Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

Page: 294 / 1518

5.134
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Directional Comparison Unblocking Scheme Logic
In addition, for a three-terminal line, program SEL
OGIC
control equations LOG1
and LOG2 as follows:
LOG1 := IN205 .
Channel 1 Loss-of-Guard
LOG2 := IN206 .
Channel 2 Loss-of-Guard
Relay control inputs IN205 or IN206 assert when the relay receives a loss-of-
guard signal from either of the two other terminals. When SEL
OGIC
control equa-
tion LOG1 (Channel 1 Loss-of-Guard) asserts, the relay asserts Relay Word bit
UBB1 (Block Permissive Trip on Receiver 1) and removes the possibility that
Relay Word bit PTRX1 (Permissive Trip on Receiver 1) will assert. These two
control inputs were chosen for this particular example. Use control inputs that are
appropriate for your application.
See Table 5.74 for the DCUB settings. The first portion of the settings (from
Z3RBD to PT1) are identical to the settings for the ECOMM := POTT scheme;
(see
POTT Scheme Logic on page 5.125 ).
Timer Setting Recommendations
GARD1D: Guard-Present Delay
This timer determines the minimum time before the relay reinstates permissive
tripping following a loss-of-channel condition. Channel 1 and Channel 2 logic
use separate timers but have this same delay setting.
Table 5.74 DCUB Settings
Setting Prompt Range
Default (5
A)
Z3RBD Zone 3 Reverse Block Time Delay (cycles) 0.000–16000 5.000
EBLKD Echo Block Time Delay (cycles) 0.000–16000 10.000
ETDPU Echo Time Delay Pickup (cycles) 0.000–16000 2.000
EDURD Echo Duration Time Delay (cycles) 0.000–16000 4.000
EWFC Weak Infeed Trip Y, N, SP N
27PWI
a
a
Make setting when EWFC := SP.
Weak Infeed Phase Undervoltage Pickup (V) 1.0–200 47.0
27PPW
b
b
Make setting when EWFC := Y or SP.
Weak Infeed Undervoltage Pickup (V

) 0.1–300 80.0
59NW
b
Weak Infeed Zero-Sequence Overvoltage
Pickup (V) 0.1–200 5.0
PT1 General Permissive Trip Received SEL
OGIC
Equation IN101 AND
PLT02
GARD1D Guard Present Security Delay (cycles) 0.000–16000 120.000
UBDURD Dcub Disabling Time Delay (cycles) 0.000–16000 180.000
UBEND Dcub Duration Time Delay (cycles) 0.000–16000 20.000
PT2
c
c
Make setting when ECOMM := DCUB2.
Channel 2 Permissive Trip Received SEL
OGIC
Equation NA
LOG1 Channel 1 Loss-of-Guard SEL
OGIC
Equation NA
LOG2
c
Channel 2 Loss-of-Guard SEL
OGIC
Equation NA