Small Hydropower & Micro Hydropower

Hi there,

I have only subscribed yesterday to the Small & Micro Hydropower Newsletter and I really need your help,we are based in South Africa and we started refurbishing a Francis turbine and will commission it early may 2009.  Our hydropower company is in Africa.

Q: Currently we are busy proposing for a new site with a 80m head and would like to install a Pelton turbine I need some info regarding the hydropower foundation setup.
Please can you give me some guidelines I will be very thankful.

Hope to hear from you soon

Mark

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Dear Mark,

We’re glad to have you join us!

A: May I suggest the first thing you need to establish for Pelton wheel hydropower design infrastructure is the same as your need for good turbine and penstock choice. Basically you need to know your static head pressure (80m) AND flow rate (m^3/s) The penstock and turbine are chosen to gain the best fit for efficiency of the available flow regime, but there is a dynamic force caveat.

Penstock length and diameter and geometry (turns & angles of turns) will determine the maximum dynamic flow forces at your thrust blocks or pipe anchor points. Every change in angle and every flow rate change will generate thrust forces, From Newton’s first law of motion. Your infrastructure & power-house design must exceed these forces by a wide margin or there will be BIG problems.

One more non-linear issue is that you must keep the linear flow rate below 5ft/s or 1.5m/s to avoid the effect of catastrophic water hammer. Remember, you are moving a freight train’s weight of water in the penstock there’s a lot of energy stored in the water’s momentum (Momentum=M x V.) The kinetic energy is (E = 1/2 m x v^2.)

If the jet(s) of a Pelton turbine gets plugged by debris the flow can stop abruptly causing a huge energy or pressure pulse to form(a.k.a. water hammer.)  This in turn will lead to huge forces on the thrust blocks and penstock walls (including the turbine mount & thrust structure) but every bit of the penstock structure will be exposed to huge pressure waves traveling back and forth at the speed of sound in water (pressure reflections).

It is not unusual for steel pipe to rupture or collapse depending on the magnitude and sign of this pressure/vacuum wave. All of these design issues are pretty much the same as large scale water conveyance pipelines in any system. For example eg. sewer or domestic supply.

So, start with your flow needs and penstock design to determine each thrust block’s forces and the terminal powerhouse (turbine foundation) forces. Make sure you consider maximum flow & catastrophic pulse generation. Then engineer each concrete and steel anchor to exceed these by a good margin. A good pipeline designer should be able to do these calculations and design this aspect of your system.

Note: All DoradoVista Small& Micro Hydropower site recommendations are not meant to replace a good design or design engineer, they are for informational and technical seeding of ideas only. You must get a locally qualified engineer to evaluate all aspects of your hydro system design including all of our recommendations for your project. Hydro system safety and economics design issues are both involved here even at 80 m of head.

That discussion on good penstock and turbine foundation design is just for starters –

Here’s a link to some more Hydropower books from Amazon.com that we’re collecting on various Hydro topics. It’s from our Small & Micro Hydro Reader’s corner.

The inexpensive CD’s on that web page (from the DOE on hydro) may likely give more detail on your topic question.

Sincerely,
Jess
DoradoVista, Inc.

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