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Power System Conference, 2008. MEPCON 2008. 12th International Middle-East

Date 12-15 March 2008

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Displaying Results 1 - 25 of 117
  • 500 kV transmission system in Egypt solving problem of voltage regulation by means of controlled shunt reactor transformer type (CSRT)

    Page(s): 178 - 182
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    This paper describes the configuration and main characteristics of the 500 kV grid in Egypt and presents an analysis for the problem of limitation the voltage drop along the transmission line connecting the southern and northern regions of Egypt with a length of 800 km during its loading from the maximum to the idle regime. It is shown that this problem can be solved by compensating the charging capacity of the line by utilization of controlled shunt reactors of a transformer type CSRT. View full abstract»

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  • A new intelligent optimization technique for distribution systems reconfiguration

    Page(s): 397 - 401
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (430 KB) |  | HTML iconHTML  

    The loss minimization problem is one of the most important problems to save the operational cost in distribution systems. Therefore, more efficient approaches are required to handle such a combinatorial problem. This paper presents an efficient meta-heuristic method for reconfiguration of distribution systems. A Tabu Search (TS) algorithm is used to reconfigure distribution systems so that active power losses are globally minimized with turning on / off sectionalizing switches. TS algorithm is introduced with some modifications such as using a tabu list with variable size according to the system size; this should lead to robust algorithm, and prevent cycling. Also, a random multiplicative move is used in the search process to diversify the search toward unexplored regions. A new method to check the radial topology of the system is presented. The proposed method is applied to 32-node and 69-node distribution systems. The obtained results using the proposed TS approach are compared with results obtained using Simulated Annealing (SA) approach and Parallel Tabu Search (PTS) approach in the previous work to examine the performance. View full abstract»

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  • Study and design of lightning protection for H.V. transmission lines in the Egyptian Unified Network

    Page(s): 18 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (65 KB)  

    High and Extra high voltages (H.V. and E.H.V.) overhead transmission lines and the associated substations have been subjected to surge overvoltages due to atmospheric lightning storms and switching operations. Overvoltages produced by surges on transmission lines may cause flashover of line insulation and can reach substations, in the form of travelling waves, and may damage its equipment apart from the economic losses due to power outages. Protection of transmission lines against the effects of lightning is secured by a combination of ground wires to minimize the possibility of insulator flashovers, and various types of protective devices. The objective of this research is to reduce the number of interruptions due to lightning to a minimum acceptable amount according to the international standards and codes. This study, at certain level of voltage, concentrates on the design of different types of arresters needed for certain level of protection according to its internal material, characteristics and advantages. Our study showed that Zinc Oxide (ZnO) arresters are the most perfect for this purpose. In this research measures were taken to protect H.V. and E.H.V. lines and substations of the Egyptian Unified Network (E.U.N). Great attention was paid to the sections of lines that are in immediate vicinity to the substations, which are normally called 'Approaches'. A safe, reliable and economical lightning protective system using Metal-Gapless Arresters (MOA) was developed and tried in the Egyptian Unified Network for different system of voltages at power frequency. This new technique was developed using a Matlab computer program. Optimization was done to select the best arrester for certain industrial application with the minimum cost based on rated voltage, discharge current and location of these arresters with respect to the selected substation. A reduced insulation withstand voltage level for substation was achieved using this novel technique. This new developed - echnique showed to be an effective tool and useful method to design engineers to select the optimum arrester type with the minimum cost and the safest location. View full abstract»

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  • Study in direct torque control of induction motor by using space vector modulation

    Page(s): 224 - 229
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (534 KB) |  | HTML iconHTML  

    In conventional direct torque control (DTC) has, over the years, become of the most popular methods of control for induction motors (IM) drive system. A single stator voltage vector of the inverter standard topology is selected every control sampling period, and it is maintained for the whole period. This makes the torque and stator flux reference values to be reached quickly, with a small number of inverter switching, resulting in a very good dynamic response. However, by this switching technique, based on hysteresis, large and small torque and flux errors are not distinguished, which cause an extra torque ripple in motor steady state operation.. A control is proposed to determine the reference value of the flux according to the value of the motor torque. The results of the Matlab- Simulink simulations with different algorithms such as classical DTC, SVM-DTC method and SVM-DTC with PI controller direct torque control without hysteresis band has been compared.. The average torque ripple is reduced over 60% with SVM-DTC with PI controller method compared with classical DTC and is reduced by 30% compared with SVM-DTC. View full abstract»

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  • Study of high power factor rectifiers based on one cycle control in aircraft electric power system

    Page(s): 325 - 329
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1097 KB) |  | HTML iconHTML  

    The object of this paper is to present further study of three-phase rectifiers based on one-cycle control in aircraft electric power system. The fundamental vector principle of one cycle control is introduced and analyzed briefly. The Simulated model of three-phase Rectifiers based on one-cycle control is build by software Saber. The 4 kW prototype of three-phase rectifiers based on the one-cycle control is presented. An investigation of steady and dynamic performance for three-phase PFC system has been carried out in aircraft electric power system conditions. The result of simulation and experiments demonstrate that one-cycle controller features excellent performance, simple circuitry, and low cost control methods for three-phase rectifiers in aircraft electric power systems. View full abstract»

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  • Study of nonlinear-carrier control stability for PFC boost converters

    Page(s): 475 - 479
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1291 KB) |  | HTML iconHTML  

    Nonlinear control considers an elegant technique for boost PFC converters. Switch duty cycle is determined by comparing a signal derived from the main switch current with a periodic, nonlinear carrier waveform that forces the input current to follow the input line voltage. That results in a near unity power factor. However, nonlinear phenomena have been detected in PFC circuits resulted in low power factor. In this paper, a study of the stability of nonlinear control in pre-regulator PFC converter with resistive load and two-stage PFC converter where DC-DC has replaced the load. Both circuits have been tested to determine the practical limitation for stable and unstable regions. Lastly, some design guidelines have been made clear for stable operation using stability maps. View full abstract»

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  • Superconducting Magnetic Energy Storage unit, an efficient energy technology for power systems

    Page(s): 447 - 452
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1388 KB) |  | HTML iconHTML  

    This paper discusses application of superconducting magnetic energy storage (SMES) unit to improve power system performance. The application of SMES unit in mitigating voltage sags and in damping dynamic oscillations in power systems is discussed. To show the effectiveness of the proposed controller in providing continuous voltage regulation and in enhancing power system dynamics, a three-phase short circuit is applied to the system and simulation is carried out with and with no SMES connected to the system. The results of these investigations are studied using the well-developed graphic facilities available in an industry standard power system package, namely PSCAD/EMTDC. Results have shown that SMES unit can effectively improve system stability and power quality of power systems. View full abstract»

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  • Tariff design for load building / energy conservation a DSM formulation

    Page(s): 571 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1107 KB) |  | HTML iconHTML  

    In this paper an optimal based tariff design formulation is introduced for achieving load building or energy conservation DSM target objectives. For a load building DSM objective tariffs are usually designed in a decreasing form (higher consumption corresponds to lower average price per kWh); while for an energy conservation DSM objective tariffs are usually designed in an increasing form (higher consumption corresponds to higher average price per kWh). The introduced optimal tariff design model determines: tariff levels and their corresponding energy levels to achieve objective revenue levels as required by the aforementioned DSM targets. The optimal tariff formulation introduced in this paper utilizes the price of energy for each energy level as its control variables, while levels of energy consumption (energy block size), the corresponding number of consumers and revenues are the state variables. Total energy consumption and total number of consumers serve as the equality constraints. The proposed optimal tariff formulation structure is applied to the real data of the Egyptian residential and commercial consumer sectors and results are compared to the existing tariff structure. View full abstract»

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  • The application of segmentation and grid shock absorber concept for reliable power grids

    Page(s): 34 - 38
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1870 KB) |  | HTML iconHTML  

    Growing grid complexity and loading are increasing the risk of cascading failures and large-scale blackouts. Traditional reliability enhancement technologies offer only incremental improvements. Emerging technologies are limited by their complexity, and need for extensive real time analyses. A better solution is to segment the grid into AC sectors interconnected by HVDC links. In a segmented system simple preset HVDC controls respond to disturbances without assistance from operators or central control. Further, transfer capability is increased when intra-sector spinning reserve responds to frequency decay. Efficient market operation and management are enabled by the controllability of power flows between grid sectors. View full abstract»

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  • The future of towers made of organic compound materials

    Page(s): 200 - 202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    Reliability of a transmission structure depends not only upon its design, but also on the development of structural arrangement, detailing of connections, uniformity of quality of structural sections, accurate fabrication, and finally material type and quality. Recently fiber reinforced polymer composites (FRP), or advanced organic materials are very attractive for use in transmission line towers. FRP composites have many benefits to their selection and use. The selection of the materials depends on the performance and intended use of the product. The composites designer can tailor the performance of the end product with proper selection of materials. This paper aims to investigate the future of towers made of organic material. Comparative study with the conventional type commonly used in Egypt will be carried out. Also the economic studies were performed to estimate the level of profitability for both technical options of steel and FRP distribution networks. View full abstract»

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  • Three-phase three-level nine switches inverter employing space vector modulation

    Page(s): 341 - 347
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1447 KB)  

    This paper studies the space vector pulse width modulation technique (SVPWM) for the three-phase three- level nine switches voltage source inverter. The proposed inverter is based on the two level inverter topology where it consists of a main inverter switches Q1, Q2, Q3, Q4, Q5, and Q6, an auxiliary three bidirectional switches S1, S2, and S3 and two capacitor banks C1, and C2. Ideal switches and diodes will be assumed and the dc bus capacitor bank voltages fluctuations will be absent. The effectiveness of the SVPWM control scheme will be verified by the simulations results in the worst case where two very low switching frequencies values of 1 kHz and 5 kHz will be considered. Open loop controller experimental measurements at 1 kHz switching frequency will be provided. View full abstract»

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  • Transient stability preventive control of an electric power system using a hybrid method

    Page(s): 141 - 145
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    This paper presents a transient stability preventive control technique based on a hybrid method. In order to maintain the power system security it is evaluated the generators output power that should be shift from the most unstable synchronous machines to the undisturbed units. The reallocation of the generators output power is carried out using an optimal power flow program. The hybrid method is a very important tool for the transient stability analysis, since it allows a fast evaluation of the stability limits and margins. This approach can also easily accommodate detailed models of the network devices and protective schemes. In order to validate the established mathematical models it was studied the transient stability of the New England test power network. The results obtained with the proposed methodology were compared with the solutions produced by another numerical formulation, showing a very close agreement. View full abstract»

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  • A new method for transmission loss allocation considering the circulating currents between generators

    Page(s): 282 - 286
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (450 KB) |  | HTML iconHTML  

    This paper presents a new method for transmission loss allocation based on the separation of transmission loss caused by load and the loss due to circulating currents between generators. Theoretical basis and derivations of the loss formula are presented using simple systems. Details of application of the proposed method for a power system of real size are presented along with the results of application to a test system. View full abstract»

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  • Types of electrical trees in solid insulation under electrical and mechanical energy basis

    Page(s): 80 - 84
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB) |  | HTML iconHTML  

    The shape of electrical trees is critical in determining the life of electrical insulation subject to this type of degradation. This paper identifies a physical basis for determining tree shape. A quantitative physical model for propagation of electrical tree structures in polymeric insulation is presented. In the present model the propagation of trees arises from the formation of electrodamage that precedes and surrounds the tree tip during the tree propagation process. A kinetic model for the electrical tree structures in solid polymeric insulation is developed, that allows for combined electrical and mechanical stresses. Also present an energy balance analysis during the tree growth process, and present results which show that the proposed model can give predicted tree shape type which in a good agreement with the experimental data of the tree growth subjected to a combined electrical and mechanical stress. View full abstract»

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  • Unity Power Factor control of permanent magnet motor drive system

    Page(s): 360 - 367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1397 KB) |  | HTML iconHTML  

    The permanent magnet synchronous motors (PMSMs) have gained an increasing interest recently. The wide variety of applications of PMSM drives makes it necessary to achieve fast and reliable drive control system design. Vector control of PMSM can achieve fast dynamic response with less complexity and parameter-independent controller, prevent demagnetization of the motor and allow maximum efficiency operation. In this paper, a novel unity power factor (UPF) control drive for PMSMs is presented. The drive is performed with constraint on the (PF) such that its steady-state value is unity. This feature provides an extension of the constant torque region, resulting in higher output power of the PMSM drive, which is desirable in many applications requiring extended speed range at rated motor torque. However, this drive is not optimal in terms of efficiency which will be less than that obtained from conventional decoupled vector control drive for the same torque. Therefore, it is concluded that before reaching the rated speed, the conventional decoupled vector control is preferable, whereas, the UPF control is optimal to have a wider range of speed operation (above the base speed of the conventional vector control) and hence, extension of the constant torque region. Above this extended base speed, the PMSM drive can be operated in constant power mode using the conventional field-weakening technique having constant supply voltage and current. The drive system is built using MATLAB-SIMULINK software. The validity is evaluated in both steady-state condition and transient response using computer simulation. View full abstract»

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  • Upgrading AC transmission to DC for maximum power transfer capacity

    Page(s): 44 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    The paper describes current developments for upgrading of existing AC transmission lines for substantial increase in power transfer capacity by a new concept of conversion to HVDC transmission. Traditionally, such a conversion has been contemplated as being three phase AC to bipolar DC. Recent patents by one of the authors have introduced the tripolar DC transmission concept, which maximizes the utilization of all three phase conductors and improves N-l operational constraints. Conversion consideration issues, e.g. selection of DC voltage rating, the need for re-insulation, etc. are investigated. The paper provides an overview of an Application Guide that is being prepared by EPRI for transmission engineers and planners contemplating upgrading AC transmission lines to HVDC transmission View full abstract»

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  • Utilization of a buck boost converter and the method of segmented capacitors in a CDI water purification system

    Page(s): 470 - 474
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (494 KB) |  | HTML iconHTML  

    A novel method for making Capacitive Deionization (CDI) water purification more efficient and cheaper using a buck- boost DC/DC converter is presented in this paper. The energy recovery is superior (51%) versus maximum reported results in the literature (30%) [1]. First, the concept of a CDI cell is introduced. Second, the existing methods for energy recovery are reported showing their advantages and disadvantages. Then, the novel method using a buck-boost converter is presented. Also, the method of segmented capacitors is presented. Simulation results are provided. Experimental data verified the new technique and agrees with simulation. View full abstract»

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  • Vector control drive of permanent magnet motor without a shaft encoder

    Page(s): 249 - 254
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1340 KB) |  | HTML iconHTML  

    Permanent Magnet Synchronous Motors (PMSMs) are receiving increased attention for drive applications because of their high toque to inertia ratio, superior power density, and high efficiency. To control PMSM, position and speed sensors are indispensable because the current should be controlled depending on the rotor position. However, these sensors are undesirable from standpoints of size, cost, maintenance, and reliability. There are different ways of approaching this problem, depending on the flux distribution. This paper presents a novel vector control for a permanent motor drive without use of a shaft sensor. The vector control drive provides a wide range of speeds, high torque capability and high efficiency. Two line-to-line voltages and two stator currents are sensed to produce the stator flux linkage space vector. The angle of this vector is then used to produce the appropriate stator current command signals which can be controlled to maintain zero d-axis current which is the condition of vector control, over a wide range of torque and speed. A speed signals is derived from the rate of change of angle of the flux linkage. Simulation is carried out in order to evaluate the behavior of the proposed method for different operating situations. The simulation results demonstrate that a good steady-state and transient performances for the proposed sensorless scheme are obtained. View full abstract»

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  • Voltage and energy utilization enhancement in a Stand-alone WECS Using a fuzzy logic controlled SPWM converter interface scheme

    Page(s): 330 - 334
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB) |  | HTML iconHTML  

    In this study, a novel sinusoidal PWM switched AC/DC/AC converter interface scheme using real novel tri-loop voltage error tracking fuzzy logic controller (FLC), to stabilize the stand alone Wind Energy Conversion Scheme (WECS) using an induction generator. The proposed novel sinusoidal Pulse Width Modulator (SPWM) switched (AC/DC/AC) converter (diode rectifier and 6-pulse IGBT inverter) interface scheme serves as a combined voltage stabilization regulator and maximum wind energy utilization and enhancement compensator. View full abstract»

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  • Widening stability zone of a multi-cell DC-DC buck converter by using Fixed Point Induced Control

    Page(s): 583 - 587
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB) |  | HTML iconHTML  

    In this paper we derive a simplified nonlinear map of a two-cell DC-DC buck power electronic converter. The nonlinear map is piece-wise smooth and has a single fixed point. Under parameter change, the fixed point loses stability through a nonsmooth period doubling bifurcation. The stability zone is located in the design parameter space. Outside this zone the system presents subharmonic oscillations and chaotic dynamics. The fixed point induced control (FPIC) technique is then applied to the system in order to widen the stability zone. The performance of the FPIC technique applied for the stabilization of the two-cell DC-DC buck converter is analyzed. With this technique, the stabilization is achieved without altering the fixed point. View full abstract»

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  • A new non-linear model for transformer oil residual operating time

    Page(s): 66 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (514 KB) |  | HTML iconHTML  

    The purpose of this paper is to implement non-linear multivariable regression technique (nlm) for the prediction of the residual operating time (ROT) of the transformer oil characteristics. This technique depends on non-linear models for each transformer oil characteristic and linear combination of these non-linear models. The characteristics under study are the oil breakdown voltage, total acidity and water content. The proposed technique has proved its accuracy and applicability by justifying the oil characteristics which have a strong impact on ROT and by giving more accurate predicted results than those obtained by previous modeling techniques. View full abstract»

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  • A new torque controller for Direct Torque Controlled Induction Machine drives

    Page(s): 244 - 248
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (497 KB) |  | HTML iconHTML  

    Hysteresis band control is one of the simplest and most popular techniques used in direct torque control (DTC) of induction machine drives. However the conventional fixed band hysteresis control has a variable switching frequency which causes serious problems in DTC. To solve these problems a new constant switching frequency torque controller is proposed to replace the conventional hysteresis-based controller in this paper. The technique, based on the same concept, but with the hysteresis band implemented with fuzzy logic is proposed to optimize the DTC drive performance. The proposed technique is verified by simulations. The system is first simulated by MATLAB/Simulink and tested by hardware in the loop. Then, it is implemented based on a TMS320C6711, 32-bit fixed point digital signal processor. Experimental results prove the feasibility of the proposed strategy as compared with the conventional method. View full abstract»

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  • A novel approach for online fault detection in HVDC converters

    Page(s): 307 - 311
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (554 KB) |  | HTML iconHTML  

    A novel approach for fault detection in high voltage DC transmission systems using neural networks is presented. In the presented method, at first, Harmonics of voltage waveform in rectifier side are derived rapidly by using an adaptive linear neuron. Then, different types of faults including DC line fault, AC system fault and converter's faults are detected property using proposed criterion. In the under study voltage DC transmission systems system, rectifier and its controllers and required filters is modeled completely. A proposed criterion is tested on a high voltage DC system by computer simulation performed in MATLAB/Simulink environment. Simulation resulted demonstrates that the proposed approach can be used for online fault detection in high voltage DC systems. View full abstract»

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  • A practical winding fault detector for power transformers

    Page(s): 130 - 135
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1158 KB) |  | HTML iconHTML  

    In this paper, a new method for detecting internal winding faults for both single phase and three phase power transformers is presented. Not only the winding faults (including phase and ground fault combinations) are covered, but those turn-turn ones are successfully detected as well. These turn-turn conditions represent a basic challenge for conventional differential protection schemes. Internal high impedance ground faults are also covered successfully with a wide range of fault resistance value. The discrimination between winding faults and the magnetizing inrush conditions is also verified. The performance of the proposed detector is investigated using EMTP simulation covering a variety of operating conditions. All applied test results verify the performance of the proposed detector for power transformer protection. View full abstract»

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  • A proposed methodology to analyze systems with distributed harmonic sources

    Page(s): 536 - 542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (499 KB) |  | HTML iconHTML  

    Harmonics is one of the major disturbances that affect the power quality of electric utilities. Many techniques were used to analyze the harmonics in power systems. These techniques generally have difficulties in determining the collective impact of distributed harmonic sources. This paper introduces a proposed methodology for analyzing harmonics in distribution systems with distributed harmonic sources. The method takes into account the effect of diversity and attenuation. The method is illustrated through a numerical application applied on a real distributor. View full abstract»

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