Siemens siprotec 7SA6, Manual

Page: 208 / 876

Functions
6-18
7SA6 Manual
C53000-G1176-C156-2
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
®
4 the values
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:
Correspondingly the following applies to the per unit length reactance of a line:
with
N
CT
— Ratio of the current transformers
N
VT
— Ratio of the voltage transformers
Calculation example:
110 kV overhead line 150 mm
2
similar to above
R'
1
= 0.19
Ω
/km
X'
1
= 0.42
Ω
/km
Current transformers600 A/1 A
Voltage transformers110 kV/ 0.1 kV
The secondary per unit length reactance is therefore:
In address
1110
the following is set
x'
=
0.229
Ω
/km.
Earth Impedance
(Residual)
Compensation 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
E
/R
L
and the reactance ratio X
E
/X
L
or by entry of the complex earth (residual) matching fac-
tor K
0
. Which of these two entry options applies was determined by the setting in ad-
dress
237 Format Z0/Z1
(refer to Section 6.1.1). Corresponding to the option de-
termined there, only the relevant addresses appear here.
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. These ratios are simply formally calculated and are not identical
with the real and imaginary part of Z
E
/Z
L
. A computation with complex numbers is
therefore not necessary! The values may derived from the line data using the following
equations:
Z
sec
Ratio of current transformers
Ratio of voltage transformers
----------------------------------------------------------------------------------- Z
prim
⋅
=
X'
sek
N
C T
N
VT
----------- X'
prim
⋅
=
X'
sec
N
CT
N
VT
---------- X'
prim
⋅
600 A/1 A
110 kV/0.1 kV
--------------------------------------- 0.42
Ω
/km
⋅
0.229
Ω
/km = = =