Siemens Argus 7SR21 - Page 641

7SR210 & 7SR220 Applications Guide
© 2013 Siemens Protection Devices Limited Page 47 of 48
5.10.3 Setting Example – 3 Pole Load Blinder
T2T1
90MVA
132/33kV
-10% to +20%
(Δ1%)
Z = 8%
1574A
1600/1A
Overcurrent
Fwd setting:
= 90% of 50%
=40.5MVA
= 709A @ 33kV
33000/110V
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.
+R
+X
Phase
Fault
Block
Zone
Load
Impedance
b
a
Nominal
Impedance
Z = 1p.u. =
V
L
/ (√3 x I)
c
-R
-X
Vpps value
Point 1
Point 2
Point 3
Point 4
0
360
Trip Level
I = Vs / Z
Operate
Zone
a = 21LB-3P Impedance
setting
b = 21LB-3P Angle +ve
setting
c = 21LB-3P Angle -ve
setting
Point 6
Point 5
Fwd
Block
Zone
Load
Impedance
b
a
c
Point 7
Point 10
Point 9
Point 8
Figure 5.10.3-1 Scheme and Impedance Illustration