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Old 01-15-2020, 10:57 PM   #1
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Default MCC maintenance

Curious if anyone here carries out any routine preventative type maintenance on MCCs, breakers, dry transformers, etc.

Reason I ask is we ran into an issue the other day. I got a call saying a pump skid had freaked out and shut off so the operators had to turn on the old back up pump. I run out there and start checking it. Power goes from a breaker in an MCC bucket to the control cabinet that came with the pump skid, which then powers the motors with built in VFDs.

Anyway I find that at the MCC breaker the third phase was dead. Checked the MCC itself and the busses had power, so shut the MCC off and pulled the bucket and it appears the clip where it clips onto the bus had relaxed and just lost contact. Squeezed the clips together a little and reinstalled the bucket and had all three phases again. Unfortunately despite the control cabinet having surge protector, overloads, and all kinds of other protection type stuff it took out something in the VFD. Have power going into it but it wont do anything and isn't talking back to the control panel.

Anyway I'm wondering if there is preventive measures that are common for some of this type of equipment. Yearly resistance checks ? Yearly cleaning, inspection, and racking of buckets etc. We have a thermal camera that I want to start doing at least yearly scans of everything with. What about breakers and transformers etc, yearly torque checks of connections? Resistance measurements? Insulation test? Just looking for ideas of useful preventive checks to implement when time allows. I have been planning to get NFPA 70B that covers maintenance, don't know if its useful or not, but figure its worth looking into.
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Old 01-15-2020, 11:42 PM   #2
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We try and line up MCC cleaning and visuals during scheduled outages, usually every 5 years. We have the latest "hot spot" report from an IR scan on hand, so we have an idea what we are focusing on. We also pull the cubicles and check the bus connections, clean and reassemble. Retorque what we can that is de-energized (cable to bus connections, secondaries, etc).
Annually, we do the IR scans with as much of a load on as possible. A big part of the scans is also interpreting the readings, so that you aren't chasing a 2 degree temp difference.
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Old 01-16-2020, 05:55 AM   #3
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What model MCC?
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Old 01-16-2020, 08:39 AM   #4
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We try and line up MCC cleaning and visuals during scheduled outages, usually every 5 years. We have the latest "hot spot" report from an IR scan on hand, so we have an idea what we are focusing on. We also pull the cubicles and check the bus connections, clean and reassemble. Retorque what we can that is de-energized (cable to bus connections, secondaries, etc).
Annually, we do the IR scans with as much of a load on as possible. A big part of the scans is also interpreting the readings, so that you aren't chasing a 2 degree temp difference.
One plant I worked at only did the IR scans in the winter. If they did it in the summer then most of the distribution would be in the danger zone. Very little concern for the infrastructure. As long as the floors had a shine and the walls had a fresh coat of paint. I quit that place after two years. A plant electrician should not be painting when equipment needs attention.
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Old 01-16-2020, 10:32 AM   #5
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What model MCC?
Multi conductor cable, I always thought but I’m here to learn.
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Old 01-16-2020, 10:36 AM   #6
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Multi conductor cable, I always thought but I’m here to learn.
No, not what kind of SO cord.

What brand of Motor Control Center.
An old FPE maybe? I liked them.
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Old 01-16-2020, 11:27 AM   #7
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Depending on the gear, we clean, check connections, grease, trip and reset breakers about yearly.

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Old 01-16-2020, 03:25 PM   #8
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Stab spring weakening on an MCC is generally a result of over heating + time. Sometimes corrosion will attack the stabs themselves, especially if there is a lot of H2S gas (hydrogen sulfide, a byproduct of anything rotting or fermenting, such as sewage). But that is usually happening on all of them at the same time, not just one.

As to the VFD failure: if your MCC was powered down (or the CB feeding the VFD was left open) for over a year, the capacitors inside of the VFD will deteriorate and fail just by being energized for the first time. The trick is that if you are going to decommission something with VFDs but keep it as a backup, energize it once per year for 2 hours or so. You don't need to operate anything with it, just put power to the VFD input. If it has sat for over a year, you need to do what's called a "capacitor reforming procedure" that involves applying low voltage over a long time, slowly increasing it until the capacitors build up their internal layers again (too long to go into).

Most VFDs are not going to be damaged just by getting single phase power. Some may trip, others may just hum along fine until the load is more than 50% of the rating.
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Old 01-16-2020, 07:10 PM   #9
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Its a westinghouse 2100 if I remember right. Would be about 25 years old now and I know it has never had anything done to it.

Just to clarify the VFD that is no longer responding was not on back up duty, it has been running. It is part of a three pump skid with VFDs integrated into the motors (grundfos). Typically only one pump runs at a time and it switches pumps every day. Changes speed of motor to match flow while maintaining a set pressure. Works really slick until now. The back up pump does not have a VFD but gets ran weekly anyway to keep the case cleaned out.
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Old 01-16-2020, 08:33 PM   #10
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You have to consider cause and affect.

If the spring clip became loose was this the cause of the drive taking a dump or did the motor/drive (presuming this is a all in one) short out and cause the clip to over heat.

Most vfd's wouldn't care if they drop a phase (some can be fussy about which phase as there controls use 2 phases). This may be something that shows up during one of you future IR pm's when your sent to investigate why 2 fuses are hotter than the third.

On remote mounted vfd's where you can access the dc bus there are simple test that can be done with the drive disconnected to test the hardware but as your seems to be built onto the motor calling tech support would probably be the best bet to see if they have a testing solution before condemning the unit.
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Old 01-16-2020, 09:14 PM   #11
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Im waiting on tech support to get back to me on further troubleshooting the drive. And yes its integrated into the motor, I opened up the drive and couldn't see any obvious spots where the smoke and fire escaped. I also couldn't get any 24VDC readings making me think something in the control/signal circuitry is fried.

As far as which is the chicken and which is the egg I'm not sure. When the skid shut down the pump shut off and the screen on the control cabinet shut off, (second hand info as I wasn't there). I found one of the 1 amp fuses on the control circuit was blown, and the overload for one of the pumps was tripped (the pump that now wont do anything). Replacing the fuse brought the screen back.

Its entirely possible that the motor/drive shorted first although there is enough protection in the control cabinet that i would think it would have tripped before overheating the MCC clip. On the other hand there is enough protection in the control cabinet that dropping the phase shouldn't have been able to hurt the drive.

Getting back to the original question, when tripping breakers, is it just manually cycling the breaker or is there a better way to actually test the breakers? Is the basic point of cycling them to make sure the contacts aren't stuck and to hopefully remove oxidation on the contact surfaces? What would need greasing inside of an MCC (big breaker linkages ?)?
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Old 01-16-2020, 10:18 PM   #12
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I had a problem with drives breaking down because the workers were turning the machines on and off by the 60 amp disconnect switch and not an orderly shut down by using the control panel. They were using the drive for speed control only. No more problems after they started to shut down the machines the right way. Maybe the drive burnt out because the feeder faulted while the drive was under load. Newer drives have safe guards.
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Old 01-16-2020, 10:42 PM   #13
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Getting back to the original question, when tripping breakers, is it just manually cycling the breaker or is there a better way to actually test the breakers? Is the basic point of cycling them to make sure the contacts aren't stuck and to hopefully remove oxidation on the contact surfaces? What would need greasing inside of an MCC (big breaker linkages ?)?
You are only dealing with small sealed breakers so there's no greasing. If you have a test button push that and make sure the breaker trips, Confirm the breaker trips on all 3 legs then reset and confirm the breaker makes on all 3 legs. If you can power the bank down safely you can do a resistance test but that really requires a low resistance meter.

Wear PPE when testing, Only do one breaker at a time as some breaker may fail and if you only stock one its better to stop once you find a bad until you get another spare. Larger sub and main breakers should be contracted out to people who have all the toys to test them.
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Old 01-16-2020, 11:04 PM   #14
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You are only dealing with small sealed breakers so there's no greasing. If you have a test button push that and make sure the breaker trips, Confirm the breaker trips on all 3 legs then reset and confirm the breaker makes on all 3 legs. If you can power the bank down safely you can do a resistance test but that really requires a low resistance meter.

Wear PPE when testing, Only do one breaker at a time as some breaker may fail and if you only stock one its better to stop once you find a bad until you get another spare. Larger sub and main breakers should be contracted out to people who have all the toys to test them.
Thanks for the input. None of our stuff is set up with any way to test it, will have to keep researching that. I'm the first person in the history of the plant to really look into any of this kind of maintenance so lots of development work to do. Our stuff is pretty small and basically designed to be set and forget but figure I might as well attempt to do what I can as far as maintenance.
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Old 01-17-2020, 10:57 AM   #15
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I had a problem with drives breaking down because the workers were turning the machines on and off by the 60 amp disconnect switch and not an orderly shut down by using the control panel. They were using the drive for speed control only. No more problems after they started to shut down the machines the right way. Maybe the drive burnt out because the feeder faulted while the drive was under load. Newer drives have safe guards.
If the disconnect is after the drive output, it should have aux contacts in it to shut the drive down before the blades open. That spike is a killer to drives over time.
There is a couple of threads were it’s been discussed.
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Old 01-17-2020, 04:59 PM   #16
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Exercising a breaker is just turning it on and off a couple of times, and that's fine. The only way to test a breaker that doesn't have a "Test" button is to do a current injection test. That's not really recommended on Molded Case Circuit Breakers (MCCBs) because that tests the breaker by actually making it carry trip current until it trips, just using low voltage so as to limit any damage to the contacts. But there is also the aspect of the trip elements getting stressed. Current injection testing is generally done on large air-break POWER Circuit Breakers (PCBs), not on MCCBs. PCBs are designed to be tested periodically and can be rebuilt. MCCBs are designed differently and you can wear out the trip system by doing injection testing too much, then they cannot be rebuilt, they are throw-away. The UL test standard only require that they can be tripped and reset so many times Yes, breaker houses claim to sell "refurbished" MCCBs, but all they can actually do is clean them and test them, and in the testing they actually consume some of the component life.
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Old 01-18-2020, 10:28 PM   #17
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Last job I did used Eaton contactors in the MCC buckets. The contactor monitors voltage, phase loss, on off condition. They trip out in the event of those conditions to protect the load.
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Old 04-01-2020, 08:46 PM   #18
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I don't have very many machines at work, so during my monthly PMs, I do a thermographic survey and just compare what I see to memory. Problems show up better in the winter months. I have seen some wires through raceway covers when they had current draw too high. Nothing was wrong in the circuit, so I added another wire in parallel and never had any issues.
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Old 07-15-2020, 10:33 AM   #19
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I worked at a water utility out west. As electricians, we were scheduled with PM's for all electrical equipment. Maintenance engineering developed the schedules. It actually worked out well. We did IR surveys twice a year. Any suspicious reading and the station was taken down and the condition was checked/corrected. We caught several loose connections that would have resulted in failures eventually, mostly on the 5kv gear and transformers. We also used an ultrasonic probe (microphone) to pick up arcing. We got several hits using that on the 480 gear; saved us a lot of failures.
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Old 07-15-2020, 11:13 AM   #20
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One plant I worked at only did the IR scans in the winter. If they did it in the summer then most of the distribution would be in the danger zone. Very little concern for the infrastructure. As long as the floors had a shine and the walls had a fresh coat of paint. I quit that place after two years. A plant electrician should not be painting when equipment needs attention.


Amen!! Reminds me of the funny guy who asked ME if I did any plumbing. NOT
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