Device to continuously determine the rate of extraction of water steam used for drying transformers

A method of continuously measuring a moisture flow through a pipeline during a vacuum process for drying of power transformers, using a device connected in series between a vacuum pump and a transformer tank;

• the device including:
• an orifice plate mounted between two flanges inside the pipeline;
• first and second pressure meters disposed on opposite sides of the orifice plate and configured to measure a pressure drop across the orifice plate;
• a dewpoint meter operably coupled to an inside of the pipeline;
• and a temperature meter operably coupled to an inside of the pipeline, the method comprising:
• determining an air flow expressed in units of mass per time units based on a power of the vacuum pump and the differential pressure caused by the orifice plate;
• determining a partial pressure of a water steam based on a measured dewpoint temperature of the moist air, considering that the partial pressure is equal to a steam pressure to the dewpoint temperature;
• determining a mole fraction of water in gas phase (yH20) by dividing the partial pressure of the water steam and a total pressure within the pipeline;
• determining a mass fraction by multiplying by respective molecular masses;
• and
• multiplying the mass fraction of water by a moist air flow, in order to obtain a speed of water removal.