Megga test motor driven of softstarter

[leitmotif]

I thought his questions were answered very well.

There are several ways to do this. Those have been mentioned and discussed well.

In all cases
NEVER
megger solid state.
ALWAYS ensure power is turned off (good way to fry megger and you) LOTO and the rest of standard electrical precautions in this era.

Dan Bentler

 

[brucechase]

Why can't you experts answer the question rather than deviate off onto your own self riteous tangents? The question clearly is to check the insulation's resistence of a large number of motors within a short amount of time. Given this information this is obviously a programmed preventaive maintenance task. As we all know prevention is better than cure and by gathering and tracking data such as this and motor currents and vibration costly down time can be prevented by effecting a repair before it is required. If there was an actual fault on any one of these motors he would obviously follow a step by step trouble shooting sequence to determine where the fault is, motor/isolator/cable etc. I enjoy reading this forum but please give our less experienced friends the actual answer(s) to the questions that they are actually asking and the simple respect that they deserve. Thankyou

Actually if you read my post, I think I explained much more than what was required. The reason to test the insulation of any system must be taken into consideration before testing can be done. We are still waiting for the OP to give more information if he wants better answers.

I completely DISAGREE with that this is obviously a programmed preventaive maintenance task. It is not obvious at all and assumptions shouldn't be made. This could be an acceptance test of a system required by a customer, or this could even be a fault finding where a system is poorly coordinated and is tripping a main breaker instead of the feeder breaker.

And if this was some kind of PM task, then low voltage and looking for 5 Megohms is useless. Any PM shold include baseline data of the system along with a Polarization Index (where the resistance increases over time) or a Dielectric Absorption Ratio (which can help filter capacitive charging currents). To perform any of these tests on a system with a soft starter still hooked up will give meaninless results. If he wanted information about PMs, then he should be asking for that information.

Thanks Peanuts
This forum seems to have sunk a bit in the last few years.

I agree. This question could have been asked much better and much more information supplied.

Which is very commonly referred to as megging a motor among electricians and other tradesmen

Yes, it is commonly referred to that, but I was just giving information from their website about their trademarked name since some people might not know http://www.biddlemegger.com/ :

The Megger trademark was first registered in May 1903 by Evershed and Vignoles and it, along with "Biddle" are jealously guarded by the company today.

By the way, I have been to many of the classes at AVO on everything from megging to DC Hipot testing and these are some great classes for anyone to go to.

 

[Peanutz]

Insulation Testing

OFGS = Oh For Goodness Sake, He clearly asks this questions - "20 motors to do and not enough time to disconnect all of them", Clearly a PM task on an operating system. All he is asking is if he will damage the VFD's / Soft Starters whilst they remain connected to the motors if he where to check them from the MCC. If he where to use a 1000V Insulation Tester the answer would be YES. If time permitted the best bet to check only the motor is to do it at the motor, if he chooses not to open 20 motor terminal boxes and check each motor in the field he should remove supply voltage from the MCC and prove disconnection, wait for capacitors in Drives to bleed off and prove 0V, disconnect each motor at Drive's output in MCC and Megger or should I say check the Insulation's Resistance of each respective motor circuit to Earth and to each other respectively, >2Mohm

For quick test any motor from 50HP to 200HP with isolation readings above 5 Mohm will be satisfactory. I have to quick inspect 20 motors and do not have time to disconnect all of them.
I know for accurate reading we set tester to 500V and take a proper readings. With my expirience if motor is bad you will see with any voltage on meggatester.

 

[leitmotif]

Many advised to disconnect motor leads at the soft start and megger motor and conductors together.
That is the way I always did it.

The Production God has two choices
1. Take the time to do the PM correctly
2. Save the time and dont do the PM - take chance on paying the bill later ie new motor / rewind and the downtime.

Dan Bentler

 

[iant]

peanutz - you have me confused
Here is the OP's original Question

What are the precaution to be taken for testing megger values of motors driven soft starter? Do i need disconnect motor supply cable from Soft starter to megga motors or can be megga tested directly on starter. I have Cutler-Hammer Softstart S801V65N3s for 50 75 and 100HP motors.

Where are PM's or 20 motors mentioned.

Guys this has been answered

 

[strujic]

Thank you all for you help in this matter, it is much appreciated.
I apologize if I caused a misunderstanding way of writing. I just wanted a simple answer to the question but the discussion is largely developed what is good for the forum because many can learn.

Peanutz
You are absolutely right and what is the closest to what I asked for.

I am working on Oil Rig with about 100 motors and have preventive maintenance plan, one step is to regular do isolation resistance test ( Meggar). We do this and this is not a problem. I have a pre shipyard / service inspection on Rig which checks all my Electrical equipment, DC and AC motors, Crane motors, generators, transformers and much more.
He won’t to checked largest motor and confirmed that all isolation readings are taken correctly. Unfortunately (but fortunately for me in normal condition because soft starter is good stuff) all this motor are supply from soft starter and MCC is small, supply cable oversized and very difficult to removed and connect back. Yes if I do regular maintenance I take time to do correctly but this is just additional test to confirm all is ok.

We are not sure we wanted to find out is any possibility to take readings with motor connected to soft starter to speed up job.
I have call help desk Cutler Hammer and answer was NO, because you can damage SCR.
Then we came up with the idea to use low voltage settings on Megger.
This is all about just wont to share some information with you.

The Megger trademark was first registered in May 1903 by Evershed and Vignoles and it, along with "Biddle" are jealously guarded by the company today.

Thank you for this information, The question is whether they are allowed to use this name in the forum or not? I don’t know and don’t wont any problems. All Electricians used this word for many many years all around the world.

 

[brucechase]

..
I am working on Oil Rig with about 100 motors and have preventive maintenance plan, one step is to regular do isolation resistance test ( Meggar). We do this and this is not a problem. I have a pre shipyard / service inspection on Rig which checks all my Electrical equipment, DC and AC motors, Crane motors, generators, transformers and much more.
He won’t to checked largest motor and confirmed that all isolation readings are taken correctly.

So obvisously this is NOT a PM, but clearly an acceptance test.

..

Thank you for this information, The question is whether they are allowed to use this name in the forum or not? I don’t know and don’t wont any problems. All Electricians used this word for many many years all around the world.

Using a tradmarked name in the forum for general discussions should be OK. I've never heard of anyone getting an order to cease the use of a name. I just included that as information for anyone who is new and didn't know where it came from.

 

[The Plc Kid]

Even with the insulation tester on low voltage you can still damage the SCR's in a softstart if you leave it connected.

If you are hell bent on replacing soft starts then go ahead.

If you need to test motor and cable condition with the softstart intact there are ways to do it and a megger is not it.

What you want is motor circuit analysis which can be done witha ll equipment connected and energized or De-Energized and is 100% non destructive as opposed to a megger or standard insulation resistance tester.

I can speak for the equipment from alltest pro and pdma as I have both and use them almost daily.

Here are links below. You can also rent this equipment if need be.


http://www.motordiagnostics.com/downloads/Troubleshooting With Motor Circuit Analysis.pdf

http://www.reliableplant.com/Read/10686/motor-circuit-analysis

http://www.pdma.com/

http://www.alltestpro.com/

 

[Calistodwt]

Peanutz wrote: Given this information this is obviously a programmed preventaive maintenance task.

Yet another assumption!
I think that too many responses on the site make too many assumptions. Rather than make assumptions the person should be asked to clarify details of what he really means to stop people jumping off on all sorts of tangents.
On a personal note I do not believe in meggering circuits with electronics in them for fear of blowing the **** out of them. One should consider very carefully the implications before applying the meeger to such circuits. I have seen to many incidents of electronic circuits misteriously packing up in construction projects and nobody has done anything!!