| 摘要 |
<p>A high dc voltage on which an ac voltage of a predetermined amplitude to superimposed is applied to the cable. The amplitude can be between 0.5 and 10 percent, e.g. between 1 and 5 percent of the dc voltage. In one method, the frequency of the ac voltage is not higher than 50 Hz, e.g. between 1 and 20 Hz. An ac and a dc voltage generator are pref. used in series, and the ac generator has an inductive device with an ohmic resistance less than that of the generator and with a resistance lower than that of the generator. The ac voltage can be applied during use of the able or during a period corresponding to that during which the cable is used. Alternative time periods, continuous or at intervals are specified.</p> |
