Delta and Wye 3-phase circuits - ibiblio

1 Delta and Wye 3-phase circuitsThis worksheet and all related files are licensed under the Creative Commons Attribution License,version To view a copy of this license, visit , or send aletter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. The terms andconditions of this license allow for free copying, distribution , and/or modification of all licensed works bythe general and methods for learning about these subjects (list a few here, in preparationfor yourresearch):1 Question 1 Label where each of the following electrical quantities would be found in boththe Y and Delta three-phase configurations: Phase voltage Line voltage Phase current Line currentIn which circuit (Y or Delta ) are the phase and line currents equal?

2 In which circuit (Y or Delta ) arethe phase and line voltages equal? Explain both answers, in terms that anyonewith a basic knowledge ofelectricity could phase and line quantities areunequal, determine which is 02201 Answer 1 VphaseVlineIphaseIphaseIphaseIlineIlineI lineIlineIlineIlineIphaseIphaseIphaseVph aseVphaseVphaseVphaseVphaseVlineVlineVli neVlineVline2Y configuration Iphase=Iline Vphase< VlineDelta configuration Vphase=Vline Iphase< IlineFollow-up question: how do Kirchhoff s Voltage and Current Laws explain the relationships betweenunequal quantities in Y and Delta configurations?

3 Notes 1 Your students will need to know what phase and line represents in both types of polyphaseconfigurations, especially when using formulae that reference quantities by these 2 Explain the difference between abalancedpolyphase system and anunbalancedpolyphase system. Whatconditions typically cause a polyphase system to become unbalanced?file 00418 Answer 2A balanced polyphase system is one where all line voltages are equal to each other, and all linecurrents are also equal to each other. Unbalanced conditions usually stem from unsymmetrical loads,although severe imbalances may be caused by faults in the 2 Ask your students which type of three-phase system (balanced or unbalanced) is easier toanalyze, andwhy that is 3In a balanced Y-connected power system, calculate the phase voltage (Ephase) if the line voltage (Eline)is 480 00412 Answer 3 Ephase= 277 VNotes 3 More important than obtaining the correct answer is for students to explain what they did to get thatanswer.

4 What general calculation may be applied to balanced, Y-connected systems relatingphase and linevoltages?5 Question 4 Calculate all voltages, currents, and total power in this balanced Delta - Delta system:SourceLoad230 V50 Eline=Iline=Ephase(source)=Iphase(source )=Ephase(load)=Iphase(load)=Ptotal=file 02203 Answer 4 Eline= 230 VIline= AEphase(source)= 230 VIphase(source)= AEphase(load)= 230 VIphase(load)= APtotal= kWNotes 4Be sure to ask your students to describehowthey arrived at the answers to this question. There is morethan one place to start in determining the solution here, and more than one way to calculate some of thefigures.

5 No matter how your students may have approached this question, though, they should all obtainthe same 5 Calculate all voltages, currents, and total power in this balanced Y-Y k Eline=Iline=Ephase(source)=Iphase(source )=Ephase(load)=Iphase(load)=Ptotal=file 02202 Answer 5 Eline= kVIline= AEphase(source)= kVIphase(source)= AEphase(load)= kVIphase(load)= APtotal= kWNotes 5Be sure to ask your students to describehowthey arrived at the answers to this question. There is morethan one place to start in determining the solution here, and more than one way to calculate some of thefigures.

6 No matter how your students may have approached this question, though, they should all obtainthe same 6 Calculate all voltages, currents, and total power in this balanced Delta -Y system:SourceLoad2400 V300 Eline=Iline=Ephase(source)=Iphase(source )=Ephase(load)=Iphase(load)=Ptotal=file 00428 Answer 6 Eline= 2400 VIline= AEphase(source)= 2400 VIphase(source)= AEphase(load)= VIphase(load)= APtotal= kWNotes 6Be sure to ask your students to describehowthey arrived at the answers to this question. There is morethan one place to start in determining the solution here, and more than one way to calculate some of thefigures.

7 No matter how your students may have approached this question, though, they should all obtainthe same 7 Calculate all voltages, currents, and total power in this balanced Y- Delta system:SourceLoad120 V580 Eline=Iline=Ephase(source)=Iphase(source )=Ephase(load)=Iphase(load)=Ptotal=file 02204 Answer 7 Eline= VIline= AEphase(source)= 120 VIphase(source)= AEphase(load)= VIphase(load)= APtotal= WNotes 7Be sure to ask your students to describehowthey arrived at the answers to this question. There is morethan one place to start in determining the solution here, and more than one way to calculate some of thefigures.

8 No matter how your students may have approached this question, though, they should all obtainthe same 8 What resistor values would we have to choose in a Delta configuration to behaveexactly the same asthis Y-connected resistor network?300 300 300 file 00429 Answer 8 Each resistor in a Delta -connected network must have a value of 900 , to be equivalent to a Y-connectednetwork of 300 8 There exist long, complicated equations for converting between Y and Delta resistor networks, but thereis a much simpler solution to this problem than that! Challenge your students to solve this problem withoutresorting to the use of one of those long conversion 9 What will happen in each of these systems to the phase voltages of the load, if one of the source phasesfails open?

9 SourceLoadWindingfails open!SourceLoadWindingfails open!file 00423 Answer 9In the Y-Y system, with no neutral wire, one of the load phases will completely lose power, while thevoltages of the other two load phases will be reduced to % of the Delta -Y system, none of the phase voltages will be affected by the failureof the source 9 Ask your students what these results indicate about the reliability of Y versus Delta sourceconfigurations. Also, be sure to ask whatdoeschange in the Delta -Y system as a result of the ,somethingmust be different from before, with one winding completely failed open!

10 11 Question 10A common three-phase source connection scheme is theDelta high-legorFour-wire Delta , where eachphase coil outputs 240 volts:ABCD elta "high-leg" source240 V 0o240 V 120o240 V 240oN (neutral)Identify the different voltages obtained from this coil configuration, and which connection points eachvoltage is measured 03817 Answer 10 VAB= 240 voltsVBC= 240 voltsVAC= 240 voltsVAN= 120 voltsVBN= 208 voltsVCN= 120 voltsNotes 10 The usefulness of this connection scheme should be clearly evident: three different voltage levels maybe accessed for use in powering circuits .