A dominant design consideration in the development of space-type power magnetic devices is the application of reliable thermal control methods in order to prevent device failure due to excessive temperature rises and hot spot temperatures in critical areas. The resultant design must also yield low weight, high efficiency, high reliability and maintainability, and long life. A transformer weight equation is developed to show that the weight is directly proportional to the 3/4th power of the kVA rating and inversely proportional to the 3/4th power of the product of the variables f, B /SUB m/, J /SUB s/, ..cap alpha.., (FF), and (SF) /SUB c/. A family of curves, obtained when the normalized specific weight is plotted as a function of the transformer's kVA rating with frequency as the parameter, show insignificant weight savings for frequencies above 50 kHz. The weight savings and high efficiency that results by going to high frequency and unique thermal control techniques is demonstrated by the development of a 25 kVA, 20 kHz space type transformer under Lewis' power magnetics technology program. Earlier work included heat pipe cooled inductors and transformers in the 3 kVA range. Present work in the area of power rotary transformers ismore » also discussed.« less