Load Flow Analysis in Power Systems

Demonstrative Video

Contents

  • 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

Introduction

  • 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:

    1. Load flow problem

    2. Optimal load scheduling problem

    3. 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

Importance of Load Flow Analysis

Investigate the following features of a power system network:

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

  2. Busbar (node) voltages.

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

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

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

  6. Optimum system running conditions and load distribution.

  7. Minimizing system losses.

  8. Optimum rating and tap-range of transformers.

  9. Improvements from change of conductor size and system voltage.

Circuit Analysis Vs Load Flow Analysis

  • 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.

Require Steps for the Load Flow Studies

  1. Representation of the system by single line diagram (SLD)

  2. Determining the impedance diagram using the informations in SLD

  3. Formulation of network equations

  4. Solution of network equations