Hello,

I'm in the process of quoting a frame 5 (Simple-Cycle Generator Drive) Mark II to A-B PLC control retrofit and wanted to know if you could shed some light into the pitfalls. I'm an Ex-GE Controls Engineer that has a lot of GE Controls experience, but little time with the A-B RSLogix5000 PLC. Any help will be greatly appreciated.

Thanks in advance.

 

Hello,

Pitfalls?

You'll have the usual pitfalls with any modern retrofit, most notably the HMI displays will consume three or four times the estimated effort (and cost) unless you are very firm with the contract, stating any changes after initial approval will be at normal field engineering rates plus T&L.

You will need to write all of the speed control (droop, and Isochronous if existing in the Mark II) and such in RSLogix. An older Frame 5 probably doesn't have a combustion monitor, but it may have water injection for emissions control. You'll have to write the exhaust temperature control algorithm in RSLogix, also.

You'll need to deal with LVDTs somehow (if the macine uses them, which it likely will if it uses gas fuel). And, you'll have to deal with the bipolar servos, which are usually two-coil servos.

Flame detectors may be an issue, too, unless you plan on re-using the existing power supply/indication modules or providing new 4-20 mA detectors.

There's the issue of speed detection for primary overspeed protection, and for that you'll need high-speed detection modules.

There's also the issue of vibration detection; you may need to have new sensors or third-party modules.

A lot of people have done this before, with mixed results. I've personally seen some nice work, but I've seen some really bad work, too. The programmer really needs to understand turbine control, especially the smooth transition from speed control to exhaust temperature control, and back. And make that happen with RSLogix programming capabilities. Start-up and acceleration and shutdown are important, too. I've seen some obvious cobjobs where more than three or four really intelligent PLC programmers obviously tried to make this or that work with that or this (notably the transition from speed to exhaust temperature control and back) that were horrible, and then a simple single value of load was used as maximum for any and all operating conditions.

A-B is very proud of their equipment, and it takes quite a bit of money to get them to part with it. Neither the hardware nor the software is cheap for a single purchaser; it does get less expensive in a volume buy but that doesn't sound like the case here.

You'll have to "translate" the Mark II Control Specification's voltages into engineering units for set points and control & protection parameters.

That's about all I can think of off the top of my head. A realistic proposal, including time for learning RSLogix and any interfaces/converters, and for getting familiar with the Mark II drawing will probably surprise you. Again, the hardware and software themselves aren't cheap. And you have to assemble them in a panel. And determinate all the existing wiring and reterminate it in the new panel (planning for short wires!), plus get the old panel out and the new panel in. Plus ship the new panel, and properly dispose of the old panel.

Hope this helps!