a new problem

Situation: 2 packs with each 4 Bitzer compressors 6J-33.2Y, part winding. No part loading.
Packs are outside the building, the main switch-cupboard (SWC) is inside (one stage lower)
It was on a start-up this summer, a lot of work, and we had to start-up rather late in the evening (7:00 PM). The morning after was the final delivery with the client so the packs had to run anyway.
The technicians had vacuumed when I arrived.
Checked quickly HP/LP settings, checked the function of the oil pressure safety devices, the setted AMPS on the safety trippers, … everything was OK.
We filled gas in the receiver and started up.
While running and further gas filling, I checked the settings of the EWCM Eliwell Pack controller.
I could not sea, nor hear the compressors while I was at the SWC.
Checked running currents, all where +/- 40 AMPS (I max +/- 60A), so OK.
We became to a situation where the compressor on the packs ran not all at once (partial load)
Suddenly, I heard a noise in SWC: the thermal safety device of compressor 1 had tripped. Checked the set AMPS again, OK, 40 amp.
Reset and set the clampAMP meter: geeeezzzz..+/- 120 AMP. I was sure I had +/-40 AMP before.
Switched off everything and went upstairs to feel if the compressor was hot: no. Asked a technician who was busy with the packs if he had heard something strange: no, he didn’t. Discussed some 20 minutes and restarted the faulty pack. Measured with al small heart the running current: 40 AMPS: OK. I checked and monitored it for at least 15 minutes and still 40 amps. I went upstairs and downstairs several times - compressors were cycling in partial load - (left my ampmeter on compressor 1 on PEAKHOLD) went back to the SWC and you won’t believe it …the thermal safety had tripped again but ....now from compressor 2. Compressor 1 was still running, 40 AMP.
It was then already 10:30PM, warm, it began to rain and the roof above the compressor was not yet installed, I was tired and I became despondent.
OK, calm down I thought. We checked with 3 technicians and everything seemed OK.
What followed now clarifies better what the cause might be and will lit up a light I think.
Starting up compressor 1. One of the technicians who was now at the pack with his mobile says ‘”OK 1 and 2 are running” I said: ”No, no... only comp 1 is running” 'No,... 1 and 2 are running." I looked at the relays of compr 2: not energized. Went upstairs, and indeed… 1 and 2 where running. Noise of compressor was normal, so the LP and HP.
Went back to the SWC again downstairs, measured the voltage on the departure of the relay (not energized at that moment!) of compressor 2 and measured 400 V on both relays. (!?) Magic a la Copperfield?
Then, suddenly my Euro felt (a Belgium expression) at almost midnight and we solved the problem in 15 minutes.
What was wrong you think?

Hi Peter.

Maybe both comprresors were connected to one contactor?

Chemi

No, the problem was something else. I sended you the solution by email.

Wires from Switch cupboard going to wrong pack & crossing ???

maybe the 'partwind' crossed between the two compressors?

cheers

richard

Both correct, this was apparanet an easy one.

From compressor 1 and 2, the numbering of the power supply to the part windings on the cables was confusing and 1 cable from each compressor was cross wired. So the second relay from each compressor led to the other compressor. So, as long as both were running in a normal condition (= 4 relays energized), everything was OK. But suppose the condition that compressor 1is running: part winding 1A energized and also part-winding 2A. But somehow, the rotating field must have generated a voltage so that we measured on the departure of both relays 3x400V of compressor 2 and they were not energized.. The phenomena happened only when the pack controller shuts down 1 or 2. At that moment, I almost sank through the ground. We changed the wires correct, tried all combinations and left the rack till the other morning. The final delivery gave no problems and the rack is still working.

chemi-cool,
I made a schematic and my son will scan it and mail it to you.
But scanner seems not properly working for the moment. I think it's crosswired with another USB device. LOL

hehe what a gremlin, have to love the problem.

i see it all the time, but with warranty calls for multihead h/wall splits... usually they either pipe up unit A to B or, wire unti A to B... of course since both units are started at the same time and run fine they must just walk away...

usually when the owners ring and say i tryed to start the split in my lounge room! but the unit in the kitchen started etc..