Siemens siprotec 7SA522 User Manual page 167

Earth Impedance
(Residual)
Compensation
with Scalar Factors
R /R and X /X
E L E L
7SA522 Manual
C53000-G1176-C119-2
When entering the resistance ratio R
 to  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:
Resistance ratio:
R

1
E ⋅
-- -
------ - =

3
R
L
Whereby the following applies
R — Zero sequence resistance of the line
0
X — Zero sequence reactance of the line
0
R — Positive sequence resistance of the line
1
X — Positive sequence reactance of the line
1
These values may either apply to the entire line length or be based on a per unit of line
length, as the quotient is independent of length. Furthermore it makes no difference if
the quotients are calculated with primary or secondary values.
Calculation example:
110 kV overhead line 150 mm
/s = 0.19 Ω/km
R
1
/s = 0.42 Ω/km
X
1
/s = 0.53 Ω/km
R
0
/s = 1.19 Ω/km
X
0
(where s = line length)
The following results are obtained for the earth impedance ratio:
R R
 
1
0
E
⋅
------ - = -- - ------ - 1 =
–
 
3 R
R
1
L
X
X
 
1
0
E
⋅
-- - ------ 1
------ - = =
–
 
3 X
X
1
L
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). Ac-
cordingly, the settings for the address  5(5/ = and  ;(;/ = are
determined with the data of the protected line while the addresses  5(
5/ =%= and  ;(;/ =%= apply to the remaining zones Z1B
and Z2 up to Z5 (as seen from the relay location).
/R and the reactance ratio X
E L
/Z . A computation with complex numbers is
E L
Reactance ratio:
R

0
------ - 1
–

R
1
2
with the following data
Positive sequence impedance
Zero sequence impedance
0.53 Ω /km
 
1
⋅
-- - ---------------------------- - 1 =
–
 
0.19 Ω /km
3
1.19 Ω /km
 
1
⋅
-- - ---------------------------- - 1
=
–
 
0.42 Ω /km
3
/X
E L
X X

1
E ⋅ 0
-- - ------ 1
------ - = –

3
X X
L 1
0.60
0.61
Functions
the addresses


6-19