Fundamental Principles and System DescriptionEngineering InformationSINAMICS Engineering Manual – November 2015Ó Siemens AG 197/5281.15.4 Parallel connection of S120 Smart Line ModulesParallel connections of Smart Line Modules can be implemented as either a 6-pulse circuit if the parallel-connectedmodules are connected to a two-winding transformer, or as a 12-pulse circuit if the parallel-connected modules areconnected to a three-winding transformer with secondary windings that supply voltages with a phase shift of 30 °.6-pulse parallel connection of S120 Smart Line ModulesWith the 6-pulse parallel connection, up to four Smart Line Modules are supplied by a common two-windingtransformer on the line side and controlled by a common Control Unit.6-pulse parallel connection of S120 Smart Line ModulesAs Smart Line Modules have no electronic current sharing control, the current must be balanced by the followingmeasures:· Use of line reactors with a relative short-circuit voltage of vk = 4 %· Use of symmetrical power cabling between the transformer and the Smart Line Modules (cables ofidentical type with the same cross-section and length)The current reduction from the rated value for individual Smart Line Modules in a parallel connection is 7.5 %.12-pulse parallel connection of S120 Smart Line ModulesWith 12-pulse parallel connections, up to four Smart Line Modules are supplied by a three-winding transformer on theline side. In this case, an even number of modules, i.e. two or four, must be divided between the two secondarywindings. It is absolutely essential that the Smart Line Modules of both secondary windings are controlled by meansof two Control Units because of the phase displacement of 30º. The use of two Control Units is necessary because,in contrast to the Basic Line Modules, the gating impulses for the IGBTs in Smart Line Modules are synchronized bythe Control Unit. Thus all Smart Line Modules controlled by one Control Unit must be connected to the sametransformer winding with equal phase position.
