Vector group matching means that the low voltage-side currents are rotated with respect to the high voltage-side currents according to the vector group of the transformer to be protected. Thereby, phase coincidence with the high voltage-side currents is restored. With the P632, this is achieved by calculating the relevant vector difference or where appropriate, by sign inversion for the low voltage-side phase currents (end b). Care must be taken to avoid distortion of the amplitude matching by this operation. For all odd vector groups, this is achieved by means of the factor 1/√3. Using vector diagrams, it can be shown that the operations listed in the following table will lead to phase coincidence of the high and low voltage-side currents while maintaining the amplitude matching. In Fig. 3-94, such a vector diagram is depicted for a transformer having the vector group Yd5 as an example. By subtraction of each phase current from the cyclically leading phase current and subsequent multiplication by the factor 1/√3, the desired matching is achieved.