The Research Of Substation Capacitor Device Dielectric Loss Online Monitoring

Normal safe operation of high voltage related to national defense, economic and the healthy and reliable development of livelihood, and high voltage for normal operation of electrical equipment play a key role in insulation. Therefore, the insulation of electrical equipment to monitor the implementation of technological research is very urgent and necessary.The early insulation detection of electrical equipment uses the after accident repair system.That is, equipment insulation damaged firstly, then the total power is turned off for maintenance, or use another one but the same device instead, and then repair the damaged one. The so-called preventive maintenance on electrical equipment is to do the preventive detection tests by regular power outages, according to test results to determine whether the insulation system need the necessary repair or replacement.Preventive maintenance system compared with the accident repair is to be more scientific and advanced in the early detection of hidden power, which has also played a good role in preventing accidents and ensuring safety in power supply .It has a high level of reliability, security, economic and social benefits, but there are obvious flaws, such as power failure diagnosis, long period, poor sensitivity,etc.Because of a variety of limitations of preventive maintenance , the current system of monitoring the insulation of electrical equipment has been from the predictability of periodic preventive direction to the predictable direction, that is, A new monitoring technology measuring technology has developed on the basis of live measurement - online monitoring, in order to reduce maintenance costs and the adverse effects of power failure. The introducing online monitoring technology to the power state of repair makes real-time monitoring to capacitive equipment as early as possible to find the insulation malfunction, besides, it can save a lot of manpower and material resources and assurance the security of grid operation with more advanced technology, more reasonable economic.In summary, a certain degree of technical difficulty of application level with transmission and distribution equipment online monitoring and diagnosis system in strong electromagnetic interference environment, further research and development must be made. So, the direction,the purpose and contents of the study was sketched up, for the research of live monitoring of tanδinsulation parameters .The key of on-line monitoring technology is improving the stability, accuracy, intelligence, product level, while the accuracy and stability of the measurement on dissipation factor of electrical equipment has always been a difficult and important thing. This paper summarized the tanδmeasurement technique of the electrical equipment at home and abroad based, adopting fourier transform for harmonic analysis, calculating by the sensors of the measured device operating voltage signal and leakage current signal fundamental Fourier coefficients by fast fourier transformation , and further calculating the phase difference between the two, in order to estimate dielectric loss factor. This paper improved the modified FFT algorithm is to improve the accuracy of dielectric loss factor tanδ, enhancing the measurement accuracy and stability of on-line monitoring system from the engineering point of view ., the hardware of ADS7818 ADC chip used to run on the DUT voltage signal and the leakage current signal acquisition, two acquisition signals transfer the data through the serial port, which together with display module; software includes the main program module, data acquisition modules, communications module, FFT data processing module and display module.First, the hardware designThe design of the hardware system is based on ARM7 LPC2136 chip processing system as the core control, coordinating data acquisition circuit, amplifier circuit, synchronous sampling circuit and the external circuit (LCD liquid crystal display, etc.) work. The current and voltage signals of the tested products were transformed by the isolation, amplification and other pre-processed into the A / D conversion unit for analog-digital conversion; A / D converted data ,then, sent to the MCU for FFT operation processing, computational results can be liquid crystal display to achieve human-computer interaction, or complete the tanδvalue computation by serial communication. The main difficulty lying in the hardware system is capturing the true leakage current of electrical equipment at the end of the weak signal screen. This made stringent requirements for the sensor, and the sensor signal becomes extremely important coupling and amplification; In addition, the monitoring system the necessary signal and various noise signals are mixed there, which requires pre-acquisition circuit must have a high level of interference capacity and monitoring of the sensitivity.Second, software designOn-line monitoring device hardware complete the current, voltage signal acquisition, amplification, A / D conversion and display functions, but to complete all the tasks and the achievement of established goals, not only depends on the hardware design, but also the appropriate software to achieve the overall measurement control, data acquisition and processing, data communications and display functions. This chapter has been designed on the basis of good hardware, then the whole measuring system software is planned and description of the functional structure, while the use of online testing device design is completed, the field conditions in the simulation of the entire system of hardware and software debugging, and the corresponding data is obtained by data analysis. Capacitance devices to the software part of the line monitoring system consists of five modules , including the main program module, communication module, data acquisition module, FFT data processing module and display module.With the development of online monitoring technology, insulation monitoring and fault diagnosis technology can be combined and harmonic analysis in the diagnosis can be based on the data, the results for a deeper analysis and judgments. This digital measurement method, that is, by monitoring equipment on the voltage and current signal acquisition, storage and processing, which reflected the situation of the insulation dielectric loss factor and capacitance, and dielectric loss factor has been applied in on-line monitoring . It will convert the extracting sensor voltage, current waveform signal by A / D into discrete digital content, and then use computer technology to store and analyze. Finally, Frequency domain analysis is made with some mathematical analysis (eg FFT), then voltage and current signals fundamental amplitude and phase angle will be obtained, Dielectric Loss Factor and Capacitance of DUT will be obtained, too. Up to now, this is one of the most promising method for the measurement of dielectric loss factor.The achievement of whole issue solve the application software and hardware problems of substation capacitor equipment for on-line monitoring of design application ,which meets the design requirements of stability and accuracy, and new online monitoring technology is put forward creatively.