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10-8
Line Current Differential Communications
Date Code 20011112
and Serial Port Communications and Commands
SEL-311L Instruction Manual
DBADX asserts. This asserts Relay Word bit CHXAL, and illuminates front-panel LED 87CH
FAIL.
During installation, inspect the estimated one-way channel delay using the
COMM X
or
COMM Y
commands described later in this section. Ensure it is as expected. Set DBADXP
two to five milliseconds higher than the maximum expected or tolerable one-way channel delay.
Setting DBADYP and Relay Word bit DBADY operate the same for Channel Y.
CAUTION
!
Longer channel delays result in slower tripping times. The operate
speeds shown in Figure 3.6 and Figure 3.7 were measured using a
back-to-back connection. One-way channel delay times that exceed
the automatic compensation capability of the SEL-311L Relay (35
milliseconds) can result in misoperation.
Relay Word Bits CHXAL and CHYAL
The bits described above are combined into a single Relay Word bit for each channel, CHXAL
or CHYAL. When any of AVAX, RBADX, or DBADX assert, CHXAL asserts. Similarly for
Channel Y, when any of AVAY, RBADY, or DBADY assert, CHYAL asserts. Default factory
settings use CHXAL and CHYAL to enable display points, alerting operators to a problem.
Relay Word Bits ROKX and ROKY
ROKX or ROKY assert if both of the previous two received packets on Channel X or Channel Y
contain no errors. They are an instantaneous, unfiltered indication of channel health. The relay
uses ROKX and ROKY to produce the other Relay Word bits described above. ROKX and
ROKY can be useful for testing.
Relay Word Bit 87LPE
87LPE asserts when 87L protection is enabled. The relay monitors the available channels and
determines if enough information is available from each remote relay to perform protection in
either two-terminal or three-terminal mode. When the relay cannot perform 87L protection,
Relay Word bit 87LPE deasserts. There are no settings associated with Relay Word bit 87LPE.
Front-Panel LED 87LCH FAIL
Front-panel LED 87LCH FAIL illuminates when the relay detects a problem on either 87L
Channel X or Y. When the hot-standby feature is enabled, a channel problem on one of the two
87L channels will cause the 87CH FAIL LED to illuminate in only the relay that cannot receive
valid 87L data. In all other cases (two-terminal mode without hot-standby, or three-terminal
mode), the 87CH FAIL LED illuminates in both relays attached to the affected channel.
Use programmable Display Points and 87L Transmit/Receive bits to generate a local indication
of a transmit problem in a hot-standby application. Transmit the status of the Channel Y alarm
bit, CHYAL, using one of the four transmit bits of Channel X (T1X, T2X, T3X, or T4X).
Likewise transmit the status of the Channel X alarm bit, CHXAL, using one of the four transmit
bits of Channel Y (T1Y, T2Y, T3Y, or T4Y). Then use a local display point to signal a problem
on either channel in either direction.
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