Investigation of the gas bubble dynamics induced by an electric arc in insulation oil

In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating growth rather than a continuous expansion.Furthermore,a theoretical model and numerical calculation method were proposed,which revealed the dynamic mechanism of bubble growth.Good agreement between the theoretical results and experimental observations verified the general correctness and feasibility of the proposed method.

Development of Mixed Insulation Oil as Alternative Liquid Dielectric:A Review

Use of traditional mineral oil(MO)as a liquid insulation in transformers has spanned more than 130 years.However,MO has poor heat resistance,a low ignition point,and is a non-renewable resource,which does not meet development requirements for high-performance and environmentally friendly insulation oil.Consequently,researchers have explored alternatives such as natural ester(NE)and synthetic ester(SE)oils,as well as mixed insulation oils.Mixed insulating oil is a blend of diverse insulating oil types,with optimal performance achieved by adjusting proportions of base oils.This article summarizes the innovative achievements and development of mixed insulation oil in terms of development of mixed ratio,basic physical chemical properties,electrical properties,thermal stability,and application including operation and maintenance technology.Through these efforts,this article aims to provide recommendations for future development of mixed insulating oils to advance liquid dielectric research based on enhancement mechanisms.

Verification of Insulation Oil Reclamation by Turbidity and Spetrophotometry Measurements

Oil reclamation with Fuller＇s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller＇s earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller＇s earth absorption capability.

Benefits of Dielectric Oil Regeneration Systems in Power Transmission Networks: A Case Study

The criticality of transformers and reactors in the power transmission network and the paramount importance of ensuring their reliability through maintenance of the insulating oil is known. This paper presents a comprehensive examination of the efficacy and economic viability of a dielectric oil regeneration system, as implemented by the Transmission System Maintenance Department (TSMD) of the Independent Power Transmission Operator (IPTO), Greece’s sole transmission operator. Through a detailed chemical analysis and performance evaluation, we assess the impact of the regeneration system on treated insulating oil quality over multiple cycles. The study reveals that the electrical properties of the insulating oil are fully restored after regeneration, negating the need to fully replace it, while the investment becomes cost-neutral within weeks from the commissioning of the regeneration system. This economic analysis, coupled with the system’s environmental benefits of reducing waste oil generation, positions the dielectric oil regeneration system as a compelling solution for the maintenance of power transmission assets.

Prediction of Stability for Polychlorinated Biphenyls in Transformer Insulation Oil Through Three-dimensional Quantitative Structure-activity Relationship Pharmacophore Model and Full Factor Experimental Design

Based on the obtained data of half-lives（t1/2） for 31 polychlorinated biphenyl congeners（PCBs）, 3D quantitative structure-activity relationship（QSAR） pharmacophore was used to establish a 3D QSAR model to predict the t1/2 values of the remaining 178 PCBs, using the structural parameters as independent variables and lgt1/2 values as the dependent variable. Among this process, the whole data set（31 compounds） was divided into a training set（24 compounds） for model generation and a test set（7 compounds） for model validation. Then, the full factor experimental design was used to research the potential second-order interactional effect between different substituent positions, obtaining the final regulation scheme for PCB. At last, a 3D QSAR pharmacophore model was established to validate the reasonable regulation targeting typical PCB with respect to half-lives and thermostability. As a result, the cross-validation correlation coefficient（q2） obtained by the 3D QSAR model was 0.845（〉0.5） and the coefficient of determination（r2） obtained was 0.936（〉0.9）, indicating that the models were robust and predictive. CoMSIA analyses upon steric, electrostatic and hydrophobic fields were 0.7%, 85.9%, and 13.4%, respectively. The electrostatic field was determined to be a primary factor governing the tt/2. From CoMSIA contour maps, tl/2 increased when substi- tuents possessed electropositive groups at the 2＇-, 3-, Y-, 5- and 5＇- positions and electronegative groups at the 3-, 3＇-, 5-, 6- and 6＇- positions, which could increase the PCB stability in transformer insulation oil. Modification of two typical PCB congeners（PCB-77 and PCB-81） showed that the lgtl/2 for three selected modified compounds increased by 13%（average ratio） compared with that of each congener and the thermostability of them were higher, validating the reasonability of the regulatory scheme obtained from the 3D QSAR model. These results are expected to be beneficial in predicting tl/2 values of PCB homologues and derivatives and in providing a theoretical foundation for further elucidation of the stability of PCBs.

Comparative Evaluation of the Thermal Aging of Solid Insulation in Mineral Oil and Methyl Ester of Palm Kernel Oil

The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped in two cooling fluids: palm kernel oil methyl ester (MEPKO) and mineral oil (MO). Two types of dielectric paper were used: Thermally Upgraded Kraft paper (TUK) and Nomex-910 paper (NP-910). An accelerated aging test was realized at 110°C during a total of 96 hours. Samples of oil and paper were collected after 0, 48, 72 and 96 hours for analyses purposes. The analyses performed included the measurement of the Breakdown voltage (BDV) of the dielectric papers, the Total Acid Number (TAN) and the Decay Dissolved Products (DDP) of the liquid dielectrics. The BDV of NP-910 is greater than the BDV of TUK. Concerning the type of oil, the BDV of dielectric papers impregnated with MEPKO is greater than the BDV of similar papers impregnated with MO, indicating a better preservation of paper when dipped in methyl esters. The analyses of TAN and DDP revealed that Nomex-910 improves the oxidation stability of MO, but reduces the oxidation stability of MEPKO. These results prove that methyl esters can be used as a substitute to replace mineral oils in power transformers. Furthermore, they show that NP can be used mainly in areas of transformer where solid insulation is subjected to high thermal and electrical stress, and TUK other places where solid insulation is required. Such combination could assure money savings and a better preservation of the oil viscosity.

Charge Transport in Oil Impregnated Paper Insulation Under Temperature Gradient Using Transient Upstream FEM

Charge transport in oil impregnated paper impacts the insulation performance of a transformer.This paper proposes a simulation method for the charge transport in oil impregnated paper insulation.The transient upstream finite element method(FEM)is applied to the transport equations of bipolar charges for establishing a numerical simulation model of charge transport in oil impregnated paper insulation.The method is validated by experimental results.The charge transport and electric field distribution in single-layer oil impregnated paper insulation under different temperature gradients is simulated.The trends of the simulation results are seen to agree with the corresponding experimental results.This paper conducts exploratory research into the simulation of charge transportation phenomenon in oil impregnated paper,and is of importance to the design of oil impregnated paper insulation.

热应力与电-热复合应力下油纸绝缘老化特性的比较研究(英文)

During the operation of power transformer,its oil-paper insulation is continuously subjected to various stresses,c.g.,the thermal,electrical,mechanical,and chemical stresses,which cause insulation aging gradually.It has been considered that the combined thermal and electrical stresses are the most important and unavoidable factors that induce insulation materials aging.In this work,accelerated aging experiments of oil-impregnated pressboards under combined thermal(130℃) and electrical stresses(4 kV/mm) are performed,while the aging experiments under single thermal stress are also carried out at the corresponding temperature(130℃).The electrical and physic-chemical properties of oil,including dielectric losses factor tanδ,resistivity,acid value and pH value etc.,are measured during the aging process.Dissolved gasses in oil and polymerization degree of cellulose are also measured.The relationship between these properties of oil-paper insulation and aging time is investigated.The results show that dissolved gases in oil,resistivity,tanδof oil under combined thermal and electrical stresses are obviously different from that tinder thermal stress during aging process while some other properties show similar changing trend.For cellulose, compared with the single thermal aging results,it even shows a slower degradation rate in the presence of electrical stress.

Influence Factors of the Generation and Accumulation of Electric Charge on the Oil-Delivery Metal Pipelines

The interfacial electrification properties play an important role in the electrochemical corrosion reaction which leads the electrostatic charge to generate and accumulate on the metal surface when the insulating oil flows through a metal pipe. In this paper, the interfacial electrification properties resulted by the oil flow rate and the action of electric charge trapper are investigated by measuring the current and potential on the surface of the test metal pipe. The measured results showed that the current and potential between the metal pipe and the earth increased with the rise of flow rate; and as the flow rate increased, the growth trends of the current and potential difference between two close flow rates increased and decreased, respectively, while there was an electric charge trapper set in the radial direction of the pipe, the measured current and potential decreased compared with that of without electric charge trapper, which was because it captured and caught part of charge in the oil flow bulk to neutralize the opposite charge on the surface of the metal pipe.