More and more high voltage transmission lines make use of rubber housed
ZnO arresters in series with another air gap (for example, the
insulator gap) as lighting protection elements. Many test results of
ZnO arresters protection performance show that this insulation
arrangement is suitable for practical lines according to results based
on only simple impulse voltage. This paper uses a composite voltage
(switching impulse voltage/alternating voltage) to determine the air
breakdown behavior of the conductor-rod gap in series with the sphere
gap. In the test, the switching impulse voltage is applied to the
conductor while the alternating voltage is applied to the rod and one
sphere and the other sphere is grounded. The results show that in some
cases, the value of the U50% sparkover voltage for the conductor-rod
gap with the composite voltage is nearly only half of that for just the
simple impulse voltage
