ABB RELION 670 SERIES Applications Manual page 490

Line distance protection

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Impedance protection

ANSI06000553 V1 EN

The currents in the phases at a double ground fault

However, it should be considered that a quite substantial residual current can also appear

temporarily at the onset of a single phase fault. This is why detection of cross-country

faults, using residual current, is typically time delayed. The time delay should then be long

enough to cover the duration of the transient residual current.

Even though there is no considerable current in the phase where the external fault is, the

voltage magnitude in this phase will decrease more or less. This voltage drop will be the

only lasting sign of a fault in this phase, as seen from the relay. The phase with the fault

on the protected feeder will of course also experience a voltage drop. The healthy phase

voltage will stay around its rated value.

Using the voltage drops, it is possible to detect the two faulty phases of the cross-country

Another advantage with using voltage, and voltage only, is that it will be the same for all

the feeders on a bus and similar for other buses. This will give the relays a better

opportunity to detect the same two faulty phases. This is important since phase preference

can only be obtained when all relays detect the two correct phases.

The PPL2PHIZ function is using the voltage criteria described above. Once the faulty

phases are detected, together with residual current, preference may be obtained and

transferred to the distance protection by activating one of three enabling signals, one for

each phase. Technically, the three signals are first coded into a word together with three

signals representing the phase-to-phase measuring loops (the ZREL output). This is to

simplify the connection between PPL2PHIZ and the distance protection.

en06000553_ansi.vsd

1MRK 506 369-UUS -

Line distance protection REL670 2.2 ANSI

Application manual