By an undulatory beam of gentle, I imply a beam that shines repeatedly upon the selenium receiver, however the intensity of which upon that receiver is subject to rapid changes, corresponding to the modifications within the vibratory motion of a particle of air during the transmission of a sound of definite quality by the atmosphere. This is the primary HVDC transmission where LCC and VSC poles cooperate in a bipole. A bipolar scheme will be applied in order that the polarity of one or both poles may be modified. Multi-terminal systems are difficult to realize using line **utated co**ers because reversals of energy are effected by reversing the polarity of DC voltage, which affects all co**ers related to the system. A bipolar system could even be installed with a metallic earth return **ductor. In particular, the polarity of the ions emitted may be managed, which ** have an enviro**al impact on ozone creation. Cross-Skagerrak **sisted since 1993 of 3 poles, from which 2 were switched in parallel and the third used an reverse polarity with a higher transmission voltage.

A similar arrangement was the HVDC Inter-Island in New Zealand after a capacity improve in 1992, during which the two **inal co**ers (using mercury-arc valves) had been parallel-switched feeding the identical pole and a brand new third (thyristor) co**er installed with opposite polarity and better operation voltage. This **figuration ended in 2012 when the 2 old co**ers were changed with a single, new, thyristor co**er. Parallel **figuration tends to be used f**iant capability stations, and sequence for decrease capacity stations. The **figuration of multiple terminals could be series, parallel, or hybrid (a mixture of collection and parallel). China Southern Power Grid began a 3 terminals VSC HVDC pilot mission in 2011. The challenge has designed ratings of
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