A B S T R A C TThe humidity or the dissolved water in insulating oils influences conduction and breakdown phenomena. The corrections between the amount of dissolved water and the electrical properties have been investigated. However, the effect of water has been based only on the total amount of water because in the past there was no way to observe the state of water in oil in an electrical field. With the availability of Fourier transform infrared (FTIR) to characterize water clusters, the effect of water in transformer oil can be reassessed based not only on the amount of water, but also on the state of water. In this paper, IR spectra of water in several liquid hydrocarbons and conduction current were measured at the same time. The selection of the liquid hydrocarbons was made on the basis of the degree of polarizability of the liquids. Because of the water molecules combine with the polar structures by hydrogen bonding, the state of water depends on the polarizability of the oil. As a result, there is a difference in conduction phenomena depending on whether water is free or combined with the polar structure of the liquid.
It has been understood that the deterioration of electrical properties was caused by the amount of dissolved water in liquid dielectrics. Moreover, it is believed that such dissolved water molecules diffuse into free space in liquid dielectrics uniformly, because the behavior of water molecule can not be observed by Karlfisher's method, though only the amount of water has been observed. But recently, by using FT-IR method, it is published that the almost dissolved water molecules behave as binding water bound by the polar bases of dielectrics. The binding force was caused by hydrogen bonds between
1.IntroductionIt is well known that the humidity or the dissolved water in insulating oils influences the conduction and breakdown phenomena of the oils. The amount of water in the purify insulating oils used for power apparatuses is regulated to make the water does not deteriorate the electrical properties, but the water supplied from the other insulating materials impregnated by the oils dissolving in the oils during the power apparatuses are working.The behavior of water in insulating oils depends on the chemical component of the oils, because the water exists as not only a water molecule but also water clusters which bounds the polarized base of the oils. Such the behavior or the states of water in the insulating materials are understood by estimating IR spectrum of the water[l-31. In saturated hydrocarbon liquids, the water behaves as like water vapor, because is no polarized base which catches water molecules by hydrogen bonding. In unsaturated hydrocarbons and aromatic hydrocarbons, the water molecules bound to the polarized base, and build up the water clusters, for example water dimmer, trimmer, and much larger clusters. It was observed that such the bound water cluster makes the conductivity increase [3].The insulating oils used for power apparatuses, especially the transformer oils, consists of saturated hydrocarbons including a few amount of the water behaving like water vapor, but the transformer oils under the electrical and thermal stress include the carboxyl groups with the bound water clusters. As supplying the water molecules from insulating paper or pressboard, the amount of water cluster increases, and the bound water clusters will influence to the conductivity.In order to consider the behavior of the water and its effects for conductivity in the aged transformer oils, this paper choose the two series of hydrocarbon materials including carboxyl group. One series of the samples have a carboxyl base at the center of saturated hydrocarbon chain, another series have a carboxyl group put on one side of the chain.In the latest investigation for the estimation of IR spectrum of water cluster in dielectric materials, the place where the bound water exists in is discussed [4]. In this paper, the behavior and effect of the bound water on conductivity is considered with the latest estimation of IR spectrum of the water.
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