Free Power Systems MCQs with Answers

• A. permeability variation
• B. corona
• C. skin effect
• D. unsymmetrical fault
• E. none of the above

Explanation: Skin effect causes alternating current to concentrate near the outer surface of a conductor, leaving less current in its core.

• A. large
• B. small
• C. fluctuating
• D. any of the above

Explanation: Series capacitors are mainly valuable for reducing transmission-line reactance and improving power transfer on heavily loaded lines.

• A. fall
• B. rise
• C. remain unchanged
• D. none of the above

Explanation: When one alternator is disconnected from a common bus, the remaining generators maintain the bus voltage through their excitation systems…

• A. the transfer of power will take place with voltage fluctuation and noise
• B. the transfer of power will take place with least loss
• C. the stations will fall out of step be¬cause of large angular displacement between the stations
• D. none of the above

Explanation: For a given transferred power, a large interconnector reactance requires a larger power-angle difference.

• A. Short transmission lines
• B. Medium transmission lines
• C. Long transmission lines
• D. Medium as well as long transmission lines

Explanation: Short transmission lines are usually treated as having negligible shunt capacitance because their length is small and the charging current…

• A. 150 to 220 kV
• B. 100 to 120 kV
• C. 60 to 100 kV
• D. 20 to 50 kV

Explanation: A 500 km transmission line is a long-distance line and commonly operates at an extra-high voltage around 220 kV, fitting the 150 to 220 kV…

• A. presence of ozone detected by odour
• B. hissing sound
• C. faint luminous glow of bluish colour
• D. all of the above

Explanation: Corona ionizes the surrounding air, producing ozone with a characteristic smell, a hissing noise, and a faint bluish glow.

• A. Frequency of the current
• B. Size of the conductor
• C. Resistivity of the conductor material
• D. All of the above

Explanation: Skin effect increases with frequency and conductor size, and it also varies with the material resistivity.

• A. large conductor area is required for same power transmission
• B. short-circuit current of the system is increased
• C. either of the above
• D. none of the above

Explanation: In constant-voltage transmission, a fault can produce a large current because the system voltage remains nearly fixed while the line…

• A. primary winding
• B. secondary winding
• C. high voltage winding
• D. any of the above

Explanation: Tappings are generally placed on the high-voltage winding because it carries lower current, making the tap contacts smaller and safer to…

• A. Static condenser
• B. Synchronous condenser
• C. Tap changing transformer
• D. Booster transformer

Explanation: A booster transformer is a comparatively simple and economical way to add or subtract a voltage component in a distribution feeder.

• A. specific volume
• B. electrical conductivity
• C. co-efficient of linear expansion
• D. resistance per unit length for same cross-section

Explanation: Aluminium has lower electrical conductivity than copper, so conductivity is the exception.

• A. 132 kV
• B. 66 kV
• C. 33 kV
• D. 11 kV

Explanation: For a transmission distance of about 200 km, 132 kV is a typical suitable voltage level.

• A. 1.5
• B. 2.7
• C. 4.2
• D. 7.8

Explanation: Aluminium has a specific gravity of approximately 2.7, much lower than copper at about 8.9.

• A. 1 kV
• B. 11 kV
• C. 22 kV
• D. 33 kV

Explanation: Pin insulators are commonly used up to about 33 kV; for higher transmission voltages, suspension insulators are preferred because they…

• A. non-sinusoidal
• B. sinusoidal
• C. triangular
• D. square

Explanation: Corona produces sharp current pulses as the surrounding air repeatedly ionises, so the resulting line current is non-sinusoidal rather…

• A. dead ended
• B. at intermediate anchor towers
• C. any of the above
• D. none of the above

Explanation: Strain insulators are used where conductor tension is highest, such as dead ends and intermediate anchor or angle towers.

• A. inductors
• B. capacitors
• C. synchronous motors
• D. all of above
• E. none of the above

Explanation: Voltage drop caused by reactive power can be reduced by an overexcited synchronous motor, which supplies leading reactive power and…

• A. 6.6 kV (r.m.s. value)/cm
• B. 11 kV (r.m.s. value)/cm
• C. 22 kV (maximum value)/cm
• D. 30 kV (maximum value)/cm

Explanation: Corona begins when the electric stress at the conductor surface reaches roughly 30 kV/cm maximum value in air.

• A. exciters
• B. series capacitors
• C. shunt reactors
• D. voltatre transformers

Explanation: Exciters belong primarily to generating stations, where they supply field current to alternators.