Criteria for phase-to-phase clearances of HV substations

To facilitate uprating of HV substations, a reexamination is made of line-to-line insulation design criteria. The basis for existing practices and the principles of line-to-line lightning surge overvoltage stresses are reviewed. Results of a digital study for a realistic substation are presented. The conclusions show that the line-to-line stresses, as limited by surge arresters, are substantially higher than line-to-ground stresses. This represents increased requirements as compared to existing standards. However, due to the low protective levels of modern arresters, substantial reduction of line-to-line clearances is still feasible