Any Motor Men Out There?

[conny]

Don't understand the full intricacies of it but basically yes, it sends a set number of pulses through the coil and measures the time taken for each coil turn.

Col wrote:

to be fair, I would have thought that basic end to end continuity and coil to coil and coil to easth IR testing would be the first thing you did prior to the fancy "ping" testing

By the highlighted section I take it you are referring to 'meggering' the coils to earth, if so, then that is part of the 'surge' test. The Hi-Pot test is looking for earth leakage over a set period of time, i.e. 1 minute.
The surge also produces a wave form and if there are 'shorted turns' then the wave form will spike and possibly oscillate from side to side. Based on this principle if two phases are in contact, (i.e. shorted then the wave form should show one of or both of these symptoms. For some inexpilicable reason none of the testers used showed this. This is what is so confusing to everyone as we then tested a motor known to have this fault and it showed up as expected.
One thing which is puzzling me is when we do a DC machine we do whats called a 'single phase' test. In this we only use leads 1 and 2 for the surge with the feed set to position 1. After we get our 'datum' wave instead of switching to position 2 we simply swap leads 1 and 2 (coil end),over and repeat the test. If the coil is sound we will get a perfect overlay. The techies machine does this automatically instead of manually so we should have got the same result. However, on his machine there was a 20% difference when we tested each phase separately. If I get chance on Monday, (I'm on a site induction first thing), I'm going to use our machine to do the same test and see what results I get.

Crikey, this is turning into an episode and a half this! I actually thought I'd get very little response to the original post! Thank you!



Col, Just reading the preview and I think I understand now what you mean by coil to coil and coil to earth. The 'surge' test is supposed to test coil to coil, the Hi Pot does coil(s) to earth.

 

[ColJack]

well yes to all of the above, but clearly it doesn't work, as you've found a fault with a simple "megger" that your fancy equipment missed..

not trying to tell you how to do your job but adding a couple of minutes to do a basic test before you do all of the posh ones wouldn't really affect productivity that much would it and it would (as you've seen) highlight faults that your fancy equipment seems to think is ok....

I'm not trying to "diss" your expensive equipment but if it missed a short on this one, how many others have gone out with similar undetected shorts?

I understand that this could well be a truly unique occurance and has not nor ever will again happen without being detected, but who knows for sure..

 

[ColJack]

http://www.skf.com/portal/skf_bak/home/library?contentId=774398&lang=en

which ones yours? I'd like to read up on it to see if I can get my head round what it's supposed to do..

 

[conny]

Hi Col, our own one is not listed. I think its a DS212 or possibly just a D212.
The techies one, and our other branch one is the AWA612.

Good luck, without going through the steps on the actual equipment it can be a bit daunting.

 

[ColJack]

so the one you mentioned above should do IR tests as well as end to end contiuity?

does yours? or does it only do the surge and soak ( Hi-Pot ) tests?

from what I've read so far, the Hi-Pot soak test only looks for leaks to earth from the windings, not leaks to other windings?
and the surge test is only looking for shorts in an individual coil ( ie between turns of it's own winding ) ?

even in it's description of "coil resistance" testing it doesn't mention reading to the other coils just end to end..

same with the "Meg-Ohm" resistance testing, it only mentions testing to the earth ( or ground as they call it over there.. ).

since this thing is software based, if it's not told to look coil to coil while doing coil resistance or IR tests then it won't...

might be worth and e-mail to Baker asking what specifically it looks at and for..

 

[jeepmadmike]

I've not read all the posts, but could the problem be a terminal block issue?

 

[ColJack]

no, he's sorted it, it was a bust thermistor tucked back into the windings shorting them out..

 

[conny]

from what I've read so far, the Hi-Pot soak test only looks for leaks to earth from the windings, not leaks to other windings?
and the surge test is only looking for shorts in an individual coil ( ie between turns of it's own winding ) ?

Haven't read the manual yet Col but agree with what you are saying. However, if the surge is looking for shorted turns on a coil it should, in theory, pick up a short between coils as the insulation of both coils will be damaged, unless the shorted turns are in such a place to be 'exactly' the same distance along the turns of each coil. I would say this is practically nigh on impossible to achieve.

Going out soon but will look at the manual later and see if I can locate the one for our model.

EDIT: Found this referring to our model.
http://www.whitelegg.com/products/p...ndition+Monitoring+-+Preventative+Maintenance

According to the 'blurb' it does test for coil turns and phase to phase insulation faults, (which we already know). Nothing specific about a standard IR first. Will keep looking.