Electric Motor Test Set

[bill1055]

My company wishes to buy a high power electric motor test set. The major players provide a choice of regulation:SCR or variable transformer. My question for the experts, which is better? Pros and Cons?
Thank you for your input.
Bill

 

[TurbineGen]

These are very different methods of control.

The variable transformer raises/lowers the voltage and still keeps a sinusoidal waveform but at a reduced amplitude.

Is your SCR a saturable core reactor, or a silicon contolled rectifier? I'm assuming saturable core reactor. The reactor has a DC winding that carries an electrical current that saturates the iron core. This varies the impedance of the reactor thus creating a variable reactor. It works kind of like a rhoestat, but with AC impedance rather than ohmic resistance.

I believe the power factor on the SCR would be a little worse and the waveform of the AC probably would be a bit distorted, but I'm not entirely certain. The reactor has no moving parts but requires a power supply versus the variable transformer which requires a mechanical operation.

What voltage are the motors you are testing?

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[electricpete]

Do you mean a high power test stand for unloaded run?
Or ac hi-pot? Or dc? Or power factor test? Or... ?

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[bill1055]

The test sets we are looking at are 1250 kVA, 7200vac max output voltage. We would be testing up to 6000 HP no load. When the sales rep was asked about the SCR regulation, he believes it to be a reactor, but wasn't sure. He is checking with the factory. I guess the rep gets the same data sheet as the potential end user.

 

[Skogsgurra]

SCR (Silicon Controlled Rectifier) means that thyristors are used. I haven't seen transductors (saturable core reactors) in about thirty years and doubt sincerely that they will used by any supplier these days.

Also, if you need AC, it is highly unlikely that SCRs will be used since they either produce DC or low-frequency AC (cycloconverters). Or, perhaps, a "dimmer" type phase controlled output. The latter could perhaps work for no load tests, but then only as a soft starter. No speed control possible.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[TurbineGen]

If I were in your place, Bill, I would probably buy the variable transformer. As Gunnar stated, the saturable core reactor is old technology (although we still use them here). The regulation might change from motor to motor on an SCR because you are varying a voltage divider circuit by a variable resistor whereas the transformer varies the voltage directly. This is just my professional opinion. I'm interested to hear what others think.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.