A design study on voltage controlled rectifier sub-stations for a rapid transit railway

The authors describe a particular DC distribution problem experienced on London Underground´s Central Line renewal project consisting of excessive volt-drop in a particular tunnel section. Three systems studies have been described on DC distribution assessment, AC distribution assessment and EMC relating to signalling compatibility, for the proposed use of voltage controlled rectifiers (VCRs). It has been found that VCRs can provide a solution to the problem of unacceptable voltage drop. It has also been found that VCRs need a stiff AC distribution system for proper operation. The study has shown that power factor is reduced and that harmonic distortion increases with the use of VCRs. An EMC problem of operating VCRs with existing power frequency signalling equipment has been identified and quantified. An engineering systems solution has been proposed