WorksheetsPower system-31-01-25
Total questions: 10
Worksheet time: 5mins
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%
