Power System MCQs Part 7

Power System MCQs Part 7

Reactance relay is generally preferred for protection against

Reactance relay is generally preferred for protection against

1. Earth faults only
2. Phase faults only
3. None of these

Correct answer: 1. Earth faults only

The most economic load on an underground cable is

The most economic load on an underground cable is

1. Greater than its surge loading
2. Equal to the surge loading
3. Less than the surge loading
4. None of the above is necessary

Correct answer: 3. Less than the surge loading

The X:R ratio for 220 KV line as compared to 400 KV line is

The X:R ratio for 220 KV line as compared to 400 KV line is

1. Greater
2. Equal
3. Smaller
4. Any of above

Correct answer: 3. Smaller

Explanation: For 400 kV transmission line, the distance between the wires is made much larger than 220 kV line which results in much higher magnetic energy storage and consequently its inductance per unit length will be higher. On the other hand the resistance depends on the cross section and material type. So for given scenario the X:R ration for 220 kV line will be smaller than 400 kV line.

Efficiency of transmission in EHV lines can be increased by decreasing the corona loss which is achieved by

Efficiency of transmission in EHV lines can be increased by decreasing the corona loss which is achieved by

1. Using bundled conductors
2. Using thick conductors
3. Using thin conductors
4. None of above

Correct answer: 1. Using bundled conductors

A synchronous phase modifier as compared to a synchronous motor used for mechanical loads has

A synchronous phase modifier as compared to a synchronous motor used for mechanical loads has:

1. Larger shaft and smaller speed
2. Smaller shaft and smaller speed
3. Larger shaft and higher speed
4. Smaller shaft and higher speed

Correct answer: 4. Smaller shaft and higher speed