Insulation levels governed by lightning arresters

INSULATION levels for transformers and circuit breakers for high voltages, to be economical, should be selected so that basic impulse insulation levels are as low as are feasible. Presently recognized basic insulation levels are too conservative for the grounded-neutral higher voltage systems. Available levels should be of such values that the user can select a level that is practical and economical for his system. If wide gaps exist between available levels, the user may find it to his economic advantage to depart from standards.