Engineering plastics are often used in electric components and systems. For these materials, many requirements such as electrical resistance, mechanical properties, temperature capability, flammability, thermal conductivity, moldability etc. are considered for material selection. In general plastics are good electric insulators (electrically safe) but poor conductors of heat (compared to metals). In electric motors, losses due to friction, windage losses, winding losses, iron losses etc. manifest as undesirable heat, resulting in temperature buildup inside the motor. So, choice of materials which offer high thermal conduction and electrical insulation can directly impact motor performance.
Material properties of engineering plastics are greatly influenced by the filler reinforcements used. Although unfilled polymers typically have a thermal conductivity of ~0.2 W/m/K, appropriate choice of fillers can increase this value many-fold. One of the challenges with injection molded plastics is that material properties, including thermal conductivity, are a function of material orientation (orthotropic). In the present work, TCEI materials have been developed for use in bobbins. Freudenberg Sealing Technologies, with its knowledge of filled polymeric systems has developed multiple TCEI grades with improved thermal conductivity compared to commercially available materials. Thermal conductivity measurements on these novel material grades have been conducted to quantify improvements. A finite element model has been developed to capture effect of material choice on temperature distribution within the system. The model incorporates varying material orientation within the bobbin and components within the motor and uses temperature dependent material properties for the analysis. The effect of varying thermal conductivity values on thermal performance and influence of an air gap are studied. Results show that materials with improved thermal conductivity show reduced bobbin and winding temperatures, offering significant performance benefits.
