Air breakdown behavior of two series gaps for composite switching impulse/alternating voltage

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 perfomrance 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 U
50%
sparkover voltage for the conductor-rod gap with the composite voltage is nearly only half of that for just the simple impulse voltage.