2012 1st International Conference on Future Trends in Computing and Communication Technologies Simulation Analysis of Harmonic Content of Transient Current During Sympathetic Inrush Current A.H Hana, N. S. Noorpi, M. Amirruddin, M.M. Nurhakimah School of Electrical Systems Engineering Universiti Malaysia Perlis (UniMAP) Perlis, Malaysia hanahalim@unimap.edu.my, nursabrina@unimap.edu.my, melaty@unimap.edu.my, nurhakimah@unimap.edu.my Abstract— This project presents the harmonic analysis in transient current during inrush sympathetic phenomena. The objective is to investigate the harmonic content of transient current during sympathetic inrush current in order to help the system to supply power to the user without loss and increase the capacity. IEEE test system used in this project as the basis for the analysis of relevant circuit current transient, harmonic and sympathetic inrush phenomenon. Electric power system embarking test using a single power source that supplies the two transformers connected in parallel are used to analyze the ability of using PSCAD software. During sympathetic inrush, the transformer differential relay may trip because of the maloperation. As to come out with analysis, the power system is designed for operating voltage and current waves at a fixed frequency. In inrush current, producing high waves did not take long time to recover the original wave, but for sympathetic inrush take a long time or forever. High current produced from the sympathetic inrush causing the transformer differential relay power cut off the supply. The result shows the effectiveness harmonic analysis in transient current during sympathetic analysis phenomenon modeling by PSCAD software and analysis the harmonic in this project paper. All the objectives are achieved in the completion of this project. regulations [2]. Moreover, the mode of operations of the system must comply with the conditions set by the standards, including the process of designing, manufacturing of equipment. Same as faults in the equipment cannot completely be excluded because of technical or human failure. The equipment and installation cannot be designed to detain any offense and the degree of damage should be limited. B. Problem Statement In any power system network, any forms of fault occur should be avoided. The protection of the security becomes the main thing that need to be considered. As in this project, the content of harmonic analysis of currents during sympathetic inrush transient phenomenon is being investigated. Before this topic is studied in detail, what is the sympathetic inrush? Sympathetic inrush happened when a transformer inrush is already connected to a supply system can experience unexpected saturation during the inrush transient of an incoming transformer. This saturation, which is established by an asymmetrical voltage drop across the system resistance caused by the inrush current in the incoming transformer magnetizing current offset demands of high magnitude in the already connected transformer [3]. When both transformers arranged in parallel, transformer that is switched to the network in which the transformer has a load, the transient inrush currents not only flow through the transformer at first but it passes through the second transformer also. This partnership is called the transient inrush current as sympathetic inrush phenomenon. The second problem is how to avoid fault at the transformer differential relay when transient current occurs in parallel the transformer. The normal inrush current in the transformers decay, usually, within a few cycles, but the sympathetic inrush current persists in the circuit for a relatively longer duration [3, 4]. Longer duration of the sympathetic inrush current may mal-operate differential relay. It may also prolong harmonic over-voltages and causes the over-current harmonic in the system installed [5]. Other than that, noise level is increase in the already Keywords- transient current; sympathetic; inrush current; transformer differential relay; PSCAD I. INTRODUCTION A. Background of Project Modern power system consists of four main parts. These are known as generation, transmission, distribution and lastly loads part. The generation, transmission and distribution parts works together in order to supply power to the load or consumers. Power system engineering is the central area of activity for power system planning, project engineering, operation and rehabilitation of power systems for electrical power supply [1]. The reliability of the supply is determined not only by the quality of the equipment but also by carefully planning and detailed knowledge of power systems, together with a consistent use of relevant standards and norms, in particular IEC standards, national standards as well as internal 73 2012 1st International Conference on Future Trends in Computing and Communication Technologies transformers can produce an abnormal flux of higher magnetizing currents [6]. This can cause a tendency of operation of the differential protection, that to be avoided request to insensibility the same during the period of inrush current duration, but keeping the protection. The capability of distinguish between the short circuit wave current and the inrush current. The inrush currents are characterized by having higher harmonic components that are not present in short circuit current and whose amplitude in fundamental percent is shown in Table 1. connected transformers. Harmonic analysis is an important point observed in the study of this phenomenon sympathetic inrush. II. HARMONIC IN SYMPATHETIC INRUSH PHENOMENA It is very well known that a transformer will experience magnetizing inrush current during energization. A transformer exhibits an inrush phenomenon during initial energization. Due to flux symmetry or temporary over fluxing, this gives rise to high current at the initial energization of a transformer core [6]. The saturation of one or more cores results in high magnitude of current [6]. In high magnitude of current, the transformer energizing current is full of harmonics. Furthermore, both of the even and odd harmonics occur during energization [6]. In inrush phenomenon, the transformer which is connected to the supply system can undergo unexpected saturation during the inrush transient. This saturation during the inrush transient was established by the voltage drop across the resistance and it is not symmetric due to the inrush current in transformers. Thus, it claims the high magnitude of magnetizing current balanced in the transformer which is connected [3]. This partnership transient inrush current is called the sympathetic inrush phenomenon. The usual inrush current in transformers decay but only in the course of a continuous which were sympathetic inrush current in the circuit for a little longer than the inrush current [3, 4]. Longer period of the sympathetic current may be mal-operate of the differential relays [3]. It may also extend the higher of harmonic over voltages in the system and enhance the level of noise in the transformer is connected. In the transformer, energizing a transient inrush current appears produced by equipment’s core saturation. It has higher magnitude and it decay after some period of time until the value of magnetizing current due the normal operation conditions [3]. Usually, the transformer inrush currents are calculating as the transformers are connecting to a system without other transformers on service. In industrial practice, this equipment are energizing in series or parallel with others transformers that are on services. This condition can cause a transient interaction or a sympathetic interaction between the energizing transformer and the other transformers on service, which change the magnitude and duration of the inrush currents. A similar situation can arise in system with higher series resistances, like some with longer transmission lines. The inrush current can be affected by different factors such as the voltage wave point where is energizing the transformers, the total system impedance through is flowing the inrush current, the saturation or maximum magnetic flux densities of ferromagnetic material from transformer core, the residual flux into the transformer core and its polarities respect to the first half cycle of alternative flux in steady state and also the saturation level reach by other transformers connected to the system. Therefore, whatever the condition that impose an instantaneous change on the induction fluxes of power TABLE I. HARMONIC AMPLITUDE IN PERCENTAGE OF INRUSH CURRENT FUNDAMENTAL [6] Harmonic Component Amplitude Fundamental) (% 2 63.0 3 26.8 4 5.1 5 4.1 6 3.7 7 2.4 III. of HARMONIC OVERVOLTAGE A harmonic is a component of a periodic wave having a frequency which is significant gain of the power line frequency of 60 Hz base. Total Harmonic Distortion is the contributed by all harmonics of the fundamental frequency current [7]. The characteristic harmonics are based on the number of rectifiers (pulse number) used in a circuit and can be determined by the following equation: h = (n x p) ± 1 (1.0) where; n= an integer (1, 2, 3, 4, 5…) p= number of pulses or rectifiers The major cause of harmonics resonance overvoltage problem is the switching of lightly transformers at the end of transmission lines [8]. Thereby inrush currents with significant harmonic content up to frequencies around 600Hz are created. They can be represented by a harmonic current source I (h) connected to the transformer bus. The relation between nodal voltages, network matrix and current injections can be represented by [9]: V(h)=Z(h).I(h) (2.0) From these equation (2.0), where h represent the harmonic frequencies f = 120, 180, 240,...Hz. The harmonic current components of the same frequencies as the resonance frequency empowered in the case of parallel resonance, thereby creating a transformer terminal voltage is higher. This leads to a higher level of saturation cause higher harmonic components of inrush current, which again will result in an increase in the voltage [9]. 74 2012 1st International Conference on Future Trends in Computing and Communication Technologies IV. APPROACH AND METHOD VI. Generally, this project is involves the development of software to complete. In the simulation tools and equipment must be identified. After all requirements sufficient, the work can be done. The detail description and methodology are discussed in this part. The process of the project started from the beginning part until it being completed. The beginning stage is started with study the past researches and the data analysis of previous related works. After it had been done, the next stage is to understand and to dwell this project and the simulation software. After all resource has been collected, the next stage is designing circuit for the simulation result. For the simulation purposes, the circuit is being designed at first. Then, the result is simulated by PSCAD software. If the results are not the same as per expected results, then the simulation is being redone again and again in order to obtain the desired results. If the simulation results in accordance with project requirements, then it can go to the next step. Comparison data should be made after the simulation is correct and should be analyzed on the graph in order to complete the project. V. SIMULATION RESULTS AND DATA VERIFICATION The variation of the harmonic content of transformer inrush current with time was firstly described. The magnitude of each harmonic component from 1st harmonic to 7th harmonic was obtained by doing simulation on simulation tool. Fig. 2 shows the peak value as a time of the main harmonic components of the transformer. The peak value of any harmonic component during operation is totally different from its peak at each every harmonic. So, these are no sympathetic interaction and the second harmonic is by far the dominant one [11]. Fig. 2 represents the value of each harmonic decreased and returned to its original shape again after the fault occurs. In this simulation, on the frequency scanner is set to N=7. That means only seven type harmonic can be scanned by the scanner for this simulation. The harmonic of order three and higher show the discontinuities with their peak values going down to zero and then it increase for oscillating until the harmonic is lowest when the system is stable. Fig. 3 shows that the value of at every harmonic has been scanned during the phenomenon. These harmonics change their phase shift from positive to negative as their magnitude passes through to zero. Harmonic content of the inrush current can cause temporary over-voltages in power system transmission line. SIMULATION TOOL For this power systems protection modeling and simulation, PSCAD software is used. PSCAD stands for Power Systems Computer Aided Design. It is a powerful and flexible graphical user interface to the world-renowned, EMTDC solution engine. PSCAD enables the user to schematically construct a circuit, run a simulation, analyze the results, and manage the data in a completely integrated, graphical environment [10]. Online plotting functions, controls and meters are also included, so that the user can alter system parameters during a simulation run, and view the results directly [10]. Fig. 1 shows the GUI for PSCAD. Fig. 2: Result Harmonic when Inrush Current Fig. 3: The Poly-meter of Harmonic Inrush Current Fig. 1: GUI for PSCAD Simulation 75 2012 1st International Conference on Future Trends in Computing and Communication Technologies Fig. 7: The Poly-Meter of Each Harmonic For sympathetic inrush phenomenon harmonic analysis, the even ordered harmonic component of the supply current decay rather quickly, where the odd harmonics increase and continue to be presented for a considerable period of time as shown at Fig. 8. At the current supply, the amount are from sympathetic inrush current and inrush current, so it becoming more symmetric as transformer 1 goes saturated [11]. Eventually, this current will have no DC neither even harmonic components, as can be seen in Fig. 8. This figure shows that these harmonics are negligible after the 0.0949s. In this case, the peak values of the harmonic components 2nd harmonic, 3rd harmonic and 5th harmonic, at the 0.0797s, are respectively 14.05115A, 0.726575A and 1.21141A, showing a significant increase of 2nd harmonic, 3rd harmonic and 5th harmonic when compared with the case without sympathetic interaction. Harmonics will be reduced to 0.006 at the time of 0.098s, and this makes the sympathetic inrush current take a long time to become a zero. Fig. 4: Result Total Harmonic Distortion (THD) of Inrush Current Fig. 4 shows the results of Total Harmonic Distortion when the system operates without any sympathetic inrush current. Harmonic is the highest ranked at 0.0931s (X-axis) is about 30.566 (Y-axis). Harmonics will be reduced to 0.001 at the time of 0.144s, and this makes the inrush current take of 0.074s. Fig. 5 shows the value of Total Harmonic Distortion for the inrush current condition. Total Harmonic Distortion simulation graph for each harmonic can be seen in Fig. 6 and Fig. 7. 1st harmonic until 7th harmonic can be viewed the maximum value for each harmonic type. It should be noted that this current decays relatively fast, with its fundamental and harmonic components reaching relatively low values after 0.925s. At the 0.059, for example, the three more predominant harmonic components 2nd harmonic, 3rd harmonic and 5th harmonic are approximately 0.00563A, 8.8164xE-5A and 9.5935xE-5A, respectively. Fig. 5: The Poly-meter of THD (Inrush Current) Fig. 8: Result Harmonic in Sympathetic Inrush Phenomenon Fig. 6: Result of at Each Harmonic Fig. 9: The Poly-meter of Harmonic Sympathetic Inrush Current 76 2012 1st International Conference on Future Trends in Computing and Communication Technologies Fig. 10: Result Total Harmonic Distortion (THD) of Sympathetic Inrush Current Fig. 12: Result of at Each Harmonic Fig.9 shows that the value of at every harmonic has been scanned during the phenomenon. These harmonics change their phase shift from positive to negative as their magnitude passes through to zero. Harmonic content of the inrush current can cause temporary over-voltages in power system transmission line. Fig. 10 shows the result of Total Harmonic Distortion when the system operates with sympathetic inrush current that occurs. Harmonic is the highest ranked at 0.0954s (X-axis) is about 24.455 (Y-axis). Harmonics will be reduced to 0 at the time of 0.1085ss, and this makes the sympathetic inrush current take of 0.0385s. Fig. 11 shows the value of Total Harmonic Distortion for the inrush current condition. Total Harmonic Distortion simulation graph for each harmonic can be seen in Fig. 6 and Fig. 7. Fig.13: The Poly-Meter of Each Harmonic Total Harmonic distortion simulation graph for each harmonic for sympathetic inrush simulation can be seen in Fig. 12 and Fig. 13. Inspection from Fig. 8, the fundamental component of the supply current presents a high value and decays at a relatively very slow rate. This can cause a prolonged and appreciable transient demand of reactive power, producing a sustained voltage drop in the system which may cause load rejection. VII. CONCLUSION AND RECOMMENDATION Harmonic traditionally seen as high-frequency interference not contribute to the dynamics of the system, and therefore does not have to be considered in stability analysis. Harmonics are usually regarded as a problem condition is stable, leading to increasing losses, extreme heat, and long life components decreased and damage to sensitive loads. As the harmonic does not affect the stability of the system, the operating point of a stable steady state is often assumed in harmonic analysis. A popular method for the harmonic analysis is a harmonic balance. Harmonic analysis is a frequency domain method that can be used repeatedly to find the steady state settlement of nonlinear networks. Nonlinear loads are modeled as harmonic current sources in the linear range. In each iteration, node voltages are calculated by solving the system of linear equations, and then the non-linear current source voltage node updated according to the better. Fig. 11: The Poly-meter of THD (Sympathetic Inrush) 77 2012 1st International Conference on Future Trends in Computing and Communication Technologies REFERENCES These also demonstrated that the supply current is greatly affected by of this interaction of the currents that emerged within the sympathetic magnetism transformer is connected to the system. The harmonic analysis of supply current when sympathetic interaction has shown that even harmonic is ordered this decay of time is quite fast but odd ordered harmonics increase and remain for a long period of time. This may evolve substantially temporarily harmonic overvoltage which may occur in the system. Overvoltage of this period depends on the essence of transformer saturation level and pattern of energy losses in the system considered. When the solution to the problem of harmonics in power system is required, there are two approaches to this settlement: i. Strengthen the distribution system that the customer can tolerate the level of harmonic that were present, while other tools to reduce of harmonic to acceptable levels. ii. Filtration current. The filter can be used in various locations. Nur’ Ain Maiza Bt. Ismail, Adaptive Arc Fault Detection for Medium Voltage, Universiti Teknologi Malaysia, Malaysia. May 2009. [2] A. Villa, “Sympathetic Interaction Between Step-Up Transformers Up 13.2/400 Kv Of Macagua Hydroelectric Complex from Cvg Edelca, Cvg Electrificación Del Caroní, C.A. (Cvg Edelca) (Venezuela), 21, Rue D’artois, F-75008 Paris, Cigre. 2006. [3] G. B. Kumbhar and S. V. Kulkarni, “Analysis of Sympathetic Inrush Phenomena in Transformers Using Coupled Field-Circuit Approach,” IEEE PES General Meeting, June 24-28, 2007, Tampa, USA. [4] S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design and Practice. New York: Marcel Dekker, Inc., Taylor & Francis Group, May 2004. [5] A.A. Mohd Zin, Hana Abdull Halim & S. P. Abdul Karim, “Sympathetic Inrush Current Phenomenon Analysis and Solution for A Power Transformer”, International Review on Modeling and Simulations (IREMOS). Vol. 4, N. 2, pp. 601-607. April 2011, ISSN 1974-9821. [6] Nikhil Mallikarjun And Devdutta Sahoo,“Transient Harmonic Analysis of Transformer”, Department Of Electrical Engineering, National Institute of Technology, Rourkela, 2009. [7] Raleigh, August, “Power System Harmonics Causes and Effects of Variable Frequency Drives”, Relative to the IEEE 519-1992 Standard, Bulletin No. 8803 pd9402, 1994, Nc, U.S.A. [8] Iman Sadeghkhani And Arezoo Mortazavian, “Analysis of Transformer Harmonic Overvoltage’s during Power System Restoration”, Advances In Electrical Engineering Systems Vol. 1, No. 1, March 2012. [9] D.Lindenmeyer, H.W.Dommel, A.Moshref, P.Kundur, “Analysis and Control of Harmonic Overvoltage during System Restoration”. IPST ’99 – International Conference on Power Systems Transients. June 20-24, 1999. Budapest – Hungary. [10] (n.d). The Electronicmagnetic Transient .Power Quality in Electrical System. Received April 23, 2012, from http://www.powerqualityworld.com/2011/06/pscadpower-systems. [11] Bronzeado H.S, Brogan P.B, Yacamini R.,“Harmonic Analysis Of Transient Currents During Sympathetic Interaction”, IEEE Trans., Vol.11,No.4, Nov 1996. [1] ACKNOWLEDGMENT The authors are grateful to thank Universiti Malaysia Perlis (UniMAP) for providing the technical and financial support for this research. The financial support through the Short Term Grant (STG) is highly appreciated. Not to forget, special thanks to all PPKSE’s staffs and our families for the constant encouragement. To all of them, the success of this project is partly due to your support and blessings. Thank you. 78