Induced Over-Voltage test set

We have an induced overvoltage test set that consists of a 2KW AC Motor coupled with a 140A 24Vdc modified car alternator.This test set must be able to able supply the test object (viz. Transformer) with a voltage that is twice the rated voltage of that object from the LV side and the frequency must be doubled(viz from 50hz to 100hz) also to avoid saturation of the magnetic device. The problem with this test it does not produce stable frequency. i was thinking of considering Motor-Gen set and where can i get one in South Africa.