Improved flashover mathematical model of polluted insulators: A dynamic analysis of the electric arc parameters

Next generation aircrafts will use more electrical power to reduce weight, fuel consumption, system complexity and greenhouse gas emissions. However, new failure modes and challenges arise related to the required voltage increase and consequent rise of electrical stress on wiring insulation materials, thus increasing the risk of electrical arc appearance. This work performs a critical and comprehensive review concerning arc tracking effects in wiring insulation systems, underlying mechanisms, role of materials and possible mitigation strategies, with a special focus on aircraft applications. To this end an evaluation of the scientific and technological state of the art is carried out from the analysis of theses, research articles, technical reports, international standards and white papers. This review paper also reports the limitations of existing insulation materials, standard test methods and mitigation approaches, while identifying the research needs to comply with the future demands of the aircraft industry.

https://www.mdpi.com/1424-8220/20/6/1654/pdf

Arc Tracking Control in Insulation Systems for Aeronautic Applications: Challenges, Opportunities, and Research Needs

Reliability in the supply of electricity depends on isolation from the electrical power system. Insulators are components that have the function of insulating and supporting the electrical grid. The design of electrical distribution network insulators can have a great influence on the distribution of the electric field over its surface. When there is a great intensity of electric field applied specifically in a location, there may be a greater chance of the development of a fault. An optimized insulator profile design can ensure that the network has better performance. In this paper, particle swarm optimization is applied to optimize the profile of an insulator of the conventional electric power grid, based on the electrical potential data obtained using the finite element method, defined in this paper as optimized finite element method. The component parameters are optimized to obtain a parametric model. The parametric model is evaluated and compared with the usually employed profiles to define an optimized design. The results show that the proposed method is a promising alternative for the design of electrical energy distribution insulators.

Particle swarm optimization for design of insulators of distribution power system based on finite element method

Polymeric composite insulators are subjected to varying work conditions like rain and heat, which create an impact on degradation during their long service period. Electrical tracking under the Alternating Current (AC) field plays a predominant role in surface degradation, which can be different for fresh and aged insulations. The tracking studies on the fresh and aged polymeric insulation therefore become significant. Motivated by this, an indigenous low-cost electrical tracking setup was developed, and the tracking studies were carried out as per International Electro technical Commission standard (IEC) 60587 on fresh, thermal-aged and water-aged silicone rubber samples. Contact angles of samples were measured to analyse the effect of ageing on hydrophobicity. Further, to analyse the influence of ageing on insulation integrity, tracking tests were conducted and parameters like leakage current pattern and magnitudes, tracking length and loss of weight in the material due to tracking were examined. The physicochemical impacts of ageing on the surface degradation of the samples were also analysed using X-ray diffraction analysis and Fourier Transform Infrared Spectroscopy analysis. The investigations added insight into the degradation mechanism of polymeric insulators in terms of their electrical performance and physicochemical changes in the material. Comparison of these changes showed that ageing could influence surface degradation of samples.

https://www.mdpi.com/1996-1073/12/19/3769/pdf

Investigation of Surface Degradation of Aged High Temperature Vulcanized (HTV) Silicone Rubber Insulators

Electricity distribution networks are built to deliver increasing amount of electricity from distributed energy resources (DERs) such as offshore and onshore wind and solar farms. Aging of network assets through low-current surface discharges is becoming a great concern for the security and reliability of the distributed energy supply. In particular coastal conditions can present a challenge for overhead line insulators through the environment of salt fog. Also, onshore areas may expose power lines to clean fog and agricultural or industrial pollution. In this paper, experimental studies are conducted to investigate electrical arc formation and growth on insulators, following the testing standards in accordance with IEC 61109. Dry-band arcs in both clean-fog and salt-fog environments are compared. It is identified that arcs are much faster to develop and have greater energy in salt-fog environments, due to the lower surface resistance and resulting higher leakage current. The time from a first arc to strike, to the situation where the arc is stable on the insulator surface is identified as a potentially critical parameter in controlling aging of an insulation surface. The time from initial appearance of an arc to full stability is eight times shorter in a salt fog of 16,000 $\mu \text{S}$ /cm compared to a clean fog of $600~\mu \text{S}$ /cm. This means the very existence of a stable low-current arc is much more likely in polluted conditions. Accumulated arc energy and heat dissipation have been calculated for both fog conditions. It is concluded that aging by low-current electrical arcs tends to be more severe in salt-fog environments, so that great care needs to be taken when designing overhead lines and insulators in such areas.

The Development of Low-Current Surface Arcs Under Clean and Salt-Fog Conditions in Electricity Distribution Networks

This paper describes the assessment of the resistance to tracking of various polymers after (i) flashover voltage (FOV) and flashover gradient (FOG); and (ii) partial discharges (PDs) measurements in dry, clean and salt fogs on one insulator model using standardised electrodes; the aim being the development of optimised methods based on flashover and PDs to the conception of new generation of piercing connectors. The investigated materials belong to two distinct classes widely used in the electrical industry: thermoplastics (namely polyphenylene sulfide and high density polyethylene) and thermosetting cycloaliphatic epoxy resins namely one unfilled material (UnCEP) and another unfilled and hydrophobic resin (UnHCEP). FOV measurements are based on the electro-geometrical parameters of each specimen and the resistance to tracking, both may be assessed through the slope of FOV curves against the leakage distance as an indicator of surface damages. Regarding PDs, the suggested technique is devoted to clean and salt fogs and provides quicker and more accurate information about PDs effects on materials deteriorations rather than IEC60109 where the exposition time to discharges is much longer at lower voltage levels by using only liquid contaminants such as sulfuric or nitric acids or ammonium chloride as described in IEC60587 or ASTM D2303.

Assessment of the resistance to tracking of polymers in clean and salt fogs due to flashover arcs and partial discharges degrading conditions on one insulator model

In many high voltage equipment, partial discharges are regarded as one of the most widespread pathology whose ignition conditions and effects are studied by scientists and manufacturers to avoid major failures. Actually, those electrical gaseous phenomena generally occur under several constraints such as the electrostatic field level, the nature of insulating surface being polluted or not, and switching or lightning transients. The present paper discusses physical mechanisms related to the creeping discharges propagation growing over insulators subjected to perpendicular electric field and positive lightning impulse voltage. More precisely, the developed discussion attempts to answer some observations especially noticed for main discharges feature namely (i) the discharges morphology, (ii) their velocity and (iii) the space charges effects on electric field computation. Several factors like (i) the influence of the type of a material’s interface, its electric conductivity, permittivity and discharges mobility, (ii) the relationship between the applied electrostatic field, the space charges, the velocity, the propelling pressure and discharges temperature are among numerous parameters that have been addressed in this study which discusses lightning impulse transients phenomena.

/pdf/ignition-and-advancement-of-surface-discharges-at-2donmf999z.pdf

Ignition and advancement of surface discharges at atmospheric air under positive lightning impulse voltage depending on perpendicular electric stress and solid dielectrics: modelling of the propagating phenomenology

The acquisition of discharges data is usually affected by external interference leading to erroneous interpretations. In the viewpoint of improving computation accuracy, the discrete wavelet transform (DWT) has been used as an effective tool for de-noising purposes. In this study, creeping discharges waveforms have been investigated under the positive lightning impulse voltage over various materials. The used polymers belong to three distinct families (i) thermoplastics (namely polyamide 6 and polyamide 66), (ii) one filled cycloaliphatic epoxy resin and (iii) one unfilled ethylene propylene diene monomer (EPDM). Two approaches namely one-dimensional (1D) and 2D DWT algorithms have been adopted for de-noising signals and images, respectively. Both techniques were applied for simulated and laboratory data using various wavelet families (Daubechies, Symlet and Coiflet). The comparison of de-noising performance for signals has been achieved through the calculation of signal-to-noise ratio, normalised correlation coefficient (Norm_corr) and root mean squared errors. Moreover, the computation of power spectral density of lightning current transients using a periodogram estimator is also analysed. For images, mean square error and peak-signal-to-noise ratio assess the quality of filtering regarding the visualisation of discharges patterns. Results show that Coiflet wavelets demonstrate their effectiveness to reduce background noise and preserve the signals shape and images edges.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-gtd.2017.1092

Creeping discharges features propagating in air at atmospheric pressure on various materials under positive lightning impulse voltage – part 1: noise suppression using the discrete wavelet transform approach

In this paper, the propagation mechanism of creeping discharges up to flashover for short air gaps is examined and described on various materials based on laboratory de-noised data (namely current, voltage and captured images). The main parameters considered for investigating the development of creeping discharges and their characteristics deal with the measurement, modelling and calculation of (i) their final/stopping length and morphology, (ii) their propagation velocity and (iii) the electric field distribution including the maximal magnitude (
 E
 max
) and the geometric coefficient (
 β
) estimation. The obtained results evidenced that both length and velocity of discharges are emphasised for polyamide-based materials (namely PA6/50 and PA66/50) whereas their ignition remains inhibited for filled cycloaliphatic epoxy resin (FCEP) and ethylene propylene diene monomere (EPDM) surfaces. As the electric field is concerned, both analytical and numerical models are developed and their results are compared and discussed. It has been shown that the presence of a polymer acts as a barrier when being incorporated between an electrodes gap whose dielectric strength depends strongly on the used material. Moreover, the FCEP barrier, in comparison to other materials, exhibits a marked dielectric reinforcement and an enhanced stability of the system making it suitable to provide a better protection to high-voltage equipment against discharges effects.

Creeping discharges features propagating in air at atmospheric pressure on various materials under positive lightning impulse voltage – part 2: modelling and computation of discharges’ parameters

Xavier Souche

Papers

Assessment of the resistance to tracking of polymers in clean and salt fogs due to flashover arcs and partial discharges degrading conditions on one insulator model

Ignition and advancement of surface discharges at atmospheric air under positive lightning impulse voltage depending on perpendicular electric stress and solid dielectrics: modelling of the propagating phenomenology

Creeping discharges features propagating in air at atmospheric pressure on various materials under positive lightning impulse voltage – part 1: noise suppression using the discrete wavelet transform approach

Creeping discharges features propagating in air at atmospheric pressure on various materials under positive lightning impulse voltage – part 2: modelling and computation of discharges’ parameters