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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Is there any problem with running a laminated mains transformer above its operating frequency? I guess the core hysteresis loss will increase but will this be a problem? I have no idea about the core loss when operated at "designed" frequency but I can imagine that the copper loss dominates (provided you do not saturate the core).
Registered Member #1370
Joined: Mon Mar 03 2008, 09:01AM
Location: Finland
Posts: 56
I have ran such transformer at about 400Hz, and it worked fine for a moment at about 15x voltage. It seemed to work at the viewpoint of core, but windings didn't of course stand it. Iron laminate is used in audio transformers.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Core losses rise at higher frequency due to both eddy currents in the lams, and tracing out the hysteresis curve more times per second. If you are after only intermittent operation and not worried about efficency, then running at 2x to 4x frequency ought to give you 2x to 4x the power output until you overheat, you should get minutes per run at only 4x. However dropping the peak flux by dropping the volts will bring the core losses back down as the sqaure, so perhaps 4x frequency with 75% voltage, you'll still get an increase in power, but longer run time and better efficiency. BTW, 400Hz aircraft trasnformers use very thin lams and a decent grade iron.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
In general the iron and copper losses will be similar in most power transformers of reasonable size. As Neil said, core losses are built up of hysteresis loss and eddy current losses.
Running transformers at a higher frequency can also make the leakage inductance more problematic because it represents a higher impedance at the new operating frequency. (So for instance if you ran an MOT at a higher operating frequency you would expect the output s/c current to be lower for the same applied voltage because of the higher series reactance at the new operating frequency.) At frequencies much higher than the intended operating frequency you may also find parasitic resonances caused by the inter-layer capacitances of the windings.
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Running laminated transformers on higher frequencies
