Investigation of transformer oil by nuclear magnetic relaxation and Z-scanning

Abstract

G K -g r a d e t r a n s f o r m e r o i l i s i n v e s t i g a t e d b y m e t h o d s o f n u c l e a r m a g n e t i c r e l a x a t i o nand Z-scanning. The size of the heterogeneous structures in the oil increases during its service. The solid-particle content in the liquid phase, however, remains essentially unchanged, and the excess particles precipitate. The feasibility of quantitative determination of the heterogeneous-structure/liquid ratio in oil samples investigated is discussed.Heterogeneous structures -colloidal, micelle-like, and solid particles -affect the properties of transformer oils (TO), and may substantially reduce the breakdown voltage, and alter the viscosity and other TO characteristics critical to power transformers, and, consequently the power systems on the whole [1, 2]. Owing to the physical and chemical processes that take place under the action of temperature, electric fields, and circulation of oil, the composition of the heterogeneous structures is altered over the life of the TO. These processes are currently being monitored by an obsolete method [3], which, in our opinion, is unreliable due to insufficient accuracy.Investigations [4][5][6][7] have indicated that heterogeneous structures always exist in TO. A method of determining the percentage of solid particles in oil products with use of nuclear magnetic (NM) relaxation is described in the literature [8]. We have been unable, however, to find information on the applicability of this method to TO. The Z-scanning method is sensitive to nonlinear optical absorption of delocalized electrons, occurring most frequently in the heterogeneous particles [9]. This study described results of TO investigation by NM-relaxation and Z-scanning methods.