ABSTRACT
Mass production of distribution transformers has made it feasible to replace stacked cores with wound cores. C-cores were first used in distribution transformers around 1940. Today, both aluminum and copper conductors are used in distribution transformers, and the choice is largely dictated by economics. The introduction of aluminum wire, strap, and strip conductors and enamel coatings presented a number of challenges to distribution transformer manufacturers. Among the coolants used to take the place of askarels in distribution transformers are high-temperature hydrocarbons, also called high-molecular-weight hydrocarbons. Today's distribution transformers almost universally use thermally upgraded kraft insulating paper that has a diamond pattern of epoxy adhesive on each side. The vast majority of distribution transformers used in North America are single-phase transformers serving single-phase, 120/240 V, residential load. Single-phase transformers can also be connected into banks comprised of two or three separate units.
