POWER FLOW ANALYSIS AND PROTECTION COORDINATION OF REAL TIME SYSTEM Thanigaivel M PG Scholar Power Systems Engineering Sri Muthukumaran Institute of Technology Chennai, India Azeezur Rahman A Assistant Professor : Electrical and Electronics Engineering Sri Muthukumaran Institute of Technology Chennai, India Abstract: This paper studies about the Power Flow and Protection Coordination of Sri Muthukumaran Institute of Technlogy (SMIT) system. Power flow studies is to plan ahead and account for various hypothetical situations. For instance, what if a transmission line with in the power system properly supplying loads must be taken offline for maintenance, then remaining line in the system must handle the required loads without exceeding the rated parameters For this project ETAP is used to calculate the voltage profile in the SMIT system. Load Flow Analysis is useful in solving power flow problems and calculate the unknown quantities. Protection Coordination is the sequence in which the devices operate to trip the circuit during faulty conditions. Circuit Breakers are the devices used in SMIT system and they are coordinated in a downstream sequence in order to avoid the blackout condition. The Circuit Breakers are sized in this system using the fault current obtained from the Short Circuit Analysis. Short Circuit Analysis is performed by faulting all the buses in order to find the fault current through all the buses. The various data collected from SMIT are used to construct the Single Line Diagram to study the Load Flow and Protection Coordination of the system. problems and to make correct decisions in planning upgrades or extensions in the power system, which lead to reduced operating cost, increased availability and minimized equipment or system failure. The analysis consists of load flow, short circuit, and Protection Coordination. The engineer should perform the analysis with a well-defined list of electrical distribution system performance criteria in mind, as follows: To design an inherently safe system. To standardize equipment sizing practices and protection methods. To improve the efficiency of the system by designing suitable protective devices for various faults. To set devices and protect the equipment from damage and to selectively shut down sections of the power system in response to a system disturbance. The proposed flow chart for this paper is as follows Keyword: ETAP, Load Flow, Short Circuit, Protection Coordination, Circuit Breakers. I. INTRODUCTION The power system infrastructure, grid to on- premise wiring and from generation resources to the electric electrical equipment, is a complex system that requires extensive analysis to operate efficiently and effectively. Every new load, upgrade, extension, and reconfiguration of the network can create unexpected stresses and interactions to the original power system which was not designed for. Power system studies provide information that allows to understand the root of present or future power system Fig. 1. Flow Diagram ISSN: 2348 8379 http://www.internationaljournalssrg.org Page 57
II.LOAD FLOW ANALYSIS ETAP provides four load flow calculation methods: Adaptive Newton-Raphson, Newton-Raphson, Fast- Decoupled, and Accelerated Gauss-Seidel. They possess different convergent characteristics, and sometimes one is more favorable in terms of achieving the best performance. You can select any one of them depending on your system configuration, generation, loading condition, and the initial bus voltages. Newton-Raphson Method The Newton-Raphson method formulates and solves iteratively the following load flow equation: where P and Q are specified bus real and reactive power mismatch vectors between specified value and calculated value, respectively; V and δ represents bus voltage magnitude and angle vectors in an incremental form; and J1 through J4 are called Jacobian matrices. The Newton-Raphson method possesses a unique quadratic convergence characteristic. It usually has a very fast convergence speed compared to other load flow calculation methods. It also has the advantage that the convergence criteria are specified to ensure convergence for bus real power and reactive power mismatches. This criterion gives you direct control of the accuracy you want to specify for the load flow solution. The convergence criteria for the Newton- Raphson method are typically set to 0.001 MW and Mvar. The Newton-Raphson method is highly dependent on the bus voltage initial values. A careful selection of bus voltage initial values is strongly recommended. Before running load flow using the Newton-Raphson method, ETAP makes a few Gauss-Seidel iterations to establish a set of sound initial values for the bus voltages. The Newton-Raphson method is recommended for use with any system as a first choice. Adaptive Newton-Raphson Method This improved Newton-Raphson Method introduces a set of smaller steps for iterations where a potential divergence condition is encountered. The smaller increments may help to reach a load flow solution for some systems where the regular Newton-Raphson method might fail to reach one. The Newton-Raphson method is based on the Taylor series approximation. For simplicity and incremental steps a linear interpolation/extrapolation of the additional time step increments is performed to improve the solution. The incremental steps are controlled by adjusting the value of ak to find a possible solution for the following solution step. The test results prove that the adaptive load flow method can improve the convergence for distribution and transmission systems with significant series capacitance effects (i.e. negative series reactance). It is also considered to possibly improve convergence for systems with very small impedance values, but that is not guaranteed. One drawback of using this method is reduced calculation speed because of the incremental steps in the solution. Fast-Decoupled Method The Fast-Decoupled method is derived from the Newton-Raphson method. It takes the fact that a small change in the magnitude of bus voltage does not vary the real power at the bus appreciably, and likewise, for a small change in the phase angle of the bus voltage, the reactive power does not change appreciably. Thus the load flow equation from the Newton-Raphson method can be simplified into two separate decoupled sets of load flow equations, which can be solved iteratively: The Fast-Decoupled method reduces computer memory storage by approximately half, compared to the Newton-Raphson method. It also solves the load flow equations using significantly less computer time than that required by the Newton-Raphson method, since the Jacobian matrices are constant. As with the Newton-Raphson method, convergence criteria of the Fast-Decoupled method is based on real power and reactive power mismatches, which are typically set to 0.001 in the order of MW and Mvar. Although for a fixed number of iterations it is not as accurate as the Newton-Raphson method, the savings in computer time and the more favorable convergence criteria makes for a very good overall performance. In general, the Fast-Decoupled method can be used as an alternative to the Newton-Raphson method, and it should definitely be given a try if the Newton-Raphson method has failed when dealing with long radial systems or systems that have long transmission lines or cables. ISSN: 2348 8379 http://www.internationaljournalssrg.org Page 58
III.SHORT CIRCUIT ANALYSIS Short-Circuit Analysis program analyzes the effect of 3-phase, line-to-ground, line-to-line, and double line-toground faults on electrical distribution systems. The program calculates the total short circuit currents as well as the contributions of individual motors, generators, and utility ties in the system. Fault duties are in compliance with the latest editions of the ANSI/IEEE Standards (C37 series) and IEC Standards (IEC 60909 and others). This chapter describes definitions and usage of different tools required to run short circuit studies. In order to give a better understanding of the standards applied to short circuit studies and to interpret output results more easily, some theoretical background, and standard information are also included. The ANSI/IEE Short-Circuit Toolbar and IEC Short- Circuit Toolbar sections explain how you can launch a short circuit calculation, open and view an output report, or select display options. The Short-Circuit Study Case Editor section explains how you can create a new study case, what parameters are required to specify a study case, and how to set them. The Display Options section explains what options are available for displaying some key system parameters and the output results on the one-line diagram, and how to set them. The ANSI/IEEE Calculation Methods section lists standard compliance information and both general and detailed descriptions of calculation methods used by ETAP. In particular, definitions and discussion of ½, 1.5-4, and 30 cycle networks, calculation of ANSI multiplying factors, and high voltage and low voltage circuit breaker momentary and interrupting duties are provided. The Required Data section describes what data are necessary to perform short circuit calculations and where to enter them. If you perform short circuit studies using IEC Standards, the IEC Calculation Methods section provides useful information on standard compliance, definitions on most commonly used IEC technical terms, and general and detailed descriptions of calculation methods for all important results, including initial symmetrical short circuit current, peak short circuit current, symmetrical short circuit breaking current, and steady-state short circuit current. Finally, the Short-Circuit Study Output Report section illustrates and explains output reports and their format. IV. PROTECTION COORDDINATTION ANALYSIS The Protection Coordination is represented by a star view in ETAP. A Star View is a presentation containing one-line diagram elements and their associated characteristic curves and diagrams. Star View provides a graphical user interface for viewing, coordinating, and customizing element curves and diagrams. Primary and Back-up Protection: For attaining higher reliability, quick action and improvements in operating flexibility of the protection schemes, separate elements of a power system, in addition to main or primary protection, are provided with a back-up and auxiliary protection. First in line of defense is main protection which ensures quick action and selective clearing of faults within the boundary of the circuit section or the element it protects. Main protection is essentially provided as a rule. Back up protection gives back up to the main protection, when the main protection fails to operate or is cut out for repairs etc. Failure of the main protection may be due to any of the following reasons:- A) D.C supply to the tripping circuit fails. B) Current or voltage supply to the relay fails. C) Tripping mechanism of the circuit breaker fails. D) Circuit breaker fails to operate. Back up protection may be provided either on the same circuit breakers which will be opened by the main protection or may use different circuit breakers. Usually, more than the faulty section is isolated when the backup protection operates. Very often the main protection of a circuit acts as back up protection for the adjacent circuit. Back up protection is provided where main protection of the adjacent circuit fails to back up the given circuit. For simplification, back up protection can have a lower sensitivity factor and be operative over a limited back up zone i.e. be operative for only part of the protected circuit. Methods of back up protection can be classified as follows:- A) Relay Back-up. B) Breaker Back-up. C) Remote Back-up. D) Centrally Co-ordinated Back-up. In this, current is measured at various points along the current path, for e.g., at source, intermediate locations, consumers end. The tripping time at these locations are graded in such a way that the circuit breaker nearest to the faulty section operates first, giving primary protection. The circuit breaker at the previous section operates only as a back-up. The tripping time at sections C, B and A are graded such that for a fault beyond C, breaker at C operates as ISSN: 2348 8379 http://www.internationaljournalssrg.org Page 59
a primary protection. Relays at A and B also may start operating but they are provided with enough time lags so that breaker at B operates only if breaker at C does not. Thus, for a fault beyond C, breaker at C will operate after 0.1 second. If it fails to operate, the breaker at B will operate after 0.6 second (Back-up for C) and if the breaker at B also fails to operate, breaker at A will operate after 1 second (Back-up for B and C). details about the flow of generated power according to the demand. A sample of the complete report is attached for the reference. The buses which are faulted are also represented in this report. The three important buses to be considered from the above result are Main Bus, Library Bus and CSE bus. Thus the Load Flow can be studied using the report and verified by using the SLD. V. SIMULATION RESULTS AND DISCUSSION In this project the systematic analysis of SMIT is analyzed using ETAP 12.6.5. The various tests performed on the system are Load Flow Analysis Short Circuit Analysis Protection Coordination The single Line Diagrams and results of the above tests are discussed below SINGLE LINE DIAGRAM OF LOAD FLOW ANALYSIS The Single Line Diagram is drawn in One Line View and the existing ratings are given in detail. Load Flow Analysis module is selected and generator bus is made as swing bus for reference. RUN function is clicked and the analysis is performed. The SLD generated after running Load Flow Analysis is as shown in Figure 5.1. From Figure 2, it is observed that there is a voltage drop of 0.05p.u in CSE BUS. The CSE BUS is highlighted in violet colour as shown in Figure 2 which represents the voltage drop in the bus. The generator in the existing system is kept as backup. During power shut down this generator (320 kva) is used to supply power for the SMIT system. Fig 2: SLD of Load Flow Analysis Fig. 3.Load Flow Analysis Report. LOAD FLOW ANALYSIS REPORT The complete Load Flow Analysis report is as shown in Figure 3. The Load Flow analysis report gives the ISSN: 2348 8379 http://www.internationaljournalssrg.org Page 60
SINGLE LINE DIAGRAM OF SHORT CIRCUIT ANALYSIS Short Circuit Analysis is performed by selecting the Short Circuit module. Fault is created in all the buses in order to make use of the calculated fault current for protection coordination. Circuit Breaker is the protective device used in the existing system. From the SLD the fault current of various buses are found, based on which the coordination of protective devices are to be performed later. In this analysis all buses are faulted in order to obtain fault current for all buses. From the SLD the devices which are over loaded are highlighted. Similar to Load Flow Analysis a separate report is generated which gives the details regarding the various buses. The fault current value obtained in this test is used in the coordination of circuit breaker. The SLD is as shown in Figure 4. Fig 4: SLD of Short Circuit Analysis SHORT CIRCUIT ANALYSIS REPORT Similar to the Load Flow Report a report is generated for Short Circuit Analysis also. The report summarizes the fault current values in various buses and other equipment.the report is generated for all the buses present in the system in the Figure 5. The report for BUS 1 is given as a sample. From the report the fault current f all the buses are found. The Impedance/Resistance value is also found using this report. Fig. 5.Short Circuit Analysis Report PROTECTION COORDINATION Circuit breakers are the protective devices used in this system and they are coordinated with respect to time and represented in the Time Current Characteristic Curve (TCC Curve). The Circuit Breakers are coordinated from downstream in order to avoid the black out in the system. The coordination of breaker is shown for a particular section of the entire SMIT system. From Figure 6.CB 25 denotes the circuit breaker present in load side,cb7 is present in CSE BUS and CB2 is present in the main bus. The curve shows that the circuit breakers are operating from the low voltage side in order to avoid blackout condition. In the curve current is plotted along X-axis and time is plotted along Y-axis. Thus from curve the time at which device operates for fault current is found. A separate setting sheet for the circuit breaker is also generated. From this curve the coordination of devices can be found with respect to time. ISSN: 2348 8379 http://www.internationaljournalssrg.org Page 61
Figure. 6. TCC CURVE VI. CONCLUSION Thus, the details collected from SMIT campus is fed in to the ETAP software. The Single Line Diagram is drawn in the One Line View and Load Flow Analysis is performed by selecting the module. From the results, an efficiency drop in CSE Bus is observed. The load flowing through the system is given in the report generated. After the completion of Load Flow Analysis fault is created in all the buses and Short Circuit Analysis is performed. Three phase fault is created and the reports are generated. Sample report of BUS 1 is given in Result. It is observed that all the protective devices present in the system are overloaded and highlighted as shown in SLD. The fault current calculated in Short Circuit Analysis is used to coordinate the protective devices. Circuit Breakers are the protective devices present in the existing system. Circuit Breakers are coordinated in downstream sequence in order to avoid the blackout condition. Further TCC curves are drawn for particular portion of the system to show the coordination of devices and device settings are generated in the report format. Thus, the simulation diagram is completed for the existing system and the various reports are generated. Delivery, Volume 3, No. 3.Power System Technology, vol. 24, no. 4, 2010. [2]. Balaguer.I, Q. Lei, S. Yang, U. Supatti, and F. Z. Peng,(2011) Control for grid-connected and intentional islanding operations of distributed power generation, IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 147 157. [3]. P. S. Bhowmik, D. V. Rajan,a nd S. P. Bose,(2012) Load Flow Analysis: An Overview World Academy of Science, Engineering and Technology 63 201 2. [4]. Carpentier (1979) Optimal Power Flows, Electrical Power and Energy Systems, Vol.1, pp 959-97 2. [5]. J. Carpentier,(1985) Optimal power flow, uses, methods and development, Planning andoperation of electrical energy system Proc. of IFAC symposium, Brazil, pp. 11-2 1. [6]. Dharamjit and D.K.Tanti,(2012) Load Flow study on IEEE 30 Bussystem, International Journal of Scientific and Research Publications, Volume 2, Issue 11, ISSN 2250-3153 [7]. H. Dommel,(1963) Digital methods for power system analysis (in German), Arch. Elektrotech., vol. 48, pp. 41-68, and pp. 118-132, April 1963. [8]. Girgis.A and S. Brahma, (2001) Effect of distributed generation on protective device coordination in distribution system, in Proc. LESCOPE, pp. 115 119. [9]. Nagrath & Kothari, Modern power system analysis, Tata McGraw Hill, June 2006. pp (177, 186,, 205,21 7). References [1]. Albert0 J. Urdaneta Member, IEEE Ram & Nadira, Member, IEEE,Luis G.Luis G.Pdrez Jimdnez,(1998) Optimal Coordination of Directional Overcurrent Relays Interconnected Power Systems,IEEE Transactions on Power ISSN: 2348 8379 http://www.internationaljournalssrg.org Page 62