Outcall: Hotel visits only
You must be logged in to view this content. Please click the button below to log in.Login
Three-phase Transformer Circuits
Since three-phase is used so often for power distribution systems, it makes sense that we would need three-phase transformers to be able to step voltages up or down. This is only partially true, as regular single-phase transformers can be ganged together to transform power between two three-phase systems in a variety of configurations, eliminating the requirement for a special three-phase transformer. However, special three-phase transformers are built for those tasks and are able to perform with less material requirement, less size, and less weight than their modular counterparts. A three-phase transformer is made of three sets of primary and secondary windings, each set wound around one leg of an iron core assembly. Essentially it looks like three single-phase transformers sharing a joined core as in Figure below. The various combinations of ways that these windings can be connected together it will be the focus of this section. Whether the winding sets share a common core assembly or each winding pair is a separate transformer, the winding connection options are the same:. Let me illustrate, starting with the figure below.
Three-phase voltage transformations can be accomplished by using three phase transformers, which are single devices with all windings constructed on a single iron core. They also can be accomplished by using three single-phase transformers that are connected externally to form a three-phase bank. While three-phase devices are usually the more cost-effective option, the single-phase option provides more versatility and can be attractive from a reliability and maintenance standpoint. If several identical transformers are needed at one location, the single-phase option can include the purchase of a spare unit to reduce outage time in the event of a failure. This practice often is seen with critical autotransformer banks and generator step-up transformers because loss of the transformer for an extended period has very significant impacts. The connections discussed in this article will be implemented using single-phase units.