Compares the current of one phase to the voltage between two other phases thus determining I X cosφ.

If this value becomes negative and higher than the preset percentage of the norminal current (1-10%) the time unit is started.

If the preset time is exceeded (1-10 sec.) the unit will trip the generator by means of the output relay.

The time unit is reset as soon as I X cosφ is less negative than the preset value.