Desenvolvimento e avaliaÃÃo de um escudo polimÃrico para minimizar a quebra de isoladores de vidro por vandalismo em linhas de transmissÃo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Electrical insulators are largely employed in the hot lines to isolate the electricity conductors from the earth and suppor them at the towers. Nowadays, there are several kinds of isolatores for such application. Particularly, the glass insulators are largely employed in Brazil, and it is known to have a long useful life, able to reach more than 40 years. From the constructive point of view, the glass insulator is made of tempered glass and has an excellent dielectric property, and it can treated as a RC electrical circuit. In good environment,dry and without pollution, a glass insulator supports up to 80 kV in air, and not more than 12 kV when it is broken. In the field, the glass insulators are subjected to a vulnerable environment and they are damaged by the vandalism actions. Energy interruption due to the vandalism is a national problem and responsible for a significant number of breakout, reaching a value of around 75%. At the present work, a study was conducted to build and test a system of protection to protect the glass part of insulator from the vandalism, using an insulator material. Among several insulating materials, the polycarbonate was selected based on an engineering procedure. The mechanical resistance of a protection system was evaluated with impact test in the laboratory and ballistic test. High-tension test was conducted with the industrial frequency (60 Hz) and impulse. Furthermore, to evaluate and improve the life of polycarbonate in the field, ultraviolet spectroscopy study and irradiation of glass were conducted. A test of the resistance to impact on the protection system made of polycarbonate of 6 mm in thickness was evaluated with a equipment of impact with pendulum setting. As a result, values of 515 J and 205 J were obtained for a system with and without polycarbonate protection. In the ballistic test, projectiles from Magnum 44, equivalent to a rifle, could break up to 3 glass insulators of the chain when each insulator was protected with a plate of polycarbonate. In terms of test with high tension, the polycarbonate practically did not showed significant influence on the values of disruptive tension. With the industrial frequency test, a chain with 16 glass insulators, with 9 broken insulators and 10 plates of polycabornate installed, found a close values, 500 kV. The policarbonato showed a good dimensional stability after the occurrence of electric discharge in the breakdown test, and it did not allowed the flame ignition. Ultraviolet spectroscopic measurement showed that the UV protection layer on policarbonato is effective to absorb subtantially the harmful rays. On the other hand, the technique to irradiate the soda-lime-silica glass with γ-ray can improve substantially the values of absorption of UV cut-off. As received glass showed the cut-off value at 325 nm. After irradiation, the cut-off value passed to 600 nm. In order to test the effect of temperature on the cut-off value, the glass samples were heated at 70ÂC for seven days. As a result, no significant changes in the values of cut-off was observed. In terms of fading, 30 days after irradiation with γ-ray, no change was observed. Furthermore, an evaluation of cost efective calculation on application of plate of polycarbonate as a protection system, a value of R$ 27,73 was found

ASSUNTO(S)

escudo polimÃrico engenharia mecanica isoladores de vidro linhas de transmissÃo vandalismo

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