On Increasing the Reliability of Line Circuit Breakers when Disconnecting Overhead Power Lines in Conditions of Slightly Negative Ambient Temperatures

At slightly negative ambient temperatures, snow or ice bridges form on the surface of line circuit breaker porcelain insulators, leading to a significant decrease in the electrical strength of the insulators. In the case of a longitudinal breakdown of the external insulation of one of the arc-extinguishing chambers, the full voltage is applied to the remaining chambers, which can lead to their breakdown (along the surface of the external insulation, between contacts, or as a result of the breakdown of voltage capacitive dividers). Disconnection of an overhead line by a line circuit breaker is accompanied by a transient low-frequency process, in which the overvoltage ratio at the breaker contacts can reach 2.15 p.u., which, taking into account the reduction in longitudinal electrical strength, leads to breakdown of the breaker. The analysis of emergency shutdowns shows that all of them occur at slightly negative ambient temperatures. To reduce the probability of line breakers failure, the authors consider such measures as the installation of electromagnetic (measuring) transformers and the use of shunt resistor breakers and nonlinear surge suppressors.