Review of diagnostic techniques for oil-paper insulated instrument transformers

Failures of instrument transformers (IT) can cause malfunction of system protections, controls and/or metering devices and, in some catastrophic failures, damage to nearby power apparatus, or injury to personnel in the vicinity. Within a project funded by the CEATI LCMSEA Interest Group (see www.ceati.com), it was found that over 95% of all ITs use oil-paper insulation and there is a large variation among different utilities in terms of using different diagnostic techniques. A comprehensive review of existing literature and a utility survey were done and various commercially available diagnostic instruments available from manufacturers around the globe were assessed on the basis of their underlying technology, costs, and evidence of operating experience. This paper presents a critical review of various popular IT diagnostic techniques.