Unconditionally sequential approach to calculate the impulse strength of air for nonstandard impulse voltages

The reliability of the power apparatus depends on the reliability of its insulation, which is tested with the standard lightning impulse voltages of wave shape 1.2/50 μs. Often it is very difficult to adjust the impulse generator to get the standard wave shape within tolerance limits. While testing higher rating transformers, part of windings can get stressed with nonstandard voltages of both unidirectional and bidirectional oscillating waves. Hence it would be appropriate to test the power apparatus for the standard 1.2/50 μs impulse voltages, and also to estimate the insulation strength for nonstandard impulse voltages. Disruptive effect method, which is a generalized method to estimate the breakdown voltage of insulation structures exposed to nonstandard lightning impulse voltages is an appropriate method to estimate the impulse strength for unidirectional nonstandard impulses. In this paper air as a basic insulating medium has been analyzed extensively for gap distances ranging from 1 mm to 5 mm for different electrode configuration from uniform to highly nonuniform field configuration. Unconditionally sequential approach, which caters to the bi-directionally oscillating voltages, has also been explained in this paper.