400 Hz transformer 1

[steve96]

Can I use a 60 Hz dry type transformer for 400 Hz power? What if I derate the transformers? What would happen?
We are a testing lab that typically sets up equipment for a week and monitors operation continuously.

 

[Skogsgurra]

You will probably have a lot higher impedance if you try to run it on 400 Hz. Leakage inductance is constant -> higher impedance at higher frequency. That means bad voltage regulation and changing voltage when load changes.

Flux will be about 1/7th of nominal flux and since iron losses are proportional to flux squared, they will be quite low - despite the fact that eddy currents increase with flux suared. The reason is that the hysterisis losses will be lower so that the total iron losses go down.

Copper losses can go up if this is a large transformer (skin effect is noticable at 400 Hz and large counductors).

What power levels are we talking about?

Gunnar Englund

http://www.gke.org

 

[steve96]

Thanks. I have a 125 KVA 400 Hz motor generator that puts out 350 to 480 volts (adjustable) phase to phase wye. Below 300 volts the voltage regulation gets bad (accordaing to Kato). From skogsgurra it seems I'd have the same problem with my existing 60 Hz transformers. Most applications would probably be between 3 and 30 kW and need 120 volt delta. My first job is actually 1 kW and needs 120/208 wye.

 

[Skogsgurra]

I wouldn't expect any voltage problems if you keep load as low as that. And no heat problems either. How big is the transformer? Primary volts? Nominal power?

Gunnar Englund

http://www.gke.org

 

[steve96]

I have 3 single phase 1KVA 480/240 volt primary to 240/120 volt secondary transformers that would be easy to use 480 delta to 120/208 wye. I also have a 75 KVA 3 phase transformer that works 480 delta to 120/208 wye.

Steve

 

[waross]

The current rating of your transformers will be the same or a little less if skin effect becomes a factor.
You can use voltages of 6 or 7 times rated voltage without saturation if the insulation will withstand the higher voltage.
However you may not be able to find standard transformers at usable voltages.
A 480:120 volt transformer may be replaced by a 80:20 volt transformer if you can find one.
respectfully

 

[Skogsgurra]

I would use the 75 kVA one. It probably has much lower impedance than the three 1 kVA.

None of these solutions is ideal, but monitor core temperature (not windings) and switch off if it gets nasty.

Gunnar Englund

http://www.gke.org