Distribution transformers are so named because they distribute low voltage power (5KV and below) to the customers who use electricity at the end of the supply grid. "Dry type" simply means it is cooled by normal air ventilation. The dry type transformer does not require a liquid such as oil or silicone or any other liquid to cool the electrical core and coils. The transformer case is ventilated to allow air to flow and cool the coil(s).