EHV CURRENT TRANSFORMERS - FAILURE MODE ANALYSIS & EVALUATION LEADING TO CORRECTIVE AND PREVENTIVE ACTIONS FOR RELIABILITY ENHANCEMENT

摘要

The Instrument Transformers (CTs , VTs , CVTs ) &Condenser Bushings are the important components ofthe EHV Substations & the Power Systems and areexpected to be maintenance free , and have atroublefree service life higher than 25 years. Manytimes the catastrophic failure of the equipmentsinvolves damage to the other nearby equipments. Thisleads to the outage of power , and also leads to thecostly reconditioning / repairs / replacement of thedefective equipments. In majority of the cases , thedefective equipments have to be sent to themanufacturer’s works . In all such cases it is necessaryfor the utility & the manufacturer to jointly arrive atthe corrections , corrective actions & preventiveactions. The joint working by the utility & themanufacturer leads to shortening the time toinvestigate & time to implement the corrective &preventive actions.This paper presents the results of a systematicinvestigative work on 420kV Class CurrentTransformers jointly carried out by the utility and themanufacturer.Three Numbers of Current Transformershad failed within 24 hours of commissioning them.Theinvestigation of failure phenomenon was necessaryfrom the view point of assessing the health of about 69balance CTs , which were required to be put intoservice immediately.The broad steps taken during theinvestigation process were ;1.??Strip Down Analysis of the Failed CTs.2.??Evaluation of Oil Samples from all the CTs forBDV , TanDelta , Moisture Content , DissolvedGas Analysis.3.??Based on the database generated , Identifying theCTs , which need correction at works.4.??Evolving new tests to support the investigation &identifying the correction procedure.5.??Service DGA Analysis and evolving the norms.6.??Identifying & Implementing the DesignImprovements.The joint investigation resulted in effectivelycompleting the investigation process in a period of sixmonths.