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- Placerville, CA, USA
- Occupation
- Retired PV System Designer
This is a continuation of a discussion started in another thread. Some starter quotes are provided here:
For support, I refer to the following reference on the web sites of a transformer manufacturer, who should be expected to get this right:
http://www.tortran.com/transformer_design_guide.html
And, a fairly complete logical analysis which argues that the 60Hz transformer will be able to handle even higher power ratings with a proportionally smaller core size than a 60/50 Hz dual rated transformer, since the smaller core will allow shorter coil turns and fewer of them:
http://music-electronics-forum.com/t16277/#post132369
Your turn.
The article did not mention about installation practices.
With the same input and output voltages and same KVA, a 50Hz transformer is smaller than a 60Hz transformer and so the arc hazard is lesser.
For 60Hz, the current taken by the transformer is less.
For 50Hz, it is more requiring more iron as you stated.
But by using thinner coil wire, the current can be kept same as in 60Hz without increasing iron size. So the coil size would be smaller and so the overall size of 50Hz transformer is smaller and so the arc hazard is lesser.
Higher the frequency, lower the AC current in an inductive circuit. So to bring the higher value current at a lower frequency to the same value at the higher frequency for a given voltage and given output KVA at the higher frequency, the resistance of the inductive circuit need to be increased.
As in 60 Hz
1) Core size same.
2)Current same
3)No of turns same
4)KVA same for 50Hz transformer. Only cross sectional area of coil wire reduced. So core flux density does not change. Due to reduction in coil size, the overall size of 50 Hz transformer is smaller.
Reduction in size of 50Hz transformer due to decrease in coil size.
Decrease in coil sizer due to thinner coil wire.
Increase in resistance of coil wire due to thinner coil wire.
Lesser arc hazard due to increase in resistance of coil wire of 50 Hz transformer.
I think that you have two fundamental problems here:
1. For a higher frequency, the current in a given inductor for a given voltage will be lower. Therefore the magnetizing current in the 50 Hz transformer will be higher for the same voltage. That requires more current, not less, and more energy loss. Or else you increase the inductance, not the resistance.
2. The magnetizing current does not really matter. We are looking at the transferred power between primary and secondary, not the magnetizing current.
And there is no avoiding the fact that the power is V x I, which has no frequency dependence at all. The only thing that will change with frequency, all other things being equal, will be the power factor of the transformer input for a given power level.
For support, I refer to the following reference on the web sites of a transformer manufacturer, who should be expected to get this right:
http://www.tortran.com/transformer_design_guide.html
Step 2. Choose your Operating Frequency
The standard line operating frequency in North America is 60 Hz. The rest of the world operates at 50 Hz.
A transformer designed for 50 Hz will also work at 60 Hz but a transformer designed for 60 Hz will not work at 50 Hz.
A 50 Hz transformer is 20% larger than a 60 Hz design so allow space for a 50 Hz design if you plan to export your product at a future date.
400 Hz is used for weight sensitive airborne and seaborne applications as it allows the transformer to be about 1/3 smaller.
And, a fairly complete logical analysis which argues that the 60Hz transformer will be able to handle even higher power ratings with a proportionally smaller core size than a 60/50 Hz dual rated transformer, since the smaller core will allow shorter coil turns and fewer of them:
http://music-electronics-forum.com/t16277/#post132369
The facts is that power transformers must make a big enough primary inductance to limit the magnetizing current below some safe level. They must also provide a sufficient number of turns and core cross sectional area to limit the magnetic field intensity to below the saturation value. These two conditions are in fact two different ways of saying the same thing.
The limitation on the amount of power a transformer can provide is the internal temperature rise versus the temperatures the insulation system can withstand. In general, higher temperature insulation classes are more expensive, so the design optimization process tends to run the transformer right up against the edge of temperature rise for the given insulation class.
Given that, one has two choices when designing a power transformer to a particular insulation temperature rise/class. (1) Use enough core stack to work OK at 50Hz and make one model. If it works OK with low enough temp rise at 50Hz, it will have extra margin at 60Hz and one model fits all, except that you pay about 20% more for the iron and 10% more for the copper on every 60Hz transformer than you need to. (2) you can design one 50Hz device about 20/10% bigger/more expensive for the 50Hz market and another for the 60Hz market and get the lowest cost for each customized build. These are the competent engineering approaches. There are choices (3) through (N) which get cheap on some part of this. To the degree that the transformer runs hotter, its life will be shorter.
If a transformer runs OK at 50Hz, it will run OK at 60Hz at the same volts per turn, and will have a bigger power capability by the amount that the lower magnetizing current decreases heating, but will still not be as good as a 60Hz transformer specifically designed for that because the longer length per turn will cause additional resistive losses in the windings unless the core stack is also made bigger still to get fewer turns and get the copper losses lower.
A competent transformer designer can take this all into account depending on what he's told to design. A beginner will miss some things.
In general, for a given insulation class, the lower the lowest frequency on the primary, the bigger the transformer.
Your turn.
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