Protecting distribution transformers from low-side current surges

The low-side surge problem in distribution transformers is discussed. The authors view the problem globally, discussing means to protect the transformer and the effect that they will have on the load appliances. The intent is to highlight the need for coordinated arrester protection at both ends of the secondary service drop in the geographical regions that have low-side current-surge problems. The authors survey the low-side surge problem and discuss alternatives for protecting the transformer and load apparatus. Rating and reliability issues of arresters are discussed. Arresters applied at the transformer or at the service entrance should have about one half of the current-surge capacity of distribution-class arresters. Arresters should have a protective level of 2 kV for the service entrance, while 4-6 kV appears adequate for the transformer