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Discussion Starter #1
i have an air compressor with a 300hp main motor and a 10hp fan motor, both running on 460v with 120v control voltage. it's a new machine that's been in service since june.

back in early september the fan's ol relay started failing. it would trip out, i would reset it and the unit would run for awhile, then trip again. over the course of a week it got so bad it would trip as soon as i started the machine. i checked the fan motor amp draw was between 12.5 -13.5 amps, the motor's nameplate says 13.3 fl amps. i replaced the ol relay and the problem went away.

this week the problem came back. sunday the compressor went down for motor overload. i reset the fan ol relay and the unit ran again. the motor amp draw is still 12.5-13.5 amps. from my past experiences dealing with motors, i don't think the motor is bad (yet). on the compressors i've delt with when the motor is shorted out i blow fusses and i haven't blown any fusses.

when i changed the ol relay last time i checked all the connections and they were tight. besides the motor what else would cause the ol relay to fail. it is a seimens esp 200.
 

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PPE Saves Fingers
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A quick glance at the spec sheet... other than an overload, the ESP will also trip on Phase Loss, Phase Unbalance and Ground Fault.

Do an Insulation Test on the motor.
 

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i have an air compressor with a 300hp main motor and a 10hp fan motor, both running on 460v with 120v control voltage. it's a new machine that's been in service since june.

back in early september the fan's ol relay started failing. it would trip out, i would reset it and the unit would run for awhile, then trip again. over the course of a week it got so bad it would trip as soon as i started the machine. i checked the fan motor amp draw was between 12.5 -13.5 amps, the motor's nameplate says 13.3 fl amps. i replaced the ol relay and the problem went away.

this week the problem came back. sunday the compressor went down for motor overload. i reset the fan ol relay and the unit ran again. the motor amp draw is still 12.5-13.5 amps. from my past experiences dealing with motors, i don't think the motor is bad (yet). on the compressors i've delt with when the motor is shorted out i blow fusses and i haven't blown any fusses.

when i changed the ol relay last time i checked all the connections and they were tight. besides the motor what else would cause the ol relay to fail. it is a seimens esp 200.
Maybe a pressure cutoff is not "CUTTING OFF", and the compressor is becoming too much of a load for the motor to handle.
 

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Discussion Starter #5
The machine has a phase monitor so it's not losing a phase.

I have it set up the modulate at 100 psi so it's not running fully loaded to reduce amp draw on the main motor.

If there is a current imbalance would swapping the leads on the starter help. Ex: swap legs 1 and 3, so I keep the same rotation?
 

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Discussion Starter #7
Wye delta soft start. I swapped phases a to b, b to c, and c to a and it still tripped out within 5 min. My current reading were 12.5, 12.5 and 13.7 across the legs before I changed them. Afterwards it read 13.8, 12.5, 12.6. The voltage is 470 when measuring 1-2,2-3 and 1-3. It's being feed from a nearby transformer.
 

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Just throwing this out there, but could heat be conducting from the contacts and affecting the overloads?
 

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Wye delta soft start. I swapped phases a to b, b to c, and c to a and it still tripped out within 5 min. My current reading were 12.5, 12.5 and 13.7 across the legs before I changed them. Afterwards it read 13.8, 12.5, 12.6. The voltage is 470 when measuring 1-2,2-3 and 1-3. It's being feed from a nearby transformer.
Testing the motor should have been step #1
 

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Wye delta soft start. I swapped phases a to b, b to c, and c to a and it still tripped out within 5 min. My current reading were 12.5, 12.5 and 13.7 across the legs before I changed them. Afterwards it read 13.8, 12.5, 12.6. The voltage is 470 when measuring 1-2,2-3 and 1-3. It's being feed from a nearby transformer.
First off, a "failure" in an overload relay means it FAILS to trip. If it is tripping, there is a 99.9% chance it is DOING ITS JOB. That is what appears to be the case here, that's why changing it did not ultimatey solve the problem.

Possible Issues: you have a phase monitor, but there is a 99% chance that is a voltage phase monitor, which is practically useless in protecting a running motor because the motor will regenerate any missing voltage on a bad leg that will fool it. Really common problem that the purveyors of voltage monitors don't bother to tell you. But you cannot fool a CURRENT based phase monitor. The ESP200 is a current based phase monitor. You have documented a current imbalance, not too bad, but it will depend on the trip level of the ESP200. It is likely doing EXACTLY what it is supposed to do. There is a dip switch on the front that you use to disable the phase imbalance trip. If you disable it and it stops nuisance tripping, you know the issue. However, DO NOT assume that "fixed it", all it did is prove that this is the basis of the nuisance tripping. Now you have to determine WHY you have a current imbalance.

Note: Even a slight current imbalance heats the motor up disproportionately, and the ESP200 will bias the thermal trip curve down in order to compensate and protect the motor, even if the Phase Imbalance Trip is disabled. The difference will be that it will take LONGER to trip.

You have done some of that investigative work already, i.e. checking connections, rolling conductors etc., and you did measure the voltages under load. But how sure are you of those voltage measurements? It would be extremely rare for all 3 to be EXACTLY the same, but a common mistake, depending on your meter type, is to accidentally leave it on "Peak Hold", so it appears they are all the same if the first one you measure happened to be the highest (done that). Even a very small voltage imbalance will create a much greater current imbalance. Your current imbalance followed the rolling of the conductors, which usually means it is a voltage imbalance in the supply. If your voltage phase monitor is set too high, it might not protect you from that.

In the event it is NOT a current imbalance, the next thing I would suspect is that the motor is starting too often. If you are measuring the running current, that is only part of the thermal picture. Every time that motor starts, the starting current is heating it up and the OL relay, as it is SUPPOSED to do, is keeping track of that in order to protect your motor. In a compressor fan motor, assuming its a cooling fan for the oil(?), the problem may be that the oil is getting too hot and the fan is cycling too often. It might also just be that the deadband setting on the oil temperature switch is set too tight, making it cycle too much.

Good luck. You are almost there, your troubleshooting skills are right on so far. I think you just needed a little more guidance on what's different about using SSOLs. They are better at protecting the motor, but if you are not used to them, you may not realize they are telling you things that an old bimetal OL would never see.


Just throwing this out there, but could heat be conducting from the contacts and affecting the overloads?
No, not on a Solid State OL like the ESP200, it ONLY sees current.
 

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Maybe a pressure cutoff is not "CUTTING OFF", and the compressor is becoming too much of a load for the motor to handle.
It's the fan OL that is nuisance tripping, not the compressor.
 

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Discussion Starter #12
The can motor runs constantly, it never stops. I'll have time later today go back and look at the dip switches. I will also reverify the voltages. Thanks for the help so far.
 

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Discussion Starter #13
I put another esp 200 in to see what happens.

The voltage on the contactor while stopped is all 470v. But when I start the machine it drops down to 459-460v.

I cut and retrimmed the leads coming from the motor. I also checked the connections at the motor. My current is now reading 13.1a, 13a and 12.4a.

I have the esp200 set for current unbalance off, but so was the other one I removed.
 

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Donuts > Fried Eggs
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Where's the overload set to trip? What other features besides imbalance are enabled or disabled? How often is this thing starting, and are you sure the starter is working properly, i.e.., have you watched your inrush? When is it tripping in relation to start times?
 

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Discussion Starter #15
The motor runs 24/7. The "new" ol relay came out of another identical compressor and was preset from the compressor factory for around 16-17a.

I have not measured the inrush current.
 

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The motor runs 24/7. The "new" ol relay came out of another identical compressor and was preset from the compressor factory for around 16-17a...
What protection class is it set for?

You said phase unbalance was off, but what about "phase loss" and "ground fault"?

What do the relays do when you hit the "test" button?
 

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i have an air compressor with a 300hp main motor and a 10hp fan motor, ...

back in early september the fan's ol relay started failing.... i replaced the ol relay and the problem went away.

this week the problem came back. sunday the compressor went down for motor overload. i reset the fan ol relay and the unit ran again....
Just want to get something clear. First you talk about the FAN tripping on OL, then you say the COMPRESSOR tripped on OL, after which you apparently reset the FAN OL relay again. So when you said the compressor tripped on motor OL, did you mean the compressor tripped because the FAN tripped on OL? That's how I interpreted it, but I just want to make sure.

Assuming that's correct, the situation sure is odd. No frequent starts, unbalance disabled (and always was it appears), not running over FLA setting, voltage seems reasonable. Running out of options, time to clutch at straws?.

The ESP200 also has GF protection in it. It's Residual GF protection, factory set for 50% of the motor FLC setting, so that means if all of the current going out doesn't come back, AND it is under 50% of the current going out, then it will trip on GF. An intermittent leakage to ground inside of a conduit can cause that, or maybe a motor winding fault to ground.

I had a large compressor once where we eventually found that the conduit from the starter to the motor was getting water in it, but only after it ran for a while. Turned out someone ran the compressor water drain line down under the slab using the hole cut in it for the conduit run. The drain line didn't really go anywhere, it just dumped the water into the dirt under the slab, but the soil was so compacted it just sat there for a while, built up and eventually worked it's way into the conduit fittings. So things only went haywire after the compressor had been running for a long enough time for the water to build up. But once the breaker tripped, by the time I got there the water had drained and everything tested fine. The only way we found it was by parking a guy there to sit around and wait for the compressor to trip again, then he immediately checked everything, thinking it was heat related. He meggered the leads and saw a short to ground where there was none before, and when I got there two hours later, it was gone again.
 

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He could mean that the fan's OL going out trips the compressor offline.
 

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Is the unloading valve sticking or weeping oil?
Is there an air dryer sharing the fan contactor?
 

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He could mean that the fan's OL going out trips the compressor offline.
Good point.

Most of our larger motors are cooled by a smaller motor and ducting. Lose the smaller to OL and you lose the larger motor control voltage via an auxiliary contact.
 
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