Loadflowsynopsis
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The document discusses load flow analysis using the Newton-Raphson method. It provides background on load flow analysis and its importance. It describes classifying buses, constructing the bus admittance matrix, and developing the power flow equations. The Newton-Raphson method is presented as the preferred technique due to its powerful convergence, low computing time, and flexibility. Key steps include initializing bus voltages, calculating mismatches, and iterating to reduce mismatches.
Loadflowsynopsis
- 1. RAJ KUMAR GOEL INSTITUTE OF TECHNOLOGY, GHAZIABAD ELECTRICAL & ELECTRONICS ENGG. SYNOPSIS ON LOAD FLOW ANALYSIS USING NEWTON- RAPHSON METHOD GROUP S.No. ROLL NO. NAME EMAIL ID PHONE NO. MEMBER 1 0903321002 AKANKSHA akanksha.arya@yahoo.com 09582015101 AKANKSHA ARYA ARYA 2 0903321012 ARCHANA archana_ydv1991@yahoo.co.in 09811520036 ARCHANA YADAV YADAV 3 0903321011 ANURAG anurag.nigam.1989@gmail.com 07599056896 ANURAG NIGAM NIGAM 4. 0903321030 MUDIT JAIN mudit.maxicool@gmail.com 09716713988 MUDIT JAIN PROJE CT GUIDE: PROJECT COORDINATOR Mr. Varun Singhal Mrs. Kiran Srivastava Associate Professor HEAD OF DEPARTMENT DR. VINAY KAKKAR (DEPT. OF ELECTRICAL & ELECTRONICS ENGG. )
- 2. OBJECTIVES: To demonstrate load flow concepts. To study system performance under different operating conditions. To experience the real feel of power system operation . BACKGROUND: LOAD FLOW ANALYSIS is probably the most important of all network calculations since it concerns the network performance in its normal operating conditions. It is performed to investigate the magnitude and phase angle of the voltage at each bus and the real and reactive power flows in the system components. Load flow analysis has a great importance in future expansion planning, in stability studies and in determining the best economical operation for existing systems. Also load flow results are very valuable for setting the proper protection devices to insure the security of the system. In order to perform a load flow study, full data must be provided about the studied system, such as connection diagram, parameters of transformers and lines, rated values of each equipment, and the assumed values of real and reactive power for each load. We should be able to analyze the performance of power systems both in normal operating conditions and under fault (short-circuit) condition. The analysis in normal steady-state operation is called a power-flow study (load-flow study) and it targets on determining the voltages, currents, and real and reactive power flows in a system under a given load conditions. The purpose of power flow studies is to plan ahead and account for various hypothetical situations. For instance, what if a transmission line within the power system properly supplying loads must be taken off line for maintenance. Can the remaining lines in the system handle the required loads without exceeding their rated parameters? ADVANTAGES OF LOAD-FLOW STUDIES: Load flow or power flow is a solution for the power system under STATIC CONDITIONS OF OPERATION. Load flow is easy to determine – Line flow Bus voltage System voltage of profile Effect of changes in circuit configuration and incorporating new circuits on system loading. The effect of temporary loss of transmission capacity or generation on system loading. Effect of In-phase and boost voltage in system loading. Economic system operation Transmission line loss minimization
- 3. Transformer tap settings for economic operation Possible improvements to an existing system by change of conductor size and system voltages. It is a starting point for many other studies like short-circuit and transient stability. A load flow solution of the power system requires mainly the following stages: Network Modelling Stage Mathematical modeling stage Solution stage. BUS CLASSIFICATION : Each bus in the system has four variables: voltage magnitude, voltage angle, real power and reactive power. During the operation of the power system, each bus has two known variables and two unknowns. Generally, the bus must be classified as one of the following bus types: 1.Slack or Swing Bus This bus is considered as the REFERENCE BUS. It must be connected to a generator of high rating relative to the other generators. During the operation, the voltage of this bus is always specified and remains constant in magnitude and angle. In addition to the generation assigned to it according to economic operation, this bus is responsible for supplying the losses of the system. 2. Generator or Voltage Controlled Bus During the operation the voltage magnitude at this the bus is kept constant. Also, the active power supplied is kept constant at the value that satisfies the economic operation of the system. Most probably, this bus is connected to a generator where the voltage is controlled using the excitation and the power is controlled using the prime mover control (as you have studied in the last experiment). Sometimes, this bus is connected to a VAR device where the voltage can be controlled by varying the value of the injected VAR to the bus. 3. Load bus This bus is not connected to a generator so that neither its voltage nor its real power can be controlled. On the other hand, the load connected to this bus will change the active and reactive power at the bus in a random manner. To solve the load flow problem we have to assume the complex power value (real and reactive) at this bus.
- 4. BASIC TECHNIQUES FOR POWER-FLOW STUDIES: A power-flow study (load-flow study) is an analysis of the voltages, currents, and power flows in a power system under steady-state conditions. In such a study, we make an assumption about either a voltage at a bus or the power being supplied to the bus for each bus in the power system and then determine the magnitude and phase angles of the bus voltages, line currents, etc. that would result from the assumed combination of voltages and power flows. The simplest way to perform power-flow calculations is by iteration: 1. Create a bus admittance matrix Ybus for the power system; 2. Make an initial estimate for the voltages at each bus in the system; 3. Update the voltage estimate for each bus (one at a time), based on the estimates for the voltages and power flows at every other bus and the values of the bus admittance matrix: since the voltage at a given bus depends on the voltages at all of the other busses in the system (which are just estimates), the updated voltage will not be correct. However, it will usually be closer to the answer than the original guess. 4. Repeat this process to make the voltages at each bus approaching the correct answers closer and closer… CONSRTUCTING YBUS FOR POWER FLOW SOLUTION : The most common approach to power-flow analysis is based on the bus admittance matrix Ybus. However, this matrix is slightly different from the one studied previously since the internal impedances of generators and loads connected to the system are not included in Ybus. Instead, they are accounted for as specified real and reactive powers input and output from the buses. Power-flow analysis equations : The basic equation for power-flow analysis is derived from the nodal analysis equations for the power system: Ybus V = I ------------------ (1) For a four- bus power system, it becomes Y11 Y12 Y13 Y14 V1 I1 Y21 Y22 Y23 Y24 V2 I2 = Y31 Y32 Y33 Y34 V3 I3 Y41 Y42 Y43 Y44 V4 I4
- 5. where Yij are the elements of the bus admittance matrix, Vi are the bus voltages, and Ii are the currents injected at each node. For bus 2 in this system, this equation reduces to Y21 V1 +Y 22 V2 +Y 23 V3 +Y24 V4 = I2 ----------------------( 2) The real and reactive power at bus i is given by : The current can be expressed in terms of the active and the reactive power at bus i as: Separating the real and imaginary parts: These are the steady-state power flow equations expressed in polar form.
- 6. THE INFORMATION DERIVED FROM POWER FLOW STUDIES : Also, comparing the real and reactive power flows at either end of the transmission line, we can determine the real and reactive power losses on each line. Power-flow studies are usually started from analysis of the power system in its normal operating conditions, called the base case. Then, various (increased) load conditions may be projected to localize possible problem spots (overloads). By adding transmission lines to the system, a new configuration resolving the problem may be found. This estimated models can be used for planning. Another reason for power-flow studies is modeling possible failures of particular lines and generators to see whether the remaining components can handle the loads. Finally, it is possible to determine more efficient power utilization by redistributing generation from one locations to other. This variety of power-flow studies is called ECONOMIC DISPATCH. TECHNIQUES OF SOLUTION : Because of the nonlinearity and the difficulty involved in the analytical expressions for the above power flow equations, numerical iterative techniques must be used such as: 1. Gauss-Seidel method (G-S). 2. Newton-Raphson method (N-R). 3. Fast decoupled method (F-D). ADVANTAGES OF NEWTON-RAPHSON METHOD: Over the past few years, developments have been made in finding digital computer solutions for power-system load flows. This involves increasing the reliability and the speed of convergence of the numerical-solution techniques. In routine use, even few failures to give first-time convergence for physically feasible problems can be uneconomical. Hence, the Newton-Raphson (NR) approach is the most preferred general method. The Newton-Raphson approach is the most preferred load flow method because of its various advantages. It has powerful convergence characteristics compared to alternative processes. Considerably low computing times are achieved when the sparse network equations are solved by the technique of sparsity-programmed ordered elimination . The NR approach is particularly useful for large networks as computer storage requirements are moderate and increase with problem size almost linearly.
- 7. The method is very sensitive to a good starting condition. The use of a suitable starting condition reduces the computation time remarkably, as well as ensures the convergence. No acceleration factors have to be determined, the choice of slack bus is rarely critical, and network modifications require quite less computing effort. The NR method has great generality and flexibility, hence enabling a wide range of representational requirements to be included easily and efficiently, such as on load tap changing and phase-shifting devices, area interchanges, functional loads and remote voltage control. The NR load flow is central to many recently developed methods for the optimization of power system operation, sensitivity analysis, system-state estimation, linear-network modelling, security evaluation and transient-stability analysis, and it is well suited to online computation . Characterizing the in numeral advantages and the future prospects we adopted the NEWTON RAPHSON METHOD for load flow analysis computations.
- 8. REFERENCES : I. International journal of research in IT and Management. II. Power System Analysis, Hadi saadat, McGraw Hill International editions. III. Kundur, P., Power System Stability and Control, McGraw-Hill, 1994 IV. Load flows, Chapter 18,Bus classification, Comparison of solution methods, N-R method–Electrical Power system by C.L.WADHWA.