Siemens Argus 7SR21 Technical Manual page 640

7SR210 & 7SR220 Applications Guide
5.10.2.2 Load Blinder 1Ph
The single phase Load Blinder provides phase segregated blocking outputs. The Inps level is not considered
whereas operation of the load blinder is inhibited during earth fault conditions i.e. when the Izps level exceeds the
I21LB-1P IZPS setting.
The single phase load blinder has the following setting parameters:
21LB – 1P Angle +ve
21LB – 1P Angle -ve
21LB – 1P Impedance
21LB – 1P VPPS
21LB – 1P IZPS
The design of single phase load blinder takes into consideration the following effects of a high unbalanced load
non-fault condition. The blinder is operated when:
a. Positive Sequence Voltage Vpps is not significantly changed. A high 21LB-1P VPPS setting will allow
inhibiting Load Blinders in case of larger voltage drops (representing fault situation).
AND
b. Zero Sequence Current Izps is lower than 21LB-1P IZPS Setting.,
AND
c. The impedance measured per phase is within the operate zone.
Zphase is calculated from Vphase (peak) and Iphase (peak). The calculated Zphase is used to
determine if the impedance for that phase is in the operate zone i.e. greater than 21LB-1P Impedance
setting and less than 21LB-1P Angle settings.
Suitable settings can be chosen to provide outputs in the forward or reverse directions.
Page 46 of 48
Figure 5.10.2.2-1 Logic Diagram 1 Phase
©2018 Siemens Protection Devices Limited