We are having a 9FA machine with LCI. During first synchro GCB opened on Reverse Power and machine continued to run on FSNL. While looking at trends it was observed that FSR (fuel stroke reference) has ramped down pretty fast as soon as the machine got synch. Could someone list out the probable reasons (including process side) which can cause such a behavior.

Transducer connections providing MW to Mark-VI were also found to be reversed and was normalized later. Does this have a bearing on the observed phenomena.

 

Debashish... the error in the MW transducer would certainly explain it, IFF, the Reverse-Power Protection signal was derived from this transducer.

Regard, Phil Corso

 

Phil Corso is right. If the MW transducer input is reversed, then when the unit is trying to increase load (which it will generally try to do on initial synchronization attempt, to what's called "spinning reserve" setpoint) as the load is increasing the feedback will go in the opposite direction, and as more fuel is applied the feedback will continue to go more negative even though the actual load is going positive, until the reverse power function of the Speedtronic panel as actuated.

I'm kind of curious, though, because there are usually two, sometimes three, MW transducers for most F-class machines. You're saying the feedback from both of them, or at least two of them, was reversed?

 

Thanks a lot Phil and CSA. Yeah CSA you are right. There are three transducers,one feeding to Mark-VI, the other two to the AVR and Gen Exciter respectively. Whereas the Mark-VI signal was going down the ones in the other two were going up.Would you like to add any other observation in view of this info ?

 

Yeah. I think you have it backwards. A 9FA probably has DLN combustors, and that means it probably uses Constant Settable Droop, which means that load (MW) is considered a critical input, which means that there are likely two (2) MW transducers feeding the Mark VI, and one transducer feeding the "AVR" (which is the same thing as the "Gen Exciter", or is on most machines, anyway).

I would be extremely surprised to find an F-class turbine with a single MW transducer input--shocked, in fact. I won't say it hasn't happened, or that the GE Energy Products-Europe people in Belfort, France, haven't taken a liberty or two, but it would be pretty unlikely given GE's control philosophy regarding redundancy for critical inputs. While it's not impossible, it would be unlikely.

I have been wrong in the past, and will be wrong again in the future, though.

The last observation I have is that if this is a new unit installation and the MW transducer input(s) wasn't(weren't) verified properly during loop-checks, well, that doesn't bode well for other inputs and outputs to work properly during commissioning. If this is a re-start of an existing unit and somehow the MW transducer input leads were swapped, and no one thought to verify this input if the wiring connections were disturbed, then that is poor maintenance practice. Particularly with regard to a device like this which can be wired incorrectly and have such a large impact on operation.

Best of luck!

 

I got a story about reverse power that just happened. We are doing testing of all units and part of the test is to take voltage 95% to 105% rated (swing the vars...give and take...leading to lagging...0.5 to -0.5 PF...13.2 to 14.4....however the heck you want to say it). This is done at various MW steps from off line to full load. Because of system loading, it was a good time to start at full load and work our way down. Got to full load, went from 1.0 to giving vars. Then went back to 1.0. Then went 1.0 to taking vars and *TRIP*. Prime mover was still online, but generator breaker was open. Reverse power flag on relay.

The testing guys are also protection engineers...and after explaining to plant staff that you don't trip reverse power on REACTIVE power, only real power, they started doing some investigating. Long story short, the polarity on one of CT (current transformers) was swapped.

Point? If you only trip on reverse power on rare occasions, check the wiring as it may be only when you are in a certain quadrant of the reactive capability curve.