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Liquid-based dielectrics have been used in the electrical power components for high voltage insulation and cooling purposes for over a century. Numerous condition monitoring techniques are used for its performance analysis. Dielectric breakdown event of insulting oil is a key failure mode which adversely impacts the transformer performance. Transformer oil is a prime source of fault diagnosis of transformer and its condition monitoring. Insulation condition of the oil, acidity, chemical degradation that occurred over the period of time can be detected by modern spectroscopic techniques. Fourier transform infrared spectroscopy (FTIR) has acquired exceptional importance in determining the chemical degradation of the oil for utility professionals. In this work, service aged oil specimens were taken from a transformer with a successful operating life of 37 years in order to investigate the reason behind its internal faults. Various testing techniques such as breakdown voltage, frequency-domain dielectric spectroscopy, UV–visible spectroscopy, charge migration and mobility and FTIR were used for comprehensive analysis of oil condition. For comparative performance analysis, pristine samples of same oil were procured from the identical manufacturer. More emphasis was laid on the capability of FTIR to access the oil condition. The experimental findings of this study could provide a valuable insight to researchers and condition monitoring engineers in this field.

In this study, epoxy resins incorporated with nano-alumina (nano-Al 2 O 3 ) are prepared with different concentrations of 0, 1, 3 and 5 wt%. The obtained epoxy resin/Al 2 O 3 nanocomposites are subsequently fluorinated using F 2 /N 2 mixture (F 2 /N 2 20% v/v) at 0.05 MPa and 40°C. The nano-Al 2 O 3 is treated with silane coupling agent γ-aminopropyltriethoxysilane (KH550) to restrict aggregation. The chemical bonding is examined by Fourier-transform infrared spectroscopy. The cross-section and surface morphological analyses are performed using scanning electron microscopy. In addition, the DC surface resistivity is measured using a resistivity test fixture. The variations in electrical properties induced by fluorination are characterized based on dielectric measurements. The experimental results show that chemical bonds are formed between nano-Al 2 O 3 and the coupling agent (KH550). Moreover, the results confirm that fluorination significantly alters the morphology and chemical structure of the sample surface. Gas-phase fluorination produces shallow traps, which consequently reduce the surface resistivity. The treatment of nano-Al 2 O 3 increases the trap energy level to yield higher surface resistivity. Furthermore, the treated Al 2 O 3 nanoparticles show improved distribution and dispersion in epoxy resin, exhibiting good dielectric performance of the nanocomposite.

The application of weak-base anion-exchange resin for removal the SO42− from the citrate solution to guarantee its good performance for adsorption of SO2 is proposed in this work. The weak-base anion-exchange resin that has prior adsorption towards SO42− compared with citrate, allows the effective removal of such impure anion. We initially chose four kinds of resins, namely D301R, D301G, D370 and D315, to investigate their behavior upon SO42− adsorption and then determined D301R and D315 to give a comprehensive understanding towards their adsorption performance in various condition. Results indicate that D315 possessing better adsorption ability than D301R could be a potential candidate for SO42− removal from the citrate acid solution during the desulphurization process using citric method. The pretreatment of protonation for resins could effectively facilitate their adsorption behavior towards SO42− under the same pH condition. Moreover, we assume that the protonated D315 would meet the practical requirement well given its good performance.

High voltage endurance is a fundamental characteristic of dielectrics. Ideally, the structure of dielectric, electrode design and type of employed electric field has no effect on internal breakdown endurance. On the other hand, experimentally estimated breakdown strengths are quite different under high voltage for the material given. This paper demonstrates space charge dynamics utilizing PEA (pulse electro-acoustic) system under high dc electric voltages to investigate the dependence of varying XLPE thickness on dielectric breakdown. As XLPE is employed for insulation of HVDC cables so it is mandatory to examine the space charge effects under high dc fields for varying insulation thickness. Generally, the influence of space charge leading to breakdown at high stresses is not considered for various bulk insulation thicknesses. However, we demonstrate the long time space charge profiles under high dc electric stresses for various thicknesses ranging from 0.07mm to 0.2mm. We examined that the time dependent internal field and space charge exhibit decreasing pattern with increasing thickness up to 0.1mm and then increasing pattern up to 0.2mm. Space charge measurements under high dc applied electric fields also depict a correspondence with short time dc breakdown test results. This observed phenomenon could find its importance in designing XLPE (material) insulation for HVDC transmission systems.

Power transformers are the most essential components of electrical power transmission and distribution networks. During the course of their operation, transformers are subjected to huge electrical and thermal stresses due to which insulation oil inside the transformer is highly degraded. The degradation of insulation oil leads to catastrophic transformer failure which further leads to power system network failure. Hence proper inspection and regular examination of transformer insulation oil is required for smooth and reliable operation of power system. In this research work, insulation oil samples from in-service transformers were taken and analyzed and the results were compared with same grade fresh mineral oil. Absorption spectroscopy techniques e.g. Fourier Transform Infrared Spectroscopy (FTIR) and UV-Visible Spectroscopy were adopted to analyze the insulation oil degradation. The outcome of absorption of aged transformer oil is so significant that absorption increased by observable margin over a wide range of wavelengths. Chemical characterization results highlight that huge amounts of impurities are added to the insulation oil that tend to highly degrade the oil and decrease useful service life of transformer. Hence a proper inspection of the most important part of transformer i.e. insulation oil is required on regular basis.

Polyhedral Oligomeric Silsesquioxane (POSS), a nanometric hybrid molecule, is being paid great attention in the field of polymeric micro and nanodielectrics, providing strong dispersion and dissolution power in solid and liquid dielectric materials which overcomes the sedimentation and agglomeration issues in nanocomposite insulation materials. This work presents the effect of temperature on electrical properties of Octa-isobutyl POSS (Oib-POSS) mineral based nanofluids prepared with two different concentrations 0.1 and 0.15 wt. % and the results are compared with fresh mineral oil. Dielectric properties that include relative permittivity, dissipation factor and volume resistivity along with the AC breakdown voltage are analyzed within a temperature range of 0-80°C in agreement with the IEC standards. Finally, 2-parameter Weibull analysis is performed over the AC breakdown voltage to validate the consistency of breakdown results. It is found that the POSS nanofluids show improved AC breakdown strength and dielectric properties e.g. relative permittivity, dissipation factor and volume resistivity compared with virgin mineral oil in entire temperature range. The results also show that the increase of POSS concentration not only improve the dielectric properties but also enhance the AC breakdown strength of mineral oil.

Insulating liquids have been applied to electrical insulation of transformers, circuit breakers and switch gears and have been investigated in different ways to enhance their performance. Dielectric liquids have been used for the transformer insulation and cooling applications since more than a century. Dielectric breakdown tests and the events and processes that affect the breakdown of the transformer insulation have been studied since last 40-50 years. Transformer oil can give a thorough picture of the internal transformer conditions. The fault diagnosis can also be done by investigating the transformer oil. For this reason, oil samples from a transformer that is out of service due to the internal faults are taken and tested to realize the reason behind the faults. Gas Chromatography Mass Spectrometry (GCMS) was employed to investigate the oil condition of the power transformer. GC-MS results show that high molecular weight substances in faulty oil are more than fresh oil. The results are compared with that of the fresh mineral oil supplied by the same manufacturer and presented in detail.

Vegetable insulating oils have different chemical compositions as compared to mineral oils, hence, dissolved gas characteristics under thermal and electrical faults have differences, thus fault diagnostic methods based on Dissolved gas analysis (DGA) used for mineral oil-filled transformers cannot be used to investigate vegetable oil-filled transformers. This paper presents experimental results of dissolved gases in the camellia insulating oil under typical thermal and electrical faults in transformers. The thermal fault simulation experiments include low temperature, medium temperature and high temperature, and the electrical fault simulation experiments include partial, breakdown and arc discharges. Experimental results show that except CO and CO 2 , H 2 and C 2 H 6 were main characteristic gases under thermal faults, the percentage contents of H 2 decreases while CH 4 , C 2 H 4 and C 2 H 6 increases with the temperature increase. In addition, H 2 and CH 4 were main characteristic gases under partial discharge faults, C 2 H 2 was the main characteristic gas under breakdown faults, and C 2 H 2 and C 2 H 4 were main characteristic gases under arc discharge faults. Characteristic parameters were extracted based on DGA, and fault diagnostic methods of camellia insulating oil-filled transformer were proposed, including graphic diagnostic method and none code diagnostic method. Results showed that faults could be effectively analyzed by triangle and pentagon diagnostic methods as well as none code diagnostic method. H 2 , C 2 H 4 , C 2 H 2 &H 2 , CH 4 , C 2 H 6 Triangle method and none code diagnostic method are better fault diagnostic methods for camellia insulating oil.

Vegetable insulating oils are gaining importance worldwide to be used in power transformers as an alternative to petroleum based mineral oils because of their biodegradable nature and higher fire points than conventional mineral oils. However, these oils (whether natural or synthetic esters) easily absorb moisture and hence tend to affect the dielectric and physiochemical properties of insulation oils. This paper presents the effect of moisture absorbed by commonly used rapeseed oil on its AC breakdown voltage. A mathematical relationship was developed between breakdown voltage and percentage moisture absorbed to access the values of BDV at any moisture level and this relationship holds good for any moisture content in the oil. Moreover, effect of suspended water molecules on breakdown voltage was simulated using COMSOL Multiphysics. Empirical relationship developed was tested and verified and can be used to find out the BDV of these oils as the percentage moisture increases.

Acrylonitrile Butadiene Styrene (ABS) is a thermo plastic material which is widely used for making bodies of countless electrical and medical appliances. It is low cost amorphous thermoplastic which belongs to poly styrene class of thermoplastics. It has very high tensile strength and almost unbreakable. It is a beneficial encapsulating and insulating material which is usually employed for indoor insulation and encapsulation purposes. A very little literature is reported on its performance when used in outdoor environment. In present work, ABS was molded into 11kV distribution class insulator and aged under several mechanical and electrical stresses in severe environmental conditions simulating outdoor environment according to IEC 1109 5000h aging standards. The aim of this study is to investigate the scope of using ABS for making outdoor insulators since it is a low cost material. Results show that this study is particularly useful for the researchers worldwide.

Nanoparticles enhance the positive and negative lightning breakdown voltages of vegetable insulating oils due to a reduced streamer velocity. Pre-breakdown streamers in vegetable oil based h-BN and Fe3O4 nanofluids were observed using the shadowgraph method under a lightning impulse voltage. The propagation of streamers until their stopping length is analyzed using shadowgraph images for the different nanofluids. The results suggest that these nanofluids present a higher breakdown voltage per unit length compared with pure oil. Secondary reverse streamers are observed to appear at the dissipation stage of the streamer. In particular, the secondary reverse streamer of the nanofluids appeared earlier and seemed to be shorter than that of pure oil under positive impulse voltages. The underlying mechanism was analyzed using space charge theory.

Surface discharge may cause irreversible damage to turn-to-ground insulation in valve windings of converter transformer, where withstand with AC-DC combined voltage. This paper analyzes the phenomenon and characteristics of surface discharge on oil-impregnated pressboard (OIP) under AC-DC combined voltage, and develops a discharge state recognition method. The cylinder-plate discharge model was used to simulate surface discharge. The results showed that discharge development and OIP failure were significantly accelerated by white marks on OIP which were essentially gaseous channels. The discharge characteristics before and after white mark occurrence were both dominated by AC component because of its bigger contribution to electrical field distribution (EFD), and the DC component had obvious effect on accelerating OIP failure. A set of features representing discharge state after white mark occurrence was selected out by the entropy weight method (EWM), based on which the discharge process was classified into three states (stable, fast development and pre-breakdown state) by fuzzy C means clustering method (FCM). A support vector machine (SVM) classifier to recognize discharge state was trained and showed a good performance, whose average assessment accuracy was up to 91.98%. Moreover, the ratio between negative and positive discharge numbers could be used as an auxiliary indicator of pre-breakdown state.

Natural esters, as the renewable resources, offer excellent physiochemical and dielectric properties such as the fire-resistance, high biodegradability and satisfactory dielectric breakdown performance. Thus, natural esters are selected as the insulation and heat dissipation medium for electrical equipment. However, the electrical performance of natural esters with different structures under the long gap and higher electrical stress needs further evaluations. In this paper, streamer propagation of various natural esters under the long gap and higher electrical stress were observed optically. The influence of voltage polarity, liquid types and gap distances on streamer characteristics of natural esters were analyzed. Results show that the maximum propagation velocity of streamer in natural esters is greater than that in the hydrocarbon liquids. Breakdown voltage of natural esters under negative polarity is much higher than that under positive polarity for the same gap distance. Among all the natural esters concerned, the camellia liquid demonstrates slower streamer velocity and slight greater lightning breakdown voltages for the positive and negative polarity. The lower content of unsaturation triacylglycerol molecules in camellia liquid contributes to the inhibition of ionization and streamers propagation. Results would be valuable reference for the design, manufacture and operation of the electrical equipment filled with natural ester.