Influence of internal vacua and ionization on the life of paper insulated high-tension cables

At the end of the year 1926 the High-Voltage Laboratory of the Electrotechnical Institute in Leningrad undertook an experimental research in order to study the influence of internal vacua and ionization on the life duration of paper insulated high-voltage cables, as well as to clear up the conditions under which such vacua may occur. W. A. Del Mar
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drew attention to the importance of internal vacua in high-voltage cables and pointed out the three probable causes of their appearance, namely: 1. Temperature changes after installation of the cable, which produce a change of volume of air and oil in the cable in view of the different thermal expansion coefficient of lead and insulation of the cable. 2. Residual deformations, occurring when the cable is put on a reel and taken off it afterwards. 3. Changes in chemical structure in the impregnating compound under the influence of ionized air, which produce a decrease of volume of the compound. The aim of the research was to clear up the part of the above mentioned causes in the formation of internal vacua, then to determine the values of those vacua and the decrease of life duration of the cable under the influence of the latter. The research is not yet finished and only its preliminary results are reported on these pages.