Load Flow Studies Eng. Edvan Moyo BEng, MEng, MBA www.kgrtc.org.zm info@kgrtc.org.zm

Expectations

Objective Partcipants should be able to understand and appreciate the importance of load flow studies and the practical application of the studies.

Learning Outcomes At the end of the presentation, participants will be able to: Understand the purpose of load flow studies Know the equations used in load flow studies Know the practical application of load flow studies Carry out a basic load flow simulation

Content Introduction Power Flow Useful Information The Load Flow Equation Number of Variables-Number of Equations Power Flow Specifications: An Example Practical Application and Simulations

Introduction Load flow studies are also known as power flow studies Most common and important tool in power system analysis Why carry out power flows? Used for: -operation of power systems -controlling of power systems -planning for future expansions -performance of the system

Introduction It allows the engineer to investigate the performance of the network under a variety of outage conditions Numerical computation are performed by means of an iterative methods; some of the commonly used methods are: -The Gauss-Seidel Method -The Newton-Raphson Method -The Fast Decoupled Load Flow

Power Flow Useful Information A load flow analysis allows identification of: -real and reactive power flow -network losses: too high? -Voltages: too high or too low? -current flow -Power factor -Overload on lines? In the network with arbitrary number of buses and branches, and with arbitrary topology

Commercially Available Software Generation and Transmission System Simulations PSS/E Etap DigSilent Matlab Based PSAT – open source Matpower Electricity Market Simulations AMES – open source Powerworld Distribution Systems Simulation DigSilent Etap

The Load Flow Equations Load Flow calculations can be made by using: -Bus admittance matrix(BAM) or -Bus Impedance matrix(BIM) However, it is simpler to use BAM approach to the solution of load flow problems. Bus: is a node at which one or many lines, or where one or more loads and generators are connected

Power flow eq.: Current is replaced by P/Q

Load Flow Eq. Are non linear In complex form: Real Variables, Active (P) and Reactive (Q) Power

Number of Variables-Number of Equations.

Number of variables-number of equations n buses 2n real equations 4n variables: 4(P, Q, V, ) 2n variables specified(must be known) 2n variables to be calculated from equations

Number of variables-number of equations At each busbar: 2 variables are specified 2 out of 4 variables are not specified at each busbar. There are 6 possible combinations: P-V P- P-Q Q-V Q- V- Practical combinationa are 1, 3, and 6

Number of variables-number of equations The following are the three special bus types for load flow studies: Bus Type Specified quantities Unknown quantities Approximate number Load Bus or P-Q bus P, Q V,  85% Generator bus or voltage controlled bus or P-V bus P, V Q,  15% Reference bus or slack bus or swing bus V=1, =0 1%

Power Flow Specifications: An Example

Results (Specifications Unchanged)

Practical Application and Simulations Short circuit studies Grid integration impact studies Protection coordination and relay setting verification Reliability studies System security and transient stability studies

Thank You