Interharmonics injected into power system by a squirrel-cage induction machine in normal and faulty operation conditions.

Abstract

 The  paper  aims  at  examining  interharmonics  injected  into  the  power  supply  system  by  a  healthy  and  faulty  squirrel  cage  induction  machine  operated  at  steady  state.  The  faulty  operation  discussed  encompasses  breaks  in  squirrel  cage  bars, breaks in squirrel cage end ring segments, combined static and  dynamic  eccentricity,  clutch  wobbling  and  vibration  of  bearings.  The  effect  of  these  ailments  is  first  investigated  through  simulations  accomplished  with  a  specially  developed  and   implemented   squirrel   cage   induction   machine   poly-harmonic  model,  as  the  fundamental  harmonic  models  are  not  capable  of  simultaneous  accounting  for  eccentricities,  slotting  and  actual  winding  configuration.  Two  case  studies,  based  on  preregistered  currents  of  big  industrial  machines,  confirm  the  frequencies    of    interharmonics    predicted    by    theory    and    simulations.  The  case  studies  refer  to  broken  bars  and  clutch  wobbling. The case study analyses were accomplished with the system Sp4   developed   for   offline   diagnoses   of   induction   machines.