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The dielectric and mechanical properties of standard (PEI), nanoscale-filled and microscale-filled varnishes are detailed and analyzed in this communication. Fumed silica (10nm and 400nm) have been tested as a filler. A particular attention has been paid to Partial Discharge Inception Voltage, Lifetime under pulse voltage and bonding strength which are crucial for varnish to be used in rotating machines fed by inverters.

Thermoanalytical investigations TGA/DTG/ DSC of polyamide-imide enamel after thermal ageing have been presented. The lifetimes at 260, 270, 280, 290, 300°C were determined. The thermograms of the enamels after attaining of their lifetimes much depend on the ageing temperature. The temperatures of 5% loss of mass that much increase after thermal ageing appear the most sensitive indicator of ageing rate. The residue of mass at 800°C increases after ageing, even to 27%, due to diffusion of copper ions from the conductor into enamel during annealing. The copper contents in aged coatings could be also an indicator of ageing rate.

Polyester and polyesterimide compounds for impregnating of electrical motors were modified by incorporating of three kinds of nanofillers: zinc oxide, fumed nanosilica and titanium dioxide so as to improve their properties. Nanosized particles were added at 1 wt.% of loading and homogeneously dispersed in polyester and polyesterimide matrix. The results on mechanical, electrical and barrier properties of standard and nanofilled compounds were compared. Thermogravimetric/differential thermal analysis showed that thermal stability of nanofilled compounds was significantly higher. Also the electrical and bonding strength of nanofilled impregnating compounds increased and at the same time water absorption decreased. The highest improvement of properties owing to nanofillers was obtained in the case of nanosilica.

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