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PCU2 Frequent Slave Failure Alarms (Symphony Harmony)
We have ABB Symphony Harmony system with PCU2,5,8,21 (4 PCUs) for the control of HRSGs and BOP Equipment. Recently, we started facing slave failure alarms on PCU2 and PCU5. We noticed high ambient humidity in control room reaching maximum of 80% which was condensing at times. The slave failure alarms came randomly mostly during night time and remained for 2-5 minutes and reset on their own. The slaves with alarms were mostly same (5-6 slaves per PCU). We increased the temperature of control room from 22 degree C to 26 degree C and situation got better. PCU5 alarms stopped altogether, while PCU2 alarms frequency and timing decreased. No alarms have been noted on other PCUs PCU8 and PCU21.
During machine standby, we also inspected the slave cards and found some impressions of humidity on them which we cleaned. We replaced one of the slave cards as well. But the alarm came on the new slave card as well during next operation.
UPDATE: Today, all the slave cards of module 3 (slave 1 to slave 33) of PCU2 got bad and reset on their own within 1 second. This instance repeated twice and reset within 1 second. In 3rd instance, alarms persisted for 5 minutes. We checked status and problem reports of BRCs and found normal. Control room humidity was noted around 60-70% and temperature 24 degree C at the time of alarms.
Background:
During annual outage in October 2019, we cleaned PCU2 and PCU5 cards after removing from backplane. Both the PCUs were restored normally afterwards and no alarms were reported from October 2019 - May 2020. From June, ambient humidity starts rising in our country and this is when alarms started coming this year.
Experts are requested to advise on:
- Are the slave failure alarms due to card power interruption or communication failure with BRC?
- Can one faulty slave card cause this?
- What can be the reasons for all module 3 cards giving failure alarm? Can it be due to power interruption or I/O expander communication interruption?
- What are the checks we can perform to identify the root cause?
During machine standby, we also inspected the slave cards and found some impressions of humidity on them which we cleaned. We replaced one of the slave cards as well. But the alarm came on the new slave card as well during next operation.
UPDATE: Today, all the slave cards of module 3 (slave 1 to slave 33) of PCU2 got bad and reset on their own within 1 second. This instance repeated twice and reset within 1 second. In 3rd instance, alarms persisted for 5 minutes. We checked status and problem reports of BRCs and found normal. Control room humidity was noted around 60-70% and temperature 24 degree C at the time of alarms.
Background:
During annual outage in October 2019, we cleaned PCU2 and PCU5 cards after removing from backplane. Both the PCUs were restored normally afterwards and no alarms were reported from October 2019 - May 2020. From June, ambient humidity starts rising in our country and this is when alarms started coming this year.
Experts are requested to advise on:
- Are the slave failure alarms due to card power interruption or communication failure with BRC?
- Can one faulty slave card cause this?
- What can be the reasons for all module 3 cards giving failure alarm? Can it be due to power interruption or I/O expander communication interruption?
- What are the checks we can perform to identify the root cause?
