A fault in a protection zone (a part of a network) can be detected by comparing the currents at both ends of the zone. If the currents are different, there is a fault in the zone.

The comparison is not straightforward, however, if there is a transformer in the zone, because the magnitudes and often also the phases of the primary and secondary currents of a transformer are different. The measured value of either the primary or secondary current must be corrected, or compensated for the differences due to the transformer before the comparison.

This Differential Protection Calculator application is designed to calculate the necessary corrections. The phase difference is corrected by multiplying the measured or calculated three phase current vector by a matrix, and the magnitude is corrected by multiplying by a constant.

In addition, some other simple operations can be done with this program to the current vector, such as the change of the sign, the calculation of the complex conjugate, and the calculation of the sequence components from the phase components, and vice versa.