ABB RET670 Applications Manual page 279

1MRK504116-UUS C
Application manual
A
I
A
21
21
ANSI09000160 V1 EN
Figure 123: Example of tapped line with Auto transformer
This application gives rise to similar problem that was highlighted in section
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
+
I I
A C
= + ×
Z Z Z
A AT TF
I
A
EQUATION2302 V1 EN
æ
+
I I
= + +
A
Z Z ç Z
C Trf CT
è
I
C
ANSIEQUATION-1750 V1 EN
where
Z and Z is the line impedance from the A respective C station to the T point.
AT CT
I and I is fault current from A respective C station for fault between T and B.
A C
V2/V1 Transformation ratio for transformation of impedance at U1 side of the transformer to
the measuring side U2 (it is assumed that current and voltage distance function is
taken from U2 side of the transformer).
F
T
I
C
C
ö æ
2
ö
V2
× × ç ÷
C
Z ÷
TF
è ø
ø
V1
Section 3
IED application
B
I
B
21
-I
B
ANSI09000160-1-en.vsd
"Fault
(Equation 187)
(Equation 188)
273