Y-Delta HP rated contactor sizes

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RUWired

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I ran across a Y-Delta starter that fused together and would not release on stop signal. Looking into the cause, i would say the springs inside the contactor are weak and need replacing.

The question i have is on the size of the M 1 and M 2 contactors for the Y-start and Delta run. Each is rated at 500 HP and 580 amps. The motor is for a chiller and the HP rating is 1171 and the FLA is 1319. Is this normal, or does M1 and M2 stay energized in the run position carrying half the load each? The unit has over 400 starts on it and is about 8 years old.

Rick
 
The smallest acceptable contactor rating for a Y-Delta combination is 58% of the motor FLA. So 58% of 1319 is 765A. Neither of those contactors is properly rated. They probably over heated and caused the plastic parts to swell, then jam the armature.

I would dump the whole shebang and replace it with a solid state soft starter and bypass contactor. 1171HP is a really nasty load to start with a Y-Delta starter. The transition spike is probably killing other pieces of electrical and electronic equipment in the plant.
 
Thanks for the tips and info guys. There are two of these type starters in the building and five with the soft start. They are having problems with both mechanical types and with the load control as well. They can ramp the soft starts down to 18% and use them year round. Not so with the first two. The peak starting current for the one has been recorded at 1700 amps starting. Not good for the demand meters either.

Rick
 
Won't affect the demand meters by the way. There is a sliding demand window, probably 15 or 30 minutes, so any specific short duration peak inside of that time is not significant. Common misconception by the way.

The biggest problem with Y-Delta starters is that they are not really reducing the starting current, they just trade one big hit for two smaller ones (kind of like what the class bully used to do to me...). But if the transition happens at the wrong moment of the sine wave, something you have no control over, it can create a HUGE current spike of up to 2000% of the motor FLA. So in this case, you can theoretically see a spike of up to 26,300A! Very bad news...

There is no valid reason for choosing Y-Delta as a reduced voltage starting method over any other method available other than it technically satisfies a utility requirement in the cheapest way possible. All other aspects of it are bad bad bad.
 
Jraef said:
I would dump the whole shebang and replace it with a solid state soft starter and bypass contactor. 1171HP is a really nasty load to start with a Y-Delta starter. The transition spike is probably killing other pieces of electrical and electronic equipment in the plant.
Click to expand...

I assume the motor is the Y-Delta as well since the starter is Y-Delta..Can you just use a solid state soft starter with Y-delta motor?
 
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