Shade Tree Power Factor Meter

Just use a phase failure relay in the control circuit or better still install a decent motor protection relay. GE Multilin, Sprecher and Schuh, Ampcontrol, Schnieder electric etc all provide top drawer units.

Please confirm if you have checked following:-

1.Incoming voltage in each phase.

2.Current drawn in each phase.

I also feel that it might be due to incoming supply, though I am mechanical engineer but I have used such motors while mfg. Cranes.

Also, if you can check the 'summed' current by getting the current clamp around the 3 phases all together, the sum should be zero amps (ideal). An imbalance of a few amps would be normal on such a size, 10s of amps imbalance implies a significant imbalance leading to lumpy operation akin eventually to 'single phasing' leading to torque loss , extra heating effects etc

Good answer.... hadn't thought of that.... makes sense! Only problem is, getting a large enough CT (current transformer) to go around 3 - 750 MCM conductors. I'm sure Grainger has one for a couple hundred.

Anyway... the problem has gone away since the power company re-terminated some wiring up-line from me. Just looking for an efficient means of determining the "quality" of 3 phase balance on the in-coming voltage for future reference. The "zero sum" check sounds like the answer I was looking for...

Thanx!!!

I had briefly thought of the zero sum method and just as quickly dismissed it. That is the method used to detect if part of the current is returning by another path but will not of its own help with phase failure. Reduced current flowing one phase is reflected by a reduction in the other two but still a zero sum equation if the cause is external. Your condition is common enough especially when the phase failure is on the upstream side of a transformer, which is why there is such a large matket for electronic motor protection relays. Had you been set up with a CRO and some CTs and compared phase angle, then the problem would have been quite visual.

If you have checked the voltage of the incoming power under load and found it to be adequate, you can try this maneuver to try to balance the amperage draw. Check the amps as now installed. Then, rotate the leads in order (L1 to L2, L2 to L3, L3 to L1) and check the amps again. Then do the same procedure and check again. Then, of course, do it one more time and check the draw. You can use the configuration that yields the best balance. That is, the one that has the least discrepency between the three legs. This doesn't always result is any big change, but it can help at times. The fact that the motor wouldn't produce the proper torque would lead me to believe that the faulty wire that the power company fixed may have been the culprit since 1) - it stopped after they fixed it and 2) - it is possible that this faulty connection was allowing power to "leak" when a load was placed on the system that may not have been evident with no load.

Rent or buy a power quality meter, TES 3600 will give all the info you could ever need.

P.S. new there only 1200. us. can be found at www.mtpinc.com

For your tong meter make your own current transformer around the three wires by geeting a decent size of insulated wire a #6 make a couple of loops surrounding the three cables tape up the bare ends (for safety) then hook your tong meter threw the loop . The value you read wont be the true value but it will give you a good idea if a problem is there without having to have a overly large tong meter . gooday

Excellent answer...that's why I post here...I knew that!!! just couldn't back away far enough to see it clearly. That's the way it goes for McGuiver... they expect him to do anything, with nothing, forever...

Thanx to all for jogging my memory...