A framework for developing a prognostic model using partial discharge data from electrical trees

Insulation breakdown is a key failure mode of high voltage (HV) equipment, with progressive faults such as electrical treeing leading to potentially catastrophic failure. Electrical treeing proceeds from defects in solid insulation, and cables are particularly affected. Research has shown that diagnosis of the fault can be achieved based on partial discharge (PD) analysis. Nonetheless, after diagnosis of a defect, engineers need to know how long they have to take action. This requires prognosis of remaining insulation life. The progression of a defect is far less well understood than diagnosis, making prognosis a key challenge requiring new approaches to defect modelling. The practical deployment of prognostics for cable monitoring is not currently feasible, due to the lack of understanding of degradation mechanisms and limited data relating defect inception to plant failure. However, this thesis advances the academic state of the art, with an eye towards practical deployment in the future. The expected beneficiaries of this work are therefore researchers in the field of HV condition monitoring in general, and electrical treeing within cables in particular. This research work develops a prognostic model of insulation failure due to the electrical treeing phenomenon by utilising the associated PD data from previous experiment. Both phase-resolved and pulse sequence approaches were employed for PD features extraction. The performance of the PD features as prognostic parameters were evaluated using three metrics, monotonicity, prognosability and trendability. The analysis revealed that features from pulse sequence approach are better than phase-resolved approach in terms of monotonicity and prognosability. The key contributions to knowledge of this work are three-fold: the selection of the most appropriate prognostic parameter for PD in electrical trees, through thorough analysis of the behaviour of a number of candidate parameters; a prognostic modelling approach for this parameter based on curve-fitting; and a generalised framework for prognostic modelling using data-driven techniques.Insulation breakdown is a key failure mode of high voltage (HV) equipment, with progressive faults such as electrical treeing leading to potentially catastrophic failure. Electrical treeing proceeds from defects in solid insulation, and cables are particularly affected. Research has shown that diagnosis of the fault can be achieved based on partial discharge (PD) analysis. Nonetheless, after diagnosis of a defect, engineers need to know how long they have to take action. This requires prognosis of remaining insulation life. The progression of a defect is far less well understood than diagnosis, making prognosis a key challenge requiring new approaches to defect modelling. The practical deployment of prognostics for cable monitoring is not currently feasible, due to the lack of understanding of degradation mechanisms and limited data relating defect inception to plant failure. However, this thesis advances the academic state of the art, with an eye towards practical deployment in the future. The expected beneficiaries of this work are therefore researchers in the field of HV condition monitoring in general, and electrical treeing within cables in particular. This research work develops a prognostic model of insulation failure due to the electrical treeing phenomenon by utilising the associated PD data from previous experiment. Both phase-resolved and pulse sequence approaches were employed for PD features extraction. The performance of the PD features as prognostic parameters were evaluated using three metrics, monotonicity, prognosability and trendability. The analysis revealed that features from pulse sequence approach are better than phase-resolved approach in terms of monotonicity and prognosability. The key contributions to knowledge of this work are three-fold: the selection of the most appropriate prognostic parameter for PD in electrical trees, through thorough analysis of the behaviour of a number of candidate parameters; a prognostic modelling approach for this parameter based on curve-fitting; and a generalised framework for prognostic modelling using data-driven techniques

China’s 10-year progress in DC gas-insulated equipment: From basic research to industry perspective

The construction of the future energy structure of China under the 2050 carbon-neutral vision requires compact direct current (DC) gas-insulation equipment as important nodes and solutions to support electric power transmission and distribution of long-distance and large-capacity. This paper reviews China's 10-year progress in DC gas-insulated equipment. Important progresses in basic research and industry perspective are presented, with related scientific issues and technical bottlenecks being discussed. The progress in DC gas-insulated equipment worldwide (Europe, Japan, America) is also reported briefly

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Effects of Power System Harmonics on Distribution Transformer Insulation Performance

Floating feeder resonances are one of the new challenges being put forward by the renewable energy based distributed generation (DG) installations. Generally, the harmonic injection from DGs are within IEEE standard 519-1992 limits. Although the harmonics are within the IEEE limits, they are a potential threat to power equipment’s insulation system integrity due to floating feeder resonances. There is a reasonable probability that at some point in time the feeder resonant frequency may coincide with one of the injected harmonics. Such phenomenon amplifies the specific harmonic causing additional stress on the equipment’s insulation system. In this thesis a feeder resonance study is done on the IEEE 34 bus distribution feeder to show the resonance shift problem in a DG loaded distribution feeder. Electric field study is then carried out on transformer winding to assess the dependence of electric field on harmonic distortion. At first the acoustic emission (AE) technique is employed to identify the change in the electric field distribution inside the winding at higher frequency. The AE technique together with the acoustic waveguide is utilized to locate the partial discharges under power frequency and high frequency operation. The results show a change in partial discharge (PD) location, which implies that the electric field redistributes in the transformer winding at higher frequency In order to further understand the electric field distribution, a high voltage air core coil is modeled by R, L and C ladder network. The R, L and C parameters are solved by finite element method and finally the electric field is calculated by computing the node potentials in the ladder network at various frequencies. The electric field results show that at high frequency distortion the electric stress enhances between fourth and fifth layer of the winding which may give rise to a PD activity; hence degrading the insulation. An aging experiment is also performed to understand the impact of high frequency distortion on transformer paper insulation. Paper samples are taken from a field aged transformer. They are aged for 72 hours under power frequency and various distorted waveforms. Dissipation factor is used as a comparison tool for paper samples before and after aging. Results show that paper samples aged under distorted waveforms showed a double increase in dissipation factor compared to the samples aged under power frequency