Looking for variable frequency power supply.

[PnCTech44]

I'm looking for a Variable Frequency / Variable Voltage Power Supply to test an old electromechanical relay used in a generator protection scheme. The relay requires voltages between 0-69VAC at 0-60Hz. Since the relay is an old solenoid type electromechanical relay has a large coil and armature that requires a significant VA to operate. I try testing the relay with a wave(function) generator type with no success. The supply did not have enough VA output to operator the relay. Anyone have any suggestions for a variable frequency power supply for this application. A fairly light and portable unit would be preferable due to the mobile nature of the testing.

 

[davidbeach]

That's what relay test sets are for. Some of them can even be carried without too much trouble.

 

[PnCTech44]

I know, if the solution were that easy I wouldn't be asking for one on here. We have many modern fault simulators in our arsenal however none of them are able to supply voltages at frequencies that are below 40Hz. The relay I am testing requires frequencies from around 5Hz to 60Hz.

 

[slavag]

Hi.
If standard relays testers are not applicable.
Maybe ( VFD duys, please don't LOL on me ) you can choice/use some small VFD for small motors with voltage output from 0 up to .. and freq. output from 0 up to 500Hz.
Regards.
Slava

 

[davidbeach]

VFD probably might not work (although you have a better chance with electromechanical than anything newer) as it puts out something at a far higher frequency that the windings of a motor interpret as the desired lower frequency, but far more zero crossings than the "output" frequency would actually have.

Always good to state that you've tried the obvious and why it didn't work for you. You could well be surprised how often the obvious hasn't been tried.

 

[ScottyUK]

A benchtop signal generator feeding a large audio amplifier will produce that output voltage directly. You can almost certainly use a smaller amplifier with a step-up transformer to produce the voltage you require. Watch the Volt/Hz ratio of the transformer as you drop in frequency otherwise it will saturate and may kill your amp.

Pacific Power have an excellent range of variable frequency, variable voltage sources. Their products occasionally pop up on ebay, and some of the larger rental outfits have the smaller types on their books.

http://www.pacificpower.com/products/index.html

You'll probably find it is less trouble to rent a larger relay test set.


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If we learn from our mistakes I'm getting a great education!

 

[DTR2011]

Sometimes, even with the older relay test equipment, you can use the transient mode, which kind of turns the test set into a similar set up as audio amplifier (COMTRADE/EMTP) type tests. Then you can generally playback the transient files, which include DC offset, etc.

I think the 40 HZ is based on a limitation of older equipments that have still a transformer based design. Most modern test sets have MOSFET amplifiers, although there are limitations on the available output powers.

As you mentioned this was generator protection, I wonder why it is needed to go much below 40Hz, especially for e/m technology - unless I miss something in your application.

 

[Skogsgurra]

Love my old faithful Kepco Power amplifier. I feed it a little FG signal and it outputs Huge A and V! Look for Kepco Bipolar Power Op Amps on eBay.

Gunnar Englund

http://www.gke.org

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