Circuit-breaker requirements for alternative configurations of a 500 kV transmission system

This paper describes the study made to assess the electrical stresses imposed on line circuit breakers of a new 500kV, AC expansion of the FURNAS transmission system, to be possibly installed in the Brazilian central region. The study has considered three configurations of the transmission lines, two of which assuming the use of compact towers. In one of these two cases the lines would have high surge-impedance loading. Digital simulations have been made with the aid of the Alternative Transients Program (ATP) to calculate the switching transients appearing as a result of line energization and reclosing, clearing of terminal and short-line faults, no-load line opening in normal and faulted conditions, and out-of phase switching. Four alternatives have been considered for the limitation of overvoltages on closing, assuming either the sole use of surge arresters on each line end or the use, in addition to the arresters, of pre-insertion resistors, synchronizers or time relays to provide a staggered closing of the breaker poles. The stresses obtained were compared with those applied by the standard IEC tests or with the maximum admissible levels usually considered by the utility for its transmission branches at the planning stage.