Toshiba GRZ100 B Series, Instruction Manual

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the presence of the zero sequence current on the power system by introduction of the residual
circuit current.
Only zero sequence monitoring is carried out for the current input circuit, because zero sequence
monitoring with the introduction of the residual circuit current can be performed with higher
sensitivity than negative sequence monitoring.
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
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: Writes/reads prescribed data and checks the storage
function.
•
Program memory monitoring: Checks the checksum value of the written data.
•
Setting value monitoring: Checks discrepancy between the setting values stored in
duplicate.
Watchdog Timer
A hardware timer which is cleared periodically by software is provided and it is checked that the
software is running normally.
DC Supply monitoring
The secondary voltage level of the built-in DC/DC converter is monitored and checked that the
DC voltage is within a prescribed range.
3.3.3 CT Circuit Current Monitoring
The CT circuit is monitored to check that the following equation is satisfied and the health of the
CT circuit is checked.
Max(|Ia|, |Ib|, |Ic|)
−
4
×
Min(|Ia|, |Ib|, |Ic|)
≥
k0
where,
Max(|Ia|, |Ib|, |Ic|) = Maximum amplitude among Ia, Ib and Ic
Min(|Ia|, |Ib|, |Ic|) = Minimum amplitude among Ia, Ib and Ic
k0 = 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 [CTSV].
3.3.4 Signal Channel Monitoring and Testing
Signal channel monitoring
In the PUP, POP or UOP schemes, when a trip permission signal is received consecutively for 10
seconds, this is considered to be an error of the signal channel and an alarm is issued. When the
signal modulation is a frequency shift method, if neither the trip permission signal nor the guard
signal can be received, an alarm of "Ch-R1. fail" is issued.