Chi Xiao-Chun

Creeping discharge performance of oil-paper insulation with streaming electrification

In this paper, the influence of streaming electrification on the creeping discharge of an oil-paper insulation system has been investigated, using experimental models. Experimental results indicate that the initial creeping discharge voltage of the oil-paper insulation system decreases with oil flow rate. The creeping discharge path develops toward the oil entrance, and there are polarity and position effects on the creeping discharge under oil flowing conditions. Reasons for failure due to dendritic discharge on the surface of barrier boards in power transformers have been revealed in these experiments.

Influence of streaming electrification on creeping discharge of oil-paper insulation system

In this paper, the influences of streaming electrification on creeping discharge of oil-paper insulation systems have been investigated, using an experimental model. The experimental results indicates that the initial creeping discharge voltage of an oil-paper insulation system decreases along with the increase of oil flow rate, the creeping discharge path develops towards the oil entrance, and there are polarity and position effects on creeping discharge under flowing oil conditions.<<ETX>>

Experimental observation on the charge density of transformer oil

In this paper, the charge accumulation caused by oil flow electrification on the surface of insulating paper was observed, using an oil-paper pipe model. An absolute charge sensor (ACS) has been used for measuring the charge density in oil. The dependence of the charge density on the flow velocity and temperature are investigated. The effects of charge density on applied dc and ac voltage are obtained. The theoretical explanations are also presented to make these effects understood.

A new type of corona discharge reactor for simultaneous removal of NO and SO/sub 2/ from flue gas

An experimental study on the simultaneous removal of NO and SO/sub 2/ in a simulated flue gas has been carried out using multipoint to water corona discharge reactor. In a simulate flue gas containing of 400 ppm NO and 400 ppm SO/sub 2/, the NO and SO/sub 2/ can be simultaneous removal. The gas phase NO is oxidized by corona discharge and converted into HNO/sub 3/ and HNO/sub 3/ dissolve velocity constant is very high, so that it is possible to remove by liquid phase absorption. The absorption into the water of gas phase SO/sub 2/ and liquid phase oxidation of HSO/sub 3//sup -/ [S (IV)] to SO/sub 4//sup 2-/ [S (VI)] is promoted by corona discharge. Most of the SO/sub 2/ removal is attributed to the liquid phase absorption and NO conversion via gas phase oxide. In a word, the corona discharge increases the mass transfer and oxidation.

Electrostatic enhanced heat transfer in a dielectric liquid

In this paper, the phenomena of electrostatic enhanced heat transfer in a dielectric fluid have been investigated experimentally using a horizontal model pipe. The saturation pressure in the model pipe, the heat flux both in heated and cooled ends are all measured under high DC voltage. Experimental results show that the heat transfer properties of dielectric working liquids can be improved by the electrostatic field.

Influences of electrical field on boiling-condensation heat transfer system

In this paper, the influences of electrical field on boiling-condensation heat transfer systems have been investigated using a cylinder heat transfer model. Freon-11 is selected as working fluid. The condensation heat transfer coefficient, the boiling heat flux and the saturation pressure are measured in this investigation. According to the experimental results, it is found that the electric field can influence heat transfer system. The boiling heat transfer is enhanced by the applied voltage, and the saturate vapor of working fluid is condensed on the high voltage electrode directly when the applied voltage is higher than 6 kV. The experimental results have been discussed, and it is considered that the high electrical field strength changes the thermal properties of the working fluid.

A preliminary study of oil-polypropylene insulating system

In this paper, the creeping discharge of oil-polypropylene insulating systems has been studied using an experimental model with flowing oil under AC voltage. The AC creeping discharge inception voltage of the oil-polypropylene system has been tested under varied conditions. According to the experimental results, all of the oil temperature, the oil flow rate and the position of polypropylene film can influence the AC creeping discharge inception voltage of the oil-polypropylene system. The AC inception voltage of this system increases along with the increase of oil temperature and oil flow rate. Moreover, the AC inception voltage is higher at a position near to the oil entrance than that at a position far from the oil entrance. Considering the experimental results, a new composite insulating system is put forward for reducing the negative effects of streaming electrification in large power transformers with forced-oil cooling systems.

A suppression method of oil flow electrification on surface of insulating paper

In this paper, the charge accumulation caused by oil flow electrification on the surface of insulating paper was observed, using an oil-paper pipe model. In order to eliminate this accumulation of charges on the surface of insulating paper, a charge generator consisting of polymer films was made in experiments. Results indicate that the negative charges on the surface of the insulating paper were eliminated by the charge generator. Thus, partial discharge due to oil streaming electrification can be suppressed.

Influence of streaming electrification on creeping discharge of oil-paper insulation systems. (Study on dendritic discharge of barrier boards in power transformers)

In this paper, in order to investigate failures due to the dendritic discharge on the surface of barrier boards in power transformers, streaming electrification and its influence on creeping discharge of oil-paper insulation systems have been studied using experimental models. According to the experimental results, the reasons of the failures have been revealed. It has been found that the creeping discharge of oil-paper insulation systems are related to streaming electrification and, as the streaming electrification makes the creeping discharge voltage lower, the creeping discharge path is also influenced.<<ETX>>

Study of influence of corona discharge on streaming electrification of transformer oil

The influence of corona discharge on streaming electrification by flowing transformer oil has been studied by means of a test model. The polarity effect of the charge density in the oil under applied DC voltage has been analyzed. When AC voltage is applied to the needle electrode of the needle-ring electrode system, the charge density in the transformer oil increases with increase of the amplitude of the AC voltage. When DC voltage is applied the polarity effect of the charge density occurs in the transformer oil, that is, when the DC voltage is of positive polarity, the charge density in the oil keeps increasing all the time. However, when the DC voltage is of negative polarity, the charge density in the oil changes from positive polarity at lower DC voltage to negative polarity at higher DC voltage. The test results obtained are useful for the design, manufacture, and operation of large power transformers with forced circulating oil cooling.<<ETX>>