Interference immunity tests of an HVDC value section consisting of two thyristor levels

The consistent thyristor valves of a high voltage direct current (HVDC) convertor bridges are commonly installed as four-high stacks, presenting the possibility of electric and magnetic coupling into the thyristor gate electronics units in one valve occurring as a result of current and voltage transients in an adjacent valve. These electronic units perform the essential functions of firing, protection and monitoring of the thyristor levels. For reliable long term operation of the convertor bridges, these functions should not be corrupted. In general, immunity to electromagnetic interference (EMI) is demonstrated during the application of type tests on a complete thyristor valve or on valve sections (modules) as described in IEC700. However, during design and development testing and, in particular, when the interactions between adjacent valves must be investigated, special tests on reduced scale test objects are often required. The authors describe three onerous tests designed to represent the most severe levels of coupling expected in practice. The tests were applied to a standard fully equipped valve section comprising two series connected 100 mm diameter thyristors to demonstrate its immunity to such interference