Influence of grading capacitors on the breaking capability of two vacuum circuit-breakers in series

Series arrangements of two vacuum circuit-breakers (VCB) per pole aiming at doubling the breaking capability are used in special applications. Usually, grading capacitors are added to these arrangements to guarantee linear voltage distribution and to lower the rate of rise of the transient recovery voltage. Other solutions are designed without the use of grading capacitors due to aspects like lack of space and reducing costs. The aim of this paper is to show the influence of grading capacitors on the breaking capability. A comparison to the performance at a nonlinear voltage distribution is presented, i.e. considering the case of "self-grading" arrangements without any additional grading tool. The view is focused on the transient behaviour of both designs in case of reignitions occurring at the vacuum tube, reignited first.