Automatic Supervision - Toshiba GRT100 Series Instruction Manual

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 is waiting
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 by itself, plays an important role. The numerical relay based on the
microprocessor operations is suitable for implementing this automatic supervision function of
the protection system. The GRT100 implements the automatic supervision function taking
advantage of this feature based on the following concept:
 The supervising function should not affect protection performance.
 Perform supervision with no omissions wherever possible.
 When a failure occurs, it should be able to easily identify the failure location.
Note: Automatic supervision function includes automatic monitor function and automatic test
3.3.2 Relay Monitoring and Testing
The relay is supervised with the following items.
AC input imbalance monitoring
The AC current input is monitored such that the following equation is satisfied and the health of
the AC input circuit is checked.
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
A/D accuracy checking
An analogue reference voltage is transmitted to a prescribed channel in the analogue-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
The memories are monitored as follows depending on the type of the memory and checked that
the memory circuits are healthy:
 Random access memory monitoring:
 Program memory monitoring: Checks the checksum value of the written data.
 Setting value monitoring:
function. For the terminology, refer to IEC IEV 60448.
Writes/reads prescribed data and checks the storage function.
Checks discrepancy between the setting values stored in
duplicate.
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