3-phase shell form cores are normally wound. A common configuration for wye-wye transf's is a 5-leg wound shell form core. Core form transf's are usually stacked. Delta-wye connected transformers commonly have 3-leg core with stacked laminations.
Shell or wound core is obviously better as it allows zero sequence flux / third harmonic flux to circulate easily keeping the corresponding impedances low. It also results in less height of the core limbs for a given transformer rating and thus is a default standard for large rating transformers (low height facilitates transportation).
Core type is economical and widely used for small and medium rating transformers.
Core losses...on 2 differing cores. First core is wound such that each sheet is 1 complete turn plus the offset. The other is cut one complete turn less the gap.
The core with 1 turn less gap should be more efficient but how to prove it and why?
