The voltage breakdown and time to breakdown for each air
terminal were recorded using Digital Impulse Analyzing
System (DIAS). The up and down method in [5] was used to
determine the voltage flashover (V50) of each air terminal. For
this method, a starting voltage (Vj) close to the anticipated
flashover value is selected. Then, equally spaced voltage
levels (V) above and below the starting voltage are chosen.
The first shot is applied at the voltage Vj. If breakdown
occurs, the next shot is applied at Vj - V. If the insulation
withstands, the next voltage is applied at Vj+V. The V50 value
is calculated using either the withstand or the breakdown
events in which the smaller of the two should be used.