Research On On-line Monitoring Of The Insulation Condition Of Transformer Bushing

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 dielectric loss factor is a significant parameter reflecting the condition of capacitive equipment, therefore, the on-line insulation monitoring of tan5 is especially important.In this dissertation/paper, the high accuracy measurement of tanδ, preprocessing of the on-line data, analysis of the data regularity and application of the novel diagnosis approaches for capacitive equipments are investigated, 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.In hardware design, the sampling unit (SU) based the voltage-divided capacitor sampling is developed to obtain leakage current signals, and an RS-485 field bus is applied to realize the distributed data sampling. The device is developed with the TMS320F28335 (DSP) acting as the core of data processing and logic controlling, including signal conditioning circuit, communication unit, system power, clock circuit, expanded RAM, etc.As for the software design, the flowing function is realized, including data sampling, data processing, Full-wave Fourier approach, fault diagnosis functions and so on, each keeps relative independence, which is easy for the maintenance and update. B/S mode is applied to realize insulation information inquiry system in WEB style.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 re analyzed by comparing the theoretical value with the two calculating method results, and he dielectric loss factor of different experimental model is monitored. The experimental results show that the device can accurately measure the dielectric loss factor.