Reduced Voltage Auto Transformer Starter Disaster 1

[mjd2000]

Recently an Owner had installed a Reduced Voltage Auto Transformer Starter. Well after it was put into service allegedly something within the starter failed. The alleged failure was catastrophic and may require a complete and total replacement of the starter along with surrounding equipment. The alleged failure occurred well after the motor was running uninterrupted for a few hours.

1. How often does failure occur?
2. Is there any good reading about Reduced Voltage Auto Transformer Starter failures?
3. Things to stay away from when selecting a new starter? (Plastics/Vacuum tubes etc…)
4. Any idea what would make it fail?
5. Any ideas how to determine the failure by inspection?
6. Should anything be taken out of the cabinet and analyzed in detail?
7. Any other considerations will be appreciated.
8. I will do my best to answer any questions you ask.
9. Anyone have a Scope of Work for a forensics team to complete a proper investigation? How much would forensics typically cost?


Thanks in advance.

 

[ScottyUK]

A little more detail on the nautre of the catastrophic fault would be useful. There are so many possibilities: fire, arcing fault, explosion, which components were affected, what voltage... I could continue the list, but you get the picture!

Any chance of a photograph or two?


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Sometimes I only open my mouth to swap feet...

 

[controlnovice]

Also, what type of design is this?

Some put the autotransformer on the cables to the motor, some put the autotransformer on the motor neutral.

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This is normally the space where people post something insightful.

 

[mjd2000]

OK, let me gather some details.
(Let's see if I can keep up with you guys.)

 

[jraef]

Actually, if as you say, the motor was RUNNING uninterrupted for a period of hours when the failure occurred, the Autotransformer itself or the configuration was not the issue. Once the starter has transitioned into the Run mode, the transformer and the associated contactors involved in starting are (or should be) out of the circuit. That leaves 2 chief possibilities for investigation of the starter itself.

1) The Run contactor failed. This could of course be any number of issues in and of itself, such as a failure of the contacts, coil, armature, control circuit, even the overload relay.

2) Something in your control circuit caused a rapid On-Off cycling of the RVAT starter. This is a remotely possible if not unlikely, for this single reason. The transformer itself is rated for a very limited duty cycle, they get hot when dropping the voltage to the motor. For this reason, they all have (or should have) a thermal cutout device on the transformer core that will open up the control circuit if you attempt to start too often and over heat it. IF however that thermal device failed AND your control circuit "chattered", you could have had a rapid cycling of the RVAT starter that would have been destructive in a matter of moments.

There is theoretically a possibility that one of the Start mode components failed and stayed in the circuit, but that would cause a failure more rapidly than a couple of hours.

The other possibility is that the failure was not in the starter itself, but in the cables, which then led to the starter failure. I have seen that more often than complete starter failures.

Lastly; Lightning. Very very bad for any starter!

Pictures would be fantastic. If you don't know how, read this: faq238-1161

My suggestion would be to replace it with a Solid State starter. They are less expensive and smaller than RVATs and not as problematic (if done right).

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[mjd2000]

I have so much to share, however I need to postpone due to legal reasons.

 

[jraef]

THAT sound ominous!

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376