Lecture-33

Introduction to Load or Power Flow Analysis

Importance of Load Flow Analysis

Circuit Analysis Vs Load Flow Analysis

Lecture-34

Bus Classification

Lecture-35

Power Flow problem

Preparation of data for Load Flow

Lecture-36

Gauss-Siedel Method

Lecture-37

Newton-Raphson Method

In PS load flow (or power flow) is used for obtaining the of the electrical network

Three major problems encountered in the in the hierarchal order are:

Load flow problem

Optimal load scheduling problem

systems control problem

Power-flow studies are of great importance in planning, operation, maintenance, and control

- determine when the specific power system elements become underloaded or overloaded

- ensure that each generator runs at their maximum operating point

of power system

of existing/ future system

In load flow studies, power flows from sending end to the receiving end through TL

The equations in terms of power are known as power flow equations.

These power flow equations are normally non-linear and must be solved by some iterative techniques.

Load flow studies are performed to determine

voltage drop on each feeder

voltage magnitude and phase angle at each bus

real and reactive powers flowing in all branches

total power losses in the system, as well as the power losses in each branch

Load flow studies are done before transient stability and contingency studies.

Sometimes, a load flow study shows an overloaded connection or transformer; then, preventive actions are taken in the real network to stop this situation.

In this case, a large number of load flow analysis is carried out that is called contingency study.

Simulation software such as ETAP, CYME, IPSA, and PowerWorld are often used for the studies.

The principal information obtained from a power-flow study is

the and of the voltage at each bus, and

the and flowing in each line

Investigate the following features of a power system network:

Flow of MW and MVAr in the branches of the network.

Busbar (node) voltages.

Effect of rearranging circuits and incorporating new circuits on system loading.

Effect of temporary loss of generation and transmission circuits on system loading (mainly for security studies).

Effect of injecting in-phase and quadrature boost voltages on system loading.

Optimum system running conditions and load distribution.

Minimizing system losses.

Optimum rating and tap-range of transformers.

Improvements from change of conductor size and system voltage.

LFA is similar to traditional circuit analysis with a key difference

**Circuit analysis:**given all values of impedances in the circuit and parameters of \(V\) and \(I\), all nodal \(V\) and branch \(I\) can be calculated directly.

The key feature is that the relationship between nodal \(V\) and branch \(I\) is linear (i.e \(V = I \times Z\))

**load ow analysis:**loads and sources are defined in terms of powers and not impedances or ideal voltage or current generators

All power network branches, transformers or overhead and underground circuits, are defined as impedances.

The relationship between \(V,~P\) and \(Z\) is non-linear and appropriate methods for solving non-linear circuits need to be used.

Representation of the system by single line diagram (SLD)

Determining the impedance diagram using the informations in SLD

Formulation of network equations

Solution of network equations