2 - Design fundamentals

Abstract

This chapter explores the design fundamentals of a transformer. It starts off a brief description of the different types of transformers. There are two basic types of transformers categorized by their winding/core configuration: (1) shell type, and (2) core type. In a shell-type transformer the flux-return paths of the core are external to and enclose the windings. Core-type transformers have their limbs surrounded concentrically by the main windings. Once the various transformers are classified, the phase relationships in different situations are described. While designing a transformer, it is essential to keep in mind the volts per turn and flux density. The flux density is as high as possible consistent with avoiding saturation within the core. It is emphasized that for a given supply frequency the relationship between volts per turn and total flux within the core remains constant. Other issues related to the design fundamentals of transformer such as tapping and impedance are also covered in this chapter. And finally, the last section is devoted to the discussion of general case of three winding transformer. The voltage regulation of a winding on a three-winding transformer is expressed with reference to its no-load open circuit terminal voltage.