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5.69
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Functions
Out-of-Step Logic (Zero Settings)
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
R 1 R 6
X 1 T 7
X 1 T 6
X 1 B 6
X 1 B 7
Line
Operate
Restrain
R 1 R 7
R 1 L7
R 1 L6
Summary of Contents for SEL-421-4
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