Insulation Life Assement of High Voltage Transformer: A Review

Abstract

The life of the transformer depends upon the insulation of the transformer. It deteriorates with due course of time in operation. It happens because of the faults in the transformer. Several techniques are used to predict the fault to diagnose it, in order to increase the life of the transformer. various artificial techniques are also used for this purpose. This paper gives the review of life assessment of insulation of transformer and various techniques are discussed. Keywords-Transformer fault , Dissolved gas analysis , various artificial techniques. I. INTRODUCTION Transformer has an important role to play in the power system where it may be used to level up the voltage for transmission distributing the energy to consumers. So it has to live long and operate stably. The main problem in the degradation of life of transformer is the degradation of insulation in the transformer. It happens in the transformer because of several factor, some of them are included in electrical stresses and thermal stresses. These are voltage level, harmonics, use of power electronic devices, evolution of gasses, heating, water content etc. the insulation used for the transformer may be inorganic and organic, dry or oil insulation, or solids insulation which include concrete blocks, spacers etc. life of the transformer depends upon the condition of insulating material [1]. Dry insulation is mainly used in windings. Reliability of insulating system of dry insulation transformers is obtained based on three models which are degradation, regression and expert judgement. The various insulating materials used in the transformer are [2]: Insulating fluid: mineral oil, synthetic or vegetable oil. Conductor insulation: Kraft and Kraft paper, Nomex, Enamel Solid insulation: barriers, blocks, spacers The introduction of power semiconductor devices in a power system also leads to insulation degradation due to high frequency hence reduces life [2]. Distorted voltage is also responsible for insulation descent [3]. In oil immersed transformers ratio method recommended by IEC /IEEE is widely accepted also some artificial intelligence techniques have been introduced in calculating the dissolved gas analysis to overcome the short coming of ratio method [4]. For the evolution of gasses in the transformers there are three main causes which are which are included in the thermal stress. These are overheating, corona and arching. the gasses which are produced in transformer during faults are Hydrogen (H 2) , Carbon monoxide (CO), Methane(CH 4), Acetylene (C 2 H 4), Ethane (C 2 H 6), Ethylene(C 2 H 2) [5]. Transformer is the most expensive equipment in the power system hence it has to be protected from faults. Power transformers are greatly influenced by condition of insulating material. The processes like degree of polymerization, dissolved gas analysis, furan analysis are wide used to determine aging processes. Artificial techniques are used for DGA to analyze the ratio of gasses to give fault type [6]. The transformer is only monitored through DGA, water...