Failure of service aged 230 kV current transformers

As of the spring of 2008 Manitoba Hydro had in service up to 39 current transformers rated 230 kV from a particular supplier. These had been manufactured in 1969, 1971 and 1975. Three failed explosively beginning in the summer of 2008. Dissolved gas-in-oil analysis revealed others with significant fault gas. As of the end of 2011 all remaining 230 kV current transformers of this type had been removed from service. The paper reviews the design, transport, service conditions and age which may have contributed to the high failure rate.