Five-Limbed Transformer Cores

There are many five limbed core configurations. In all the existing configurations specific loss (loss per kg at a given flux density) is higher than the three phase three legged core. The reasons are yoke areas not matching with the amount of the flux fl owing and the mitered joints also not matching with the quantity of the flux flowing. Compared to the non-split cores, the split cores are posing manufacturing problems and higher losses. Model core of a new configuration and two model cores of existing configurations were built and tested. Relative merits of the new core configuration and reduction in losses are tabulated. This new core configuration can be adopted easily for both non-split and split cores. Relative advantages and disadvantages of different core configurations are discussed.

Tests conducted on model cores described in this paper are limited to five-limbed core type transformer cores. Iron losses were measured at different flux densities on model five-limbed cores with different core configurations. The first model (Type 1) is the typical configuration being used by transformer manufacturers around the world. An attempt is made to build another model five-limbed core (Type 2) by modifying the position of mitered joints of main end limbs laminations. This modification was done so that the flux from the main end limbs can fl ow from limbs to yokes without overcrowding at mitered joints. Often, the diameter of the main limbs is greater than the maximum widest width lamination normally available (1000 mm). For this reason, five-limbed cores often have split limbs. A third model (Type 3) representing the split core was also built to get a loss comparison with non-split cores.