SEL-411L Data Sheet Schweitzer Engineering Laboratories, Inc.
8
noise condition could result in corrupted data and an
unwanted 87L operation, the SEL-411L has sensitive and
fast-acting disturbance detectors as Figure 7 illustrates.
Corrupted data that would activate the 87L elements or
assert the 87 direct transfer trip (87DTT) would be short
lived and constitute typically just a single packet. The
SEL-411L supervises the 87L elements and 87DTT with
the disturbance detector. As Figure 8 illustrates, the 87L
element or 87DTT element is delayed slightly without
losing dependability even if the disturbance detectors
were to fail to assert.
The disturbance detectors are sensitive, but they will not
assert under load conditions for periodic current or volt-
ages, even for heavily distorted load current or voltages.
No user settings are necessary for the disturbance detec-
tion logic.
87 Channel Monitoring
To aid commissioning and to help maintain security and
dependability, the SEL-411L provides a set of channel
monitoring and alarming functions. Considering that the
87L function is communications-dependent, it is benefi-
cial to monitor the status of the communications chan-
nels. The 87L function itself responds to some monitored
channel characteristics in real time to maintain proper
security and dependability.
The monitoring functions of the SEL-411L include a round-
trip channel delay, step change in the round-trip delay
signifying path switching, noise burst and momentary
channel break detection, channel asymmetry, 40 second
and 24h lost packet counts, data integrity alarm, and
wrong relay address alarm signifying cross-connection
of communications paths. These monitoring functions
provide overall assessment of channel quality for the user
and feed into the internal 87L logic for security.
87L Communications Report
The SEL-411L provides an 87L communications report
to visualize and summarize basic 87L configuration, as
well as real-time and historical channel monitoring and
alarming values. The report covers three major areas:
➤87L configuration and overall status such as relay
identification, number of terminals in the 87L scheme,
master or slave mode, channel problems, stub bus
condition, in test, etc.
➤Detailed channel configuration, diagnostics, and
health information on a per-channel basis. Such
information includes remote relay address, data
synchronization method and status, list of any specific
channel alarms asserted, round-trip channel delay,
and channel asymmetry.
➤Long-term channel characteristics on a per-channel
basis as channel delay histogram, and worst-case
channel delay with time stamp.
87L Channel Redundancy
The SEL-411L provides optional channel redundancy in
two-terminal serial applications. You can order the SEL-411L
with two 87L serial communications ports, which you
can then use to connect two relays in a redundant fash-
ion, incorporating different, typically independent com-
munications equipment and paths. Often a direct point-
to-point fiber connection is the primary channel, and a
multiplexed channel over a SONET network serves as
backup. The SEL-411L simultaneously sends data on
both channels, and incorporates channel monitoring
functions and logic to automatically switch between the
primary and backup channels on the receiving end to
maximize dependability and security. Excessive round-
trip channel delay, elevated lost packet counts, detected
channel asymmetry, and user-programmable conditions
can all serve as triggers to initiate channel switchover.
Complete Distance Protection
The SEL-411L simultaneously measures as many as five
zones of phase and ground mho distance protection plus
five zones of phase and ground quadrilateral distance
protection. You can apply these distance elements,
together with optional high-speed distance elements, in
communications-assisted and step-distance protection
schemes. You can use expanded SELOGIC control equa-
tions to tailor the relay further to your particular application.
The relay includes LOP detection, load encroachment,
and CCVT transient detection logic for enhanced security.
Optional series-compensated line logic can also be added
to prevent overreach of the Zone 1 distance element,
resulting from the series capacitor transient response.
Figure 7 Adaptive Disturbance Detector Algorithm
Figure 8 SEL-411L Disturbance Detection Application
kTH
1-cycle
buffer
–IIR
Filter
87DD
IN mag
∑
W1
87DD
87L)
0
W1
0
87DD
87PRAW
87DTTRECEIVED
87DTT
(To Trip Logic)
(To Trip Logic)
