Characteristics of dimension restrained dry-type transformers

It is pointed out that dry type transformers are often restrained in one or more directions to permit their use in confined areas. This is particularly true in underground coal mines where the height is limited by the seam thickness. The historical increase in machinery horsepower fuels the escalation of transformer capacity required within these confined areas. The author investigates how a restrained dimension affects the operating characteristics of a transformer. Each characteristic is examined from a relational standpoint, with changes in the horizontal and vertical dimensions. The derived conclusions are then compared to empirical data obtained from families of commercial designs. The families of commercial designs show the critical nature of using volts/turn for controlling the total transformer volume. The actual volts/turn used must also satisfy the requirements of ratio and impedance. Each restraint placed upon the volts/turn, such as additional windings, can have an adverse effect upon the overall volume.<>