ABB RELION 670 Series Applications Manual page 116

Section 6
Differential protection
be activated either externally via binary input or derived internally by built-in logic. Internally, this
"zone switching" feature will be activated if the following conditions are met:
• bays have parameter
• internal zone selection logic concludes that this particular bay shall be simultaneously
connected to both internal differential zones
This situation only means that for this particular bay both busbar disconnectors are closed and
therefore zone interconnection switching is happening in the station.
When zone switching feature is activated inside the IED, each individual bay current will behave in
the predetermined way as dictated by a parameter setting
every bay, can be set to only one of the following three alternatives
ForceOut
•
ForceIn
•
Conditionally
•
If for a particular CT input setting parameter
will be disconnected from both the differential zones, regardless of any other set value or active
binary input, while zone switching feature is active within the IED. This setting is typically used for
bus coupler bay in double busbar stations.
If for a particular CT input setting parameter
will be connected to both the differential zones, regardless of any other set value or active binary
input, while zone switching feature is active within the IED. This setting is typically used for all
feeders bay in a station with two single zone interconnected by a sectionalizing disconnector.
If for a particular CT input setting parameter
input will be connected to both the differential zones only if it was included to any of the two
zones for 2ms before the zone switching feature was activated. This setting is typically used for all
feeders bay in double busbar stations. With this setting all feeder bays, which were not connected
to any of the two zones before the zone interconnection activation (that is, out for scheduled
maintenance), will not either be included during zone interconnection.
This practically means that for double busbar station, when zone switching feature is active, all
feeder bays will be connected to both differential zones, while bus coupler CT will be disconnected
from both zones. In this way simple but effective solution is formed. It is as well important to
notice that all necessary changes in the individual bay tripping arrangements will be automatically
performed within the internal logic.
A dedicated binary signal will be immediately activated in the internal logic when zone
interconnection feature is activated. If this feature is active longer than the pre-set time separate
alarm binary signal is activated, in order to alarm the station personnel about such operating
conditions.
arrangements where it is not required that is, single busbar stations, breaker-and-a-half stations
and so on.
Discriminating zones (that is, Zone A and Zone B) in the IED includes a sensitive operational level.
This sensitive operational level is designed to be able to detect busbar ground faults in low
impedance edgrounded power systems (that is, power systems where the ground-fault current is
limited to a certain level, typically between 300 A and 2000 A by neutral point reactor or resistor)
or for some other special applications where increased sensitivity is required. Operation and
operating characteristic of the sensitive differential protection can be set independently from the
operating characteristic of the main differential protection. The sensitive differential level is
110
ZoneSel set to either CtrlInclude or CtrlExcludes
ZoneInterconnection feature can be disabled by a parameter setting for substation
ZoneSwitching . This parameter, for
ZoneSwitching is set to ForceOut , then this CT input
ZoneSwitching is set to ForceIn , then this CT input
ZoneSwitching is set to Conditionally , then this CT
1MRK 505 337-UUS A
SEMOD127483-4 v3
Application manual