Reactors, like capacitors are basic to and an integral part of both distribution and transmission power systems. Reactors can be either dry type or oil immersed. Dry type reactors may be of air core or iron core construction. Dry type air core reactors features fully encapsulated windings with the turns insulation provided by film, fiber or enamel dielectric. Dry type air core reactors have traditionally been used for current limiting applications due to their inherent linearity of inductance Vs current. For this application fully encapsulated construction usually became the design of choice because its improved mechanical characteristics enabled the reactors to withstand higher fault currents. These reactors fully encapsulated with solid dielectric insulated windings are employed over the full range of distribution and transmission voltages including high voltage series reactors, filter reactors and smoothing reactors. Dry type iron core reactors are usually used at low voltage and indoors, for applications such as harmonic filtering and power conditioning.

Dry Type Transformers include solid insulation between winding turns, between each winding and another, and between conductors and ground dry transformers are usually air-cooled by self-ventilation or by forced air ventilation. Cast coil transformers are a variation of dry transformers and have an epoxy resin casting over each set of windings. With air cooling, the steel enclosure of dry transformers must include ventilation grilles. Most dry transformers are designed for indoor applications. Outdoor units are available but are very popular. Generally, dry transformers are cheaper to construct and provide shorter life expectancies.