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Date Code 20150401 SEL Application Guide 2015-12
Note that when not in test mode, the relay differential element is supervised by both local and
remote disturbance detectors. An operation of the differential element that occurs without
assertion of the disturbance detection logic (sometimes due to channel asymmetry or unaligned
ramping of local or remote currents during testing) can cause a watchdog error. Two counters are
started when these spurious assertions take place, and their outputs are represented by the
targetable Relay Word bits 87ERR1 and 87ERR2. If these Relay Word bits are asserted at any
time, the relay is disabled, 87L function is inhibited, the 87L ALM and 87L LOST LEDs
illuminate on the front panel (assuming default LED programming), and you can no longer
continue testing. The command to reset this watchdog error is COM 87L WD C, issued from
Access Level 2 on the terminal as follows:
Level 2
=>>COM 87L WD C
Clear 87L watchdog counters?
Are you sure (Y/N) ?Y
87L watchdog counters cleared
=>>|
The test mode also allows you to bypass the watchdog timer logic in the SEL-411L and gives you
the ability to ramp local and remote currents into the relay in an independently adjustable manner.
This provides additional flexibility to find acceptable test points without needing to worry about
inhibiting 87L function.
Note: For applications that use SEL-411L Relays with firmware older than version R108, the
watchdog counters cannot be cleared from Access Level 2. You must log in to the
calibration level of the relay and clear the counters with the same command (i.e.,
COM 87L WD C).
For more information on the watchdog timer logic, please see the SEL-411L Instruction Manual
or contact SEL for further assistance.
PRELIMINARY CHECK
Changes may need to be made to the relay settings and test procedure, depending on the
application and protection scheme configuration.
Before entering test mode, ensure that the relays are communicating remote and local data with
each other by targeting the status of Relay Word bit 87CH1OK. This bit is a snapshot of the
channel health. To monitor this bit, use the command TAR 87CH1OK.
You should also use the Sequential Events Recorder (SER) in the SEL-411L to monitor Relay
Word bit 87CH1OK over a larger time frame to make sure the bit does not de-assert due to an
excess number of lost packets. Doing so verifies that the channel is healthy.
If the channel-addressing settings in the relay (87TADR, 87R1ADR, 87R2ADR) are configured
correctly, and the direct fiber and multiplexer arrangements are physically sound, the expected
result of the target command should be as follows:
=>>TAR 87CH10K
87MTR 87SLV 87LST 87CH10K 87CH20K 87CH30K 87SYNH 87SYNL
1 0 0 | 1 1 0 1 0
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