Detection and continuous monitoring of moisture content in transformer oil using fractal-based capacitive sensor

The contaminated transformer oil is one of the major causes of failure in the power system. Detection and continuous monitoring of moisture content in transformer oil is required for the smooth operation of a system. In this paper, a Fractal-based Sinusoidal-shaped Capacitive Sensor (FSCS) is proposed to increase the contact area between capacitor plates and dielectric medium by 17.3%. The proposed design offers minimal resistance to the flow of a mixed medium and can detect moisture content accurately. The variation in transformer oil, water, and mixture due to the temperature is considered to avoid false readings and alarms. The Equivalent Series Resistance (ESR) is also measured along with the equivalent capacitance to increase the accuracy of FSCS. A minimum detection limit of 5PPM is observed for a proposed sensor. The switching mechanism is integrated with the proposed design to make it reconfigurable and change the contact area with the impurity and sensitivity of the sensor. The large contact area and higher sensitivity mode are activated separately in order to avoid false readings. The sensor with a higher fractal stage achieves a sensitivity (fF/5PPM) that is 18.22 times greater than that of the lower fractal stage, making the higher stage more sensitive. As a result of switching, further substages of the fractal stage are formed. Each fractal stage can have multiple substages. The sensitivity of any particular substage increases as its fractal stage increases.