Rotary transformer design

A high power rotary transformer (1 k W ) was considered as a replacement for slip-rings in a future satellite. A study was done to determine the best electrical design taking into account mechanical limitations while maximizing efficiency. Ferrite was used in a configuration which can be ground by any good machine shop. A design procedure is described which provides the engineer with a rough estimate of size and weight of a near optimum transformer given the power level, frequency of operation, and material to be used. The electrical circuit used should be considered during the transformer design. In the widely used voltage controlled push-pull square wave converter there is the problem of transistor storage and fall time. Usually one transistor is turned on before the other is off. The latter transistor then traverses through a high power dissipation region, the peak power being twice the input voltage times input current. Transistors picked for low saturation voltage are usually slower devices aggravating the turn-off dissipation problem. An operating procedure which minimizes these turn-off losses and prevents excursion through high instantaneous dissipation regions has been devised. It allowed the construction of a 1000 watt converter (dc-dc rotary transformer) which runs at a 92% efficiency (including rectifier losses) with just a total of 10 watts of transistor dissipation. Operating levels are 24 volts, 50 amps in and out.