Numerical Simulation of Temperature and Pressure Changes due to Partial Discharges in Spherical Cavities Within Solid Dielectrics at Different Ageing Conditions

Abstract

Partial Discharges (PD) behavior during ageing of the insulation systems exhibits variations that depend on changes in gas filling characteristics and surface condition. In this article, numerical simulations of temperature and pressure behavior in an air-filled spherical cavity within a homogenous solid dielectric material due to PD activity are presented. An Analytical-Finite Element Analysis simulation approach was implemented in MATLAB and results exhibit reasonable agreement with experimental measurements reported by other authors. Simulation results allow concluding that pressure changes are directly related to variations in the PD behavior. In addition, affectations to cavity surface due to temperature increments can be discarded.Energies 2019, 12, 4771 2 of 11 Analytical models, in spite of their simplicity, are electrostatic field-based approaches and when homogeneous and symmetrical conditions are considered, such as cylinders or spheroids, the solutions obtained through analytical and FEA models are similar [15], and have the advantage that less computational time is required when simulations for a great number of periods of the AC-voltage signal are required such as in ageing analysis.PD are inherently multi-physical phenomena where electrical, thermal and mechanical physics are involved in each PD event [16]. Processes such as electron generation rate and surface charge decay through surface conduction are temperature and pressure dependent [17][18][19]. On the other hand, temperature affects the ageing process in solid dielectrics mainly due to the acceleration of chemical ageing dynamics [1].In this paper, the analytical and thermal models are presented in Section 2. In Section 3, PD in a spherical cavity are simulated using the analytical model at different ageing phases and results are compared with measured values reported by other authors. In addition, temperature and pressure variations due to PD events are calculated using a heat transfer FEA model, and the effect of temperature and pressure along ageing on the electron generation rate and in inception and extinction field magnitudes is analyzed and correlated with measured variables. A discussion on the simulation results is presented in Section 4. Finally, a conclusion is presented in Section 5.

Computer Simulation of Partial Discharges in Voids inside Epoxy Resins Using Three-Capacitance and Analytical Models

“…A good approximation may be using an adaptive fitting procedure for adjusting the values taking in to account the measured PRPD pattern. Simulations were carried out using a MATLAB application implemented by authors named PDSym1S developed for these purposes [12].…”

“…The modelling and simulation of PD allow us to analyse the process from an incipient state to breakdown and to understand the dielectric ageing process [12] as well as its relationship with factors and variables such as temperature, voltage amplitude and frequency [13]. In addition, PD simulation can complement measurement systems in order to improve diagnosis procedures [14].…”

A Study on the Life Estimation and Cavity Surface Degradation Due to Partial Discharges in Spherical Cavities within Solid Polymeric Dielectrics Using a Simulation Based Approach

“…However, due to their low energy, is required the simultaneous occurrence of great temperature risings and under normal conditions it only appears as a worsening factor of existing damage [8]. On the other hand, the increment on the local temperature in the cavity can accelerates the chemical reactions, but other thermal degradation mechanisms, such as, the direct melting are negligible [35].…”

Finite‐element‐analysis models for numerical simulation of partial discharges in spherical cavities within solid dielectrics: a review and a novel method

“…Temperature consequences on surface degradation can be ignored in comparison with chemical reactions and particle impact [17]. At the end of the ageing process, it is assumed that the ratio O 2 /N 2 is very small which promotes the apparition of swarming microPDs and pits that originates treeing [3].…”

“…It is considered that the electric field within the cavity and surface charge distributions on the cavity surface is uniform, which is unreal [15]. However, this model is accurate enough because it is based on a field approach and exhibit good agreement when compared with experimental studies for different conditions of ageing and stresses [16, 17].…”