Ct Circuit Current Monitoring - Toshiba GRL100-701B Instruction Manual

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 the system checks that the data after A/D conversion is within the prescribed
range and that the A/D conversion characteristics are correct.
Memory monitoring
The memories are monitored as follows depending on the type of memory, and the health of the
memory circuits is checked:
• Random access memory monitoring:
• Program memory monitoring: Checks the checksum value of the written data.
• Setting value monitoring:
Watchdog Timer
A hardware timer, which is cleared periodically by software, is provided and the system checks
that the software is running normally.
DC Supply monitoring
The secondary voltage level of the built-in DC/DC converter is monitored and the system checks
that the DC voltage is within the prescribed range. If a failure is detected, the relay trip is blocked
and the alarm is issued.
Furthermore, DC supply is monitored by using the binary input signal in the current differential
protection. If the binary input signal is "OFF" (= DC supply "OFF" or "Failure"), the ready
condition of the differential protection is "OFF" and both local and remote relays are blocked.
(Refer to Table 3.2.1.2.) This monitoring is provided to surely block the unwanted operation of
remote terminal relays caused by sending the remote terminals an uncertain data even for short
time at DC supply off or failure, though the former monitoring is enough at DC supply off or
failure in general.
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(|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 [CTSV].
Writes/reads prescribed data and checks the storage
function.
Checks for discrepancies between the setting values stored in
duplicate.
 174 
6 F 2 S 0 8 5 0