Monitoring HV transformer conditions: The strength of combining various diagnostic property observations

Power utilities are constantly increasing their demand for on-line monitoring systems able to dynamically assess the condition of their electrical assets, in order to perform cost-effective maintenance. The power transformers connected to the transmission and distribution networks represent a wide population of electrical apparatus where the on-line monitoring of their overall conditions can allow maintenance and asset manager to prevent major outages or damages, having sometimes cost higher than the whole apparatus. The condition, or health index, of a transformer can be assessed by off-line and on-line property measurements, repeated in time or monitored permanently. This paper presents the results of a case study of on-line monitoring of HV power transformers, considering different techniques available such as partial discharge analysis, dissolved gas analysis, and capacitance and loss tangent measurements. It is highlighted how the combined results of the different techniques allows condition evaluation and early detection of insulation problems or faults to be achieved.