Compressor issues

[FirtstKnight]

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

So for anyone who has been following on Tuesday (7/6/21) I got a call at home and was told that there was a power outage at work for 2.5- 3 hrs but the air compressor would not come on and had no display. I advised the lead man to check the breaker in the I-Line that controls the power to our compressor shed. When he returned to the phone he said that was it and air pressure was coming up. Wednesday I was out, so on Thursday I was told that they had replaced a transformer about 2 blocks from here. We have been told that we are the last business in this grid. so anything that happens upstream is going to affect us. Today 6/9/21 I went do some more testing under the direction of one of our fellow members. This is the results that I have now. Voltage coming into the disconnect in the compressor shed A-B Phase 234 VAC, B-C Phase 236 VAC, C-A Phase 237 VAC A - Grnd = 205 VAC , B - Grnd = 118 VAC, C- Grnd = 116 VAC Amp draw A - Phase = 110A,
B Phase = 112A, C Phase = 114 A Sorry for the long post but I want to make sure you have as many details as I can give you .

 

[marconi]

Line voltages and currents now look balanced. Phase voltages out of balance which makes me wonder if you have a weak or broken neutral if provided to your site and used. Is your incoming neutral connected to ground and if yes where? Measured line currents very close to what I calculated - 114A. Grateful if you would keep us updated.

ps: Is motor connected as 3 phase 3 wire or 3 phase 4 wire?

 

[marconi]

Just remembered your supply is 3 phase 4 wire open delta so phase to ground/neutral voltages are fine.

 

[FirtstKnight]

So it looks like my last communications was on 7/9/21. This morning (7/19/21) we switched back to the old compressor, to see what happens, I checked the Voltage and is as follows A-B = 233 B-C =235 A-C =232
Amp Draw: A=100A B= 101A C= 95A, A-Phase to GRND = 204 B- Phase to GRND = 115 C-Phase - GRND = 116

 

[marconi]

It’s much appreciated when an OP keeps the EF up-to-date - thank you.

 

[marconi]

Just curious - where are you in Texas? I'd like to look up in my atlas. What is the compressor used for?

 

[FirtstKnight]

Just curious - where are you in Texas? I'd like to look up in my atlas. What is the compressor used for?

City of Temple almost Right in the middle between Dallas and Houston

 

[FirtstKnight]

City of Temple almost Right in the middle between Dallas and Houston

I took some more reading this morning. everything still looks good to me, we are on or third day with the 20+ year old compressor

 

[marconi]

Thank you. Sorry for delay in replying. I looked up City of Temple. What sort of industry or business supports this city? I could not find out.

 

[FirtstKnight]

Thank you. Sorry for delay in replying. I looked up City of Temple. What sort of industry or business supports this city? I could not find out.We Build hydraic cylinders among other this . out competor is acroos town. there are are a couple of foundries with machinshops in the area. there are seveal diffrent tyes of bussineses in this area