ABSTRACT
Modern electrical systems are almost exclusively three-phase systems, notwithstanding the many miles of distribution circuits that are configured as single-phase taps off of these systems. In addition, there still exist remnants of two-phase systems (typically in mining operations) that were fairly common years ago. When two polyphase systems have different voltages and/or phase angles, these systems can be interconnected using transformers having various possible types of connections. Any one of these connections can be accomplished either with a bank of single-phase transformers or by a single polyphase transformer. As we shall see in this chapter, it is in fact possible to interconnect two polyphase systems having a different number of phases using special transformer connections.
