Electrical Power Transmission MCQs Part 18

Electrical Power Transmission MCQs Part 18

A string of insulators in a 33 kV overhead transmission has 3 units. Voltage across string is

A string of insulators in a 33 kV overhead transmission has 3 units. Voltage across string is:

1. 33 kV
2. 66 kV
3. 33/√3 kV
4. 27.92 kV

Correct answer:  3. 33/√3 kV

Wind pressure is directly proportional to

Wind pressure is directly proportional to:

1. Square of speed of wind
2. Speed of wind
3. Square root of speed of wind
4. None of these

Correct answer: 1. Square of speed of wind

If span length is doubled without changing other factors, the sag of line will become

If span length is doubled without changing other factors, the sag of line will become:

1. 1.5 times
2. 2 times
3. 4 times
4. 8 times

Correct answer: 3. 4 times

Explanation:

Mathematical formula for sag is: S = (wl²)/8T

Considering other factors as constant, assume S = S1: Sag ∝ l²

Now when doubled assuming new sage S = S2: Sag ∝ (2l)²

Now S2/S1 = (2l)²/ l² or S2 = 4 S1

Hence Option 3: 4 times is correct.

With an increase in length of transmission lines, the inductive reactance X_L

With an increase in length of transmission lines, the inductive reactance X_L:

1. Increases
2. Decreases
3. Remains unchanged
4. None of these

Correct answer: 1. Increases

Explanation: With an increases in length of line, the inductance L increases. Formula for inductive reactance is: X_L =2π fL

So, with increase in inductance, the inductive reactance will accordingly increase.

Bundled conductors are used in order to

Bundled conductors are used in order to

1. Reduce corona loss and line inductance
2. Increase corona loss and reduce line inductance
3. Increase line inductance as well as capacitance
4. Reduce line inductance as well as capacitance

Correct answer: 1. Reduce corona loss and line inductance

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Electrical Power Transmission MCQs