Schweitzer Engineering Laboratories SEL-251 - Sequence Coordination; Figure 2.10: Sequence Coordination, Ground;Residual Overcurrent Elements

Date Code 20000421 Specifications 2-19
SEL-251, -2, -3 Instruction Manual
Sequence Coordination
To keep in step with line reclosers, the reclosing relay includes sequence coordination. Sequence
coordination can prevent overreaching relay overcurrent elements from tripping for faults beyond
line reclosers. A sequence coordination example follows.
Figure 2.10: Sequence Coordination, Ground/Residual Overcurrent Elements
A partial setting list is given:
M79SH = 11000 (79SH = 1 for only shot = 0 and 1)
Using SELOGIC Control Equations:
B(12) = 50NLT
G(34) = 79SH
X(56) = B*G
TR(1246) = 51NT+X (effectively, TR(1246) = 51NT+(50NLT*79SH))
SEQ(1) = 50NL
close TRIP output contacts = TR + ...
= 51NT+50NLT*79SH + ...
The M79SH setting selects for which shots (0, 1, 2, 3, or 4) the 79SH bit is asserted
(79SH = 1). 79SH supervises 50NLT for tripping. 50NL is the pickup for 50NLT.
The SEQ(1) variable can be set to any OR-combination of elements in Relay Word row R1. The
combination you select determines which overcurrent conditions control sequence coordination.
If the circuit breaker is closed and the TRIP output contacts are not asserted, SEQ(1) increments
the reclosing relay shot counter every time SEQ(1) goes from the state SEQ(1) = 1 to
SEQ(1) = 0.