AN INVESTIGATION OF SULPHIDES IN TRANSFORMER OIL  

This month’s Featured Technical Paper is from the Proceedings of the 2019 International Conference of Doble Clients. The paper is titled: An Investigation of Sulphides in Transformer Oil.

Abstract

A  1982  vintage,  free-breathing,  auto  transformer  (245/144kV,  150  MVA)  experienced  two  internal  faults,  one  in  2012  and  the  second  in  2017.  After  the  first  failure,  the  tap  changer  selectors  were  replaced,  returning the original oil (filtered) to the transformer.  The corrosivity was determined as low risk based on historical  risk  assessment  factors  (no  excessive  high  ambient  temperatures,  light  loads,  enamel  coated  winding conductors, and high oxygen content in the oil).  The second failure investigation discovered silver sulphide  deposits  on  the  new  selector  contacts  after  only  five  years  of  service.    Lab  analysis  of  the  HV  winding  paper  insulation  confirmed  presence  of  copper  sulphide.  This paper will focus on the potential sources of sulphides related to oil reclamation with a reactivated media process.   As part of the transformer fleet asset management program, transformer mineral oil is refurbished based on oil quality results and prioritized by importance of the unit.  Typically units are in service 25 to 30 years prior to oil quality limits triggering the first oil reclaim.  A comparison of historical results from two different oil reclamation machines showed corrosivity correlation with  one  specific  machine  as  well  as  a  specific  oil  processing  method.  The process variation relates specifically to handling the volume of waste oil left over from the media reactivation process and the slow dissipation of residual heat after the columns of Fuller’s earth are reactivated.  This  paper  will  provide  a  summary  of  the  investigation  into  the  source  of  the  corrosive  sulphur  and  recommendations to reduce the risk of creating volatile sulphur compounds during oil reclamation utilizing a regenerative media process.

Doble Service Agreement Clients

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