Power system-31-01-25

A feeder in an electrical distribution system is designed to:

• Transmit power from a substation to the distribution transformers

• Step up the voltage

• Deliver power to individual consumers

• Control the voltage regulation

The main advantage of using a ring main distribution system is:

• Increased reliability

• Lower cost

• Simplified design

• Higher power loss

For a 100 km long transmission line, D.C. transmission is preferred over A.C. transmission because:

• It has no reactive power losses

• It is more economical for short distances

• It requires no insulation

• It has better voltage regulation

In an A.C. power transmission system, the skin effect:

• Causes the current to flow on the surface of the conductor

• Increases the power factor

• Reduces power losses

• Occurs only in underground cables

The most economical voltage for transmitting power over 1000 km is:

• ±500 kV DC

• 765 kV AC

• 33 kV AC

• 132 kV AC

For a leading power factor load, the voltage regulation of a transmission line is:

• Always positive.

• Zero.

• Negative.

• Cannot be determined.

A copper conductor has a resistance of 0.15 Ω/km. Calculate the total resistance of a 20 km long conductor.

• 3 Ω

• 2 Ω

• 4 Ω

• 1.5 Ω

A single-phase overhead line has conductors 2 m apart. The radius of each conductor is 0.01 m. Calculate the inductance per kilometer.

• 1.38 mH/ km

• 1.23 mH//km

• 1.44 mH/km

• 1.56 mH/km

A 3-phase transmission line delivers 100 kW at 0.8 power factor lagging to a load. The line resistance is 5 Ω and reactance is 10 Ω. The sending-end voltage is 11 kV11. Calculate the voltage regulation.

• 8.2%

• 10.4%

• 12.5%

• 6.8%

A transmission line delivers 200 kW200 to a load at 0.9 power factor lagging. If the total line losses are 10 kW, what is the efficiency of the line?

• 80%

• 90%

• 95%

• 85%