Power transformers are the most expensive asset in a substation. Monitoring the moisture and hydrogen levels present in the dielectric oil gives a clear indication of the overall condition of the transformer. With this information it can be decided with greater certainty if maintenance is needed or if there is some type of internal failure. In addition, with a little data analysis and trending, it is possible to know how urgent it might be to intervene, if there is a worsening condition or if it is stable. The information provided by a monitoring system saves money by preventing a power transformer from going out of service due to a failure, optimizes maintenance by avoiding outages by performing them in a planned manner and based on real-time information, which prolongs the useful life of these assets and in the worst case can prevent a catastrophic failure.

Spot measurement of transformer oil moisture, ppm, in power transformers can present major drawbacks, since it is constantly migrating between the paper and the oil as a function of temperature. Vaisala proposes the measurement of water activity as the most reliable measure, since it is possible to know when you have free water conditions, where the insulation can fail generating partial discharges or free arcs. VAISALA offers equipment that can monitor two or three transformer oil variables:

• Humidity and oil temperature
• Moisture, temperature and hydrogen in the oil