ABSTRACT
Three-phase transformer banks are found in the distribution substation, where the voltage is transformed from the transmission or subtransmission level to the distribution feeder level. In most cases, the substation transformer will be a three-phase unit, perhaps with high-voltage no-load taps and, perhaps, low-voltage load tap changing (LTC). For a four-wire wye feeder, the most common substation transformer connection is the delta–grounded wye. A three-wire delta feeder will typically have a delta–delta transformer connection in the substation. Three-phase transformer banks downstream from the substation will provide the final voltage transformation to the customer's load. A variety of transformer connections can be applied. The load can be pure three-phase or a combination of single-phase lighting load and a three-phase load such as an induction motor. In the analysis of a distribution feeder, it is important that the various three-phase transformer connections be modeled correctly.
