Distribution Transformers usually use copper or aluminum conductors and are wound around a magnetic core to transform current from one voltage to another. Distribution transformers come in two types; dry-type and liquid. The Distribution Transformers are usually smaller and do not generate much heat and can be located in a confined space at a customer's location. The liquid type usually have oil which surrounds the transformer core and conductors to cool and electrically insulate the transformer (see also Oil Filled Transformers). The liquid distribution transformer types are usually the larger and need more than air to keep them from overheating thus the oil insulator.
Distribution transformers can vary in size, with the most common ranging in size from 5 KVA single phase to 2500 KVA. They come in single phase and three phase and can be pad mounted or pole mounted. The three phase Distribution transformers are used with an underground primary circuit and three single-phase pole type transformers for overhead service. Where large concentrations of businesses or large cities they are usually installed in an underground vault. Power is then sent via underground cables to each customer. One of the main advantages of distribution transformers are that they can usually withstand overloads.
