Problem 4-11


a) Use the node voltage method to determine the six branch currents shown.

Node voltage variables selected are shown in brown.
Voltages added to assist in the solution are shown in blue.


I will sum the currents out of the nodes.


Node A

Since we have voltage sources in series with resistors connected to node A, we need to determine the voltage across each of the resistors in order to find the currents.

For Vx

VB - VA = - Vx + 110
Vx = VA - VB + 110

For Vy

VA = 110 - Vy
Vy = 110 - VA

KCL now gives

Multiply through by 6

2 VA - 2 VC + 3 VA - 3 VB + 330 - 330 + 3 VA = 0
8 VA - 3 VB - 2 VC = 0 (Equation 1)


Node B

Using the expression for Vy derived above, KCL at node B gives

Multiply through by 16

2 VB - 2 VC - 8 VA + 8 VB - 880 + VB = 0
- 8 VA + 11 VB - 2 VC = 880 (Equation 2)


Node C

KCL at node C gives

Multiply through by 24

8 VC - 8 VA + 3 VC - 3 VB + VC = 0
- 8 VA - 3 VB + 12 VC = 0 (Equation 3)


Solving the three equations yields

VA = 82.5
VB = 157.143
VC = 94.286


The branch currents are thus

i1 = Vx / 2 = (VA - VB + 110) / 2 = 35.357 / 2
i1 = 17.679 A

i2 = (VC - VA) / 3= 11.786 / 3
i2 = 3.929 A

i3 = Vy / 2 = (110 - VA) / 2 = 27.5 / 2
i3 = 13.75 A

i4 = (VB - VC) / 8 = 62.857 / 8
i4 = 7.857 A

i5 = VC / 24= 94.286 / 24
i5 = 3.929 A

i6 = VB / 16 = 157.143 / 16
i6 = 9.827 A


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