ABB RELION RET670 Applications Manual page 498

Section 8
Impedance protection
492
en06000551_ansi.vsd
ANSI06000551 V1 EN-US
Figure 246: The voltage increase on healthy phases and occurring neutral point
voltage (3V0) at a single phase-to-ground fault and an occurring cross-
country fault on different feeders in a sub-transmission network, high
impedance (resistance, reactance) grounded
PPLPHIZ is connected between Distance protection zone, quadrilateral characteristic
function ZMQPDIS (21) and ZMQAPDIS (21) and Phase selection with load
encroachment, quadrilateral characteristic function FDPSPDIS (21) as shown in
figure 247. The integer from the phase selection function, which gives the type of fault
undergoes a check and will release the distance protection zones as decided by the
logic. The logic includes a check of the fault loops given by 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 ground-fault checks are done which mode of tripping to be
used, for example ABCAc, which means that fault in the phases are tripped in the
cyclic order A before B before C before A. Local conditions to check the phase-to-
ground voltage levels and occurring zero sequence current and voltages completes the
logic.
1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual