DOI link for Transformer Connections
Transformer Connections book
The applications of the transformer connections are dependent on whether the transformation is distribution service, generation step-up, transmission transitions, or special applications. This chapter specifically addresses the most common connections for conditions of service in distribution and transmission systems. Three-phase connections can be made either by using three single-phase transformers or by using a three-phase transformer. Unbalanced system faults and loads can cause significant zero-sequence magnetic flux to occur for some three-phase connections. The existence of zero-sequence flux either within or outside the core depends on both core configuration and winding connections. In all types of wye–wye transformer connections, only the transformer positive-sequence impedance limits the fault current during a system three-phase system fault. For any three-phase connection of three-limb core-form transformers, the impedance to third-harmonic flux is relatively high on account of the magnetic coupling between the three phases, resulting in a more stabilized neutral voltage.