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Diagnostic alarms in Z VPRO
Diagnostic alarms are coming in Z VPRO intermittently and are getting reset...

Dear Sir,

We are facing a problem in our Frame -5 Mark VI VPRO card. The following diagnostic alarms are coming in Z VPRO intermittently and are getting reset after diagnostic reset after sometime:

1) Fault code 200, l4etr1_fb voting mismatch (K1_fdbk voted logic X-1 , Y-1 ,Z -0)
Trip solenoid 20FG-1 is connected to terminal - 1

2) Fault code 201 ,l4etr2_fb voting mismatch(K2_fdbk voted logic X-1 , Y-1 ,Z -0)
Trip solenoid 20FL-1 is connected to terminal-2

3) Fault code 100 ,TREG Solenoid Voltage -02 mismatch requested state

This may be due to following reason:-
1) ETR KZ1 and KZ2 are in de-energized condition (May be due to 28V power supply failure in VPRO Z or corresponding relay driver has failed)

2) The auxillary contacts of KZ1 and KZ2 from which the feedback (energized or de-energized) has been taken is malfunctioning intermittently

Z VPRO power- normal, Status - alarm state

Are there any other reasons which can generated above alarms?

What are the possible checks which can be done online (unit running condition) to ascertain the root cause of the above diagnostic alarms?

1 out of 1 members thought this post was helpful...

The 'etr' in L4ertn_fb refers to the Emergency Trip Relays on the TREG card, which are controlled by the VPRO cards. It would appear that for some reason, the ETRs for <Z> are dropping out and then resetting.

If the Mark VI is a TMR control system, the usual conditions which will cause the ETR relays to drop out are overspeed, and rate of change of <P> core speed pick-up input(s). So, if the speed feedback from one of the speed pick-ups connected to the <P> core is intermittent, then it can cause the ETRs to drop out, and then pick-up. BUT, there should be alarms (Process- and/or Diagnostic) to indicate a problem with the <P> core speed pick-up inputs. You can use Toolbox to monitor the VPRO speed pick--up inputs (in the Pre-vote tab) to see if <Z>'s speed pick-up input is stable or fluctuating when the other two <P> core speed pick-up inputs are stable.

If that isn't the problem, then the 28 VDC power supply for the <Z> VPRO could be the problem. BUT, I think (and I don't have access to the Mark VI System Guide at this writing to verify this) that the rack the VPROs are mounted in provides the DC power to all three VPROs--but I could be wrong on this. If the VPRO module rack supplies power to all three VPROs then it could be a rack problem, which might require replacing the rack (not likely, because there should be other Diagnostic Alarms to indicate a problem with the power supply(s)). If it's a VPRO 28 VDC problem, then the first thing would be to try replacing the <Z> VPRO with a new or refurbished VPRO. If the problem goes away by replacing the VPRO, then it's likely a VPRO problem. If the problem continues after replacing the VPRO, then it's likely a rack problem.

If the turbine control panel is dusty, then it could be that there is too much dust which could be causing a problem with connections in the <P> module--and it's just beginning with <Z>. Cleanliness is important, as is temperature. The <P> module is located in the top of the turbine control panel, and is exposed to the most heat in the turbine control panel.

The compartment/room where the Mark VI is located should be properly temperature-controlled--which DOES NOT mean it should be as cold as possible! The primary purpose of the Air Conditioner(s) in the compartment is to control humidity, so if it's too cold in the compartment/room where the Mark VI is located, and the outside ambient is humid and the cable entry area below the Mark VI is not properly sealed, then moisture will condense in the turbine control panel. And if there's dust in there, that's a perfect recipe for problems.

The ETRs are located on the TREG. There is at least one cable which connects each of the VPROs to the TREG; it could be a loose cable connection, or corrosion in the cable connectors, that's causing a problem. It's a good idea to check all the Mark VI cable connections during a turbine maintenance outage (when the Mark VI can be powered down), and check for corrosion, and reseat the cables and make sure the cable connector clips are properly "clipped". The connectors should be evenly seated in their connectors on the cards, and the clips should be holding them in place.

It's NOT likely that two ETR relays are bad, but it could happen. There should have been spare ETR relays provided with the Mark VI; just be sure to use the proper relays (check the operating coil voltage rating on the relay label!).

A VPRO can be replaced while the unit is running, but it is risky (meaning the turbine could trip) if there are other Process- and Diagnostic Alarms, which could indicate a problem with one of the other processors/modules. It's best to shut down the turbine to replace the VPRO.

But, that's about all the problems which could cause these nuisance alarms.

Hope this helps!!! Please write back to let us know how you fare in resolving the issue!

according to my humble experience, and as I am checking the TREG board drawing in the manual, I don't think that the problem is a 28V loss, because if so we should have P28Z alarm. Also you can check the K4Z relay directly in the terminal board (if it is hot or not) to verify if it is energised.

Also I want you to check the JZ1 cable, remove and tighten it correctly
hope this will help.

Waiting for your feedback.

1 out of 1 members thought this post was helpful...

Dear Partyman, CSA has given some great information and suggestions for diagnosis.

I would like to offer a few comments.

Each VPRO is supplied 125VDC from the PDM, it has its own internal power supplies to generate 5VDC and 28VDC. So it is not dependent on any control cores or other power supplies.

It is possible it is a cable or terminal board problem, but in my experience intermittent problems like this with the VPRO are an actual failure of the VPRO module itself. Not to say it could not be due to dust, cable issues or temperature control problems. But in my years of experience I have replaced at least 3 VPRO assemblies for issues similar to yours.

I have replaced a VPRO module with a unit online, at least 5 times. But you need to make sure there are no other diagnostic or voter mismatch alarms that could trip the unit when shutting down the VPRO core. I would suggest that if you or management want a 100% guarantee that the unit will not trip when trying to replace the VPRO, then the unit should be shutdown. The cost of lost generation compared to a scheduled shutdown is usually a great reason to schedule a shutdown for replacement.

Not saying its not possible to replace online as I have done it plenty of times, but there are simple mistakes that can cause a trip that I don't want to be remembered for. Please let us know how things work out for you.

Dear all,

First of all, I would like to thank you everyone for your valuable inputs.

I would like to mention that we received three more alarms intermittently (NOT ALWAYS) along with the above three alarms:

4)Speed Difference Protection Activated
5) Input signal "tnh_os_v" voting mismatch
6) Input "PR1_Accel" voting mismatch

But these three alarms 4), 5), 6) were getting reset and the alarms 1), 2), 3) were not. There was no fluctuation in speed input in <X>, <Y>, <Z>.

It seems that <Z> ETRs were getting de-energized due to intermittent fluctuation in speed signal to <Z> but is not getting energized after normalization of <Z> speed signal.

After discussion with the management regarding involved risk of GT tripping while replacing the VPRO <Z> on-line, one extra STG was started to cater the load demand in case of the GT tripping.

After ensuring no other diagnostic alarm in VPRO, VPRO <Z> was replaced on-line. the above alarms got reset but started coming again after sometime.

Then, OEM personnel recommended for jumpering of speed signal to VPRO <Z> with speed signal to <T> (77 NH-3) even though there was no speed signal loss or mismatch in VPRO <Z>. Actual 77 HT-3 speed signal was disconnected. The above alarms got reset and there were no further diagnostic alarms in VPRO <Z>.

I would also like to mention that there is no provision for monitoring of 28 V supply in VPROs in out toolbox. Signal P28Z does not exist. However , there is provision for monitoring of 28 V supply in case of <R>,<S>,<T>.

Thanks VERY MUCH for the feedback!

And, congratulations on successfully switching VPROs on-line!

It's not exactly clear which alarms are Process Alarms and which are Diagnostic Alarms (I presume 5 is a Process Alarm, and 4 & 6 are Diagnostic Alarms). And, I believe the alarms are pointing to a difference between the speed pick-up inputs to the VTUR cards and the speed pick-up inputs to the VPRO cards.

The protection in the VPRO, I believe, runs at 100 Hz, and the application code probably runs at 25 Hz. The VPRO (which primarily generates speed-related Diagnostic Alarms under such circumstances) is going to see the problems much more "often" than the application code (which generates Process Alarms), hence some of the reasons for not getting all the same alarms all the time.

At any rate, it seems you have isolated the problem to the speed pick-up, OR the wiring between the speed pick-up and the VPRO....

Please write back when you get a chance to check the pick-up and the wiring!