msoucy

I have two, 480V, Three-Phase, Blower motors. These motors actually blow in line with each other in a vent duct on a Machine.

Yesterday the operators indicated they had a problem. The motors tripped.

When the terminal box was opened there was a lug on the winding blown out. The other terminations were very hot, and found to be charred upon oppening up the splicing tape.
(very good amount of tape, good protection)

These terminations were done with ring terminals, washers, screws, and nuts.

The terminations that were taken apart has good solid connections. I cannot say how the one that blew out was.

During the investigation, the 2nd blower motor was opened up. These terminations looked the same way. Very hot, and charred.
These were looked at and after the tape was removed the connections were very tight. When taking them apart, the metal surface between the lugs was very shiny, and we could see there was no arcing yet the terminals were all black and seemed to be covered in a carbon like substance.

The motor has a rating of 36FLA, they were running at around 30A.
The wire to the motor from the bucket was #8-AWG. (short run lenght)
The wiring in the motor terminal box was #10-AWG.

These motors are fed from seperate buckets.
The terminations were inspected by several individuals to ensure that the proper configuration/connections were made. (High Voltage Wye)
4 to 7, 5 to 8, 6 to 9, and L1 to 1, L2 to 2, L3 to 3

Can anyone let me know how the one log on one motor blew out?
Can anyone let me know how the terminals on the motor got so hot even on the motor with all good connections.

I was wondering if there was something common to both motor in the MCC, while they are in two seperate buckets.

I am not looking for a concrete answer, only possible scenarios

drsparky

How is power quality?

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Mike_586

Harmonic distortion could cause that.

paul d.

i seem to recollect a blower motor getting very hot because some one/thing had closed a damper so the air had no where to go causing a back pressure. the duct itself was about to blow apart and was splitting welded seams. ???????????? ( good luck on you're problem and let us know what you find. )

brian john

Highly unlikely .

But what does cause this is

Poor quality workmanship, poor choice of connectors and that's 99.9 percent the truth.

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MDShunk

Mic the crimp dimensions and check against manufacturer's spec. Visually examine crimp pattern and check against manufacturer's spec'd crimping die for that terminal (diamond vs round crimp, one or two crimps, serrations, etc.) If the rings were tight to each other, I'd almost bet money that something was amiss with the crimp. Wrong crimp tooling for the terminal, wrong terminal for the type/gauge of wire, incomplete or improper crimp dimension, wrong terminal for the current, etc.

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Mike_586

While I agree that the vast majority of the time problems are poor workmanship or defective equipment. From what the OP is saying, all the connections seem to have been done properly and appear to be tight, but are showing unexplained signs of excessive heat and its sounds similar to something I ran into in the past.

The first time I ran into an extreme case of bad harmonics, the building displayed a lot of tell tale characteristics pointing to it though I didn't realize it. I really knew very little about the causes and effects at the time. Actually its still something I rarely have to think about or ever deal with, so my knowledge on the subject is a little sparse.

The main lobby seemed to devour lamps, the neutrals were carrying 40+ amps even though phases were pretty well balanced, there were a lot of nuisance tripping issues and a lot of equipment failures showing similar (to the OP's post) unexplainable signs of heat damage, the list goes on.

After having a power quality survey done, and thermal images of panels and other equipment taken, a few things turned up, extreme harmonic distortion being one of the biggest problems. I never got the chance to get any further into it then that, one day the customer was hounding us to schedule a meeting to consult with the guys who did the power quality survey and come up with a plan of action ASAP, the next the tech bubble burst and the whole facility got mothballed and we were told to forget about it *shrugs*

MDShunk

It has nothing to do with harmonic current or the failure would not be localized to inside the splice wrap.

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wildleg

I agree with this 100%

Also, is there something you aren't telling us ? (aluminum conductors with terminals that aren't AL/CU , or AL to CU connections ?

did you measure the resistance from conductor to conductor through the connection points ?

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Richard Rowe

I think you will need more information to find the problem. When you replace the motors you will run checks on your power amps pulled on phases voltage drop and any hot points at your connections. Hopefully you will find the problem fast.

micromind

As stated above, I'd bet on the crimp terminals on the #8s. Likely the wrong tool was used, or maybe it wasn't crimped hard enough, or even too hard.

It's rare to have a crimp terminal fail, but sometimes they do.

How much wire was wadded up in the terminal box? Excess wire = excess heat. It pays to keep leads reasonably short.

Were the terminals bolted together back to back? Or was there a washer between them?

Rob

MDShunk

Anybody double-checked that these motors have the right overloads or overload settings in the controller? I find too many motor melt-downs that were more or less doomed from the get-go by oversized overloads installed or someone turning the overload dial way up to keep it running. This surely has nothing to do with your present described symptoms, but part of "leaving no stone unturned" when sorting out these sorts of problems, you owe to to yourself to double-check this type of thing before you put a new motor into service.

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brian john

It is really not rare to have crimps fail, I can post IR pictures of failed factory and field crimps.

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msoucy

These terminals are rated for 50A. They are using the high temperature ring terminals.
My initial worry was that they used the type intended for thermocouples or Nychrome wire.
It was determined that they used the standard High temp Ringe terminals that are intended for general wiring of motors and equipment in High temp areas. The motor is not in a high temperature application.

The stack up was correct. The terminals were back to back and when taking these apart they were very clean where the contact was made. The areas where metal to metal contact was made were very clean. When I took them apart i did expect to see loose connections but found that they were very tight.

Before loosening the screw the whole assembly was black and had a carbon-like dusty, crusty residue covering it.
(? was this just the adhesive of the fiberglass tape that was applied before the splicing tape? {is this even the proper application of these tapes?})

One thing of note was that the terminals that were on the wiring from the bucket (L1-1, L2-2, L3-3) Were fine. They seemed to have not gotten nearly as hot as the winding interconnects. (4-7, 5-8, 6-9)
This makes me want to second guess and wonder if these were miswired?
They were, however, inspected by more than a few electricians and engineers before they were unwired.

Richard Rowe

How long were the motors in service before the went out? You may have said how long but I missed it if you did. What is the hp of the motors?

msoucy

30HP, 230/480 VAC, 3-Ph, 72/36 FLA, 1770 RPM, 60 Hz, Ser 1.15, Code-H, Des-B, Class-F, EFF-94.1, PF-83, 40C Amb.

MDShunk

My money is still on improper crimp tooling or an improperly applied crimp. What was the manufacturer and part number of the ring terminal and what model crimper was used to apply it?

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John Valdes

If the air has no where to go the motor does no work. No work means low current. A closed damper on the suction side or the pressure side would decrease current.

Loose Neutral

What about loss of a phase? That will burn up a motor and since you have the same problem with both motors fed out of separate buckets? As far as the fiberglass tape I have never seen that although some put the first couple wraps on backwards so they can break the splice easier not as much mess. Usually if the motor is swapped out frequently.

John Valdes

Phase loss. Yes, it's very possible. This needs to checked at the buckets and any other place the motor conductors terminate. I have found many high resistance connections in my career. They are not always visible, so you will need to shut down this particular section and go through everything. Do you guys ever have have thermal imaging performed. It's a great way to find problems and also to prevent them.

Years ago the fiberglass tape ( varnish cambric?) had no sticky side. It was hard to work with and now with the stickum on one side it is almost impossible to remove. I am one who wraps the sticky side up for the first couple layers then roll the tape over and finish with the sticky side down. It does make for easier removal. I very rarely use it anymore as the new connectors have almost made this tape obsolete along with friction tape. The only people using alot of these tapes are the POCO's. They put friction tape on everything it seems.