Free Power Systems MCQs with Answers

• A. line is energized
• B. there is no current in the line
• C. line is on full load
• D. circuit breaker is not open

Explanation: An isolator is an off-load switching device and has no arc-quenching facility for interrupting current.

• A. Current only
• B. Current and voltage
• C. Current, voltage and frequency
• D. Current, voltage, frequency and short time current

Explanation: A bus-bar is specified by its continuous current, rated voltage and frequency, along with its short-time withstand current for fault…

• A. compensate for skin effect
• B. neutralise proximity effect
• C. reduce line inductance
• D. increase the tensile strength

Explanation: Aluminium has good conductivity but relatively low mechanical strength, so a steel core is added in ACSR conductors to carry tensile loads…

• A. Using a guard ring
• B. Grading the insulator
• C. Using long cross arm
• D. Any of the above
• E. None of the above

Explanation: A guard ring, insulator grading, and a suitably long cross-arm all make the voltage distribution across a suspension-insulator string more…

• A. current flows through the half cross-section of the conductor
• B. portion of the conductor near the surface carries more current and core of the conductor carries less current
• C. portion of the conductor near the surface carries less current and core of the conductor carries more cur¬rent
• D. any of the above
• E. none of the above

Explanation: Alternating current produces greater inductive opposition toward the conductor’s centre, so current crowds toward the outer surface.

• A. Ring bus-bar scheme
• B. Single bus-bar scheme
• C. Breaker and a half scheme
• D. Main and transfer scheme

Explanation: The single bus-bar scheme has the simplest arrangement with the fewest circuit breakers and isolators, so it has the lowest installation…

• A. insulin
• B. bitumen
• C. varnish
• D. no insulation is required

Explanation: In an ACSR conductor, aluminium strands are laid around a galvanised steel core without an insulating layer between them.

• A. semi-circle
• B. triangle
• C. ellipse
• D. catenary

Explanation: A flexible conductor carrying its own weight between supports assumes a catenary shape.

• A. 20-25 km
• B. 40-50 km
• C. 60-70 km
• D. 80-100 km

Explanation: An 11 kV line is generally used for relatively short transmission or primary-distribution distances, commonly up to about 20 to 25 km.

• A. Low cost
• B. High mechanical strength
• C. Longer life
• D. All of the above

Explanation: Transmission-line supports should be economical, mechanically strong enough for conductor and weather loads, and durable over a long…

• A. Radial system
• B. Tree system
• C. Ring main system
• D. All are equally reliable

Explanation: A ring-main distribution system can feed a load from either direction, so supply can often continue when one section develops a fault.

• A. alloy steel
• B. stainless steel
• C. mild steel
• D. high speed steel
• E. all of the above

Explanation: The steel core of a steel-cored conductor provides mechanical strength and is commonly made from galvanised mild steel.

• A. Impedance relay
• B. Mho's relay
• C. Reactance relay
• D. None of the above

Explanation: A mho relay is inherently directional and has a circular characteristic well suited to long, high-voltage transmission lines.

• A. Reversal of power can be controlled by firing angle
• B. Very good dynamic behavior
• C. They can link two AC system operating unsynchronized
• D. All of these

Explanation: HVDC links allow controlled power reversal, offer good dynamic control, and can connect AC networks that are not synchronized.