Weijun Xing

Experimental study of partial discharge inception voltage of special fluorocarbon gases and their mixtures in rod-plane gaps under power frequency

Because of the high global warming potential (GWP), SF6 gas was listed as one of the six restricted gases in 1997. Some fluorocarbon gases with low environmental effect and high dielectric performance are studied as the substitution candidates for SF6. This paper presents the partial discharge (PD) capability of some gas mixtures with fluorocarbon at different pressures and ratio of fluorocarbon in rod-plane electrodes under power frequency. The PD inception voltage (PDIV) is measured and analyzed. The experimental results show that the PD capability of some gas mixtures with fluorocarbon is better than that of SF6 and the gas mixtures has a possibility to substitute for SF6.

Study on decomposition gas for faults diagnostic of electrical equipment using fluorocarbons

As the increasing demand for large capacity, high voltage and high reliability power transformers in urban power grid, oil-free, non-flammable and non-explosive equipment is recommended. For this reason, evaporative cooling transformers, gas insulated transformers and other electrical equipment using fluorocarbon as coolant and dielectric have been developed. This paper presents an experimental survey of the main components of decomposition products generated by several faults of electrical equipment using fluorocarbon; here evaporative cooling transformer and gas insulated transformer are taken as example. All experimental studies are carried out by simplified testing setups. The gaseous decomposition products formed during the tests are analyzed and assayed by means of GC/MS (gas chromatography/mass spectrometry) method. The amount of decomposition products varied with temperature, time and discharge capacity are studied. Based on these results, criterions for judging the fault type of this kind equipment is suggested, and it could be helpfulness to develop a diagnostic method for the new electrical equipment using fluorocarbon.

Cooling capability of gas mixtures with fluorocarbon in a gas-insulated transmission Line Model

Because of its high-capacity, low losses and no electromagnetic interference, the gas-insulated transmission line (GIL), which is a replacement of an overhead line in special environments, has been used for over 40 years, mainly as bus ducts of gas-insulated substations or underground connections in power plants. The insulated and cooling gas in GIL is mainly SF6 or its mixtures, which have high global warming potential (GWP) and are listed as restricted gases in the 3rd Conference of the Parties to the United Nations Framework Convention on Climate Change in 1997. Therefore, a lot of researches have been made to find a substitute gas for SF6. In this paper, the cooling capability of gas mixtures with fluorocarbon, which has a lower GWP than SF6 and outstanding insulating performance, is investigated. Heat transfer coefficients of gas mixtures are calculated by measuring the surface temperature of a metal pipe under a certain current. The heat transfer coefficients of gas mixtures with fluorocarbon are analyzed and compared with that of SF6 mixtures. Based on the heat transfer coefficients, the maximum permissible currents of our GIL model with fluorocarbon mixtures or SF6 mixtures are also calculated and compared.

Simulation of oil flow process of insulation structure for high efficiency cooling shell transformers

Thermal stress is one of the major causes of deterioration of insulation material for power transformers. An efficient cooling system is important to keep the operating temperature at lower levels. In shell-form transformers, the insulation structure plays an important role in not only insulation but also cooling efficiency. It is known that insulation of shell-form transformers is barrier insulation, composed of spacers. Though some experimental suggestions are given to improve the cooling oil flow for shell-form transformers, effect of various spacer shapes and distributions which are important for cooling oil flow are not discussed before. Simulations of oil flow process under various insulation structures are implemented in this paper. Accurate models are made for the insulation structure of a 630KVA shell-form transformer in order to optimize the cooling efficiency of insulation structure in this paper. Suitable insulation structure is suggested which is very helpful for optimizing design and improving manufacture technologies for shell-form power transformers.

Puffer characteristic calculation of a circuit breaker using fluorocarbon gas mixtures

Because of its high dielectric strength, good partial discharge capability, low global warming potential (GWP), none ozone depletion potential (ODP) and nontoxicity, fluorocarbon gas is possible substitute for SF6, and can be used hopefully in electrical equipment, such as circuit breaker. In this paper, we calculate the pressure characteristic of circuit breaker using gas mixture containing fluorocarbon gas as arc quenching gas based-on the first law of thermodynamics and the law of hydrokinetics. The pressure characteristic curves of the gas chamber and the gas mass flow pass the nozzle are obtained through computation. In addition, the influences of mixtures ratio and nozzle throat diameter to the pressure and gas mass flow rate are achieved. It shows that the bigger ratio of fluorocarbon is corresponding to the bigger chamber pressure and relative bigger mass flow as to the same structural factor with no energy input; while considering the arc energy bigger ratio corresponding to smaller chamber pressure. And the nozzle throat diameter has a large impact on the pressure and gas mass flow rate. Besides, we also compared the gas pressure and gas mass flow rate of mixture gas with that of SF6 gas. These results provide a helpful reference for the design of the new type circuit breaker.

Partial discharge performances under non- uniform electric field in gas mixtures with small fluorocarbons

This paper describes the partial discharge (PD) performances of gas mixtures with small fluorocarbons because their global warming potential (GWP) is smaller than that of SF6 gas, which was regulated as one of six restricted gases. It is difficult to apply pure fluorocarbon gases as insulating medium directly in gas insulated switchgear (GIS) and gas circuit breakers (GCB), because their liquefying temperature is high. Thus, the mixtures have various contents and ratios. The PD inception voltages of gas mixtures containing fluorocarbon and N2 are measured and analyzed as a function of gas pressure, electrode distance and the ratio of the fluorocarbon. The PD performances of fluorocarbon gas and its mixtures are compared with those of SF6 gas, which is now widely used as the insulating medium in GIS and GCB. The results show that gas mixtures containing special fluorocarbon have a possibility to substitute for SF6 gas.

Electromagnetic field problem of magneto acoustic tomography with magnetic induction

Method for electromagnetic field problem of magnetoacoustic tomography with magnetic induction (MAT-MI) is presented, in which the static magnetic field need not rotating, and the transient electromagnetic effect which produced by the time-varying excitation can be taken into account. Beside, the huge computational effort for 3D cases can be reduced effectively. Program which based on the method was developed and applied. Through a number of calculating, the scope of application of the method has been researched, and the availability and efficiency of the method has also been demonstrated.