ABSTRACT
This chapter discusses the British and North American low-voltage distribution systems which are different from each other, with North America tending to use a greater number of distribution transformers. If the polarities of the adjacent high and low voltage terminals are same, then the transformer has 'subtractive polarity' wheareas if the opposite high and low voltage terminals are identical, then the transformer has 'additive polarity'. The chapter focusses on three-phase transformers which are connected in parallel. Angular displacement determines whether the three-phase transformers are connected in parallel with each other. A transformer's percentage impedance can be determined by short-circuiting the secondary winding with an ammeter, and gradually increasing the primary voltage until rated current flows in the secondary. In the United States and Canada, a completely different system is used for residential supplies. It is a dual-voltage system, termed as 'split phase' system, or sometimes referred to as a 'two-phase' system.
