Finite Element Analysis of Electrical Machines Used in Two-Frequency Indirect Temperature Rise Tests

Abstract

Heat  runs  of  large  asynchronous  machines (AM)  are  hardly  ever  conducted  under  load  but  with synthetic approaches, such as the two-frequency  method. In  its  classical  variant,  the  AM’s  stator  is  fed  by  two series-connected  synchronous  machines  (SM)  with  dif-ferent  frequencies,  for  instance  50  and  40  Hz.  While  the 50  Hz  voltage  determines  the  AM’s  flux,  the  40  Hz source  causes  an  AM  stator  current  close  to  its  rated value. Together, voltage and  current  yield approximately full  load  losses  in  the  AM  without  mechanical  loading. For  designing  the  amortisseurs  of  the  synchronous  gene-rators,  damper  losses  were  calculated  using  the  Finite Element  method.  Additionally,  calculated  full  load  AM losses  were  compared  against  their  respective  values  for the two-frequency method.