A synthetic test circuit is used to test the Garabi II HVDC thyristor va lves.This synthetic test circuit comprises a conventional Back-to-Back direct test circuit and a voltage oscillating circuit to reproduce the current and volt age stresses that the thyristor valves could meet in service.The test circuit parameters are carefully chosen to give a close representation of the system par ameters.The sample test results from this synthetic test circuit are comparable with that acquired previously from a conventional Back-to-Back direct test circu it.However
this synthetic test circuit offers several technical advantages and i s superior to the Back-to-Back direct test circuit in terms of economy as well.