Turbine selection for small low-head hydro developments.
J. L. Gordon, P. Eng.
Abstract – There are many different types of turbine configurations available for low-head small hydro developments. Both axial flow (propeller) and radial flow (Francis) turbines can be used in about 10 different configurations, resulting in considerable difficulty in arriving at the most economical and appropriate unit. This short article outlines the steps used in conjunction with a computer program, to arrive at the types of units available for the site. The input data for the program includes the flow, desired number of units, the head, the system frequency, the tailwater level, and the operating pattern in hours per annum at each flow, as obtained from a flow-duration curve. The program calculates the runner size and setting relative to tailwater, speed, power output, provides charts showing turbine efficiency as a function of both flow and power, the powerplant kWh output and the turbo-generator water-to-wire cost, for 10 different turbine configurations. The data is then screened for applicability to the site, and the inappropriate units discarded. The remaining units are further compared, and two units are recommended, one based on maximum weighted efficiency, and the other on minimum cost per kWh output.
Two options are included in the program, one for the maximum allowable gearbox capacity (where used), and the other for the quality of the generator and SCADA system – either industrial or utility. These options are explained further in this article.
The program is limited to powerplant capacities up to about 30MW, turbine heads up to 30m, and maximum flow per turbine up to 200m3/s. Typical turbine-generator configurations, obtained from manufacturer’s brochures, are provided for all 10 generating units.
A short site cost screening program is included within the turbine program, to be used to determine whether the site is worth further study.
This article and computer program prepared for the pre-conference workshop
“INNOVATIVE SMALL HYDRO TECHNOLOGIES”
NATURAL RESOURCES CANADA
July 29, 2003, Buffalo, New York, U.S.A.
Turbine selection for small low-head hydro developments.
Turbine types. 3.
Unit #1. Inclined axis, very low head Kaplan gear turbine. 3.
Unit #2. Horizontal axis bulb or pit Kaplan turbine. 4.
Unit #3. Horizontal axis “S” type Kaplan turbine. 5.
Unit #4. Vertical axis small Kaplan turbine with elbow draft tube. 6.
Unit #5. Horizontal axis “S” type propeller turbine. 7.
Unit #6. Horizontal axis pit type propeller turbines. 7.
Unit #7. Horizontal axis Francis turbine. 8.
Unit #8. Horizontal axis, double runner Francis turbine. 9.
9. Unit #9. Vertical axis “Saxo” axial flow Kaplan turbine. 10.
Unit #10. Horizontal axis, angled inlet, axial flow Kaplan turbine. 11.
Turbine selection program.
Program input data – line by line instructions for page 1. 13.
Program output data summary – line by line for pages 1 and 2. 14.
Program turbine output data – line by line for pages 3 to 22. 15.
Project screening program.
Screening program input/output data – line by line for page 2. 18.
Small hydro, low head reaction unit cost comparison program. 22 pages.
Turbine selection for small low-head hydro developments.
The development of a low-head small hydro site is difficult at the best of times. Low head means low power per unit of flow, and hence a relatively higher cost than for sites with higher heads. Also small powerplants suffer from the inverse scale effect, with higher costs relative to larger sites. Hence, all means possible are needed to arrive at an economical development.
Many entrepreneurs are under the impression that any rapids in a river can be developed as an economical source of power. Unfortunately, this is not the case, and to assist such developers in assessing whether the site is worth investigating, a simple screening program is attached to the turbine selection program. Data for both the screening and turbine programs can be obtained from a short site inspection, and some analysis of flow records.
The program is easy to use. It runs on Microsoft Excel 97 or later versions. Simply fill in the necessary data in the blue cells, and if instructions are needed, hold the cursor over the adjacent yellow comment cell, and a box will open instructing the user on the input. Similarly, some of the output cells have adjacent comment boxes, where assistance in the interpretation of the output is available. The program cuts off at powerplant capacities over about 30MW (small hydro), at heads over 30m (low head), and at flows larger than 200m3/s. per unit.
The program covers 10 different turbine configurations, as described in the following paragraphs. Each turbine type uses 2 pages in the program, and, with some minor exceptions, the line numbers are the same for all data in each turbine configuration.
Unit #1. Inclined axis, very low head Kaplan gear turbine – pages 3 to 4.
The turbine axis is usually inclined at an angle of 15 to 45 degrees to the horizontal. It is primarily intended for use in very low head sites, where the net head is between 2 and 8 meters. Maximum unit capacity is about 2.6MW. The bevel gear bulb turbine has – a bulb within the water passage with turbine thrust bearing and right angle gear drive; stay vanes and wicket gates; Kaplan runner
Figure 1. Illustration of inclined axis, very low head Kaplan gear turbine unit.
Source – Sulzer Hydro brochure e/21.59.30 – RA 95-20.
and bent cone draft tube. The generator is mounted above the right angle gearbox. A typical layout is included in Figure 1.
An alternative configuration has the shaft continuing upstream to emerge through the inlet pipe bend, with or without a gear drive to the generator. This alternative is identical in cost and dimensions to unit 10 (pages 21 – 22). A typical layout is shown in Figure 2. As with all inclined axis units, this arrangement requires ladders and platforms for access and maintenance, and with the larger units, harnesses and safety equipment adds further to maintenance costs. For these reasons, layouts with either vertical or horizontal axis are preferred.
Inclined axis, axial flow Kaplan turbine with bent cone draft tube.
Source – Canadian Hydro Components brochure, figure dated 06/27/98
Unit #2. Horizontal axis bulb or pit Kaplan turbine – pages 5 to 6.
In this layout, the generator is contained within either a bulb or a pit within the upstream water passage. A pit installation has an open-topped bulb, permitting far easier access to the generator. To keep the generator size within reason, there has to be a gear unit to increase generator speed to between 600 and 1000 rpm. Gears are not required at runner speeds over about 257 rpm. A typical installation is shown in Figure 3.
Downstream of the bulb or pit there are the stay vanes, wicket gates, Kaplan runner and finally a conical draft tube. The runner shaft is usually set about one runner diameter below minimum tailwater. As noted in Figure 3, there is easy access around the turbine unit for maintenance. Also, as with all horizontal shaft units, the runner can be removed for maintenance without removing the generator. Bulb units are only available in the larger diameters, and should be avoided due to the “confined access” problems associated with the bulb. Pit type units are far preferable.
Horizontal axis pit Kaplan turbine with right-angle gear driven generator.
Source – Voith hydro brochure “Standard machines for small hydro power plants” t 2977e.
Unit #3. Horizontal axis “S” type Kaplan turbine – pages 7 to 8.
This is the most common type of low-head, small hydro plant arrangement, and is now available from most manufacturers as a pre-engineered unit. Runner sizes range from 1.0m up to about 4m, heads from 5m to 25m, with power output up to about 12MW.
Horizontal axis “S” type Kaplan unit with offset speed increaser and high speed generator.
Source – Bell Engineering Works Ltd. brochure 21.04.30 KB 84-60 e.
There is a small upstream bulb containing controls for the Kaplan blades, and the thrust bearing. The bulb is held in place by the stay vanes. Immediately downstream is the distributor ring with the wicket gates. The runner is contained within a horizontally split throat ring, which can be removed for access to the runner. Downstream there is a long shaft to the draft tube gland and the turbine/generator guide bearing. After the bearing there could be a speed increaser or a direct connection to the generator. Sufficient space in the powerhouse, downstream of the DT gland, must be provided to install and remove the long shaft. A typical layout is shown in Figure 4.
With the thrust bearing housed in the upstream bulb, the forces are transmitted into the upstream powerhouse wall. Absolutely no deflection is allowed in this wall, otherwise turbine alignment is compromised. Wall deflection can be countered with buttress piers between the units – an absolute necessity. In some early units, problems with shaft breakage were encountered. Failures were found to be due to fatigue cracking at the turbine flange from stress concentrations at the flange-shaft junction. Using a larger radius curve at the joint has rectified this deficiency.
With the runner enclosed by an exposed steel throat ring, the powerhouse is very noisy, and ear protection is a necessity. If located within a residential area, measures will be required to reduce noise by means of acoustic insulation. Where there is a large rise in the tailwater at flood, access to the powerhouse is usually by means of roof hatches and a rented mobile crane, as shown in Figure 4. In remote areas, the concrete block above the upper draft tube elbow is usually enlarged to provide an access platform at a higher elevation, above the generator floor.
Unit #4. Vertical axis small Kaplan turbine with elbow draft tube – pages 9 to 10.
There are many arrangements for small vertical axis Kaplan units. Often, they are set with the runner well above normal tailwater level, see Figure 5, thus avoiding the use of draft tube gates.
Vertical axis small Kaplan unit with offset speed increaser and high-speed generator.
Source – Ateliers Bouvier brochure “Hydraulic turbines for low heads”
The powerhouse contains a semi-spiral concrete casing. As can be seen in Figure 5, access to the turbine headcover is restricted, with insufficient headroom. This is the main limitation with this arrangement, and if possible, it is prudent to increase the height of the generator plinth and length of turbine shaft to provide more room for maintenance access. Also, removal of the turbine runner requires removal of the generator and speed increaser, at added cost. For this reason, preference should be given to arrangements with a horizontal shaft, using an “S” unit. However, installation procedure is very simple as shown in Figure 6.
Installation procedure for vertical axis small Kaplan turbine, offset gear generator.
Source – Sulzer hydro brochure “Compact Kaplan” e/21.60.30-RA 95-20
Unit #5. Horizontal axis “S” type propeller turbine - pages 11 to 12.
This type is identical to the horizontal axis “S” type Kaplan turbine described in part 3, with the exception of the runner, which is a fixed blade propeller. This turbine has a very peaked efficiency curve, and is only suitable for sites where there is minimal change in head and flow. For this reason, very few are installed, preference being given to the Kaplan alternative.
Horizontal axis “S” propeller turbine in low head setting. Geared generator.
Source – Voith brochure “S-turbines in standardized sizes” t 2787 e printed 6.94
Unit #6. Horizontal axis pit type propeller turbines - pages 13 to 14.
Again, the turbine-generator and setting is identical to that described in part 2, except for the runner, which is a fixed blade propeller. The turbine has the same peaked efficiency curve as the propeller “S” unit, and for this reason, few are installed. The unit is best suited to sites where the flow and head are constant, or where more than 3 units are installed, thus achieving some diversity in flow efficiency.
Horizontal axis pit unit with offset generator and gear speed increaser.
Source – Alstom Mini-Aqua brochure 03.01/SP/1704
Unit #7. Horizontal axis Francis turbine - pages 15 to 16.
These units are only available with runner diameters less than about 1.8m. Above this size, the turbine requires a vertical shaft. Power is limited to about 12MW per unit, with most installations having an output below about 5MW.
Horizontal axis small Francis turbine, with single runner, direct drive generator.
Source – Sulzer Hydro brochure “Compact Francis” e/21.58.30 – RA 95-20
Net head ranges from 20m up to over 100m. The turbine is usually set just above tailwater, with the bottom of the runner at least 0.3m above normal tailwater level. This avoids the necessity of draft tube gates, and facilitates access to the runner for inspection and maintenance. There are many manufacturers producing this type of equipment.
With the turbine and draft tube elbow fully exposed, there is considerable noise in the powerplant. On the other hand, the equipment can easily be accessed for maintenance. Powerhouse concrete is very simple, comprising a thick slab, with a rectangular conduit below for discharge of water back to the river. In single unit powerplants, a monorail hoist located above the shaft, can be used for installation and maintenance, thus reducing crane cost.
Horizontal Francis turbine at Transkei, South Africa. 3MW, 27m head, 300rpm, d = 1.47m.
Source – Gilkes brochure “Fluid movement hydro” M 91/A
Note that the layout is identical to that for a vertical shaft unit, hence efficiency and performance is also similar. There is no shaft through the draft tube.
Unit #8. Horizontal axis, double runner Francis turbine - pages 17 to 18.
At some sites, the head is too low for a single runner. To increase the runner speed, a double runner Francis unit could be selected instead. The layout is similar to that for a single runner, horizontal axis Francis unit, with the turbine installed above tailwater as shown in Figure 11.
Schematic showing arrangement for horizontal axis, double runner Francis turbine.
Source – Alstom brochure “Mini Aqua – the new mini-hydro solution” 03.01/SP/1704
There is a shaft through both draft tubes, reducing draft tube efficiency somewhat. However, this is countered by the ability to operate on only one runner, increasing the efficiency at low flows, over that attainable with one runner. Most installations have capacities below about 5MW. Head range is from 15m to over 100m, and power from about 1MW to 15MW. Due to the shaft through the draft tubes, access to the runners is more difficult than with a single runner layout.
Two views of a horizontal axis double runner Francis turbine.
Source – Author’s photo files.
Figure 12 shows the installation of a Norcan Hydraulic Turbine Inc. Francis turbine unit at Petite High Falls. 500kW at 15m head, 720rpm.
9. Unit #9. Vertical axis “Saxo” axial flow Kaplan turbine - pages 19 to 20.
This unit has an abrupt bend just upstream of the turbine distributor, as shown in Figure 13.
Drawing showing arrangement for a vertical axis “Saxo” axial flow Kaplan turbine.
Source – Bofors-Nohab brochure “Small scale hydro turbine program” 5702.
Due to the close proximity of the bend to the distributor, and abruptness of the bend, there is a substantial hydraulic loss at the inlet pipe (Bennett). This results in a marked reduction in turbine efficiency as flow increases. The loss can be reduced by a larger inlet pipe/runner diameter ratio, and by decreasing the angle of the bend, as shown in the arrangement in Figure 14. The turbine selection program includes options for varying the pipe/runner ratio and the inlet angle. Both have a marked influence on the efficiency.
Schematic showing arrangement of 45-degree bend at inlet to “Saxo” turbine.
Source – Sulzer Hydro brochure “Compact axial turbine CAT” e/21.73.30 – ZC 98 – 10.
The unit is named after the shape of the water passage, which resembles a saxophone. Due to the presence of the inlet pipe above the turbine, arrangements should be made to remove the turbine runner from below. Also, due to the long shaft above the turbine, substantial headroom above the generator is needed to install the unit. Very few of these units have been built.
10. Unit #10. Horizontal axis angled inlet, axial flow Kaplan turbine – pages 21 to 22.
This unit is similar to that shown in Figure 14, but with a horizontal axis, and straight conical draft tube, as shown in Figure 15.
Schematic showing horizontal axis angled inlet Kaplan turbine generating unit.
Source – Alstom brochure “Mini Aqua – the new mini-hydro solution” 03.01/SP/1704
As with the vertical axis unit, there is a substantial loss at the inlet bend. The turbine selection program includes options for varying the pipe/runner ratio and the inlet angle. Both have a marked influence on the efficiency. Access by crane to the generator is difficult, as indicated in Figure 16, due to the presence of the penstock pipe above the generator. This can be mitigated by angling the penstock off to one side.
View of angled inlet penstock and horizontal axis generating unit at Chaudiere.
Source – Author’s photo files.
Figure 16 shows the generating unit at Chutes-de-la-Chaudiere, where a head of 35m is developed to produce 12MW, with a 2.12m diameter runner. (Boucher)
Turbine selection program.
The program has been designed to calculate the parameters, efficiencies and water to wire cost of all the above types of turbines. The program then filters the data to determine which types are suitable for use at the site, based on the head and flow. Non-suitable types are discarded, and the remaining are reviewed to select the optimum based on two criteria – one on minimum cost per kWh production, and the other on maximum weighted efficiency. Sometimes the program will select one unit only, since it meets both criteria. The program runs on Microsoft Excel 97 or later editions.
The first two pages in the program are a summary of the input and selection process. Thereafter, two pages are devoted to the output for each type of turbine. The user can print the two summary pages, followed by the two pages of data for the recommended or selected turbine.
Input data is confined to the blue cells. Yellow cells contain comments – just hold the cursor over the yellow cell, and the comment box will open. The comments are either an instruction for input data to the adjacent blue cell, or explanation and interpretation of the output. The A column (first column) contains a line number, used to identify the line in the following suggestions on program use. The program data for each type of turbine is identical, hence the line numbers for all the turbines are identical. All input data is on page 1, with the exception of two or three numbers needed for the Saxo (turbine #9) and horizontal axis, inclined inlet turbines (turbine #10), where inlet angle and pipe/runner ratio are needed.
Program input data – line by line instructions for page 1.
Line 8. Insert project name in cell B8.
Line 9. Insert total powerplant flow in cubic meters per second in cell C9.
Line 10. Insert desired number of units in powerplant in cell C10. If, after inserting data in cells 9, 10 and 11, none of the turbines prove suitable, a notice to this effect will appear on line 20. Try changing the number of units to see if some prove suitable. For example, enter C9 = 50, C10 =1, and C11 = 30. See note on line 20. Now change number of units in C10 = 2, line 20 changes, and note that 1 turbine is now suitable in lines 41 to 50.
Line 11. Enter rated net head in C11. There is a limit on power output at about 30MW, hence if the multiple of C9 x C11 > 3400, a note to this effect appears in cell C13. For example to go back to the previous data, enter C9 = 200 and C11 = 30, and note effect in C13.
Line 12. Enter system frequency, 50 or 60 cycles in cell C12.
Line 14. Enter normal operating tailwater level at powerhouse in meters above sea level.
Line 15. Enter summer water temperature in degrees Celsius in cell C15. Data in cells 14 and 15 are needed to calculate the tailwater barometric pressure.
Line 16. Enter the expected conduit head loss as a percentage of the net head in cell E16. The usual range is from about 3 to 15. If this is not known, use 5 for a base loaded powerplant, where the load factor is over about 60% and 8 if the powerplant load factor is less than about 50%. This number is used to calculate the energy production assuming no change in water levels at intake and tailrace.
Line 17. Some turbines, operating at below 257rpm may use a speed increaser to reduce the cost of the generator, or to fit the generator into a bulb or pit. Speed increasers have a relatively shorter life than the generator, and some utilities try to avoid their use, or to limit the maximum output to below about 5MW or 8MW. If the maximum allowable speed increaser output is less than the turbine output, and if the turbine speed is below 257rpm, the program will select a higher cost direct-connected generator. Set the desired maximum speed increaser power in cell C17.
Line 18. Set desired generator power factor in cell C18.
Line 19. There are two qualities of generators available for small hydro powerplants. The “industrial” quality is a motor as manufactured by Kato or Ideal. It costs less than a “utility’ quality generator as manufactured by General Electric or Siemens. Most small hydro powerplants use industrial quality generators. If the turbine output is 1.5MW or below, the program assumes the use of an induction generator, to reduce the cost.
Lines 26 to 36. This is where the flow pattern or turbine use pattern is entered. The hours at each flow, per unit, can be obtained off a flow duration chart. The data is needed to determine the kWh output of the powerplant, and select the appropriate turbine. For example, if all the flow can be passed at rated flows above about 85% wicket gate opening, a fixed blade propeller unit would be recommended. However, if the flow has to be passed at smaller rated flows, down to about 30% flow, then a Kaplan unit would be recommended. Note – a single runner Francis unit should NOT be operated at flows below about 45%, and preferably not below 60% rated flow.
The operating hour data (Lines 26 to 36) is not essential. If this is not known, use a best guess, and discard the energy generation output data as inaccurate. Try to obtain a calculated plant capacity factor (Line 134) of between 0.55 and 0.65, the most common range for powerplants. The program defaults if the operating hours are too large.
If the program indicates that either a Saxo unit, or an angled inlet horizontal or inclined shaft turbine can be used, (turbines #9 and #10) as indicated on lines 49 and 50, then additional data has to be inserted in the program, in the blue cells on lines 114 and 130 on pages 19 and 21, and line 120 on page 21.
Line 114. For the “Saxo” and angled inlet horizontal axis turbines shown on pages 19 and 21, the inlet angle has to be entered into the blue cell on line 114. This is important – it has a significant effect on the turbine efficiency.
Line 120. To indicate an angled shaft or a horizontal shaft for the angled inlet Kaplan turbine, the option has to be selected on this line on page 21. An inclined shaft will slightly increase the cost of the installation, but has no significant effect on performance.
Line 130. For the “Saxo” and angled inlet horizontal axis turbines shown on pages 19 and 21, the inlet pipe/runner diameter ratio has to be entered into the blue cell on line 130. This is important – it also has a significant effect on the turbine efficiency. This ratio is usually in the range of 1.6 to 2.0. The higher the ratio, the lower the bend losses, and hence the turbine efficiency increases as the ratio becomes larger. However, the cost also increases, due to the larger inlet pipe. Recommended ratio is around 1.8.
This completes all the data required to select a unit.
Program output data summary – line by line explanation for pages 1 and 2.
Lines 41 to 50 – C cells. These indicate what turbine types are suitable for the combination of flow per unit and head. If none of the turbines are suitable, a notice will appear on line 20.
Lines 41 to 50 - D cells. One cell will indicate which turbine has the highest weighted efficiency. The weighting is based on the operating hours at each flow entered in cells C26 to C36.
Lines 41 to 50 – E cells. One cell will indicate which turbine has the lower water to wire cost per kWh generated. Again, generation is based on the flow pattern in cells C26 to C36.
Lines 55 to 83 – C cells. These cells show the estimated water to wire cost of all the suitable turbines in $US, 2003. No cost appears for the unsuitable turbines. The water to wire cost includes all supply and installation costs from the turbine inlet to the low voltage side of the transformers. It does NOT include costs for ancillary electro-mechanical equipment in the powerplant not associated with the generating unit. Ancillary equipment includes draft tube gates, cranes, water pumps and piping, heating lighting and ventilation. Transportation to a remote site is extra – add 3% to 8%. The water to wire cost is an approximation based on an analysis of current bids for similar equipment. The turbine industry is now undergoing consolidation, with only a few large companies remaining in the business, plus several small companies building turbines with runners of less than about 1.5m diameter. As with all inquiries for equipment, the advantage often goes to the company with existing detailed designs for equipment identical to that needed at the site. Hence, bids for equipment from such companies may be lower than the cost estimated by the program. On the other hand, currency fluctuations may increase the cost substantially, particularly if the local currency has decreased in value relative to other major currencies.
Lines 55 to 83 – D cells. These show the total powerplant capacity for all types of turbines. Disregard the data for the unsuitable turbines.
Lines 55 to 83 – E cells. These show the annual energy generated by the powerplant in GWh. Again, disregard data for unsuitable turbines. The cell below the energy output indicates the program page number where further details on the turbine can be seen.
This completes the program data output summary.
Lines 85 to 100. These are for a project costing and screening program not associated with the turbine program, and will be discussed later.
Program turbine output data – line by line explanation for pages 3 to 22.
Pages 3 to 22 contain further details on the 10 types of turbines and generators. The text on all the pages is identical, and hence the line numbers are the same. For continuity, the input data is repeated for all turbines. For example, the rated head entered in cell C11 is repeated in cell C on line 106. Only the output data will be discussed for each line. Note that after page 4, the line number, as shown in cell A, is no longer equal to the cell number.
Line 110. Runner submergence is the runner setting relative to tailwater. It is negative above tailwater, positive below. If = 0, the runner is set at tailwater. The setting is based on data published in the following paper: -
"Hydro Turbine Submergence" WaterPower "89. Vol. 3, Pg. 1365-1374. Niagara Falls, N.Y., Aug. 1989.
Line 111. Runner cavitation coefficient. This is set at a level about equal to minimal cavitation, with k = 0.025 for runners with a diameter below about 2.5m, and at 0.006 (no cavitation) for larger runners. The weight of metal lost in kg per annum is then = k x d2 where d = runner diameter in meters. On this basis, a runner with a diameter of 2m would have a loss of 0.025 x 4 = 0.1kg per 8000 hours of operation. Note that these numbers are much lower than that allowed in the IEC code. The cavitation coefficient is based on data in the following two papers:-
(1)"Hydroturbine Cavitation Erosion" proceedings ASCE, Journal of Energy Division. Vol. 118, No. 3, December 1992. Pp. 194-208
(2) "Determination of turbine runner metal loss due to cavitation erosion" Water Power and Dam Construction Vol. 43, No. 8, Aug. 1991.
For the ultra low head turbine on pages 3 and 4, the cavitation coefficient is calculated instead of being specified. This is due to the different program used to define the parameters of this particular turbine. The coefficient in line 111 on page 3 will be below about 0.1
Line 112. Shows number of runner blades expected on the turbine. The number of blades is based on data published in the following paper: -
"Hydraulic turbine sizing" Hydro Review, Vol 9, No. 1 February 1990. Pg 74-78.
Line 113. The manufacturing number defines the manufacturing process assumed for the turbine runner. An explanation of the number can be seen in the adjacent yellow comment box.
Line 114. The draft tube factor varies according to the type of turbine. It is required to calculate turbine efficiency. It has a value of 0 = elbow draft tube; 1 = “S” type draft tube; 2 = cone or bent cone draft tube.
Line 115. This is the plant capacity factor assumed by the program, based on the flow pattern, and is used to determine runner size and submergence. This number should be within about +/- 0.03 of the calculated plant capacity factor in line 134.
Line 116. This indicates the wicket gate opening for the rated turbine load, a few percentage points below full stroke. Modern units are designed to produce the rated load at about 97% wicket gate opening. The 3% spare stroke is used as a safety factor in case the unit does not produce the rated power. About 60 years ago, this spare stroke was usually about 10% to 20%, resulting in the term “overload capacity” where the unit was operated at overload, often with significant cavitation on the turbine runner. The cavitation coefficient at overload is shown on line 127. Modern turbines do not have any “overload capacity”, unless this is a specified requirement.
Line 118. The calculated generator efficiency at full load. Generator efficiency is based on data published in: -
“Water power development” Vol. 1. By E. Mosonyi. Published by - The Hungarian Academy of Sciences. Budapest, 1963, 2nd edition, page 482.
Line 121. The calculated runner diameter. Defined as the outside blade diameter on a propeller unit, or the runner throat diameter in a Francis unit. All turbine and draft tube dimensions can be calculated from this number, by reference to published papers and manuals. (See references) The runner diameter and setting is based on formulae published in the following papers: -
“Francis Turbine Setting" Water Power and Dam Construction Vol. 41. N8, August 1989.
(2) "Submergence factors for hydraulic Turbines" proceedings ASCE, Journal of Energy Division, Vol. 115, No. 2 August, Pg. 90-107, 1989.
(3) “Hydraulic turbine submergence and cavitation" Transactions Engineering and Operating Division, CEA 29, Part 2, 1990.
(4) "Hydroelectric turbine assessment for new units and runner retrofits" Report No. 712-G-688 Canadian Electrical Association, June 1990.
(5) “A Statistical Method for Determination of Hydraulic Reaction Turbine Size and Setting” CEA spring meeting, Vancouver, March 1999.
Line 122. The calculated runner speed. If this is below 257rpm, a gearbox may be used to increase generator speed. If this is the case, the speed will not be equal to a synchronous speed, and the gearbox will increase speed to 900rpm if an industrial generator is used, or to 600rpm if a utility quality generator is required. The runner speed is based on data in the following paper: -
"A new approach to turbine speed" Water Power and Dam Construction Vol. 42 No. 8, Aug. 1990. Pp 39-46.
Line 123. The calculated turbine specific speed, metric, based on flow = nq.
Line 124. The calculated peak turbine efficiency, using the ASME definition, to include draft tube exit losses. For the Saxo and horizontal axis angled inlet (HAAI) turbines on pages 19 and 21, this is NOT the peak efficiency, but instead the efficiency at 80% gate opening. This is due to the high losses in the entrance pipe bend affecting the turbine efficiency, as will be noted on the corresponding efficiency charts on pages 19 to 22. The operating head also has an effect on efficiency in the SAXO units and curves are provided for the efficiency at +/-28% of the rated head, plotted against flow. Efficiency curves for the SAXO units should be regarded as preliminary, since there is a paucity of information on this type of unit. Peak efficiency is based on formulae extracted from:-
“Hydraulic Turbine Efficiency”, Canadian Jour. of Civil Engineering, Vol. 28, #2, April 2001.
Hydraulic losses at the inlet bend are based on the chart published in:-
“Hydropower Engineering Handbook” by J. S. Gulliver and R. E. A. Arndt, published by McGraw-Hill Inc, New York, 1991. Page 5.52.
Line 125. The calculated flow at peak efficiency. This is the flow, which should be used most of the time to obtain maximum energy from the unit.
Line 126. The calculated turbine setting. Can be corrected as shown for line 115. Note that the turbine setting is slightly different from the turbine submergence. The setting is the centerline elevation of the distributor, runner centerline in vertical axis units, and elevation of the shaft centerline in horizontal axis units. For inclined units it is the intersection of the shaft and runner.
Line 127. Calculated cavitation coefficient at full wicket gate opening – a situation to be avoided.
Line 128. The calculated speed – no – load flow for turbine synchronization.
Line 129. The calculated flow at full wicket gate opening.
Line 130. A statement on whether a speed increaser has been selected.
Line 131. The calculated turbine output in MW at rated flow and head.
Line 132. The calculated generator output in MW, and generator rotor weight. For small generators, where the entire generator is lifted as one piece, the weight is about equal to twice the rotor weight. The rotor weight is based on data in the following two papers: -
(1) "Determination of Hydro Generator Rotor Weight and Its Effect on Powerhouse Crane Capacity", Trans Eng. Op. Division, CEA 17: part 2, 1978.
"Estimating Hydro Powerhouse Crane Capacity", Water Power and Dam Const. 30: 25-26, Nov. 1978.
Line 133. The calculated unit output in GWH, based on the use pattern (lines 26 to 36), the unit efficiency (see charts), and the conduit losses (line 16). The calculation assumes no change in headwater and tailwater levels.
Line 134. The calculated plant capacity factor based on the unit efficiency and use pattern.
Line 135. The estimated water to wire cost for the electromechanical equipment in $US 2003.
Line 136. The calculated average flow per unit. Used as a check on the hydrology input.
Lines 127 to 152. A chart showing efficiency as a function of flow. Can be used in more sophisticated energy programs. Efficiency is based on data published in the following paper: -
“Hydraulic Turbine Efficiency”, Canadian Journal of Civil Engineering, Vol. 28, #2, April 2001.
Line 156. The calculated weighted average turbine efficiency.
Lines 162 to 182. Data on flow and corresponding turbine efficiency.
Line 184. The total operating hours per annum – used as a check on input data – obviously unit cannot be operated for more than 8760 hours per annum. Time should also be allowed for maintenance. Operating hours rarely exceed about 7500 hours per annum.
Lines 186 to 203. A chart showing efficiency as a function of turbine power output. For comparison with manufacturers efficiency charts.
This completes an explanation of the program output.
Project screening program.
Many entrepreneurs believe that every set of rapids in a river constitutes an attractive hydro- power site. Unfortunately, this is not the case. A rule of thumb, used by the author as a very first screening tool, is that within the service area for a North American utility, a site with a potential head of less than about 150m, is not economic unless there is an existing dam. If there is a dam, then there is a possibility that the site may be economic. As a second screen, the author has used formulae based on the following two published papers:-
“What we must not forget” Transactions, First Convention – Small hydropower plants, sponsored by Quebec Ministry of Energy, Hydro Quebec and Energy Mines and Resources, Canada. Sherbrooke, Quebec, August, 1991.
“Determining Ballpark Costs for a Proposed Project” HRW, Vol. 11, #1, March 2003, pages 37 – 41.
to develop the screening tool program incorporated within the tan-colored frame between lines 85 and 100 on page 2 of the turbine selection program. The screening program is independent of the turbine selection program, but requires some data developed in the turbine program, as will be explained in the following line by line description of the program input and output.
Screening program input/output data – line by line explanation for page 2.
After completing the input data for the turbine selection, proceed as follows: -
Lines 86 and 87. After selection of the turbine type to be used at the site, determine the corresponding powerplant capacity and energy generation, and enter the data in lines 86 and 87.
Line 88. Enter the expected selling rate for the energy in cents per kWh.
Line 89. From an atlas, determine the average number of days per annum at the site, when the temperature is below freezing. Range is from 100 to 300. The number is used in the cost equation, since work in colder climates is more difficult and hence more expensive. Anything less than 100 days has an insignificant effect on the project cost, hence for warm climates use 100 as a minimum. Enter the frost-day number on line 89.
Line 90. Enter the number for the type of development, as obtained from the adjacent yellow comment box. Range is from 33 to 100.
Line 91. Enter the cost factor for the country; again obtain the number from the adjacent yellow comment box. At present there is only data for the USA and Canada. For other countries, the user is referred to the “Ballpark” paper referenced above, for a methodology used to determine cost factors for other countries.
Line 92. The calculated ballpark site cost as developed by the program, in the currency of the country used to select the cost factor in cell C91. The site cost does NOT include access, transmission and legal fees.
Line 93. Enter the expected length of transmission line to the nearest substation, or point of delivery for the power.
Line 94. Enter the expected length of new access road to the site, including any additional length required to the powerplant.
Line 95. Enter the terrain difficulty factor, as obtained from the adjacent yellow comment box.
Line 96. Enter the expected transmission voltage in kV.
Line 97. The calculated expected project cost including access, transmission and legal fees, but NOT including any cost for the land and population relocation.
Line 99. Estimated project payback time. The number of years required to return the sum spent on development of the project, after deducting operating costs, but NOT any taxes.
Line 100. A comment on the project viability, as assessed by the program.
Caution – this is only a “Project Screening” program – NOT a cost estimating program.
The screening program can also be used to check project estimates. If the project estimate lies within 75% to 125% of the “Ballpark” cost, the estimate is in the right order. If below 75% of the “Ballpark” cost, the site has to be very attractive, with features likely to reduce cost, such as a small dam, or short conduit from the intake to powerhouse, or good quality exposed rock foundations. If such features are not present, the project cost is likely to have been underestimated. If the project cost exceeds 125% of the “Ballpark” cost, the site may include unattractive and expensive features such as permeable foundations, or long conduits or large underground works. A long conduit is where the head to conduit length ratio exceeds about 10.
Bennett, K. J., Swiderski, J. A. and Huang, J. “Solving small hydro problems with computational fluid dynamics” Hydro Review, Vol. XXI, #1, March 2002, pages 56 – 63.
Boucher, P. J. “Chutes-de-la-Chaudiere: optimizing hydraulic potential, enhancing natural beauty” Hydro Review, Vol. XX, #4, July 2001, pp. 76-80.
For sizing turbine water passages after obtaining the turbine runner size:-
USBR Engineering monograph No. 20 “Selecting hydraulic reaction turbines”
Schweiger, F. and Gregory, J. “Developments in the design of Kaplan turbines” Water Power & Dam Construction, Vol. 39, #11, Nov. 1987, pp 16-20.
Lugaresi, A. and Massa, A. “Designing Francis Turbines: trends in the last decade” Water Power & Dam Construction, Vol. 39, #11, Nov. 1987, pp 23-28.
Servio, F. and de Leva, F. “Modern trends in selecting and designing Francis turbines” Water Power & Dam Construction, Vol. 28, #8, Aug. 1976, pp 28-35.
Sadek, R. and Sinbel, M. A. “Water turbines and dimensional analysis” Water Power Vol. 12, #10, Oct. 1960, pp 381-389.
Small hydro, low head reaction unit cost comparison program.