Research On Electronic Voltage Transformers Based On Detecting Current Of Capacitor And Its Transient Characteristic

With continuous increase of power transmission capacity, strict high power voltage and intelligence requirements in power system monitoring, control and protection, traditional electromagnetic voltage transformer and capacitor voltage transformer can not meet the requirements of digital development and electric power system automation due to the unavoidable problems presented by limitations in sense mechanisms. Therefore, electronic transformer based on optical fiber technology, microelectronics and computer technology, is a hot topic at home and abroad nowadays.Based on the analysis and comparison of several existing Electronic Voltage Transformers, after integrating advantages and disadvantages of optical voltage transformer and partial pressure capacitor voltage transformer, a new electronic voltage transformer is proposed by analyzing principle of capacitive current testing. This new EVT characterizes high voltage capacitor as voltage-current converter and high-precision transformer device as current sensor. Firstly, an in-depth analysis of its voltage sensing principle is investigated and an overall program design of testing capacitor current-mode EVT is completed. Secondly, an equivalent circuit of primary voltage sensor is established with error expression, theoretical analysis is carried out from many aspects such as grid frequency, ambient temperature changes and stray capacitance. Finally, analysis and simulation are given about transient'performance of electrical capacitance current EVT which shows that transient process, better than CEVT, is very short. Based on theoretical analysis, an 110kV electronic voltage transformer prototype with capacitive current detection is developed, and a series of tests were implemented in the laboratory and Hunan Zhuzhou Electric Co., Ltd. The results indicates that this newly transformer meets the requirement of 0.2-level measurement and 3P-level protection with perfect transient performance.In this new EVT, because direct current signal is transmitted in the form of between high side and control room without any electrical/optical conversion, dealing circuit does not exist in high voltage side and there is no high side power supply design problem, it not only ensures transmission reliability, simplifies signal processing circuit, but also improves the reliability of transformer a lot with a good practical extension and application.