Functions
2.1 General
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
59
Likewise, the following goes for the reactance setting of a line:
where
N
CT
= Current transformer ratio
N
VT
= Transformation ratio of voltage transformer
The following applies for the capacitance per distance unit:
Calculation example:
110 kV overhead line 150 mm
2
as above
R'
1
= 0.19 Ω/km
X'
1
= 0.42 Ω/km
C' = 0.008 µF/km
Current transformer 600 A / 1 A
Voltage transformer 110 kV / 0.1 kV
The secondary per distance unit reactance is therefore:
In address 1111 the setting x' = 0.229 Ω/km is entered.
The secondary per distance unit capacitance is therefore:
In address 1112 the setting c' = 0.015 µF/km is entered.
Earth impedance ratio
Setting of the earth to line impedance ratio 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)
compensation factor K
0
. Which of these two entry options applies, was determined by the setting in address
237 Format Z0/Z1 (refer to Section 2.1.2.1). Only the addresses applicable for this setting will be displayed.
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