test in which the a.c. voltage of power frequency in done under conditions of rain is applied across the insulators and increased at a uniform rate of about 2 per cent per second of 75 % of the estimated test voltage, to such a value that a breakdown occurs along the surface of the insulator, katse, mille korral alalisvoolu võimsussageduse pinget vihma tingimustes rakendatakse üle isolaatorite ja suurendatakse ühtlase kiirusega umbes 2 protsenti sekundis 75 % hinnangulisest katsepingest, sellisele väärtusele, et isolaatori pinnal toimub lahendus