Six lead part-winding star compressor ( semi-hermetic)Copland
Hello everyone. I am a new member, and would like to wish you all GOOD DAY. I have a question and will appreciate if a solution is suggested. A six lead part-winding star compressor was rewound (380-415/3phase/50Hz).The leads were given sleeve color 2 X red, 2 X blue and 2 X yellow. The winding continuity and resistances between each star point showed okay and equal (1.4,126.96.36.199 ohms).
However when the compressor was started as a 2Y DOL, the main circuit breaker tripped.
When this compressor was started on the test bench on only one star (or the other), without load, the compressor started and ran (no scrapping or screeching sound).
My question is how to find out which leads of the second star winding are to be connected for proper operation. I have tried to interchange two leads of the second star but without success. The open star winding when tested with a DVM showed 362,372,365 volts. Is the problem in the connection or the rewinding is incorrectly done. please reply
What is the model number of the compressor?
Originally Posted by amarakbar
Is this similar to what you have?
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Thanks for the reply. Yes the connection is a part winding as your diagram.The model is Copeland 4RH1-2500. The customer now wants to run this as a 2Y DOL. As I have stated; how to determine if the second star connection is in phase with the first winding, or else is the winding connection wrong.
When you ran each winding separately, was the rotation the same? As long as the motors are wound correctly, T1 and T7 will get A phase, T2 and T8 will get B phase, and T3 and T9 will get C phase. Are you positive that it was wound for 380 and not some lower voltage? If it were delta wound for a lower voltage, it'd definitely trip the breaker with 380 across the line. You could have some wires crossed up at the contactors/starters, too.
I'm not the sharpest when it comes to Copeland's nomenclature, but that sounds like it is a 25 hp semi-hermetic reciprocating compressor? Rotation might be kind of hard to observe, unless you pulled the oil pump and bumped the motor for a split second. Just FYI, I don't recommend doing this...
The motor should run just fine in either part winding or across the line, but is your breaker big enough to handle the inrush current of across the line start? Is the compressor starting with a lot of head pressure, or are the pressures equalized on both sides prior to starting?
You've also got a 1.6% voltage imbalance there. I've seen problems caused by less than that.
Last edited by Tech Rob; 03-11-2012 at 08:51 PM.
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I pulled this from Emerson's website using your model number. It seems to contradict some of what you posted.
They also list winding resistance as 0.58 ohms.
Last edited by hvacrmedic; 03-11-2012 at 11:33 PM.