ABB RELION 670 Series Applications Manual page 383

Transformer protection

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1MRK 504 152-UEN B

the phase selection and if the fault type indicates a two or three phase fault the integer

releasing the zone is not changed.

If the fault indicates and earth-fault checks are done which mode of tripping to be used, for

example 1231c, which means that fault in the phases are tripped in the cyclic order L1 before L2

before L3 before L1. Local conditions to check the phase-to-earth voltage levels and occurring

zero sequence current and voltages completes the logic.

IEC06000552 V3 EN-US

Figure 234: The connection of Phase preference logic function PPLPHIZ between Distance

As the fault is a double earth-faults at different locations of the network, the fault current in

the faulty phase on each of the lines will be seen as a phase current and at the same time as a

neutral current as the remaining phases on each feeder virtually carries no (load) current. A

current through the earthing impedance does not exist. It is limited by the impedance to below

the typical, say 25 to 40 A. Occurring neutral current is thus a sign of a cross-country fault (a

double earth- fault)

Application manual

protection zone, quadrilateral characteristic ZMQPDIS and ZMQAPDIS and

Phase selection with load encroachment, quadrilateral characteristic function

W2_FSD1-BLKZ

W2_FSD1-BLKZ

Impedance protection

IEC06000552-3-en.vsd