Abstract
The limitation of switching overvoltages on very high voltage transmission lines is traditionally carried out with the aid of circuit breakers — fitted with closing resistors. This widely used system has repeatedly shown itself to be highly efficient. Nevertheless, it is possible to envisage other methods, in particular, those giving control of the circuit breaker instant of closing. This paper examines the possibilities offered by controlled switching on UHV transmission lines and compares existing solutions. It takes into account the various network characteristics that may be encountered. It details the results in terms of overvoltage levels which could be attained, due to the performance of the circuit breaker. The paper also highlights the critical points relative to the application.
Highlights
The /imitation of switching overvoltages on very high voltage transmission lines is traditionally carried out with the aid of circuit breakers - fitted with closing resistors
This paper examines the possibilities offered by controlled switching on UHV transmission lines and compares existing solutions
Within the simulations carried out, the circuit breaker as sumed has a rate of decrease of dielectric strength (RDDS) of 1 pu, covered by the pre-arcing times taken into account by these simulations
Summary
A sudden change in the configuration of the electrical trans mission network caused by the operation of a circuit breaker, or alternatively, by the appearance of a fault, can cause a rapid surge voltage known as a switching surge which propagates throughout the network. Given that the use of non-re striking circuit breakers is widespread, it is at the instant of clos ing, and above all, re-closing of a line which has held a trapped charge, that the strongest oveNoltages appear Faced with this problem, the options chosen by the various operators of very high voltage networks throughout the world are varied. Typi cally, these are the types of networks on which the operator uses three phase re-closing operations following a single phase fault, which implies numerous re-closings on lines holding a trapped charge Thanks to this closing resistor, the oveNoltage level is limited to a value of around 2 to 2.2 pu. Could a controlled switching on the lines be a new method? What sorts of problems are caused by the use of such a system, and what are its limitations?
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