We have gas turbine MS5001PA generator drive, the control system is Mark V TMR. I remark that during normal operation the control servo current of IGV on R, S, and T core are different.

In the PreVote data file is showing

In core R = - 4.7%
In core S = + 7.8%
In core T = - 4.9%

My question why in core S the value is positive and R and T are negative. The polarity is ok for all 3 ore.

Thanks and best regards

 

Great question!

Are there any Diagnostic Alarms related to the TCQA card also "active" at this time?

What is the Null Bias Current value for the IGV regulator/servo-valve output from the I/O Configurator?

What is the CSGV value for <R>, <S>, and <T>?

What is the CSRGV value for <R>, <S>, and <T>?

At what load is the unit running at? Base Load? Part Load?

Does the unit have conventional combustors or DLN combustors?

Is the unit operating at part load on IGV Exhaust Temperature Control when this is occurring? If so, what is TTRXGV for <R>, <S>, and <T>?

I think you will find that <S> thinks the IGVs are open much more than <R> and <T> (AND--more than the reference, CSRGV) think they're open, so therefore it's putting out positive current to close the IGVs.

It's also possible, though unlikely, that <R> and <T> think the IGVs are not as open as they should be and are putting out excessive negative current to close them and <S> is countering them because it believes the IGVs are closer to the reference than <R> and <T>. (Unlikely, but not impossible.)

Lastly, how have you verified that the polarity of the current being applied to each individual servo coil is correct?

 

Could be a problem with the TCQA/TCQC on the <S> Controller or, less likely, the servo. If you have spare cards, I would try a replacement. If you have no spares, you could try switching the <S> cards for <R> or <T> and see if the fault moves. In it's present condition, I would be a bit wary of re-booting controllers while running, especially the <R> or <T>

 

> Are there any Diagnostic Alarms related to the TCQA card also "active" at this time? <

The diagnostic alarm appeared is D1316 TCQA servo current #5 disagrees W/Ref
This alarm is coming time to time but it didn’t trip the unit

> What is the Null Bias Current value for the IGV regulator/servo-valve output from the I/O Configurator? <

Null Bias Current is: 3%
Current Gain is: 30%

> What is the CSGV value for <R>, <S>, and <T>? <

56.9 DGA for <R>
56.6 DGA for <S>
56.9 DGA for <T>

> What is the CSRGV value for <R>, <S>, and <T>? <

57DGA for the 3 cores <R>, <S>, and <T>

> At what load is the unit running at? Base Load? Part Load?
Part load, 7 MW <

> Does the unit have conventional combustors or DLN combustors?
Without DLN <

> Is the unit operating at part load on IGV Exhaust Temperature Control when this is <

Speed control

> If so, what is TTRXGV for <R>, <S>, and <T>? <

> Lastly, how have you verified that the polarity of the current being applied to each individual servo coil is correct? <

I opened the IGV with one servo connected, other 2 disconnected.

 

Bob Johnston has made a good call on this one. It appears that all three processors are calling for the same IGV position and all three processors believe the IGVs are at the same position, so it would seem there is some problem with the output of <S>.

I neglected to ask when this problem started. (My bad!) Did you find this discrepancy while investigating the Diagnostic Alarm, which is trying to tell you that there is some difference between what it thinks the servo current should be and what the actual servo current is. (Most Diagnostic Alarms don't result in a turbine trip; they are the result of a turbine trip or they are pointing to a problem, which if left unresolved, could result in a turbine trip.)

Have you verified the positions of the hardware ("Berg") jumpers on the TCQA and TCQC on <S> match those on <R> and <T>? (Jumper setting should not be changed while the processor is energized, and, also as Bob Johnston says, it's not recommended to power down <R> or <T> in the condition you describe.)

Have you checked the resistance of all three coils (without power)? They should all be approximately 1000 ohms, or thereabouts.

If you replace a TCQA, it's recommended to re-calibrate LVDT feedback (for all devices equipped with LVDTs). This is because the tolerances of analog components can cause small differences in the LVDT voltage feedback which may cause differences in feedback.

If the problem follows the card that's a pretty good sign the problem is on the card. So, if you have the time and the inclination it's a good idea to exchange cards between processors, and if the problem follows the card then replace that card with a new one from spares.

If the problem does not follow the card but stays with the same processor, then it could be that there is something wrong with IGV servo circuit wiring for <S>, or with the IGV servo coil for <S>. If you've checked the coil resistance and wiring outside of the Mark V and all is okay, then the ribbon cable connectors of the Mark V have been know to develop some corrosion and this could be at least part of the problem.

Has conductive grease been used on all the ribbon cables/connectors? (A tube is usually supplied in the box with each spare card.) The easiest way to apply the grease is to remove the cable from the receptacle on the card and wipe a light film evenly across the connector on the cable covering each of the pin "holes" and then insert the cable
into the card connector. I usually unplug and replug the connector a couple of times to try to make sure the grease gets distributed evenly on the pins and to make sure the connector is seated properly in the connector.

If you look at the diagrams in Chapter 7 of the Mark V Application Manual, GEH-6195, Sect. 7-6 (see Fig. 7.17), you will see that, as Bob Johnston has noted, servo output circuits include the TCQA and TCQC cards, as well as TBQC and QTBA cards, so all of the ribbon cables that interconnect these cards should be examined.

Please write back and let us know what you find.

 

Hi,

I found the abnormally during my check in the Pre-vote file and it was during the normal operation of the unit.

As you are asking, I check all the hardware “Berg” jumpers on the TCQA and TCQC on <R>, <S> and <T> and found in the same position for all 3 cores. I also measured the resistance on the 3 coils of the servo valve and found 1 K&#937;.

I can not Swap in the moment the TCQA/TCQC cards because the turbine is just started. I will came again for this subject when the unit will in shutdown.

Thanks a lot for your excellent cooperation