Power transformers are the most expensive asset in a substation. Monitoring the moisture and hydrogen levels in the dielectric oil provides a clear indication of its overall condition. With this information, it is possible to determine with greater certainty whether maintenance is necessary or if there is any type of internal fault. Furthermore, with a little data analysis and trend monitoring, it is possible to determine how urgent an intervention might be, whether a condition is worsening, or if it remains stable. The information provided by a monitoring system saves money by preventing a power transformer from going out of service due to a failure, it allows for the optimization of maintenance by avoiding outages through planned maintenance based on real-time information, which extends the useful life of these assets and, in the worst-case scenario, can prevent a catastrophic failure.

Point measurements of moisture in transformer oil (in ppm) in power transformers can present significant challenges, since moisture is constantly migrating between the paper and the oil depending on temperature. Vaisala recommends measuring water activity as the most reliable method, since it allows you to detect the presence of free water, which can cause insulation failure and lead to partial discharges or open arcs. VAISALA offers instruments that can monitor two or three variables in transformer oil:

• Oil Moisture and Temperature
• Moisture, Temperature, and Hydrogen in Oil