High voltage circuits for application of composite voltages to test gaps

There is a need for high voltage laboratory testing using `composite voltages´, where impulse and either direct or alternating voltages are combined. The central problem is that of isolating the circuits prior to, and after, the impulse. This is achieved either with a capacitor or a spark gap, so that the voltages are respectively truly superimposed or, alternatively, comprise a peak composite voltage equal to the impulse voltage but preceded by the direct or alternating voltage. A variety of combined circuits is possible; some practical compromises are described and resulting efficiencies of the circuits compared where switching impulses are used