Robust measurement, monitoring and analysis of partial discharges in transformers and other HV apparatus

This paper describes and practically illustrates modern methods for robust, and at the same time sensitive measurement of partial discharges; applied in the laboratory, onsite and during on-line monitoring of HV apparatus. For conventional, electrical measurements, the principle of dynamic noise gating is illustrated. Above this, amplitude-based and spectrum-based impulse correlations allow for discrimination between noise and partial discharges, but also for separation of several discharge sources. Automatic pattern recognition then classifies the separated sources and provides basic risk assessment. Acoustic waves of partial discharge events serve for PD localization, but, due to their high damping, often require combination with electrical or electro-magnetic methods. Measurements in the UHF range, well-known from gas-insulated equipment, are of particular benefit for noise-immune analysis of oil-filled equipment, too and compared to the traditional, electrical method in this paper.