The influence of core geometry on no-load losses of medium power transformers

The paper deals with the analysis of power transformer's no-load losses according to its geometry. The object of the study was a series of medium power transformers (6.3-40 MVA) produced for the Polish Electric Power System. Those transformers were installed in 110 kV's grid. The main customers are the energy distribution companies such as PGE, Enea, Energa and Tauron. Due to the high requirements of those companies, the no-load losses are a significant issue. The no-load losses have been calculated and measured. The calculation was carried out using the own algorithm. The following types of measured losses are considered: losses from the final test of the entire transformer and losses from the test of the core before the complete transformer assembling. The tests of only the core were executed by two independent laboratories: the producer of the core and the producer of the transformer. The tests were conducted according to the norm PN-EN 60076-1:2011. The calculations and measurements' results are in close agreement. Moreover, the relation between the percentage of corners and additional losses was observed. The knowledge about this dependency may be effective to design transformers with reduced losses.