A 3-phase, 3-line, 100 Km long transmission line is loaded at 110 kV. If the loss per phase is 5 MW and the load is 150 MVA, the resistance of the line is.

A 3-phase, 3-line, 100 Km long transmission line is loaded at 110 kV. If the loss per phase is 5 MW and the load is 150 MVA, the resistance of the line is.

Right Answer is:

8.06 ohms per phase

SOLUTION

3 phase power loss can be calculated as

PL = 3 VIcosϕ

PL = √3 VIcosϕ  

Where,

V= Phase voltage

I= Phase current

V= Line voltage

I= Line current

Power loss per phase-

PL = I2 x R

Calculation:

All the calculations are done in per phase only-

Now load current (I) can be calculated as

I = (150 x 106)/(√ 3(110 x 103)) per phase

I = (15 / 11√ 3) x 103

Now, using power loss Formula-

PL = I2 x R

5 x 106 =   (225/121× 3) x106 x R

So, R = 8.06 ohm/phase

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