While some textbooks mention 50%, the industry standard for modern distribution transformer design typically targets the 60% to 75% range to balance capital cost and operational efficiency.
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: The CRO measures voltage by observing the vertical displacement (amplitude) of the waveform on the screen. By multiplying the number of vertical divisions by the Volts/Div setting, the peak-to-peak or RMS voltage can be determined.
2. Frequency: The CRO measures the time period (T) of a signal by observing the horizontal distance of one complete cycle. Since frequency (f) is the reciprocal of the time period (f = 1/T), the frequency can be accurately calculated.
3. Phase: By using the dual-trace mode (comparing two different signals on the same screen), the time shift between two waveforms can be measured. This time difference, relative to the period, allows for the calculation of the phase difference between the two signals.
Since the CRO can measure all three parameters, option 'd' is the correct choice.
Hydroelectric power plant is mainly located in ____________.
A)
Flat areas
B)
Deserts
C)
Hilly areas
D)
Deltas
Hydroelectric power generation relies on the conversion of potential energy of water into electrical energy. The amount of power generated is proportional to the 'head' (the vertical distance the water falls). Hilly and mountainous areas provide the necessary natural elevation changes to create high-head reservoirs and steep drops, which are essential for driving turbines efficiently.
Why other options are incorrect:
- Flat areas: Lack the necessary elevation (head) to generate significant power without massive, expensive artificial pumping or pumping-storage systems.
- Deserts: Generally lack the consistent and abundant water sources (rivers/streams) required for hydroelectric plants.
- Deltas: These are low-lying areas where rivers slow down and split; they lack the steep gradients required for hydroelectric power generation.
Ampere is SI unit of:
A)
Current
B)
Voltage
C)
Frequency
D)
Power
The Ampere (symbol: A) is the base unit of electric current in the International System of Units (SI). It is defined as the flow of one coulomb of electric charge per second (1 A = 1 C/s).
Analysis of other options:
- b. Voltage: The SI unit of voltage (electric potential difference) is the Volt (V).
- c. Frequency: The SI unit of frequency is the Hertz (Hz).
- d. Power: The SI unit of power is the Watt (W).
What is the primary purpose of grounding in LV electrical installations?
A)
Voltage control
B)
Equipment cooling
C)
Personnel safety and equipment protection
D)
Power factor correction
Grounding (or earthing) in Low Voltage (LV) electrical installations is primarily implemented to ensure safety.
1. Personnel Safety: By connecting the non-current-carrying metal parts of equipment to the earth, any insulation failure that causes the metal casing to become energized will create a low-resistance path to ground. This triggers protective devices (like circuit breakers or fuses) to trip, preventing electric shock to personnel who might touch the equipment.
2. Equipment Protection: Grounding helps stabilize voltage levels during surges and provides a path for fault currents to dissipate safely, preventing catastrophic equipment failure.
Why other options are incorrect:
- Option (a) Voltage control: While grounding helps stabilize voltage relative to earth, 'voltage control' usually refers to regulators or transformers.
- Option (b) Equipment cooling: Cooling is handled by heat sinks, fans, or liquid cooling systems, not by electrical grounding.
- Option (d) Power factor correction: This is achieved using capacitor banks or synchronous condensers, not by grounding.
Which of the following is the main field of application of pin type insulator?
A)
Distribution system
B)
Transmission system
C)
Transmission and distribution system
D)
EHV transmission system
Pin type insulators are designed to be mounted on the cross-arms of poles, where the conductor is tied to the top of the insulator. Due to their design and material constraints, they are generally economical and effective only for voltages up to 33 kV. In modern power systems, voltages above 33 kV (Transmission systems and EHV systems) require suspension or strain insulators to handle the higher electrical stress and provide necessary flexibility. Therefore, pin type insulators are primarily used in the distribution system (typically 11 kV and 33 kV lines) rather than high-voltage transmission systems.
- Option (b) is incorrect because transmission systems usually operate at higher voltages (66kV, 132kV, etc.) where suspension insulators are used.
- Option (c) is incorrect because they are not suitable for the high-voltage side of the transmission system.
- Option (d) is incorrect because EHV (Extra High Voltage) systems require massive insulator strings (suspension type) to prevent flashovers.
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 full current of the branch flows through the instrument.
3. Internal Resistance: An ideal ammeter has zero internal resistance (and a practical ammeter has very low resistance). This is to ensure that inserting the meter into the circuit does not significantly change the total resistance or the current it is intended to measure.
4. Why Parallel is Incorrect: If an ammeter were connected in parallel, its very low resistance would create a 'short circuit' path. Most of the current would bypass the load and flow through the ammeter, likely blowing a fuse or damaging the meter and the circuit.
5. Comparison with Voltmeter: Conversely, a voltmeter is connected in parallel because it measures the potential difference between two points and has very high internal resistance to avoid drawing current from the circuit.
Which device is used to measure earth resistance directly?
A)
Megger
B)
Thermostat
C)
Multimeter
D)
Earth tester
Step-by-step reasoning:
1. The objective is to identify the device used to measure earth resistance directly.
2. An Earth Tester (also known as an Earth Resistance Tester or Ground Tester) is specifically designed for this purpose. It typically uses the 'Fall of Potential' method, employing auxiliary spikes driven into the ground to inject a current and measure the voltage drop, allowing for the direct calculation and display of the earth electrode's resistance.
3. Evaluating other options:
- a. Megger: While a Megger is an insulation resistance tester used to measure very high resistances (MΩ) between conductors or between a conductor and ground, it is not the primary tool for measuring the specific resistance of an earth electrode to the soil.
- b. Thermostat: This is a temperature control device and has no function in measuring electrical resistance.
- c. Multimeter: A standard multimeter can measure low resistances, but it cannot measure earth resistance because it cannot inject the necessary current into the ground or account for the soil's potential gradient.
Therefore, the Earth Tester is the only correct device for this specific application.
Which of the following is not a part of transformer installation?
A)
Conservator
B)
Breather
C)
Buccholtz Relay
D)
Exciter
A transformer is a static electrical device that transfers energy between circuits through electromagnetic induction.
1. Conservator (Option a): This is a small tank located above the main tank of a transformer. It allows for the expansion and contraction of oil due to temperature changes, ensuring the main tank remains full.
2. Breather (Option b): This is attached to the conservator. It contains silica gel to remove moisture from the air entering the transformer as the oil level fluctuates, preventing the degradation of the insulating oil.
3. Buchholz Relay (Option c): This is a safety device installed in the pipe connecting the main tank to the conservator. It detects internal faults (like short circuits or insulation failure) by sensing the accumulation of gas or sudden oil surges.
4. Exciter (Option d): An exciter is a component used in synchronous generators (alternators) to provide the necessary DC current to the field windings to create a magnetic field. It is NOT a part of a transformer, as transformers are passive devices and do not require a separate DC excitation system to operate.
What tool measures the specific gravity of the electrolyte to check charge level?
A)
Voltmeter
B)
Ammeter
C)
Hydrometer
D)
Ohmmeter
In lead-acid batteries, the state of charge is directly related to the density (specific gravity) of the electrolyte (sulfuric acid and water). As the battery discharges, the sulfuric acid is consumed and converted into water, lowering the specific gravity. A hydrometer is a device that measures this specific gravity by determining the buoyancy of a float in the liquid.
Why other options are incorrect:
- a. Voltmeter: Measures electrical potential difference (voltage) between two points.
- b. Ammeter: Measures the flow of electrical current in amperes.
- d. Ohmmeter: Measures electrical resistance in ohms.
Which of the following is the most popular method for measuring low resistance?
A)
ducter ohmmeter method
B)
kelvin double bridge method
C)
ammeter-voltmeter method
D)
potentiometer method
Measuring low resistance (typically below 1 ohm) is challenging because the resistance of connecting leads and contact resistances can be equal to or greater than the resistance being measured.
1. **Kelvin Double Bridge Method (Correct):** This is the most popular and standard laboratory method for measuring low resistance. It is a modification of the Wheatstone bridge that uses a second set of ratio arms to eliminate the effect of lead and contact resistances, providing extremely high accuracy.
2. **Ducter Ohmmeter Method:** While used for measuring low resistance (especially in power systems for joints and contacts), it is a portable instrument method rather than the fundamental 'most popular' theoretical method for precision measurement compared to the Kelvin bridge.
3. **Ammeter-Voltmeter Method:** This method is unsuitable for low resistance because the voltage drop across the low resistance is very small, and the voltage drop across the ammeter itself becomes significant, leading to large errors.
4. **Potentiometer Method:** While highly accurate for voltage measurement, it is not the primary or most popular method specifically designed for the specialized problem of low resistance measurement (lead resistance elimination).
The chemical used in breather is:
A)
asbestos fiber
B)
silica sand
C)
Aluminium alloy
D)
silica gel
A transformer breather is a device used to remove moisture from the air entering the conservator tank as the transformer oil expands and contracts. The chemical used for this purpose is silica gel, which is a desiccant (a hygroscopic substance). Silica gel absorbs moisture from the air; when it is fresh, it is typically blue, and as it becomes saturated with moisture, it turns pink.
Analysis of other options:
- a. Asbestos fiber: Used for insulation or heat-resistant gaskets, not for moisture absorption.
- b. Silica sand: While it contains silica, it does not have the porous structure required to act as an effective desiccant for air filtration.
- c. Aluminium alloy: A metal used for structural components or heat sinks, not a chemical desiccant.
An analog ammeter is:
A)
a recording instrument
B)
a controlling instrument
C)
an absolute instrument
D)
an indicating instrument
Electrical measuring instruments are classified based on their function into three main categories: 1. Indicating Instruments: These provide a visual representation of the magnitude of the quantity being measured at that specific instant using a pointer and a scale (e.g., an analog ammeter, voltmeter). 2. Recording Instruments: These keep a continuous record of the variations of the quantity over a period of time (e.g., a chart recorder). 3. Integrating Instruments: These measure the total amount of energy or quantity over a period (e.g., an energy meter). An analog ammeter uses a pointer to indicate the current flowing through a circuit, making it an indicating instrument. Option (b) 'controlling instrument' refers to a component within the meter (like a spring) rather than the type of meter itself, and option (c) 'absolute instrument' refers to instruments that give the magnitude of the quantity without calibration against another instrument (e.g., a tangent galvanometer), which is not the general classification for a standard analog ammeter.
The All day (energy) efficiency is the term related to:
A)
Power Transformer
B)
Distribution transformer
C)
Current transformer
D)
Voltage transformer
The 'All-day efficiency' is a specific metric used for distribution transformers because they are not loaded at full capacity throughout the 24-hour period. Unlike power transformers, which typically operate at a nearly constant load, distribution transformers experience fluctuating loads (peaking during the evening and dropping significantly at night).
1. **Definition**: All-day efficiency is the ratio of the total energy delivered to the load over 24 hours to the total energy supplied to the transformer (including core losses and copper losses) over the same period.
2. **Why Distribution Transformers?**: Since core losses (iron losses) occur as long as the transformer is energized, regardless of the load, calculating efficiency based on a single point in time is misleading. All-day efficiency accounts for these constant losses over a full day of varying load.
3. **Why not others?**:
- **Power Transformers (a)**: These are designed for maximum efficiency at full load or near full load because they operate consistently.
- **Current (c) and Voltage (d) Transformers**: These are instrument transformers used for metering and protection; their performance is measured by accuracy classes and ratio errors, not by energy efficiency over a 24-hour cycle.
Transformer cores are built up from laminations rather than from solid metal so that:
A)
oil penetrates thecore more easily
B)
eddy current loss is reduced
C)
less insulation is required for the windings
D)
turn ratio is higher than voltage ratio
Step-by-step reasoning:
1. **Understanding Eddy Currents**: When a transformer core is subjected to an alternating magnetic field, circulating currents are induced within the conductive bulk of the core material. These are known as eddy currents.
2. **The Problem with Solid Cores**: In a solid metal core, there is a large, uninterrupted path for these currents to flow. Since the core has some electrical resistance, these currents generate heat (I²R loss), leading to significant energy waste and potential overheating.
3. **The Solution (Laminations)**: By constructing the core from thin sheets (laminations) coated with an insulating layer (like varnish), the path for the eddy currents is physically interrupted.
4. **Effect of Laminations**: The resistance to the flow of eddy currents is greatly increased because the current is forced to flow in very narrow paths within each thin lamination. Since the magnitude of the eddy current is proportional to the square of the thickness of the lamination, reducing the thickness drastically reduces the total eddy current loss.
Analysis of other options:
- Option (a) is incorrect because oil penetration is related to cooling and insulation, not the structural choice of laminations over solid metal.
- Option (c) is incorrect because the insulation of windings is independent of whether the core is laminated or solid.
- Option (d) is incorrect because the turn ratio and voltage ratio are determined by the number of turns in the primary and secondary windings, not the physical construction of the core material.
Which of the following is a non-technical loss in the power system?
A)
Conductor resistance loss
B)
Insulation breakdown loss
C)
Meter tampering
D)
Core losses
In power distribution, losses are categorized into two main types: Technical Losses and Non-Technical Losses (Commercial Losses).
1. Technical Losses: These are losses inherent to the physical properties of the electrical system. They occur due to the laws of physics (e.g., Ohm's Law).
- Option (a) Conductor resistance loss (I²R loss) is a technical loss.
- Option (b) Insulation breakdown loss (leakage current) is a technical loss.
- Option (d) Core losses (hysteresis and eddy current losses in transformers) are technical losses.
2. Non-Technical Losses: These are losses that do not involve the physical dissipation of energy as heat but rather the failure to account for or bill the energy consumed. These are often referred to as 'commercial losses'.
- Option (c) Meter tampering involves illegally manipulating the energy meter to record less electricity than is actually consumed. This is a human-induced, non-physical loss of revenue for the utility company, making it a classic example of a non-technical loss. Other examples include theft of electricity (hooking) and billing errors.
After storage, the strength of cement:-
A)
Decreases
B)
Increases
C)
Remains same
D)
May increase or decrease
Cement is a hygroscopic material, meaning it readily absorbs moisture from the atmosphere. When cement is stored, it is exposed to atmospheric moisture and carbon dioxide. This leads to a process called 'pre-hydration,' where the cement particles react with moisture before they are actually mixed with water for construction. This partial hydration creates a layer of hydration products around the cement grains, which reduces the reactivity of the remaining unhydrated core. Consequently, the overall binding capacity and the compressive strength of the resulting concrete or mortar decrease as the storage period increases. For example, cement typically loses a significant percentage of its strength after 3 months of storage if not kept in moisture-proof conditions. Therefore, the strength of cement decreases after storage.
An imaginary line joining the points of equal elevation on the surface of the earth represents:-
A)
Contour surface
B)
Contour line
C)
Level line
D)
Contour gradient
Step-by-step reasoning:
1. Definition: In surveying, a contour is defined as an imaginary line on the ground surface connecting all points that have the same elevation relative to a specific datum (usually mean sea level).
2. Analysis of Options:
- (a) Contour surface: This is not a standard surveying term; a surface is a 2D area, whereas the question asks for a 'line'.
- (b) Contour line: This matches the definition perfectly. It is the line joining points of equal elevation.
- (c) Level line: A level line is a line that is tangent to the curvature of the earth at every point and is perpendicular to the direction of gravity. While it represents a constant elevation, it is a physical/geometric concept of 'level', whereas the mapping of equal elevation points on a terrain surface is specifically called a contour line.
- (d) Contour gradient: This refers to the rate of change of elevation between two contour lines (the slope), not the line itself.
3. Conclusion: The correct technical term for an imaginary line joining points of equal elevation on the earth's surface is a Contour line.