Siemens SIPROTEC 7SA522 Manual page 87

Resistance
Tolerance
7SA522 Manual
C53000-G1176-C155-3
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 = Current transformer ratio
CT
N = Transformation ratio of voltage transformer
VT
Calculation Example:
110 kV overhead line 150 mm
s (length) = 35 km
= 0.19 Ω/km
R /s
1
= 0.42 Ω/km
X /s
1
= 0.53 Ω/km
R /s
0
= 1.19 Ω/km
X /s
0
Current Transformer 600 A/5 A
Voltage transformer 110 kV / 0.1 kV
The following line data is calculated:
= 0.19 Ω/km · 35 km = 6.65 Ω
R
L
= 0.42 Ω/km · 35 km = 14.70 Ω
X
L
For the first zone, a setting of 85 % of the line length should be applied, which results
in primary:
= 0.85 · 14.70 Ω = 12.49 Ω
X1 = 0.85 · X
prim L
or secondary:
The resistance setting R provides a reserve margin for fault resistance which appears
as an additional resistance at the fault location and is added to the impedance of the
line conductors. It comprises, for example, the resistance in arcs, the earth distribution
resistance of earth points and others. The setting must consider these fault resistanc-
es, but should at the same time not be larger than necessary. On long heavily loaded
lines, the setting may extend into the load impedance range. Fault detection due to
overload conditions is then prevented with the load trapezoid. Refer to margin heading
"Load Range" in Subsection 2.2.1. The resistance tolerance may be separately set for
the phase–phase faults on the one hand and the phase–earth faults on the other hand.
It is therefore possible to allow for a larger fault resistance for earth faults for example.
2
with the following data:
2.2 Distance protection
87