Causes of Electrical Current Transformer saturation problems

The saturation of the Electrical Current Transformer can be divided into two categories: one is the saturation caused by the large-capacity short-circuit steady-state symmetrical current (steady-state saturation) and the other is the saturation caused by the non-periodic component of the short-circuit current and the residual magnetism of the iron core. (Temporary saturation)

Steady-state saturation: When the secondary electromotive force generated by the steady-state symmetrical short-circuit current through the Electrical Current Transformer exceeds a certain value, the transformer core will begin to saturate. The characteristic of the secondary current in this saturation situation is that the distorted secondary current is pulse-shaped. The positive and negative half-waves are roughly symmetrical. For protections that react to current values, such as overcurrent protection and impedance protection, saturation will reduce sensitivity. For differential protection, the differential current depends on the difference in the saturation tolerance of the transformers on both sides.

Transient saturation: Short-circuit current generally contains non-periodic components. This will seriously deteriorate the transmission characteristics of the Electrical Current Transformer. The reason is that the excitation characteristics of the Electrical Current Transformer are designed according to the power frequency. When the non-periodic component with a very low equivalent frequency is transferred, the core magnetic flux (ie, the excitation current) needs to be greatly increased. The non-periodic component causes the secondary current waveform to be asymmetric when the transformer is temporarily saturated, and it takes a long time to start to saturate. But when the iron core has remanent magnetism, it will increase the degree of saturation and shorten the start of saturation time.