| 1. |
- Amarasinghe, Dulan, et al.
(författare)
-
Channel tortuosity of long laboratory sparks
- 2007
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 65:8, s. 521-526
-
Tidskriftsartikel (refereegranskat)abstract
- Channel tortuosity of 50 cm long laboratory sparks were measured by analyzing a set of images taken by three cameras. The cameras were placed at a radial distance of 200 cm from the spark gap. The angle between any two cameras was 120 degrees. The sparks were generated between a steel rod and. a plane electrode. The distribution of the direction change of the channel was found to be Gaussian with a standard deviation of 15.3 degrees. The average tortuosity of the channel defined as the mean absolute value of the direction change was 11.8 +/- 1.4 degrees, which is smaller than the average tortuosity of natural lightning and close to the tortuosity of triggered lightning. The average tortuosity is dependent on the segment length used in calculating the direction change. A gradual increase in the average tortuosity (0.08 degrees/cm) was seen when the sparks propagated towards the plane electrode.
|
|
| 2. |
- Amarasinghe, Dulan, et al.
(författare)
-
Fractal dimension of long electrical discharges
- 2015
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 73, s. 33-37
-
Tidskriftsartikel (refereegranskat)abstract
- The fractal dimension of 500 mm long electrical discharges is presented by analyzing a set of photographic images. Three popular fractal dimension estimation techniques, box counting, sandbox and correlation function methods were used to estimate the fractal dimension of the discharge channels. To remove the apparent thickness due to varying magnitudes of current in the discharge channels, edge detection algorithms were utilized. The estimated fractal dimensions for box counting, sandbox and correlation function for long laboratory sparks were 1.20 +/- 0.06,1.66 +/- 0.05 and 1.52 +/- 0.12 respectively. Within statistical uncertainties, the estimated fractal dimensions of positive and negative polarities agreed very well. (C) 2014 Elsevier B.V. All rights reserved.
|
|
| 3. |
- Eklund, Petter, 1989-
(författare)
-
Design of Rare Earth Free Permanent Magnet Generators
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low speed permanent magnet (PM) synchronous generators (SGs) are commonly used in renewable energy. Rare earth (RE) PMs such as neodymium-iron-boron are a popular choice due to their high performance. In 2011 supply and cost issues were added to the previously existing environmental concerns regarding REPM raw materials as the world's major producer China imposed export restrictions. This thesis aims to investigate and propose design solutions for PMSGs that do not use REPMs. Two approaches are used: to design generators using the cheaper and more abundant ferrite PM materials, and to investigate how properties of new PM materials influence SG design.A ferrite PM rotor is designed to replace a REPM rotor in an experimental 12 kW wind power generator. The new design employs a flux concentrating spoke type rotor to achieve performance similar to the old REPM rotor while using ferrite PMs. The ferrite PM rotor design is built. The air gap length, magnetic flux density in the air gap, PM remanence, and voltage at both load and no load are measured. The generator has lower no load voltage than expected, which is mainly explained by lower than specified remanence of the ferrite PMs in the prototype. With the measured remanence inserted into the calculations some discrepancy remains. It is found that the discrepancy can be explained by the magnetic leakage flux in the end regions of the spoke type rotor, which is not modeled in the two dimensional simulations used for the design calculations.To investigate the influence of PM material properties three different PM rotor topologies are optimized for torque production using PM materials described by their remanence, recoil permeability, and demagnetization resistance. Demagnetization is considered using currents determined by a novel, winding design independent short circuit model. It is found that the spoke type rotor gives the highest torque of the three rotor topologies for low remanence materials as long as the PMs have sufficient demagnetization resistance. For high remanence materials the surface mounted PM rotor can give higher torque if the demagnetization resistance is high, but otherwise a capped PM rotor gives higher torque.
|
|
| 4. |
- Eklund, Petter, 1989-, et al.
(författare)
-
Experimental Evaluation of a Rare Earth-Free Permanent Magnet Generator
- 2021
-
Ingår i: IEEE Transactions on Energy Conversion. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0059 .- 0885-8969. ; 36:1, s. 3-10
-
Tidskriftsartikel (refereegranskat)abstract
- Low speed, high torque machines are used in wind turbines where the turbine rotor is directly connected to the generator. A permanent magnet synchronous generator using high-energy rare-earth permanent magnets (PMs) is one common choice for this application, but rare-earth PMs have supply insecurities and cost risks. A rare-earth free 32-pole PM generator, using ferrite PMs in a spoke-type rotor, for use in a 12 kW experimental wind turbine is built and tested. Voltages and currents at load and no load are measured, as well as the magnetic field in the end regions of the machine. The generator can deliver the required power at nominal speed and has low harmonic content in the output. The electrical measurements are compared to two-dimensional finite element design calculations and the experimental results are lower than expected from simulations. The measured voltage is lower than expected, requiring a higher current than calculated for the rated power. Three-dimensional magnetic field simulations show that there are leakage flux paths in the end-regions that the two-dimensional design calculations overlook, explaining the discrepancy between simulations and measurements.
|
|
| 5. |
|
|
| 6. |
|
|
