EEE 302 Electrical Networks II

1. EEE 302Electrical Networks II Dr. Keith E. Holbert Summer 2001 Lecture 10

2. Source/Load Connections • The equivalent load may be in an equivalent delta () or wye (Y) configuration • the delta load configuration has no neutral line • the current is zero in the neutral line for a balanced wye load configuration • Source/Load connections can be connected in any of the possible combinations: Ysource-Yloadsource-Yload Ysource-loadsource- load • Analysis prefers the first connection (Y-Y) Lecture 10

3. Balanced Wye-Wye Connection a ZY Van + – b ZY + – Vbn c ZY + – Vcn n Load Lecture 10

4. Balanced Wye-Wye Connection • The line-to-line voltages (or line voltages) are Vab = VP3 30° Vbc = Vab-120° Vca = Vab-240° where VP is the magnitude of the phasor voltage between any two lines • The magnitude of the line voltage is VL = VP3 Lecture 10

5. Balanced Wye-Wye Connection • The line current for phase a is Ia = Van / ZY = Vp0° / ZY • In a Y-Y connection the magnitude of the line current (IL) equals the magnitude of the load current (IY) • The neutral current In is In = Ia + Ib + Ic = 0 • Balanced Y-Y three-phase ac circuits may be analyzed on a per phase basis Lecture 10

6. Balanced Wye-Delta Connection Van a + – Z Vbn b + – n Z Z Vcn c + – Load Lecture 10

7. Summarizing • A very good summary appears on pages 568-9 of the textbook including a figure and table for explanation Lecture 10

8. Class Examples • Extension Exercise E10.1 • Extension Exercise E10.2 Lecture 10

9. Three-Phase Power Relationships • The real and reactive power per phase are • The total real, reactive, and complex powers are Lecture 10

10. Class Examples • Extension Exercise E10.8 • Extension Exercise E10.10 Lecture 10