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Project: T183700 #30/124

Aging instrument transformers can cause safety problems and may restrain power system operations. The catastrophic failure of instrument transformers could cause a widespread fault in the substation and endanger personnel working nearby. During service, high-voltage instrument transformers (HVITs) are exposed to various stresses, namely, electrical, thermal, mechanical and environmental. These stresses can cause the breakdown of the insulation system (oil and paper), which is associated with partial discharge (PD) activity. Therefore, the overall significance of the condition assessment of HVITs cannot be overstated, given the current environment in which electric utilities operate. The success of such a condition assessment process is bound to increase the reliability of operation of HVIT units. This, in turn, eliminates any safety concerns and catastrophic failures associated with the functioning of HVITs.

The primary objective of this project is to provide a comprehensive summary of the best practices for the testing and successful on-site condition assessment of HVITs for rated voltages of 69 kV up to 500 kV. This report aims at guiding utilities towards evaluating the condition of their in-service HVIT units based on the latest guides and standards, best industry practices, and METSCO’s expertise in the field of HVIT testing and condition assessment.


High-voltage instrument transformers, instrument transformer testing, dissolved gas analysis, partial discharge monitoring, dielectric frequency response, capacitance and dissipation factor.