| With the development of the national economy, electric power is more and more required by different sectors. Electric power networks have been enlarged steadily. How to assure the safety operation has been becoming the key issue of the electric power system. Therefore, an applicable detection method should be adopted to know well the actual operating situations of the networks' equipments, so that they can be managed properly. The insulation failure is the main accident of networks' equipments, so their detection is of great significance. As for the plastic power cables widely used in power systems, the variable frequency series resonant test is a comparatively ideal detection measure, items of which when carried out in field normally include voltage-withstand and dissipation factor measurement, the latter's measuring results may reflect the integral situation of the cable insulation, so its accurate measurement is very important.The author has developed a dissipation factor measuring system using the variable frequency series resonant voltage. This system has adopted quasi-synchronous sampling harmonic analysis method, and related theoretical deduction and computer-aided analysis for the method have been completed. On this basis, the hardware, based on a single chip computer and used for the measuring system, has been manufactured, and the virtual device system, based on a personal computer, also constructed. Furthermore, the corresponding software for them has been programmed.By the computer-aided analysis, the paper finds that this method, using the quasi-synchronous sampling harmonic analysis to measure the dissipation factor, has the advantages of high accuracy and better anti-jamming characters. This is also verified by the practical measurement results which indicate that the measuring precision of the manufactured measuring system is better than 1(10-4, and it satisfies fully the requirements of the dissipation factor measurement in field.
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