The co-ordination of electrical equipment with basic insulation levels

W. H. Cooney (General Electric Company, Pittsfield, Mass.): Since the principles of co-ordination were started more than ten years ago, the units of measurement have changed from insulators, to rod gaps, to kilovolts, as the knowledge of impulse voltages was increased by work in laboratory and field, but the fundamental ideas have been retained. Now we are thinking in terms of basic insulation levels, and Messrs. Foote and North have shown by three excellent examples how the insulation strengths of the component pieces of equipment of a station can be properly related.