This idea is not patented, but it has been published for the scientific community. It was first published a few days ago at the EPNC 2018 conference and an extended paper has been submitted for journal publication.
During the process of cooling, a large part of the heat generated by the losses in the machine is conducted through the iron core. All the iron losses and a significant part of copper losses generated in the windings should pass the iron core in order to be conducted to the fluid regions where the losses are finally dispersed into the cooling medium. There are two main directions along which the heat is conducted through the iron core, radial and axial direction. In the case of conduction in radial direction, the heat is transferred radially towards the air gap and the outer stator surface. In the case of conduction in the axial direction, the heat is transferred towards the radial cooling ducts (if the machine has them) and towards the end regions of the machine. At this point we should mention that in order to limit the existence of eddy current losses, the iron core has a laminated structure. This laminated structure causes a high level of anisotropy regarding the ability to conduct heat in different directions.
The thermal conductivity of the iron core, especially in axial direction, could be significantly increased by the use of a material with higher thermal conductivity in the insulation between the laminations. A diamond enriched material will be the right choice because besides the high thermal conductivity it can also act as an excellent electrical insulator. Its high level of rigidity can easily withstand the mechanical stresses due to pressure applied during the stacking process and the period of exploitation. The thermal conductivity of the diamond = 2.200 [W/mK] is even more than 50 times higher than the steel used for manufacturing the laminations and even more than 10.000 times higher than the varnish. We can conclude that if the insulation between the laminations contains a certain amount of diamond-based material, the thermal conductivity of the insulation layer can be improved significantly.
The largest benefit of a diamond-based core insulation is in electrical machines in which the losses are conducted axially to the coolant. These are machines with radial ducts and effective cooling in the end regions. The main benefit will be in reducing the number of radial ducts that positively affects the size, production costs and the copper losses of the machine. The diamond enriched insulation also improves the cooling due to conduction in radial direction of the lamination stack, toward air gap and ambient.
There are many options of how to implement a diamond- based insulation in the space between the laminations:
- Thin diamond flakes between the laminations;
- Diamond-based powder coating of the laminations;
- Using a varnish enriched with a diamond powder;
- Using an epoxy enriched with a diamond powder in the impregnation process.