Calculating the switching surge critical flashover voltage of phase-to-ground and phase-to-phase bundle conductor gaps

The paper presents a method for calculating the 50% breakdown voltages of conductor-to-plane and conductor-to-conductor air gaps for any bundle design, all the three phases of lines being taken into account. The method is developed for switching impulses with long time front (/spl tau/f=1000-4000 /spl mu/sec) which are the most typical for UHV lines. The results of calculations are extensively compared with previous experimental results for different bundles and over a wide range of gap spacings. The influence of bundle configuration, type of phases displacement (flat, delta or inverted delta) and voltage distribution among phases for UHV lines are analyzed.>