| According to the characteristics and requirements of dielectric loss measurement of transformer bushing, this paper presented the principles and solutions using method of software analysis and hardware processing to on-line monitor dielectric loss of transformer bushing. Designed and executed hardware circuit and monitoring software. Installation, test and practical measurements of the whole system also have been implemented. Studied the various methods of digital monitoring dielectric loss for transformer bushes: harmonic analysis method. Sine-shape parameters method and integration method, states the principles of the three methods, its computational formula has been inferred and compared. Among them, harmonic analysis method was used to test practically both in lab and on site. Results have showed its high stability and accuracy. The selection of signal sensor is the key to implement hardware circuit. It designed signal program-controlled amplifying circuit, frequency tricking circuit, data sampling and keeping circuit. The choose of 12 bits high accuracy A/D integrated data sampling card made program simply. high flexible and expandable On hardware and soft ware, good anti-disturbances measures has been adapted considering environmental factors such as, high altitude, great temperature different .the anti-disturbances ability was enhanced. Cooperation of hardware and software make hardware circuit simple and little effect of zero point shifting, and easy for software system to be modified. Practical operation analysis has showed that Dielectric loss monitoring system is reasonable and reliable and can be used to diagnose their insulation state of transformer bushing. This system in this paper has been on site tested. It has showed high efficiency, stability and accuracy to on line monitor dielectric loss, leaking current and equivalent capacitance for transformer bushing.
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