PROJECT TITLE :
Impact of local overheating on conventional and hybrid insulations for power transformers
For a lot of than a century, standard mineral oil/cellulose insulation is getting used as main insulation for power transformers. The lifetime of these major assets is set amongst others by the insulation system???s mechanical resistance to face up to short circuit current forces. Since cellulose paper aging is accelerated by temperature, moisture and oxygen, poly-aramid-primarily based artificial insulation paper, with higher thermal stability emerged for application in transformers. However the relatively restricted variety of studies on hybrid insulation and the price of aramid paper still limit their use in distribution transformers. This contribution makes an attempt to demonstrate that despite the high value of aramid paper, hybrid insulation may be employed in large power transformers that represent a vital money investment. To do that, the quality of mineral oil aged with hybrid solid insulation and also the thermal aging of the cellulose paper of this insulation are investigated. Comparison was made with ancient mineral oil impregnated cellulose paper to provide a benchmark for comparison. The samples underwent thermal accelerated aging procedure according to ASTM-D1934 commonplace and, furthermore, were submitted to local overheating. The condition of oil samples collected from every aging vessel was assessed using many diagnostic techniques, specifically the relative amount of the Dissolved Decay Products (DDP), Turbidity, and Interfacial Tension (IFT). The Degree of Polymerisation (DPv) and Dissolved gas Analysis (DGA) were used to watch the thermal aging of the cellulose paper samples. The results indicate that oil aged with hybrid solid insulation yield fewer decay product at some aging stages, especially after the applying of a local overheating. The results also indicate that the cellulose paper within solid hybrid insulation is slightly less degraded compared to that of conventional insulation.
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