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.
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.
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.
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?
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.
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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