ABB Relion 615 series, Technical Manual

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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.
Differential protection
(87A, 87B, 87C) for
Zone A
Differential protection
(87A, 87B, 87C) for
Zone B
Zone A
Zone B
Stabilizing
resistor R
s
Stabilizing
resistor R
s . . . .
. . . .
Incoming / Outgoing
Feeder for Zone A
Incoming / Outgoing
Feeder for Zone B
Bus coupler
GUID-4149A38D-C708-4945-A004-75B13F4E0B4A V1 EN
Figure 284: Differential protection on busbar with bus coupler (Single-phase
representation)
Flux-balancing principle
87A, 87B, 87C can be used to realize flux-balance based phase-segregated three-phase
differential protection. Stabilizing resistors are not needed in this application as core
balance current transformers are used instead. They must be wired so that the measured
current will be the differential current between the motor terminal and the neutral sides.
Section 4
1MAC059074-MB A
Protection functions
560 615 series ANSI
Technical Manual