The Effect of Saturation

Author: N.H. Crowhurst

Saturation begins at a specific magnetization density. The back emf produced by this density depends on frequency, being directly proportional to it. This means that the power-handling capacity of a transformer is approximately proportional to the square of frequency. It is not a constant figure! Below saturation the relation between voltage and magnetizing current approximates that of simple inductance. Above the point on the current wave where saturation occurs, the current peaks up rapidly.

Waveforms when saturation occurs

If the primary of the transformer were connected to a source of voltage having zero resistance, the sudden rise in magnetizing current due to saturation would make no difference. Drawing this heavy current from a voltage source that possesses internal resistance, however, causes a voltage drop coincident with the current peaks, distorting the primary voltage waveform as well.

The effect of saturation

Frequency response below saturation is controlled by the relationship between primary inductance and the associated source and local resistances. Regardless of the point, however, primary inductance causes a low-frequency loss at all voltage levels.