Compressor issues

[FirtstKnight]

I haven't posted yet but the old compressor went down yesterday 7/21/21 around noon. it tripped the motor overload in the cabinet. blew a fuse on phase c and tripped the breaker in the I-Line. The plan is to come in on Saturday and inspect the breaker at the I-Line among other things

 

[marconi]

May I ask you to do all the basic tests on a three phase induction motor and report the measurements? I will post tomorrow what tests I mean, but things like insulation resistance, inter-winding resistance, winding resistance, winding currents and voltages? I don't want to teach you to 'suck eggs' so forgive me if this is very familiar to you.

In the EF we love pictures of the installation. Could you supply some please?

Teaching grandmother to suck eggs - Wikipedia - https://en.wikipedia.org/wiki/Teaching_grandmother_to_suck_eggs

 

[marconi]

Here is a guide to standard three phase induction motor tests.

How To Test Three - Phase AC Motors - https://www.electricalengineeringtoolbox.com/2015/12/how-to-test-three-phase-ac-motors.html

Also, I would stick a glass thermometer to the outside of the motor and measure its temperature after it has been running for at least an hour.

 

[Megawatt]

I am a maintenance man but I do hold a journeyman's license I'll do my best to explain what is going on. I have 2 ea 50 Hp air compressor. one is approx. 2 yrs old (Com-05) the other is 20+ (Com-01). I seem to be having similar problems with both.
We are running 240 VAC 3 phase into the building to a 400 amp I-line from there a 150 amp breaker carries power to a 200 amp disconnect. with 150 amp fuses. from there it goes to a switch box that allows me to select which compressor I want to use. Com-01 the older one will run for 5-6 hrs. then it will trip the motor overload in the cabinet. by the time I get there (5 Min) I am able to reset the overload and it will run for a couple of more hrs. then it will do it again. During the cooler months we were able to run it for weeks then it started this as the temps started to rise. oil temps on the gauges seem well with in range. I have tested and replaced the temp switches they seem fine. I have replaced the motor starter with the overload and the thermal units. More recently we sent the motor out to a motor shop for evaluation . They did $1300 dollars of work to it. We reinstalled it on 6/30/21
and had the same result.. Com-05 runs most of the time but back in April while I was on vacation it tripped the breaker and blew one fuse, then the week after I got back it blew one fuse (not the same fuse) it has ran fine until 6/30/21 then it tripped the breaker and blew one of the fuses. I have done an amp draw on both compressors . Readings are A Phase= 100 amps B Phase = 87 Amps and C Phase= 88 Amps. All connections seem fine. I am at a loss

Is your breaker been calculated wrong. In article 430 of the NEC code book it covers a wide range of protection for motors. If you are using inverse breakers you can multiply the the full load amperage of the motor by 225% to size your breaker and if you are using fuses you can multiply it by 175% of your full load amperage on your motor. What HP size is the motor and what size is your overload protection. The code book will allow you to go up on size on the overloads one size up. If your overload is what’s tripping then what is the running amperage of your motor and what size wire is installed.