could you explain what it is that causes harmonics in transformers?
I've read that these are the reasons, but it still doesn't give me a proper explanation.
- Saturation of the core
- Magnetizing current
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Sign up to join this communitycould you explain what it is that causes harmonics in transformers?
I've read that these are the reasons, but it still doesn't give me a proper explanation.
could you explain what it is that causes harmonics in transformers?
A transformer is only approximately linear, and that only within limits.
The net current in a transformer (the magnetizing current) creates an "H" field proportional to the instantaneous current. The "H" field induces a "B" field, but the relationship between H and B is non-linear. Changes in the "B" field, create induced voltage in the windings, and this voltage is proportional to the rate of change of "B".
The relationship between "H" and "B" becomes especially non-linear when the core is "saturated". That is, when "H" is very high, a change in "H" causes very little change in "B" (compared to the change in "B" when "H" is small).
All this entails that if the voltage is a perfect sine wave, the current will not be a perfect sine wave, but a distorted sine wave. Every distorted sine wave is equal to the sum of a sine wave of the fundamental frequency and sine waves of harmonic frequencies.
A bit more detail: because of core saturation, the output signal will vary linearly with the input signals only for small signals. When saturation first appears the predominant nonlinearity will be cubic, so for sinusoidal input sin(x) (where x = 2 pi f) the output will have one term proportional to sin(x) and another one proportional to sin(x)^3. The cubed term contains sin(3x):
$$\sin^3(x) = \frac{3\sin(x) - \sin(3x)}4$$