Siemens SIPROTEC 7SA6 Manual page 208

Functions
Earth Impedance
(Residual)
Compensation
Earth Impedance
(Residual)
Compensation
with Scalar Factors
R /R and X /X
E L E L
6-18
1110 or 1112 or the line length in address 1111 or 1113 have been entered, the line
data must be entered again for the revised unit of length.
When entering the parameters with a personal computer and DIGSI
may optionally also be entered as primary values. The following conversion to second-
ary quantities is then not required.
For the conversion from primary to secondary values the following applies in general:
Ratio of current transformers
---------------------------------------------------------------------------------- - Z
Z =
sec
Ratio of voltage transformers
Correspondingly the following applies to the per unit length reactance of a line:
N
CT
⋅
X' ---------- - X'
=
sek prim
N
VT
with
N — Ratio of the current transformers
CT
N — Ratio of the voltage transformers
VT
Calculation example:
110 kV overhead line 150 mm
= 0.19 Ω/km
R'
1
= 0.42 Ω/km
X'
1
Current transformers600 A/1 A
Voltage transformers110 kV/0.1 kV
The secondary per unit length reactance is therefore:
N
CT ⋅
X' = --------- - X'
sec prim
N
VT
In address 1110 the following is set x' = 0.229 Ω/km.
Matching of the earth to line impedance is an essential prerequisite for the accurate
measurement of the fault distance (distance protection, fault locator) during earth
faults. This compensation is either achieved by entering the resistance ratio R
and the reactance ratio X
tor K . Which of these two entry options applies was determined by the setting in ad-
0
dress 237 Format Z0/Z1 (refer to Section 6.1.1). Corresponding to the option de-
termined there, only the relevant addresses appear here.
When entering the resistance ratio R
1116 to 1119 apply. These ratios are simply formally calculated and are not identical
with the real and imaginary part of Z
therefore not necessary! The values may derived from the line data using the following
equations:
⋅
prim
2
similar to above
600 A/1 A
-------------------------------------- - 0.42 Ω/km ⋅
=
110 kV/0.1 kV
/X or by entry of the complex earth (residual) matching fac-
E L
/R and the reactance ratio X
E L
/Z . A computation with complex numbers is
E L
®
4 the values
0.229 Ω/km
=
E
/X the addresses
E L
7SA6 Manual
C53000-G1176-C156-2
/R
L