Polarity of Measured PD Impulses How Useful Is It?

If the polarity of the PD impulses is accurately recorded and the polarity of the applied voltage at that time is known, it is possible to infer some information about the location of the PD. Specifically, in some situations, it can indicate whether the PD is originating from the insulation connected in series with the measuring impedance. In practical applications, this information can help determine if the PD is occurring within or outside the equipment being tested or, in some cases, if it comes from a specific accessory. This publication examines if and how this information can be utilized for PD diagnostic of shielded power cables, power transformers, and stator windings. It begins with practical measurements conducted on simple test circuits to explain the underlying theory of the direct and indirect PD measurement circuits. Later, it presents measurements taken from medium voltage cables, power transformers, and stator windings done to investigate if there are advantages of assessing PD polarity. Additionally, it discusses the challenges faced by PD instruments in achieving accurate detection of PD polarity.