Star Delta motor problem.

[IrishSparks]

So I have a 55kw Star Delta starting motor. The motor was moved about 10feet from original position so I had to put new cabling in from Isolator to Motor. That's all was changed.
When I went to start it it blew a fuse when kicking into Delta.
Changed fuse and it happened again only this time it was a different phase fuse blew.
Have checked operation of star Delta contactors with no load and they are working. Have also done an insualtion resistance test on motor windings and new cables and all ok.
Is it possible when it's going into Delta that it's also going into reverse?
Anyone any ideas of what else it could be?

 

[Pete999]

So I have a 55kw Star Delta starting motor. The motor was moved about 10feet from original position so I had to put new cabling in from Isolator to Motor. That's all was changed.
When I went to start it it blew a fuse when kicking into Delta.
Changed fuse and it happened again only this time it was a different phase fuse blew.
Have checked operation of star Delta contactors with no load and they are working. Have also done an insualtion resistance test on motor windings and new cables and all ok.
Is it possible when it's going into Delta that it's also going into reverse?
Anyone any ideas of what else it could be?

Could be you have reconnected the Motor incorrectly, can you post a picture or a drawing of how you have connected the Motor? And the Starter.

 

[telectrix]

a double check of phase rotation on all connections would be my first shot.

 

[Bobster]

You're shorting a phase through one of the winding's.

So when it changes to delta the motor is running on 2 phases.

Trace it out.

Edit

So for example L1 - U1 - U2 - L1 rather than L1 - U1 - U2 - L2

U1 and U2 being the start and end of a winding. L1 & L2 being phases.

 

[IrishSparks]

You're shorting a phase through one of the winding's.

So when it changes to delta the motor is running on 2 phases.

Trace it out.

Edit

So for example L1 - U1 - U2 - L1 rather than L1 - U1 - U2 - L2

U1 and U2 being the start and end of a winding. L1 & L2 being phases.

Would that not show up on a Insualtion resistance test?

 

[Bobster]

Would that not show up on a Insualtion resistance test?

Draw it out. You'll see that it wouldn't.

 

[IrishSparks]

Draw it out. You'll see that it wouldn't.

I wasn't doubting you I was only asking!
I'll check out what you said. Thanks.

 

[Bobster]

Just figured it would be easier to understand with a drawing. Wasn't having a dig.

 

[IrishSparks]

Ok I switched two phases and now it's no longer blowing a fuse when switching to Delta but it's just cutting out /motor stopping when it switches to Delta.

 

[Andy-1960]

It sounds like you now have the same phase on the end of all three sets of windings, i.e L1 is across u1 & u2, L2 is across v1 & v2 and L3 is across W1 & W2.
As stated by Rob, starting at the starter, draw out the wiring all the way thru to the motor, then if you cannot spot what is worng post your sketch.

 

[IrishSparks]

Have it working now lads thank you all for your help. I don't work on motors that often so today was certainly a learning experience. Thanks again.

 

[Pete999]

Have it working now lads thank you all for your help. I don't work on motors that often so today was certainly a learning experience. Thanks again.

What was the problem?

 

[IrishSparks]

What was the problem?

As Rob and Andy said above I had the phases mixed up on the windings. Drew it out as he suggested and it made more sense.

 

[Bobster]

Glad you've got it sorted. The amount of trainees I've had make the same mistake first time I let them loose on one.

Don't get much call for star delta starters anymore with soft starts an vsds becoming cheaper.

 

[PEG]

Usually,someone decides to manually operate one of the contactors,whilst the other is energised,to "see if it changes the outcome" .....eye protection,obligatory