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Commercial transformers for variable frequency & voltage

  1. Jun 17, 2015 #1
    I am looking to step up the voltage of a 3 phase PM generator which has variable AC output of 200 - 400 Vl-l, and 15 - 30Hz. I am looking for a step up ratio between 1:1.5 and 1:2, and need this transformer to be a commercial device.

    What i have been finding is that most commercial transformers have defined input voltage and frequencies (i.e. 240/480 V, 60Hz), which is not ideal of course.

    Does anybody know of commercial devices for this type of application? I have considered back to back VFDs but that seems overly complicated.

    Thanks in advance.
     
  2. jcsd
  3. Jun 17, 2015 #2

    CalcNerd

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    Consider using a readily available 50 Hz (or use 60 Hz and de-rate even more) transformer. Be aware that you will need to determine your Reactance of the Transformer and then de-rate it to the lowest frequency it will see. Transformers have two impedance qualities, one is simple resistance, the other is reactance. You can easily measure the resistance with an ohm meter. Most transformers have an x:r ratio of 5-7. However that is at 60 Hz. Remember to de-rate.
    .
    What is really going on is that your transformer will burn up if it offers too little resistance to the primary side power. Since the reactance approaches zero as the frequency approaches zero, your transformer will carry larger currents than it should for the power transfer. So you will likely need a 4 X larger transformer at half the freq (I am not doing the math, but power is an i^2 issue. 2 x the current = 4 x the power. So if you thought you needed a 1 KVA transformer, but you are using a 60 Hz rated transformer in place of a need to use a 30 Hz transformer, you will need to use a 4 KVA xfmr for the application. And you will suffer from leakage due to lower frequencies for this inductor ie it will look more and more like a short circuit as the frequency goes from 30 to 15 Hz. If you operate at 15 Hz you will probably need a 16 KVA transformer (and probably suffer too much energy loss, again, you need to crunch the numbers to help you analyze your energy losses).
    .
    The reason aircraft use 400 Hz is because they get to reduce the size of their on board transformers. By going in the opposite direction, you have to increase the size (or physically make your own, if you can't buy an off the shelf item).
     
    Last edited by a moderator: Jun 19, 2015
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