Browsing by Author "Mathee, Alexander"

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    Development of a magnetic gear for dry-cooling power plant applications
    (Stellenbosch : Stellenbosch University, 2017-03) Mathee, Alexander; Wang, R-J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Due to excessive mechanical gear failure in air cooled condenser (ACC) for dry cooling applications there is a need to investigates possible alternatives. In this study research is conducted into magnet gear (MG) technologies which could potentially replace mechanical gears for dry cooling applications. Three promising magnetic gear topologies are identified which include the magnetic harmonic gear (MHG), the magnetic planetary gear (MPG) and the flux modulated magnetic gear (FMMG). Of the three identified MG topologies the MPG and the FMMG are deemed more viable from a manufacturing perspective. Two small prototypes are constructed and tested to gain further knowledge on the potential advantages and disadvantages of each topology. The PMG achieved the highest torque density of 139kNm/m3 compared to the FMMG with 87kNm/m3. Although the PMG achieved the highest stall torque output it also suffered from the highest losses with efficiency of 70% at full load compared to the FMMG prototype with 95% efficiency. These losses were caused by frictional losses in the PMG due to mechanical complexity. The relatively simple mechanical design of the FMMG topology makes it a suitable candidate for this study. To have a more objective comparison between the FMMG and the mechanical gear, a new FMMG prototype is optimally designed using 2D finite element method (FEM) according to the same specifications of an existing single-stage helical mechanical gear. The design is further refined to achieve higher efficiency after which the performance is verified by 3D FEM calculation. The mechanical design is also checked by performing mechanical stress analysis on all the critical sections of the design. Experimental tests of both the FMMG and the equivalent mechanical gear are conducted for performance comparison. The mechanical gear achieved a maximum efficiency of 95% under rated conditions of 132Nm torque and 160 rpm on the output shaft. The gear is also tested at 1.5 pu condition (198 Nm) and obtained an efficiency of 96%. The magnetic gear achieved results trailing within 2% of the mechanical gear's efficiency. The measured maximum efficiency of the FMMG are 93.5% and 95% at rated and 1.5 pu conditions, respectively. The power rating of the gears at 1.5 pu conditions is about 3.3 kW. The magnetic gear performed reasonably well in comparison with the mechanical counterpart. Both gears achieved efficiency in the mid 90% range. With the added advantage of over load protection and reduced noise transfer the magnetic gear appears to be a valid replacement for the mechanical gear in this specific application.