ABB RELION REX640 Technical Manual page 565

1MRS759142 C
REX640
Technical Manual
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Figure 305: 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 306: Basic protection principle
The differential current I∆ (I
formula:
I I I
= LOC + REM
d
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The stabilizing current I
the formula:
I I
−
LOC REM
I
=
b
2
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Depending on the location of the star points of the current transformers, the polarity
of the local end remote currents may be different causing malfunction of the
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
bias b
Section 4
Protection functions
RED 615
(Equation 88)
(Equation 89)
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