No abstract

Abstract-Partial discharge (PD) is one of the most critical insulation deterioration processes that can be monitored in any electrical equipment. It is a complex phenomenon that requires understanding the physical, chemical and electrical repercussions for its interpretation. PD generates a plethora of signals in the electrical domain that need to be properly captured and measured for estimating the impact of degradation. However, the correlation of the physics of this process with the manifestation of the measured signals is extremely complex due to the presence of various possible conditions and parameters that affect it. One of the novel methods of measuring this intricate process uses ultrahigh frequency (UHF) antennas which can receive the radiated electromagnetic waves from PD pulses. An attempt is made to simulate the radiation process using first principles of physics, for such discharges. The behaviour of a group of charged particles under the influence of external field is considered from the point of view of their motion and the electromagnetic radiation from them. This paper aims to shed more light on the physical processes which possibly generate the kind of signals that are received by an antenna.

Abstract-Insulation degradation is the primary reason for aging and eventual failure of electrical equipment. Any measurement that forewarns an impending breakdown of the equipment can be a boon to asset managers. Partial discharge (PD) is one such phenomenon that can be monitored for assessing the quality of insulation. However, the phenomenon of PD is quite intricate and requires an understanding of various concurrent processes. In this paper, some of the methods used to simulate this complex event have been reviewed. At the fundamental level, PD is a localized breakdown that occurs without complete bridging of the insulation. These are feeble and extremely fast, nanosecond discharges. They can be thought of as motion of charges under the influence of an external electric field, which has exceeded the breakdown strength in a small region of the insulation. When such discharges occur in voids in solid insulation, they generate signals in the electrical, chemical and acoustic domains. Also, PD causes physical damage due to bombardment of these charged particles on the walls of the void. The charges are generated by ionization of the gas filled in the void. Once ionized, the motion of these particles is governed not only by the external field, but also by the space charge so created. There are various methods that can be used to simulate the motion of these charges. Of these, particle-in-cell (PIC) method can be applied in a Lagrangian frame of reference, where the particles retain their identity, and their trajectories are monitored by calculating the force on them. This force is determined by the field at their location. This method is fairly intuitive. The other class, Eulerian, treats the charges as a density distribution and then determines its motion. In this, the flux-corrected transport (FCT) scheme basically considers the motion as governed by the charge continuity equations coupled with the Poisson's equation. The continuity equations also account for the generation of the charges, due to ionization, and their possible subsequent recombination or attachment. However, these events, as recorded, are also statistical in nature, and the effect of previous discharges on the subsequent ones can hardly be ignored. The method of including these in the simulation has also been reviewed.

The phenomenon of corona has been addressed in this paper. The theoretical description of the events occurring during such a discharge has been given. Experiments have been conducted to detect corona using ultra-high frequency (UHF) antennas. The results obtained have been analyzed for their frequency content on the basis of these physical processes. An attempt has been made to understand the effect of space charge on the radiated field.