Star Delta

DEAR,

LOOKS STARTING TORQUE IS LESS IN STAR OPERATION.

JUST CHECK THE STAR CONTACTOR'S POWER CONTACTS. ALL THE 3 PHASE CONTACTS MAY NOT BE CLOSING PROPERLY.\]\

WHAT IS THE TIMER SETTING ? IS IT 6 SEC. ?

REGARDS

Confirm your unloader is functioning correctly.

I agree to what Codemaster and others mentioned. Generally the load like compressor is not suggested to start with star-delta starting. With star connection, the motor is developing 1/3^rd of the starting torque and it is less than the load torque that is required to start the compressor. So, the motor stalls with star connection. To confirm it, I would suggest you to detach the motor from the load and start with the star-delta starting. If the motor runs with star at this condition, it is confirmed that the motor is stalled with star connection with the load. Then go for the DOL starting or use Soft Starter instead of star-delta.

- MS

I presume that this compressor has operated in the past ok, and has started normally.If this is the case, I would suspect that there has been a failure of 1 of the contacts on the star contactor. A simple test to find this would be to use a clip on ammeter and measure the current on each of the phases when in the star startup mode. If one of the phases draws little current, then you have a problem with the star contactor circuit or contactor. The star contactor is usally the contactor that has the most work to do, even though it is in operation for a small amount of time. It has to start the motor, from 0-60% full speed, this is when the high currents exist, it gets the most load and is usally rated at a lesser current rating than the other contactors in the circuit.

I would also advise if this is the problem to replace the main and delta contactors, sell up and increase your profit!!!!!

Because they will cause problems, possibly in the future.

May the force be with you

Cheers

Joe

Hi Brich,

Never thought of this idea for testing the polarity of the windings, it a good idea.

You have my vote.

Cheers

Joe

you;re welcome... I've been doing it for way to many years than I care to remember!

Don't know if the OP has sorted the problem yet, but your comment in #5 is a good one. If it's worked OK in the past and now doesn't, something has gone wrong and needs fixing. If it's a new installation more likely there's a basic problem. Wasn't clear from the original.

Cheers........Codey

Nor was I,

I have had problems with star delta starters in the past, most of the time it has been due to an underrated star contactor. Electricians sometimes forget about the current on the star contactor when starting and under-rate the star contactor. I suppose we will have to wait until the person that posted the question, submits a reply wont we.

Cheers

Joe

Hi

ain't it great one someone says "Thanks".. More please