Analysis On Moisture In Oil-paper Insulation Using Frequency Domain Spectroscopy

With the rapid and steady development of Chinese economy, its power industry also developed rapidly over the past few decades. Now the number of power transformers on operation is increasing. The safe operation of power transformers is the first defense system to avoid the major accident of grid, if a large power transformer in the system run-time failure, it may lead to blackouts, and the maintenance generally takes six months or more. So it may cause large loss to the national economy, and bring a huge inconvenience to the people. At present oil-immersed transformer is the most widely used in power system, and oil-paper insulation of oil-immersed transformer directly affects the electrical performance and operational life. Water is an important factor which impact performance of oil and paper insulation, and water will reduce the breakdown voltage of the insulation system and increasing dielectric loss. When the oil in moisture content exceeds a certain threshold, the insulation performance of device will greatly reduce. Oil-paper insulation system absorbing water caused degradation, aging, increased dielectric loss, lowed the insulation resistance, and PD starting voltage was declining, leading to the operational life of the transformer be seriously affected. Therefore, testing the whole water content of oil-paper insulation system has a great significance for transformer's safe and stable operation.The moisture content of transformer oil can be tested by collecting sample and laboratory analysis, and generally testing methods is the Karl Fischer titration—KFT. But once the transformer is operational, due to inability to obtain samples of the insulation paper, to estimate the moisture content of paper is more difficult. The traditional method is to determine water content in oil and indirect access water content values through water content distribution curve. So if we can directly analyze the oil-paper insulation system posed by paper/oil insulation, it will be very important the for analysis of water content particularly.This paper used the dielectric spectrum method (Frequency Domain Spectroscopy) which basis of the dielectric response theory, with laboratory equipment and facilities, built the experimental test platform for oil-paper dielectric response test. Simulated the oil-paper insulation system model by Ansoft12 Maxwell2D electromagnetic simulation software to study the the electromagnetic field distribution between the electrodes of dielectric plate capacitance sensor, the current density and dielectric loss distribution oil-paper insulation. Simulated the actual operation of the transformer, and accelerated thermal aging tests by laboratory simulation of transformer oil-paper insulation aging, set the oil-paper insulation system directly as a measured object, studied the dielectric spectra at different temperatures and different conditions of water content variation; analysis the dielectric properties of oil-paper insulation, got its information of the water content, so it can supply an important basis for the correct diagnosis of transformer insulation condition, assessment of transformer's remaining life and improving power supply reliability.