Abstract
Moisture is an important variable that must be kept under control to guarantee a safe operation of power transformers. Because of the hydrophilic character of cellulose, water mainly remains in the solid insulation, while just a few parts per million are dissolved in oil. The distribution of moisture between paper and oil is not static, but varies depending on the insulation temperature, and thus, water migration processes take place continuously during transformers operation. In this work, a sensor is presented that allows the determination of the moisture content of the transformer solid insulation in the steady state and during the moisture migration processes. The main objective of the design is that the electrodes of the sensor should not obstruct the movement of water from the solid insulation to the oil, so the proposed prototype uses a metallic-mesh electrode to do the measurements. The measurement setup is based on the characterization of the insulation dielectric response by means of the frequency dielectric spectroscopy (FDS) method. The sensitivity of the proposed sensor has been tested on samples with a moisture content within 1% to 5%, demonstrating the good sensitivity and repeatability of the measurements.
Highlights
Power transformer reliability is essential for the adequate operation of power systems
IEEE Standard C57.106.2006 discourages the use of this kind of direct calculation, as the charts are only valid under equilibrium conditions, and their use might lead to errors in the estimation of moisture of up to 200% [8]
Methods based on the characterization of the dielectric response have been used for years to estimate the moisture content in transformer solid insulation in field conditions
Summary
Power transformer reliability is essential for the adequate operation of power systems. Some of the main causes of transformer failures are related to their electrical insulation These failures usually result in huge economical costs for the electric companies in terms of damage to infrastructure and penalization for interruptions of the electricity supply [1]. Its presence increases the aging rate of the insulation, reduces its dielectric margin and decreases the partial discharge inception voltage [2]. These phenomena increase the probability of unexpected failures, so being able to estimate the water content of transformer solid insulation is highly desirable to make adequate decisions related to maintenance operations, as well as to predict potential failure conditions [3,4]
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