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.
Development of new technology to access the energized phase by walking along the strain string on 500 kV transmission lines and substations
The maintenance of 500 kV transmission lines and substations requires a great amount of manual services on its insulator strain strings, conductors and hardware. The conventional method of gaining access to the hot end of strings uses a long insulated ladder (longer than 6 m), numerous accessories, which involves great effort and the work of many electricians. This paper looks into a method developed by ELETRONORTE to access the energized parts of transmission lines and substations by walking directly on the insulator strain string without having to use an insulated ladder. The results of the experiment show that this method can meet safety standards. This method was further experimented on suspension strings. However, the outcome of such an experiment led us not to recommend its use.
How the switching-surge family affects line insulation
Full-scale switching-surge flashover tests were made at an outdoor laboratory that covered a range of V-string and vertical insulator string lengths, tower sizes, and waveshapes. The response of line insulation to these surges was explored. Effects of precipitation and preceding trapped charge (bias voltage) were investigated, along with rod-to-ground and conductor-to-ground flashover. Estimated performance curves of EHV transmission line structures indicate economic justification for switching-surge limiting apparatus.