The complex power injected by the source into the th bus of a power system is
Where is the voltage at the th bus with respect to ground and is the source current injected into the bus.
The load flow problem is handled more conveniently by use of rather than . Therefore, taking the complex conjugate of Eq. , we have Substituting for , we can write
Equating real and imaginary parts

In polar form

Real and reactive power can now be expressed as


- DECOUPLED LOAD FOLW METHODS
An important characteristic of any practical electric power transmission system operating in steady state is the strong interdependence between real power and bus voltage angles and between reactive power and voltage magnitudes. This interesting property of weak coupling between and variables gave the necessary motivation in developing the decoupled load flow (DLF) method, in which and problems are solved separately.
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