Impulse performance of a tower for transmission at 1300 kV

As part of a programme of research on ultrahigh voltage (u.h.v.) lines, the impulse performance of a rig simulating the critical portion of a 1300 kV system transmission tower with 9.3 m clearance has been determined. Outcomes include the following: The minimum strength corresponds to a mean field of 230 kV m¿1, and occurs with positive polarity on the conductor and with a front time of about 350 ¿s. The minimum withstand level corresponds to 1.8 p.u. The time lags before breakdowns are given over the range of crest times 50¿750 ¿s. The effects of small changes in the dimensions of the rig were determined, and the performance was found to be relatively insensitive to these. A ratio of rig conductor length to gap spacing of 2.5:1 is shown to be adequate. Tests of the switching-impulse performance of the window were made over a period of one year, in a considerable variety of weather conditions, and negligible variations were found.