ABB RELION RET670, Applications Manual

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GUID-77388095-4EE8-4915-A1D4-D0767D1E04F5 v1
C
A
B
BC
ANSI05000224-2-en.vsd
ANSI05000224 V2 EN-US
Figure 198: Example of tapped line with Auto transformer
This application gives rise to a similar problem that was highlighted in section Fault
infeed from remote end , that is increased measured impedance due to fault current
infeed. For example, for faults between the T point and B station the measured
impedance at A and C will be:
Z
A
=Z
AT
+ ·Z
TF
I
A
+ I
C
I
A
DOCUMENT11524-IMG3509 V3 EN-US
(Equation 325)
A C
2
C Trf CT TB
C
I I V2
Z Z (Z Z ) ( )
V1
I
+
= + + × ×
EQUATION1714 V1 EN-US
(Equation 326)
Where:
Z
AT
and Z
CT
is the line impedance from the A respective C station to the T point.
I
A
and I
C
is fault current from A respective C station for fault between T and B.
Table continues on next page
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 411
Application manual