Under normal transformer operating conditions, insulating oil temperature regularly changes with fluctuations in load and ambient conditions. During heavy loading conditions, the oil temperature rises, which causes an increase in oil volume inside the transformer. On the contrary, under light loading conditions, oil temperature cools causing a decrease in oil volume. In a conservator-style transformer, this movement of the oil level causes what is referred to as the transformer “breathing” cycle, as air is brought into the tank and then expelled again later.
During the breathing cycle of a transformer, it is crucial to prevent atmospheric moisture from entering the transformer, which can contaminate the oil and cause damage over time to internal parts. The transformer windings are insulated with cellulose paper and fully submerged in insulating oil, both of which have very high dielectric strengths. When the insulating oil becomes contaminated with moisture, it can cause a number of issues inside the transformer. These include, but are not limited to, decrease in the dielectric strength of the oil and cellulose, accelerated breakdown of the insulating cellulose paper increasing the risk of partial discharge, increased risk of bubble formations at higher temperatures, and the condensation or accumulation of this moisture during cooling which can cause corrosion inside the tank leading to further problems.
The easiest way for atmospheric moisture to enter the transformer is through a fully saturated traditional breather that is past its maintenance requirement. When the silica gel inside a traditional breather is fully saturated, it will no longer absorb atmospheric moisture as it enters the transformer and it must be replaced. Traditional breathers require visual inspection to determine if the silica needs to be replaced, and it is not always easy to determine whether the unit is providing protection still. Depending on the breather, color changing silica can sometimes be fully saturated internally and show no color change externally. In addition, with everyone trying to reduce maintenance costs, the replacement of silica may no longer be a priority that can be kept up on as needed.
The next generation STB000 Smart Transformer Breather from Qualitrol helps eliminate all of the shortcomings of traditional breathers while preventing atmospheric moisture from entering the transformer. The Qualitrol STB000 continuously monitors the moisture level of the silica gel and triggers a regeneration cycle as the transformer oil expands, during the "exhale phase”. The "smart" aspect of the breather is that it uses a pressure sensor and a pattern recognition algorithm to ensure that the transformer is expelling the moisture, not bringing it into the tank upon regeneration. By using a pressure sensor, it directly measures the breathing pattern as opposed to guessing at it based on temperature trends. Using an onboard heater, it regenerates the desiccant and eliminates the need for frequent maintenance to replace the silica gel. Silica gel regeneration can be triggered using either a percent relative humidity (%RH) or an industry first moisture parts per million (PPM) set point.
The Qualitrol STB000 also boasts other additional features including an easy, universal design, that can be used on both Main Tank and LTC oil conservation systems with a single model. It does this by detecting the breathing cycle of the tank it is being used on and automatically switching between programmed modes that are optimal for that tank. This eliminates the need to specify and stock different models to handle the various irregularities in breathing cycles between the different types of tanks. The STB000 also includes data logging for trending and tracking breathing cycles along with RS-485 Modbus and Analog Output for remote communication.
The STB000 provides the same protection of breathers that have been used in the industry for decades but eliminates the need for unnecessary maintenance, freeing up utility workers for more important work elsewhere. Even better, by directly measuring the breathing of the transformer, it offers a universal design that simplifies ordering and stocking requirements. Finally, the new communications features and watchdog alarm gives you the confidence that your tank is protected.
Here is a video clip from Qualitrol explaining how the technology works.