BPSC ASSISTANT ENGINEER ELECTRICAL PAST PAPER 2025
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چار آپشن میں سے کسی ایک پر کلک کرنے سے جواب سرخ ہو جائے گا۔
- To eliminate the need for transmission line
- To replace traditional circuit breakers
- To enhance the controllability and stability
- None of these
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Explanation
FACTS devices allow dynamic control of voltage, impedance, and phase angle, improving power flow and grid stability.
They help integrate renewable energy, reduce losses, and prevent voltage collapse in modern power systems.
- Eliminate harmonics from the power system
- Improve power factor by compensating for inductive reactance
- Increase the voltage level at the receiving end
- None of these
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Explanation
Series capacitors partially cancel the line’s inductive reactance, reducing voltage drop and increasing power transfer capability.
They help improve power factor and overall efficiency of long-distance AC transmission lines.
- They are less expensive to install than AC systems.
- They eliminate the need for transformers.
- They reduce transmission losses and improve efficiency.
- None of these
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Explanation
HVDC systems transmit power with lower resistive losses over long distances compared to AC systems.
They also allow better control of power flow and can connect asynchronous grids efficiently.
- It operates independently of the fault type.
- It responds only to overcurrent conditions.
- It determines fault location based on impedance measurement.
- None of these
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Explanation
Distance protection measures the impedance between the relay location and the fault to detect and isolate faults accurately.
This allows fast and selective protection of high-voltage transmission lines, even for faults far from the relay.
- To act as a coolant and transfer heat to the turbine
- To absorb excess neutrons and prevent overheating
- To slow down fast neutrons and sustain the chain reaction
- None of these
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Explanation
Moderators (like water or graphite) reduce the speed of fast neutrons, increasing the probability of fission in fuel nuclei.
This helps maintain a sustained and controlled nuclear chain reaction in the reactor core.
- The system can be controlled using a single input.
- All state variables can be reconstructed from output measurements.
- The system remains stable for all input conditions.
- None of these
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Explanation
Observability ensures that the internal states of an LTI system can be determined using its outputs over time.
This property is essential for designing state estimators and observers in control systems.
- Manual control of power distribution
- Centralized power generation
- Advanced energy storage and real-time demand response
- None of these
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Explanation
Smart grids use energy storage systems and real-time monitoring to balance variable renewable generation with consumption.
This enables efficient integration of solar, wind, and other renewables while maintaining grid stability.
- It does not require external power.
- It lacks a rotating magnetic field.
- It cannot operate at high speeds.
- None of these
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Explanation
A single-phase induction motor produces only a pulsating magnetic field, which cannot start the rotor on its own.
An auxiliary starting mechanism (like a start winding or capacitor) creates a phase shift to generate a rotating field for initial rotation.
- The applied DC voltage
- The presence of permanent magnets in the rotor
- The interaction between the motor’s rotating magnetic field and rotor currents
- None of these
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Explanation
In a three-phase induction motor, the stator produces a rotating magnetic field that induces currents in the rotor.
The interaction between these induced rotor currents and the rotating field generates torque, causing the rotor to turn.
- Lower installation cost
- Higher voltage drop
- Improved reliability and continuity of supply
- None of these
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Explanation
A ring main system allows electricity to flow from two directions, so if one section fails, supply can continue from the other direction.
This reduces outages and improves overall reliability compared to a radial distribution system.
