In some situations, excitation of the distance protection system by overcurrent alone cannot ensure reliable fault detection because the fault currents are not significantly different from the largest operating current. This can occur, for example, in meshed networks in which the current is split into parallel paths or in networks with low feed-in power. In such cases, voltage must be included as an excitation criterion in addition to current.
The resulting characteristic curve for the voltage-dependent overcurrent starting can be automatically checked and evaluated using the U/I monitor.
For this purpose, test ramps are parameterized on the one hand with a constant voltage value and on the other hand with a constant current value. The respective other test variable is changed in ramp form and the excitation value is determined in this way.
