Running head: WIND TURBINE REPORT
Vertical Axis Wind Turbine Project Report Jace Thompson and Derrick Sietien ENGR 196-1AH Dr. M. Hall Ivy Tech Community College of Indiana December 14, 2015
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Table of Contents Objectives ....................................................................................................................................... 3 Theory of Operation ........................................................................................................................ 4 Diagrams and Photographs ............................................................................................................. 5 Bill of Materials .............................................................................................................................. 7 Description of the Design Process .................................................................................................. 9 Electrical System ......................................................................................................................... 9 Blade Structure .......................................................................................................................... 10 Mechanical Load Bearing Structure .......................................................................................... 10 Narrative of the Build and Testing Process .................................................................................. 11 Discussion of Features included (and not included) in the Product.............................................. 13 Measurements, including Graphs and Illustrations ....................................................................... 15 Measurements of Prototype Turbine ......................................................................................... 15 Measurements of Final Turbine ................................................................................................ 16 Summary, Conclusions, and Next Steps ....................................................................................... 18
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Objectives The purpose of this project was to build a working wind powered generator from basic components under the constraints of assembly time and cost effectiveness. Additionally, the following objectives were included from the project description: 1. Solve an engineering problem by incrementally developing solutions 2. Apply CAD software skills and electronics knowledge to develop a product. 3. Apply math and physics principles to a real-world situation. 4. Understand the basics of electrical generation and wind turbines. 5. Work in a team, coordinating development and responsibilities. 6. Document your results in a notebook and a formal written report. 7. Deliver an oral presentation on your project.
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Theory of Operation (Abstract) Our vertical axis wind turbine (VAWT) works by capturing energy from the wind through its blades. The vertical orientation allows the device to be driven from any standard direction of the wind. The blades turn a rotor assembly that has powerful neodymium magnets adhered to the bottom. Underneath these magnets lies coils arrayed so that they break the most lines of flux from the magnets. The coils are wired in 3 phases, and the phases are connected in a pattern known as a “3phase Wye” configuration (figures 4, 5, 9). The Wye configuration allows for a higher voltage to be produced relative to other configurations of coils in 3 phases. The higher voltage at lower revolutions per minute allows for our turbine to reach the break in voltage necessary to charge a battery earlier than other coil configurations. Three phase power has several advantages over single phase power. In single phase, power output falls to zero three times per cycle, in 3 phase power output never drops to zero. In three phase, the power delivered to the load is the same at any instant. Additionally in three phase, the conductors need to be only 75% of the size of conductors for equivalent single phase power output.
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Diagrams and Photographs
Figure 3
Figure 4 Hugh Piggott Figure 2
Figure 1
Figure 7 Hugh Piggott
Figure 6 Cal-EPower Figure 5
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Figure 8
Figure 9
Figure 10
Figure 11
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Bill of Materials Qty 1 1 2 1 1 1 1 1 1 1 3 1 1 1 1 1 1 6 1 1 1 1 8 8 8 1 1 6 * 1 2 1 1 10 1 1
Cost * Qty 2' x 2' x .25" particle board salvaged 3/8" OD 24" drive shaft $13.76 3/8" ID Fafnir S3PP ball bearing $6 1" painters tape salvaged plastic foam project panel $5 electrical tape salvaged hot glue + hot glue gun Dr. Hall JB Weld epoxy salvaged Gorilla brand tape salvaged Kraft paper roll salvaged Nuvo newspaper salvaged roll of 2' wire mesh salvaged leatherworking needle salvaged spool of leatherworking thread salvaged holepunch salvaged miter box + saw Dr. Hall drill + bitset salvaged unopened soup cans salvaged compass (magnetic) salvaged compass (drafting) salvaged 3 in 1 silicon oil salvaged roll of paper towels salvaged 1" x .25"neodymium magnets Dr. Hall PVC retaining rings (PVC pipe) salvaged 1" OD fender washers $1.36 oscilloscope Dr. Hall digital multimeter Dr. Hall silicon diodes Dr. Hall resistors - for measurement Dr. Hall coping saw salvaged triangles Dr. Hall Sharpie salvaged jumper wire salvaged index card shims salvaged Sta-Flo starch salvaged Elmer's Glue-All salvaged
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8 quarters 1 heatgun 1 1 ton press coil winding rig 1 vice 1 hand drill 1 1" OD socket 2 circular foam board cutouts 1.5 rolls of magnet wire frame 1 2" x 2" x 1' piece of wood 4 mild steel tabs with hole 2 ~2' mild steel angle iron 1 welder 2 wood screws 2 bolts 2 washers 2 nuts 1 spool of thin cord 4 screw eyes Total Spent:
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$2.00 salvaged salvaged salvaged salvaged salvaged salvaged Dr. Hall salvaged salvaged salvaged salvaged salvaged salvaged salvaged salvaged salvaged salvaged $28.12
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Description of the Design Process A preliminary model was constructed to provide a baseline understanding of a simple vertical axis wind turbine and accompanying alternator (see figure 1). It was apparent from the preliminary model that the design had three basic components: the electrical system; the blade structure; and the mechanical load bearing structure. The design also needed to maximize the score of the grading rubric. Tradeoffs were inevitable. Electrical System Several designs for the electrical system were considered. One of our earlier designs involved using the housing from a ceiling fan to contain the electrical system. This design was rejected for the following reasons: it required a coupler, lack of a ceiling fan, and poor compatibility with the given magnets. After we read sections from Hugh Piggott’s A Wind Turbine Recipe Book and his PMG Construction Manual, we decided that an axial flux permanent magnet alternator wired in a 3phase Wye configuration would be the best fit for our turbine. The 3-phase Wye (figures 4, 7) was chosen because according to our research, it allows for more efficient power delivery, and the Wye configuration allows for less resistance that our rotor and blade assembly would have to overcome during start up. This was more of a concern because our blades are Darrieus style (compare figures 1, Savonius, figure 2, Darrius). The final consideration of our electrical system involved minimizing the airgap between the coils and the magnets. A smaller airgap results in increased power output. The axial flux permanent magnet alternator design fits this requirement.
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Blade Structure Our research into the blade structure of our turbine consisted of Abraham and Plourde’s Small Scale Windpower and Caleb Engineering’s videos on VAWTs available on YouTube. An early design, inspired by a minidocumentary on California Energy and Power (figure 6), involved a concentrator and Savonius style blades. We decided on a 3 bladed Darrieus style structure. This is because Darrieus style blades operate using lift and not drag, and are more efficient in harnessing the wind’s energy. We chose 3 blades because according to Caleb Engineering, an odd number is easier to balance and diminishing returns occur when more blades are added to a design (figures 2, 8). Mechanical Load Bearing Structure The primary design consideration of our mechanical load bearing structure was to eliminate excess weight, and extraneous motion in non-productive directions. The design manifested itself as a steel drive shaft, which doesn’t rotate, mounted to a frame that can tolerate the vibration produced from a rotor that is not precision balanced. The coupling of rotor to drive shaft is accomplished through ball bearings that are held up by a thin layer of tape adhered to the shaft. Another consideration was to keep the magnets from flying off due to centrifugal force. This was accomplished using PVC retaining rings that were adhered to the rotor with JB Weld. The overall assembly was placed along the diagonal axis of the particle board base to maximize room for an optional concentrator (figure 5).
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Narrative of the Build and Testing Process The construction of individual components as well as anything that had contact with the mechanical load bearing structure took place primarily off campus at Jace’s residence. The assembly of completed components took place during common lab hours. The reasons for this include: first, maximizing the time available when team members were together; second, increased access to tools and temporary rigging; third, this allowed for night time work to be done on components; fourth, the increased time for component construction allowed for a calmer pace, resulting in increased safety during construction and higher quality components. The turbine was frequently transported between Jace’s residence and the classroom, which influenced the design of the turbine, and the build process due to the possibility of mechanical damage during transport. The build occurred as follows: 1. Cut wood and drilled holes for first frame. 2. Assembled and adhered first frame to base using hot glue on wood. 3. Sculpted two sets of blades forms by hand from wire mesh. a. Sculpted Darrieus or lift type forms. b. Sculpted Savonius or drag type forms. 4. Sculpted form of concentrator. (unused, see figure 5) 5. Adhered paper mache using Sta-Flo starch to Darrieus type forms and concentrator. 6. Adhered muslin cloth using Elmer’s Glue-All to Savonius type forms (built as a backup) 7. Cut and sanded shape of plastic-foam rotors. 8. Press fit a PVC jacket to each bearing (to avoid having to use adhesives directly on the bearings)
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9. Adhered bearing to center of plastic foam rotors using JB Weld, hot glue, and PVC electrical tape 10. Cut magnet retaining rings from 1” inner diameter PVC pipe. 11. Adhered retaining rings and washers for magnets using JB Weld. 12. Put magnets into retaining rings. 13. Preliminary assembly of above components. 14. Catastrophic failure of wood and glue frame due to accidental drop. 15. Welded new frame from angle iron and iron tabs 16. Drilled holes and bolted frame to base with bolts, nuts, washers. 17. Screwed rod holder to top of frame using wood screws. 18. Reassembled rod, rotors, and frame. 19. Aligned rotors using soup cans. 20. Balanced rotors with stack of quarters. 21. Stitched tops of Darrieus style blades to upper rotor 22. Gorilla-taped bottoms of Darrieus style blade to lower rotor 23. Wound coils using homebrew winder (see figure 3) 24. Adhered coils to base using Gorilla-tape and index card shims (to minimize airgap). 25. Routed coils into desired 3-phase Wye configuration with electrical tape and jumper wire. 26. Wrapped tape to couple rotors to rod at correct height. 27. Adjusted airgap by shimming coils with index cards
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Discussion of Features included (and not included) in the Product Notable features of our wind turbine include a lightweight blade and rotor assembly. The paper mache blades were built with three layers of Kraft packing paper adhered to wire mesh. The wire mesh was removed to decrease the weight of the overall structure, which resulted in an increased speed of the rotor. The design of frame that holds the shaft was carefully considered so that the rotor and blade assembly could be removed to allow for later modification; the improvement of components; and the inevitable assembly error. Due to the modifiable design of our turbine, we were able to risk using Darrieus style blades. The risk was that these blades are difficult to start relative to their Savonius counterparts. An additional set of Savonius blades were made to cover the contingency of the Darrieus style blades being unable to start. Our design features two Fafnir S3PP ball bearings mounted to a drive shaft. The shaft allows for the design to be modular in that there are a variety of mechanical devices that are designed to mount to a precision drive shaft. Standard ball bearings are designed to accept force in two directions. However, we needed our ball bearings to accept a third direction, the downward force from the weight of the blade and rotor assembly. After researching terminology, we found that angular contact ball bearings were able to fit this requirement. The S3PP has an additional steel case that keeps enables the bearing to tolerate force in a third direction. We opted not to use a gear system because in an axial flux PMA (permanent magnet alternator) the “gearing” is accomplished by having a larger diameter rotor, and mounting the magnets at the end of the rotor. Factors affecting power generation include: the speed of the
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magnets relative to the coils, and the airgap between magnets and coils. Like a gear system, our system behaves like a lever, without losses due to friction between gears. In a full size VAWT, a gear system may be more efficient due to material and space constraints. The S3PP’s were press fit into a segment of PVC pipe so that they could later be reused in other projects without the potential of being rendered inoperable by adhesives. The electricity produced by our turbine can be rectified and potentially used to charge a single battery cell. A prominent features that was not included in our final product was a concentrator (figures 5, 6). A concentrator is a parabolic surface that protects the return side of the blade while channeling an increased amount of air from the test fan onto the productive side of the turbine’s blades. This feature was not included in the final test because 1) the designers felt it was too risky to include an untested component that could result in unforeseen results; 2) a concentrator eliminates the VAWT’s ability to be rotated by the wind from all directions; 3) the test fan was able to be positioned only on the productive side of the blades; however additional airflow is unable to be redirected productively. We were unable to include a rectifier because our output waveform was not sinusoidal, and thus our output was not usable.
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Measurements, including Graphs and Illustrations Measurements of Prototype Turbine
Artist’s representation of a chair seat sine wave Our baseline turbine was able to output 20.7 milliwatts at 0.593 Vrms. Due to a small misalignment between magnets and coils, our output waveform was a “chair seat”, as depicted above. A chair seat is characterized by its long rise and short fall, with the nominal seat occurring during the “rise” of the wave.
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Measurements of Final Turbine
Combined waveform and measurement of all 3 phases.
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Waveforms of phases 1, yellow, and 3, blue Power output for our 3 phase Wye configuration was calculated with the following equation: 𝑃=
3𝑉 2 𝑅
Where R is the sum of the resistance of two phases and V is the voltagerms measured across those two phases. The measurement of our rebuilt wind turbine was 114 milliwatts at 1.75 Vrms. The designers assume that several coils were installed incorrectly. The resulting rectified 3 phase waveform should have resembled figure 11; the separate phases plotted together should have looked like figure 10.
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Summary, Conclusions, and Next Steps Summary: We were successfully able to build a desktop vertical axis wind turbine. We used instructor-supplied magnets and wire, salvaged supplies, and $28.12 of mechanical devices to create an effective system to harness small scale wind power. Each team member gained an in-depth knowledge of new engineering concepts during the secondary research phase from books and videos authored by experts. The research was naturally motivated from our assigned task of designing a requirements-driven wind turbine. We also participated in primary research during the assembly stages of our project. If time permitted, our next step would be to fix the installation of the coils, and retake our measurements. After that, we would install our simple rectifier and measure what our DC output would be. If the output was adequate to charge a small cell, then we would attempt to do so using a simple circuit to regulate the charging of our cell. It would then be feasible to use our wind turbine to power a small device at a remote location.
