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1. Simplified methods of calculating the voltage across the insulator string are presented based on field-theory concepts for a stroke to the tower with zero towerfooting resistance. 2. The voltage across the insulator string is composed of two components: (a). that produced by the rent and the charge fed into the tower and ground wires, and (b). that produced by the charge above the tower. 3. To calculate the voltage produced by the current and charge fed into the tower and ground wires, conventional traveling-wave theory and methods can be used provided the proper value of surge impedances are used. 4. Equations, based on field theory, are presented to calculate the ground wire and tower surge impedances and the conductor-to-ground mutual impedances. 5. The development of travelingwave theory directly from field theory places traveling-wave theory on a more rigorous basis. 6. To calculate the voltage produced by the charge above the tower, approximate simplified equations are given for a given stroke mechanism. These can be modified for other assumptions. 7. From examples and calculations given in this paper it is possible to gain some insight on the effect of tower geometry, number of ground wires, and position of the conductor on the voltage across the insulator string. Voltages were calculateed across the top and bottom insulator strings of the single-groundwire AEP-OVEC 345-kv tower, across the top insulator string of the two-groundwire AEP-OVEC 345-kv tower, and across the insulator string on the PW&P 220-kv tower.