Study On Embedded Online Monitoring System For Power System Overvoltage Based On Leakage Current Of Capacitive Equipment

It is very effective on overvoltage accident analysis of power grid and improvement of insulation coordination for power system by online monitoring power system overvoltage to obtain waveform and characteristic parameters. Most of the existing monitoring systems for overvoltage adopt voltage divider to get signal based on centralized monitoring. But, because of the divider's self-deficiencies, its application under the higher voltage grade is limited. And long distance transmission of high frequency analog signal using coaxial cable will result in signal attenuation and distortion so as to systems have poor disturbance rejection. Aimed to solve these problems, in this thesis, the key technologies of overvoltage online monitoring system are researched deeply and a new type of embedded monitoring system for power system overvoltage based on leakage current of capacitive equipment is developed.The system based on distributed monitoring is mainly composed of voltage transducer, embedded monitoring device and background monitoring computer. Transducer which is designed according to differential-integral measuring principle has fine characteristic of electric safety with small dimension, and doesn't affect power grid security. Embedded monitoring device installed near to voltage sensors to capture and store overvoltage signal with high speed can improve system performance of anti-interference. Ethernet communication is accomplished between embedded device and background monitoring computer with high transmission rate and reliability.The structure and basic principle of voltage transducer and the influencing factors on transducer is introduced in detail in the paper. The modularity idea was adopted in the design of hardware of embedded device which is made up of signal conditioning module, data acquisition module and monitoring module. Data acquisition unit employs the CPLD as the main control chip to realize data acquisition with high speed. Monitoring unit adopts high performance ARM chip as the CPU on which the CF card memory, Ethernet and real-time clock circuit are extended to accomplish data storage to CF card and network transmission. The components and implementation principle of function modules of hardware software and hardware of embedded device are described in detail. Based on ARM hardware platform the embedded real time operation systemμC/OS-II and TCP/IP protocol stack LwIP are transplanted and the corresponding software is programmed. The online monitoring software idea and flowchart are introduced in detail. At last, performance tests of monitoring system are accomplished in laboratory. The results show that the transducer can reveal the internal overvoltage of high voltage power network with fine precision and linearity, the embedded monitoring data acquisition control works fine and can accomplish the data communication with high transmission rate. The online monitoring system for power system overvoltage based on embedded technology works stably and reliably and can satisfy the requirements of overvoltage monitoring in power grid.