High-voltage insulation co-ordination: timelags of parallel-plate, rod-plane, rod-rod gaps, cap and pin insulators and surge diverter

Percentage overvoltages against timelag characteristics show that, while for simulated lightning strokes a rod-rod gap, set to yield the same 50 percentage sparking voltage as a rod-plane gap, will protect it and cap and pin insulators for all magnitude of overvoltages, for a simulated switching surge a rod-rod gap is wholly inadequate. For complete protection, uniform field geometries like those produced by Rogowski profiled electrodes are required and this is almost achieved with surge diverters