Volt-time areas of impulse spark-over

On the basis of classification of impulse wave shape, the paper shows that impulse spark-over characteristics of electrodes with nonuniform fields cannot be represented by single volt-time curves but must be represented by volt-time areas of considerable extent. This classification explains the large difference obtained by various laboratories when investigating sparkover between one and five microseconds. The effect of impulse generator discharge circuits in producing these differences is explained. The necessity of insulation co-ordination on the basis of volt-time areas is pointed out.