Modern trends in D.C. insulation

The early history of electrical insulation for large D.C. motors and generators is a story of the engineer´s ability to combine the best materials available to him at the time for separating the conducting circuits from the magnetic circuits. Separation of the circuits is no longer adequate for the demanding performance of the rotating machines of today. Electrical circuits must be insulated to resist the extreme conditions of heat, moisture and foreign contaminates and perform satisfactorily with a minimum of maintenance over long periods of time. The trend toward smaller machine sizes with proportionately less space has increased the demand for a better overall insulation performance.