Abstract: A non-rotating portable voltage sag generator includes for each phase a pair of cascaded standard industrial auto-transformers each having, for example, six taps and when they are cascaded the final output voltage of each phase is a product of the per unit value of each individual auto-transformer. Closed transition switching is provided to switch the auto-transformer into and out of the circuit effectively only during the time a voltage sag is desired. All of the switches and auto-transformers are conveniently carried in a single portable enclosure. There are no moving parts or diesel engines; thus, the non-rotating sag generator is useable in any part of an industrial plant.