How is the saturation of the current transformer identified? -Solutions - Huaqiang Electronic Network

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Photocoupler

The more severe the saturation of the current transformer, the smaller the excitation impedance, and the greater the excitation current, which doubles the error of the transformer and affects the correct operation of the protection. At present, the selection of TA has considered or paid attention to its transient saturation problem, such as the use of TPY-class current transformers in the protection of high-voltage systems or large generator transformers, and the selection of PR-level current transformers with small air gaps. The protective device itself is required to have a certain ability to resist TA saturation. The following is an additional stable characteristic zone discrimination method for anti-TA saturation selected in transformer differential protection.

The TA saturation caused by a short-circuit fault occurring in the protected transformer zone is not easily distinguished by the ratio of the differential current to the brake current. This is because the measured values ​​of the differential current and the braking current are affected, and their ratio immediately meets the protection operating conditions. At this time, the operational characteristics of the ratio differential protection are still effective, and the fault characteristics satisfy the operating conditions of the ratio differential protection.

For faults that occur outside the protected transformer area, the TA saturation caused by the large through-short-circuit current generated by it produces a large false differential current, which is more severe when the TA saturation at each measurement point is different. If the operating point caused by the resulting magnitude falls within the operating characteristic region of the ratio differential protection, and the measure of differential ratio differential protection is not taken, the ratio differential protection will malfunction. The differential current obtained by calculating the current amount on each side of the transformer according to Kirchhoff's current law is basically balanced in the short time at the beginning, and only a small unbalanced current is generated, which will produce a large difference after the TA is saturated. The moving current causes the transformer differential protection to malfunction.

Therefore, the transformer differential protection can be provided with an additional stable characteristic region when the TA is saturated, which can distinguish the fault conditions in the transformer from the inside and outside.