Load Flow Models are based on Static Network Model.

Utilities use real-time on-line models in SCADA for the optimization of generation, VAR control, losses, and tie-line control.

A load-flow study is carried out to determine the steady-state bus voltages, active
and reactive power flows, transformer tap settings, component or circuit loading,
generator exciter regulator voltage set points, system performance under contingency or emergency operations, and system losses.

Load flow can also be used to determine voltage profile at the time of starting a large motor. The starting motor is modeled as a constant-impedance shunt with the X/R ratio based on a locked rotor or starting power factor. The load-flow case is run with the starting motor disconnected, and the voltage at the relevant buses is recorded. The starting-motor locked-rotor impedance
is connected as a shunt, and the new case is run. The difference in voltage at any bus
is the voltage drop at the instant of starting the motor.

Two algorithms, Gauss-Siedel and Newton-Raphson, are used to solve the loadflow
equations.

The Gauss-Siedel method gives a simple and stable solution and works well up to 100 buses. The
solution iterates one bus at a time, corrects that bus voltage to the specified value, and continues until an error is detected.

The solution may not converge for the following reasons:
1. Error in the input data
2. System is too weak to carry the load
3. Insufficient VAR in the system to support the voltage

In the Newton-Raphson method, the n quadratic equations are first linearized by forming a Jacobian matrix. The present value of the bus voltage is then calculated, and then n linear equations are solved in steps. The number of iterations is small, between five and ten.