RAJ KUMAR GOEL INSTITUTE OF TECHNOLOGY, GHAZIABAD ELECTRICAL & ELECTRONICS ENGG. SYNOPSIS ONLOAD FLOW ANALYSIS USING NEWTON- RAPHSON METHOD GROUPS.No. ROLL NO. NAME EMAIL ID PHONE NO. MEMBER1 0903321002 AKANKSHA firstname.lastname@example.org 09582015101 AKANKSHA ARYA ARYA2 0903321012 ARCHANA email@example.com 09811520036 ARCHANA YADAV YADAV3 0903321011 ANURAG firstname.lastname@example.org 07599056896 ANURAG NIGAM NIGAM4. 0903321030 MUDIT JAIN email@example.com 09716713988 MUDIT JAINPROJE CT GUIDE: PROJECT COORDINATORMr. Varun Singhal Mrs. Kiran Srivastava Associate Professor HEAD OF DEPARTMENT DR. VINAY KAKKAR (DEPT. OF ELECTRICAL & ELECTRONICS ENGG. )
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 itconcerns the network performance in its normal operating conditions. It is performed toinvestigate the magnitude and phase angle of the voltage at each bus and the real and reactivepower flows in the system components.Load flow analysis has a great importance in future expansion planning, in stability studies andin determining the best economical operation for existing systems. Also load flow results arevery valuable for setting the proper protection devices to insure the security of the system. Inorder to perform a load flow study, full data must be provided about the studied system, such asconnection diagram, parameters of transformers and lines, rated values of each equipment, andthe assumed values of real and reactive power for each load.We should be able to analyze the performance of power systems both in normal operatingconditions and under fault (short-circuit) condition. The analysis in normal steady-state operationis 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 hypotheticalsituations. For instance, what if a transmission line within the power system properly supplyingloads must be taken off line for maintenance. Can the remaining lines in the system handle therequired 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
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 andreactive power. During the operation of the power system, each bus has two known variables andtwo unknowns. Generally, the bus must be classified as one of the following bus types:1.Slack or Swing BusThis bus is considered as the REFERENCE BUS. It must be connected to a generator of highrating relative to the other generators. During the operation, the voltage of this bus is alwaysspecified and remains constant in magnitude and angle. In addition to the generation assigned toit according to economic operation, this bus is responsible for supplying the losses of the system.2. Generator or Voltage Controlled BusDuring the operation the voltage magnitude at this the bus is kept constant. Also, the activepower 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 theexcitation and the power is controlled using the prime mover control (as you have studied in thelast experiment). Sometimes, this bus is connected to a VAR device where the voltage can becontrolled by varying the value of the injected VAR to the bus.3. Load busThis bus is not connected to a generator so that neither its voltage nor its real power can becontrolled. On the other hand, the load connected to this bus will change the active and reactivepower at the bus in a random manner. To solve the load flow problem we have to assume thecomplex power value (real and reactive) at this bus.
BASIC TECHNIQUES FOR POWER-FLOW STUDIES:A power-flow study (load-flow study) is an analysis of the voltages, currents, and power flowsin a power system under steady-state conditions. In such a study, we make an assumption abouteither a voltage at a bus or the power being supplied to the bus for each bus in the power systemand then determine the magnitude and phase angles of the bus voltages, line currents, etc. thatwould 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 internalimpedances 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 thepower 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
where Yij are the elements of the bus admittance matrix, Vi are the bus voltages, and Ii are thecurrents 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.
THE INFORMATION DERIVED FROM POWER FLOWSTUDIES :Also, comparing the real and reactive power flows at either end of the transmission line, we candetermine the real and reactive power losses on each line.Power-flow studies are usually started from analysis of the power system in its normal operatingconditions, called the base case. Then, various (increased) load conditions may be projected tolocalize possible problem spots (overloads). By adding transmission lines to the system, a newconfiguration resolving the problem may be found. This estimated models can be used forplanning.Another reason for power-flow studies is modeling possible failures of particular lines andgenerators to see whether the remaining components can handle the loads.Finally, it is possible to determine more efficient power utilization by redistributing generationfrom one locations to other. This variety of power-flow studies is called ECONOMICDISPATCH.TECHNIQUES OF SOLUTION :Because of the nonlinearity and the difficulty involved in the analytical expressions for the abovepower 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 forpower-system load flows. This involves increasing the reliability and the speed of convergenceof the numerical-solution techniques. In routine use, even few failures to give first-timeconvergence 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 variousadvantages. 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.
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-networkmodelling, security evaluation and transient-stability analysis, and it is well suited to onlinecomputation .Characterizing the in numeral advantages and the future prospects we adopted the NEWTONRAPHSON METHOD for load flow analysis computations.
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, 1994IV. Load flows, Chapter 18,Bus classification, Comparison of solution methods, N-R method–Electrical Power system by C.L.WADHWA.