Condition assessment of 132/220 kV oil-paper current transformers in Sri Lanka

Current transformers (CTs) are extensively used in electrical switchyards and substations for metering and protection purposes [1] and are expected to operate properly for at least 30 years [2]. Normally, aging of CTs under service conditions is relatively slow, but they also may fail prematurely due to various reasons, such as design faults, inadequate quality during manufacture, lightning strikes, operation beyond rated conditions and inadequate maintenance [3]. Compared with other high voltage apparatus, failure of a CT can be violent or even catastrophic, causing damages to the CT itself as well as to nearby located assets and humans [4–9]. Build-up of internal pressure during a failure of a CT results in an instant fire due to burning of oil and explosion of porcelain housing, where porcelain pieces can spread to a distance up to 100 m [4], [6].