CoolBLUE® toroids made from the nanocrystalline material NANOPERM® are being used increasingly to reduce damaging motor bearing currents in modern high power inverter systems operating at high switching frequencies. As a result of these unwanted currents, the bearings corrugate, leading to electrical breakdown in the lubrication and finally to a standstill of the entire motor.
The use of CoolBLUE® cores not only significantly reduces the over voltage peaks at the motor terminals, but also suppresses the asymmetrical EMI currents which are generated by the parasitic capacities of the motor itself together with the motor cable. In order to achieve an efficient reduction in these destructive effects, one or more CoolBLUE® cores of suitable geometry have to be placed together over the connector cables in the DC-link as well as at the inverter output. In this configuration, the cores operate as a common-mode choke.