in-house three phase power quality issues

[ghostinthemachine]

I am attempting a three phase power quality analysis at the shop where I work. We produce our own 3PH power with an idler motor and run/start capacitor bank. I have already completed the analysis of our single phase system but Im stumped by the 3 phase. Since there is no transformer supplying the actual 3PH, where do I get my preliminary numbers from? (like reactance, or even voltage/amps?)
do I take the average volts and amps supplied by the idler legs? Just how does the 3 PH idler motor interact with the 1PH system? Im a mechanical engineer, so please forgive my ignorance.

 

[waross]

Hi ghostinthemachine
On your three phase system, line to line faults and ground faults on the the two phases common to the single phase supply will be basically the same as single phase faults. The current in a fault involving the derived phase will be limited by the impedance of the idler motor. I would suggest using 5 to 8 times the rated full load current of the idler motor plus the current supplied by the capacitors as a starting point to estimate available current on the third phase. This is a starting point. I expect to be corrected on the available current of a running motor.
Hope this gets you started.
yours