Arthur says ---
Flateby 180323
We have passed the spring equinox!
But still it is at least one meter snow covering garden flowers.
Another concern is the normal definition of Net Head.
Hn = H1 – H2 where
H1 = ( z1 + h1 + v12/2g ) = zintake – headrace losses and
H2 = ( z2 + h2 + v22/2g ) = zoutlet + tailrace losses.
For a constant design flow head- and tailrace losses will be constant.
h1 + v12/2g is related to inlet area and can be considered to be independent of that area. But the properties of items as stay vane, guide vane etc. will be influenced by area selected.
The outlet properties related to h2 + v22/2g deviates from the inlet case due the abrupt change in area destroying velocity head recovery. This is due to the geometry related to gate chamber etc..
Empirically h2 is a function of tail water loss and velocity head v22/2g is practically lost.
Normally the discharge velocity head is considered as a tailrace loss, but the designer of the tailrace system is not responsible for draft tube design which may result in an in-optimal solution.
I am therefor of the opinion that the draft tube outlet velocity head should be considered as a turbine property.
For Francs units this will marginally influence design, but high discharge velocity will be unfavourable comparing unit’s property.
For Kaplan turbines this effect must be considered.
Bulb turbines design velocity head is close to net head. The velocity head recovery in the draft tube and outlet velocity is dominating losses and must be handled with respect.
According to this Alab considers draft tube outlet velocity as a turbine property.
Arthur.
Flateby 180125
Flateby 171111
Alab is a “Window program”
In Norway the FIKS-standard defines acceptable dynamic response for Power Plants.
From Alab’s point of view Hydro Power Plants are focused.
This standard will be replaced by EU-rules.
Alab has powerful methods for dynamic operation simulation handling black start, uploading, downloading, load rejection et cetera. Different grid-models are available demonstrating effect on stability and damping.
Coming task will be to study the EU-rules and design new matching Alab-methods.
Arthur.
Flateby 171109
A grey and rainy November day.
A couple of weeks ago I attended “Forum for Generators” arranged by Tekna - The Norwegian Society of Graduate Technical and Scientific Professionals and Energy Norway.
Working continuously to improve Alab’s dynamic operational simulation for complete Power Plants my hope was to learn more about generators general properties.
Most papers presented were very specific and the target was obviously persons interested in details near the "airgap". Even if I am a mechanical engineer I fully understand that there are problems of interest here.
After many years in Hydropower business I have also experienced the almost watertight border, or in this case, may be Faraday cages, existing between the turbine- and the generator engineer.
During breaks, as small talk, I tried to learn more about voltage control. The signal was that the voltage governor should be as fast as possible to guarantee a constant voltage?
What is the natural inertia of a generator?
The question was answered by a mechanical engineer based on statistics.
I had expected that an experienced generator designer would give an overview concluding with inertia related to normal design.
Well, I have understood that all elements necessary to make a complete Power Plant are secrets of business and are publicly unavailable.
A seminar like this mostly becomes a possibility for marketing products.
During the happy years around 1968 planning, design and construction of Power Plants was just done!
Today, a Power Plant has become a research possibility.
Arthur.