Systems & Electronics

ZFP8N – Out-of-step protection relay

ection relay ZFP8N belongs to SIGMA-N digital protection fine and it performs the function of out-of-step protection far generators.


Out-of-step protection relay



The operation of the ZFP8N protection relay is based on the impedance measurement method.

The impedance vector is computed from the positive sequence components of the measured voltages and currents; the protection relay verifies the absence of negative sequence components of the currents.

The evolution of the measured impedance vector is checked on the X-R diagram with the polygonal out-of-step characteristic to identify power swing occurrences.

When an out-of-step condition occurs, a timer is started and a counter is increased; during the programmed time delay the protection relay will verify the number of out-of-step occurrences and will increase the counter if any.

The protection relay will trip if the counter reaches the programmed maximum number of allowed out-of-step occurrences in the lime delay.