Session #: High Voltage Power Transformer Paper Insulation Assessment Techniques High Voltage Maintenance Forum – IDC Technologies 1 Session Number: (3) High Voltage Power Transformer Paper Insulation Assessment Techniques Norazhar Abu Bakar and A. Abu-Siada Department of Electrical and Computer Engineering, Curtin University, Perth, Australia Abstract Energized parts within power transformer are isolated using paper insulation and are immersed in insulating oil. Hence, transformer oil and paper insulation are essential sources to detect incipient and fast developing power transformer faults. Several chemical diagnoses techniques are developed to examine the condition of paper insulation such as degree of polymerization, carbon oxides, furanic compounds and methanol. The principle and limitation of these diagnoses are discussed and compared in this paper. Introduction Power transformers represent a vital link in any electrical transmission or distribution network. Unexpected failure won’t only cause loss of revenue but it may lead to a catastrophic failure including environmental hazards due to oil spillage. Therefore, it is essential to adopt appropriate monitoring and diagnostic techniques for incipient fault detection to avoid catastrophic failures and help to provide efficient predictive maintenance that improves the reliability of the equipment [1 ]. Often, power transformer health is referred to the quality of its insulation system which consists of paper insulation immersed in insulating oil [2 , 3 ]. Hence, samples of transformer oil and paper insulation are essential sources to detect incipient and fast developing faults. Transformer faults generally result from the long term degradation of oil and paper due to the combination of heat (pyrolysis), moisture (hydrolysis) and air (oxidation) [4 , 5 ]. Due to electrical and thermal stresses that in-service power transformer experiences, oil and paper decomposition occurs resulting in a number of gases related to the cause and effect of various faults. Gases produced due to oil decompositions are hydrogen (H 2 ), methane (CH 4 ), acetylene (C 2 H 2 ), ethylene (C 2 H 4 ) and ethane (C 2 H 6 ), while carbon monoxide (CO) and carbon dioxide (CO 2 ) are mainly produced by paper decompositions and can be used as a trigger source for paper monitoring [6-8 ]. The characteristics and concentrations of the gases dissolved in transformer oil vary by the nature of fault, and hence can be used to identify the type of fault. However, the analysis is not always straightforward as there may be more than one fault present at the same time. Transformer internal faults are categorised into thermal or electrical where each fault evolves particular characteristic gases and produces energy from low level to high level of sustained arcing. Partial discharge which produces H 2 and CH 4 is a low level energy fault, whereas arcing that capable to generate all gases including C 2 H 2 is considered high level energy fault [6 , 8 , 9 ]. Various faults and characteristic gases it produce are illustrated in Fig. 1.