5.132
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Functions
Permissive Overreaching Transfer Tripping Scheme
Figure 5.96
POTT Scheme Logic (ECOMM := POTT3) With Echo and Weak Infeed
IL
OP
EL
OP=Y1
SPO
A
MA
G3
XA
G2
EBLKD=OFF
ETDPU=OFF
PT
A
TP
A
KEY
A
Z3RB
A
EKEY
A
EC
TT
A
WF
C
|V
ab|
|V
bc|
|V
ca|
27PP
W
59NW
|3V0|
EWF
C=Y
,SP
Not
e:
PTB
, KEYB f
or B-Phase
PT
C,
KEY
C
f
or C
-phase
MA
G2
Z2P
APS
Z2G
Z3G
67G3
67Q3
XA
G3
Z3P
67QGSP=Y
Multi-Phase
Fault
3PO
67G3
67Q3
ETDPU
0
0
EBLKD
0
EDURD
0
2
CY
C
0.
5
CY
C
Z3RBD
0.
75
CY
C
0
Summary of Contents for SEL-421-4
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