Development On On-Line Insulation Monitor Of Capacitive Equipment Based On DSP Chip

Along with the development of the power system to ultrahigh voltage and large capacity, it is highly important to monitor the insulation of device in order to ensure the safe operation of high-voltage electrical equipment. The on-line insulation monitoring is a new technology that the insulation of device is real-timely monitored under the operating voltage making up for the lack of the preventive trial. Owing to a large proportion using in substations and power plants and, simultaneously, the dielectric loss factor is a significant parameter reflecting the condition of capacitive equipment, therefore, the on-line insulation monitoring of tanδis especially important.In this paper, an on-line insulation monitor based on DSP is developed to measure the dielectric loss factor more accurately. Because of the lack of the harmonic analytical approach, the modified harmonic analytical approach is proposed to calculate the dielectric loss factor. The windowed interpolation algorithm is involved to amend the difference of the phase measurement caused by the frequency fluctuation. Simultaneously, analytical transformation structured by the Hilbert Transformation is used to counteract the negative-frequency. In addition, a FIR digital filter is designed to wipe off the interference signal. Due to the dissatisfying performance of traditional insulation diagnosis based on the relative comparison method, the fuzzy diagnosis method is involved to analyze the insulation state of capacitive equipment.Taking into account of the environmental factors and the interference of the device circuit of its own, the device is developed with the TMS320F2812 (DSP) acting as the core of data processing and logic controlling. The device is composed of system power, signal conditioning circuit, expanded RAM, etc. As for the software, the flowing function is realized, including data sampling, analytical filtering, digital low-pass filtering, Full-wave Fourier approach, window function amending the frequency fluctuation, fault diagnosis functions and so on.Finally, the experiment model of the capacitive equipment is built to validate whether the designed device can effectively monitor the capacitive equipment's dielectric loss factor online. The performance of the basic approach and the modified harmonic analysis approach are analyzed by comparing the theoretical value with the two calculating method results, and the dielectric loss factor of different experimental model is monitored. The experimental results show that the device can accurately measure the dielectric loss factor.