PLC BASED DIGITAL GOVERNOR VS PROCESSOR BASED DIGITAL GOVERNOR 1

[subash148]

I am in the process of writing a specification for Governor of 112 MW hydropower plant.The old mechanical governor is going to be replaced with new digital governor. Now a days, we can find the vendor which supplies both the PLC based digital governor as well as Processor based digital governor. I would like to know the basic difference bewteen PLC based digital governor and precessor based digital governor. If you have had the experience of using both which one would you recommend?

SG

 

[ScottyUK]

They're both processor-based' so on face value the question is kinda meaningless. There are probably three major families of digital governor: custom-designed; PLC-derived; DCS-derived, so I guess that's what you are really asking about.

If you take, say, a PCS-7 controller as an example of the PLC-derived type and an Emerson Ovation controller as an example of the DCS-derived type, there really isn't a massive gap between the two in capability. The PLC-derived stuff has really closed the gap in the last ten years or so. Both offer redundant processors and so on. In my opinion the DCS-derived types generally have a better - or perhaps more mature - set of software tools, but it's not a deal-breaker these days. Compared to either a PLC-derived or DCS-derived solution, custom-designed solutions usually have far poorer operator interfaces, more awkward engineering interfaces, are generally less flexible, and harder to support in the long term.

 

[mgtrp]

Interestingly, my experience with governor controllers is somewhat the opposite - I have had nothing but problems with PLC-based governors, and very good experience with dedicated governors.

The PLC-based units tend to offer enormous flexibility in terms of what they can do, which in my experience only tempts people to use this flexibility - this results in the use of unique governor solutions for different sites. Because of this, the user manuals tend to be more general making the governor harder to support unless very familiar with the program (lots of vendor support required!). I've also had a lot more issues with faults, although I suspect that this may be more due to PLC firmware bugs etc than issues with the governor controller per se (all of the PLC-based solutions have been on the same PLC platform).

In comparison, I've found that the only dedicated governors that I've used (Woodward 505H, in multiple sites with several different utilities), while inflexible, steered the plant designers into a simpler, more robust design; have been much more reliable in terms of hardware and software bugs; and are simpler to configure etc, with better documentation.

I have not worked with a DCS-based hydro governor to compare.