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Past Questions
Inadequate earthing in a pump house may result in:
A)
Low discharge
B)
High friction loss
C)
Pipe leakage
D)
Electric Shock
Inadequate earthing means faulty or insufficient connection of electrical equipment to the ground. In a pump house, this can cause leakage current to remain on metal parts of pumps, motors, or panels, creating a serious risk of electric shock. The other options are unrelated to earthing: low discharge and high friction loss are hydraulic issues, and pipe leakage is a plumbing/mechanical issue.
Power factor of an AC circuit is defined as the ratio of:
A)
Active power to apparent power
B)
Reactive power to apparent power
C)
Apparent power to active power
D)
Reactive power to active power
Option A is correct: Active power to apparent power.
The detention period of a septic tank is generally:
A)
2–4 hours
B)
5 days
C)
24–48 hours
D)
10 days
The detention period of a septic tank is the time sewage is retained in the tank for sedimentation and anaerobic digestion. In general design practice, it is about 24–48 hours.
Why others are incorrect:
- (a) 2–4 hours: too short for effective settling and digestion.
- (b) 5 days: much longer than the usual septic tank detention period.
- (d) 10 days: far too long for normal septic tank design.
In an electrical rotating machine, the primary mechanical necessity of providing an air gap between stator and rotor is to:
A)
Reduce copper loss
B)
Improve cooling
C)
Enable rotation
D)
Improve power factor
The air gap is the small physical clearance between the stator and rotor in a rotating electrical machine. Its primary mechanical purpose is to provide space so the rotor can rotate freely without rubbing against the stator. The other options are not the main mechanical reason: copper loss is an electrical loss, cooling is a secondary benefit in some designs, and power factor is an electrical performance issue, not the main purpose of the air gap.
If the contact resistance of a circuit breaker is high, the immediate risk is:
A)
Nuisance tripping
B)
Excessive heating
C)
Incorrect settings
D)
Reduced capacity
High contact resistance in a circuit breaker causes extra power loss at the contacts, which is dissipated as heat. This can quickly lead to overheating, insulation damage, contact deterioration, and even failure. Nuisance tripping, incorrect settings, and reduced capacity are not the immediate direct effect of high contact resistance.
Which of the following protective relays is most sensitive to ground faults in a power system?
A)
Overcurrent relay
B)
Under-voltage relay
C)
Thermal overload relay
D)
Earth fault relay
An earth fault relay is specifically designed to detect ground (earth) faults and is therefore the most sensitive relay for this purpose. It operates on small residual or zero-sequence currents that appear when insulation fails and current flows to earth.
Why others are incorrect: Overcurrent relay responds to excessive current in general but is not as sensitive specifically to ground faults. Under-voltage relay operates when voltage drops below a set value, not primarily for fault-to-ground detection. Thermal overload relay protects against overheating due to overload, mainly in motors and equipment, not ground faults.
For starting of an induction motor in a pump house, different starters are employed depending on starting current and system conditions. Which starter applies full line voltage directly to the motor?
A)
Star-Delta starter
B)
Auto-transformer starter
C)
Soft starter
D)
Direct On Line (DOL) starter
A Direct On Line (DOL) starter connects the induction motor directly to the supply, so it applies full line voltage at starting. This gives the highest starting current, so it is used only for small motors or where the supply system can tolerate the inrush current.
Why others are incorrect:
- Star-Delta starter: starts the motor at reduced voltage in star connection, then switches to delta.
- Auto-transformer starter: applies reduced voltage through a tapped autotransformer during starting.
- Soft starter: gradually increases the voltage using power electronics to limit starting current and mechanical stress.
The minimum residual chlorine recommended in drinking water is:
A)
0.01 mg/L
B)
1.5 mg/L
C)
0.2 mg/L
D)
5 mg/L
The recommended minimum residual chlorine in drinking water is about 0.2 mg/L to ensure disinfection safety in the distribution system. Option (a) 0.01 mg/L is too low to provide adequate protection, while (b) 1.5 mg/L and (d) 5 mg/L are excessively high for normal drinking water and may cause taste and health issues.
The most common material used for septic tank construction is:
A)
Timber
B)
Steel sheet
C)
RCC
D)
Plastic
Septic tanks are commonly constructed using Reinforced Cement Concrete (RCC) because it is strong, durable, waterproof when properly built, and suitable for underground sewage storage. Timber is unsuitable due to decay, steel sheet is prone to corrosion, and plastic is used only in some prefabricated systems, not as the most common material.
For a given real power and voltage, if power factor decreases, the line current:
A)
Decreases
B)
Increases
C)
Remains same
D)
Becomes zero
For a single-phase AC load, real power P = VI cosφ, where cosφ is the power factor. For a given real power P and voltage V, line current I = P / (V × power factor). So if power factor decreases, the denominator becomes smaller and the current must increase. Hence, the correct answer is (b) Increases.
The purpose of chlorination is:
A)
Disinfection
B)
Softening
C)
Sedimentation
D)
Aeration
Chlorination is the process of adding chlorine to water mainly to destroy disease-causing microorganisms, so its primary purpose is disinfection. It does not soften water, remove suspended particles by sedimentation, or add oxygen by aeration.
If a three-phase induction motor in a pump house is found to rotate in the wrong direction during trial run, what should be done to correct the direction of rotation?
A)
Change starter
B)
Interchange any two phases
C)
Increase voltage
D)
Replace motor
In a three-phase induction motor, the direction of rotation depends on the phase sequence of the supply. If the motor rotates in the wrong direction, reversing the phase sequence reverses the rotation. This is done by interchanging any two of the three supply phases. Changing the starter, increasing voltage, or replacing the motor will not correct the direction of rotation.
A pump motor trips immediately after starting. Which instrument helps verify if starting current is abnormally high?
A)
Voltmeter
B)
Clamp Meter
C)
Megger
D)
Frequency Meter
A clamp meter is used to measure current directly in a live circuit without disconnecting the conductor. If a pump motor trips immediately after starting, checking the starting current with a clamp meter helps determine whether the current is abnormally high. A voltmeter measures voltage, a megger checks insulation resistance, and a frequency meter measures frequency, so they are not suitable for verifying starting current.
The resistivity of a semiconductor compared to a conductor at room temperature is:
A)
Slightly lower
B)
Zero
C)
Higher
D)
Much lower
A semiconductor has far fewer free charge carriers than a conductor at room temperature, so it offers more resistance to current flow. Therefore, its resistivity is much higher than that of a conductor. Option (b) is wrong because resistivity is not zero, and (a) and (d) are incorrect because conductors have much lower resistivity than semiconductors.
RCC stands for:
A)
Reinforced Clay Concrete
B)
Ready Cement Concrete
C)
Reinforced Concrete Column
D)
Reinforced Cement Concrete
RCC is the standard abbreviation for Reinforced Cement Concrete, a composite material in which steel reinforcement is embedded in concrete to improve tensile strength. The other options are incorrect because RCC does not mean Reinforced Clay Concrete, Ready Cement Concrete, or Reinforced Concrete Column.
The Mizoram Water Supply (Control) Act mainly regulates:
A)
Road construction
B)
Forest management
C)
Electricity supply
D)
Water supply and distribution
The Mizoram Water Supply (Control) Act is concerned with the regulation, control, and management of water supply systems, including distribution. It does not deal with roads, forests, or electricity. Therefore, the correct option is (d) Water supply and distribution.
Tree branches coming into contact with a 33 kV overhead line can result in:
A)
Improved insulation
B)
Reduced line impedance
C)
Flashover and faults
D)
Higher tensile strength
When tree branches touch or come very close to a 33 kV overhead line, the insulation between the conductor and the tree is disturbed. This can cause arcing or flashover, leading to line faults and possible outages. The other options are incorrect: tree contact does not improve insulation, reduce line impedance, or increase tensile strength of the line.
Given that MVA denotes Mega Volt-Ampere, MW denotes Mega Watt, and cos φ is the power factor, which of the following relations is correct?
A)
MVA = MW × cos φ
B)
MW = MVA × cos φ
C)
cos φ = MVA / MW
D)
cos φ = MW × MVA
In AC circuits, real power (MW) = apparent power (MVA) × power factor (cos φ). Since MVA is the apparent power and MW is the active/real power, multiplying MVA by cos φ gives MW. Therefore, option (b) is correct. Option (a) is incorrect because MVA is not obtained by multiplying MW by cos φ; rather, MVA = MW / cos φ. Option (c) is incorrect because cos φ = MW / MVA, not MVA / MW. Option (d) has no correct physical meaning.
HDPE pipes are preferred because they are:
A)
Corrosion resistant
B)
Brittle
C)
Heavy
D)
Expensive
HDPE (High-Density Polyethylene) pipes are widely preferred in water supply and piping systems because they do not corrode like metal pipes. They are also lightweight, flexible, and durable. The other options are incorrect: HDPE pipes are not brittle, not heavy, and are generally cost-effective rather than expensive.
The primary objective of preventive maintenance in electrical Operation and Maintenance is to:
A)
Minimize failures
B)
Reduce capital cost
C)
Increase energy use
D)
Raise operating temperature
Preventive maintenance is done before a breakdown occurs, with the main aim of detecting and correcting faults early so that equipment remains reliable and unexpected failures are reduced. It is not primarily meant to reduce capital cost, increase energy use, or raise operating temperature. Therefore, the correct answer is 'Minimize failures'.
The most suitable pump for deep bore wells is:
A)
Centrifugal pump
B)
Reciprocating pump
C)
Submersible pump
D)
Air lift pump
A deep bore well requires a pump that can work at great depth, remain submerged, and lift water efficiently from below ground level. A submersible pump is designed for this purpose because it is installed inside the bore well below the water level. Centrifugal pumps are generally used for low to moderate lift and are not suitable for deep bore wells. Reciprocating pumps are not preferred for such applications due to complexity and limited discharge. Air lift pumps can be used in special conditions, but they are not the most suitable general choice for deep bore wells.
Which of the following materials is most commonly used for overhead transmission line conductors due to its good conductivity and low cost?
A)
Copper
B)
Aluminium
C)
Silver
D)
Tungsten
Aluminium is most commonly used for overhead transmission line conductors because it offers a good balance of electrical conductivity, low weight, and low cost. Copper has higher conductivity but is heavier and more expensive, so it is less preferred for overhead lines. Silver is too costly, and tungsten is not used for this purpose due to poor suitability and high cost.
Twin pit latrine is commonly adopted in:
A)
Airports
B)
Industries
C)
Rural sanitation
D)
Hotels
Twin pit latrines are a low-cost, on-site sanitation system mainly promoted for rural areas. They are suitable where sewerage is not available and can safely decompose excreta in alternating pits. Airports, industries, and hotels generally require more advanced or high-capacity sanitation systems, so they are not the common setting for twin pit latrines.
Rainwater harvesting primarily aims to:
A)
Increase wastewater generation
B)
Conserve water resources
C)
Increase runoff
D)
Reduce evaporation
Rainwater harvesting is the collection and storage of rainwater for later use or for groundwater recharge. Its main purpose is to conserve water resources by reducing dependence on external water sources and improving water availability. Option (a) is incorrect because it does not increase wastewater generation. Option (c) is incorrect because harvesting aims to reduce runoff, not increase it. Option (d) may happen indirectly in some systems, but it is not the primary aim.
In a 33 kV sub-station, which instrument is used to step down high voltage to a safe and measurable level for metering and protection purposes?
A)
Power transformer
B)
Potential transformer
C)
Current transformer
D)
Lightning arrester
A potential transformer (PT), also called a voltage transformer, is used in a 33 kV sub-station to step down high voltage to a low, safe, and standardized value for metering and protection circuits. A current transformer (CT) is used for stepping down current, not voltage. A power transformer is used for transmitting power between voltage levels, and a lightning arrester protects equipment from surges, not for metering.