Development of a magnetic gear for dry-cooling power plant applications

[摘要] ENGLISH ABSTRACT: Due to excessive mechanical gear failure in air cooled condenser (ACC) fordry cooling applications there is a need to investigates possible alternatives.In this study research is conducted into magnet gear (MG) technologies whichcould potentially replace mechanical gears for dry cooling applications. Threepromising magnetic gear topologies are identified which include the magneticharmonic gear (MHG), the magnetic planetary gear (MPG) and the flux modulatedmagnetic gear (FMMG).Of the three identified MG topologies the MPG and the FMMG are deemedmore viable from a manufacturing perspective. Two small prototypes are constructedand tested to gain further knowledge on the potential advantages anddisadvantages of each topology. The PMG achieved the highest torque densityof 139kNm/m3 compared to the FMMG with 87kNm/m3. Although thePMG achieved the highest stall torque output it also suffered from the highestlosses with efficiency of 70% at full load compared to the FMMG prototypewith 95% efficiency. These losses were caused by frictional losses in the PMGdue to mechanical complexity. The relatively simple mechanical design of theFMMG topology makes it a suitable candidate for this study.To have a more objective comparison between the FMMG and the mechanicalgear, a new FMMG prototype is optimally designed using 2D finite elementmethod (FEM) according to the same specifications of an existing single-stagehelical 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 onall the critical sections of the design.Experimental tests of both the FMMG and the equivalent mechanical gear areconducted for performance comparison. The mechanical gear achieved a maximumefficiency of 95% under rated conditions of 132Nm torque and 160 rpmon 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 trailingwithin 2% of the mechanical gear's efficiency. The measured maximumefficiency 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 mechanicalcounterpart. Both gears achieved efficiency in the mid 90% range. Withthe added advantage of over load protection and reduced noise transfer themagnetic gear appears to be a valid replacement for the mechanical gear inthis specific application.

[发布机构] Stellenbosch University