Converter Stations

Abstract

The central point of the entire d.c. transmission link is the valve. A distinction is made between genuine and non-genuine valves. Genuine valves have a physically determined, definite direction of conduction, whilst the conduction direction of non-genuine valves is determined by external circumstances. The mechanical valve of the contact converter is an example of a non-genuine valve, since the direction of current flow depends on which of the two alternating voltage half-waves coincides with the making of the contact. A non-genuine valve more suited for high-voltage purposes is the spark discharge valve, in which triggering of a spark gap initiates the conduction period. Despite extensive development work which led to the erection of an experimental transmission link, it proved impossible to achieve results which would encourage the introduction of these valves in commercial transmission links. There is therefore no need to discuss this type of valve in greater detail here; instead we shall simply note that so far only genuine valves have led to practical results. This limitation, the existence of which has already formed the basis of our introduction, is regrettable because non-genuine valves have a distinct advantage over genuine valves. The complete valve set according to Fig. 1.5 would have to be made up of only six valves, the change in power direction could be brought about by changing the current direction instead of the voltage direction, and polarity changing of the converter connection, especially in multi-terminal transmission links, would be superfluous resulting in constant voltage system properties in this respect as well.