PMMA films with dye additive were prepared by the solution-grown casting method. Three kinds of dye were used: p-aminoazobenzene (Ab), p-nitorobenzeneazo-resorcinol (Nb) and Methyl-yellow (My). The film, 100μm thick, was set on PMMA board of 3mm thick. The film with the board was sandwiched between a sphere electrode of 50Hz HV and a plane electrode connected to the ground potential.
In the case of the film with Ab additive at 0.05 wt%, the number and total charge quantity of the PD pulses were reduced to about 50% less than those in the case of the film without additive. The reduction of ac PDs on the Ab film was effective under an electric field strength little higher than the ac partial discharge's inception. In the cases of the films with the other dyes, the reduction of ac PD was un- observed.
The reduction of ac PD on the Ab film was explained by using the results of the surface voltage distribution on the film measured at zero-crosses of ac voltage applied. It was considered that ionization of the electron donor type of dye (Ab) in the film plays an important role on the surface voltage distribution on the film where ac PD generates.