Strength Characteristics of Air Gaps Subjected to Interphase Switching Surges

The present philosophy in the selection of phase-to- phase clearances has been examined. On the basis of a number of oscillograms of switching surges in an EHV system, some characteristics of the overvoltage stresses between phases that have not been considered by the interphase testing methods adopted up to now are demonstrated. By means of a series of switching impulse laboratory tests, it has been shown that these characteristics of thephase-to- phase overvoltages cannot be overlooked in assessing the dielectric strength of phase-to-phase air-insulated structures of substations.