Need help on how to troubleshoot an air compressor that is stopping because the breaker is tripping.

The motor is connected to 460A, and the legs are pulling 206A, 210A, 206A (from motor plate it should only pull 170A).

I checked the starter and it looks ok, all contacts are good and connections are tight. But I don't know what elements I should check in the all air compressor system beside the motor.

Thanks.

 

Your motor seems to be running OK. It seems that your compressor is drawing too much power from the motor. Check your discharge pressure, and see whether it is within the compressor design. Check also the following:

1. Non-return valve after compressor whether it is jammed half shut (this increases back pressure on compressor, but most probably you cannot see it as pressure gauge is fitted after it).
2. Charge air cooler between compressor stages whether it is cooling properly, cooling medium flow is ok. At the same time check whether your interstage pressure is within compressor design
3. If you have unloading valves, check their operation. Does the motor current go to its normal offload rating when the compressor unloads or does it remain relatively high (one or more unloading valves jammed or not traveling properly).
4. Compressor discharge piping to reservoir, whether there is a blockage or restriction there (valve half shut, blocked pipes, etc.). This increases back pressure on compressor.

One other thing, is the compressor new, or has it been running for some time, and now this is happening? Hasn't the compressor been changed from one system to another and the latter is operating at a higher pressure?

Sorry one final thing, is the compressor duty cycle (i.e. onload - offload) the same as has been specified when ordering, or is the compressor running continuously on full load and has been specified for this duty? Sometimes to save on costs, when it is anticipated that the compressor will run on duty cycles which allow the motor to cool down when offload, the motor is specified smaller than that required to run continuously on full load.

 

Have you checked input voltage? A defect in a step up/down transformer or a load elsewhere in your facility could be causing a low voltage condition which would cause an increase in the amps drawn by equipment set up for a higher voltage than what is available.

 

Also, unless it is a straight across the line arrangement, (and sometimes even if it's an across the line arrangement) you have to be careful about how you measure current. Some instruments have a really hard time with the non sinusoidal waveforms at both the input and the output of AC drive or even softstarts that don't bypass after the start.

An electrician I worked with had an amp clamp type meter that read wrong on 90% of the motors we tried it on. Way wrong. Fluke has even produced a "special" multimeter to deal with this. When there is a question, I connect a power quality analyzer which shows the waveform and check for plausibility. So be careful.

And you might ask how the manufacturer measures the current. It might be that they are getting bogus readings. But the breaker tripping is a strong clue that something has changed. Check for a change in lube. Or operating pressures. Or for hot bearings. Or for a screw compressor, the scavenge line might be coked up. If the power is OK, you likely have a load problem of some sort. The thing I have to tell people the most is that current = torque and if nothing drastic is going on, it's probably the load and not an electrical problem. Sometimes it takes a nasty motor R&R before they believe.

Regards
cww

 

The motor is not OK! Tt's overloaded by about 22%. Scott's comment to check the input voltage is the proper next step!

Phil Corso