Sel 411L - Figure 3.209 Channel Switchover Logic (87 HSB); Table 3.158 Hot Channel Standby Logic Relay Word Bits

P.3.299
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Standby Channel Switchover Logic
Figure 3.209 Channel Switchover Logic (87HSB)
The relay provides symmetrical logic to declare Channel 2 as problematic.
If Channel 1 is set as primary (87PCH = 1), and logic declares Channel 1 to be
problematic (while Channel 2 receives no such declaration), logic asserts the
87HSB bit to switch the relay from Channel 1 to Channel 2. If Channel 2 is
problematic as well, there is no 87HSB assertion and the relay continues to
use Channel. This usage depends on Channel 1 impairment and varies from
use of current data in the master mode to loss of the 87L function entirely,
depending upon other conditions.
The logic for Channel 2 is fully symmetrical. With both channels equal (both
problematic or both not problematic) no switchover occurs (87HSB
deasserted) and the system uses the primary channel, as the 87PCH setting
indicates. A delay timer set to 250 ms is used to prevent switching between the
channels when they are near equal quality. In steady states, the switchover is
instantaneous. However, after the switch, it will take the intentional time delay
to switch back to the previous channel.
The relay provides an overriding logic to facilitate the channel loopback test
mode. When in the loopback test mode (87LOOPT Relay Word bit asserted)
relay logic forces the 87L function to work with the channel you selected for
loopback with the LOOPC test parameter, regardless of the 87HSB logic (see
Figure 3.209) or the 87PCH setting.
Relay
Word Bits
S2 = Position 1 if
Timer Output = 1
87CH1OK
ECH1OUT
87CH1NS
87CH1FO
87CH2NS
87CH1LS
87CH2HS
Setting
87PCH = 1
Setting
87PCH = 2
87CH2OK
ECH2OUT
87CH2NS
87CH2FO
87CH1NS
87CH2LS
87CH1HS
Test Param.
LOOPC = 1
Setting
87PCH = 2
Setting
87PCH = 1
Test Param.
LOOPC = 2
0
250 ms
2
1
S2
Timer Output
87LOOPT
S1 = Position 1 if
87LOOPT = 1
1
2
S1
Word Bit
87HSB
Table 3.158 Hot Channel Standby Logic Relay Word Bits
Name Description
87HSB Standby channel in use
ECH1OUT 87L Channel 1 forced out of service
ECH2OUT 87L Channel 2 forced out of service