On-line monitoring of partial discharge in rotating machine windings and auxiliaries including the use of external sensors

An online partial discharge test which is suitable for rotating machine windings and metalclad switchgear is described. Sensors are placed on the grounded envelope of the high voltage apparatus with no contact to the high voltage terminals. The sensors are connected to a portable pulse height analyzer. A similar measuring system can be used on a continuous basis in those applications where there is perceived to be a need. Examples are included of measurements made in various locations in the USSR as well as at Northern States Power and Manitoba Hydro.