I got this question from a student I was helping. This circuit is a WheatStone bridge type circuit.

The image of the circuit is show here below.

These types of circuits are usually solved with Delta-Y or Delta-star, etc , kinds of techniques.

And I solved it this usual way.

BUT, I have always been wondering if this kind of circuit can be solved by using just Thevinin Theorem and using the regular Kirchoffs laws for series and parallel resistors:

Original circuit:

Note: this circuit has inductors, but just replace all inductors with resistors and replace the henry with ohms.

Next I did some circuit reduction and re-drew the circuit to a form that is a Wheatstone Bridge type of circuit.

I made a drawing of this reduced circuit:

We want to find Vth and Rth, between points A-B.

Based on my analysis, Va-b = Vth = Vsource = 120 volts.

The difficult part is finding Rth.

Using Thevinin Theorem, one must take the voltage source and short circuit it.

Then try to used Kirchoff rules to find the equivalent resistance between points A-B.

Without using Delta-Y type of transformation, I am not sure how to reduce these resistor just with Kirchoffs rules.

My question is: is it even possible to get equivalent resistance with Thevinin approach.

Or is it only possible via the Delta-Y type of transformations.

In the Electrical Engineering circuit courses I took as an undergrad, they "Never Proved" the theorems such as Thevinin, Norton and Delta-Y transformations, never showed the derivations or proofs for these.

They just showed how to use them, and presented these as the Holy Bible, to be accepted as Holy Facts, not to be questioned, just used.

Due to this way of teaching in Engineering, one does not have the proper knowledge to understand when a certain approach is to be applied and when not.

Hope someone can help.

Regards,

P