It is shown by test results that the breakdown voltage of insulating material under high field decreases with the increase of free-radical concentration. The concentration of free-radical can be taken as a characteristic parameter to measure the extent of electrical damage in insulating material. In order to enhance the stability of insulating material under high stress, the free-radical scavengers are added into several test samples in this paper. Test results show that the breakdown strength of polyethylene thin plate aged under corona and the initiation voltage of treeing in polyethylene increase greatly. The gassing behaviours of transformer oil under high field can also be improved. Finally the inhibition mechanism of free-radical scavenger is discussed.
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