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Past Questions
The efficiency of a pump is the ratio of:
A)
Head to flow
B)
output power to input power
C)
Discharge to suction
D)
pump speed to flow
In engineering and thermodynamics, efficiency (η) is universally defined as the ratio of the useful output power to the total input power. For a pump, the 'output power' is the Water Power (the energy imparted to the fluid to overcome head and maintain flow), and the 'input power' is the Shaft Power (the energy supplied by the motor to the pump shaft).
Mathematically: Efficiency (η) = (Water Power / Shaft Power) × 100%.
Analysis of other options:
- Option (a) 'Head to flow' is incorrect; the ratio of head to flow is related to the pump's characteristic curve, not its efficiency.
- Option (c) 'Discharge to suction' is incorrect; this relates to pressure or flow changes across the pump.
- Option (d) 'Pump speed to flow' is incorrect; this relates to the specific speed or affinity laws of the pump.
Duty point of a pump is the point where the pump characteristic curve intersects with the:
A)
system resistance curve
B)
pump efficiency curve
C)
suction head
D)
maximum head
The 'Duty Point' (also known as the Operating Point) of a pump is the specific point of operation where the pump's performance matches the requirements of the piping system.
1. **Pump Characteristic Curve**: This curve represents the head (H) the pump can produce for a given flow rate (Q) at a constant speed. It typically slopes downwards as flow increases.
2. **System Resistance Curve**: This curve represents the total head required to move fluid through the system, consisting of static head (elevation difference) and friction losses (which increase quadratically with flow rate). It typically slopes upwards as flow increases.
3. **Intersection**: The point where these two curves intersect is the only point where the head supplied by the pump exactly equals the head required by the system. This is the Duty Point.
Why other options are incorrect:
- **b. pump efficiency curve**: This curve shows how efficiency varies with flow; while engineers aim to place the duty point near the Best Efficiency Point (BEP), the duty point itself is determined by the system resistance, not the efficiency curve.
- **c. suction head**: This is a parameter (input condition) of the system, not a curve that determines the operating point.
- **d. maximum head**: This is the 'shut-off head' (where flow is zero), which is a single point on the pump curve, not a curve that intersects to create a duty point.
Which one of the following is a higher pair?
A)
Cam and follower pair
B)
Sliding pair
C)
Turning pair
D)
Rolling pair
In the Theory of Machines, kinematic pairs are classified based on the type of contact between the two mating elements:
1. **Lower Pair**: A pair is called a lower pair when the two elements have a surface contact. Examples include sliding pairs (piston and cylinder), turning pairs (shaft in a bearing), and rolling pairs.
2. **Higher Pair**: A pair is called a higher pair when the two elements have a point or line contact.
Evaluating the options:
- **a. Cam and follower pair**: The contact between the cam profile and the follower is typically a point or a line. Therefore, it is a higher pair.
- **b. Sliding pair**: This involves surface contact (e.g., a rectangular block sliding in a guide). It is a lower pair.
- **c. Turning pair**: This involves surface contact (e.g., a shaft rotating inside a circular hole). It is a lower pair.
- **d. Rolling pair**: This involves surface contact (e.g., a ball bearing). It is a lower pair.
Thus, the cam and follower pair is the only higher pair among the given options.
The pump shall not run when:
A)
NPSHA is greater than NPSHR
B)
outside the recommended range
C)
water enters into suction pipe
D)
NPSHA is less than NPSHR
The question refers to the conditions under which a pump will fail to operate correctly or will cease to function effectively due to cavitation.
1. **Understanding NPSH**: NPSH stands for Net Positive Suction Head.
- **NPSHA (Available)**: The actual pressure available at the suction port of the pump, determined by the system installation (static head, friction losses, and vapor pressure).
- **NPSHR (Required)**: The minimum pressure required at the suction port to prevent the liquid from flashing into vapor, as specified by the pump manufacturer.
2. **The Condition for Cavitation**: If NPSHA < NPSHR, the pressure at the impeller eye drops below the vapor pressure of the liquid. This causes vapor bubbles to form (cavitation). When these bubbles collapse, they create shockwaves that damage the impeller and cause a drastic drop in flow and head. In severe cases, the pump will 'lose prime' or experience 'vapor lock,' meaning it will not run/pump fluid effectively.
3. **Evaluating Options**:
- **Option a**: If NPSHA > NPSHR, the pump is operating safely and will run normally.
- **Option b**: While running outside the recommended range (e.g., too far left or right on the pump curve) is inefficient or risky, the pump usually still 'runs' unless it hits a physical limit or trips a safety switch.
- **Option c**: Water entering the suction pipe is the fundamental requirement for a centrifugal pump to operate.
- **Option d**: When NPSHA < NPSHR, cavitation occurs, which can lead to the pump failing to move fluid entirely.
What is the main purpose of maintaining a logbook in a Water Supply System?
A)
To record personal attendance
B)
To track daily weather report
C)
To record operational data and performance of system
D)
Sedimentation tank
In the context of System Maintenance for a Water Supply System, a logbook serves as the official technical record of the facility's operation.
1. Why Option (c) is correct: A logbook is essential for tracking critical operational parameters such as pump running hours, flow rates, pressure readings, chemical dosage (e.g., chlorine levels), and energy consumption. This data allows engineers to monitor the system's performance, identify trends, predict potential failures (predictive maintenance), and ensure compliance with water quality standards.
2. Why Option (a) is incorrect: Personal attendance is recorded in an attendance register or biometric system, not a technical system logbook.
3. Why Option (b) is incorrect: While weather might occasionally be noted if it affects raw water turbidity, the 'main purpose' of a system logbook is the operation of the machinery and distribution network, not meteorology.
4. Why Option (d) is incorrect: A sedimentation tank is a physical component (infrastructure) of a water treatment plant, not a purpose for maintaining a record book.
What is the unit of measurement for earthwork volume?
A)
Square meters
B)
Liters
C)
Cubic meters
D)
Tons
In Civil Engineering, 'earthwork' refers to the process of moving, removing, or adding soil, sand, or rock to prepare a site for construction. Since earthwork involves calculating the space occupied by the material (Volume = Area × Depth/Height), it is measured in three dimensions.
1. Cubic meters (m³) is the standard SI unit for volume, making it the correct unit for earthwork volume.
2. Square meters (m²) is a unit of area, used for tasks like plastering or flooring, not volume.
3. Liters is a unit of volume typically used for liquids, not for bulk construction materials.
4. Tons is a unit of mass/weight, used for weighing materials, but not for measuring the geometric volume of an excavation or embankment.
The discharge of water flowing through a circular pipe of 100 mm diameter, having a velocity of 1.0 m/s is :
A)
28.26 m3/hr
B)
30.50 m3/hr
C)
25.62 m3/hr
D)
38.26 m3/hr
Step-by-step calculation:
1. **Identify Given Data**:
- Diameter of the pipe (d) = 100 mm = 0.1 m
- Velocity of flow (v) = 1.0 m/s
2. **Calculate Cross-sectional Area (A)**:
The area of a circular pipe is given by the formula: A = (π/4) * d²
A = (3.14159 / 4) * (0.1)²
A = 0.7854 * 0.01 = 0.007854 m²
3. **Calculate Discharge (Q) in m³/s**:
Discharge is the product of area and velocity: Q = A * v
Q = 0.007854 m² * 1.0 m/s = 0.007854 m³/s
4. **Convert Discharge to m³/hr**:
Since there are 3600 seconds in one hour:
Q (m³/hr) = Q (m³/s) * 3600
Q = 0.007854 * 3600 = 28.2744 m³/hr
Rounding to two decimal places, we get 28.27 m³/hr, which most closely matches option (a) 28.26 m³/hr (the slight difference is due to the precision of π used in the question's source calculation, likely using π ≈ 3.14).
The slope of an open channel affects:
A)
Width of pipe
B)
Flow velocity
C)
Temperature
D)
Odour level
In open channel flow, the movement of water is driven primarily by gravity. The slope of the channel (bed slope) provides the gravitational force necessary to overcome the frictional resistance offered by the channel boundaries. According to Manning's Equation (V = (1/n) * R^(2/3) * S^(1/2}), the flow velocity (V) is directly proportional to the square root of the slope (S). Therefore, increasing the slope increases the flow velocity.
Why other options are incorrect:
- a. Width of pipe: The width of a pipe or channel is a geometric design parameter determined by the required discharge capacity, not by the slope itself.
- c. Temperature: Temperature is a thermodynamic property of the fluid and is not affected by the physical slope of the channel.
- d. Odour level: Odour is caused by chemical composition and biological decomposition of organic matter in the water, which is independent of the channel's slope.
A septic tank system is mainly used in:
A)
Rural and semi-urban areas
B)
Industrial treatment plants
C)
Desalination
D)
Water distribution
A septic tank is a small-scale, decentralized wastewater treatment system. It is designed to treat domestic sewage through anaerobic digestion and sedimentation.
1. Why Option (a) is correct: Septic tanks are ideal for rural and semi-urban areas where a centralized municipal sewerage system (large-scale underground pipe networks leading to a central treatment plant) is either unavailable, impractical, or too expensive to install. They provide an on-site solution for waste management.
2. Why Option (b) is incorrect: Industrial treatment plants require complex chemical, biological, or physical processes to remove heavy metals and toxic chemicals, which a simple septic tank cannot handle.
3. Why Option (c) is incorrect: Desalination is the process of removing salts from seawater to produce fresh water; it has no relation to sewage treatment.
4. Why Option (d) is incorrect: Water distribution refers to the system of pipes and pumps used to deliver potable water to consumers, whereas a septic tank is part of the wastewater disposal/sanitation system.
The key reason for conducting a water supply survey is to:
A)
Increase groundwater level
B)
Assess rainfall patterns
C)
Improve road network
D)
Plan intake and reservoir location
A water supply survey is a preliminary engineering activity conducted to gather essential data for the design and implementation of a water supply system. The primary objectives include identifying available water sources (surface or groundwater), determining the topography of the land, and analyzing the population distribution. This data is critical for the strategic planning of the 'Intake' (where water is collected from the source) and the 'Reservoir' (where water is stored for distribution), ensuring that gravity can be utilized where possible and that the system is cost-effective and sustainable.
Why other options are incorrect:
- Option (a): Increasing groundwater level is a result of rainwater harvesting or groundwater recharge, not a reason for conducting a survey.
- Option (b): While rainfall patterns are studied during a survey, they are a component of the data collection process, not the 'key reason' or ultimate goal of the survey itself.
- Option (c): Improving the road network is a function of transportation or civil infrastructure planning, not water supply planning.
What is the main purpose of trenching in rural sanitation?
A)
Laying pipelines
B)
Disposal of night soil
C)
Foundation laying
D)
Water harvesting
In the context of rural sanitation, 'trenching' refers to the practice of using trench pits for the safe disposal of human excreta (night soil) and organic waste. This is a common method in areas where centralized sewerage systems are unavailable. The process involves digging a trench, filling it with waste, and covering it with layers of soil to allow for anaerobic decomposition and to prevent the spread of pathogens and odors.
Why other options are incorrect:
- Option (a) Laying pipelines: While trenches are used for pipelines, this is a general civil engineering activity, not a specific 'rural sanitation' disposal method.
- Option (c) Foundation laying: This is a structural engineering process for building stability, unrelated to sanitation.
- Option (d) Water harvesting: This involves collecting rainwater in ponds or tanks, which is the opposite of waste disposal via trenching.
HDPE pipes are mostly preferred for:
A)
Electrical wiring
B)
Portable water supply due to flexibility
C)
Sewer lines only
D)
Road construction
HDPE (High-Density Polyethylene) pipes are widely preferred for potable (drinking) water supply systems for several technical reasons: 1. Flexibility: They can bend to accommodate terrain changes, reducing the need for numerous joints and fittings. 2. Corrosion Resistance: Unlike metal pipes, HDPE does not rust or corrode, making it ideal for transporting clean water. 3. Durability: It is resistant to chemical degradation and impact. 4. Leak-proof joints: Heat-fused joints create a monolithic system that prevents leakage.
Analysis of other options:
- Option (a): While HDPE is used as a conduit for electrical cables, the context of the exam (Public Health Engineering Department - Water Supply topic) makes water supply the primary intended answer.
- Option (c): While HDPE can be used for sewers, it is not used 'only' for sewer lines; it is a primary choice for pressurized water mains.
- Option (d): HDPE is not a material used for road construction itself, although it may be buried beneath roads.
What is the purpose of a circuit diagram?
A)
To show cable lengths
B)
To reduce power cost
C)
To show electrical layout
D)
To increase circuit load
A circuit diagram is a graphical representation of an electrical circuit. Its primary purpose is to illustrate the electrical layout, showing how various components (such as switches, loads, and power sources) are interconnected using standardized symbols.
Analysis of options:
- Option (a) is incorrect because cable lengths are typically specified in a 'wiring schedule' or 'bill of quantities,' not the circuit diagram itself.
- Option (b) is incorrect because while a well-designed circuit can optimize efficiency, the purpose of the diagram is documentation and planning, not the act of reducing cost.
- Option (c) is correct as it defines the fundamental role of the diagram: to map out the electrical layout for installation, troubleshooting, and analysis.
- Option (d) is incorrect because increasing circuit load is a result of adding more appliances, not a purpose of drawing a diagram.
Which of the following pipe materials is corrosion-resistant?
A)
DI
B)
CI
C)
HDPE
D)
ERW
To determine which pipe material is corrosion-resistant, we analyze the chemical properties of each option:
1. **DI (Ductile Iron):** While stronger than cast iron, DI is still a metallic material susceptible to corrosion (rusting) when exposed to moisture and corrosive soils. It typically requires external coatings (like zinc or polyethylene) and internal linings (like cement mortar) to prevent corrosion.
2. **CI (Cast Iron):** Like DI, Cast Iron is a ferrous metal. It is highly prone to corrosion and tuberculation (the buildup of iron oxide nodules) over time, which restricts water flow.
3. **HDPE (High-Density Polyethylene):** This is a thermoplastic polymer. Plastics are non-metallic and do not undergo electrochemical corrosion. HDPE is chemically inert to most acids, bases, and salts, making it inherently corrosion-resistant. This makes it ideal for water supply in aggressive soil conditions.
4. **ERW (Electric Resistance Welded) Steel:** These are steel pipes. Steel is highly susceptible to oxidation and corrosion unless it is galvanized or coated with specialized epoxy/bitumen layers.
Conclusion: Among the given options, HDPE is the only non-metallic material and is therefore the most corrosion-resistant.
What is the main function of a magnetic core in transformers and motors?
A)
Concentrate magnetic flux
B)
Increase the winding resistance
C)
Provide insulation to windings
D)
Increase current
In electrical machines like transformers and motors, the magnetic core is made of ferromagnetic materials (such as silicon steel) which have high magnetic permeability. The primary purpose of this core is to provide a low-reluctance path for the magnetic flux, thereby concentrating and guiding the magnetic field lines to ensure maximum coupling between the primary and secondary windings (in transformers) or between the stator and rotor (in motors).
Why other options are incorrect:
- Option b: Increasing winding resistance would lead to higher I²R losses (heat), which is undesirable.
- Option c: Insulation is provided by enamel, varnish, or specialized plastics, not by the metallic magnetic core.
- Option d: The core does not increase the current; current is determined by the applied voltage and the impedance of the circuit.
A pump set draws more current than rated during operation. The most likely electrical cause is
A)
High voltage supply
B)
Proper earthing
C)
Motor overloading
D)
Low winding temperature
Step-by-step reasoning:
1. Understanding Current Draw: In an electric motor, the current drawn is directly proportional to the mechanical load (torque) applied to the shaft.
2. Analyzing Motor Overloading: When a pump set is overloaded (e.g., due to a jammed impeller, high fluid viscosity, or pumping beyond rated capacity), the motor must produce more torque to maintain its speed. To produce this additional torque, the motor draws more current from the power supply, often exceeding its rated current (Full Load Amps).
3. Evaluating other options:
- (a) High voltage supply: Generally, an increase in voltage does not lead to a significant increase in current for an induction motor at a constant load; in some cases, it may slightly decrease current or cause saturation, but it is not the 'most likely' cause of overcurrent compared to overloading.
- (b) Proper earthing: Earthing is a safety mechanism to prevent electric shock and does not affect the operational current draw of the motor under normal conditions.
- (d) Low winding temperature: Lower temperatures typically result in lower resistance in the windings. While this might slightly affect current, it would not cause a motor to draw 'more than rated' current during operation; in fact, overheating is usually a result of high current, not the cause of it.
What is the main purpose of using a starter for motors in a pumping station?
A)
To reduce water flow
B)
To cool the motor
C)
To limit starting current
D)
To increase voltage
When an electric motor (especially an induction motor used in pumping stations) is started directly from the mains, it draws a very high initial current, often 5 to 7 times its rated full-load current. This is because the motor starts from a standstill (zero speed), meaning there is no back-EMF to oppose the supply voltage. This high 'inrush current' can cause voltage dips in the power system, damage the motor windings due to overheating, and put excessive mechanical stress on the pump couplings. A motor starter (such as a Star-Delta starter or an Auto-transformer starter) is used to reduce the starting voltage applied to the motor, thereby limiting the starting current to a safe level.
Analysis of other options:
- (a) To reduce water flow: Water flow is controlled by valves or Variable Frequency Drives (VFDs), not by the starter.
- (b) To cool the motor: Cooling is handled by fans or cooling jackets; starters do not provide cooling.
- (d) To increase voltage: Starters are designed to either maintain or temporarily reduce voltage to protect the motor; they are not used to increase voltage.
Night soil collection refers to:
A)
Manual collection of human waste
B)
Storage of rainwater
C)
Collection of grey water
D)
Water sample testing
In the context of sanitation and public health engineering, 'night soil' is a traditional term used to describe human excreta (feces and urine) that is collected from pit latrines or buckets rather than being carried away by a sewage system. 'Night soil collection' specifically refers to the practice of removing this waste manually or via vacuum trucks, typically during the night to minimize public nuisance and odor.
Analysis of other options:
- Option b (Storage of rainwater) refers to rainwater harvesting.
- Option c (Collection of grey water) refers to the management of wastewater from baths, sinks, and washing machines, which does not contain fecal matter.
- Option d (Water sample testing) refers to water quality analysis, not waste collection.
Which protective device melts to disconnect the circuit in case of overload?
A)
Relay
B)
Circuit Breaker
C)
Fuse
D)
Contactor
A fuse is a protective device consisting of a thin strip of metal or a wire with a low melting point. When an overload or short-circuit occurs, the current flowing through the fuse increases, causing the metal strip to heat up due to the I²R (Joule heating) effect. Once the temperature reaches the melting point of the material, the fuse 'blows' (melts), physically breaking the circuit and disconnecting the power to protect the downstream equipment.
Why other options are incorrect:
- a. Relay: A relay is an electromagnetic switch that detects a fault and sends a signal to a circuit breaker to trip; it does not melt to disconnect the circuit.
- b. Circuit Breaker: A circuit breaker is a reusable mechanical switch that trips due to thermal or magnetic action; it does not melt (melting would destroy the device).
- d. Contactor: A contactor is an electrically controlled switch used for switching a power circuit (like a motor); it is not primarily a protective device and does not operate by melting.
If the earth resistance at a pump control panel is measured to be 67 ohms, which is higher than the recommended value, what action should be taken?
A)
Increase voltage supply
B)
Change relay settings in the control panel
C)
No action needed
D)
Add salt and charcoal to the pit
Step-by-step reasoning: 1. Understanding the Problem: The measured earth resistance is 67 ohms, which is significantly higher than the standard recommended values for electrical installations (which typically require resistance to be below 5 ohms for power installations or 1 ohm for sensitive equipment). High resistance prevents fault currents from flowing safely to the ground, increasing the risk of electric shock and equipment failure. 2. Evaluating the Solution: To lower the earth resistance, the conductivity of the soil surrounding the earth electrode must be increased. 3. Analyzing Option (d): Adding a mixture of salt and charcoal to the earth pit is a traditional and effective method to reduce soil resistivity. Charcoal retains moisture and increases the surface area for current dissipation, while salt increases the ionic conductivity of the soil. 4. Evaluating other options: (a) Increasing voltage supply is dangerous and irrelevant to grounding. (b) Changing relay settings does not fix the physical grounding problem; it only changes how the system reacts to a fault. (c) 'No action needed' is incorrect because 67 ohms is an unsafe resistance level for a pump control panel.
What is the major advantage of ERW pipes?
A)
High flexibility
B)
Corrosion resistance
C)
Smooth surface and economical
D)
Fire resistance
ERW stands for Electric Resistance Welding. ERW pipes are manufactured by rolling a strip of steel into a cylindrical shape and welding the seam using high-frequency electric current.
1. Why 'Smooth surface and economical' is correct: The manufacturing process ensures a very smooth internal surface, which reduces frictional losses (head loss) during water transport. Additionally, because they are produced from steel strips (rather than seamless casting), they are significantly more cost-effective to produce in bulk, making them economical for large-scale water supply networks.
2. Why other options are incorrect:
- High flexibility (a): Steel pipes, including ERW, are rigid. They do not possess high flexibility compared to HDPE or PVC pipes.
- Corrosion resistance (b): Steel is naturally prone to corrosion. ERW pipes require additional coatings (like epoxy or galvanization) to resist corrosion; it is not an inherent advantage of the ERW process itself.
- Fire resistance (d): While steel is non-combustible, fire resistance is not the 'major advantage' specifically associated with the ERW manufacturing method in the context of water supply engineering.
What is the purpose of lightning arrester in a transmission line?
A)
To divert surge voltage to earth
B)
To block power theft
C)
To filter harmonics
D)
To increase voltage
A lightning arrester (also known as a surge arrester) is a protective device used on transmission lines and at substations to protect the insulation of the system from the effects of lightning.
1. **How it works**: Under normal operating voltage, the arrester acts as an insulator. However, when a high-voltage surge (caused by a lightning strike or switching operation) occurs, the arrester's resistance drops sharply, providing a low-impedance path to the ground.
2. **Purpose**: By diverting the high-voltage surge to the earth, it prevents the surge from reaching and damaging expensive equipment like transformers and insulators, thereby preventing flashovers and equipment failure.
**Analysis of other options:**
- **Option b**: Power theft is prevented by metering and physical security, not by lightning arresters.
- **Option c**: Harmonics are filtered using harmonic filters (passive or active), which typically consist of LC circuits.
- **Option d**: Voltage is increased using step-up transformers, not lightning arresters.
Which of the following values indicates the best power factor?
A)
0.8
B)
0.5
C)
0
D)
1
Power factor (PF) is defined as the ratio of Real Power (kW) to Apparent Power (kVA), or mathematically as the cosine of the phase angle (cos φ) between the voltage and current.
1. Range of Power Factor: The value of the power factor ranges from 0 to 1.
2. Ideal Condition: A power factor of 1 (known as 'Unity Power Factor') indicates that the voltage and current are perfectly in phase. In this state, all the power supplied to the circuit is utilized as real power to perform useful work, and there is zero reactive power (kVAR) flowing in the system.
3. Efficiency: A higher power factor (closer to 1) is 'best' because it reduces current flow for the same amount of real power, thereby reducing energy losses (I²R losses) in transmission lines and improving the efficiency of the electrical system.
Comparing the options:
- 0: Worst possible power factor (purely reactive load).
- 0.5: Poor power factor.
- 0.8: Common acceptable power factor, but not the 'best'.
- 1: Ideal/Best power factor (Unity).
In internal wiring, what determines the size of wire to be used?
A)
Room size
B)
Load Current
C)
Number of lights
D)
Wall thickness
In electrical wiring, the primary factor that determines the gauge or size of the conductor (wire) is the amount of current it must carry, known as the Load Current. This is based on the principle of current-carrying capacity (ampacity). If a wire is too thin for the load current, it will overheat due to resistance (I²R losses), which can melt the insulation and lead to electrical fires.
Why other options are incorrect:
- a. Room size: While room size might influence the length of the wire (affecting voltage drop), it does not determine the thickness/size of the wire itself.
- c. Number of lights: The number of lights is a component of the total load, but the determining factor is the total current (Amperes) those lights draw, not the count of fixtures.
- d. Wall thickness: Wall thickness affects the installation method (conduit routing) but has no bearing on the electrical capacity or size of the conductor required.
What does the breakdown voltage test of transformer oil measure?
A)
The oil level inside the transformer
B)
The cooling efficiency of the oil
C)
The insulation strength of the oil
D)
The temperature rise of the winding
The breakdown voltage (BDV) test is a critical diagnostic test performed on transformer insulating oil. The primary purpose of transformer oil is twofold: to provide cooling and to act as an electrical insulator between the windings and the tank. The BDV test involves applying an increasing voltage across two electrodes immersed in the oil sample until a spark (electrical breakdown) occurs. The voltage at which this occurs indicates the dielectric strength of the oil. A low BDV value typically indicates the presence of contaminants such as moisture, dissolved gases, or particulate matter, which reduce the oil's ability to resist electrical stress.
Why other options are incorrect:
- Option (a): Oil level is measured using a physical oil level gauge or conservator tank sight glass, not through a voltage test.
- Option (b): Cooling efficiency is related to the oil's thermal conductivity and viscosity, measured through heat dissipation tests or flow rate analysis.
- Option (d): Temperature rise is measured using thermometers or thermal imaging, not by applying high voltage to the oil.