Effect of de-aeration on the electrical breakdown characteristics of water

In the study of electrical breakdown in liquids, attention is typically paid to the contamination of the liquid, and particularly ionic impurities. However, the purity of the sample is also compromised by dissolved gases as well as ionically charged species. To test the effect of de-aeration, water, a highly gas-soluble liquid, was chosen as the test liquid. The delay time to breakdown was measured under the action of a rectangular pulse of 50 kV peak amplitude, 4 μs duration and 250 ns risetime to planar electrodes. The de-aeration apparatus and a test to verify the complete degassing of the water is described. The breakdown properties are strongly affected by the presence of dissolved air: the air saturated water takes significantly longer to breakdown. The experiment suggests that the breakdown strength in some liquids may be raised by careful degassing