Ex, 92 -Voltage and Current Relationships Conclusion this exercise, you connecte

Question

Ex, 92 -Voltage and Current Relationships Conclusion this exercise, you connected a 1:1 three-phase transformer in wye-delta and delta- CONCLUSION wye configurations secondary either increased or decreased by a v3 factor. You also confirmed that the outgoing line voltages at the secondary were shifted 30 with respect to the incoming line voltages at the primary. REVIEW QUESTIONS1 1. Delta-wye and wye-delta configurations both produce a. b. c increases in the secondary voltages and currents. decreases in the secondary voltages and currents phase shifts between the incoming and outgoing line voltages d. additional v3 increases in the secondary voltages and currents The line voltage at the secondary of a 10:1 wye-delta connected transformer will be 2. a. equal to the line voltage at the primary times 1/v3 b. equal to the line voltage at the primary times 3 c. equal to the line voltage at the primary times 0.1 times 1/3 d, equal to the line voltage at the primary times 0.1 times v The line voltage at the secondary of a delta-wye connected transformer is a. greater than it is with a wye-delta connection. 3. b. less than it is with a wye-delta connection c the same as it is with a wye-delta connection. d. only dependent on the turns ratio. 4. The sum of the phase voltages in three-phase transformers a. depends on the connection. b. equals zero when the transformers are properly connected. c. is v3 times the turns ratio. d. can only be determined when a load is connected to the secondary 5. Before three-phase transformers are put into service a. the phase sequence of the incoming lines must be verified b the winding connections must be checked to ensure proper phase relationship. the load must be balanced. the phase shift must be measured. c. d. © Festo Didactic 30328 00 312

Explanation / Answer

1. c) Phase shift between incoming and outgoing phase voltages.

Explanation: Wye/Delta and Delta/Wye type of connection inherently create 30 degree phase shift between primary and secondary winding.

3. a)

Explanation: the ratio of secondary voltage to primary of delta/wye transformer is 3 times its transformation ratio.

4 b)

Explanation: Sum of phase voltages of 3 phase xmer at any instant is always zero.

5 b)

Explanation:

Before putting any xmer into service, it is necessary to ensure that all phase relationships are maintained since, there is a phase shift associated with transformers.

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