Thevenin equivalent of a network

In summary, the conversation is about finding the Thevenin equivalent of a network across the terminals a,b. The solution involves finding the Thevenin voltage (Vth) and impedance (Zth), using Kirchoff's laws and lumping series reactances. The conversation also discusses different attempts at solving for Zth, including using a dummy current source and a voltage source, and the importance of calculating the Norton current (In). There is a typo in one of the equations, which is corrected.
  • #1
bishshoy007
7
0

Homework Statement



The question is to find the Thevenin equivalent of the network across the terminals a,b.
The circuit is as follows:--
pbxqs.jpg

The solution is Zth = 12.166 angle(136.3*)ohm and Vth = 7.35 angle(72.9*)
I can find out the Vth, that's easy. But I can get the Zth right coz there is the dependent source. Please help ! I have tried almost 50 times, with different methods.

Homework Equations



The two basic laws (comon everyone knows this):--

Kirchoffs' Voltage law = sum of voltages in a loop = 0
Kirchoffs' node law = sum of current through a node = 0

The Attempt at a Solution



k9yk9s.jpg

First I have lumped all series reactances.
At node 1 :--
5 + 0.2V0 = -V0/(8+4j)
Solving V0 = -16.22 - 2.7j

Now writing the KVL for the loop :--
Vth + V0 - (4 - 2j)*0.2-V0 = 0
Solving we get Vth = 2.16 + 7.027j = 7.35 angle(72.89*)

For the Zth I have tried solving by adding a dummy current source at the terminals a,b. It didnt work. Then i tried adding a voltage source across the (8 + 4j) impdedance. Still I couldn't get the answer correct.
 
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  • #2
You can calculate the Norton current In.
Zth = Vth/In.
 
  • #3
Yes I haven't tried that. But still I would like to have the thevenin voltage. Any mind helping me, with the solution.
 
  • #4
There is a typo in the equation of the loop, otherwise it is correct. I have not checked your calculations.

The equation should be

Vth + Vo - (4-2j)*0.2*Vo = 0

You have posted:

Vth + Vo - (4-2j)*0.2-Vo = 0
 
  • #5
Thanks buddy. It works like a charm.
 

FAQ: Thevenin equivalent of a network

1. What is the Thevenin equivalent of a network?

The Thevenin equivalent of a network is a simplified representation of a complex electrical network. It consists of a single voltage source in series with a single resistor, which can be used to model the behavior of the original network.

2. How is the Thevenin equivalent calculated?

The Thevenin equivalent is calculated by first finding the open-circuit voltage (Voc) and the short-circuit current (Isc) of the original network. The Thevenin voltage is equal to Voc, and the Thevenin resistance is equal to Voc/Isc.

3. What is the purpose of finding the Thevenin equivalent?

Finding the Thevenin equivalent allows us to simplify a complex network into a single voltage source and resistor, making it easier to analyze and understand. It also helps in determining the maximum power that can be delivered to a load connected to the network.

4. Can the Thevenin equivalent be used for both AC and DC circuits?

Yes, the Thevenin equivalent can be used for both AC and DC circuits. However, the calculations for AC circuits may involve complex numbers, while DC circuits only require real numbers.

5. What are some limitations of the Thevenin equivalent?

The Thevenin equivalent is only accurate for linear circuits, meaning that it may not accurately represent the behavior of non-linear components. It also assumes that the network is in a steady-state and does not take into account any transient effects.

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