International comparison of impulse-voltage tests

A number of impulse-voltage tests have been made under the auspices of the International Electrotechnical Commission in certain high-voltage laboratories in Europe. The tests were devised to ascertain the extent of agreement which can be reached on the measurement of impulse voltages at the present time, and to act as a guide to the Commission in framing a specification for impulse-voltage testing of electrical apparatus. The dispersion of results obtained on the measurement of the sparkover voltage of a simple test gap in eight European laboratories is at present very wide, being as great as ± 8%, though good agreement exists between the average values so obtained and the average values for similar tests recently published in the U.S.A. The tests on line insulators also reveal a wide diversity of results, but it has been established that insulators which have successfully withstood power-frequency voltage tests may sometimes be fractured by impulse voltages, and sufficient information is now available to warrant the introduction of impulse-voltage tests on line insulators by the I.E.C.