A
B
C
Three-phase
differential
protection
(87A, 87B, 87C)
I
d3
I
d1
I
d2
I
L1
I
L2
I
L3
GUID-EECAE612-8A8F-4F89-BE9A-43C8762BBA75 V1 EN
Figure 285: Three-phase differential protection for motors based on flux-balancing
principle
In this scheme, the currents flowing through the core balance transformer cancel each
other out when there is no fault within the protected zone. When fault occurs within the
protected zone, the currents flowing through the core balance transformer add up so that
the differential protection trips when the differential current exceeds its threshold.
87A, 87B, 87C uses the peak-to-peak measurement mode.
4.3.4.6 Example calculations for busbar high-impedance differential protection
The protected object in the example for busbar differential protection is a single-bus
system with two zones of protection.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 561
Technical Manual
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