Thevenin and Norton Theorems: Simplifying Complex Circuits, Slides of Electrical Engineering

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ELECTRICAL CIRCUITS

Thevenin’s and Norton’s Theorems

These Theorems may be applied to both d.c. and a.c.

circuits.

C Kawerawera

Thevenin’s and Norton’s Theorems

• (^) Many of the networks analysed using Kirchhoff’s laws, mesh-current and nodal analysis and the superposition theorem can be analysed more quickly and easily by using Thevenin’s or Norton’s theorems.
• (^) Each of these theorems involves replacing what may be a complicated network of sources and linear impedances with a simple equivalent circuit.

The polarity of voltage E is chosen so that the current flowing through an impedance connected between A and B will have the same direction as would result if the impedance had been connected between A and B of the original network. Figure (b) is known as the Th´evenin equivalent circuit.

Four-step procedure adopted when determining, by means of Th´evenin’s theorem, the current flowing in a branch containing impedance ZL of an active network:

The open circuit or the Thevenin equivalent voltage

The open circuit or the equivalent Thevenin impedance is determined with the voltage sources removed and set to zero

Branch Currents

Use Th´evenin’s theorem to determine the current flowing in the 80 Ω resistor in the network shown.

By voltage division the part of the circuit to the left of BB may be reduced to a Th´evenin equivalent circuit.

By voltage division the part of the circuit to the left of CC may be reduced to a Th´evenin equivalent circuit.

TUTORIAL

Using Thevenin Theorem find the current through resistor R 4 in the network shown