Sweep frequency response analysis test as tool for distribution transformers management

Abstract

Distribution transformers used in secondary substations are strongly affected during faults in low voltage grids. Transformers are expected to survive a number of short circuits without failure but, once any significant winding deformation or core damage is produced, the service life and the likelihood of surviving further short circuits is greatly reduced because of locally increased electromagnetic stresses. Given the need for diagnosing failures and quickly putting the unit back into service it is evident that a complete set of tests, as done in power transformers’ condition assessment, is not an option. The main objective of this paper is to present Sweep Frequency Response Analysis (SFRA) test as an alternative to assess the mechanical condition of distribution transformers. For this purpose, a special design of a distribution transformer was used to simulate some failure modes and improve interpretation criteria.