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Delta and Wye 3-Phase Circuits
15 questions By Tony R. Kuphaldt
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Question 7 of 15
Calculate all voltages, currents, and total power in this balanced Y-Delta system:
- Eline =
- Iline =
- Ephase(source) =
- Iphase(source) =
- Ephase(load) =
- Iphase(load) =
- Ptotal =
Reveal answer- Eline = 207.8 V
- Iline = 0.621 A
- Ephase(source) = 120 V
- Iphase(source) = 0.621 A
- Ephase(load) = 207.8 V
- Iphase(load) = 0.358 A
- Ptotal = 223.4 W
Notes:Be sure to ask your students to describe how they arrived at the answers to this question. There is more than one place to start in determining the solution here, and more than one way to calculate some of the figures. No matter how your students may have approached this question, though, they should all obtain the same answers.
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Question 8 of 15
What resistor values would we have to choose in a Delta configuration to behave exactly the same as this Y-connected resistor network?
Reveal answerEach resistor in a Delta-connected network must have a value of 900 Ω, to be equivalent to a Y-connected network of 300 Ω resistors.
Notes:There exist long, complicated equations for converting between Y and Delta resistor networks, but there is a much simpler solution to this problem than that! Challenge your students to solve this problem without resorting to the use of one of those long conversion formulae.
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Question 9 of 15
What will happen in each of these systems to the phase voltages of the load, if one of the source phases fails open?
Reveal answerIn the Y-Y system, with no neutral wire, one of the load phases will completely lose power, while the voltages of the other two load phases will be reduced to 86.7 % of normal.
In the Delta-Y system, none of the phase voltages will be affected by the failure of the source phase winding.
Notes:Ask your students what these results indicate about the reliability of Y versus Delta source configurations. Also, be sure to ask what does change in the Delta-Y system as a result of the failure. Certainly, something must be different from before, with one winding completely failed open!
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