Sel 411L - Figure 3.208 Principle of Hot Standby Channel Switching; Table 3.157 Hot Standby Logic Settings

P.3.298
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Standby Channel Switchover Logic
Figure 3.208 Principle of Hot Standby Channel Switching
Table 3.157 lists settings applicable to the 2SD switchover scheme.
Figure 3.209 presents the switch-over logic. The logic develops an indication
of a problematic channel, compares the overall quality of the two channels,
and switches over via the 87HSB Relay Word bit accordingly, taking into
account your assignment of primary and standby channels with the 87PCH
setting.
Because the relay can use external time sources for synchronization, the
preliminary determination of degraded channel quality includes not only
reception of data or low level of data errors, but also the quality of data
synchronization. The time fallback logic (see 87L Time Fallback Logic) may
intentionally mark a given channel as unusable in the context of the 87HSB
logic so that the hot standby logic can switch channels and potentially
preserve 87L function dependability if the other channel does not use external
time sources for data synchronization.
Additionally, the relay provides SEL
OGIC control equation ECH1OUT to
force switchover with such user-defined conditions as excessive channel
latency or noise. You can use the channel-alarming Relay Word bits (see 87L
Channel Monitoring and Alarming Logic) to design the custom condition
ECH1OUT for marking Channel 1 as problematic.
The 87HSB logic declares Channel 1 problematic for any of the following
cases.
➤ Channel 1 is not OK (87CH1OK deasserts).
➤ The time fallback logic forces out Channel 1 (87CH1FO
asserted).
➤ The SELOGIC control equation ECH1OUT marks Channel 1 as
problematic.
➤ Channel 1 loses the ability to align current data (CH1NS
asserted), while Channel 2 can align data (87CH2NS
deasserted).
➤ Channel 1 is of low synchronization quality (87CH1LS
asserted) while Channel 2 has high synchronization quality
(87CH2HS asserted).
Table 3.157 Hot Standby Logic Settings
Setting Description Range Default
87PCH Primary channel for the 2SD application 1, 2 1
ECH1OUT Enable Channel 1 out of service in the
2SD application
SEL
OGIC control
equation
NA
ECH2OUT Enable Channel 2 out of service in the
2SD application
SEL
OGIC control
equation
NA
Remote data over primary
channel (87PCH)
87L Channel
Monitoring and
Alarming
Hot Standby
Channel
Switching Logic
Align, filter,
calculate aux
signal features
87L
Apply proper security
when switching
Relay Word Bit
87HSB
Remote data over standby
channel
0
1