ABB 615 series Technical Manual page 471

1MAC059074-MB A
615 series ANSI
Technical Manual
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Figure 224: Inrush current detection logic
Differential calculation
The operating principle is to calculate on both ends differential current from currents
entering and leaving the protection zone by utilizing the digital communication channels
for data exchange. The differential currents are almost zero on normal operation. The
differential protection is phase segregated and the differential currents are calculated
separately on both ends.
RED 615
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Figure 225: Basic protection principle
The differential current I∆ (I
formula:
I I I
LOC REM
= +
d
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The stabilizing current I
bias
formula:
Communication
PROTECTED ZONE
) of the protection relay is obtained on both ends with the
d
(I ) of the protection relay is obtained on both ends with the
b
Section 4
Protection functions
RED 615
(Equation 66)
465