Basic impulse insulation levels

AS A RESULT of a great deal of operating experience and from a survey of the then current practice as regards insulation of high-tension equipment, it began to be evident some 9 years ago that too little, if any, attention had been paid to co-ordination of insulation in power systems. Apparatus was being built to specifications which were primarily formulated on a 60-cycle basis, with consideration given mainly to the ability of the apparatus to withstand 60-cycle voltages and almost no consideration to impulse strength. Further, very little consideration was given to insulation margins between the different types of apparatus used on the same system voltage. This was first brought to the attention of the membership of the AIEE in 2 papers presented some 9 years ago.