LOAD_FLOW_STUDY.pptx
- 2. AGENDA What is a load flow study? Why have a load flow study completed? When to have a load flow study completed? What is the use of load flow study? Load flow objective What are the inputs & output of load flow analysis? Load flow assumptions, constraints and limitations Load flow calculation methods
- 3. WHAT IS LOAD FLOW STUDY? Load flow (power flow) analysis is a basic analysis for the study of power systems and also trickiest of the critical four power system studies. The reason these four studies are so powerful are that they require much of the same data, and when completed together they have the ability to save time and money, versus completing them one at a time. it evaluates your power system’s capability to adequately supply the connected load while staying within proper voltage and current ranges. The load flow study report will determine the voltages and power factor at all your buses, as well as currents or power flow on all your feeders.
- 4. WHY HAVE A LOAD FLOW STUDY COMPLETED? Completing a load flow study on an existing system will provide recommendations for system operation and optimize the system operation to minimum operational costs. Understanding the power flows on various system feeders will allow the operators to understand if there is spare capacity, if there are areas of the plant that are overloaded, and if there are operational configurations that will save energy and the associated costs.
- 5. WHEN TO HAVE A LOAD FLOW STUDY COMPLETED? The information that is critical from a proper load flow is the voltages and power factor at all your buses, and currents or power flow on all your feeders. With this information you will be able to make important decisions on where to add or remove load, and where power factor correction can be added to increase the efficiency of your system.
- 6. WHAT IS THE USE OF LOAD FLOW STUDY? It is used for normal, steady-state operation. It gives you the information what is happening in a system. The load flow helps in continuous monitoring of the current state of the power system, so it is used on daily basis in load dispatch/power system control centers. It can also be a support during examining effectiveness of the alternative plans for future system expansion, when adding new generators or transmission lines is needed.
- 7. LOAD FLOW OBJECTIVE The objective of load flow calculations is to determine the steady-state operating characteristics of the power system for a given load and generator real power and voltage conditions. Once we have this information, we can calculate easily real and reactive power flow in all branches together with power losses.
- 8. WHAT ARE THE INPUT & OUTPUT OF LOAD FLOW ANALYSIS? BUS DATA LINE DATA GENERATOR DATA LOAD DATA VOLTAGE MAGNITUDE VOLTAGE ANGLE REALREACTIVE POWER CURRENT FLOW POWER LOSSES LOAD FLOW
- 9. BUS DATA For PV buses: • Real power (generation and demand), • Reactive power (demand), • Voltage magnitude. For PQ buses: • Real power (generation and demand), • Reactive power (generation and demand). For slack bus: • Voltage magnitude (usually 1 per unit), • Voltage angle(specified to be zero), • Real power (demand), • Reactive power (demand).
- 10. LINE DATA Transmission lines: • Resistance, • Reactance, • Capacitance (can be negligible). Transformers: • Winding resistances on low and high voltage side, • Leakage reactance on low and high voltage side, • Magnetization reactance, • Iron loss admittance
- 11. LOAD FLOW ASSUMPTIONS, CONSTRAINTS AND LIMITATIONS Assumptions for load flow calculation: System is in steady state (no transient changes) Three phases system is assumed to have balanced loading Per-unit system is used for simplification There also some constraints in load flow problem for: Voltage magnitude, |Ui|min≤|Ui|≤|Ui|max|Ui|min≤|Ui|≤|Ui|max Voltage angle, |δi−δk|≤|δi−δkmax||δi−δk|≤|δi−δkmax| Physical limitations: Real generated power, PGimin≤PGi≤PGimax Reactive generated power, QGimin≤QGi≤QGimax
- 12. LOAD FLOW CALCULATION METHODS Gauss- Seidel Newton- Raphson Fast- decoupled The number of nodes in real power systems is so high that the calculation are to complex to make it by hand. That’s why, we use numerical methods. They are,
- 13. GAUSS - SEIDEL NEWTON - RAPHSON FAST - DECOUPLED Complexity Easy Complex Less complex (constant Jacobian, you do not have to inverse it) Convergence Linear Quadratic - the fastest Geometric Sensitivity Not available Available Available System size Problematic with large systems (the time of calculation increases linearly with system size) Appropriate for any system size (the time of calculation does not depend on system size, 3-4 iterations usually needed) Appropriate for any system size (the time of calculation does not depend on system size, 5-6 iterations usually needed) Accuracy Good The best Average
- 14. GAUSS - SEIDEL NEWTON - RAPHSON FAST - DECOUPLED Type of system May have a convergence problem with ill- condition system No problem with ill- condition system No problem with ill- condition system Accuracy Good The best Average Sensitivity It is sometimes advisable to have one or two Gauss-Seidel iterations before Newton- Raphson, which may decrease the iteration to some extent and it helps with the “flat start” which is sometimes causing non-convergence for Newton - Raphson method.