Mamadou Lamine Coulibaly

Insulation system used in power transformers is exposed to different constraints and particularly to thermal stress combined with oxidation and hydrolysis phenomenon. Such process can lead to the gradual degradation of the cellulose/oil insulation by ageing, then a deterioration of transformer reliability. Nowadays, due to the increase demand for energy consumption and the use of various types of energy on electrical network, ensuring the service operation continuity with reliability is not a choice but a key requirement which involves a continuous assessment and rigorous monitoring of the transformer insulation system. For the assessment of cellulosic insulation ageing status, the most important characteristic to be evaluated by direct measurement is the degree of polymerization (DP). The disadvantage of this method is the non-accessibility of cellulose based materials in service. Fortunately, indirect methods can be achieved by using the diagnosis via the analysis of cellulose degradation byproducts like markers (dissolved gas, furfural content, alcohol, etc.) produced in the insulating oil. In addition, DGA diagnosis techniques (online monitoring and/or direct sampling of oil) can be also used to identify faults in transformers and prevent equipment failures and service interruption. This lecture is dealing with the transformer insulation system and the main factors affecting its ageing status as well as the monitoring through the ageing markers in oil. In addition, DGA diagnosis methods, mainly focused on Duval Pentagons and Triangles, for faults identification in power transformers is presented and the method applied to a service case study.

Ključne reči: power transformer, ageing, transformer oil, DGA