1 、 the transformer is polluted when it is installed
When the transformer is installed, it contains dust and impurities, and after a period of operation, the colloidal impurities are gradually dispersed. Colloidal particles are small in diameter, generally only in the 10-9 - 10 - 7m, diffusion is slow, but there is a certain activity energy, particles can automatically coalescence, from small to large, for coarse dispersion system, in a non-equilibrium unstable state. When the colloid range is exceeded, it is deposited by gravity, but the stability of colloid is large, the deposition time is slow, and it is affected by temperature and voltage. The automatic colloid coalescence instability in non equilibrium, the dispersion concentration in each horizontal plane range, generally, the dielectric loss at the bottom and bottom oil concentration equipment value is large, the upper oil dielectric loss value is smaller, therefore, different sampling positions will also directly affect the determination of transformer oil medium loss.
2, oil and solid insulation water balance exchange
In oil filled equipment, the sources of insulating oil and oil immersed insulation are: external immersion and internal self formation.
External immersion. The first is the process of manufacturing transformers and other electrical equipment of the insulating material although after drying treatment, but its deep still contains residual moisture in the course of transportation and installation such as improper protective measures the insulating material will again damp, moisture into the respiratory system operation, through the infiltration of oil within the oil surface.
Autogenic. The equipment inside water is the solid insulating materials and transformer in the operation process, because the oxidation and thermal cracking and formation water, insulating oil and dissolved oxygen in the operation temperature, accelerate the oxidation of organic acids produced to generate water.
The water in the air and fiber fiber oil at a certain temperature to reach the equilibrium distribution, containing oil and moisture in the paper can be mutual conversion, when the temperature is high, the increase rate of oil and water, reducing the moisture content of paper, paper moisture diffusion to oil; when the temperature decreases, the rate of increase of water water paper, and oil moisture content decreased, insulation paper will absorb the water from the oil, water and oil containing oil, season of transformer (temperature) of the resulting changes. The water content in oil is high in summer and low in winter. But can not balance moisture between the oil and the paper in the short term, for large transformer is relatively stable in the operating temperature, the balance should be several months to achieve, therefore, high temperature insulating oil dielectric loss due to changes in different seasons were.
3, microbial pollution
Because the oil contains water, air, carbonized organic matter and various minerals, the basic conditions for microbial growth are formed. Microorganisms live and reproduce in this particular environment. High temperature dielectric loss test of the oil in the oil microorganism is extremely sensitive, the main variable in different periods with different load, operation temperature and microbial propagation speed at different temperatures are different, so the value is not high temperature stable dielectric loss of oil.
4 measurement difference of different test equipment
When the same oil sample is tested by the oil loss test equipment of different types and manufacturers, there are random and operational errors. When the high voltage standard capacitor has a large loss, the accuracy of the bridge is not up to the standard, or the heating device is too fast and too slow, it is the direct cause of the loss of dielectric loss.