Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.53 OST Scheme Logic Resistive and Reactive Blinders

5.69
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Out-of-Step Logic (Zero Settings)
Figure 5.54 shows the logic that determines whether the positive-sequence
impedance (Z1) falls within the Zone 6 and/or Zone 7 polygons, provided there is
no three-pole open (3PO) or loss-of-potential (ILOP) conditions.
Figure 5.53 OST Scheme Logic Resistive and Reactive Blinders
R
jX
XT 7
XT 6
XB 6
XB 7
RR 7
RR 6
RL 6
RL 7
R1R6
X1T7
X1T6
X1B6
X1B7
Line
Operate
Restrain
R1R7
R1L7
R1L6