Considerations & type tests for steep fronted DV/DT & DI/DT fault events in voltage sourced converter HVDC valves

This paper proposes two important new tests that should be included in the type test requirements of all voltage sourced converter HVDC valves. The ultrafast dv/dt test replicates the very fast electrical insulation breakdown voltage transient that occurs during the dielectric breakdown within SF6 wall bushings. The fast di/dt test replicates short circuits occurring within a valve structure where the local valve capacitors can feed the fault with merely the valve stray inductance to limit the resulting di/dt. Both tests can cause maloperation and damage to HVDC valves if valves are not designed to cope with them. The circumstances surrounding the fault conditions that mandate these tests are discussed, suggested type test methods are presented and typical results from these tests for GE's new Generation 2 VSC valve are stated.