Newbie; 3 phase, 460V, 12 wire motor; what if wrong hook up? 1

[BBN75]

Hello! I realize this is more of an engineer forum but I've looked all over trying to find an answer to what a motor would do if hooked up wrong. Hopefully some of the experts here know the answer as it's driving me crazy! This is for a motor on a fire suppression water pump at a large industrial plant. This was a complete system upgrade. I'm 99.9% sure I hooked this motor up as the attached 460//380V diagram shows. It's a 12 lead motor with the 4-7, 5-8, and 6-9 winding hookup and the L1-T1-T12, L2-T2-T10, and L3-T3-T11 motor lead connections. The motor was checked for proper rotation and I was told that it was correct. I wasn't present when this was done so I don't know if it barely turned or if it turned freely for a little while. It's in a very noisy environment and it wasn't noticed if the enclosed breaker did or didn't trip. A few days later, water was sent through the attached pump and the breaker kept tripping. I was told the hook up was looked at and it was hooked as L1-T1-T2, L2-T10-T12, and L3-T3-T11 connections. My question is; Would this have been a direct short with an accompanying BOOM if L1-T1-T2 and L2-T10-t12 connections were improperly did this way? Or, would the motor have even turned at all? Just curious as to what the motor reaction would have been if the wrong connections were made this way. I'm an industrial electrician with 29 years experience. Any and all input is greatly appreciated!

 

[jraef]

Here is what the windings look like inside of that motor. Draw out the connections you are questioning and see what you get.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[edison123]

it was hooked as L1-T1-T2, L2-T10-T12, and L3-T3-T11 connections.

It should work. In Jeff's above left image, you just switched left and bottom phases and it is still a valid delta connection.

Muthu

http://www.edison.co.in

 

[ScottyUK]

Will it?

It looks like the change in wiring effectively reversed the T1-T4-T7-T10 winding group. I'm not certain because I don't see these multi-tapped motors very often and I'm only halfway through my first coffee, but I think that the magnetics will be messed up if that winding is reversed (rather than a supply phase swap).

 

[zlatkodo]

Hi,
The motor can not work with this wiring:

L1-T1-T2, L2-T10-T12, and L3-T3-T11

Motor Repair and Winding Design

 

[dArsonval]

Tracing the incorrect connection out on a piece of paper it does not appear to be
a direct short. Each phase would still be passing through the same number of coils.

As ScottyUK suggests, the internal "magnetics" (North/South polarities of the internal coils) would have been messed up.

The motor may have turned under no load, yet it likely would have been very noisy
which if the motor is already in a loud environment could/would have gone undetected.
It's doubtful during the direction "bump" test it came up to full operating speed.

I don't believe connecting it improperly as described would have caused a "boom" as it
appears the miss-connection was found, re-connected for proper operation and the motor survived.

Not knowing what the labeling on the lead wires look like, one could see a situation
where the mistake in connecting the apparatus could have happened.

Motor leads sometimes are marked with a number actually spelling out
Eleven, Twelve, etc. which can be more helpful to an electrician in the field.
If the motor's leads were identified with numerals 11, 12 and so on... the chance
for error in connecting the machine can increase.

BBN75, if connecting this motor was possibly a mistake on your part and it's the worst thing you've ever
done in your 29-year career as an electrician, I'd say you're doing pretty good.

John

 

[zlatkodo]

Although it is obvious what the outcome will be, an analysis of such a incorrect connection has been made for the simplest case: 24 slots, 2 poles.

Motor Repairs and Winding Design

 

[dArsonval]

After further scribbling out the internal connections for the improper EXTERNAL connection,
I'll stick with ScottyUK's term of magnetics being messed up for lack of a better term.
For it appears the improper connection would still produce the proper polarity on the internal electrical poles, its just
they would not be in the correct physical location in relation to the other properly connected pole coils.

John

Post Script: zlatkodo's illustration above is also helpful

 

[edison123]

Upon review, I find I was wrong. With L1-T1-T2, L2-T10-T12, and L3-T3-T11 connections, one phase will be reversed in delta connection and thus will produce messed up magnetics, as Scotty and others have pointed out.

Sorry about my earlier wrong reply.

Muthu

http://www.edison.co.in