The Research And Development On The Measurement Technology Of Dielectric Loss Of Insulating Oil

With the rapid development of electric power enterprise, the demand on the reliability of electric power system is further more, and the development of on-line insulation monitoring technique has been paid more attention. Oil-filled equipment plays a very important role in power system, and the dielectric loss factor (tgd) is an important parameter to reflect the insulation condition. Therefore, studying the tgd of insulating oil is of important practical meaning.The traditional means and the method based on microcomputer of tgd measurement are narrated in this paper. The digital methods for the measurement (zero-crossing mean, harmonic analysis method and the sine wave parameter method) are discussed in detail, the formulas of each method are derived and the characteristic of them are compared. There maybe have some disturb and error during the measuring, the means to reduce the error and anti-disturb is studied. The bi-directional zero-crossing means is present to reduce the zero drift error. Considering the difficulty consist in the insulating oil dielectric loss measurement, such as the influence of harmonics and the leakiness of frequency spectrum due to the excursion of the fundamental wave in power system, a digital signal processing method which combines the digital filter and correlation is presented. Comparing with the traditional FFT algorithm, the method can avoid the spectrum leakiness and acquire the better accuracy in certain frequency range.Applying the achievement studied, it developed an insulating oil dielectric loss measurement system successfully based on digital signal processor (DSP). The design principle and integer structure of the system is described. It presents the components choosing, the hardware circuit designing and the control procedure flow. It describes the working principle and implementing scheme in each unit, such as signal gathering, signal adjusting, signal sampling, central processing, temperature measuring and controlling, etc. The measure system self-adjust and anti-disturb technique are also studied.In the end of the paper, it gives the calibrate experiment data and the results of contrast experiment with the same kind of domestic instrument, and it proves the measure system has many advantages. The instrument can measure fast, steady, precision and automatically, so it is practical and can be used widely.