24 / 2018-08-02 18:45:28

Research on low temperature insulation characteristics of oil-immersed current transformer

current transformer , low temperature characteristic, frequency domain dielectric response，partial discharge, power frequency loss

Current transformer is an important electrical equipment in the power grid. Its operation state directly determines the security and stability of the power grid. At present, oil-immersed inverted current transformer is widely used in power system because of its many advantages. With the increasing number of oil-immersed inverted current transformers put into operation in the power grid, the number of faults occurring is also increasing. Common faults include main insulation breakdown, capacitor plate breaking, metal expander roof breaking etc. Therefore, it is particularly important to evaluate the insulation aging state of transformers. There are three kinds of evaluation of the traditional insulation aging state. Such as, analysis of dissolved gas in oil, content of furfural in oil and degree of polymerization of insulating paper. The above three methods can evaluate the insulation aging of the current transformer, but the operation is difficult, and the internal insulation of the equipment may be damaged to some extent. Considering the shortcomings of the above methods in evaluate the aging state of insulation, in recent years, the frequency domain dielectric spectroscopy based on dielectric response technology has developed rapidly. As a non-destructive testing method, the method has the advantages of strong anti-interference ability and rich information, it has been used by many researchers to evaluate and diagnose the aging state of electrical equipment or insulation materials. Oil-paper insulation is the main insulation of oil-immersed inverted current transformer. Researchers are mainly focused on high temperature dielectric properties. The reliability and life of oil-paper insulation are evaluated by accelerated thermal aging test. However, many regions of the world are in the extreme cold zone, electric power equipment will face the test of cold environment. Therefore, it is necessary to study the low temperature characteristics of oil-paper insulation. In this paper, the oil-immersed inverted current transformer was respectively carried out frequency domain dielectric spectrum test, partial discharge test and power frequency capacitance loss factor test under low temperature 0℃-60℃. The test results show that, at different temperatures, the frequency domain dielectric spectrum of the oil-immersed inverted current transformer decreases first and then rise. When the temperature dropped to below 40℃, the change of frequency domain dielectric spectrum in the low frequency difference is very small, almost overlap phenomenon. The partial discharge signal was produced under -45℃. The power frequency loss factor of oil-immersed inverted current transformer increases with the decrease of test temperature, and the change rate is from slow to fast, and the capacitance decrease uniformly with the reduce of temperature. According to the test results, the laws of dielectric spectrum, partial discharge, power frequency loss factor and electric capacity change with temperature at low temperature are analyzed from the perspective of dielectric physics theory. The test results of this paper have certain reference value to study the low temperature characteristics of oil-paper insulated power equipment.