Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
153
Figure 2-59 Setting the reach - example for device A
s1, s2 Protected line section
When using a personal computer and the DIGSI software to apply the settings, the values can be optionally
entered as primary or secondary values.
In the case of parameterization with secondary quantities, the values derived from the grading coordination
chart must be converted to the secondary side of the current and voltage transformers. In general:
Accordingly, the reach for any distance zone can be specified as follows:
where
N
CT
= Current transformer ratio
N
VT
= Transformation ratio of voltage transformer
Calculation Example:
110 kV overhead line 150 mm
2
with the following data:
s (length) = 35 km
R
1
/s = 0.19 Ω/km
X
1
/s = 0.42 Ω/km
R
0
/s = 0.53 Ω/km
X
0
/s = 1.19 Ω/km
Current Transformer 600 A/5 A
Voltage transformer 110 kV / 0.1 kV
The following line data is calculated:
R
L
= 0.19 Ω/km · 35 km = 6.65 Ω
X
L
= 0.42 Ω/km · 35 km = 14.70 Ω
For the first zone, a setting of 85 % of the line length should be applied, which results in primary:
X1
prim
= 0.85 · X
L
= 0.85 · 14.70 Ω= 12.49 Ω
or secondary:
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