Research On Internal Pressure Estimation And Lifetime Evaluation Of Vacuum Switches

Vacuum switches are important control and protect equipments in electrical power system. Vacuum interrupters, which supply the vacuum switches with high quality vacuum environment for insulation and arc extinction, are key components of vacuum switches. According to the research results and practical experiences, ensuring the internal pressure of vacuum interrupter below 1.33×10^-2 Pa is the prerequisite to realize reliability of vacuum switches. However, the vacuum degree of vacuum switches would degrades as the time of operation and storage goes on, and exists a limited vacuum lifetime. Implementing internal pressure estimation in vacuum switches and ensuring that they are operating in the vacuum lifetime, are important parts of overhaul and maintenance of vacuum switches. In order to resolve the problem in current internal pressure estimation techniques, an internal pressure estimation and lifetime evaluation system scheme based on high frequency (HF) pulse current method and grey forecasting model is proposed in this paper. This paper elaborates the design and application of the system.In terms of the responsive relation between the peak value of HF pulse current that superimposed on the prebreakdown current between the electrodes of vacuum switches, HF pulse current method carries out internal pressure estimation by means of measuring the peak value. The method can measure the vacuum degree of vacuum interrupter, and offer a quantitative result with simplified operations and high sensitivity. As a result, HF pulse current method becomes an effective method to be applied in field. Combining with the forecasting method basing on grey system theory, this paper develops an internal pressure estimation and lifetime evaluation system by microprocessor control unit (MCU) and personal computer (PC), and realizes the internal pressure estimation and vacuum lifetime evaluation. The foundation of this system provides a good reference to promote the standardization and intelligence of the overhaul and maintenance of vacuum switches.This paper develops a special HF pulse power supply for internal pressure estimation, which achieves the output of HF-HV sinusoidal pulse wave whose frequency and amplitude can be modified respectively, and meets the design requirements according to the results of Simulink simulation and practical experiments. With the help of AT89S52, this paper designs an I²C serial bus based signal detection system for peak value signal acquisition of HF pulse currents, which communicates with the upper computer by asynchronous serial communication for uploading the data. In the upper computer, a human computer interface is developed by Matlab software, whose functions are to do some computation and graphic display, such as calibrating the relation curve of vacuum degree and peak value of HF pulse currents, vacuum degree computation, and vacuum lifetime evaluation analysis basing on grey forecasting model as well as making relative suggestions. All these above compose the internal pressure estimation and lifetime evaluation system.Related experiments and simulation analysis indicate the feasibility of the scheme, which provide some useful experiences and the reference for the further research of internal pressure estimation and lifetime evaluation. At last, this paper concludes the research and points out the development direction.