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Thermal Analysis of Potted Litz Wire for High-Power-Density Aerospace Electric MachinesIncreasing the power density and efficiency of electric machines (motors and generators) is integral to bringing Electrified Aircraft (EA) to commercial realization. To that end an effort to create a High Efficiency Megawatt Motor (HEMM) with a goal of exceeding 98% efficiency and 1.46 MW of power has been undertaken at the NASA Glenn Research Center. Of the motor components the resistive losses in the stator windings are by far the largest contributor (34%) to total motor loss. The challenge is the linear relationship between resistivity and temperature, making machine operation sensitive to temperature increases. In order to accurately predict the thermal behavior of the stator the thermal conductivity of the Litz wire-potting-electrical insulation system must be known. Unfortunately, this multi material system has a wide range of thermal conductivities (0.1 W/m-K – 400 W/m-K) and a high anisotropy (axial vs transverse) making the prediction of the transverse thermal conductivity an in turn the hot spot temperatures in the windings is difficult. In order to do this a device that simulates the thermal environment found in the HEMM stator was designed. This device is not unlike the motorettes (little motors) that are described in IEEE standards for testing electrical insulation lifetimes or other electric motor testing. However, because the HEMM motor design includes significant rotor electrical and thermal considerations the term motorette was not deemed appropriate. Instead statorette (or little stator) was adopted as the term for this test device. This paper discussed the design, thermal heat conjugate analysis (thermal model), manufacturing and testing of HEMM's statorette. Analysis of the results is done by thermal resistance network model and micro thermal model and is compared to analytical predictions of thermal conductivity of the insulated and potted Litz wire system.
Document ID
20190030263
Document Type
Conference Paper
Authors
Woodworth, Andrew A. (NASA Glenn Research Center Cleveland, OH, United States)
Smith, Andrew D. (NASA Glenn Research Center Cleveland, OH, United States)
Sixel, William R. (NASA Glenn Research Center Cleveland, OH, United States)
Edwards, Ryan D. (NASA Glenn Research Center Cleveland, OH, United States)
Jansen, Ralph H. (NASA Glenn Research Center Cleveland, OH, United States)
Mccormick, Sean P. (NASA Langley Research Center Hampton, VA, United States)
Robbie, Malcolm G. (Vantage Partners, LLC Brook Park, OH, United States)
Szpak, Gerald M. (Vantage Partners, LLC Brook Park, OH, United States)
Naghipour, P. Ghezeljeh, Paria (Ohio Aerospace Inst. Brook Park, OH, United States)
Shin, Euy-Sik E. (Ohio Aerospace Inst. Brook Park, OH, United States)
Date Acquired
August 27, 2019
Publication Date
August 22, 2019
Subject Category
Electronics and Electrical Engineering
Report/Patent Number
GRC-E-DAA-TN70196
Meeting Information
AIAA/IEEE Electric Aircraft Technologies Symposium (EATS)(Indianapolis, IN)
Funding Number(s)
CONTRACT_GRANT: NNC13BA10B
WBS: 081876.02.03.05.02.04.01
CONTRACT_GRANT: NNC12BA01B
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Motor
Generator
Thermal
Electric Machines
Litz Wire

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