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3.3 Automatic Supervision
3.3.1
Basic Concept of Supervision
Though the protection system is in a non-operating state under normal conditions, it waits for a
power system fault to occur at any time, and must operate for the fault without fail. Therefore, the
automatic supervision function, which checks the health of the protection system during normal
operation, plays an important role. The GRL150 implements an automatic supervision function,
based on the following concepts:
• The supervising function should not affect the protection performance.
• Perform supervision with no omissions wherever possible.
• When a failure occurs, it is recorded as Alarm record, the user should be able to easily identify
the location of the failure.
3.3.2
Relay Monitoring
The relay is supervised by the following functions.
AC input imbalance monitoring
The AC current input is monitored to check that the following equation is satisfied and the health
of the AC input circuit is checked.
• CT circuit current monitoring
Max(|I a |, |I b |, |I c |) − 4 × Min(|I a |, |I b |, |I c |) ≥ k 0
where,
Max(|I a |, |I b |, |I c |) = Maximum amplitude among I a , I b and I c
Min(|I a |, |I b |, |I c |) = Minimum amplitude among I a , I b and I c
k 0 = 20% of rated current
The CT circuit current monitoring allows high sensitivity detection of failures that have occurred
in the AC input circuit. This monitoring can be disabled by the scheme switch [CTSVEN].
A/D accuracy checking
An analog reference voltage is input to a prescribed channel in the analog-to-digital (A/D)
converter, and it is checked that the data after A/D conversion is within a prescribed range, and
that the A/D conversion characteristics are correct.
Memory monitoring
Memory is monitored as follows, depending on the type of memory, and checks are done to verify
that memory circuits are healthy:
• Random access memory monitoring:
• Program memory monitoring: Checks the checksum value of the written data.
• Setting value monitoring:
Watchdog Timer
A hardware timer that is cleared periodically by the software is provided, which checks that the
Writes/reads prescribed data and checks the storage function.
Checks discrepancies between the setting values stored in
duplicate.
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