Technical & Economical Evaluation of Using Silicone Rubber RTV Coating for H.V. Substation in Polluted Area

Abstract: High  voltage  insulators  have  to  be  used  as  insulating supporters  in  various  environments  in  polluted  area.  The electrical  performance  of  insulators  will  be  degraded.  The polluted insulators will have over withstand voltage, flashover can occur easily when the air becomes wet by humidity or fog, which affects on the reliability of the power systems. In order to define effective counter measures against pollution flashovers  there  are  conventional  methods  such  as periodically water washing and also using silicone grease for insulation.  Water  washing  of  insulators  which  is  normally recommended so as to remove the pollution from the insulator surface  needs  to  be  done  more  frequently  than  other maintenance methods. Though involves some limitation in practice from the technical and economical point of view. Applying  of  silicon grease on insulators with high cost  of performance  also  is  not  recommended  for  use  in  an environment where high level of NSDD pollution is present. In this paper room temperature vulcanizing (RTV) silicone rubber coating have been presented as a novel approach for improvement of outdoor substation insulators maintenance in polluted area. This method can be used in areas characterized with  “Instantaneous  pollution”  and  or  with  “High  or  Low level of NSDD” with long life expectancy. Financial analysis shows that this method is also economic and optimal choice.  1-Introduction HV  insulation  separates  voltage  levels.  Wet  polluted deposition  forms  conductive  layer.  This  layer  extends gradually and causes electrical breakage as well as outage. Therefore,  appropriate  insulation  design  plays  important roll in system reliability improvement and faults reduction in  polluted  regions.  According  to  utility  records, inappropriate insulation constitutes 70 percents of HV lines faults. Respecting to international standards, coastal regions of  Persian  Gulf  and  Oman  Sea  are  classified  in  "very heavy"  pollution  degree  and  their  hot  and  humid  climate, sea  adjacency  and  salty  water  provide  specific  condition. Present insulation design of HV device-lines design in the regions  is  based  on  "very  heavy"  pollution  degree standards,  but  the  insulation  performance  is  inefficient. Insulation weaken is the main effect of pollution. Different methods, e.g. periodical washing, are used to reduce these effects in southern regions of Iran. In  this  paper,  traditional  maintenance  methods  in  HV substation  as  well  as  RTV  silicon  rubber  coating,  as  a replacement,  with  their  technical-economical considerations  are  presented  and  calculations  for  a  typical substation performed.