Lightning Protection for Distribution ransformers Field Studies of Lightning Arrester Protection, Including the Effect of Interconnection

A cooperative field study with portable impulse generator and cathode ray oscillograph was made of the lightning protection of transformers connected to a 4.45-mile 4,600-volt rural distribution circuit. The tests described were made with the pellet arrester. Some of the conclusions are: 1. Although the arrester discharge voltage is but a fraction of the strength of the transformer, yet for the usual connection to ground now commonly employed, arrester ground resistances may be high enough so that the transformer is not protected, resulting in either blownfuses or a windingfailure. 2. Interconnection of the primary arrester ground and secondary neutral gives a high degree of protection to the transformer from surges originating on either primary or secondary regardless of the arrester ground resistance. 3. The interconnection of primary arrester ground and secondary neutral does not increase the magnitude of voltages which appear between various grounded objects on the consumers' premises over that now experienced with exposed secondary conductors and possible bushing flashovers or transformer failure. The effect of the interconnection is to increase the number of impulses reaching the secondary circuits but not their magnitude.