A step forward in the characterization of the partial discharge phenomenon and the degradation of insulating materials through nonlinear analysis of time series

The partial discharge (PD) phenomenon is an electrical discharge that affects only part of a dielectric connecting two conductors [1]. This process may occur in the vacuoles of solid insulation, in gas bubbles in insulating liquids, or between dielectric layers. PDs can also occur on spikes or sharp edges of metal surfaces. Generally, the PDs affect the insulator integrity only if it persists for a long time. However, the continuous release of small amounts of energy may cause a slow and progressive deterioration of the dielectric that can lead to its final breakdown [2], [3]. The degradation rate depends more or less on the microscopic structure of the dielectric, the production process, the types of electrical stresses, and other operating conditions [4]. At the beginning of the 20th century, the problem was not even recognized. However, after the middle of the century, along with the introduction of new dielectrics, the development of more compact insulators, and a general increase in the operating voltages, diagnostics of PDs have become a primary issue in electrical engineering [5]. Today, measuring PDs is a common practice even in operational medium- and high-voltage devices. The data gathered are useful to determine the weak points of the components before irreversible damage occurs. Thus, PD detection and recognition have become important tools for the evaluation of insulating degradation in large power devices. The phase ϕ, the apparent charge q, and the occurrence n have generally been accepted as the basic parameters for the pattern recognition of PDs by means of the standardized algorithm termed phase-resolved PD analysis (PRPDA) [6].