screw compressor failure

[aygul]

Hello everybody,
I have a big problem about our chiller units (water cooled evaporator, water cooled conderser and R22; screw compressors).
We have a chiller unit with water cooled condensers and the unit have 3 independent circuits with semi-hermetic screw compresors. At that moment two compressors were burnt and only one compressor is runing. One of them these burnt compressors was failure at start up , and it worked only 5 minutes. The other one was failure in five days after start up.
In attached file you can find the measurements for running compressor. Could you please give me answers of questions?

1- According to attached file, I think superheat is very low... Is there a flood back problem in the system?

2- If txv is adjusted again, can this problem be solved?

3- How can i understand oil migration? (These compressors have oil sperators)

4- Is there any other reasons for burnt compresors?

Thanks for your comments and helps.....

Regards

[chemi-cool]

There are two major reasons for burnout.

electrical problems, check the power circuit.

Something inside the compressor brakes and caused a short.

If the system was OK before, I don't see how sudden changes can happened.
Also could be some problems with the controls.
What make is it?
How old?
What HP?
Chemi

[aygul]

This unit is new, three months ago it was start up... In start up first compressor was burnt out and second compressor was also burnt one week later from start up.

HP value (from attached file "2.point") is 261psi measured from high pressure side gauge.


Regards

[shogun7]

Aygul
Here are somes things to consider when asking the question “what can cause a burnout”?
Overheating problems occur when oil in a compressor is heated to the point where it loses its ability to lubricate. ( is the oil cooler keeping the oil below 225*F and is it leaking water into the oil?) If the heat is high enough, the oil breaks down chemically and if there is any moisture with hi discharge temperatures , this creates acid. Major reasons for overheating due to discharge temperatures are:
· Low suction pressures
· High condensing pressures
· High compression ratios
Low suction pressure is normally the result of incorrect pressure switch settings, pressure drop in suction line, light load operating conditions or restricted evaporator coils.

High condensing pressures can be caused by inadequate waterflow through the condenser, and overcharge of refrigerant or noncondensables in the system.

High-pressure ratios are a combination of low suction pressures and high condensing pressures. If the compressor is operated within the manufacturer guidelines, this condition will not cause a problem. Then there is also the possibility that the 3 phase power is single phasing . Do you have single protection on these compressors? If and when you solve the cause you also need to know the proper procedure for cleaning up these burnouts so you don’t have any more failures.

[aygul]

1-
These compressors have part winding start.
Winding measurements:

1. compressor:
L1-L2: 22,5 ohm
L1-L3: 0,9 ohm
L1-L4: 22,3ohm
L1-L5: 0,6ohm
L1-L6: 22,2 ohm
burnt compressor

2.compressor:
L1-L2: 3 ohm L2-L3: 0,8ohm L3-L4: 1,2ohm
L1-L3: 2,4 ohm L2-L4: 0,6ohm L3-L5: 16,2ohm
L1-L4: 3,3 ohm L2-L5: 16,3ohm L3-L6: 0,3ohm
L1-L5: 18,2 ohm L2-L6: 0,9ohm
L1-L6: 2,4 ohm
burnt compressor

2-
What do you thing about superheat and subcooling values for running compressor:
superheat: 3C
subcooling:10C

I have to increase superheat, haven't i?

3-
In addition to that, i want to ask another question...
What do you thing about oil analysis test?... Can test results help us?

Thanks & Regards

[chemi-cool]

Hi Aygul.
How do you check superheat and subcooling if compressors are burnout?

What make is the unit?
Why don't you get the dealer to check the unit? If its new, you are under warranty.

Chemi