The insulated capacity of the electric equipments has great effect on the security of electric power. From 70 years of twenty century, the measurement of dielectric loss on line had been taken widely to monitor the insulated conditions of electric equipments, which made a remarkable progress against the electric accidents arose by the problems of insulation. However, many of the measurement systems lose control even disable due to the shortcomings of the measurement methods. This dissertation introduces and analies detailedly several main measurement methods at present such as fundmental wave analysis, zero-crossing monitoring and integral monitoring, and elaborates the emerged demerits of these methods and reasons of bringing them when running on the spot. After studying the deficiency of above method a new idea was put forward to design the measurement system based on analog-digital multiplication optimization correlative filter(OCF) in this dissertation. And in the third chapter, the principle and the characteristic of analog-digital multiplication OCF are described in detail. At the same time, the effect of A/D quantizing error and modulating noise on analog-digital multiplication OCF is also analyzed theoretically, and the result of this analysis is satisfying. This dissertation also designs the hardware circuits of measurement system based on the theory of analog-digital multiplication OCF and expounds the elements of this system later. Incidentally, in the forth chapter, several difficulties such as choice and compensation of current sensor, the instrument design of measurement on-line and distant transmission are described particularly. At last, an electrocircuit of phase shift was made up by resistances and capacitances to vertify the angle resolution and linearity of the measurement system designed, and the results of the experiment were listed. The results indicate the angle resolution of the system is able to achieve 0.0002(rad) and the linearity is perfect. Therefore, author believes this method can be used widely on the measurement system of dielectric loss in electric power department.

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