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Discussion Starter · #1 ·
Hi All

I have experienced two mysterious failures on two different compressors in the same location on the plant.

Here are the facts:
First Incident
A compressor contractor came to site to service our compressor. The compressor is an Ingersolrand driven by a 200kW 400V motor connected to a star/delta starter. While testing, the contractor claims that he heard a loud bang, the electrical panel door swung open and he dropped on to the floor. This contractor had test run the machine about 3 times, starting and stopping it. There were no welded contact tips on the main, star and delta contactors. There was no sign of soot on the panel door and the contractor had no burn marks.
Cause remains a mystery.

Second Incident
This one happened today 22 Feb 2014. The compressor that caused the first incident was replaced with an Atlas Copco GA160, 400v star/delta. The reason for replacing it was to minimise risk of that compressor hurting someone since the cause of the incident was not established. The replacement compressor has been running for 2 weeks now. Today it flashed across phases on the main contactor while running. Not much has been checked on it as of now. Investigation will be done on Monday.

Supply MCB is a 630A Klockner Moeller set to 315A.
Supply cable is oversized at 240sq mm
Starter is a star/delta

Any ideas as to what's happening?

Mukanya
 

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Dose it have the mec. inter-locs in place for the y-delta start and has it been calibrated?
The timeing relays/current could be off cal.
 

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What kind if compressor, roto vane, screw, or reciprocal. Also what is the purpose of the compressor, process gas, instrument gas, operating air tools? Worked join compressor skids for a loving time, that sort if thing sounds like a screw compressor with bad oil.
 

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Discussion Starter · #5 ·
It is a screw compressor.
Air is used for process (lifting and lowering work tables, pnematic transfer of powder etc)
Starter has mechanical and electrical interlocks and the unit is controlled through an 'Electronica' HMI.
 

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You mentioned transferring powder? Is there any conductive dust in this facility? Just a small amount of marginally conductive dust, lint, or particles can create a real catastrophe in electrical equipment.
 

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Discussion Starter · #7 ·
The dust is non conductive, the inside of the electrical panel is very clean.
The root causing will be done today by an RCA team, I had done preliminary checks on it.
 

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Could the lugs, where the cables terminate to the starter or breaker be too close? Often, on breakers of this size, if insulated crimp lugs are not used, there is a potential for flash over due to the close proximity of the terminations.
 

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that seems to be a direct short somewhere
I would start by taking megger value for the incomer power cables. and even the power cables inside the panel
am also assuming your panel is earthed
now we also have atlscapo type that use. vfd to run the motor that could be the next option after you have cleared the fault. the drive can give you a short cct msg whenever there is one
all the best

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do you have high humidity, maybe that could be something. what do you produce at your plant?
 
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