3ph star delta starter motor drawing high amps

[Pete999]

I understand this Pete but a motor that only draws 3A on start up doesn't need to be connected to a star delta starter to reduce starting current does it? without seeing the rating plate it's obviously small motor

What does the information relate to on the starting procedure? there must be some information regarding this. I f it's a small motor then we must ask the question why is star delta mentioned, what has happened to the rating plate?

 

[marconi]

 

[Pete999]

No not blown it out but it runs fine when connected to dol started with links in motor 3 wire.
It seems like losing a phase / low voltage high current???

If you were trying to start this motor via a star delta starter, there should be no links in at the motor terminal block, you would need 6 six wires from the starter to the motor.

 

[Rocboni]

What does the information relate to on the starting procedure? there must be some information regarding this. I f it's a small motor then we must ask the question why is star delta mentioned, what has happened to the rating plate?

This is my point, the OP has gathered components off a shelf and assembled to test either that the star delta starter is operational or that the motor is ok, but not every motor can be connected to a star delta motor as you know.

Never said was a star delta motor. It's just 2 items out of stores we were checking that are ok.

 

[Rocboni]

It really has to be the delta contactor if running fine in star, proves windings are ok, loosing a phase when delta contactor comes in.

 

[Pete999]

Never said was a star delta motor. It's just 2 items out of stores we were checking that are ok.

This is my point, the OP has gathered components off a shelf and assembled to test either that the star delta starter is operational or that the motor is ok, but not every motor can be connected to a star delta motor as you know.

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I would like to see a photo of the OPs connections if running fine in star, proves windings are ok, loosing a phase when delta contactor comes in.

It really has to be the delta contactor if running fine in star, proves windings are ok, loosing a phase when delta contactor comes in.

Can the OP provide pictures of how he has connected the motor and the starter? this may help us to get to the answer, after all it may be just a simple mistake in the final connections.

 

[marconi]

Please ignore my post #22 which has a gross wiring error in the diagram - can you spot it?

 

[Rocboni]

Could a set of the windings be connected to the same phase e.g. U1 and U2

Edit, Andy 1960 already mentioned this.

 

[ipf]

I would double check the wiring as the motor could be single phasing when it goes into delta ( same phase across both end of the one winding)

It shouldn't take 5 seconds to trip. though.
Delta contactor problem.
....then again, if there are motor links, who knows? Someone playing about with something they shouldn't be springs to mind.

 

[marconi]

Star delta starter / motor problem.
Starter starts runs as should on bench with no motor connected. Getting 230v to e on all 6 uvw 1s and uvw2. 415 u1 to v2 etc etc. But nothing 1 to 2s. As expected.
When motor connected up. (Single speed) it takes 3a in start on all . Drops into run fine but is taking 38a on all.
After 5 seconds it trips breaker.

This statement is anomalous if you consider what you would measure with a voltmeter between the terminals of the Star and the Delta diagram in my post #15.

eg for STAR - One would measure 230V from each 1 to any 2 but between any 2s would measure zero Volts.

eg for DELTA - One would measure 415V between any pair of 1s or any pair of 2s.
Between U1 - W2, V1-U2 or W1-V2 one would measure zero Volts.

 

[MJPD29]

Have you checked delta contactor? Could be a phase down

 

[Pete999]

You have removed the links when you connected the motor to the star delta contactor?

 

[Simon-0116]

Hi yes we was testing separate items out of stores. So not knowing conditions of either item.
Motor was original connected to dol and ran fine.
Obliviosly links were took out to connect to 6 wire star delta.
Thinking must be delta contactor problem.
But just curious now as someone mentioned not all 6 wire motors will run on. Motor reminders confirm motor will run in either.
Anyway items been put back on shelf for another rainy day tidy up.
Thanks for everyone's help.

 

[Pete999]

Hi yes we was testing separate items out of stores. So not knowing conditions of either item.
Motor was original connected to dol and ran fine.
Obliviosly links were took out to connect to 6 wire star delta.
Thinking must be delta contactor problem.
But just curious now as someone mentioned not all 6 wire motors will run on. Motor reminders confirm motor will run in either.
Anyway items been put back on shelf for another rainy day tidy up.
Thanks for everyone's help.

Three phase squirrel cage motors will have 6 ends at the terminal block, it's how they are connected that determines how they start and run.

 

[Bobster]

My money is it not being wired correctly.

When going into delta it's ending up running on 2 phases. Seen it dozens of times with people who don't have much experience with them.

If it runs fine in star then the motor is fine.

 

[Bobster]

This is exactly the mistake I presume it to be, should have read the comments before responding.

 

[static zap]

This is exactly the mistake I presume it to be, should have read the comments before responding.

Using the Erroneous diagram , with K3 closed .
Are we looking at a form of symmetry forcing L1 and L3
into a tussle , and possible some circulating currents in the V1 & V2 contacts of K3 ?
Not Pretty !
(Spotted quite a few suspect /tweaked diagrams -Googling!)

 

[marconi]

As static zap said - The erroneous diagram in delta mode connects the U and W windings in parallel across L1 and L3 and shorts the V winding (and connects it to L2 only at one end but no current is drawn from L2). Acting as a three similar winding transformer and Lenz's Law, the alternating magnetic fluxes around each winding must be equal in magnitude and together sum to zero. Thus the currents in each winding are the same in magnitude. The OP sort of told us this in his first post - 'taking 38A on all' - the currents being 120 electrical degrees apart).