Experimental study on total dissolved gas supersaturation in water

More and more high dams have been constructed and operated in China. The total dissolved gas （TDG） supersaturation caused by dam discharge leads to gas bubble disease or even death of fish, Through a series of experiments, the conditions and requirements of supersaturated TDG generation were examined in this study. The results show that pressure （water depth）, aeration, and bubble dissolution time are required for supersaturated TDG generation, and the air-water contact area and turbulence intensity are the main factors that affect the generation rate of supersaturated TDG. The TDG supersaturation levels can be reduced by discharging water to shallow shoals downstream of the dam or using negative pressure pipelines. Furthermore, the TDG supersaturation levels in stilling basins have no direct relationship with those in reservoirs. These results are of great importance for further research on the prediction of supersaturated TDG generation caused by dam discharge and aquatic protection.

Hybrid Dissolved Gas-in-Oil Analysis Methods

Dissolved gas analysis is the most widely used diagnostic test in power transformers. The aim of this paper is to introduce the dissolved gas analysis (DGA) methods able to diagnose the transformer conditions. The faults cause the transformer oil, pressboard, and other insulating materials to decompose and generate gases, some of which dissolve in the oil. The results of DGA must be accurate if faults are to be diagnosed reliably. There are different established methods used in industry for interpreting DGA results. We will compare the result of IEEE Key Gas Methods and Rogers’ Ratios. The transformer conditions are evaluated by the Key Gas Method with total combustible gas method (TCGM) and then verified by the Rogers’ Ratios. As result, the aging pattern and trend of the power transformer deterioration can be determined. The 30 sample data from IEEE with known faults and dissolved gas concentrations were used as the basis of comparison.

Effects of total dissolved gas supersaturated water on lethality and catalase activity of Chinese sucker(Myxocyprinus asiaticus Bleeker)

Total dissolved gas(TDG) supersaturation caused by dam sluicing can result in gas bubble trauma(GBT) in fish and threaten their survival.In the present study,Chinese suckers(Myxocyprinus asiaticus Bleeker) were exposed to TDG supersaturated water at levels ranging from 120% to 145% for 48 h.The median lethal concentration(LC 50) and the median lethal time(LT 50) were determined to evaluate acute lethal effects on Chinese suckers.The results showed that the LC 50 values of 4,6,8,and 10 h were 142%,137%,135%,and 130%,respectively.The LT 50 values were 3.2,4.7,7.8,9.2,and 43.4 h,respectively,when TDG supersaturated levels were 145%,140%,135%,130%,and 125%.Furthermore,the biological responses in Chinese suckers were studied by assaying the catalase(CAT) activities in gills and muscles at the supersaturation level of 140% within LT 50.The CAT activities in the gills and muscle tissues exhibited a regularity of a decrease after an increase.CAT activities in the muscles were increased significantly at 3/5LT 50(P<0.05) and then came back to the normal level.However,there were no significant differences between the treatment group(TDG level of 140%) and the control group(TDG level of 100%) on CAT activities in the gills before 3/5LT 50(P>0.05),but the activities were significantly lower than the normal level at 4/5LT 50 and LT 50(P<0.05).

A laterally averaged two-dimensional simulation of unsteady supersaturated total dissolved gas in deep reservoir

Elevated levels of the Total Dissolved Gas （TDG） may be reached downstream of dams, leading to increased incidences of gas bubble diseases in fish. The supersaturated TDG dissipates and transports more slowly in reservoirs than in natural rivers because of the greater depth and the lower turbulence, which endangers the fish more seriously. With consideration of the topographical cha- racteristics of a deep reservoir, a laterally averaged two-dimensional unsteady TDG model for deep reservoir is proposed. The dissi- pation process of the TDG inside the waterbody and the mass transfer through the flee surface are separately modeled with different functions in the model. Hydrodynamics equations are solved coupling with those of water temperature and density. The TDG con- centration is calculated based on the density current field. A good agreement is found in the simulation of the Dachaoshan Reservoir between the simulation results and the field data of the hydrodynamics parameters and the TDG distribution in the vertical direction and their unsteady evolution with time. The hydrodynamics parameters, the temperature and the TDG concentration are analyzed based on the simulation results. This study demonstrates that the model can be used to predict the evolutions of hydrodynamics para- meters, the temperature and the TDG distribution in a deep reservoir with unsteady inflow and outflow. The results can be used in the study of the mitigation measures of the supersaturated TDG.

Experimental study on the impact of temperature on the dissipation process of supersaturated total dissolved gas

Water temperature not only affects the solubility of gas in water but can also be an important factor in the dissipation process of supersaturated total dissolved gas （TDG）. The quantitative relationship between the dissipation process and temperature has not been previously described. This relationship affects the accurate evaluation of the dissipation process and the subsequent biological effects. This article experimentally investigates the impact of temperature on supersaturated TDG dissipation in static and turbulent conditions. The results show that the supersaturated TDG dissipation coefficient increases with the temperature and turbulence intensity. The quantitative relationship was verified by straight flume experiments. This study enhances our understanding of the dissipation of supersaturated TDG. Furthermore, it provides a scientific foundation for the accurate prediction of the dissipation process of supersaturated TDG in the downstream area and the negative imp）acts of high dam projects on aquatic ecosystems.

Gas sorption and non-Darcy flow in shale reservoirs

Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shale matrix, while the latter is concentrated near the solid walls of pores. In this paper, the Langmuir equation is used to describe adsorption and Henry’s law is used to describe dissolution. The K coefficient in Henry’s law of 0.052 mmol/(MPa g TOC) is obtained by matching experimental data. The amount of dissolved gas increases linearly when pressure increases. Using only the Langmuir equation without considering dissolution can lead to a significant underestimation of the amount of sorbed gas in shales. For non-Darcy gas flow, the apparent permeability model for free gas is established by combining slip flow and Knudsen flow. For adsorbed gas, the surface diffusion effect is also considered in this model. The surface diffu- sion coefficient is suggested to be of the same scale as the gas self-diffusion coefficient, and the corresponding effective permeability is derived. When 1/ increases,k/ kincreases, but the relationship is not linear as the Klinkenberg effect suggests. The effect of adsorption on the gas flow is significant in nanopores (r≤2 nm). Adsorption increases apparent permeability in shales at low pressures and decreases it at high pressures.

The generalized method for estimating reserves of shale gas and coalbed methane reservoirs based on material balance equation

As the main unconventional natural gas reservoirs,shale gas reservoirs and coalbed methane(CBM)reservoirs belong to adsorptive gas reservoirs,i.e.,gas reservoirs containing adsorbed gas.Shale gas and CBM reservoirs usually have the characteristics of rich adsorbed gas and obvious dynamic changes of porosity and permeability.A generalized material balance equation and the corresponding reserve evaluation method considering all the mechanisms for both shale gas reservoirs and CBM reservoirs are necessary.In this work,a generalized material balance equation(GMBE)considering the effects of critical desorption pressure,stress sensitivity,matrix shrinkage,water production,water influx,and solubility of natural gas in water is established.Then,by converting the GMBE to a linear relationship between two parameter groups related with known formation/fluid properties and dynamic performance data,the straight-line reserve evaluation method is proposed.By using the slope and the y-intercept of this straight line,the original adsorbed gas in place(OAGIP),original free gas in place(OFGIP),original dissolved gas in place(ODGIP),and the original gas in place(OGIP)can be quickly calculated.Third,two validation cases for shale gas reservoir and CBM reservoir are conducted using commercial reservoir simulator and the coalbed methane dynamic performance analysis software,respectively.Finally,two field studies in the Fuling shale gas field and the Baode CBM field are presented.Results show that the GMBE and the corresponding straight-line reserve evaluation method are rational,accurate,and effective for both shale gas reservoirs and CBM reservoirs.More detailed information about reserves of shale gas and CBM reservoirs can be clarified,and only the straight-line fitting approach is used to determine all kinds of reserves without iteration,proving that the proposed method has great advantages compared with other current methods.

A new hypothesis for cavitation nucleation in gas saturated solutions:Clustering of gas molecules lowers significantly the surface tension

Cavitation in water generally takes place at much lower negative pressure than predicted from theories.In this work,we try to stress the discrepancy from the influence of the dissolved gas on cavitation nucleation.By combining molecular dynamics simulation and thermodynamic analysis,we evaluated the lowering of surface tension as a function of density of gas molecules in gas clusters formed in aqueous solution.We found that the obtained surface tension of small gas clusters is much more substantially reduced than expected.The surface tension lowering and the non-ideality of gas molecules in the clusters are then taken into account in determining the nucleation of cavitation,and as a consequence,the required negative pressure for cavitation becomes comparable to experimental values.Thus,we give an alternative explanation for the discrepancy of cavitation pressure between experiment and theory,i.e.,it is the substantially reduced surface tension for small gas nuclei,which have not been taken into account in theory,along with the ideal gas approxiamtion that induce its deviation from the experimental values.

Microanalysis of supersaturated gas release based on wall-attached bubbles

Supersaturation of dissolved gases in natural water,due to spillage from high dams and other factors,may cause fish mortality.In previous experiments,the dissipation coefficient has been used to denote the degassing process of total dissolved gas(TDG)saturation.These experiments mainly analyzed supersaturated TDG dissipation from a macroscopic view.To precisely clarify the mechanism of supersaturated TDG release,this study investigated bubble adsorption at a wall surface from a microscopic view.The experiment was conducted in a Plexiglas-wall container filled with supersaturated TDG water.A model that calculates the adsorption flux of supersaturated TDG by a solid wall,and helps describe construction for a contact angle at a three-phase intersection,was developed according to Young's equation.This model was used to investigate the formation process of bubbles adsorbed on a solid polymethyl methacrylate(PMMA)surface in supersaturated TDG water.The adsorption effect of a solid wall on TDG release was analyzed based on the experimental data.The modeling results were compared with observations under different wall area conditions,and it was found that TDG release tended to increase with wall area.This study helps improve our understanding of the mechanisms of supersaturated TDG release and provides an important theoretical method for accurate calculation of the release process.The adsorption flux model of the solid wall provides mitigation measures to combat the adverse effects of TDG supersaturation,which will be beneficial to the protection of aquatic organisms in hydropower-regulated rivers.

Fault Diagnosis of Power Transformer Based on Improved ACGAN Under Imbalanced Data

The imbalance of dissolved gas analysis(DGA)data will lead to over-fitting,weak generalization and poor recognition performance for fault diagnosis models based on deep learning.To handle this problem,a novel transformer fault diagnosis method based on improved auxiliary classifier generative adversarial network(ACGAN)under imbalanced data is proposed in this paper,which meets both the requirements of balancing DGA data and supplying accurate diagnosis results.The generator combines one-dimensional convolutional neural networks(1D-CNN)and long short-term memories(LSTM),which can deeply extract the features from DGA samples and be greatly beneficial to ACGAN’s data balancing and fault diagnosis.The discriminator adopts multilayer perceptron networks(MLP),which prevents the discriminator from losing important features of DGA data when the network is too complex and the number of layers is too large.The experimental results suggest that the presented approach can effectively improve the adverse effects of DGA data imbalance on the deep learning models,enhance fault diagnosis performance and supply desirable diagnosis accuracy up to 99.46%.Furthermore,the comparison results indicate the fault diagnosis performance of the proposed approach is superior to that of other conventional methods.Therefore,the method presented in this study has excellent and reliable fault diagnosis performance for various unbalanced datasets.In addition,the proposed approach can also solve the problems of insufficient and imbalanced fault data in other practical application fields.

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.

An improved oil recovery prediction method for volatile oil reservoirs

To describe the complex phase transformation in the process of depletion exploitation of volatile oil reservoir,four fluid phases are defined,and production and remaining volume of these phases are calculated based on the principle of surface volume balance,then the recovery prediction method of volatile oil reservoir considering the influence of condensate content in released solution gas and the correction method of multiple degassing experiments data are established.Taking three typical kinds of crude oil(black oil,medium-weak volatile oil,strong volatile oil)as examples,the new improved method is used to simulate constant volume depletion experiments based on the corrected data of multiple degassing experiment to verify the reliability of the modified method.By using"experimental data and traditional method","corrected data and traditional method"and"corrected data and modified method",recovery factors of these three typical kinds of oil are calculated respectively.The source of parameters and the calculation methods have little effect on the recovery of typical black oil.However,with the increase of crude oil volatility,the oil recovery will be seriously underestimated by using experimental data or traditional method.The combination of"corrected data and modified method"considers the influence of condensate in gas phase in both experimental parameters and calculation method,and has good applicability to typical black oil and volatile oil.The strong shrinkage of volatile oil makes more"liquid oil"convert to"gaseous oil",so volatile oil reservoir can reach very high oil recovery by depletion drive.

Power Transformer Fault Diagnosis Using Fuzzy Reasoning Spiking Neural P Systems

This paper presents an intelligent technique to fault diagnosis of power transformers dissolved and free gas analysis (DGA). Fuzzy Reasoning Spiking neural P systems (FRSN P systems) as a membrane computing with distributed parallel computing model is powerful and suitable graphical approach model in fuzzy diagnosis knowledge. In a sense this feature is required for establishing the power transformers faults identifications and capturing knowledge implicitly during the learning stage, using linguistic variables, membership functions with “low”, “medium”, and “high” descriptions for each gas signature, and inference rule base. Membership functions are used to translate judgments into numerical expression by fuzzy numbers. The performance method is analyzed in terms for four gas ratio (IEC 60599) signature as input data of FRSN P systems. Test case results evaluate that the proposals method for power transformer fault diagnosis can significantly improve the diagnosis accuracy power transformer.

Application of Extreme Learning Machine in Fault Classification of Power Transformer

Reliability of power system is very essential for every nation to generate and transmit power without interruption. Power transformer is one of the most significant electrical apparatus and hence it must be kept in good health. Identification and classification of faults in power transformer is a major research area. Conventional method of fault classification in transformer uses gas concentrations data and interprets them using international standards. These standards are not able to classify the faults correctly under certain conditions. To overcome this limitation, several soft computing tools namely artificial neural network (ANN), Support Vector Machine (SVM) etc. are used to automate the process of classification of faults in transformers. However, there is a scope exists to improve the classification accuracy. Hence, this research work focuses to design Extreme Learning Machine (ELM) method for classifying fault very accurately using enthalpy of dissolved gas content in transformer oil as an input feature. The ELM method is tested with two databases: one based on IEC TC10 database (DB1) and the other one based on data collected from utilities in India (DB2). The application of ELM to Power Transformer fault classification based on enthalpy as input feature outperforms over the conventional classification based on gas concentration as input feature.

Thin layer gas electrode and its application to measurement of dissolved oxygen

A novel thin layer cell equipped with thin layer gas electrode(TLGE)was studied as electrochemical gas sensor for the measurement of dissolved oxygen in water or aqueous solutions. The working electrode(TLGE)is a hydrophohic gas diffusing electrode placed between the cell electrolyte and the solution to be tested.The hydrophobic pores in TLGE serve as a gas chamber. After the sampling period,in which the partial pressure of dissolved oxygen in test solution becomes in equilibrium with that in the gas chamber,the TLGE is polarized with square wave or linear potential signal.Then the Faradaic charge (Q) consumed in depletion of the oxygen contained in pores of TLGE is measured.The main merits of this system are good linearity between the partial pressure of dissolved oxygen in test solution and Q,low zero-reading,negligible liquid-gas difference,con- venient calibration and very low temperature coefficient(ca.0.5%/℃).This technique can also be applied to the measurement of oxygen partial pressure in gas phases.