P.3.45
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Differential Elements
sensitivity/security balance of the line differential protection.
Likewise, the relay under stub bus ignores the external fault-
detected (EFD) bit it receives from the remote peers, and
remote faults in the power system have no effect on the
sensitivity/security balance of the stub bus differential
protection (see Figure 3.30).
➤ Upon 87L operation, the relay does not send the 87 transfer trip
to the remote relay peers, because clearing the remote
terminals is unnecessary when the line disconnect is opened.
Likewise, the relay in stub bus ignores 87 transfer trips it
receives (see Figure 3.25 and Figure 3.26).
➤ The relay in stub bus suspends line charging current
compensation if enabled, and the remote relay(s) compensates
for the entire line (see Line Charging Current Compensation
for more details).
The ESTUB Relay Word bit indicates stub bus mode. All relevant 87L logic
diagrams depict use of the ESTUB Relay Word bit. You can use the ESTUB
bit for better targeting and identification of faults on the line versus in the bus
work. In particular, you can block autoreclosing for 87L trips that assert under
the stub bus condition.
Use caution when programming the ESTUB SEL
OGIC control equation. In
particular, ensure the equation does not assert spuriously because of noise
coupled in the dc circuitry, ground faults in the dc circuitry, or performance
issues with the 89 auxiliary contacts. Spurious assertion of ESTUB is likely to
cause a misoperation of the 87L elements, both local and remote, depending
on applied settings and the amount of current the local terminal is carrying at
the time.
Use a sufficient debounce time for the digital input interfacing the 89 position
against battery ground faults and other induced noise. By also using both the
89a and 89b contacts in the ESTUB SEL
OGIC control equation, you can
improve security against auxiliary contact failure of the line disconnect
switch.
Note that the relay allows for the 87L test mode and provides for the 87L
blocking input. Avoid using the ESTUB condition to facilitate testing or
blocking.
Some applications work best by using bus protection relays to protect the bus
work between the line CT (or CTs) and the line disconnect switch under the
stub bus condition. You can, if necessary, use the ESTUB Relay Word bit to
suppress trips from the local 87L elements. The remote 87L elements will still
respond correctly to the stub bus condition and protect the line between the
remote terminal or terminals and the opened disconnect switch.
Table 3.13 Stub Bus Settings
Setting Description Range Default
ESTUB Enable stub bus protection SELOGIC control equation 0
Table 3.14 Stub Bus Relay Word Bits
Name Description
ESTUB Stub bus condition asserted for the 87L function
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