High order mode waves excited in GIS

UHF signal measurement based on the high order mode waves, is an important tool for the partial discharge detection in GIS (gas insulated substation). In this paper, the high order mode wave excitation and propagation are discussed. From experimental results, some properties are derived: the velocity of the high order mode waves (TE and TM modes) is less than the TEM mode velocity; the high order mode wave in GIS is dependent on the GIS geometry and on the source of excitation; and the resonant cavity is important for the high order mode signal detection.