Research on thermal insulation materials properties under HTHP conditions for deep oil and gas reservoir rock ITP-Coring

Deep oil and gas reservoirs are under high-temperature conditions,but traditional coring methods do not consider temperature-preserved measures and ignore the influence of temperature on rock porosity and permeability,resulting in distorted resource assessments.The development of in situ temperaturepreserved coring(ITP-Coring)technology for deep reservoir rock is urgent,and thermal insulation materials are key.Therefore,hollow glass microsphere/epoxy resin thermal insulation materials(HGM/EP materials)were proposed as thermal insulation materials.The materials properties under coupled hightemperature and high-pressure(HTHP)conditions were tested.The results indicated that high pressures led to HGM destruction and that the materials water absorption significantly increased;additionally,increasing temperature accelerated the process.High temperatures directly caused the thermal conductivity of the materials to increase;additionally,the thermal conduction and convection of water caused by high pressures led to an exponential increase in the thermal conductivity.High temperatures weakened the matrix,and high pressures destroyed the HGM,which resulted in a decrease in the tensile mechanical properties of the materials.The materials entered the high elastic state at 150℃,and the mechanical properties were weakened more obviously,while the pressure led to a significant effect when the water absorption was above 10%.Meanwhile,the tensile strength/strain were 13.62 MPa/1.3%and 6.09 MPa/0.86%at 100℃ and 100 MPa,respectively,which meet the application requirements of the self-designed coring device.Finally,K46-f40 and K46-f50 HGM/EP materials were proven to be suitable for ITP-Coring under coupled conditions below 100℃ and 100 MPa.To further improve the materials properties,the interface layer and EP matrix should be optimized.The results can provide references for the optimization and engineering application of materials and thus technical support for deep oil and gas resource development.

Copper Release Kinetics and Ageing of Insulation Paper in Oil-Immersed Transformers

The paper provides a general overview of chemical processes leading to the degradation of oil-paper insulation in oil-immersed electrical current transformers. Previous knowledge available in literature is complemented by new results placing a specific emphasis on the physicochemical factors which affect the copper release in the insulation oil and the oil oxidation kinetics. It is demonstrated that various ageing processes interact with each other, with one or another process dominating under specific conditions. Comprehensive but disjoint studies focusing on separate sub-processes may produce rather misleading results, and occasionally, lie behind rather irrelevant quality demands imposed on the insulating liquids.

Low Frequency Dispersion Mechanism of Dielectric Response for Oil-paper Insulation Diagnosis

Both the real part and imaginary part of complex permittivity approximately have a log-linear frequency dependency at low fre- quencies, especially at ultra-low frequencies under conditions of different moisture concentrations and temperatures, which is recognized as the low frequency dispersion (LFD). In order to explain this dispersion, a new mechanism of dielectric response of LFD of oil-paper insula- tion is proposed. A simplified one-dimensional mathematical model of concentration polarization carrier caused by slow migration is developed and solved, which indicates that ion mobility is closely related to the size of gap and the adsorption capacity of cellulose molecu- lar chains to ions. A stochastic statistical model of the carrier mobility induced LFD is also developed. Moreover, actual tests under 50 °C and 2% moisture content were put forward, as well as simulations with according current waveforms. The simulation results agreed well with the experimental data in that concentration polarization of carriers caused by slow migration is the probable cause of low frequency dispersion of dielectric response for oil-paper insulation diagnosis.

Surface Partial Discharge Characteristics of Oil-paper Insulation Under Combined AC-DC Voltage

The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.

Space Charge Characteristics of Oil-paper Insulation with New Paper and Aged Oil

Oil-paper compound insulation has been widely used in power transformers for quite a long time because of its good performances. The insulation gradually degrades under combined thermal, electrical and chemical stresses during routine operations, mainly because of space charges inside. This work investigated the space charge characteristics in oil-paper insulation under oil aging circumstance. New trans- former oil samples are thermally aged to obtain different aging states, and their physical and chemical properties are analyzed. New Kraft papers are dried in vacuum and fully immersed in these different aged oil samples, and three kinds of oil-paper samples are obtained. We use the pulsed electro-acoustic (PEA) method to measure space charge under both DC voltage-on and voltage-off conditions at room temperature. The effect of oil aging state on characteristics of space charge injection, accumulation, and decay is analyzed and discussed. The results show that comparing with the DC voltage-off condition, more charges are injected into samples at the interface of electrode and dielectric when DC voltage is on. When the oil-aged state gets worse, more charges are induced at both cathode and anode, more space charges are accumulated in the bulk, the area of negative charges is larger, and local electric field is distorted more seriously. Moreover, for the voltage-off condition, aged oil is good for space charge decay, and trapped positive space charges decay faster than trapped negative charges.

Improvement on Condition Assessment Model for Oil-paper Insulation

Identification of the aging condition and the failure probability of oil-paper insulation in transformer is important for improving the reliability of electric power transmission system and applying life cycle cost (LCC) management to electrical equipment. Based on data obtained in a series of multi-accelerated-aging experiments, two approaches for calculating failure probability of oil-paper insulation were compared in aspects of degree of polymerization (DP) and condition ranking. In the experiments, mineral oil and cellulose paper are sub- jected to electrical and thermal stresses, and several parameters, including dissolved gases’ volume fraction, furfural content, moisture content, and degree of polymerization, are measured after the aging process. Results show that weight of carbon oxide, which has a close relationship with cellulose paper degradation, is much higher in DP model than in condition ranking model. Moreover, it is concluded that DP model is more practically accurate than condition ranking model, because aging of cellulose paper rather than mineral oil is the key and critical factor of oil-paper insulation aging.

Aging Effect on Characteristics of Oil Impregnated Insulation Paper for Power Transformers

This paper deals with experimental investigations of the electrical and physical properties of oil impregnated insulation paper for power transformers at different temperatures. The ac breakdown voltage, tensile strength and water content of insulation papers impregnated in mineral oil for different time periods were investigated. The effect of insulation paper thickness on the electrical and mechanical properties has also been studied. The results showed that the breakdown voltage and the tensile strength decreased with increasing the time of immersion of insulation paper in oil at room temperature, at 5℃ and at -12℃. Also, the thermal aging effect on the characteristic of insulation paper has been studied. It was found that high temperatures affect the breakdown voltage and the tensile strength to a great extent.

Chaotic Characteristic of Time Series of Partial Discharge in Oil-Paper Insulation

The chaotic characteristics of time series of five partial discharge （PD） patterns in oil-paper insulation are studied. The results verify obvious chaotic characteristic of the time series of discharge signals and the fact that PD is a chaotic process. These time series have distinctive features, and the chaotic attractors obtained from time series differed greatly from each other by shapes in the phase space, so they could be used to qualitatively identify the PD patterns. The phase space parameters are selected, then the chaotic characteristic quantities can be extracted. These quantities could quantificationally characterize the PD patterns. The effects on pattern recognition of PRPD and CAPD are compared by using the neural network of radial basis function. The results show that both of the two recognition methods work well and have their respective advantages. Then, both the statistical operators under PRPD mode and the chaotic characteristic quantities under CAPD mode are selected comprehensively as the input vectors of neural network, and the PD pattern recognition accuracy is thereby greatly improved.

The Research of Connection between Degree of Polymerization and Frequency Domain Dielectric Spectroscopy Characteristics during Oil-Paper Insulation Aging

In order to study the linkage effects between degree of polymerization and frequency domain dielectric spectroscopy characteristics of oil-paper insulation, the frequency domain dielectric response test platform of oil-paper insulation is set up. Complex permittivity of oil-paper insulation respectively composed by new or aged oil and insulation paper with different DP are tested, and complex permittivity of oil-paper insulation respectively composed by insulation respectively composed by new oil and insulation paper with different DP and low or high moisture content are tested. The test results are analyzed, and the analysis results show that the degree of polymerization of insulation paper has an influence on complex permittivity of oil-paper insulation though influencing the distribution of moisture and acids between oil and paper.

Assessment of the Influence of Paper Insulation on the Discharge Initiation in Oil

The results of the assessment of the influence of paper insulation on the discharge initiation in oil were presented in this paper. This assessment based on the results of performed experimental works and on the analysis of electrical field distribution. Both types of the studies were connected with the model HV （high voltage） electrode setups covered by paper and immersed in oil. Experimental works indicated that the source of ＂weak points＂ of paper-oil model electrode setup is oil, not the surface of metal or insulation wrapping. Such hypothesis, resulting mainly from the measured times to initiations of discharges developing from bare and insulated HV electrodes, was verified by the analysis of electrical field distribution performed on the basis of finite element method applied in the COMSOL Multiphysics software. This analysis confirmed preliminary the made hypothesis. Correlation with the most stressed oil volume law was also observed.

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.

Bio-Based Rigid Polyurethane Foams for Cryogenic Insulation

Cryogenic insulation material rigid polyurethane(PU)foams were developed using bio-based and recycled feedstock.Polyols obtained from tall oil fatty acids produced as a side stream of wood biomass pulping and recycled polyethylene terephthalate were used to develop rigid PU foam formulations.The 4th generation physical blowing agents with low global warming potential and low ozone depletion potential were used to develop rigid PU foam cryogenic insulation with excellent mechanical and thermal properties.Obtained rigid PU foams had a thermal conductivity coefficient as low as 0.0171 W/m·K and an apparent density of 37-40 kg/m^(3).The developed rigid PU foams had anisotropic compression strength properties,which were higher parallel to the foaming direction.Moreover,the compression strength was also influenced by the type of applied bio-based polyol.The bio-based polyols with higher OH group functionality delivered higher crosslinking density of polymer matrix;thus,the mechanical properties were also higher.The mechanical strength of the foams increased when materials were tested at liquid nitrogen temperature due to the stiffening of the polymer matrix.The thermal properties of the developed materials were determined using differential scanning calorimetry,dynamic mechanical analysis,and thermogravimetric analysis methods.Lastly,the developed rigid PU foams had good adhesion to the aluminium substrate before and after applying cyroshock and an excellent safety coefficient of 4-5.Rigid PU foams developed using Solstice LBA delivered adhesion strength of~0.5 MPa and may be considered for application as cryogenic insulation in the aerospace industry.

Study on the Economic Insulation Thickness of the Buried Hot Oil Pipelines Based on Environment Factors

It is important to determine the insulation thickness in the design of the buried hot oil pipelines.The economic thickness of the insulation layer not only meets the needs of the project but also maximizes the investment and environmental benefits.However,as a significant evaluation,the environmental factors haven’t been considered in the previous study.Considering this factor,the mathematical model of economic insulation thickness of the buried hot oil pipelines is built in this paper,which is solved by the golden section method while considering the costs of investment,operation,environment,the time value of money.The environmental cost is determined according to the pollutant discharge calculated through relating heat loss of the pipelines to the air emission while building the model.The results primarily showed that the most saving fuel is natural gas,followed by LPG,fuel oil,and coal.The fuel consumption for identical insulation thickness is in the order:coal,fuel oil,LPG,and natural gas.When taking the environmental costs into account,the thicker the economic insulation layer is,the higher cost it will be.Meanwhile,the more pollutant discharge,the thicker the economic insulation layer will be.

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.

Influence of Moisture Content on the Degradation of Natural Ester Impregnated Paper Insulation

Natural ester is a kind of fire-resistant and environmentally friendly dielectric liquid, which has already been widely used in power transformers. The influence of moisture content on the degradation of natural ester (camellia oil and FR3 oil) impregnated paper in- sulation was investigated and compared with that of mineral oil impregnated paper in this paper. The initial moisture contents of insulating paper samples were 0.3%, 2% and 4%, respectively. Thermal aging experiment was conducted at 130 °C in hermetical stainless vessels for 80 days. Aging parameters such as the degree of polymerization (DP) of insulating paper, furfural mass concentration in oil and acid number of oil were measured. Chain scissions number (CSN) of aged insulating paper was calculated. The results show that moisture could accele- rate the degradation of both natural ester impregnated paper insulation and mineral oil impregnated paper insulation, while the degradation rate of natural ester impregnated paper insulation is much lower than that of mineral oil impregnated paper insulation. High moisture satura- tion solubility and hydrolysis process of natural ester may be the reason.

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.

EXPERIMENTAL STUDY OF ACOUSTICAL INSULATION OF CEMENT-BASED BOARD PREPARED WITH WASTE COCONUT COIR AND OIL PALM FIBERS

Among the major challenges facing the modern era of technological and industrial advancements are pollution and exponentially growing energy consumption.Pollution continues to be a menace affecting different aspects of life such as health,productivity,and comfort.This paper focuses on the elimination or reduction of sound pollution in buildings using cement-based boards made from pretreated coconut coir and oil palm fibers obtained from agricultural residues.The study includes an account of the preparation of fiber cement boards made from Portland cement Type 1,limestone powder,water,sand,and pretreated coconut coir and oil palm fibers at 5,10,15,and 20%by weight of powder materials,respectively,and a high-range water reducer in order to make sure that the natural materials would be spread in an even way throughout the specimens.Sound insulation tests were performed as key indicators of the performance of the fiber cement boards.It was found that an increase in the proportion of natural materials resulted in fiber cement boards with decreased density,compressive strength,and flexural strength.Furthermore,in relation to both physical and mechanical performance,the boards incorporating coconut fibers were superior to those incorporating oil palm fibers.With an increased proportion of natural fibers,sound insulation performance tended to improve.The boards prepared with coconut coir and oil palm fibers in this study yielded acceptable physical and mechanical properties and showed promise in relation to providing insulative protection against sound.

Effects of temperature on creepage discharge characteristics in oil-impregnated pressboard insulation under combined AC–DC voltage

Due to the complexity of the valve side winding voltage of the converter transformer, the insulation characteristics of the oil-impregnated pressboard(OIP) of the converter transformer are different from those of the traditional AC transformer. The study on effect of temperature on the creeping discharge characteristics of OIP under combined AC–DC voltage is seriously inadequate. Therefore, this paper investigates the characteristics of OIP creepage discharge under combined AC–DC voltage and discusses the influence of temperature on creepage discharge characteristics under different temperatures from 70 °C to 110 °C. The experimental results show that the partial discharge inception voltage and flashover voltage decrease with increasing temperature. The times of low amplitude discharge(LAD) decrease and amplitude of LAD increases. Simultaneously, the times of high amplitude discharge(HAD) gradually increase at each stage of creepage discharge with higher temperature. The analysis indicates that the charge carriers easily accumulate and quickly migrate directional movement along the electric field ahead of discharging. The residual charge carriers are more easily dissipated after discharging.The ‘hump’ region of LAD moves to the direction of higher discharge magnitude. The interval time between two continuous discharges is shortened obviously. The concentration of HAD accelerates the development of OIP insulation creepage discharge. The temperature had an accelerating effect on the development of discharge in the OIP under applying voltage.