Research On Measuring Method Of Dielectric Loss And On-line Monitoring Terminal For Phase-shifting Capacitors

With the rapid development of electric power enterprise,the demand on the reliability of electric power system is further more,and the development of insulation monitoring technique has been paid more attention.Phase-shifting capacitor is an important reactive compensation devices, it has been widely used because of its low-cost unit capacity, small active power loss (approximately 0.3%-0.5% of the rated capacity ) and simple operation and maintenance.Therefore, the the research of dielectric loss factor online monitoring techniques phase-shifting capacitor has a high degree of theoretical significance and a wide range of practical value.The paper pointed out the main factors influencing phase-shifting capacitor dielectric loss, higher-order Sine fitting algorithm,correlation function algorithm, fundamental harmonic separation algorithm,and harmonic analysis method ,and points out. advantages and disadvantages of these methods. Harmonic analysis method requires synchronous sampling for measurement signals.However, it's difficult to achieve complete synchronous sampling for the influence of power frequency fluctuation.It's the reason of spectrum leakage and fence effect. The paper has an in-depth study of the cause of spectrum leakage and fence effect,analysis the role of weighted, according to the characteristics of cosine window, puts forward the method of harmonic analysis method based on cosine windowing in dielectric loss angle measurement,and gives the detailed derivation process. Compared with windowed interpolated harmonic analysis method, the method without interpolated is easy to realization based on DSP. The measurement error of harmonic analysis method based on hanning-windowed interpolated and hanning-windowed are compared through MATLAB simulation. The simulation results show that the harmonic analysis method based on hanning-windowed possesses good accuracy, real-timing and anti- interference characteristics.On the basis of the algorithm, an online monitoring terminal for phase-shifting capacitor based on advanced DSP technology and real-time operating systemμC/OS-Ⅱwas designed, the general schematic of the hardware design was given., and the current of the main control module, the data acquisition module and the man-machine interactive module was detailed designed and analyzed.