Up to a certain limit, stability in the event of external faults is ensured by means of the bias. Due to the triple-slope tripping characteristic, the stabilization is particularly pronounced for high currents. However, as an additional safeguard for through-currents with transformer saturation, the P632 is provided with a saturation discriminator.

After each zero crossing of the restraining current, the saturation discriminator monitors the occurrence of the differential current over time. For internal faults, the differential current appears after a zero crossing together with the restraining current. In the case of passing currents with transformer saturation, however, a differential current will not appear until transformer saturation begins. Accordingly, a locking signal is generated on the basis of level monitoring of the differential current as compared to the restraining current, and thus the desired through-stabilization is achieved. Locking is restricted to the measuring system where an external fault was detected.

There will be no blocking if the differential current exceeds the set threshold DIFF: Idiff>> PSx.