Load cell PFVL141C-1.6MN

Load cell PFVL141C-1.6MN

Load cell PFVL141C-1.6MN

For this example with a fault between T and B, the measured impedance from the T point to the fault will be increased by a factor defined as the sum of the currents from T point to the fault divided by the IED current.

For the IED at C, the impedance on the high voltage side U1 has to be transferred to the measuring voltage level by the transformer ratio. Another complication that might occur depending on the topology is that the current from one end can have a reverse direction for fault on the protected line.

For example, for faults at T the current from B might go in reverse direction from B to C depending on the system parameters (see the dotted line in figure 133), given that the distance protection in B to T will measure wrong direction. In three-end application, depending on the source impedance behind the IEDs, the impedances of the protected object and the fault location, it might be necessary to accept zone 2 trip in one end or sequential trip in one end.

Generally for this type of application it is difficult to select settings of zone 1 that both gives overlapping of the zones with enough sensitivity without interference with other zone 1 settings, that is, without selectivity conflicts. Careful fault calculations are necessary to determine suitable settings and selection of proper scheme communication.