Sel 411L - Configuration, Monitoring, Alarming, and Logic for 87 L Channels

P.3.279
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Configuration, Monitoring, Alarming, and Logic for 87L Channels
Configuration, Monitoring, Alarming, and Logic for
87L Channels
This section describes how to control overall 87L function behavior through
use of advanced channel configuration options, channel monitoring and
alarming features, and several essential logic schemes that respond to the real-
time status of the 87L channels and external timing sources.
The section begins with a description of 87L function enable and blocking
logic and the use of general 87L application configuration settings. It then
provides definitions of active and required channels. This can be helpful in
understanding use of 87L communications at any given time according to
relay ordering options and available 87L communications ports, overall
configuration of the 87L function, impact of the stub bus condition, and such
present status of the 87L channels as channel failure or loss of
synchronization.
Included are descriptions of such channel-monitoring functions embedded in
the relay as round-trip channel delay, step change in the round-trip delay,
channel asymmetry, and lost packet count. Also included are explanations of
settings associated with alarming functions that respond to the provided
channel measurements.
The section describes logic schemes that respond to channel and timing source
conditions and which control the 87L function in the following fundamental
ways:
➤ Channel alarm logic
➤ Logic determining quality and method of 87L data
synchronization
➤ Channel switchover logic for two-terminal applications over
redundant serial channels
➤ Fallback logic for unavailable or degraded external time
sources when used by the 87L function
➤ Logic determining the master, outstation, and loss of 87L
protection status
Finally, it describes content of the 87L communications report. The report
summarizes basic 87L configuration and presents both present and historical
information about 87L channel function.
Out-of-sequence
packets
Checks sequence (SNTX) number
of each packet.
No tolerance. One out-of-
sequence packet causes 87L
unavailability.
Two cycles after receipt of first
packet with sequentially incre-
mented sequence number.
Excessive channel
delay
b
N/A 50 ms There is no recovery. The relay can-
not check for this condition. If 87L
data is delayed longer than 50 ms,
the relay may misoperate.
a
Jitter = variation in the expected packet arrival time from the remote terminal.
b
Channel delay time = the total delay from the time the packet is transmitted to the time the packet is received. Channel delay is not the
time delay between two consecutive packets. The channel delay time must be added to the specified trip speed of the 87L elements.
Table 3.145 Impact of Network Performance on 87L Protection (Sheet 2 of 2)
Cause Detection Method Limit 87L Recovery time
NOTE: To ensure proper
communication and protection,
please refer to the firmware
compatibility in Table A.2.