DC NETWORK THEOREMS – PART – 02 – THEVENIN’S THEOREM

Leon Charles Thevenin was born in Paris on March 30^th 1857.

He graduated from the Ecole Polytechnique in 1876 and two years later joined the Corps of Telegraph Engineers. Appointed as a teaching inspector at the École supérieure de télégraphie in 1882, he was interested in the problems of measurement in electrical circuits. As a result of studying Kirchhoff's circuit laws and Ohm's law, he developed his famous theorem, Thévenin's theorem, which made it possible to calculate currents in more complex electrical circuits and allowing people to reduce complex circuits into simpler circuits, called Thévenin's equivalent circuits. His Theorem was published in three separate scientific journals in 1883 in a paper entitled "Extension of Ohm's Law to complex electrical circuits". Three more articles followed in that year. The first gave a method of using a galvanometer to measure potential, and made use of the new theorem. The second described a method for measuring resistance, and the third was on the use of the Wheatstone Bridge.

He was described as a humble man, a model engineer and a kind hearted person. He died on 21^st September 1926 in Paris. He lived for 69 years on this planet and even today he lives in every basic electrical and electronics textbooks.

THEVENIN’S THEOREM

Any linear active bilateral network can be replaced by an equivalent circuit consisting of voltage source in series with a resistance. The voltage source is open circuit voltage across the open circuited load terminals and the resistance being the internal resistance of the source network looking from the open circuited load terminals.

[OR]

Any two terminal linear network, containing independent voltage and current sources, may be replaced by a constant voltage source V_TH in series with a resistance R_TH where V_TH is the open circuit voltage between the terminals and R_TH is the resistance of the network as seen from the two terminal with all sources replaced by their internal resistances.  

APPLICATIONS

1. This theorem is extensively used in networks to determine the current through any element or voltage across any element in a network without rigorous calculation for solving a set of network equations.

2. It is useful in circuit analysis when it necessary to find the current only in one branch of a circuit.

3. It is also useful when it is necessary to study the variation in the current in a branch of the circuit when the resistances of this branch is varied.