Siemens siprotec 7SA522 - Page 75

2.2 Distance protection
75
7SA522 Manual
C53000-G1176-C155-3
Load Range On long heavily loaded lines, the risk of encroachment of the load impedance into the
tripping characteristic of the distance protection may exist. To exclude the risk of un-
wanted fault detection by the distance protection during heavy load flow, a load trap-
ezoid characteristic may be set for tripping characteristics with large R-reaches, which
excludes such unwanted fault detection by overload. This load area is considered in
the description of the tripping characteristics (see also Section 2.2.2 and Section
2.2.3).
The R-value 5ORDG( (address ) refers to the phase-earth loops, 5ORDG
 (address ) to the phase-phase loops. The values are set somewhat (ap-
prox. 10 %) below the minimum expected load impedance. The minimum load imped-
ance results when the maximum load current and minimum operating voltage exist.
Calculation Example
:
110 kV overhead line 150 mm
2
with the following data:
maximum transmittable power
P
max
= 100 MVA corresponds to
I
max
= 525 A
minimum operating voltage
U
min
= 0.9 U
N
Current Transformer 600 A / 5 A
Voltage Transformer 110 kV / 0.1 kV
The resulting minimum load impedance is therefore:
This value can be entered as a primary value when parameterizing with a PC and
DIGSI
®
. The conversion to secondary values is
when applying a security margin of 10 % the following is set:
primary: 5ORDG = 97.98 Ω or
secondary: 5ORDG = 10.69 Ω.
The spread angle of the load trapezoid ϕORDG( (address ) and ϕORDG
 (address ) must be greater (approx. 5°) than the maximum arising load
angle (corresponding to the minimum power factor cosϕ).
Calculation Example
:
Minimum power factor
cos ϕ
min
= 0.63
ϕ
max
= 51°
Setting value ϕORDG = ϕ
max
+ 5° = 56°.