Condition Monitoring of Transformer Breather Using a Capacitive Moisture Sensor

Ambient air flows into the conventional dehydrating breather due to cyclic loading of transformer. It is the major source of moisture contamination of the transformer oil. Presence of moisture causes failure of insulation strength of the oil. In the proposed work, a moisture sensor-based health monitoring technique of a dehydrating breather is proposed. A parallel plate capacitive sensor to measure and monitor the moisture inside the breather was designed and fabricated by electrochemical anodization method. A phase detection electronics circuit for converting the capacitance change of the moisture sensor to voltage signal was designed and implemented. To maintain the moisture at the desired level in the breather, the power supply of an electric heater of 40 W is controlled by controlling the duty cycle of the pulsewidth modulation (PWM) signal. The duty cycle of the PWM wave is controlled using the designed moisture sensor. Experiments are performed to monitor the moisture of a dehydrating breather of 0.5 kg capacity in the laboratory. The proposed moisture-controlled breather reduces the error due to wrong visual inspections of the moisture level in the drying agent; timely replacement of the drying agent; and the improvement of the operational reliability of the transformer.