The ground differential protection function (Br.: restricted earth fault protection) can be applied to transformer windings with grounded neutral point where the neutral-point-to-ground connection is fitted with a current transformer.

One ground differential protection function is available per transformer winding. The P632 display shows the winding end associated with a particular ground differential protection function. Connection for and operation of the ground differential protection function will now be presented with end a as an example. Equivalent considerations apply to end b.

Ground differential protection may be applied to transformer ends with a grounded neutral-point, but in this case the neutral-point-to-ground connection must be fitted with a CT.

Ground differential protection is based on comparing the vector sum I̲N of the phase currents of the relevant transformer end to the neutral-point current I̲Y. The P632 calculates the vector sum of the phase currents. For the connection, see Chapter “Conditioning of the Measured Values”.