P.3.227
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Permissive Overreaching Transfer Tripping Scheme
overvoltage level detector to qualify a weak-infeed condition. If setting EWFC
equals Y, the relay enables the weak-infeed logic and settings 27PPW and
59NW are active. For single-pole tripping applications, set EWFC to SP and
setting 27PWI is active.
The weak-infeed logic sets the ECTT (echo conversion to trip) element upon
satisfaction of the following.
➤ No reverse-looking elements have picked up (the reverse-
looking elements override operation of the weak-infeed and
echo logic for faults behind the relay location).
➤ LOP is deasserted when the setting ELOP equals Y1.
➤ At least one phase-to-phase undervoltage element or the
residual overvoltage element operates.
➤ The local circuit breaker(s) is closed.
➤ A permissive trip signal is received for ETDPU time period.
The EWFC setting enables the weak-infeed feature of the relay. When the
EWFC setting is Y, the ECTT (echo conversion to trip) logic is enabled. When
the setting EWFC is SP, the relay can convert echo to a single-pole trip at the
local terminal. ECTT logic is disabled when the setting is N.
Three-Terminal Lines
If you apply the POTT scheme to a three-terminal line, program SELOGIC
control equation PT1 as follows:
PT1 := IN205 AND IN206 General permissive trip received (SELOGIC
equation)
Relay control inputs IN205 and IN206 assert when the relay receives a
permissive signal from each of the two other terminals. The relay cannot high-
speed trip until both inputs assert. These two control inputs were chosen for
this particular example. Use control inputs that are appropriate for your
application.
Cross-Country Faults
The relay POTT scheme logic (ECOMM = POTT2 or POTT3) includes
additional logic that ensures proper single-pole tripping at both stations during
cross-country faults. A cross-country fault consists of simultaneous single
phase-to-ground faults on both of the parallel lines. If the simultaneous ground
faults are beyond Zone 1 reach with respect to the local station, unwanted
three-pole tripping could occur.
Table 3.119 POTT Settings (Sheet 1 of 2)
Setting Description 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
Weak infeed phase undervoltage pickup (V) 1.0–200 47.0
27PPW
b
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 (when ECOMM = POTT or POTT2) SEL
OGIC equation NA
PT3 Three-pole permissive trip received (when ECOMM = POTT2) SEL
OGIC equation NA
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