# Compressor keeps tripping breaker - please help!



## ads295 (Aug 27, 2021)

Hey everyone,
I’d like to share a few issues we’ve been facing with our compressor. We’ve tried all we can to nail down the problem but can’t get to the root cause. I hope you can help.
First up, a summary of the setup:
It’s an Ingersoll-Rand Type-30 71TD piston type compressor that is accompanied by a 12.5HP (9.3kW) motor to run it. The motor’s plate specifies a current of 18A, speed of 1440RPM, and is Type “TEFC”, whatever that means.

Here’s a summary of what’s been happening.

The compressor had been running fine for over 2 decades, the last 3 years of which have been on proper pressure cycles (maintaining at 6 bar of pressure for more than 12 hours a day). Before that it was doing light duty work.
It has never faced an issue picking up pressure while running. Even when it was running under relatively higher load, the duty cycle is barely 10%, maybe 15% if I’m being pessimistic (this is from measured data)
In the recent past, the motor started developing hiccups when it went into delta-mode through the starter. In star-type it moves fine. But when switching to delta it would keep bouncing between the two, sometimes for up to 10-15 seconds on end. We checked the starter, its contacts, everything, but nothing out of the norm was observed.
Suddenly one fine day the motor did not start under load. It kept tripping the MCB (which throws sparks at starter contacts if we force the switch to stay on.) Starter looked OK so we didn’t do anything there.
We called in a specialist in electric motor repair above and beyond our on-staff electrician who has 10+ years of experience. They both checked out the motor and said it was OK.
After some minute inspection, we saw that the pulley was loose on its axis and there was scope for it to move back and forth (just a little) on the compressor’s crankshaft. The knurling on the shaft was worn, so we drilled a hole into the pulley and turned it into a bolt system where the bolt would tighten and hold the pulley onto the shaft after the pulley was mounted and the key slotted into the keyway.
To rule out any issue with the starter, we checked the motor startup on another starter we had, which was running on another compressor, also rated for a 12.5HP compressor motor, also star-delta type. The same issue persisted – would keep sparking the contacts and refuse to go into delta.
Then we called Ingersoll-Rand and they came to check things out. They felt the starter was an issue, in particular the timer. The main tech guy recommended that we switch over to dual-starter type starter if the motor power is 12.5HP, since Ingersoll normally delivers compressors with these ratings with dual starters. We argued against it since we had ruled out the starter as a problem, but he would not let go of that issue.
So rather than spend on a new timer, I took his advice to heed and purchased a brand new dual starter with a 20A minimum relay. The Ingersoll Rand tech said he would not recommend anything over 19A on an 18A motor, but we decided to try it out anyway since our machines were facing a lot of downtime and we just wanted to get to the root cause of the issue.
The motor would refuse to start, again tripping MCBs or the relay. We managed to start the motor but only after setting the starter relay to 28A. Did not feel like continuing for fear of burning out the motor. It also got pretty hot at this time.
Ingersoll tech quickly changed the root cause diagnosis to the motor and not the starter. We shipped the motor out to a specialist that he himself uses for his work. The guy sent us a video with the motor running under no load, pulling 6A on all 3 wires. I did not understand why it would be pulling 18A under no load but this is not my area of expertise so I did not comment. Ingersoll tech told me the motor is OK and that now the compressor itself is main culprit (bear in mind that the compressor has NEVER failed to pick up pressure in a jiffy, has NEVER been run for more than 15% duty cycle throughout its lifetime, and that during the last oil change we filtered the oil and found ZERO metallic residue.)
The compressor was opened up. There are no obvious signs of damage. Yes, one small bit of the casting has broken off where the bearing sits, but only the side face of the bearing goes against that part and nothing else. The head is clean, the pistons are clean, and so is the liner. I am told that the crankshaft has runout and that it should be remedied in order to solve the issue once and for all.
I ship out the crankshaft to a compressor specialist who works in refurbishing old compressors. He says the main bearing is quite worn and should be replaced, but other than that the crankshaft is fine. He measured runout at 125 micron (0.125mm).
Ingersoll Rand tech guy tells me the crankshaft runout MUST be less than 20 micron (0.02mm). I pass on this tidbit to the third part compressor repair guy and he says 125 micron is not bad at all and we shouldn’t have any problems.
I got the crankshaft back to my premises and I checked the runout myself. True to his word the runout measures between 120-140 micron (0.12-0.15mm). The seat of the worn bearing (the bearing is now removed) is measured for runout and on that surface its barely 100 micron (0.1mm).

So, I’m now at the end of my wits as to the root cause of our problem. I don’t understand why it won’t start. Can you help me out with a solution?
Here are a few things of note:
1. When we measured the current the motor was pulling, on one of the phases we got only 1.4A current draw on the motor (without load). I have a video of this as well. From my memory this was what the Ingersoll-Rand guy used to point out that there was an issue with the motor.
2. When the third-party motor repair specialist measured the current, he got ~6.5A of current draw on each terminal. He used that to tell us that the motor was OK.
So why are the two readings different at different places? Both places used a dual starter for checking.
3. The MCB switch used here was a 16A unit. Can it be used with a motor that is supposed to draw 18A? Assuming it can’t be used, why did we not face this issue even once in the past 3 years?
4. The “worn” bearing makes a slight rattle (we cleaned it up good) but it seems normal to me, like the sound would disappear if I greased the bearing. Could it really be the cause for the motor taking so much load that it trips the switch and refuses to go to delta?
5. The Ingersoll-Rand guy has been dropping hints that my motor actually may be a 15HP motor rather than the 12.5HP it claims to be on the plate. I don't know how this is possible but how do we check that? And I still don't understand why all this issues are occurring now, rather than years ago.

Thank you so much for reading this!


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## iowagold (Jan 22, 2020)

what country are you in?
and what is the mfg setting? what do you make?
and what is the rated voltage and HZ on the line?
and 
and what is the measured voltage and HZ on the line during start up?

you could have bad power feed coming in some where to the bad location.
or a bad breaker.
yea check every thing on the power feeds first...
use 3 live meters to watch the line power during run up.
and also check it at the mcc bucket room if you have one.

so did the motor shop dyno test the motor under load?
they need to do that if they are a real shop.

we use a second motor with a resistive coil load that we can turn up of down the load.
and also a hydro motor with a brake load setup that works best on compressor motors...
depends on how large of power load we need up to 2000 hp.


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## ads295 (Aug 27, 2021)

Hello

I'm based out of India. We don't know the manufacturer setting because the plate is all worn off. But the other compressor we use, with similar specs, is rated for 11bar of pressure. We keep ours between 4.5 to 6.5 bar. The rated voltage is ~240V and 50Hz on the line.
The shop did NOT check the motor under load, I agree that they should have done that, no-load figures tells us very little. I'll speak with them again.

About testing the ratings under startup, the compressor is currently dismantled (did it to check crankshaft runout). I'd like to rule out all other possibilities first before assembling everything again. After its been put back together I can put together some readings on startup...

Thanks for your inputs.


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## iowagold (Jan 22, 2020)

india is a rough country to be in for sure...
kinda the wild west of mfg right now.
we have seen pix of the electrical poles in some areas...
and youtube videos of when things go wrong.
WOW!

ours here in the USA is pretty clean utility poles.
and pretty good on power supply.

use a 3 phase recorder voltage and current meter setup to look at your utility power.
search that.
here in my area the power engineers for the utility will set those at your meter location if you are having supply issues..
that way they can see the real usage...
and now we have smart meters too!
pretty cool as you can log in to your utility meter and see real time data.


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