Copyright AIST Reprinted with Permission. Presented at the 2013 Iron and Steel Technology Conference and Exposition (AISTech 2013). Unit substations have long served as the method for reducing voltage from higher distribution levels to lower, locally usable voltages. One of the main considerations affecting the design of the substation and the electrical protection and distribution system as a whole is the primary switching device of a substation. By comparing the abilities and options inherited with both types of primary switching devices, an informed decision can be made for specific system designs.