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PowerPoint® Presentation Chapter 4 Transformer Connections Voltage Transformation Three-Phase Circuits Delta Connections Wye Connections Delta-to-Wye Connections Wye-to-Wye Connections Wye-to-Delta Connections Delta-to-Delta Connections Open Delta Connections Delta Connection with High Leg to Ground Three-Phase Transformer Polarity Chapter 4 Transformer Connections The low-voltage winding of a standard distribution transformer connected to a single-phase circuit is normally made with two equal coils. These sections are arranged so that they may be connected in series or parallel. Chapter 4 Transformer Connections Transformer polarity may be subtractive or additive. Chapter 4 Transformer Connections The polarity of a transformer may be determined using a known transformer or with AC voltage. Chapter 4 Transformer Connections A delta connection has the wires from the ends of each coil connected end-to-end to form a closed loop. Chapter 4 Transformer Connections Studying the current in a delta-connected system at both 0° and 90° illustrates the current flow in a deltaconnected system. Chapter 4 Transformer Connections A wye connection has one end of each coil connected together and the other end of each coil left open for external connections. Chapter 4 Transformer Connections Studying the current in a wye-connected system at both 0° and 90° illustrates the current flow in a wyeconnected system. Chapter 4 Transformer Connections A 3-phase delta-towye connection is often used for distribution where a four-wire secondary distribution circuit is required. Chapter 4 Transformer Connections Three single-phase transformers may be connected in a wye-to-wye connection to form a 3-phase transformer. Chapter 4 Transformer Connections A wye-to-delta connection permits single-phase and 3phase loads to be drawn simultaneously from the deltaconnected secondary at the same voltage. Chapter 4 Transformer Connections In a wye-to-delta connection of three singlephase transformers, one unit may be disconnected from the circuit and service maintained with the secondary operating in open delta connection at 57.7% of normal bank capacity. Chapter 4 Transformer Connections In a delta-to-delta connection, the voltage of each transformer is equal to the 3-phase line voltage and the current in each of the transformers is only 57.7% of the line current. Chapter 4 Transformer Connections Grounding one of the midpoints of the windings provides 240 V/120 V, single-phase, 3-wire service for lighting applications. Chapter 4 Transformer Connections An open delta connection makes 3-phase power available anywhere along the distribution line with the use of only two transformers rather than the usual three. Chapter 4 Transformer Connections A delta connection with a high leg to ground provides 240 V, 3phase power to equipment and 120 V power for lighting and receptacles. Chapter 4 Transformer Connections The phase sequence on the secondary of a three-phase transformer is the same as the phase sequence on the primary. Chapter 4 Transformer Connections Transformers are classified into connection groups according to their phase shift. Chapter 4 Transformer Connections Chapter 4 Transformer Connections