Partial discharge based diagnostics for impurities in insulating fluid

A novel test method for the condition assessment of dielectric fluids is proposed based on measurement of the fluid's partial discharge (PD) characteristics in a needle-plane electrode geometry under AC field using a tungsten needle of 20 μm tip radius and a lowfield electrode blocked by a dielectric barrier. This system facilitates acquisition of partial discharge inception voltage (PDIV), streamer repetition rates, and phase resolved PD (PRPD) patterns without the risk of needle-damaging breakdowns. To demonstrate the approach, PD experiments were conducted on thermally and electrically aged hexadecane and on commercially available paraffinic and naphthenic base oils with typical field-aged concentrations of naturally occurring degradation products.