Anti-remanence CT’s

This  is  a  variation  of  the  over dimensioned  current transformer and has small gap(s) in the core magnetic circuit,  thus  reducing  the  possible  remanent  flux  from approximately 90% of saturation value to approximately 10%.  These gap(s) are quite small, for example 0.12mm total,  and  so  the  excitation  characteristic  is  not significantly  changed  by  their  presence.    However,  the resulting  decrease  in  possible  remanent  core  flux confines  any  subsequent  d.c.  flux  excursion,  resulting from  primary  current  asymmetry,  to  within  the  core saturation  limits.    Errors in current transformation are therefore significantly reduced when compared with those with the gapless type of core. Transient protection current transformers are included in IEC 60044-6 as types TPX, TPY and TPZ and this specification gives good guidance to their application and use.