Increasing Life Span by Cooling the Laminated Core Segment of Motors to Reduce Material and Energy Costs Over the Lifecycle of Motors

Internal losses in motor windings and cores result in unwanted heat. According to International Energy Agency, majority of motors in service today are AC induction motors between 0.75 and 375 kW. For these motors, internal losses (heat) are conducted to the surrounding environment by internal conduction to the casing and then to the surrounding environment by convection. For small motors of up to 5 kW, the cores are mounted in a simple round housing and as they get larger the housings are ribbed and external fans are installed. Motors are designed assuming an environmental maximum temperature of 40 °C and with a hot spot allowance of 10 °C can withstand up to 155 °C (class F) at the winding position. However, due to changes in environmental temperatures, system voltage variations and harmonics, winding temperatures often exceed this limit. Consequently, this range of motors last only approximately 3 years. This paper investigates the possible application of thermoelectric cooler (TEC) to increase the heat flow from the core to reduce the temperature at the winding position, potentially providing longer insulation and motor life. For small motors, they can be simply attached to the outer surface. For larger motors with frames incorporating cooling ribs, they could be installed between the cores and the frames. The experimental results found that the application of TEC reduces the winding temperatures by 25.4%. Ability to incorporate this technology allows the opportunity to add a controlled device that can reduce temperatures at the windings when the temperatures exceed normal ratings.