Identify problems at intakes

Phone survey:

The telephone survey was carried out by Steinar Lund, a Norwegian Master student, among 50 hydropower plant owners whose power plants were located in 12 of the 19 Regions of Norway.

Power plant visits:

Lars Jenssen, BEDUIN project’s coordinator, Steinar Lund (Norwegian Master student ) and Dorothée Huber (French Master student) have visited 18 power plants from the 50 of the telephone survey. The power plants were located in the Sør and Nord-Trøndelag Regions and in the Sogn og Fjordane Region.

The power plants were either owned by one or a group of private individuals, or owned by a cooperative. Most of the owners were farmers who have planned, designed and built their power plant themselves. Because of the cost, very few owners hired a consulting company.

For each power plant, we discussed with the owners about the problems related to the choice of the site, the planning, the design, the construction, the operation of the power plant and the energy production. It gave us a better idea about the kind of information and advice they would have needed and that should be included in the BEDUIN report.

Photo library and sketches of some power plants, here.

Results:

The table below presents the results from the telephone survey and gives the number of power plants which encountered problems for each category. The numbers in brackets represents power plants where the problems have been solved.

Categories of problems	Types of problems	Number of intakes
Floating debris	Leaves, turf, twigs, branches	19
	Other problems	2
Air	Vortex formation, air entrainment	4 + (1)
	Air in pipe	(1)
Sediment	Sediments in the intake pond	10 + (1)
	Wear on the turbine	2
Ice	Frazil ice blocking the entrance to the reservoir	4
	Frazil ice blocking the trash rack	3
	Ice formation in the penstock	3
	Breaking-up of ice blocking the trash rack	1
	Breaking-up of ice leading to damage	1
	Ice problem in the spillway area	1
	Freezing of the gate	1
	Other problems or unspecified	4
Environmental	None	0

Floating debris:

Floating debris is the most common problem at intakes. Usually, the trash rack gets clogged with debris resulting in increased head loss. The problem is most serious during the autumn when the leaves fall from trees and in some cases it can lead to the total blockage of the intake, keeping water from being diverted. The only solution to keep the head loss low and the power plant running is to clean the trash rack as often as needed. The cleaning frequency varies a lot from one intake to another. It can get as frequent as several cleaning per day during the worst periods.

Air:

Air is not a widespread problem and when it occurs, the problem is often due to a vortex which forms at the water surface and goes down in the penstock through the trash rack. If the vortex is very developed, it may entrain air and debris into the intake.

Sediment:

Sediment can be anything from big rock to stones, clay and silt. The problem caused by sediments is usually that the intake reservoir gets filled up with sediments. It is possible to remove the sediments at regular intervals with a mechanical digger, but it is feasible only when the reservoir is small enough and has a road access. In addition it can be quite expensive and it is not a long term solution. The turbine can also get worn out by sediment and has to be changed. A problem with small hydropower plants is that service control is not always very well and regularly done. In consequence the owner may not be aware of wear on the turbine.

Ice:

As shown in the table above, there are many different problems related to ice. Frazil ice is ice crystals formed in supercooled water which is water that is below 0°C and which has usually been cooled by sub-freezing air. A supercooling of just a tenth of a degree Celsius or so is sufficient to produce frazil ice. The main problem with frazil ice is that it sticks to the metal bars of the trash rack and blocks it.