Method and system for drying an active part of a transformer

A system for drying an active part of an electric transformer, the active part includes at least one winding and solid cellulose-based insulation, the system comprising:

• at least one first temperature sensor for continuously sensing temperature inside a drying oven, the drying oven enabled to carry out a vapor phase drying;
• at least one first pressure sensor for continuously sensing pressure inside the drying oven;
• at least one second temperature sensor for continuously sensing ambient temperature outside the drying oven;
• at least one relative humidity sensor for continuously sensing relative humidity outside the drying oven;
• at least one third temperature sensor for continuously sensing temperature in the active part once it is removed from the drying oven;
• at least one second pressure sensor for continuously sensing pressure inside a hermetically sealed transformer tank containing the active part being dried;
• a control unit in communication with the first temperature sensor, the first pressure sensor, the second temperature sensor, the relative humidity sensor, the third temperature sensor, and the second pressure sensor, the control unit includes:
• at least one programmable memory for presetting a start temperature and pressure for drying;
• and
• an electronic processor enabled to:
• continuously determining a moisture content in the solid insulation in function of temperature and pressure sensed inside the drying oven by the first temperature sensor and the first pressure sensor, respectively;
• determining the moment when the moisture content of the solid insulation inside the drying oven reaches an equilibrium moisture content in function of a moisture desorption from the solid insulation;
• continuously determining a moisture content in the solid insulation outside the drying oven in function of temperature of the active part, ambient temperature, and relative humidity sensed outside the drying oven by the third temperature sensor, second temperature sensor, and relative humidity sensor, respectively;
• continuously determining a moisture content in the solid insulation in function of the temperature of the active part and vacuum pressure sensed inside the transformer tank by the third temperature sensor and second pressure sensor, respectively, once vacuum pressure has been applied to the tank to continue drying the active part;
• and
• determining the moment when the moisture content of the solid insulation inside the tank reaches an equilibrium moisture content in function of a moisture desorption from the solid insulation.