Any branch in a linear network can be substituted by a different branch without disturbing the voltages and currents in the entire network, provided the new branch has the same set of terminal voltage and current as the original network.
In a linear network any passive element can be equivalently substituted by an ideal voltage source or an ideal current source, provided all the other branch currents and voltages are kept constant. This is possible only when the original passive element and the substituted active sources absorb same power.
- This theorem is applicable only for linear networks i.e. the networks with R, L, C. transformer and linear controlled sources as elements.
- The presence of dependent sources makes the network active and hence substitution theorem is used for both active as well as passive networks.