Research On On-Line Monitoring For Dielectric Loss Of Capacitive Equipment

The aging and invalidation of high voltage electric power equipments insulation is a slow process. There are many capacitive equipment in the transformer substation. Using the dielectric dissipation factor and capacity as the characteristic parameter to reflect the insulation status and by analyzing the measures, we can make an impersonal evaluation to the equipments' insulation performance. So it can enhance the stability and reliability of insulation system.Firstly in this paper, the important significance of developing the on-line monitoring about the insulation, the technique status actualities and the development trend of this project in the world is narrated. In succession it expounds the physics concept of dielectric dissipation factor and introduces the digital wave analytical method based on the Fourier Transform. By the Fast Fourier Transform the fourier coefficients of the base wave both normative voltage signal and leakage current can be calculated. Then through working out the phase angle difference between them, it is easy to figure out the dielectric dissipation factor. In order to reduce the influence of the leakage effect and the barrier effect and advance the precision of the Fast Fourier Transform, the Windows function is adopted to the sampling serials.Secondly, selecting the distributing system as the structure of the on-line monitoring system, giving the circuit of data acquisition device. It takes charge of sampling data, disposing data and communicating with the topper computer. The DSP CMOS chip TMS320F206 is selected as the CPU. Cooperating with the magnifying circuit, filter circuit and PLL circuit, it is easy to realize the synchronizing and whole periodic sampling. The data communicating between the data sampling unit and the computer adopts RS485 fieldbus. At the same time, the communication protocols and RS485 communication interface are designed. Subsequently, the software for the data-acquisition unit is designed. The software is made up of the main program, A/D sampling data sub-program and the communication sub-program.At last, the paper discusses the anti-jamming problem of the on-line monitoring system and puts forward some anti-jamming measure.