- 149 -
function; the operation for the zone1 shall retarded rather than the main relay. As shown in
Figure 2.10-53, the reach of the zone1
(X)
is required to cover the majority of the line length AB,
whereas the zone1
(X)
should be independent on faults that occur beyond the busbar B. Given
the existence of the measuring errors in the VT and the CT, approximate 80 to 90% of the line
AB is required to set for the reach setting at the zone1
(X)
.
For the CTI as the backup relay, the delay timer in the zone1
(X)
should be set to retard.
The delay timer is programmed using the setting [TZ1S or TZ1G].
(ii) Setting for adjacent lines (Zone2 serviced as a backup relay)
The reach setting in the zone2
(X)
is required to cover 100% of the line AB plus about 20% of the
adjacent line BC. To preserve the operation selectivity for the adjacent line BC (i.e., the
operation in the zone1
(Y)
), the user should set the reach of the zone2
(X)
not beyond the reach of
the zone1
(Y)
.
Note that setting TZ2
(X)
does not influence the CTI regarding the zone1
(Y)
. If delayed
tripping in the zone1
(X)
is preferred, the CTI between the zone2
(X)
and the zone1
(Y)
should be
taken into account. Note that setting TZ2
(X)
should be satisfied with Equations (2.10-39) and
(2.10-40):
where we have defined
T
p
(Y)
: Maximum operating time in the main (primary) relay
(Y)
,
T
cb
(Y)
: Opening time in the circuit breaker
(Y)
,
T2
(X)
: Minimum operating time for the zone2
(X)
,
T
Zone2
(X)
: Reset time for the zone2
(X)
Figure 2.10-54 shows that the adjacent line BC is too short so that the coordination
between the zone1
(Y)
and the zone2
(X)
is
not realized straightforward. Hence, setting TZ2(X) is
required to be larger than setting TZ2(Y); consequently, the coordination between is achieved.
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