The Study On The On-line Dielectric Loss Tangent Monitoring Technique Of Capacitive-Type Equipment

The on-line insulation monitoring of power apparatus is very important to guarantee the safety of power delivery, find insulation faults in time and increase the reliability of power supply. With the development of electrical engineering and the further demand on the service reliability of power systems, the on-line insulation monitoring has been put more value on. high voltage capacitive-type equipment plays a very important role in power systems, and dielectric loss tangent (tan5) is an important parameter to reflect its insulation condition. Therefore, the study on the on-line tan5 monitoring of high voltage capacitive-type equipment has practical values.The measured results are greatly influenced by the property of the wave sampling system. Two parameters: sampling accuracy and sampling frequency, which are the most important ones for sampling system, are discussed deeply. The way how these two parameters affect the performance of sampling system is concluded. On the basis of these, the principle and the method of determining the optimal sampling parameters are presented.For the sake of assuring the accuracy of the measured results of tan8 better, digital filtering algorithm is introduced to the measurement of tan8. A kind of FIR digital filter is designed, simulation indicates that the designed filer has satisfying effect.Considering the difficulties of on-line monitoring research of the high voltage capacitive-type equipment local and overseas, such as the excursion of the fundamental wave of power system, the existence of the harmonics and the electromagnetic interference, Windows and Interpolation Fast Fourier Transform algorithm is applied to the measurement of tan. With this method, the spectrum leakage can be avoided more effectively than Fast Fourier Transform algorithm and better accuracy can be assured in certain frequency range.On the basis of the study of the theories above, a kind of on-line tan 5 monitoring system of high voltage capacitive-type equipment is developed which follows the principles of high accuracy, strong utility, low cost and high reliability. During the designing, every step is analyzed theoretically and parts of steps are simulated, the design of the monitoring system obtains anticipated purpose.