Power invariance in electrical networks

Kron´s method of network analysis is based on the assumption of invariance of power between the primitive and actual networks. It is shown by an example and also theoretically that this assumption needs some explanation. The necessary transformation formulas are proved by an application of Kirchhoff´s laws to the networks and lead to an equation more general than Kron´s; the voltage and current transformation matrices in the equations derived are not necessarily transposes of each other.