Motor controllers tripping, panel doors must be left open 2

[Keith53]

Hello,

A 480 volt, 3 phase motor control center for one of my chillers experiences frequent tripping on 3 of the starter controllers if the panel doors are shut.

Our Chief Electrician's answer to this problem has been to prop the panel doors open and direct a large fan on the panels.

This condition has existed for the 6 years I have worked here. In my mind, 480 volt panel doors left open present a serious safety risk and increase the potential damage from possible arc flash. I have never witnessed any form of preventive maintenance performed on these cabinets or any of our switchgear.

I also noted we have a rather large voltage/amperage imbalance indicated on two of my chiller control panels....The remaining chiller panel does not offer volt/amp indications. The imbalance varies up to 10-12 volts and 60-70 amps between phases.

We have also experienced frequent motor failures on tower fans and pumps.

A few months ago one of our older hermetic chillers experienced a motor burn out. We replaced the chiller and MCC, but still have large volt/amp imbalance at chiller.

This is a Federal facility.

I need help building my case to prove all these conditions are related, and most likely caused by lack of preventive electrical maintenance and deterioration of switchgear.

I am not an electrican, so please advise what is considered good engineering practice in reqards to preventive maintenance on this level of equipment.

Thanks Gents!

 

[wbd]

I would be very concerned about leaving the panel doors open.

A couple of things come to mind:

1. have you verified the panel meter readings with a multimeter? I would be suspicious of the panel meters and double check it. That's a large imbalance.

2. If the meter readings are correct, is anything tapped off any of the phases going to the motors? if it is an older facility, things like that happen when power is needed elsewhere.

3. Are the MCC panels located in a different environment, than where the fed equipment is located? It's been awhile but I do remeber having to make overload changes based on different environments. There is info in the manufacturer's literature for the overload heaters.

4. What maintenance has been done on the motors? Have they been maintained?

 

[Skogsgurra]

The 2.5 percent imbalance is higher than recommended. It is probably the cause for the current difference and may be the cause for motor failure. But the thermal protection should have shut off before that happened. Is the thermal setting OK?

And, yes. If the cabinets are acessible to operators (not in an electrical room) they shall not be left open. Never!

BTW: they should not be left open even in a locked room with limited access.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MikeHalloran]

Build a case, for whose court?

You, presumably a "mechanical" guy, will not win any arguments with the Chief Elecrician, because he is the >Chief< and because he is >Electric..<, and you are neither.

I suspect you are being maneuvered, e.g. used as a projectile in someone's subtle war with the Chief.

Projectiles are expendable.

The cannoneer is not your friend.

Proceed carefully.

Probably the limit of what you can do without making it a career decision is make a fuss about the motor failures, report the voltage imbalance, cite some written reference (other than Eng-Tips) that that is a Bad Thing, and request that a consulting Electrical Engineer evaluate the situatioin.



Mike Halloran
Pembroke Pines, FL, USA

 

[jraef]

Start off by stating facts, not feelings.
Facts:
1) Motor Control Center equipment is designed to operate with the doors closed and without fans blowing on them. This includes the operation of the thermal overload devices that are protecting the motor windings and motor leads. Propping the doors open and blowing fans on them does nothing more than "fool" these thermal devices into NOT tripping when it is obvious that they should (because they were). So in essence, this "solution" has now cause more problems than it solved. The old concept of ambient compensation (controller in a greatly different ambient temperature than the motor) might apply but see below before you ASS-U-Me.

2) It is completely and utterly ILLEGAL to operate any electrical equipment with the doors propped open if it was designed to be enclosed. They are in a very serious fire and safety violation condition. If there were a fire and subsequent investigation, the insurance adjuster would see that condition and could void coverage of the fire because of the blatant and willful violation. If you don't believe me, ask them! A fire could also result in criminal negligence prosecution not only of the owners but of the Chief Electrician personally as well. In addition, OSHA could shut your operation down at any moment if they saw it. When considering the cost of fixing this problem, they must consider the real costs of not fixing it for comparison, i.e. downtime, lawsuits etc.

3) Overload is overload. The fact that they have successfully tricked the protective devices into not doing their job does not mean the overload is not present. Is there a correlation to the loss of your motors? That cannot be proven as fact, but the likelihood is there. Running a motor into the overload curve and then NOT tripping it out will significantly shorten the insulation life. An old rule-of-thumb about increasing the heater element size (the thermal device in an Overload Relay) was that for every 10% increase in overload current, you decreased the motor life by 50%. 10% is essentially increasing the heater element by just one size.

4) Your 2-1/2% voltage imbalance may not be as bad as it appears, but is still a cause for concern. Current imbalance increases at a logarithmic rate to voltage imbalance, so a 1% voltage imbalance can result in a 5% current imbalance, and 2% can mean over 10%. However, many utilities in the US will only regulate their supply voltage to within 2-1/2%, or if they follow ANSI C84.1, they may even allow 3%. For that reason, NEMA requires that motors not need derating until voltage imbalance exceeds 3%. That does not necessarily mean that your chillers motors are following NEMA standards however, they tend to be custom built. In addition, if your motor load is right at the edge of the utilization curve for that motor, as many chillers are, that additional heating from voltage imbalance could be pushing it over the edge. I doubt however that this amount of imbalance had much to do with your cooling tower fans or pumps as they would have NEMA designed motors in all likelihood.

Here are my suggestions:
Step 1) CLOSE THOSE DOORS!

Step 2) Find out what the REAL motor nameplate Full Load Amps (FLA or FLC) is of those chillers. This may not be as easy as it would seem. My experience is that a lot of older chillers had NO nameplate on them whatsoever and many that did have had them removed over the years. What you can do however is get the chiller model number and go back to the manufacturer to find out. It could very well be that the Overload heater or setting selection is just too low for that chiller because nobody knew what it was supposed to be, so they guessed based on motor HP based on the Tonnage rating of the chiller, a very inexact method derived from another inexact method.

Step 3) If the overload setting is correct, then you need to figure out if your chillers are really overloading. Don't trust meters on the cabinet doors, use calibrated test instruments, your electricians should have good clamp-on Ammeters. If they are not truly overloading (measured current is above nameplate current) then you do have an ambient compensation issue, which needs to be addressed.

Step 4) Assuming that you ARE overloading the motors then you need to figure out why. If the chillers are centrifugal, it may be the vane position, a change in refrigerant etc. You are the mechanical engineer I assume, so that should be your dept.

Step 5) Fire that Chief Electrician. He should have known better and is therefore a walking time bomb. Who knows what other "solutions" he has come up with to avoid doing things properly!

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Keith53]

I'm the cannon in this case, but not gathering ammo, just trying to verify my aim. Was hopeing electrical engineers here would give insight on possible causes and typical industry maintenance schedules.

You are correct that I am the mechanical guy, not an electrican. There is no conspiracy to harm the Chief Electrican, only seeking his cooperation and that he accept the causes and address them....Trying to handle this at lowest level possible, so no formal complaints to management or OSHA types are planned.

I'm concerned with equipment safety and reliability foremost. Worker safety also. I'm watching this facility degrade from lack of electrical maintenance and now my equipment is beginning to suffer.

As a 20 year nuclear submarine mechanic I'm accustomed to seeing constant switchgear maintenance....Breakers racked out, bus bars being cleaned and retorqued, contacts cleaned/aligned/examined....None of that goes on here or ever has....Now we are leaving panel doors open to keep stuff running and starting to suffer large motor failures and nuisance tripping.

Thanks for the replies, but I just found our instruction that addresses my concerns....Just as I suspected it requires annual and 36 month inspection and testing of all switchgear and distribution systems...It lays it out in great detail. I'll print it out and go visit him.

 

[Keith53]

Thank you Jraef,

You and I think alike.

I just examine the old chiller starter cabinet they removed when the new chiller was installed.

All contactors severely burned and pitted. Found two loose lugs on interconnecting line voltage wiring with the lugs scorched from high resistance/loose connections. Looks like our old chiller moter single phased from lack of maintenance on panel and starter contactors. These components are desinged to be inspected and contacts easily cleaned/replaced, so there is no excuse for this.

 

[jraef]

That is a very likely cause to the problems on that unit, but I would still insist on checking everything now. You will find that often times people are reluctant to do maintenance on working controllers because of the "if it ain't broke, don't fix it" attitude. One way around this is to insist on a semi-annual thermal scan with an infra-red camera. This would have picked up those loose connections, as well as many other pending catastrophies. Being a non-contact test that is best done with the equipment operating (not to mention involving cool looking high tech camera-like equipment), it's more likely to take place on a regular basis. The IR scanners can be rented or outside services can be called in to do it for you as well.

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Keith53]

Thank you again JRaef,

The Chief Electrician is retiring this month..........

I'm going to tote my problems, suggestions, and all the physical evidence up to the Chief Engineer and lay it on his desk as soon as the guy is gone....I've salvaged all the old contactors and other burned items from the old chiller....I dug out old logs that reflect the increasing trend of voltage imbalance and will be able to overlay the increasing trend of motor failures and show the relationship.

These guys are actually planning a project to A/C our switchgear to 'fix' this problem!...I truely believe it is like you say-that the problem is an overload condition or is due to high resistance connections and that the problem will not go away until it is properly addressed. Their plan to A/C those cabinets is just another step beyond leaving the doors open and directing a fan on them. I'm thinking the gear will continue to degrade and we will experience more failures unless we start doing some preventive maintenance.

Thank you for suffering my ignorance and answering my questions. I sincerely miss working with professionals like you folks here.

 

[rbulsara]

I can only a real experience of very similar nature. The starter was heating up requiring fan cooling. The current was within limits of the motor, 200HP 415V. It was going on for a long time before I joined the company (straight out of college).

I was told there is nothing else that can be done. I reviewed the situation and saw that the feeder cables where connected to long motor leads in a junciton box next to the motor. The "joint" was made by bolting the two lugs of each cable without any proper stright thru splice lug or a bus. This "joint" was a constant PM item as it kept burning out insulation. To make the story short, I took upon myself to replace the junction box with a proper bus bars installed in it on insulator stand-off and terminated the cable lugs on those busbars. The issue went away to other people's amazement.

 

[rbulsara]

The starter was sevaral feet away from that "joint" I mentioned in my previous post, and it was heating up.

 

[LionelHutz]

Hmm, it sounds like you have the situation fairly well addressed. Or figured out I guess, I hope you get it actually addressed.

Last time I saw a situation like yours a 1600A chiller starter cabinete eventually burned down filled the whole top floor of a 26 story office building full of smoke and set off the fire alarms. I think it took about a week to clean up the mess and install all new equipment in the cabinet incurring lots of extra rush costs.

I guess the moral is that this can lead to much more serious issues besides a starter tripping or a motor failing.

 

[Keith53]

Thank you everyone for your advice and assistance.

However, I must report that now our beautiful York #2 Chiller is down hard. We called that chiller our 'Bread n Butter' chiller becuase it is relatively new and could carry our whole load when pressed.

Just as I predicted, we finally totally destroyed the circ pump MMC and perhaps burned the pump motor by continuing to neglect the conditions discussed in the above posts.

To make matters worse, the main breaker for that chiller is tripped and will not reset. I'm afraid we may have also damaged the chiller compressor starter and/or that chiller compressor motor too.

This event mirrors exactly the failures that led to the destruction of our #1 chiller last year.

Thanks for all your suggestions, but they fell on deaf ears. Sorry for the waste of your tax dollars also.

 

[jraef]

Like I said, they failed to consider the cost of failure compared to the cost of fixing it. CPP* syndrome to be sure.







*Capitis Penitus Pyga (look it up, it's Latin).

 

[wrsharper]

just a note, we have many ammonia comprssor star/delta controllers of various types. sometimes in the summer we have to prop a few of the doors open too, with the fan blowing on the insides. this too has been done for years (by refrigeration people and not electricians) and the controllers that have had this done are not the ones we have had trouble with. never found or investigated the cause becuase the compressor would be running and needed and the blowing air cured the problem.

 

[waross]

I agree with jraef. I am a "Don't fix it if it isn't broke" type. I think that tearing an MCC down to clean and retorque connections often causes as many problems as it solves.
However, I do believe in checking for excess temperatures. An IR scan is often the best choice.
Another method that often works and is available to those who have trouble convincing management of the need for IR scans is a voltage drop test.
A fused switch is installed close to the transformer and connected directly to the transformer lugs. Drill and bolt or tap the lugs to get a connection that is independant of other lugs if you have to. Use the lowest current fuses available. Run a three phase extension cord to the equipment to be tested. A bad connection anywhere between a transformer and an MCC or motor starter will show up as an excess voltage drop between the extension cord and the same phase on the equipment.
respectfully
respectfully
AND, when the heat is such that the doors must be left open and fans used, IT IS BROKE! FIX IT!

 

[ScottyUK]

...compressor would be running and needed and the blowing air cured the problem.

It doesn't cure anything, it just hides it until it gets out of hand, wrecks the equipment, or sets the installation on fire. Good cure!


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Well.... That is a cure.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Haha Keith,

Yes, there are certain bits of equipment I work with where watching them burn would fill me with a malevolent sense of glee, but that is scarcely a responsible attitude to take, however tempting that option becomes...

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Sometimes I only open my mouth to swap feet...

 

[jraef]

If, at the "end-of-the-year-bonus-time", they came up wih an excuse that the operating budget emergency repair expenses cut into my bonus, I would not be gleefull of such wanton mismanagement....