Use of controlled switching systems in power system to mitigate switching transients. trends and benefits - Brazilian experience

Switching transients in power systems have always been a matter of concern in studies of power equipment insulation coordination. However, considering the new institutional, environmental and economic existing constraints in most of the power systems all around the world, and, still, with the growing of the use of sensitive loads - from home digital clocks to fully automated industrial production lines, in the last few years, these power system transients could become, more and more, a big issue. This paper aims to present some aspects regarding relevant switching transients in power systems and the means to mitigate them. It will present the classical means of mitigation, such as circuit breakers with pre-insertion resistors, etc. However, the main focus will be on controlled switching systems (CSS), since it is becoming more and more an attractive way, technically and economically speaking, to mitigate such switching transients and to improve power quality (PQ), in order to cope with the new power system requirements and constraints. In the case of Brazilian interconnected power system, supply is usually provided by long EHV transmission lines, not only to connect far hydroelectric power plants to the main load centres, but also to interconnect power systems of different regions. Due to the long distances between load centers and generation plants, several transmission lines and substations of 550 kV up to 800 kV had to be built in the country, soon after these voltage levels started to be used by utilities in other parts of the world. And, as a consequence of such peculiar characteristics of the Brazilian power system, there is the need of many voltage control equipment, such as shunt capacitor banks and reactors. Still, the switching of long EHV transmission lines and power transformers in such system has become a special issue. Examples of switching transients problems occurred in the Brazilian interconnected power system and how they can be mitigated will also be presented. Whenever possible, it is also presented available data considering cost reduction regarding power equipment, due to the use of such controlled switching systems. The cost reduction is possible, mainly, by reducing insulation levels of large capacitor banks, eliminating circuit-breakers auxiliary chambers, reducing transmission lines costs, due to a possible compaction and reducing arresters rating.