Hydro governor on float control 3

[CuriousElectron]

Hi,
I'm not sure anyone would be able to answer my question, but I was trying to get a better understanding of how the float control mode for a hydro generator with governor works. I think the basic premise here is that the reservoir never gets depleted by constant inflows and runoffs. I can see that in a wet season with frequent precipitation, but in a dry year, is there still any inflows?
I guess Lake mead is a perfect example..The lake level keeps dropping..

Thanks,
EE

 

[crshears]

I'm curious to find out what you mean by float control; at first blush, it sounds like forebay level comes up, unit starts, synchronizes, and loads until forebay level drops, at which point unit unloads and shuts down.

At second blush, it sounds like a control mode from one of the very modern automated and semi-autonomous run-of-the-river plants I used to operate whereby there was a minimum allowable forebay level which fed into a P&I controller that ran back the generator['s] output then modulated it in such a way as to regulate said level at said minimum.

I'm no Lake Mead expert, but it seems to me that despite the prevailing climatic conditions leading to next to inadequate water inflow, water is being dawn off anyway, because it's needed/desired; of course eventually the bank will be empty, and there simply won't be any water left to release - and no, creation does not recognize the concept of continuous deficit spending in such circumstances.

In my view, this practice will eventually bring about massive disruptions to all downstream populations who will eventually find themselves with not a drop to drink.

Incidentally, during weeks-long stretches without precipitation of any kind, we used to encounter "negative inflow," which was the term we used to describe the situation where all outlets / release points from a lake were closed off / at zero flow and the water body level would drop anyway due to evaporation/transpiration. Of course in instances where that body of water was the only supply to a river, closing all outlets was not feasible, as minimal releases had to be maintained to sustain the river's flora and fauna, not to mention the riverside's human inhabitants.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

That makes sense, CR.
Consider a reservoir fed hydro plant and a downstream Run-of-the-River plant.
At steady load conditions, the Run-of-the-River plant will pass enough water to maintain the level of the forebay.
The reservoir based plant will generate enough additional power to service the load.
Now the load drops. The upstream generator needs less water, and with less flow, the water level starts to drop in the forebay of the RotR plant. The RotR plant then passes less water to maintain the forebay level.
The upstream plant opens up to make up the power difference.
A RotR plant must balance its water use to match the river flow. A swing generator located elsewhere will compensate for variations in output of the RotR plant as the river flow varies.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Hi Bill et al,

In the scenario you describe, the generation dispatchers would very likely reduce the output of the RotR GS concurrently with the reduction of output at the ResFed GS, using the actual volume of water passed at each station as a guide so as to balance them to each other. This would mitigate the creation of the otherwise-inevitable oscillations of river elevation that would result.

Numerous hydraulic plants here in Ontario are cascading plants without additional inflow between them, but the distances between them can be all over the map resulting in various time constants between plants. By sheer experience, operators/generation dispatchers very quickly learn to take these physical time constants into account when deploying the generating facilities under their control.

If water control on a grand scale interests you, this

https://legacyfiles.ijc.org/tinymce/uploaded/Plan2014_CompendiumReport_1.pdf

is the link to Plan 2014, as established and adopted by the International Joint Commission, for the regulation of outflows of Lake Ontario, this being a boundary body of water between Canada and the United States and therefore requiring mutual agreement and co-operation by both nations to control.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[CuriousElectron]

Thank you for the explanation. Based on the provided response, it seems that unless there is precipitation or seasonal runoffs(inflows) that would increase lake elevation, operating a generator would cause the forebay elevation to drop rougly as a function of operating MW output of the unit.

 

[waross]

Don't confuse the forebay level of a large reservoir with the forebay level of a run of the river plant.
It may take weeks a or months or years for generator loading to significantly change the level of a large reservoir.
A R-o-t-R plant may draw the forebay down in an hour or less.
It was reported that the weight of water in Williston Lake, the reservoir for the W.A.C. Bennett Dam, caused the city of Prince George to settle 1/4 inch.
Prince George is 90 Miles from the end of Williston Lake and 150 miles from the W.A.C. Bennett Dam.
With a surface area of 1,761 km[sup]²[/sup] it would take about 1.7 cubic kilometers of water use to drop the level one meter.
I agree with CR that the levels are probably maintained by good operating practice, but I suggest that level control is a back-up in the event of operator shortcomings.
A similar situation may be the frequency control at our small island plant.
There was a check list that the operators completed every 15 minutes. One of the checks was trimming the frequency to 60 Hz.
Between checks the frequency was held reasonably close by droop control. In the event of operator shortcomings, (Sleeping on the job? It was hard to get good help.) droop control took over until the next operator intervention.
I can see level control being a similar back up that is seldom activated.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Based on the provided response, it seems that unless there is precipitation or seasonal runoffs(inflows) that would increase lake elevation, operating a generator would cause the forebay elevation to drop roughly as a function of operating MW output of the unit.

Roughly, yes, but unless the reservoir has nothing but completely vertical walls all the way around, the delta V : delta H [ the change in stored volume with changes in elevation ] is not constant. Drawing the second million cubic metres of water from a reservoir will cause a greater elevation change than drawing off the first million [use billion for extremely large reservoirs].

I suggest that level control is a back-up in the event of operator shortcomings.

I can see level control being a similar back up that is seldom activated.

Hi Bill, my background comports well with you thinking; the plant I cited above and one other of very similar design are the only two plants in Ontario that I am aware of as having any functioning automated forebay level control system in service, and both of those plants are ROTR. High or low reservoir annunciations are very common indeed, but systems to backstop operator shortcomings as regards automated reservoir level control are in my experience virtually nonexistent.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

Hi CR;
I understood you to say that the operators balanced the main loads with the RotR loads to keep the forebay level within limits.
My meaning was that level control will be a back-up to load balancing, not as a back-up to automated level control.
I think that we are in agreement.
In any event, I defer to your first hand experience.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

It's curious that CuriousElectron never answered the question I posed at the start of my first post of response; I'd like to know if I'm missing the mark somehow.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[CuriousElectron]

Hi CR,
I must admit that was a bit confused by the two scenarios you have briefly explained in your first post. In my mind, they are the same operating modes, except that first scenario presumes forebay with a penstock feeding the generator, and the second scenario presumes a run of the river forebay whereby the forebay in this second scenario is more "dynamic" - multiple inflows and possibly outflows as well? Regardless, you have helped me answer some of the basic questions I had.

Thank you.
Best Regards,
EE

 

[waross]

The reservoir area has more to do with it that the presence or absence of a penstock.



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Hi Curious, and thanks for the feedback.

Scenario 1 is not one I've ever seen; it's just that when I read "float control" the image of the sump pump in my basement sprang to mind . . .

The two types of forebays you mention fall within a continuum of forebay types, ranging as you suggest, from highly dynamic to almost rock-steady, as Bill alluded to.

As to penstocks, some plants have such low head that they really don't have them at all; others with higher head will have proportionally longer ones that can address both vertical head and considerable horizontal travel; the ones here

https://www.google.com/maps/place/K...cc6225965b9e9c04!8m2!3d44.383333!4d-80.533333

are ~ 2 miles long and handle a fall of about 490 feet [ the shadows of the twin surge towers can be seen about two-thirds of the way along from right to left ] .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

Kootenay Canal in British Columbia is an interesting run of the river hydro generating station.
It is located between Nelson BC and Castlegar BC
There is a diversion dam and water excess to the needs of the generating station is spilled back into the original river bed.
While I do not know the control scheme of this plant, it may be a text-book example for the possible application of level control.
If the natural river flow drops below the plant usage, the forebay will be rapidly depleted unless usage is quickly curtailed.
The canal is about 2 3/4miles long.
Look for it here. Kootenay Canal
The diversion dam is near Corra Linn. The generating station is under the red pin.

ps, the system uses penstocks.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Hi Bill,

Interesting indeed!

Based on some scrolling around in Google's satellite view, penstocks would clearly be needed for the Kootenay Canal GS, considering how in the main channel of the river the vertical fall is divided between four different cascading sites.

There is a diversion dam and water excess to the needs of the generating station is spilled back into the original river bed.

I'm curious about this statement, Bill; If I was to interpret from what I can see from space, I would guess that KCGS seems to have been a later build, since it seems to contain no provisions for spill [ at least not that I can discern; might you have better local knowledge and be able to tell me where these are? ], these already being present at the original sites and therefore not a requirement at the new one. Again, just my interpretation.

Just reverse operating, for lack of a better description, I'd think the prevailing river flow would be an amount that varies directly with the change in elevation of the water level some distance upstream of this area. [ When I did the job, hourly elevation readings would have been taken to keep constantly aware of how much water was coming toward you so you'd know how best to split it up. Great and frequent operator dereliction of duty would be required to be happening before such a minimum forebay level "float control" scheme would ever be economically justifiable. ]

Said flow would be divided between the two flow paths in such a way as to obtain optimized power generation from the water available; I was privileged to be an operator at the Saunders Generating Station in Cornwall, Ontario from 1990 to 1997, during which time a scheme called Targeted Optimization { TarOpt ] to perform exactly this type of calculation was developed and implemented by what is now Ontario Power Generation. Very precise measurements were taken for variations in head, water flow, and power generated for each type of generating unit in the plant [three different types, at the time ]. Ontario Hydro worked with a mathematics professor out of Queens University in KIngston, Ontario to harness something called quadrential calculus to iteratively perform the calculations and present the recommended load division for a given flow in an easy-to-interpret, almost intuitive human-machine interface [ HMI ] .

The neat thing about TarOpt was that by using this quadrential calculus it was able to derive optimal flow splits in less than two seconds, and if memory serves it ran every six seconds or so; it was reported at the time that other mathematical means, even with high-powered computers would have taken several minutes to perform the same trial-and-error calculations just once. TarOpt therefore enabled very quick plant balancing on the fly, in real time.

I was the single point of contact for this project, and found it fascinating.

But I digress.

The two plants to which I refer that actually had it, had it to address rapid fluctuations in forebay level; if you look at this link

https://www.google.com/maps/@44.1377025,-77.5860868,4065m/data=!3m1!1e3?hl=en

you will see that the distance between Sonoco GS [ power displacement for the factory that produces Sonotubes ] and Sidney GS is quite short, and both are paralleled by sets of locks that are part of the Trent-Severn Waterway. Since the timing of the lockages and the clustering of vessels between the two sites is quite unpredictable, forebay fluctuations at Sidney can be quite violent. Steady control of water elevations greatly assists in ensuring that if vessels remain in the buoyed channel, they will not go aground.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

Dam Dam Dam. The short stretch of river between the upstream end and the downstream end of the Kootenay has run of the river dams operated by three utilities.
The operation of these plants must be in accordance with:
Power demands.
Water license requirements of at least four license holders.
Minimum water flow for fisheries.
International Agreements for downstream water flow.
Flood control on the Columbia river system downstream in the US states.
As well as the group of dams at the canal location, there are several more Run of the River dams downstream before the international border.

There were\are four existing run of the river power plants on the Kootenay River between the upper end of the Kootenay Canal and the lower end of the Kootenay Canal.
Corra Linn Dam and Power Plant. This dam controls the level of Kootenay lake and controls the flow in the Kootenay River exclusive of the flow through the Kootenay Canal.
This dam also diverts the water into the Kootenay Canal.
City of Nelson Power plant. (Upper Bonnington?)
Lower Bonnington Dam and Power Plant.
South Slocan Dam and Power Plant.
Here is a timeline:
April 23, 1892: Nelson Electric Light Co. is incorporated with the goal of erecting and maintaining electric lights for the city.

February 1, 1896: The Cottonwood Creek plant, consisting of a pair of 36-inch (91-centimetre) Pelton wheels belted to two 35 kilowatt DC generators, finally begins operating. It’s the first hydroelectric generating facility in BC. (Nelson Electric Light Co.)

1897: The plant is enlarged. A six-foot Tutthill water wheel drives two new and slightly bigger generators. (Nelson Electric Light Co.)

1898: Nelson Electric Light Co. is bought by the City of Nelson.

1900-01: <Mayor> Houston and city engineer Andrew McCulloch explore the hydroelectric potential of the Kootenay River. The city obtains a water license and a deed to 40 acres on the south side of Upper Bonnington Falls — much to the chagrin of West Kootenay Power, which has a plant downstream.

1904: The city <of Nelson> is granted another water license at Bonnington, bringing the total to three times the capacity of the Cottonwood Creek plant.

1905: In a pair of referendums, residents overwhelmingly approve $200,000 to build a powerhouse at Bonnington.
January 26, 1907: City power plant starts operations.

1908: Voters approve $85,000 bylaw for a second generator, which goes into service on June 1, 1910.

1928: Bylaw adopted for third generator, which begins operating July 7, 1929.

1932: <West Kootenay Power and Light, Now Fortis> The Corra Linn Dam was initially built in 1932 to control upstream storage in Kootenay Lake and generate power through three 19,000 horse power units operating under the depth of water behind the dam of approximately 16 meters. The generating capacity is 51 MW. The Corra Linn Dam is located on the Kootenay River, approximately 15 km (nine miles) downstream of Nelson on Provincial Highway 3A.

1946: Bylaw adopted for fourth generator. It officially goes into service on December 7, 1949.

1971: The province threatens to expropriate 38 acres of city-owned land for BC Hydro’s Kootenay Canal project.

1972: City council agrees to sell the land if BC Hydro buys the city’s power plant and distribution system. The province says no. Eventually, the government expropriates a little over 25 acres and the city receives a reputed $400,000.

1974: Generator No. 1 and 2 are retired with the completion of the Kootenay Canal, reducing the city’s power production by 15 per cent.

1975: The city’s power plant becomes fully automated, eliminating two of three worker shifts. The employees are reassigned elsewhere within the city.

1988: After extensive negotiations with the province, the city gains increased water rights — generating an extra 1,200 kilowatts and $250,000 per year. Generator No. 2 is fired back up.

1993: Residents approve an $8.75 million power plant upgrade and addition of a fifth generator.

June 1995: Generator No. 5 unit officially commissioned to take the place of units No. 2 and 3.

1996: The city’s electrical department is rebranded Nelson Hydro.

2007: The Bonnington plant celebrates its centennial, along with its by-now silent Generator No. 1. Three years later, the still-operable Generator No. 2 turns 100.
Web searches show contradictory ownership, but the dams are there despite ownership.
Fortis may be operating some of Nelson Hydro's dams. It is unclear on the web.

After looking into the system further, I suspect that they may not be using forebay level control.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Short answer to your spillway question CR;
The Corra Linn Dam provides spill control for the system and the Kootenay Canal takes water from what may be considered as the forebay of the existing Corra Linn Dam.
Kootenay Lake is the reservoir for the system.
The Kootenay river rises in Canada just a few feet from the rise of the Columbia River. The headwaters were joined by a canal many years ago. The Columbia flows north. The Kootenay flows south into Montana, west into Idaho and back north into Canada and into Kootenay Lake.
The Kootenay River joins the Columbia River about 25 Miles downstream from the Kootenay Canal Powerhouse.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Yes. I worked through there in the early 60s and there was no Canal.
I was back working in the area in the mid 80s and the canal was in service.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Awesome, Bill! Thanks for all the background; I had to do a lot of scrolling around on Google maps to find all the things you wrote about. Fascinating!

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]