Calculation of Ninimum Safety Distances for Live-Line Mintenance - A Statistical Mehod Applied to 765 kV AC Itaipu Lines
This paper presents a statistical method to calculate the miniumm safety distance for live-line maintenance. The method takes into account the complexity of the tower gap configuration and the presence of the lineman working at the line potential. It includes the inherent dispersion of the dieletric characteristics of the air gaps such as the probability of flashover and the tirnes-to-flashover. Laboratory tests were also performed to corroborate the results of the study, checking not only the performance of the various live-line tools but also the effectiveness of the by-passing insulators protective device and the occurrence of broken insulators in the string.
Behavior of Long Insulator Strings in Dry Conditions
The behavior of long insulator strings under switching and lightning impulses and AC voltage is studied up to 750 kV. With increasing short-circuit currents, it is necessary to fix the spark between specially designed electrodes in order to preserve other metallic pieces from the thermal effects of the arc.
Influence of Air Density on Electrical Strength of Transmission Line Insulation
Flashover tests were conducted at the Leadville EHV Test Facility of the Public Service Company of Colorado and Project EHV at Pittsfield, Mass., to obtain comparative data to evaluate the influence of air density on switching surge and impulse flashover strength of transmission line insulation. The tests showed that negative polarity flashover voltages are greater than those of positive polarity. Therefore, positive polarity will be the critical requirement for transmission line design for switching surge duty.