Incomplete discharge - definition

The incomplete discharge is a local electrical phenomenon occurring in dielectric insulation, consisting of a partial penetration of the insulating material under the influence of an electric field whose intensity locally exceeds the dielectric strength of the medium in question. In contrast to a complete discharge (full penetration), a partial discharge does not cover the entire thickness of the insulation and does not directly lead to a short circuit between conductors or to a short circuit. It is, however, a damaging process because, in the long term, it can cause degradation of insulation materials and lead to equipment failure.

This phenomenon can occur in various forms, such as corona, surface, interior discharges or around gaseous inclusions and structural defects in the insulation material. Incomplete discharges generate current pulses of very short duration and high frequency, accompanied by the emission of sound, ultraviolet light and gases such as ozone. Repeated discharges can result in a gradual deterioration of the properties of the insulator, carbonisation of the surface, formation of micro-cracks and development of conductive channels.

Detection and analysis of incomplete discharges is an important element in the diagnostics of power equipment such as transformers, cables high voltage, switchgear or generators. Detection is usually carried out using electrical, acoustic, optical or radio methods, and the parameters assessed include intensity, repeatability and location of the phenomenon. IEC 60270 defines standard procedures for measuring incomplete discharges in high-voltage insulation.

In electrical engineering, incomplete discharges are considered an early signal of insulation wear or damage, so their monitoring forms the basis for predictive maintenance and condition assessment of high-voltage equipment.

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