Translated Abstract
Because of high electric strength and good physical and chemical properties，SF6 gas is the most ideal insulation and arcing medium by far. Its electric strength is 2.5 times of the air and arcing ability is more than 100 times of the air.Therefore, SF6 is widely used in electric equipment such as circuit breaker and composite electrical equipment (GIS) of 35kV and above voltage grade. A large number of studies have shown that more frequent discharge occurs on normal operating electrical equipment, which can cause gas decomposition in the equipment and generate new derivatives. In the long term, the concentration of derivatives will increase, leading to a decline of the insulating capacity of the gas, and accelerating the aging and corrosion to the metal surface, resulting in safety hazards. The chemical properties of SF6 gas is stable,whose decomposition temperature is above 500℃. In the case of normal operation, breakdown products are very less. But when electric arc, spark and corona discharge or overheating fault occur, it can cause a complex decomposition of the SF6 gas and generate a variety of toxic gases, In this thesis, a platform to detect partial discharge and discharge gas component detection device in SF6 by pulse current method is constructed. The partial discharge detection used RC impedance, whose main effect is to acquire the current signal of partial discharge and to suppress low and power frequency signal. Gas chromatography detection used gas discharge components. The process of chromatography analysis and the components of chromatography are described in detail in thesis..
The results showed that: the initial voltage of partial discharge under the needle plate electrode is 20kv while 15kv under free metal particles.Pulse discharge occurs mainly in the negative half cycle of power frequency voltage amplitude under needle plate electrode, while near the positive half cycle amplitude only a pulse discharge occurred. The discharge pulse decay quickly under free metal particles. After the highest peak amplitude is often followed by a number of very low amplitude equal and mutual overlapping pulses. But from the appearance, it looks like trapezoid shape, trapezoidal small fluctuations on the bottom, then fully attenuation.As can be seen from the PRPD spectrum chart, under lower voltage, the discharge of free metal particles are mainly concentrated in the positive half cycle, with less negative half cycle. In the contrast of the gas composition of arc discharge and partial discharge, thesis get the following conclusion: when the device produces the larger energy fault such as arc discharge, it mainly produces SOF2, SO2, H2S and HF, When the small partial discharge occur, the main gas is SO2F2 and HF. For the large energy discharge of the needle plate arc, the SOF2, H2S, and HF from its discharge is more than that of the free particle, and its decomposition gas increases faster. In the case of partial discharge with small energy, the SO2F2 is more. It provides a theoretical basis for comparison of gas discharge components in the field. In thesis, the fault diagnosis process based on the test results is presented, and the process method is verified by two examples.
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