# FEMM - Transformer design and frequency

I am trying to design a transformer in FEMM and I have this issue.

First of all, I simulated my transformer with 0Hz frequency and the Magnetic field is illustrated in the following figure Then, I did the same simulation with 50 Hz frequency and the Magnetic field is illustrated in the following figure If someone observes these two figures, it can be seen that they are pretty similar. However, we all know that the transformer operates under AC current/voltage, so someone could expect that the results of the simulation when f=0Hz to be very different than the results when f=50 Hz. I can not understand why the transformer at 0 Hz operates similarly with the transformer at 50 Hz.

• Are you following this example Link? – Tyler May 7 '18 at 14:34
• If the DC current is the same as the momentary AC current you simulated, you got a good result of simulation: The theoretical magnetic field is identical with the simulated magentic fields for both cases. – Uwe May 7 '18 at 20:13

I think you will find the small differences you observe are due to there being no Eddy current losses in a DC (0Hz) case compared to those automatically applied under FEMM when a frequency is specified.

This is talked about in several of the examples, but try reading here.

• Thank you all for your time. Yes I use a specific current to power the primary. Zero frequency corresponds to a DC current. How is it possible to have magnetic field created by DC current flowing through the primary of the transformer. I have never seen a DC transformer and I did not expect to see a magnetic field when the frequency was set at 0 Hz. – Yiannis S. May 7 '18 at 15:45
• Like any magnetic material it can be magnetized by a DC current ....think of a solenoid, it's just a transformer with only one winding. – Jack Creasey May 7 '18 at 16:12
• @Yiannnis: There is a magnetic field at 0 Hz but it is constant. If there is no change of the magnetic field, there will be no induced secondary voltage. – Uwe May 7 '18 at 20:07
• @Uwe, correct, so there are no eddy current losses to consider. – Jack Creasey May 7 '18 at 20:34

I can not understand why the transformer at 0 Hz operates similarly with the transformer at 50 Hz

More than likely this is because the primary inductance is too small for a proper 50 Hz transformer and therefore the current flowing is limited by circuit resistance.

On the other hand, if you are "powering" the primary by setting a current, then the same magnitude of current will flow as in the DC case and both will have the same amount of magnetic flux generated.

You need to state what you are doing for any further help I think.

• I agree, at DC current , depend on DCR can either saturate or look same as 50Hz depend Tesla levels relative to Bmax . Since ferrite is <0.6T f can be raised much higher for a rated V/f ratio, depending on winding parameters. – Tony Stewart Sunnyskyguy EE75 May 7 '18 at 15:13