ABB REB670 Applications Manual page 121

1MRK 505 370-UUS A
Busbar protection REB670 2.2 ANSI
Application manual
zone the outgoing current is used as stabilizing current instead of total incoming
current in order to guarantee the check zone operation for all possible operating
conditions in the station. The check zone operating characteristic is shown in Figure
42. Note that the check zone minimum differential operational level OperLevel shall be
set equal to or less than the corresponding operating level of the usual discriminating
zones.
OperLevel
IEC06000062 V2 EN-US
Figure 42: Check zone operation characteristic
The built-in check zone feature has to be enabled (that is, setting parameter Operation
shall be set to On) in order to fully enable the check zone. For substations where
traditional "CT switching" is not required (that is, single busbar station or one-and-half
breaker station), a check zone must not be used. For such applications, the check zone
shall be disabled by the setting parameter Operation to Off.
The check zone measures only the currents from the bays which leaves the station.
Exactly which CTs shall be measured by the check zone varies, depending on the
version of the IED used:
• In two-zone busbar differential protections, it is freely settable by using the setting
CheckZoneSel at each bay function block.
• In six-zone busbar differential protection, the currents of all active feeder bays are
measured unconditionally by the check zone, if the check zone is able to operate.
By an active feeder, we mean a feeder bay which is not deactivated, that is, neither
its operMode is Off nor it is out of service.
And the check zone supervises differential protection zones. Exactly which differential
protection zones shall be supervised by the operation of the check zone also varies,
depending on the version of the IED used:
Operate
region
Slope (settable)
I [Primary Amps]
out
IEC06000062-2-en.vsdx
Section 6
Differential protection
115