ABB RELION 620 Series Technical Manual page 482

Section 4
Protection functions
476
considered in calculating differential current. During normal condition, the summation of
the current on each bus section is zero. However, if there is a fault in any busbar section,
the difference current is no longer zero and the protection operates.
Zone A
. . . .
Incoming / Outgoing
Differential protection
Feeder for Zone A
(87A, 87B, 87C) for
GUID-4149A38D-C708-4945-A004-75B13F4E0B4A V1 EN
Figure 224: Differential protection on busbar with bus coupler (Single-phase
representation)
Another example of differential protection employed on bus transfer scheme is shown in
Figure 225. Basic principle of operation remains same.
Bus coupler
Stabilizing
Stabilizing
resistor R
resistor R
s
Differential protection
(87A, 87B, 87C) for
Zone A Zone B
1MAC504801-IB E
Zone B
. . . .
s
Incoming / Outgoing
Feeder for Zone B
620 series ANSI
Technical Manual