Measurements and modeling of moisture diffusion processes in transformer insulation using interdigital dielectrometry sensors

The presence of moisture in a transformer deteriorates the transformer insulation by decreasing its electrical, mechanical, and thermal strength. Therefore, it is important to monitor the moisture condition in both liquid and solid insulation to assure transformer performance. There are commercially available sensors to measure the moisture in oil. When the transformer system is in equilibrium, moisture partitioning curves for the oil-paper system can be used to find the moisture in paper from the oil measurement. A comprehensive study of the classic moisture equilibrium curves is given, historical mistakes are corrected, and all relevant concepts are clarified. This research serves as a useful tool to utilities and manufacturers. A new set of moisture equilibrium curves is constructed for moisture in oil up to the saturation moisture content. A measurement technique exploiting the linearity between the relative humidity of the oil and the moisture content of the oil to indirectly measure the oil solubility is developed. Solubility tests are performed for differently conditioned oils: Fresh Shell Diala AX oil, lab-aged Shell Diala A oil, used oil from Ramapo Substation, and used oil from Texas Utilities. Results show that aging under normal operation at service temperature is not very likely to significantly change the water solubility. When the system is not in equilibrium, the equilibrium moisture curves are not applicable and the three-wavelength interdigital dielectrometry sensor developed at the MIT Laboratory for Electromagnetic and Electronic Systems provides a unique way to measure the spatial profile of the moisture distribution in transformer pressboard.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

1999

Author dc:creator

• Du, Yanqing, 1971-

Advisor dc:contributor.advisor

• Markus Zahn and Bernard C. Lesieutre.

• Electrical Engineering and Computer Science

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/16725

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16725