Transformers – Saturation

Transformer saturation distorts the secondary current waveform and the extent of distortion depends on the value of the remaining flux in the CT core and the presence of a DC offset in the primary current.

It is common, in transmission lines, to occur situations that generate overcurrent in the circuit. These situations usually lead to the loss of some phase or a short circuit. And, in general, they are called fault currents. Saturation causes a cut in the secondary waveform that increases with saturation in the nucleus.             Gates Rubber 1760-8MGT-30

The effect of the hysteresis causes the CT to saturate by an accumulation of small fault currents, this occurs when these occur in non-zero points of the waveform and are abruptly interrupted, not having time to demagnetize the nucleus.

In this situation, the core remains magnetized and with a high flux density. This causes a new small fault current to override the nominal CT operating values, leading to saturation.

It is common to happen in certain external faults, when the fault currents are very high, the appearance of significant DC offset components that overlap symmetrical fault currents.