Free Power Systems MCQs with Answers

• A. primary transmission
• B. secondary transmission
• C. primary distribution
• D. secondary distribution

Explanation: A three-phase four-wire arrangement provides three phase conductors plus a neutral, allowing both three-phase loads and single-phase…

• A. dry weather
• B. winter
• C. summer heat
• D. humid weather
• E. none of the above

Explanation: Moist air contains ions and lowers the dielectric strength of the surrounding air, making ionisation and corona more likely.

• A. Quartz
• B. Kaolin
• C. Felspar
• D. Silica

Explanation: Porcelain insulators are commonly made from kaolin, feldspar and quartz.

• A. Steel cored aluminium
• B. Galvanised steel
• C. Cadmium copper
• D. Any of the above

Explanation: Steel-cored aluminium, galvanised steel and cadmium copper have all been used as overhead-line conductors for different strength and…

• A. corona losses are minimum
• B. reactance is high
• C. sending end voltage is more
• D. receiving end voltage is more

Explanation: For a given system and sending conditions, reducing corona loss leaves more of the generated power available for transmission.

• A. distributors
• B. generating stations
• C. service mains
• D. all of the above

Explanation: A feeder carries bulk power from a substation or generating source to distribution points, called distributors.

• A. reduces power factor
• B. corrodes the material
• C. gives odour
• D. transfer energy to the ground
• E. none of the above

Explanation: Corona produces ozone, and ozone is a strong oxidising agent that attacks and corrodes metal and insulation materials.

• A. 400 V
• B. 11 kV
• C. 66 kV
• D. 400 kV

Explanation: Large industrial consumers are commonly supplied at 11 kV to reduce current and distribution losses while avoiding the very high voltage…

• A. 2 m
• B. 3.5 m
• C. 6 m
• D. 8.5 m

Explanation: A 220 kV overhead line requires wider phase spacing to withstand its higher electric stress and limit flashover risk.

• A. 4.3 m
• B. 5.5 m
• C. 7.0 m
• D. 10.5 m

Explanation: Higher-voltage lines need greater ground clearance for safety and to prevent flashover during normal operation or voltage surges.

• A. lead
• B. rubber
• C. copper
• D. iron

Explanation: Lead is commonly used as an underground-cable sheath because it is impervious to moisture and provides good chemical and corrosion…

• A. aluminium
• B. steel
• C. brass
• D. copper

Explanation: Steel is generally used for cable armour because its high mechanical strength protects the cable against impact, crushing and tension.

• A. copper
• B. wood
• C. R.C.C.
• D. steel

Explanation: Transmission-line cross-arms are generally made of steel because it provides the required mechanical strength and durability for…

• A. copper conductors
• B. all aluminium conductors
• C. A.C.S.R. conductors
• D. none of these

Explanation: ACSR combines aluminium strands, which give low weight and good conductivity, with a steel core that provides mechanical strength.

• A. unity
• B. lagging
• C. leading
• D. zero

Explanation: Industrial loads contain many induction motors and transformers, both of which draw magnetising current and therefore operate at a lagging…

• A. balanced
• B. unbalanced
• C. either of the above
• D. none of the above

Explanation: Distributor loads are usually spread unevenly among single-phase and three-phase consumers, so their phase currents are generally…

• A. suspension insulators
• B. pin insulators
• C. both A. and B.
• D. none of the above

Explanation: Suspension insulators are used on high-voltage transmission lines because strings of units can support greater voltage and mechanical…

• A. single phase
• B. three-phase three wire
• C. three-phase four wire
• D. none of the above

Explanation: Residential distributors generally use a three-phase, four-wire system, with the neutral providing single-phase supply to homes and…

• A. underground
• B. overhead
• C. either of the above
• D. none of the above

Explanation: Most high-voltage transmission lines in Pakistan are overhead because overhead construction is much cheaper and easier to inspect and…

• A. Radial system
• B. Ring system
• C. Inter-connected system
• D. None of the above

Explanation: A radial distribution system has a single path from the source to each load, making its layout simple and its initial cost lowest.