Condition assessment of transformer oil using UV-Visible spectroscopy

Transformer plays an important role in both the transmission and distribution system in electrical power system network. During continuous long period of its operation, transformers are mainly subject to huge thermal and electrical stresses, which can cause the degradation of the insulating oil present inside the transformer. The degradation of such insulation leads to catastrophic failure of transformer which further leads to power system network failure. Since there is a great necessity of inspecting the oil time to time, absorption spectroscopy is considered for condition assessment tool because it has the potential to take measurements during operation, which has better measurement ranges for low concentrations. In this work, a novel method used for transformer health assessment is developed based on the characteristic of spectral absorption by adopting ultraviolet absorption technique. The outcome of the absorption of in-service and laboratory aged transformer oil is so significant that absorption increases by observable margin over a wide range of wavelengths. From the obtained results, the sensitivity and reliability of the UV-Visible method in monitoring degradation of oil is analysed and discussed.

I. Introduction

Power Transformers are one of the most important components in the power system network. They are also considered as the costliest equipment in the field of electrical power system. To have reliable electricity supply, there is need to give sufficient attention to the transformer maintenance. In power transformers incipient faults can degrade the oil and cellulose insulation, leading to the formation of dissolved gases. Mineral oil performs two important functions in transformers i.e. it cools the transformer and provides electrical insulation, as well [1]–[2]. Therefore any deterioration in the oil can lead to premature failure of the equipment. When the mineral oil is subjected to high thermal and electrical stresses, gases are generated from the decomposition of the mineral oil [3]–[8]. Different type of faults will generate different gases, and the analysis provides useful information about the condition of the oil and the identification of the type of fault in the transformer. The chemical analysis of these gases is called dissolved gas analysis or DGA [9]. In oil filled transformers, DGA is used as one of the entrenched techniques to predict incipient faults inside its enclosure. Electrochemical sensors and gas chromatography encountered many problems that optical detecting methods are widely used in on-line monitors for dissolved gas-in-oil of power transformers, but some fatal defects exist [10]–[12]. There are very good detection techniques to analyze the aged transformer oil which have been used by many researchers and obtained influential results. In this work absorption spectroscopy is used for condition assessment of transformer oil. This is a spectroscopic technique that measures the absorption radiation as function of frequency or wavelength due to the interaction with a sample. It is performed across the electromagnetic spectrum. Absorption spectroscopy is used to determine the presence of particular substance in a sample and also quantify the amount if the substance present. Some of the common applications of this are: FTIR and Ultraviolet-Visible spectroscopy.