Short Ckt Current Calculation Direct

Mike waved his hand. “It’s a small factory. The grid is strong. What’s the worst that could happen?”

“If you open that valve fully, the water rushing out has force . That force is your short-circuit current. But here’s the trick: the narrower the pipe, the lower the force. The wider the pipe, the more destructive the rush.” short ckt current calculation

“Just connect it to the main 11 kV bus,” said the project manager. “The breaker we have in stock is rated for 25 kA. That should be plenty.” Mike waved his hand

[ I_{SC} = \frac{I_{Full\ Load}}{Z_{pu}} ] What’s the worst that could happen

“Your full load current on the low side (400V) is about 3,600 amps. With 5% impedance (0.05 pu), your short-circuit current is 3,600 / 0.05 = (72 kA).” Mike’s face went pale. “But our breaker is only rated for 25 kA.”

Zara pulled out her laptop and ran a proper short-circuit study per IEC 60909.

“We are toast,” she said. “The breaker will explode before it even trips.”