I AM PROVIDING TRAINING FOR OUR PLANT ELECTRICIANS, AND I WANT TO CONFIRM A COUPLE BITS OF POWER THEORY PRIOR TO GOING LIVE.

EXAMPLE: 13,800V DELTA, 480-277V WYE, 2000KVA TRANSFORMER. X1 HAS 1000 AMPS X2 HAS 1200 AMPS X3 HAS 1400 AMPS

I HAVE ASKED THEM TO CALCULATE: NEUTRAL CURRENT ALL 3 DELTA LINE CURRENTS ALL 3 DELTA PHASE CURRENTS

TO SOLVE FOR NEUTRAL CURRENT; THE SQUARE ROOT OF... 1000 SQUARED + 1200 SQUARED + 1400 SQUARED = 2098 AMPS DELTA PHASE A CURRENT = 1000A/49.819 = 20AMPS ............B CURRENT = 1200A/49.819 = 24AMPS ............C CURRENT = 1400A/49.819 = 28AMPS 49.819 IS 13800/277. DELTA A LINE CURRENT = 20 X 1.732 = 35AMP ......B LINE CURRENT = 24 X 1.732 = 42AMP ......C LINE CURRENT = 28 X 1.732 = 48AMP

I REALIZE THAT WITH THESE IMBALANCES, THERE WILL BE PHASE SHIFTS, BUT 120 DEGREE ANGLES WERE USED TO SIMPLIFY. I HAVE A 50/50 CONFIDENCE LEVEL WITH MY CALCULATIONS.

The Delta line currents are the vector sum of the phase currents at each node, so you can't simply multiply the phase currents by root three. Even if you are making the simplifying assumption of 120 degrees between each phase, I get 38.16A, 41.62A, 45.08A...I've not double checked this.

-Jon

Re: 3 phase current calculations#129349 01/26/0509:21 AM01/26/0509:21 AM