Siemens siprotec 7SD5 User Manual

2 Functions
144
7SD5 Manual
C53000-G1176-C169-1
When using a personal computer and DIGSI
®
to apply the settings, these can be op-
tionally 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
:
Resistance
Tolerance
The resistance setting R allows a reserve for fault resistance which appears as an ad-
ditional resistance at the fault location and is added to the impedance of the line con-
ductors. It comprises, for example, the resistance in arcs, the earth distribution resis-
tance of earth points and others. The setting must consider these fault resistances, 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 (only for impedance pickup)“ in Subsection 2.5.1. 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.
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Siemens siprotec 7SD5 Specifications

General

Brand	Siemens
Model	siprotec 7SD5
Category	Relays
Language	English