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Meggering Electric Motor Every Month?

03/01/2016 8:15 PM

Hi Everybody,

Sometime working with some moron are really difficult especially with moron who do not really understand any technical background. They proposed to megger all the electrical motor (operating voltage at 380 Vac) every month with 500V megger and I am not agree with that, as it will cause stress to the motor winding.

So what you guys say.... any comment on it.

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#1

Re: Meggering Electric Motor Every Month?

03/01/2016 8:36 PM

why?

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#3
In reply to #1

Re: Meggering Electric Motor Every Month?

03/01/2016 9:16 PM

Our plant has stopped for 6 month maintenance works and in order to ensure all the equipment's, especially all the electric motor, are in healthy condition, we, were ask to megger all the electric motor every month.

I basically do not agree with this procedure to megger all electric motor every month.

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#7
In reply to #3

Re: Meggering Electric Motor Every Month?

03/01/2016 9:36 PM

unless you ( they) have reason to suspect the integrity of the varnish I don't see why. is this a toxic environment like a lot of chlorine or other corrosives in the immediate air?

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#8
In reply to #7

Re: Meggering Electric Motor Every Month?

03/01/2016 9:52 PM

Nope. Our plant is a Air separated plant and the environment area are clean.

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#9
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Re: Meggering Electric Motor Every Month?

03/01/2016 9:59 PM

You would do well to not refer to someone - who is likely in a position of influence on your career - as a moron.

Much better to put forward - in a respectful manner- a convincing argument against actions that you see as ineffective.

If that argument does not effect a change of practice, then either your points were not sufficiently strong, you did a lousy job of delivering them, or the powers that be simply don't want to change.

In any of those cases, all you can do is defer to their wishes and do as is requested.

As to the question:-

Regular testing will not protect the motors from any deterioration.

They will either deteriorate or they won't, testing will not change that.

If you do find deterioration at an early period of downtime, will you immediately repair and return the motor so that further deterioration then occurs, or will you wait until later to effect such repairs?

Far more efficient to take steps to protect them and then test them all at some closer stage to recommissioning and repair any problems that are found at that point.

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#2

Re: Meggering Electric Motor Every Month?

03/01/2016 9:07 PM

I am not aware that meggering the windings of any motor causes any damage...It is a non-destructive test, if done properly....although once a month seems like a lot to me, I guess it depends on the critical nature of the application...If this is an aggressive preventative type of program, then it's necessary to have an average reading depending on environmental conditions for comparative analysis...What matters is who is in charge, and must take responsibility....

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#4
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Re: Meggering Electric Motor Every Month?

03/01/2016 9:19 PM

I agree with your comment. Meggering the winding of the motor every month is really too much and I believed it is really not practical to do so. May be once every 6 month will do the job.

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#5

Re: Meggering Electric Motor Every Month?

03/01/2016 9:31 PM

The few places I ever worked that had any sort of inspections like that were done either at annual inspection periods or if there had been a moderate power issue with the whole system that had damaged one or more components in the the facilities.

Personally I find doing a 500 volt test on a 380 volt system rather pointless. If it was me I would be doing a 1000 volt test once a year and only be doing closer inspections for motors that test at under 500K ohms warmed up.

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#6

Re: Meggering Electric Motor Every Month?

03/01/2016 9:33 PM

If you call the guy that tries to keep you in the job a moron then I call you lazy.

If you think you understand the technical background I call you out on it.

Why does it bother you to do a repetitive job every month to make sure you still have something to do and getting paid?

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#10
In reply to #6

Re: Meggering Electric Motor Every Month?

03/01/2016 10:04 PM

Basically, that guy is just from another department so call Automation Section. In fact he is just having some HV chargeman certificate, just to do switching of the HV system. Unfortunately, even the simplest electrical circuit diagram don't understand.

Credit will goes to him leaving all the responsibility to you. So who do you call this guy ...?

Just for discussion only. No heart feeling...

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#11
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Re: Meggering Electric Motor Every Month?

03/01/2016 11:20 PM

In the UK he would be an authorised person or maybe a senior authorised person. He takes on the responsibility of protecting morons like you from electrical danger. Believe me, obtaining your "AP" ticket is damned hard work.

From your previous posts you don't seem to grasp the principals of routine testing. What minimum IR has been given as the lowest acceptable? Testing only has to highlight one critical drive to prove its worth.

If there is a moron in your organization it is you.

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#12
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Re: Meggering Electric Motor Every Month?

03/01/2016 11:38 PM

I really don't agree with your comment. Why do you want to do monthly meggering all the electrical motor since all these motor are in good condition and it only been installed 1 year ago. Now, we stopped the plant for maintenance works and I don't see why all these motors need to megger every month.

When the plant start to operation then we will do the resistance and insulation test on it before we switch on back these motors. Isn't this is the correct ways to do it.?

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#13
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Re: Meggering Electric Motor Every Month?

03/02/2016 12:11 AM

While it sounds correct what you said it still does not prevent you from doing what your boss says.

I still think you are lazy and not really concerned about the motors.

If you need to argue your points do it with your boss. If this is not possible then nothing will change for you by discussing it here.

Megger it and follow your day job. Are you getting paid by month, per megger test (stupid question as you would do it daily)? Is the facility stopped and you need something to do not to be laid off?

Think about it!

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#14
In reply to #13

Re: Meggering Electric Motor Every Month?

03/02/2016 12:31 AM

Hi everyone, I think there is some miss understanding on this matters.

First, of all, the Guy is NOT my Boss, just another person from other department.

Second, generally, his position is just a Manager level and My level is Plant Manager which give me higher title level than him.

My background is in Electrical, Electronic and Mechanical base and I have working in a maintenance department for almost 28 years in various steel mills maintaining Electrical, Electronic and Mechanical equipment's for the plant. Recently, in this new company I was offer to take care of the Auxiliary Plant and my title is a Plant Manager.

I would like to know it is a good idea to do monthly meggering all the new motor or it is practical to do so. Base on my experience, we do not do so. Periodic and weekly maintenance, yes we carry out to do the checking according to our standard checklist.

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#15
In reply to #14

Re: Meggering Electric Motor Every Month?

03/02/2016 1:02 AM

You answered your own question.

If you are the plant manager and you do not think meggering is necessary, then why do it?

If in doubt ask an international forum to prove your point!

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#16
In reply to #14

Re: Meggering Electric Motor Every Month?

03/02/2016 1:44 AM

If you have an electrical background and have been doing this for 28 years, I cannot understand why you would waste your, and our, time by asking total strangers for technical guidance.

You either have the authority to specify test intervals or you don't.

Get on with it.

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#21
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Re: Meggering Electric Motor Every Month?

03/02/2016 9:29 AM

If you're in charge tell the "moron" you will take full responsibility for any plant failure on start up.

I'll bet the plant owners will take a different view when they are loosing money due to your incompetence.

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#17

Re: Meggering Electric Motor Every Month?

03/02/2016 1:53 AM

After reading all the posts, it seems there are two questions. Here's my 2 cents' worth:

Firstly: In my opinion, it is generally not worth meggering monthly. It won't damage the motors at 500V (as another poster mentioned, 1000V would probably be better, but confirm with the motor manufacturer). However, each time you megger you have to open terminal covers, disconnect wires, etc. This could cause the introduction of connection related failures. So now you have to increase your infrared scans... The old principle of if it aint broken dont fix it still applies. All of this depends a lot on the nature and criticality of the motors. Also, doing these tests takes time and usually the job of maintenance engineers are to ensure minimum downtime. Your failure rate will guide you. If you have a 6-monthly plant outage for maintenance or product changeovers or whatever, by all means do it then.

Secondly there are the management issues:

  1. Your maintenance program was hopefully determined by some formal methodolgy, e.g. RCM. So, any changes must follow that same methodology. It cannot just be changed on a whim. It must be substantiated with legal requirements, manufacturer/warranty stipulations, operating conditions, failure rates/patterns, criticality/failure consequences, etc. Just because it can be done, doen't mean it has to be done.
  2. There are probably extra costs associated with extra inspections: both extra labour hours (unless your electricians were sitting around waiting for work, which I very much doubt!) and extra downtime (which translates into lost production). This usually satisfies the management if two subordinates can't sort something out.
  3. Most importantly, the issue of asset ownership. Assets should have one owner. In this case it seems to be you. No colleague of yours can tell you what to do. They can suggest or request, but the decision is yours. You have to explain any consequences, you alone are held accountable (both inside the company and legally).
  4. Again, as mentioned by another poster, the idea is to explain and convince them why you are doing what you do - this is for their education (often suggestions made in ignorance are made in good faith), but also to stop them from running to the bosses and then you have to have much more formal sessions, time that could have been better explained. If you cannot explain it to a colleague, then you'll probably struggle with the boss too! I usually find it useful to explain using examples they can understand, e.g. I assume he has a car: does he test/megger his alternator and starter and ventilation fan motors monthly (or ever)? Maybe a bad example, but I hope you get the principle?

Good luck!

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#18
In reply to #17

Re: Meggering Electric Motor Every Month?

03/02/2016 2:05 AM

Thanks for your advice and your guidance and this is the best advice I received. I think, I know what to do now. Basically there are really some management issues too in here that why I need to search some answer before I speak up on this matters.

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#19
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Re: Meggering Electric Motor Every Month?

03/02/2016 2:26 AM

There is only management issues.

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#20
In reply to #17

Re: Meggering Electric Motor Every Month?

03/02/2016 5:35 AM

Do you have to disconnect the supply cables to do the test? I wouldn't want to do that too often on a big motor. But when I thought about it I concluded that if the breaker is open (as it would be when working on the motor) the test can be done OK. Is that right?

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#23
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Re: Meggering Electric Motor Every Month?

03/02/2016 6:52 PM

Basically, it will depend the type of starter of the motors used. If it is a DOL starters or Star Delta starters, it can be megger directly from the terminal of the connection inside the control cabinet, with the MCCB in the OFF Position. But for soft starters, speed drives, inverters, liquid starters and auto transformer starter, (depend the type of connection), we need to dismantle the connection from the terminal at the cabinet or at the motors side to megger the motors windings otherwise, we worry it will damage the electronic parts of the electronic starters.

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#25
In reply to #23

Re: Meggering Electric Motor Every Month?

03/03/2016 2:17 AM

My sympathies for having to execute a procedure that you see as technically stupid. You are lucky to have not had this as customary.

It could be that the meggering is somebody's idea of achieving regular inspection beyond a walk-by.

If you trust your own judgement enough to know it is a complete waste of time, consider ignoring it but be ready for the possible battle.

As to your view of management, how in the world does this ridiculous idea keep cropping up?

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#30
In reply to #23

Re: Meggering Electric Motor Every Month?

03/04/2016 7:03 AM

Having read all the replies, I can only add that it is easier to go with the flow without a paddle and to try and fight against it!

It would seem to me that your boss, be he a man of lower IQ than yourself as he cannot read a drawing, is covering his own ass! He's the boss and you don't have a paddle!!

He has started a Planned Maintenance schedule, and you are expected to follow it. I suspect that he has done this because of the very attitude you are displaying.. you are fighting him! Did you object to the PM schedule in the first instance? I guess you did!

So why megger the motors? Because it MAKES you and the others stop and do a proper job of PM on ALL the equipment.

My guess is you all didn't do a good job, so now he's made it so you have to!

I think you are trying to fight him, gather info from us so you can use a bullets to shoot him down.

Be careful, he might get you first!

As for the damage to windings.... most motor insulation have a high rating and a 500v insulation tester (to use its proper name) will not damage the motor, but only make you aware, if you compare your monthly readings, as to the state of said motor.

FYI.. and you are being lazy if you go to the switchboard and the output cable of the starter and megger the motor from there... you are also testing the cables! duh!
How will you know the difference between a damaged cable and a earth fault in the motor.

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#31
In reply to #30

Re: Meggering Electric Motor Every Month?

03/05/2016 11:06 AM

"FYI.. and you are being lazy if you go to the switchboard and the output cable of the starter and megger the motor from there... you are also testing the cables! duh!

How will you know the difference between a damaged cable and a earth fault in the motor."
Actually from practical hands on experience doing that way is just fine being that if a test comes in below spec it's a good indicator that a closer inspection of both the cabling and the motor be done independently. If things test out fine then obviously both parts of that circuit are in working order.

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#32
In reply to #31

Re: Meggering Electric Motor Every Month?

03/05/2016 11:09 PM

Basically, we always megger from the cable terminal at the cabinet as to ensure that the cables to the motors are in good conditions. If any low insulation detected, then we will re megger at the motor terminal to see if the cables is low insulation or the electric motor is low insulation. In this way, we confirm the all system are in good condition.

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#33
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Re: Meggering Electric Motor Every Month?

03/06/2016 12:18 AM

So now its changed from testing the motor to testing the motor and cable!

Does your PM schedule tell you to test the motor or go to the terminal cabinet and test both cable and motor?

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#34
In reply to #33

Re: Meggering Electric Motor Every Month?

03/06/2016 6:08 AM

Speaking for myself, logically he "hits two birds with one stone" by including the cable, so if no problem is seen, he has saved time.....

Also, no need to keep opening the motor plate, he can do that from the starter, which might be a) more accessible and b) in an environmentally better place...

But (I don't know code for where he is!), adding a proper (waterproof?) socket to allow the megger to be plugged in without opening the starter panel, might help even more....

Doing them so often would bug me personally anyway.....

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#35
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Re: Meggering Electric Motor Every Month?

03/07/2016 12:19 AM

The" hit two birds" is all well and good, but I'm old school and if you are to do that, then you disconnect the cables at the point at which you want to test from.

BUT my point is while the "Moron" (his boss) as stated by the OP, has no technical knowledge (really? so how come he's the boss and not the OP?), he is getting the men to work, and check equipment. To test a motor you have to remove the terminal cover, disconnect the cables, test and then reconnect. I would bet that this has not been done and motor failures (while the OP will deny it) has been from burnt connections, etc.

On top of that the WHOLE purpose of PM is to CHECK the connections..... just meggering from the terminal strip does not constitute PM nor does it ensure that the terminal connections are tight, and we are ONLY getting one side of the story..

To me it sounds like our OP is a lazy SOB!

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#36
In reply to #35

Re: Meggering Electric Motor Every Month?

03/07/2016 3:44 AM

He actually cleared up that point, the person is NOT his boss!! Read back to his posts.....

Also, doing it as you want to will bring with it eventually possible damage to either the motor wiring or the cable wiring, depending upon which one is disconnected.

Working from the starter, with the fuses out/breaker off, it is electrically disconnected and is the safest way for the person and the equipment, (almost!) nobody can switch it on if you are right there! I would not want to have my hands in the motor when that happens.

The exposure is very high with so many tests per year to both extra damage and an accident to the personnel.

Even where with the best safety procedures are in use, there are always idiots who ignore them!!!

Also, someone may not tighten up a screw terminal properly, being distracted, causing overheating of the connection, seen it FAR too many times.....working from the starter, no need to remove cables, as they are electrically disconnected already....

I like that idea far better than yours myself, especially seen as part of testing, that is far more frequent than usually needed.....

Remember, we have not been told what the exact history of the motor failures are, so we are assuming its insulation problems because of the test, but that has, as far as I am aware, NOT been stated categorically!!!

If the colleague is an idiot, as almost stated, that may be the only test he knows of! It has not been stated that the colleague is even electrically trained!!!

It could even be an environmental problem that motor heaters might "fix" for example....there are still many possibilities.....we have simply not been told enough!!

But, I still prefer his possible method to yours. Remember its really only going to be a quick check!!! Lets make it quick!!

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#37
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Re: Meggering Electric Motor Every Month?

03/07/2016 5:01 AM

There is NEVER going to be a 'right or wrong' answer to this situation. AS "old school" having served my time in the Steelworks, PM was a way of life and we did test motors once a month, we did remove the connections, we did tighten them back up and we did "brush pluck".

It was what we were paid for. To test cables, we removed the connections and tested them if required, but usually a visual inspection was written on the PM request sheet and we followed it.

Safety.. Well there is good and bad in all situations. Permits to work are required, Lock out, tag out, and a whole bunch of other safety stuff required to cover most problems.. however as we all know there is no cure for "stupid".

Our OP has only given us his side of the story, and there is a lot of "If's" in his statements.

So I will refer to my statement that he's a lazy SOB!

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#29
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Re: Meggering Electric Motor Every Month?

03/03/2016 8:36 AM

GA and worth more than 2ยข.

You mention IR scans but there are other condition monitoring systems readily available on the market which attach to motors and other equipment. Perchance some money spent on this type of monitoring equipment would be a wise investment in the OP's case. Proper analysis of the data collected should lead to "predictive/planned" maintenance, just as long as the data is collected and used.

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#22

Re: Meggering Electric Motor Every Month?

03/02/2016 6:47 PM

Do let the forum know how the telephone discussions with the motor manufacturer went.

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#24

Re: Meggering Electric Motor Every Month?

03/02/2016 11:14 PM

Sir,

You asked one question which has not been answered. Your motor operates at 380VAC. This is the RMS (root-mean-square) voltage. Mathematically, the instantaneous peak voltage is 1.414 times this, or 537 volts. At times, during the year, I suspect the actual plant voltage may be higher (and lower) than the nominal 380 volts, which would mean the peak voltage on the motor windings could vary in a similar manner.

Therefore, megger testing the motor at 500VDC is actually putting a lower voltage on the windings than they are exposed to every second while the motor is running. For that reason, I would suggest that the 500VDC test is too low of a voltage instead of too high. The meggers I normally use have test voltage settings of 250, 500, and 1000 VDC. For a motor designed for 380 volt service, the 1000 may be too high--a 750 volt test would be suitable, but probably not available from your megger.

Now at the 500 volt level you could do a polarization index test, which will give you useful details about the winding condition. A good PM practice would be to repeat the test at the 1-month interval as requested, and then compare the results. If they are essentially the same, then space the next test to 3-months, and if essentially the same, then to 6-months.

I won't try to explain the theory, but with a VFD the actual voltage on the motor leads can be much higher than the peak voltage predicted from its RMS value. If the motor is on a VFD a 1000 volt megger test may be appropriate.

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#27
In reply to #24

Re: Meggering Electric Motor Every Month?

03/03/2016 3:56 AM

Thank for all the valuable advice and comment. I really appreciate it.

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#26

Re: Meggering Electric Motor Every Month?

03/03/2016 3:04 AM

Has the plant a history of motor failures?

If yes, then maybe keeping an eye on any changes, say for 6 moths or so, may help with future diagnosis.

If no, then prepare a simple cost analysis of what it will cost the company, using a worker and the needed down time, when say a once a year test will be surely enough....

Money talks.

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Join Date: Apr 2011
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#28

Re: Meggering Electric Motor Every Month?

03/03/2016 7:50 AM

I don't know about every month, BUT:

I would seriously run a Battery of Tests including Insulation Resistance, Polarization Index and Winding Resistance just to get a BASELINE....

Then Quarterly re-run the same tests, paying attention to how atmospheric conditions affect the tests (temp, humidity). then you can push that a little further to say 6 months or a year and stay there.

Careful Tracking/Trending may identify impending situations before they become a Shut-Down attention grabber. Last thing a plant manager needs is negative attention, especially when a Junior member of management can point a finger and say I-Told-You-So....

Try a Google Search on Non Destructive Testing of Electric Motors.

Pdma is a good place to look into as well....

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