| 11. |
- Forslund, Johan, 1985-, et al.
(författare)
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Power And Energy Needed For Starting A Vertical Axis Marine Current Turbine
- 2017
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Konferensbidrag (refereegranskat)abstract
- A marine current power station has been deployed in Söderfors, Sweden. It comprises a five bladed fixed pitch vertical axis H-rotor turbine directly connected to a permanent magnet synchronous generator. The turbine is rated for 1.3 m/s, but at lower water speeds the turbine is generally not self starting. This paper investigates the energy and power needed to at low speeds start the turbine electrically with a BrushLess DC (BLDC) motor until he turbines gives a net positive torque to the generator. A range of startup BLDC powers have been investigated. It is shown that for three water speeds (0.98 m/s, 1.04 m/s and 1.16 m/s) the energy needed for start up is equivalent to less than 1.2 s of power production at maximum power capture of the turbine. The startup time is mostly dependent on BLDC power setting, not on water speed. A BLDC power of 1/7th of rated power of the machine is enough to start the machine within 2 seconds. The results suggest that a higher BLDC power than that will not significantly reduce the startup time nor reduce the energy needed (increase the efficiency of the startup process). The water speed has the highest impact on the time it takes to recover the energy needed for startup once the BLDC power is well above the losses in the system.
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| 12. |
- Frost, Anna E., et al.
(författare)
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Partial Stator Overlap in a Linear Generator for Wave Power : An Experimental Study
- 2017
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study on how the power absorption and damping in a linear generator for wave energy conversion are affected by partial overlap between stator and translator. The theoretical study shows that the electrical power as well as the damping coefficient change quadratically with partial stator overlap, if inductance, friction and iron losses are assumed independent of partial stator overlap or can be neglected. Results from onshore experiments on a linear generator for wave energy conversion cannot reject the quadratic relationship. Measurements were done on the inductance of the linear generator and no dependence on partial stator overlap could be found. Simulations of the wave energy converter's operation in high waves show that entirely neglecting partial stator overlap will overestimate the energy yield and underestimate the peak forces in the line between the buoy and the generator. The difference between assuming a linear relationship instead of a quadratic relationship is visible but small in the energy yield in the simulation. Since the theoretical deduction suggests a quadratic relationship, this is advisable to use during modeling. However, a linear assumption could be seen as an acceptable simplification when modeling since other relationships can be computationally costly.
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| 13. |
- Hettiarachchi, Pasan, 1977-
(författare)
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Measurements of X-Ray Emission from Laboratory Sparks and Upward Initiated Lightning
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In 1925 Nobel laureate R. C. Wilson predicted that high electric fields of thunderstorms could accelerate electrons to relativistic energies which are capable of generating high energetic radiation. The first detection of X-rays from lightning was made in 2001 and from long sparks in 2005. Still there are gaps in our knowledge concerning the production of X-rays from lightning and long sparks, and the motivation of this thesis was to rectify this situation by performing new experiments to gather data in this subject.The first problem that we addressed in this thesis was to understand how the electrode geometry influences the generation of X-rays. The results showed that the electrode geometry affects the X-ray generation and this dependency could be explained using a model developed previously by scientists at Uppsala University. The other missing information was the distribution of energy. Using a series of attenuators, we observed how the X-ray photons were attenuated as a function of barrier thickness and using a simple model we obtained the average and the maximum energy of X-rays. All the studies conducted previously was based on the lightning impulses, but in switching impulses, the voltage waveform rises very slowly compared to lightning impulses, and according to some scientists the rate of rise is an important parameter in X-ray development. Our study showed that the switching impulses were as efficient as lightning impulses in generating X-rays even though the rate of rise of voltage in switching impulses was hundreds of times slower.All the observations on X-ray generation from lightning by other scientists were based on either natural downward lightning flashes or triggered lightning in Florida. The first experiments to study the X-ray generation from upward lightning flashes systematically was conducted within this thesis work at Gaisberg Tower in Austria. The results showed that the X-ray emissions from these flashes were much weaker than the ones produced by either natural downward or triggered lightning. An attempt was made to explain this observation by invoking the possible differences in the charge distribution of leaders associated with the triggered lightning flashes in Florida and upward initiated lightning flashes at Gaisberg tower.
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| 14. |
- Hettiarachchi, Pasan, et al.
(författare)
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Time Domain Analysis of the Lightning Interaction with Wave Energy Converters
- 2018
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Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
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Konferensbidrag (refereegranskat)abstract
- In this work, we present a simulated study of lightning interactions with wave power generators submerged in seawater in Lysekil, in the southwest coast of Sweden. A time domain 3D electromagnetic simulation involving a Wave Energy Converter (WEC) and the surrounding seawater, air, and the current injection to the WEC from a typical return stroke of a lightning is conducted. The results show that the injected current to the wave power generator is considerably low even under a direct lightning strike. The study also shows that the wave-shape of the injected current to the WEC is significantly altered from a typical return stroke current impulse. It is concluded that likelihood of damages to the WEC or injection of electrical surges to the electrical grid is low. However, in order fully understand the implications of lightning strikes to a WEC further studies should be conducted.
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| 15. |
- Hultman, Erik, et al.
(författare)
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An updated cable feeder tool design for robotized stator cable winding
- 2018
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Ingår i: Mechatronics. - : Elsevier BV. - 0957-4158 .- 1873-4006. ; 49, s. 197-210
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Tidskriftsartikel (refereegranskat)abstract
- We have previously suggested a method for robotized stator winding of cable wound electric machines and demonstrated the method successfully in full-scale experiments. The cable feeder tool used to handle the cable during the complete winding process is an essential component of this robot cell. To take the robot winding method to the next level, into an industrial product, require further developments regarding durability, independency, flexibility and implementability. In this paper, we present an updated cable feeder tool design. This tool is designed to be used in a robot cell for cable winding of the third-generation design of the Uppsala University Wave Energy Converter generator stator. In this work, three cable feeder tool prototypes have been constructed, experimentally evaluated and validated for the intended application. Key performance parameters are presented and discussed, including suggestions for further developments. We completed a durable, compact, high performance tool design, with fully integrated control into industrial robot controllers. The experimental results presented in this article are very promising and hence, the updated cable feeder tool design represents another important step towards an industrial solution for robotized stator cable winding.
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| 16. |
- Hultman, Erik, et al.
(författare)
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Automated Cable Preparation for Robotized Stator Cable Winding
- 2017
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Ingår i: Machines. - : MDPI AG. - 2075-1702. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- A method for robotized cable winding of the Uppsala UniversityWave Energy Converter generator stator has previously been presented and validated. The purpose of this study is to present and validate further developments to the method: automated stand-alone equipment for the preparation of the winding cables. The cable preparation consists of three parts: feeding the cable from a drum, forming the cable end and cutting the cable. Forming and cutting the cable was previously done manually and only small cable drums could be handled. Therefore the robot cell needed to be stopped frequently. The new equipment was tested in an experimental robot stator cable winding setup. Through the experiments, the equipment was validated to be able to perform fully automated and robust cable preparation. Suggestions are also given on how to further develop the equipment with regards to performance, robustness and quality. Hence, this work represents another important step towards demonstrating completely automated robotized stator cable winding.
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| 17. |
- Hultman, Erik, et al.
(författare)
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Integration of real-world project tasks in a course on automation and robot engineering
- 2019
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Ingår i: IEEE Global Engineering Education Conference, EDUCON. - : Institute of Electrical and Electronics Engineers (IEEE). - 2165-9567 .- 2165-9559. ; April-2019, s. 107-114, s. 107-114
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Konferensbidrag (refereegranskat)abstract
- © 2019 IEEE. The modern engineering profession requires classical technical skills combined with creativity and a high proficiency in cooperation and sustainable development. Research indicates that the engineering education should adapt better to this. This paper introduces a teaching approach where open-ended project tasks are fully integrated into a complete course, in a context relating to the students' future working life. The teaching approach was implemented in a course on automation and robot engineering. Extensive written student course evaluations, the students' examination results and the teachers' experience were used for evaluation and compared with the previous classical course. Both the students and the teachers greatly appreciated the course. It was strongly indicated that the students' theoretical knowledge and understanding of the subject had benefited, both with regards to the technical depth and to the non-technical engineering skills. It is likely that the presented teaching approach can be used also in other engineering courses.
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| 18. |
- Hultman, Erik, et al.
(författare)
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Robotized stator cable winding
- 2018
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Ingår i: Robotics and Computer-Integrated Manufacturing. - : Elsevier BV. - 0736-5845 .- 1879-2537. ; 53, s. 197-214
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Tidskriftsartikel (refereegranskat)abstract
- Automated stator winding assembly has been available for small and medium sized conventional electric machines for a long time. Cable winding is an alternative technology developed for medium and large sized machines in particular. In this paper we present, evaluate and validate the first fully automated stator cable winding assembly equipment in detail. A full-scale prototype stator cable winding robot cell has been constructed, based on extensive previous work and experience, and used in the experiments. While the prototype robot cell is adapted for the third design generation of the Uppsala University Wave Energy Converter generator stator, the winding method can be adapted for other stator designs. The presented robot cell is highly flexible and well prepared for future integration in a smart production line. Potential cost savings are indicated compared to manual winding, which is a backbreaking task. However, further work is needed to improve the reliability of the robot cell, especially when it comes to preventing the kinking of the winding cable during the assembly.
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| 19. |
- Kamf, Tobias, et al.
(författare)
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Automated Mounting of Pole-Shoe Wedges in Linear Wave Power Generators-Using Industrial Robotics and Proximity Sensors
- 2017
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Ingår i: Machines. - : MDPI AG. - 2075-1702. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- A system for automatic mounting of high tolerance wedges inside a wave power linear generator is proposed. As for any renewable energy concept utilising numerous smaller generation units, minimising the production cost per unit is vital for commercialization. The linear generator in question uses self-locking wedges, which are challenging to mount using industrial robots due to the high tolerances used, and because of the fact that any angular error remaining after calibration risks damaging the equipment. Using two types of probes, mechanical touch probes and inductive proximity sensors, combined with a flexible robot tool and iterative calibration routines, an automatic mounting system that overcomes the challenges of high tolerance wedge mounting is presented. The system is experimentally verified to work at mounting speeds of up to 50mms(-1), and calibration accuracies of 0.25mm and 0.1 degrees are achieved. The use of a flexible robot tool, able to move freely in one Cartesian plane, was found to be essential for making the system work.
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| 20. |
- Lindblad, Liselotte, et al.
(författare)
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Portable Data Acquisition System for Offshore Applications
- 2019
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Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 44:3, s. 719-727
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Tidskriftsartikel (refereegranskat)abstract
- In the development of ocean energy technologies, full-scale sea trials have proven technically challenging and expensive. As a contribution to the development of flexible, reliable, and affordable measurement systems for such sea trials, this paper presents and evaluates a portable data acquisition system. The system offers a cheap and flexible option for when and where signal infrastructure at site is not available. It is battery powered and consists of a sensor system and a logger unit. The sensor system is placed inside the object of study, which for this application is a wave power generator standing on the seafloor. The logger unit, which contains a logger with integrated data storage and a battery, is placed outside the object of study in a submersible and retrievable vessel. Sensor output is carried with 4-20-mA current signals between the sensor system and the logger, which makes the system directly compatible with a wide range of industrial sensors. For the specific setup implemented in this paper, the sensor system was used to measure voltage and current inside the generator. Beyond this, the system is designed to be adaptable for a wider range of sensors, with 16 individual signals and a sampling frequency up to 1 kHz. The custom logger is programmable and offers many options to apply different logging schedules and to limit the sensor system power supply accordingly. Evaluations show that the implemented system offers 5-22 weeks of 1-kHz and 16-bmonitoring of 16 signals, depending on a chosen logging schedule. Suggestions are also given for how to raise the operation time up to 50 weeks. The system has been tested offshore for the collection of power production data from two wave energy converters, with good results.
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