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Collie
13-12-2010, 09:10 PM
Hi lads, have a lovely problem for you to get stuck into! :D

CIAT air cooled water Chiller with 2 circuits. Each circuit has two stages so there are four compressors in the chiller all of equal capacity. I dont have chiller details as name plate is long gone at this stage.

Copeland Compressor
D8SK-600X-AWM

The fault is identical in each compressor.
I have 3 phase compressors which use Part-wound starting. The two motors turning the shaft split the load 60% and 40%. So in my terminal
box I have 6 terminals, the "larger" motor being supplied with 3 phases
and the "smaller" one also. The windings are in a star/star star
configuration.
They are set to run at 50hz, full load current 102 amps, 60kW, 1450rpm.
There is no Cos value given on the name plate though.

Mechanically they start and run fine but when running, the larger motor
pulls approximately 32-35 Amps which is fine, but the smaller motor
pulls 45 amps!!!. The MCB rating is 50 Amps and during the summer when
it was hot they were tripping regularly.

I've measured the voltages at 230 volts AC to earth and apporx 400
between phases. I've put a megger on the windings and thats ok too.
I've measured the resistances with my meter and found the smaller
winding equal at approximately 1.2 Ohms and the larger winding also
equal at 0.4 Ohms.

According to all my data, they should be running fine?? I've ruled out
incorrect wiring as ive belled out the cables and reconnected them as
per terminal box wiring diagram and still the same.

Originally I had found the oil in the compressors had turned acidic so
i changed it and thought this would resolve the problem by reducing
friction in the mechanics but it has not changed anything and im realy
at a loss as to where to go from here. I thought maybe the acidic oil had damaged the insulation on the windings but its passed the megger test a couple of times over. I've checked the oil regularly and its still fine now.

Not sure why the oil was acidic??......thats a whole other thread :off topic:


Any thoughts on this current issue guys??

Thanks

install monkey
13-12-2010, 09:34 PM
compressor siezing?
is crankcase heater working?
whats the oil pressure?
oil filter gauze clean?
did u fit a burn out drier? or use acid away?
oil level on sight glass ?

mad fridgie
13-12-2010, 09:59 PM
Where are you measuring the current at the comp terminals or at the switch board.
If at the switch board, i would say that it is the switchboard/control board which is wired/labelled incorrectly
Large moter on small moter switch gear and visa versa.

GHAZ
13-12-2010, 10:33 PM
Hi the copeland model d8sk 600x awm is a 66%/33% and pins 1-2-3 should have a lower ohms reading then pins 7-8-9 , the pins 7-8-9 should have about 2/3 higer readings on ohms reading ,eg 1-2-3 =0.2 ohms and pins 7-8-9 = 0.6 ohms roughly , the bigger the winding the lower the ohms reading and the smaller the winding the higer ohms reading. from your reading your post it looks like the control wiring is wrong , the first contactor should energise the pins 1-2-3 and then the second contactor should come and energise the second half of partwind 7-8-9 ,

Collie
15-12-2010, 12:18 AM
compressor siezing?
is crankcase heater working?
whats the oil pressure?
oil filter gauze clean?
did u fit a burn out drier? or use acid away?
oil level on sight glass ?


Hi,
Yes crank heater working, oil pressure is 2 bar g (net), oil filter clean. Activated cores fitted and full oil change done on system with oil filed to half way on sight glass

Collie
15-12-2010, 12:21 AM
Where are you measuring the current at the comp terminals or at the switch board.
If at the switch board, i would say that it is the switchboard/control board which is wired/labelled incorrectly
Large moter on small moter switch gear and visa versa.

Hi
I've been measuring the current at the contactors in the elec. panel. I've considered this incorrect labelling and confirmed that everything is labelled correctly by belling out each cable and reconnecting as per wiring diagram.

Collie
15-12-2010, 12:27 AM
Hi the copeland model d8sk 600x awm is a 66%/33% and pins 1-2-3 should have a lower ohms reading then pins 7-8-9 , the pins 7-8-9 should have about 2/3 higer readings on ohms reading ,eg 1-2-3 =0.2 ohms and pins 7-8-9 = 0.6 ohms roughly , the bigger the winding the lower the ohms reading and the smaller the winding the higer ohms reading. from your reading your post it looks like the control wiring is wrong , the first contactor should energise the pins 1-2-3 and then the second contactor should come and energise the second half of partwind 7-8-9 ,

Hi
Yes thats correct the larger winding on pins 1,2,3 has the lower ohm reading of 0.4 and the smaller winding on 7,8,9 has about 1.2 ohm. The larger one starts and within a second the smaller one kicks in too. The figures you've quoted for resistance of 0.2 and 0.6, are they by any chance from the manufacturer or just for example? Because my values are slighty higher which might indicate a potential fault occurring with the winding. Bare in mind this is happenig to all 4 comps in the same chiller, so whatever the fault is, its common to them all :rolleyes:

mad fridgie
15-12-2010, 12:35 AM
I am 99.99999% sure copeland wiring diagram would be correct. But i am not convinced that your control board wiring diagram/label is correct. To be 100% sure, check your resistance of the windings at the board not the compressor end.
because it is happening on all comps it has to be a common problem.
My first though would have been that the rotation of the smaller windings was incorrect, but i would of thought that the larger winding would also have a very high current draw (to compensate) but this not the case.

Collie
15-12-2010, 05:03 PM
I am 99.99999% sure copeland wiring diagram would be correct. But i am not convinced that your control board wiring diagram/label is correct. To be 100% sure, check your resistance of the windings at the board not the compressor end.
because it is happening on all comps it has to be a common problem.
My first though would have been that the rotation of the smaller windings was incorrect, but i would of thought that the larger winding would also have a very high current draw (to compensate) but this not the case.

Hi
I will check the resistance at the outlet of the contactors and compare thanks.

I thought about the rotation idea too and was wondering would it be possible for one of the windings, lets say the smaller one, to have incorrect rotation and continue to run? unfortunately i dont have a phase rotation monitor :confused:

monkey spanners
15-12-2010, 05:38 PM
I'm sure it would burn out the motor in a few seconds if it was trying to run the both ways at once.

I believe those inverter checkers can be used for phase rotation as well, also these fluke testers do phase rotation despite only having two wires,

http://www.products4testing.co.uk/catalog/product/view/id/733/category/218/

I have got one but never used it for testing phase rotation as most of the stuff i do is smaller and i just see if it going the right way!

Jon :)