# POWER FLOW ANALYSIS

Power flow, or load flow, is widely used in power system operation and planning. The power flow model of a power system is built using the relevant network, load, and generation data. Power engineers are required to plan, design, and maintain the power system to operate reliably and within safe limits. Numerous power flow studies are required to ensure that power is adequately delivered at all-time despite normal load fluctuations and undesirable events such as contingencies.

# Different Techniques to Solve Power Flow Equations

Outputs of the power flow model include voltages at different buses, line flows in the network, and system losses. These outputs are obtained by solving nodal power balance equations. Since these equations are nonlinear, the iterative techniques are commonly used to solve this problem.

# Newton-Raphson Power Flow Method

Newton Raphson method is a numerical technique for solving non-linear equations. It is often classified as iterative root finding scheme. The reason it is called root finding is, it is geared towards solving equations like f(x)=0 (or f(x)=0). The solution to such an equation, call it x* (or x*), is clearly a root of the function f(x) (or f(x)). The first order Newton-Raphson (NR) method is considered as the state of the art for power flow calculations. This method has been widely used in industry applications.

The advantages and disadvantages of Newton-Raphson Power Flow Method are discussed comprehensively here.

# Gauss-Seidel Power Flow Method

In Gauss Seidel method, the computations appear to be serial. Further, each component of new iteration depends upon all previously computed components. Updates cannot be done simultaneously. In addition to this, new iteration depends on the order in which equations are examined. If this ordering is changed, the components of new iteration (and not just their order) also change. These limitations persuade engineers and researchers to go for Newton Raphson method.

# Fast Decoupled Power Flow Method

In high voltage transmission systems, the voltage angles between adjacent buses are relatively small. In addition, X/R ratio is high. These two properties result in a strong coupling between real power and voltage angle and between reactive power and voltage magnitude. In contrary, the coupling between real power and voltage magnitude, as well as reactive power and voltage angle, is weak.

Fast Decoupled Power Flow technique includes two steps which are discussed here in detail.

# Industry Application of Power Flow Methods

There are a number of very high-quality commercial power flow programs on the market today, some of which include those developed by the Electric Power Research Institute (EPRI), Power Technologies Incorporated (PTI), Operation Technology, Inc., and EDSA. Most of today’s commercial software packages are menu-driven from a Windows environment. Few of the commonly used software are discussed briefly here.

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