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Original scientific paper

Investigating core influence on transformers insulation diagnostics

Roberto Borges
Ronald D. Hernández
Waldemar Ziomek
Ryan Plater

Full text: english pdf 1.223 Kb

page 108-117

downloads: 234



In a healthy power transformer, the power factor (PF) of the low-voltage winding insulation to the ground (CL) is expected to be less than 0.5 %. In recent cases, the CL PF measured during the factory testing exhibited high values close or above 0.5 %. Investigations have determined that
the issue might be related to a higher than usual core steel interlaminar resistance, occurring due to a combination of shorter burrs and higher non-uniform insulation resistance between laminations. This article describes the phenomena and proposes a test protocol to differentiate the
problem from other issues that cause high CL PFs, such as moisture or contamination / deterioration of the insulation.


core interlaminar resistance, insulation, insulation power factor, transformer diagnostics

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