| The Metal ZnO Arrester(MOA) are important over-voltage protection device. They are widely used in electric power system due to their excellent nonlinear and high surge absorbing capability. But some of MOA will deteriorate gradually under operating voltage and some of them will be moistenend because of structure problems. The two faults can lead to increasing of leakage current of the arresters, even to accident of power system when they are severe. Resistive first-harmonic current and high-harmonic current are the two fault eigenvector reflecting MOA's performance. Mesurement cann't reflect MOA's real state because of the effect of interphase interference and harmonics, including interharmonics. a MOA's model monitoring on-line is established to eliminating the effect of the two interference sources.In this paper, based on former production, the effects of interphase interference and harmonics to MOA's resistive leakage current are simulinked and validated by using Matlab. Because of wide using of many electron devices , The effects of interharmonics should not be ignored. The simulation has been made to find a few interharmonics lead to biggish errors during detecting MOA.In this paper, based on harmonics analytic method and vector analytic method, voltage and current figures are plot on first-harmonic and third-harmonic and fifth-harmonic, eliminating effects of interphase interference and harmonics, including interharmonics. MOA's model monitoring on-line is then built. By using the model, the two fault eigenvector can be figured during MOA's operation.Finally, this paper demonstrates the model on theory by using an example and polyfit average U-I characteristic curve of MOA with the results. By comparing with the average U-I characteristic curve of the example, we find that the model is feasible on theory and we can bring it into the network system monitoring on-line. We are sure that the model will play a great role in the condition based maintenance.
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