Microwave-based sensor for power transformers' insulation oil monitoring

Here, a new device is presented to supervise the ageing process of insulating oils used in power transformers. It is based on the use of a microstrip antenna whose electrical properties are very sensitive to the permittivity and conductivity of the medium. As many works showed that the drift of permittivity due to transformers aging is very small, the achieved sensor must exhibit a great sensitivity. In order to assess the aging of the insulation oil, the authors will track the resonant frequency of the antenna which is directly related to the permittivity of the oil, and the reflection coefficient level of the antenna at the resonance frequency which is linked to the conductivity. The experiments have been made on vegetable oil and results revealed to be enthusiastic. The sensor is proposed to be used in an embedded system in order to achieve a low cost and safe preventive diagnosis.