Effect of Supply Unbalance on Harmonic Emissions of Uncontrolled Six-Pulse Rectifiers

Abstract

Standards dealing with power quality disturbances and emission limits for equipment and installations are constantly evolving as additional knowledge is gained.  Often, each type of disturbance,  such  as  harmonics,  is  considered  individually  and  without   regard   for   the   possible   effects   of   other   types   of   disturbances, such as unbalance.  The interdependencies between the  disturbance  phenomena  are  often  disregarded.    The  work  reported in this paper is focused on quantifying and correlating the effect of supply system unbalance on the harmonic emissions of the  most  basic  harmonic-producing  converter,  the  uncontrolled  six-pulse  rectifier.    Six-pulse  rectifiers  with  different  loading  conditions   are   supplied   by   sources   with   varying   levels   of   unbalance  to  determine  the  effect  of  the  unbalance  on  harmonic  emissions    via    simulation.        Different    unbalanced    supply    conditions,  all  within  credible  levels,  are  considered  and  the  effects  on  the  harmonic  emissions  of  the  six-pulse  rectifier  are  evaluated.  The  results  of  these  simulations  show  that  as  source  unbalance increases, THD and triplen harmonics also increase in a   nearly-linear   pattern.      This   type   of   relationship   may   be   appropriate    for    consideration    in    the    ongoing    efforts    in    standardization  related  to  both  harmonics  and  unbalance  so  that  more coordinated decisions can be made.