Abstract: A method of identifying partial discharge events in a multi-phase electrical supply. The method comprises measuring characteristics of each phase of the electrical supply in respect of a common measurement period; comparing the respect characteristics across the phases; and determining from the comparison if the respective characteristics are indicative of a partial discharge event or of the presence of electrical noise. The method allows automatic rejection of noise, and identification of phase to ground and phase to phase partial discharge. The comparison of characteristics may be performed using ternary diagrams, which facilitates performance of the method by unskilled persons.