We had a problem recently and had an alarm Voltage unbalance on reg 5 in all R, S, T processors after 5 seconds of a trip. machine tripped on trouble, and observed CSGV went to 44 deg from 57 deg and tripped. and also command CSRGV was at 57 deg before trip, then immediately responded to giving 60 deg while tripped. IGV actually closed slightly, as CPD was also lowered. Is there any problem on servo or the hydraulics? servo was replaced, as the LVDTs were on maximum selected. Is LVDTs could also create problem. When do this Voltage unbalance alarm will come.

 

It's not very clear the sequence of events, and I have never seen the Diagnostic Alarm you have alluded to.

Precisely, what was the exact Diagnostic Alarm that was annunciated?

Also, are there any grounds on the 125 VDC battery? What is the voltage split of the incoming 125 VDC supply (as measured on the input terminals of the <P> core)?

Also, is there a <DACA> module (or modules as in more than one) used to supply DC to the Mark V from an AC source (or sources)? If so, what is the AC source, and what was it doing during this event?

Next, what other alarms, Process and Diagnostic, are present on the panel? I'm referring to just prior to the event, and any which might be present at all times, and specifically when the unit is running? Not the alarms that came up during the event, but the alarms that were present and acknowledged but not resolved? Including any LOCKed alarms.

Lastly, what was occurring in the plant or on the grid when this event occurred? Was there a frequency disturbance? A lightning strike? A heavy rainstorm? Some other plant disturbance, like loss of gas fuel supply pressure or something similar?

Please provide all of the requested information; without it we can't hope to provide a useful response.

 

Dear CSA.

Thanks for response. Machine run for three days without any problem (!) and unfortunately yesterday we had this similar trip "IGV trouble trip" when IGV commands were 57 deg as per trip log ; this time incidentally we observed immediately after trip that the LVDT-2 was showing a varying higher value up and above a mean value of 43 deg while LVDT1 was at the required 32.5 deg in all processors. Voltage excitation and feedback were checked in mark-V and field JB and also found as actual (0.70 for LVDT-1 and 1.2 V for LVDT-2). Physical inspection shown the LVDTs are not loose and was in closed position. After a 10 seconds gap, this LVDT-2 also came down to 32.5 deg .While checking the IGV junction box, we observed when we pulled the LVDT2 wires inside JB, there was movement in the IGV slightly, as we are on autocalibration mode with 32 deg command. As there was a visible difference between LVDT1 & 2, LVDT2 was replaced.

The old LVDT2 wires were checked and no serious insulation damages were found. JB terminals tightness were found okay and was found intact. As we are not having LVDT-1,2 data archiving, and our system has only CSGV (volted) value monitoring, CSGV was checked against command CSRGV and observed CSGV feedback has shown hunting prior to trip. Whether actually there was movement in both LVDTs is not clear ( CPD should have been checked..missed yesterday. What we concluded is that, as this LVDT was hunting, controls will take maximum value of LVDT2 and thus may have given command to reduce this, and by doing so IGV was closed to less than 50 deg, and thus causing immediate trip.

Also observed that the alarm mentioned in the thread : The alarm in <I> was for " LVDT voltage unbalance Reg#5 " which was there found started as toggling for almost 12 hours (!!) prior to trip, in the diagnostic alarms list.The help diagnostic alarm file was ,mentioning the alarm drop number with in a range of drop numbers giving details as " position deviation between calculated LVDT values >5 deg ".

 

Dear CSA.
earlier post has not covered some of your queries. I have checked the alarms again and following are the observations.

1)No DC Voltage is present in MarkV

2)The voltage split is okay +56 / -74; There is a steady DC source as well as a 110 vac supply for the second supply from UPS, which is again converted to DC through a rectifier unit to augment the DC source. There is no abnormal functioning in this

3) There was no grid disturbance, lightening etc. Other units were not affected at same time.

4) On the first trip process/ diagnostic alarms before the event relevant to this unit is not there except a diagnostic alarm TCD1 contact input failure toggling in <CD>, which is a known and is persisting for a long time. But after the trip we had a diagnostic alarm (5 seconds after trip) TCQA LVDT voltage unbvalanaced reg#5 in all processors. IGV Trouble alarm (|CSRGV-CSGV|>7.5 deg for 5 seconds came, after 5 seconds of trip on IGV Trouble TRIP ( which can be also from CSGV<50 deg after 95% speed condition or from earlier discussed trouble alarm condition)

On the second time trip, ( when we got some concrete issues with the LVDT2), only notable alarm before trip was
DALARM TCQA LVDT voltage unbalanced REG#5
PALARM INLET GUIDE VANE CONTROL TROUBLE TRIP
EVENT Master Protective\Turbine Trip