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.