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SUMMARYIn AC electric railways, three-phase voltage is changed into the single-phase circuit of two circuits with the Scott-connected transformer. If unbalancing of the load between single-phase circuits becomes large, voltage fluctuation becomes large on the three-phase side. Railway static power conditioner (RPC) was developed for the purpose of controlling voltage fluctuation on the three-phase side. An RPC is comprised of a pair of self-commutated PWM inverters. These inverters connect the main phase and teaser feeding buses, coupled with a DC side capacitor such as a back-to-back (BTB) converter. In this way, the two self-commutated inverters can act as a static var compensator (SVC) to compensate for the reactive power and as an active power accommodator from one feeding bus to another.20 MVA/60 kV RPCs started commercial operation in 2002 at each two substations on the newly extended Tohoku Shinkansen for compensating voltage fluctuation on the three-phase side caused by traction loads, absorbing harmonic current. The results of operational testing indicate that an RPC can accommodate single-phase loads such as those of PWM-controlled Shinkansen and thyristor phasecontrolled Shinkansen, and handle the exciting rush current of transformers, as well as compensate for harmonics successfully.

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