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Functions
2.1 General
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
60
Earth Impedance (Residual) Compensation with Scalar Factors R
E
/R
L
and X
E
/X
L
When entering the resistance ratio R
E
/R
L
and the reactance ratio X
E
/X
L
the addresses 1116 to 1119 apply.
They are calculated separately, and do not correspond to the real and imaginary components of Z
E
/Z
L
. A com-
putation with complex numbers is therefore not necessary! The ratios are obtained from system data using the
following formulas:
Where
R
0
= Zero sequence resistance of the line
X
0
= Zero sequence reactance of the line
R
1
= Positive sequence resistance of the line
X
1
= Positive sequence reactance of the line
These values can be applied either to the entire line or as per unit of length values since the quotients are in-
dependent of length. Furthermore, it makes no difference whether the quotients are calculated with primary, or
secondary values.
Calculation Example:
110 kV overhead line 150 mm
2
with the data
R
1
/s = 0.19
Ω
/km positive sequence impedance
X
1
/s = 0.42
Ω
/km positive sequence impedance
R
0
/s = 0.53
Ω
/km zero sequence impedance
X
0
/s = 1.19
Ω
/km zero sequence impedance
(where s = line length)
For earth impedance ratios, the following emerge:
The earth impedance (residual) compensation factor setting for the first zone Z1 may be different from that of
the remaining zones of the distance protection. This allows the setting of the exact values for the protected line,
while at the same time the setting for the back-up zones may be a close approximation even when the following
lines have substantially different earth impedance ratios (e.g. cable after an overhead line). Accordingly, the
settings for the address
1116 RE/RL(Z1) and 1117 XE/XL(Z1) are determined with the data of the protected
line, while the addresses 1118 RE/RL(> Z1) and 1119 XE/XL(> Z1) apply to the remaining zones Z1B and
Z2 up to Z6 (as seen from the relay location).
Resistance ratio: Reactance ratio: