| With the development of automation technology, the maintenmace method of high voltage devices used in the electric power system is evolvementing. Condition-based maintenance, as an advanced thchnology, will be widely used in the near future. The data acquired by on-line monitoring system is the basis of condition-based maintenance. To actualize condition-based maintenance for Metal-Oxide Arrestor (MOA), which is a kind of important device used to restrain overvoltage in the electric power system, the research of on-line monitoring of MOA is important and necessary.According to simplified equivalent circuit of ZnO element, the characteristic of leakage current of MOA and some disturb factors are discussed. Then the paper deeply analyzed the existing methods used in MOA monitoring. On account of the rich harmonic voltage exisiting in electric railway system, using basic resistance wave current as a monitoring element is more reliable than using third harmonic wave current. With digital waveform analysis method the basic resistance wave current can be easily got. As for the structure of monitoring system, the distributed system is more suitale for MOA monitoring than centralized system. Based on the conclusion mentioned above, a distributed online-monitoring scheme using control area network and digital siginal processor technology is designed. Chooseing TMS320LF2407ADSP as the system processor, the hardware platform of the local monitoring unit is designed carefully, especially the leakage current signal getting circuit and the primary-secondary isolation circuit. Also the printed circuit board is accomplished and debugged. Based on the hardware platform, the flow chart of the main programme and module programme are given in the paper. Using CAN2.0B protocol, the application layer communication protocol between local units and center unit is also designed. In the end, some conclusions and expectations are made.
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