P44x/EN AP/Hb
MiCOM P40 Agile P442, P444
(AP) 5-
which the residual compensation factor kZ1 is set to a lower value than normal (typically
≤ 80% of normal kZ1).
Z1 G/F (Optional)
Z1 G/F (Normal)
Z
MO
P3048EN
Figure 18: Zone 1 reach considerations
Effect of Mutual Coupling on Zone 2 Setting:
If the double circuit line to be protected is long and there is a relatively short adjacent line, it
is difficult to set the reach of the zone 2 elements to cover 120% of the protected line
impedance for all faults, but not more than 50% of the adjacent line. This problem can be
exacerbated when a significant additional allowance has to be made for the zero-sequence
mutual impedance in the case of earth faults. For parallel circuit operation the relay Zone 2
earth fault elements will tend to underreach. Therefore, it is desirable to boost the setting of
the earth fault elements such that they will have a comparable reach to the phase fault
elements. Increasing the residual compensation factor kZ2 for zone 2 will ensure adequate
fault coverage.
Under single circuit operation, no mutual coupling exists, and the zone 2 earth fault elements
may overreach beyond 50% of the adjacent line, necessitating time discrimination with other
Zone 2 elements. Therefore, it is desirable to reduce the earth fault settings to that of the
phase fault elements for single circuit operation, as shown in Figure 19. Changing between
appropriate settings can be achieved by using the alternative setting groups available in the
relay series relays.
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