A Single-Platform Analysis of Selected Cooling Variants of Electric Machines

This paper presents a theoretical study of alternative thermal management systems in application to electrical machines. A case study permanent magnet (PM) motor for propulsion has been selected as a platform for comparing an array of cooling methods. Starting from commonly used techniques like air- or -liquid cooling via the motor housing and finishing with less conventional concepts, with integrated or embedded winding cooling including alternative coolants, e.g., deionised water, oil, or liquid metal. The single motor platform offers a unique insight into the key performance measures when comparing the alternative thermal management systems. Here, the commonly used figures of merit like winding/conductor current density and electric loading is supplemented with thermal resistance between the heat source (winding) and reference heat sink (coolant). Such approach provides more insight into the heat transfer effects, which would otherwise be difficult to deduce. The initial theoretical finings suggests that the integrated or embedded motor (winding) cooling offers clear performance benefits, i.e., significantly improved heat removal path. However, this is not very clear when comparing the current density or electrical loading data. E.g., liquid cooled hollow conductors and liquid cooled housing offer here similar current density and electric loading ratings, but significantly higher winding to coolant thermal resistance is found for the latter cooling variant. This highlights the importance of more in-depth data analysis when comparing alternative thermal designs of electrical machines, where multitude of design and manufacturing factors need to be accounted for.