GE LM 6000 VBV position error

L

Thread Starter

Liji

In our gas turbine (GE LM 6000 with netcon 5000 control), while running condition VBV A & B position showing a difference of 8-10 %. We stroked/calibrated VBV with high speed crank and it shown a position f/b difference of 1-2% only. But with the startup it went to the previous condition.

We checked on engine and off engine cables for recommended resistance and found it is matching. After that we have replaced both VBV actuators with feedback and on-engine cable of actuator which is showing higher value. Still no result and f/b is showing the same difference of 8-10%.

Have any idea what to check next?
 
Hmmm....

Have you tried swapping the two inputs and seeing if the difference is the same?

Are the two inputs connected to different terminal boards, or the same terminal board? Do you have a spare terminal board to try?

Have you verified the cabling between the terminal board(s) and the Netcon cards?

Are the two inputs connected to the same Netcon card? Do you have a spare Netcon card, or can you swap cards to see if the problem follows a card?

Please write back to let us know what you find?
 
Hi,

1. We swapped the cables and checked. the problem also got swapped.

2. From the field the inputs for both VBVs (VBV A & B prim, sec 1, sec 2 and T/M) are coming to same card TBA09 along with that of VSVs. We changed the card, but same condition only.

3. The inputs connected to same Netcon card and we changed the card also.

The problem is still existing only while running and only after 30 mw (vbv dmd at 15%). Normal behaviour during stroking.
 
Liji,

Thank you VERY MUCH for the detailed information.

It would appear that the condition is real--there is truly a difference in VBV position above 30 MW. Do you have data from before the problem started to see if the axial compressor discharge pressure is lower (or higher) when the differential exists than when it didn't? (You must compare axial compressor discharge pressures at roughly the same ambient and load for the best comparison.) If so, you can say with a fair degree of certainty that the VBVs are not in the same position.

Are you certain the condition is not real?

Is there something about the way the sensors are mounted that would make them or their mounts "move", say, when heat or pressure was higher?

It would seem that's where you need to concentrate your efforts at this point--trying to understand what is causing the apparent differential at high load. You have replaced just about all of the control elements (cables; sensors; cards) so it would seem that for some reason the differential is "real" (either the VBVs are not at the same position, or something about the sensor/mounts is being affected by heat/pressure and causing the appearance of a differential).

Remember: Troubleshooting is many times a logical progression of steps, eliminating various 'suspects' along the way until you finally arrive at the cause. And, some times, when problems are allowed to persist for some time (I'm <i>not</i> saying that has happened at your site--but it does happen at lots of other sites, and many people read these threads) there can be more than one cause or contributor to a problem.

Please write back to let us know how you fare!
 
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