Refurb of 4kv motor with good global vpi winding - opinions on need for dip and bake? 4

[electricpete]

My personal approach (spec) for refurbishment of VPI windings is clean/bake/test but no dip and bake unless there’s some good reason.

The reason for my approach: about 20 years ago a shop did a dip and bake on one of our motors and the winding temperature went up. Later I saw the cooling channel dimensions were reduced. There may have been a thermal insulation layer as well. Perhaps they did a particularly bad job of dip and bake, but my thought is why take the chance if it doesn’t add any value. On a good global vpi winding, I don’t see any value added from to dip and bake unless there is a particular reason.

So…. I’m using a new repair shop that I’ve never worked with before. We sent them our motor and my expectations on dip and bake were not clear initially. They disassembled and did as-found inspection/testing and submitted an updated proposal for refurbishment with some additional cost for a variety of added items. Their proposal included dip and bake (it was in their initial proposal too, but this is the first time that it caught my attention). I called up the author of the proposal to discuss this and a few other things in the quote. Here's how that went.
[ul]
[li]Me: I prefer not to dip and bake this motor. Why are you recommending it?[/li]
[li]Him: To replenish the insulation.[/li]
[li]Me: It's just a refurbishment, what do we need to replenish? [/li]
[li]Him: It makes the insulation more reliable[/li]
[li]Me: This is a global vpi insulation, what does dip and bake accomplish?[/li]
[li]Him: It’s an industry standard, we’ve done it that way for 32 years on every motor we do[/li]
[li]Me: Is there anything special you saw on inspection of the winding that leads you to think this particular motor needs a dip and bake? Any signs of looseness or bad vpi?[/li]
[li]Him: No sir.[/li]
[li]Me: Then I don’t want dip and bake.[/li]
[li]Him: Then we won’t warranty it.[/li]
[li]Me: You were going to warranty someone else's winding after a refurb?[/li]
[li]Him: No, but what I mean is you're asking for trouble by not dipping and baking. You’ll be on your own.[/li]
[li]Me (as politely as possible): Who is the go-to technical expert on winding at your shop?[/li]
[li]Him: That’d be me. I’m the owner.[/li]
[/ul]

You may have guessed that I'm inclined to judge this guy's technical judgement harshly based on this conversation. Do you think I'm way off base in that judgement of him?
(as far as customer relations and not having a spec/proposal agreed ahead of time, I'll take some blame on that)

 

[waross]

It is unfortunate that you did not share your history with dip and bake with the shop owner.
But, no judgment, There is probably an hard to explain reason why not.
But, it's too bad that you didn't ask if the warranty included corrective action at the expense of the shop if the motor ran hotter due to partially restricted air passages.
Don't take this as criticism, Pete.
Over the years I have come to respect your judgment on motor issues.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[electricpete]

Yes I understand where you're coming from in terms of communication. Each party should state their objections and concerns and give the other side a chance to address them.

In terms of defending my own self to you on the flow of this conversation, I have to say it was a tense conversation from the very beginning due to a misunderstanding on whether or not our original spec had been sent to them. It may have been productive to explore the subject more fully but that didn't happen. Arguably it would be more productive to call him back and discuss with him more than discuss it here, but those two avenues aren't mutually exclusive. I'm sure he'd tell me what a high quality job they'd do in their dip and bake with zero chance for problems.

Since it is the subject of this thread I'll voice the opinion about the limited benefit for VPI windings since during initial VPI those resins penetrate deeply and fill nooks and crannies. There's no way any subsequent dip and bake after curing would put any resin anywhere useful unless the original vpi was not done well or it is somehow significantly degraded (which should be apparent).

I don't say it's necessarily a slam dunk conclusion one way or the other. There may be room for debate. As customer it is my right to follow my opinion. But this guy made it sound like there was only one answer and no room for customer preferences (he used the words "industry standard"). I'll be interested to hear what fraction of responders think it's necessary or prudent to dip and bake a good vpi winding during refurbishment.

 

[waross]

I have to say it was a tense conversation

I suspected as much.

In terms of defending my own self to you on the flow of this conversation,

No need to defend. I know what it is like when something that could be said, cannot be said due to "a tense conversation".
It sounds as if you are on track.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[edison123]

Dip and bake for a previously dipped and baked motor does diddlysquat in making the insulation 'reliable' and only possibly makes it worse by blocking the vents as you noted.

And no, a simple overhaul aka refurbishment won't get a warranty from me either.

Muthu

http://www.edison.co.in

 

[electricpete]

Thanks Kumar. It's good to know I'm not out in left field on this one.

And no, a simple overhaul aka refurbishment won't get a warranty from me either.

Exactly, and even if refurbisher did provide some type of "warranty", it would cover workmanship on the things they did but there's now way it would ever cover winding problem on a winding that was done by someone else!

So he made an empty meaningless warranty threat....
Either he is clueless, or else he thought I was clueless and wouldn't know the difference.

Oh well, we have some scope issues to work through and a motor to refurbish. Maybe my opinion of him will change by the time we get through all that (but he's not starting out on a good foot!)

 

[TugboatEng]

It's not always best to state all concerns with vendors immediately as they will often reply with answers but not solutions.

As a customer that most electric shops reject because my motors aren't valuable enough for their time, is there a way to quantify the effect of a dip and bake? For our little stuff a megohm reading can quantify the insulation quality of a motor. I know that doesn't apply to megavolt motors but surely the OEM has some list of parameters the motor must comply to before being released to a customer. The repair shop won't warranty a motor that meets OEM specifications?

 

[electricpete]

The repair shop won't warranty a motor that meets OEM specifications?

I'm not bothered by the fact that the winding will not be covered by warranty after a motor refurb which does not include a rewind.

It's typical for a rewind vendor to warranty their rewind.

But when a refurbishment is done without a rewind, the previous winding is reused (after steam clean, bake, and test).

So no shop is going to warranty another shop's winding. It doesn't matter what testing they do, there is still the underlying materials/process/workmanship of the winding that they can't vouch for. The testing is certainly an important part of providing soome degree of assurance to the customer, but that's different than warranty

If we did experience a winding problem and I could somehow trace it back to workmanship during refurb (for example winding damage due to careless handling), then in that case there might be a valid claim about refurb shop liability.

But anything protected by dip and bake simply does not fall in that category of refurb shop workmanship. Dip and bake is apparently intended to protect or "replenish" the insulation of the winding, but it's certainly not intended to protect against refurb shop errors.

So his threat that skipping dip/bake would affect the refurb warranty on a winding done by someone else.... that was just an empty threat (and he pretty much admitted that when I called him on it). Again I'm not 100% sure if he didn't realize that at the time.... or maybe he realized it and thought I wouldn't.

 

[edison123]

pete

My convo usually goes the other way around

Cl: We want a bake and dip.
Me: It is pointless and will worsen cooling and will trap any dust/debris in inaccessible places (there are many) forever.
Cl: We still want it.
Me: Will cost you more.
Cl: We want warranty.
Me: No, sorry can't do. We warranty only full rewinds, not overhauls/part repairs of someone else's winding (or even our own winding after a few years of service). Hell, a brand new motor gets not more than 12 months warranty and you are paying me only a fraction of a new motor cost for an overhaul and still expect a warranty?

My definition of refurbishment is entirely different which would include a full rewind with warranty.

Tugboat - Can't expect the warranty for the engine when you send your car for a lube change or for a routine service. I too avoid small motors rewinds since a) not much value added to my bottom line b) they are most abused in service with little or poor maintenance at their end and the client will still blame me for any failures. Just not worth it.




Muthu

http://www.edison.co.in

 

[Gr8blu]

E-Pete: Dip and bake causes two problems from the shop perspective. The first one is as you described - the "partial or fully blocked" duct leading to increased thermal stress on the winding insulation. The second one is even more of an issue for the shop: they don't want to contaminate their (very expensive) consumable product with whatever debris may be floating around on your equipment. Think about it this way: the shop resin tank may hold a few thousand gallons of resin, which equates to a several HUNDRED thousand dollar investment. Getting even a bit of oil or other debris into the resin system voids the whole shebang, requiring a clean out of the existing (now contaminated) resin and replacement with new.

Shop warranty is typically worded to only cover what the shop actually touched. So a refurbish / recondition that does not physically change out the coils means no extended warranty on the winding - because there was nothing done to extend the life on the insulation (i.e., exchange it for "new").

Converting energy to motion for more than half a century

 

[electricpete]

Thanks Gr8blue!

With your input and edison's input, my suspicions are reinforced, this guy was just waaaay off base to push so hard on dip and bake.

And my thoughts on warranty are exactly the same as both of yours. It was a silly empty threat for him to imply there would be a warranty impact from a decision not to dip and bake someone else's winding. I spent a lot of words talking about warranty above only to respond to tugboat's question.

You bring up an interesting point about the contaminating the resin and I've certainly heard that before that some shops refuse to put anything other than newly rewound stator into their vpi resin. I don't really care if they incur a cost in mismanaging their resin but I do care about the quality of their work on rewinds (even though we're not doing a rewind right now). In my mind that would be another strike against them if the resin they propose to dip and bake with is the same pool of resin as used for their vpi (because it would invariably put pressure on them to tolerate less than optimal resin condition for their vpi process). I didn't think to ask him about that, but that's definitely something I'll put on my list to ask next time I talk to him.

 

[edison123]

Toshiba did a big study on how VPI resin gets contaminated and degraded after each machine dip and how the disposal of the expired resin is an environmental nightmare.

I am not a fan of VPI (despite all the hype around it) and dip & bake. Resin rich and trickle impregnation gets you fresh, quality resin every single time.

Muthu

http://www.edison.co.in

 

[waross]

trickle impregnation

An octogenarian with a very much younger wife?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Gr8blu]

Back to E-Pete from Aug 30: "over-dip and bake" would get really expensive really fast. Every (reputable) shop would be adding the cost to refill their resin reservoir just in case of contamination. So how would that look? A "refurb with dip and bake" coming in just shy of $1 million ... instead of the expected 30k,

Converting energy to motion for more than half a century