Highly sensitive thin-film capacitive sensor for online moisture measurement in transformer oil

摘要

This study describes a low-cost sensor-based scheme for online moisture measurement in transformer oil. Considering a harsh environment, moisture measurement of oil at ppm level is challenging, so the sensor should be highly sensitive and thermally and chemically stable. The conventional methods are mostly offline, have long test times and are costly. A thin-film parallel plate capacitive moisture sensor has been fabricated using inexpensive materials to measure the moisture of fresh, aged and 0.5% water content oil samples. The moisture sensing film is highly hydrophilic and is made of alumina oxide, a very stable material. Experiments were conducted to determine the response parameters of the sensor in the presence of moist nitrogen gas, the concentration of which was measured by a commercial SHAW dew point meter. Experiments were also performed to measure the moisture of different oil samples in the laboratory. Results show that the output of the sensor is sensitive (6 pF/ppm moisture), has negligible hysteresis (similar to 1% at 1 kHz) and has fast response and recovery times (T-res = 70 s, T-rec = 170 s).