R.1.91
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Permissive Overreaching Transfer Tripping Scheme
Figure 1.61 DCB Logic Diagram
Permissive Overreaching Transfer Tripping Scheme
Use MIRRORED BITS
®
communications to implement a Permissive
Overreaching Transfer Tripping (POTT) scheme efficiently and economically.
M
IRRORED BITS communications technology improves security and improves
the overall operating speed. If the communications channel is reliable and
noise-free (as with fiber-optic channels), then POTT provides both security
and reliability. You can also implement a POTT scheme with other
conventional communications channels such as leased telephone lines and
microwave. The DCUB trip scheme is a better choice if the communications
channel is less than perfect, but communications channel failures are unlikely
to occur during external faults.
POTT Scheme
Selection
The SEL-421 offers three POTT schemes: POTT, POTT2, and POTT3. The
type of communications channel(s) in your application best determines which
scheme to implement.
2
CYC
0
21SD
0
0
1/4
CYC
67SD
0
0
BTXD
Z3XPU
Z3XD
—
+
—
+
—
+
Relay
Word
Bits
Relay
Word
Bits
BT
DSTRT
67G2
67Q2
Z2G
M2P
50G3
50Q3
67G3
67Q3
Z3G
M3P
M3P
Relay
Word
Bits
Z3XT
DSTRT
NSTRT
Z2PGS
67QG2S
STOP
BTX
VPOLV
ICAL
IBCL
IABL
0.1 • I
nom
SEL
OGIC
Setting
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