powerpoint ® presentation chapter 4 transformer connections voltage transformation three-phase...

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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

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Slide 2 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 Slide 3 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. Slide 4 Chapter 4 Transformer Connections Transformer polarity may be subtractive or additive. Slide 5 Chapter 4 Transformer Connections The polarity of a transformer may be determined using a known transformer or with AC voltage. Slide 6 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. Slide 7 Chapter 4 Transformer Connections Studying the current in a delta-connected system at both 0 and 90 illustrates the current flow in a delta- connected system. Slide 8 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. Slide 9 Chapter 4 Transformer Connections Studying the current in a wye-connected system at both 0 and 90 illustrates the current flow in a wye- connected system. Slide 10 Chapter 4 Transformer Connections A 3-phase delta-to- wye connection is often used for distribution where a four-wire secondary distribution circuit is required. Slide 11 Chapter 4 Transformer Connections Three single-phase transformers may be connected in a wye-to-wye connection to form a 3-phase transformer. Slide 12 Chapter 4 Transformer Connections A wye-to-delta connection permits single-phase and 3- phase loads to be drawn simultaneously from the delta- connected secondary at the same voltage. Slide 13 Chapter 4 Transformer Connections In a wye-to-delta connection of three single- phase 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. Slide 14 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. Slide 15 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. Slide 16 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. Slide 17 Chapter 4 Transformer Connections A delta connection with a high leg to ground provides 240 V, 3-phase power to equipment and 120 V power for lighting and receptacles. Slide 18 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. Slide 19 Chapter 4 Transformer Connections Transformers are classified into connection groups according to their phase shift. Slide 20 Chapter 4 Transformer Connections Slide 21