Surge Protection of Distribution Systems

A quantitative investigation of the surge protective requirements of distribution systems and the power frequency voltage requirements of protectors for these systems, has been made which leads to the conclusions that: 1. The surge current discharge capacity of protectors should be 100,000 amperes to prevent damage from lightning. In general, 50,000 amperes capacity will give satisfactory results. 2. The surge voltage breakdown characteristics should be similar in shape and lower in value than the transformer insulation. 3. Field experience, as well as laboratory tests, have proved that a high degree of protection is obtained with a ratio of protective device initial discharge voltage to normal frequency voltage of 9 to 1 in voltage classes up to 13.8 kv, compared to the present conventional arrester rates up to 3.5 to 1. 4. Testing of protective devices under conditions more nearly representative of their service requirements should be considered.