Developing Fiber Optics Moisture Sensors and System used in Transformers and Bushings

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Precise measurement of humidity and moisture has many applications particularly monitoring environmentslike agricultural seed storage, in chemical, biomedical, food, and electronic processing, hospitals, museumslibraries and generally, in most buildings. Moisture measurement in high voltage engineering formeasurements of water content in transformer oil is very important. Currently the industry is relying on variousmethods of measuring partial discharge (PD) to determine when a transformer needs to be serviced. Mostmethods only give indications when damages are already done. The measurement of moisture in the windinginsulation paper and frame allows the transformer to be serviced before damages happened, this will lead to amore robust power system and considerable savings. Among several techniques such as electrical sensors, fiberoptic sensors are capturing more attention due to small size, light weight, susceptible to multifunctional sensingand more importantly their immunity to electromagnetic interference. Fiber Bragg Grating (FBG) based opticalsensors have become widely known and popular. FBGs are compact intrinsic sensing elements, which arerelatively low cost to produce, easy to multiplex, and applicable to a range of strain and temperature sensingapplications. Recently QPS Photonics Inc. has developed a moisture sensor using two types of FBGs, astandard FBG and an advanced phase shifted gratings. This sensor was developed by incrementally applying 10layers of polymide coating over the grating area, and cured at 300 C. The coating upon contact with moisture,absorbs the moisture, slightly expands and recovers from the inherent strain. The objective of this project is todevelop a high sensitive and cost effective optical sensor for monitoring the temperature and moisture inside ahigh voltage power transformer. This project is involved with the design of packaging and characterizing theperformance of the sensor which capable to detect small trace of moisture. This would be the first time in theworld that such a capability will be developed, allowing transformer owners to understand, in real time, thetransport of moisture which depends on the operating oil temperature, and loading.