Siemens Argus 7SR21 Technical Manual page 641

5.10.3 Setting Example – 3 Pole Load Blinder
90MVA
132/33kV
-10% to +20%
(Δ1%)
Z = 8%
1574A
1600/1A
33000/110V
Point 8
Point 7
Load
Impedance
Point 10
Point 9
© 2013 Siemens Protection Devices Limited
Load blinders used to block overcurrent
relay so that tripping does not occur for
load current levels with a P.F. 0.94 to
Unity.
T1
Overcurrent
Fwd setting:
= 90% of 50%
=40.5MVA
= 709A @ 33kV
Fwd
Nominal
Impedance
Z = 1p.u. =
V / (√3 x I)
L
Block
Zone
a
b
-R
c
Figure 5.10.3-1 Scheme and Impedance Illustration
7SR210 & 7SR220 Applications Guide
T2
+X
Operate
Vpps value
Zone
Phase
b
Fault
0
360
+R
c
a
a = 21LB-3P Impedance
setting
b = 21LB-3P Angle +ve
setting
c = 21LB-3P Angle -ve
setting
-X
Point 1
Point 2
Block
Trip Level
Zone
I = Vs / Z
Load
Point 6
Impedance Point 5
Point 3
Point 4
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