# Motor re-winds



## davepros (Jan 24, 2009)

I have recently had a number of pumps back from repair that have displayed some odd characteristics, when running they change over from star to delta OK but pull a much lower current than usual, they still seem to run OK and pump but will burn out after a few weeks. 

The motors are all 3 phase 415v star/delta. I have check all the controls and tried various different wiring configurations (as you start to think you have done something wrong) but can only see it as a fault with motor, the re-winders say there is nothing wrong. Any one with more of an idea about rewinds may be able to shed some light on this.


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## 5volts (Jan 11, 2008)

davepros said:


> I have recently had a number of pumps back from repair that have displayed some odd characteristics, when running they change over from star to delta OK but pull a much lower current than usual, they still seem to run OK and pump but will burn out after a few weeks.
> 
> The motors are all 3 phase 415v star/delta. I have check all the controls and tried various different wiring configurations (as you start to think you have done something wrong) but can only see it as a fault with motor, the re-winders say there is nothing wrong. Any one with more of an idea about rewinds may be able to shed some light on this.


 
Are you using closed transition or open transition?


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## davepros (Jan 24, 2009)

I have no idea what you mean. Can you please explain, It may be that we call it somthing diffrent in the UK.


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## davepros (Jan 24, 2009)

Soory I know what you mean now, Open transition (three contactors).


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## 5volts (Jan 11, 2008)

davepros said:


> Soory I know what you mean now, Open transition (three contactors).


A closed transition would be a better way to go because it limits current, through resistors during the transition. 

It seems you are having trouble with your motor windings the open transition may be too tough for your motor to handle, sometimes the transiton from wye to delta on an open transion may be out of phase at the point of closure and that can result in electrical and mechanical damage. Its also very hard on motor windings contacts etc..


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## nick (Feb 14, 2008)

Well i agree with p logix on his post . Question when you say lower current now ? is this running full or is this during starting and transfer to wye /delta does it trip overloads or does motor just burn out . how long after rewind do they last ? are these motors fed with 6 conductors leads from starter or just three ? just wondering about connections . who makes motors type ? best to ya :huh:


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## 5volts (Jan 11, 2008)

nick said:


> Well i agree with p logix on his post . Question when you say lower current now ? is this running full or is this during starting and transfer to wye /delta :huh:


Sorry if I didn't make my post clear enough the resistors are only in the circuit for a fraction of a second, and thats why they are added into the circuit for is to reduce the magnitude of the switching transients. 

Lower current? Definetly during the transfer.This has no effect running full. 

On a open transition you may be o.k. every once in a while if your are in phase. If you are 180 degrees out of phase thats when you can have some problems.

Are the motor overloads sized properly? It should be kicking out. Did you perform a voltage drop test, check all contacts? 

I agree with you nick the overloads should be kicking out.


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## davepros (Jan 24, 2009)

These motors have all worked well until they have come back from a rewind. They are normally the same motor refitted or a direct like for like replacement as we have a large number or the same pumps so you can't guarantee the same motor being fitted but were possible it is. What I'm trying to get across is it should not mater about voltage drop/open closed transition or the overloads as I can fit a different same spec motor to the control panel and it will work fine. What I need is some one who knows more about the internal winding of motors who may now causes this.

The motors all have 6 connections, as they are submersible pumps it is not ideal to start looking at the internal connections as they are warrantied against water ingress.
The low running current is observed after the change over from star to delta and continues to be low wile the motor is running. There is nothing wrong with the control circuit it will run another pump with no problems.


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## John Valdes (May 17, 2007)

Take a resistance reading on a known good motor. Note the ambient temperature. When the motor comes back from rewind the resistance should be the same at that temperature.
This will verify that the winder did not add or delete resistance by the amount of turns he installed.
Many motor shops just count the turns and verify the wire size and rewind it exactly as it is. The good shops check the existing winding vs the data available through the EASA data base, or manufacturer standards. If this is done several times with mistakes they add up and can cause problems. Ask the repair facility if they are winding to data or just copying what came in. 

Soft starts are helping greatly in motor life, and in some cases are less expensive than starters.


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