Star Delta motor problem.

IrishSparks · Jun 15, 2018

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 · Jun 15, 2018

IrishSparks said:
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 · Jun 15, 2018

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

Bobster · Jun 15, 2018

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 · Jun 15, 2018

Rob said:
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 · Jun 15, 2018

IrishSparks said:
Would that not show up on a Insualtion resistance test?

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

IrishSparks · Jun 15, 2018

Rob said:
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 · Jun 15, 2018

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

IrishSparks · Jun 15, 2018

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 · Jun 15, 2018

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 · Jun 15, 2018

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 · Jun 15, 2018

IrishSparks said:
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 · Jun 15, 2018

Pete999 said:
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 · Jun 15, 2018

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 · Jun 15, 2018

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

Bobster · Jun 15, 2018

PEG said:
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

Any SD starter built or modified since 2004 needs a mechanical interlock along with an electrical interlock to the contactors to stop that from happening.

Andy-1960 · Jun 16, 2018

Rob said:
Any SD starter built or modified since 2004 needs a mechanical interlock along with an electrical interlock to the contactors to stop that from happening.

Hi Rob, which regulations are you referring to that states mechanical interlocking is mandatory?

Bobster · Jun 16, 2018

I'll dig it out when I get back to my office on monday.

It's not specifically stated in 60204-1 but a standard that it quotes. I'll dig out an post the section.

Pete999 · Jun 16, 2018

Rob said:
I'll dig it out when I get back to my office on monday.

It's not specifically stated in 60204-1 but a standard that it quotes. I'll dig out an post the section.

Thanks Rob I would be interested as well, whilst not doubting you in any way, just for my own curiosity.