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 Volume 4, 2009
Print ISSN: 1790-5060
E-ISSN: 2224-350X








Issue 1, Volume 4, January 2009

Title of the Paper:  Static and Dynamic Analysis of Reconnection of Former Two UCTE Synchronous Zones


Authors: Ivica Toljan, Eraldo Banovac, Sejid Tesnjak

Abstract: Considering the European electric power systems there is a yearly increased consumption of electricity everywhere (from 1% to even 4% in some cases). The processes of developing and connecting existing electric power systems are very complex. Preconditions for connecting two UCTE synchronous zones (1st and 2nd Pan-European synchronous zones) in one European electric power system were created in 2000. The UCTE synchronous zones were formed when the outage of the 400 kV overhead line Ernestinovo – Mladost on September 26, 1991 caused the system to separate. The reconnection was carried out on October 10, 2004 following the important decision which was passed by the UCTE Steering Committee at its meeting in early 2002 in Brussels. Static and dynamic analysis with respect to reconnection of electric power systems, such as transit analysis, analysis of capacity flows, short circuits, N-1, dynamic behavior, angle analysis, voltage stabilities, frequency oscillations, changes of capacity flows in a short time period, were outlined in the paper. Special attention is paid to the mathematical base significant for carrying out the analysis of conditions in certain electric power system.

Keywords: European transmission system, Reconnection, Static and dynamic analysis, Synchronous zone

Title of the Paper:  A Novel Approach to Evaluate Incremental Transmission Losses


Authors: P. M. De Oliveira-De Jesus, M. A. Alvarez, M. T. Ponce de Leao, J. M. Yusta

Abstract: During the past thirty years, the evaluation of incremental losses in transmission systems has been widespread around the world encompassing a fundamental task in order to solve the well-known economic dispatch problem. Nowadays, incremental losses or computation of penalty factors has gained a new relevance allocating transmission losses among market participants being integrated in the spot pricing model. Nevertheless, vagueness in power injections from load demand and renewable resources has a fundamental influence on transmission incremental losses, and consequently affecting spot prices of the energy. This paper presents a new method to compute Incremental Transmission Loss (ITL) factors taking into account the effect of uncertainty on power injections due to measurement errors or future estimation. Fuzzy Set Theory is applied to deal with vagueness of information about power injections. The proposed technique provides a broad spectrum of feasibility of incremental losses in order to perform operational planning tasks by Transmission System Operators or network regulators. A 3-bus system is used to illustrate the proposed methodology.

Keywords: Incremental transmission loss factors, loss allocation, spot pricing

Title of the Paper:  Problem Solving of Partial Discharge on the Distribution Line


Authors: Narong Mungkung, Tanes Tanitteerapan, Werachai Chaokumnerd, Karun Morasilp, Panumat Limsuwan, Warawut Poolperm, Toshifumi Yuji

Abstract: This paper presents the mitigation methods of PD on PIC in distribution line system. The area located near the coast will be selected as the pilot project because of having strong occurrence of PD which is mainly caused by salt contamination. The methods applied in this experiment consist of using tie wires made from an insulation sheath of low voltage cable, the sheath of PIC itself; composite tie wire and aluminium tie wire (reverse loop binding). Following the trial results, there are two methods that considered as the most effective ways for PD solving; binding PIC by using the PIC’s insulation sheath and the composite tie wire instead of aluminium tie wire (conventional binding).

Keywords: Partial discharge, Partially Insulated Cable, Tie wire, Burn down, Mitigation

Title of the Paper:  Voltage Stability Enhancement of Low Voltage Radial Distribution Network Using Static VAR Compensator: A Case Study


Authors: Kishor Porate, K. L. Thakre, G. L. Bodhe

Abstract: In this paper power flow analysis of 33/11 kV distribution substation and feeder is carried out to know the status of voltage and power flow at each bus. To maintain the rated voltage at load end, low rated static VAR compensators (SVC) are installed. For the case study typical heavily loaded distribution substation where the voltage variation on all the buses are maximum during peak load condition has been selected. Simulation of the distribution network with SVC has been developed in the Electrical Transient Analyzer Program (ETAP) environment. With the insertion of SVC, enhancement in voltage at various buses, reduction in system power loss, improvement in power factor and power flow are the objectives of the study. Description of the study network, simulation model and the results of simulation with comparison of recorded results are presented in the paper.

Keywords: Distribution network, Voltage stability, Power flow Analysis, Static VAR compensator, FACTS, ETAP

Issue 2, Volume 4, February 2009

Title of the Paper:  Applying Grey Theory Prediction Model on the DGA Data of the Transformer Oil and Using it for Fault Diagnosis


Authors: Anjali Chatterjee, Nirmal Kumar Roy

Abstract: This Non-Destructive Evaluation of Power transformer by monitoring various parameters, to predict its in-service behavior, is very much necessary for operating engineer to avoid catastrophic failures and costly outages. Dissolved Gas Analysis (DGA) is an important tool for transformer fault diagnosis. It is observed that the results of DGA doesn’t have a perceivable change over a short period. For less population of data availability grey modeling is used. To apply probability theory, statistics, and fuzzy systems, there is a requirement for a large number of data, then only conclusion or some inference can be drawn. The advantage of using the grey system theory is that, it gives a fair accuracy in predicting the volume of the gases, expected to be generated after some time period, using a small sample of data. In this paper we have done a comparative study on the predicted results obtained by different model of Grey theory mainly whitened model, connotation model and modified grey model. It is found that the error generated from the prediction by all the three model are within the limit of 15% which is acceptable. Additional by linear regression we are establishing a correlation between the key gases. This helps us to detect the abnormality of the situation and diagnose the type of fault. Additional this paper deals with the study on the behavior of the gas dissolved in the oil which has undergone filtration and the one without filtration. Through graphical means it has been clearly shown that filtration at periodic interval will extend the life of the transformer. It has been shown that the rate of gas generation also plays an important role to detect an active fault.

Keywords: Transformer, Dissolve gas analysis (DGA), Grey model, Modified grey model, Regression theory, Correlation, Fault diagnosis, filtration

Title of the Paper:  Security Constrained Unit Commitment Problem with Operational, Power Flow and Environmental Constraints


Authors: S. Prabhakar Karthikeyan, K. Palanisamy, C. Rani, I. Jacob Raglend, D. P. Kothari

Abstract: An algorithm to solve unit commitment problem (UCP) with operational, power flow and environmental constraints under contingencies has been developed to plan an economic and secure generation schedule. The unit commitment (UC) solution for the environmental constrained problem has been formulated as a multi-objective problem by considering both Economic load dispatch (ELD) and Economic emission dispatch (EED) simultaneously. The combined economic emission dispatch (CEED) bi-objective problem is converted to single objective function by adding a modified price penalty factor. The UCP solutions without operational and power flow constraints are not practical due to secure operation of the power system network. This proposed algorithm introduces an efficient UC approach that obtains the minimum operating cost satisfying both unit and network constraints when contingencies are included. Repeated OPF for the satisfactory unit combinations for every line removal under the given study period has been carried out to obtain UC solutions with both operational, power flow and environmental constraints. This proposed algorithm has been tested on IEEE 14, 30, 57, 118 buses and practical Indian utility systems. The solutions obtained are quite encouraging and useful in the economic emission environment. The algorithm and simulation are carried through Matlab environment.

Keywords: Combined economic emission dispatch, Contingency Analysis, Dynamic Programming, Economic dispatch, Lagrangian multiplier, Newton Raphson, Optimal power flow, Price penalty factor, Unit commitment

Title of the Paper:  Comparison of Electric Field and Potential Distributions on Silicone Rubber Polymer Insulators under Clean and Various Contamination Conditions Using Finite Element Method


Authors: Winai Onchantuek, Boonruang Marungsri, Anant Oonsivilai, Thanatchai Kulworawanichpong

Abstract: This paper presents the simulation results of electric field and potential distributions along surface of silicone rubber polymer insulators under clean and various contamination conditions. Alternate sheds silicone rubber polymer insulator having leakage distance 290 mm was used in this study. Two type of contaminants, plywood and cement dusts, have been studied the effect of contamination conditions on the insulator surface. The objective of this work is to comparison the effect of contamination conditions on potential and electric field distributions along the insulator surface when water droplets exist on the insulator surface. Finite element method (FEM) is adopted for this work. The simulation results show that contaminations have no effect of potential distribution on the insulator surface while electric field distributions are obviously depended on contamination conditions. Water droplets caused higher magnitude of electric field on the trunk portion surface than the shed surface. The simulation results confirmed electrical performance of polymer insulators under contamination conditions.

Keywords: Electric field distribution, potential distribution, silicone rubber polymer insulator, alternate shed, clean condition, contamination condition, water droplet, plywood dust, cement dust, finite element method

Issue 3, Volume 4, March 2009

Title of the Paper:  Distributed FACT Controllers as an Effective Tool for Reduction in Environmental pollution due to Thermal Power Plant


Authors: Kishor Porate, K. L. Thakre, G. L. Bodhe

Abstract: Flexible AC Transmission (FACTS) devices are installed in the transmission network to divert the power flow, minimize the power losses and to improve the line performance but it has some limitations and drawbacks. Distributed Flexible AC Transmission (D-FACTS) is a improved version of FACTS devices which is used to improve the security and reliability of the network in a cost effective manner. This paper discusses the concept of D-FACTS technology for saving of electrical energy, minimization of losses, reduction of coal consumption and minimization of environmental pollution from thermal power plants. This paper also discusses comparative evaluation of passive and active approaches in design of controllers for transmission line. Analysis also deals with computer simulation for reactances, equivalent voltages required for injection in the transmission line, and number of distributed modules per conductor per kilometre. Computations for saving of coal and associated environmental pollution have been achieved. System details are presented in the paper along with simulation results.

Keywords: Distributed series compensator, D-FACTS, FACTS, Electrical energy saving, Coal economics, Environmental pollution

Title of the Paper:  Universal Power Quality Conditioner


Authors: Moleykutty George, Kartik Prasad Basu

Abstract: This manuscript proposes a novel control technique for three-phase shunt active power line conditioner to determine the compensation current associated with three-phase parallel converters. The proposed control scheme is effective in achieving purely sinusoidal balanced source currents in phase with respective source voltages. The method assumes that the active power line conditioning system (APLC) supplies all the real power and imaginary power of the load that differ from positive sequence fundamental average power consumed by the load. Asymmetry, unbalance and distortion in the terminal voltages and load currents have been considered in this manuscript. Since the proposed control technique considered asymmetry, unbalance and distortion in both terminal voltages and load currents, the developed APLC system can be treated as a universal power quality conditioner for the power quality problems. The supremacy of the proposed approach has been discussed and compared with synchronous detection equal current approach (SDECA).

Keywords: APLC, parallel converters, PSFAP, SDECA, asymmetry, unbalance, distortion, THD

Title of the Paper:  Tunning of Fuzzy Logic Power System Stabilizers using Genetic Algorithm in Multimachine Power System


Authors: Manisha Dubey, Nikos E. Mastorakis

Abstract: This paper presents an approach for the design of fuzzy logic power system stabilizers using genetic algorithms. In the proposed fuzzy expert system, speed deviation and its derivative have been selected as fuzzy inputs. In this approach the parameters of the fuzzy logic controllers have been tuned using genetic algorithm. Incorporation of GA in the design of fuzzy logic power system stabilizer will add an intelligent dimension to the stabilizer and significantly reduces computational time in the design process. It is shown in this paper that the system dynamic performance can be improved significantly by incorporating a genetic-based searching mechanism. To demonstrate the robustness of the genetic based fuzzy logic power system stabilizer (GFLPSS), simulation studies on multimachine system subjected to small perturbation and three-phase fault have been carried out. Simulation results show the superiority and robustness of GA based power system stabilizer as compare to conventionally tuned controller to enhance system dynamic performance over a wide range of operating conditions.

Keywords: Dynamic stability, Fuzzy logic based power system stabilizer, Genetic Algorithms, Genetic based power system stabilizer, Power system stabilizer

Issue 4, Volume 4, April 2009

Title of the Paper:  Tracking of Fluctuating Load Power Quality Using Normalized Embedded Zero-tree Wavelet Coding Considering Data Compression


Authors: Shu-Chen Wang, Cheng-Ping Huang, Chi-Jui Wu

Abstract: In this paper, the data compression technique using the normalized embedded zero-tree wavelet (NEZW) coding is presented for the long-duration monitoring of a DC electric arc furnace and a railroad tracking load. For those power quality disturbing loads, harmonics, voltage fluctuation, and loading fluctuation are critical and stochastic load characteristics. In the power quality measurement, while keep enough stochastic load information, it is desired to reduce data size in long duration recording of voltage and current waveforms. The effects of multi-resolution analysis levels and threshold values in the NEZW coding are investigated. From the calculation results of field measurement data, the NEZW coding almost preserves the values of voltage fluctuation and power quantities. For storage of the field measurement voltage and current waveforms, the NEZW coding can not only greatly reduce data size, but it also can preserve sufficient load information.

Keywords: Electric power quality, data compression, discrete wavelet transform, multi-resolution analysis, normalized embedded zero-tree wavelet coding

Title of the Paper:  Discussion on the Existing Deterministic Approaches for Evaluating the Voltage Deviation due to Distributed Generation


Authors: Tsai-Hsiang Chen, Nien-Che Yang

Abstract: This paper investigates uncertainties in the existing deterministic approaches for evaluating steady-state voltage deviation due to distributed generation. Nowadays, deterministic approaches are widely adopted by the persons proposing the interconnection of distributed generation. However, the existing deterministic approaches overlook some operation conditions that may give rise to incorrect results and lead to wrong decisions in practical applications. In this paper, the interconnection rules for distributed generations and the existing deterministic approaches for evaluating steady-state voltage deviations are introduced first. Then, various factors effecting steady-state voltage deviation and the determination of maximum allowable DG capacity are discussed. Finally, the uncertainties of the existing deterministic approaches are discussed. It is intended for reference by utility engineers processing distributed generation interconnection applications.

Keywords: Distributed generation, Distribution system, Power flow analysis, Power quality, Voltage deviations, Wind power

Title of the Paper:  Effects of Renewable Distributed Generation on the Operational Characteristics of Meshed Power Distribution Systems


Authors: Wen-Chih Yang, Tsai-Hsiang Chen, Jun-Den Wu

Abstract: This paper analyzes the effects of renewable distributed generation on the operational characteristics of meshed power distribution systems. Meshed power distribution systems are more reliable than radial and closed-loop ones; however, their structures and operating conditions are more complex than the latter. Hence, operating these types of systems is not easy for power engineers, especially in the case of combining renewable distributed generation sources. This paper first develops the constant power model of a renewable distributed generation source, then constructs the network model of a medium-voltage meshed distribution system in the professional simulation software, Matlab/Simulink. The effects of renewable distributed generation sources on the operational characteristics of meshed distribution systems are evaluated in detail. The evaluation takes into account the generation capacity, connecting location, and operating power factor of renewable distributed generation sources. The results shown in this paper can contribute well to electrical utilities with meshed power distribution systems.

Keywords: Meshed power distribution system, Renewable distributed generation, Operational characteristics

Title of the Paper:  Research of the Impact of Voltage Imbalance on Power Distribution Systems and Equipment


Authors: Tsai-Hsiang Chen, Cheng-Han Yang, Ting-Yen Hsieh

Abstract: This paper investigates the impact of voltage imbalance on power distribution systems and equipment in various practical cases. The definition of voltage imbalance is introduced first, followed by description of the origins of voltage imbalance, and finally simulation results and discussion of the impact of voltage imbalance on systems and equipment for specific cases are presented. A commercial software package, Matlab/Simulink® was utilized to build full-scale mathematical models of power distribution systems. The simulation results of the study cases have indicated clearly, the causes and impacts of voltage imbalance. The results are of value to engineers and experts in designing suitable power distribution systems, balancing single-phase loads in three phase systems and thereby improving system efficiency.

Keywords: Voltage unbalance, power distribution system, system efficiency, neutral wire

Issue 5, Volume 4, May 2009

Title of the Paper:  Atmospheric Fluidized Bed Biomass and Waste Gasification


Authors: Martin Lisy, Marek Balas, Jiri Moskalik, Jiri Pospisil

Abstract: Biomass as fuel is a significant source of renewable energy. In comparison with fossil fuels, however, its effective use is more complicated. This is the reason why other than conventional technologies of combustion are sought to make energy use of biomass. One of the ways of converting biomass to thermal energy or electric power is thermal gasification. The generated gas can consequently be used in combustion engines, gas turbines, or be directly burnt in the furnaces of steam boilers. Yet another interesting way of using the gas is separation and use of its individual constituents, e.g. separation of hydrogen for fuel cells. This paper is focused on survey of research of biomass and waste gasification at the Faculty of Mechanical Engineering, Brno University of Technology. The first part of this paper deals with testing of the most frequent biomass by gasification process. Second part is focused on catalytic methods of gasification gas cleaning using at experimental unit.

Keywords: Biomass, syngas cleaning, renewable energy sources, gasification, dolomite, nickel catalysts

Title of the Paper:  Circuit Breaker Type Disconnector for Overvoltage Protector


Authors: Hitoshi Kijima, Masao Shibayama

Abstract: A disconnector for an overvoltage protector is equipment that disconnects a circuit when the overvoltage protector may fail in a short circuit mode. The disconnector and the overvoltage protector are connected in series. A fuse or a circuit breaker is normaly used as a disconnector. However there are problems with both methods. A fuse is not recyclable once it goes out. Even a circuit breaker is resetable, a lightning surge current causes a swichgear of circuit breaker to open unnecessary. This malfunction prevents the overvoltage protective function which eliminates a lightning surge current into an instrument. If the problem which a switchgear of circuit breaker comes floating can be solved, even when a lightning surge current flows through it, an instrument can be protected by the overvoltage protector. This paper presents a way of preventing circuit breker type disconnectors from the malfunction.

Keywords: Circuit breaker, disconnector, overvoltage protector, short circuit mode , lightning surge

Title of the Paper:  A Novel Method of Coordinating PSSs and FACTS Devices in Power System Stability Enhancement


Authors: M. Ahmadzadeh, S. S. Mortazavi, A. Saeedian

Abstract: This paper shows the effect of power system Stabilizers (PSS) and Flexible AC Transmission Systems (FACTS devices) based stabilizers containing Thyristor controlled Series Compensator (TCSC), Static var compensators (SVC), Thyristor Controlled and phase shifter (TCPS) on stability of power systems. Moreover this paper presents a novel approach for designing coordinated controllers of PSS and FACTS such as coordination of PSS with SVC, PSS with TCSC and PSS with TCPS for enhancing small disturbance stability. The coordinated control problem is formulated as a constrained optimization with eigenvalue-based objective function .The proposed approach employs genetic algorithm (GA) for optimization. To study the effectiveness of the proposed controllers, three different loading conditions including light, normal and heavy loading conditions are considered. Moreover in order to determine effect of proposed design, three case studies are considered too. These include: 1-without compensation (base case), 2-single compensation and 3-coordinated compensation. Simulation results show that the controller design approach is able to provide better damping and stability performance.

Keywords: Power system stabilizer, PSS, FACTS devices, SVC, TCSC, TCPS, Optimization, coordinated design, small disturbance stability

Issue 6, Volume 4, June 2009

Title of the Paper:  A New Solar Position Sensor Using Low Cost Photosensors Matrix for Tracking Systems


Authors: Alin Argeseanu, Ewen Ritchie, Krisztina Leban

Abstract: A solar tracking system is a machine that is designed for the orientation of different solar energy receivers, photovoltaic arrays or thermal receivers. The paper proposes a new solution of the solar position sensor used in tracking system control. The new matrix solar sensor (MSS) is an economic device but in the same time MSS advantages are the robustness and the accuracy. An actual tracking system that uses the new MSS achieves a position accuracy better then 1°. The main innovative concept of the new MSS is to use the ancient concept of solar clock to digitize the data set provided by the photosensors matrix area. The new MSS uses eight ordinary photo-resistors. These sensors working principle is to operate in two extreme conditions: in bright area or in shaded area. This binary principle simplifies the operating of the tracking control device.

Keywords: Solar energy, tracking systems, optimum receiver position, photo-resistors, matrix sensor, digital code converter, digital comparator

Title of the Paper:  Thermal Model Parameters Transformers


Authors: Marius-Constantin Popescu, Nikos Mastorakis, Gheorghe Manolea, Aida Bulucea, Liliana Perescu-Popescu

Abstract: The study of thermal model structural parameters is performed in this work. Different methodologies to estimate thermal parameters with data from standardised heat-run tests are compared.

Keywords: Estimate thermal parameters, Control temperature

Title of the Paper:  Cost Allocation of Losses in Autonomous Power Systems with High Penetration of RES


Authors: K. A. Papadogiannis, E. S. Karapidakis, N. D. Hatziargyriou

Abstract: Cost allocation of losses in power networks is an essential issue especially under modern electricity markets with high penetration of renewable energy sources (RES). This paper proposes the application of an efficient loss allocation method developed to evaluate the marginal loss coefficients of dispersed generation. The coefficients provide the contribution to the active and reactive losses of each producer/consumer in order to define the respective tariffs. One innovative feature of the proposed loss allocation method is that, unlike other proposed approaches, it is irrespective of the reference bus selection and takes in consideration the impact of reactive flows on active power losses. Crete's power system has been considered as a representative study case for the demonstration of the presented method.

Keywords: Distributed generation, marginal loss coefficients, high renewable energy penetration, transmission and distribution loss allocation

Issue 7, Volume 4, July 2009

Title of the Paper:  Construction and Evaluation of Modern EVs Drive System


Authors: Hossein Mousazadeh, Alireza Keyhani, Arzhang Javadi, Hossein Mobli, Karen Abrinia, Ahmad Sharifi

Abstract: Ever–increasing in climate changing forces to shift to friendly and clean energy alternatives such as renewable energies that their output is usually electricity. 9oticeable part of these air pollutions is from tailpipe of internal combustion engines. EVs could be parity by conventional Internal Combustion Engine Vehicles (ICEV) in near future. They are simplest way to replace fossil fuel powered vehicles. EVs are relatively cheap, have little environmental impact and are a technology which is available here and now. Using an electronic control board and two power boards, a high power EV drive system was designed and constructed (designed for the vehicles up to 100 kW). The controller uses power IGBT module and microcontroller technology to simultaneously control two DC series motors. The driver controls direction of motion and causes differential speeds of motors relative to steering rod and acceleration pedal position. Driver simulation in MATLAB proved that the required conditions of the problem were satisfied by PID controller; and the optimum values for the control parameters Kp, Ki and Kd were found to be 320, 350 and 40, respectively. The result of simulation for these motors indicated that for start up a high torque is available.

Keywords: Duty cycle, Motor driver, PID control, Simulink, Unit step, steady-state error

Title of the Paper:  Control Systems for High Power Induction Machines


Authors: Marcel Ionel, Mihail-Florin Stan, Corneliu Ioan Salisteanu, Octavian Marcel Ionel

Abstract: Issues orders in a power drives should be viewed in a more complex and different from how do Electronics engineers of control systems. It is best to look at the control system as a set of black boxes cascading with mathematical models defined on a system of alternating current application. Even if it takes a vector control strategy and obtain a similar behavior to that of a DC motor, many problems remain unresolved because of the particular structures of the converter and the motor due to their interaction with load and source. This paper recommends to the experts and to the users of command systems with frequency converters the usage of speed command and position command to the variable frequency drives. There are analyzed also the commands without position transducers, speed transducers or flux transducers based on approximately results. There are included also logic elements and it’s proves how the velocity evolution of the technology command of electrical machines in different branches of the world economy finds a specific field in modern electrical applications [10]. Powerful microprocessors and DSP (Digital Signal Processor) are able not only to directly calculate the time of ignition of a power semiconductor circuit such as the bridge phase, operating on frequency of feed, but also perform other important tasks in applications industrial automation as well as startup and shutdown sequencing, self monitoring and diagnosing faults. The most important contribution is that power chips have opened new frontiers in implementing sophisticated control systems for electric drives.

Keywords: Electrical commands, scalar control, vector control, mechanical characteristics, transducers control, direct control approach, indirect control approach, harmonic unit, test signal injection method.

Title of the Paper:  Possible Impact of Global Financial Crisis on Prices in Croatian Electricity Sector


Authors: Ivona Stritof, Tomislav Gelo, Slavko Krajcar

Abstract: A regulatory method chosen for setting allowed revenue in transmission and distribution of electricity in Croatia is a traditional Rate of Return method. The main feature and, at the same time, the main drawback of this method is that a price is in a direct relationship with the costs of regulated company. A parameter used in this method, which does not solely depend on the costs and management decisions, is the rate of return. The rate of return is usually calculated using the weighted average cost of capital formula (WACC). The WACC reflects two types of finance used to fund investments, debt and equity respectively. The cost of equity is calculated using the Capital Asset Pricing Model (CAPM). This Paper provides the WACC calculation based on the estimates of particular parameters which could be applied in the case of electricity transmission and distribution in Croatia. The estimates are given for two scenarios, for the period prior to and immediately after the beginning of domestic crisis (reflection of the global financial crisis) and secondly for the period throughout the domestic crisis. Thus, reflecting possible impacts of financial crisis on national and global level on cost of capital in transmission and distribution of electricity.

Keywords: Distribution, Transmission, Rate of return, WACC, CAPM, tariff system

Issue 8, Volume 4, August 2009

Title of the Paper:  Dynamic Simulation of an Innovative Compressed Air Energy Storage Plant - Detailed Modelling of the Storage Cavern


Authors: Lasse Nielsen, Reinhard Leithner

Abstract: An innovative concept of an compressed air energy storage (CAES) plant is developed at the Institute for Heat- and Fuel Technology (IWBT) of the Technische Universit¨at Braunschweig. This concept aims to minimise the negative aspects of state-of-the-art CAES-plants and is named isobaric adiabatic compressed air energy storage plant with combined cycle (ISACOAST-CC). To increase the storage efficiency, one aspect of this concept is to reduce compressor losses due to high differences of the storage pressure within the cavern by the use of a brine shuttle pond at the surface to drive out the stored air at nearly constant pressure. The main focuses in the presented article are the modelling and the calculation results of the simulation of the isobaric air storage cavern which is used in this concept. Furthermore, the results of a complete dynamic simulation of an ISACOAST-CC cycle are presented. The storage efficiency as well as plant efficiency and specific storage capacity are calculated.

Keywords: Compressed Air Energy Storage (CAES), Enbipro, Dynamic simulation, Underground salt cavern

Title of the Paper:  Determination of the Induced Voltages by 220 kV Electric Overhead Power Lines Working in Parallel and Narrow Routes. Measurements on the Ground and Mathematical Model


Authors: Flavius Dan Surianu

Abstract: The paper presents the measurements that the author has done in the South - West area of Romania for the 220 kV double circuit overhead power lines having a passive circuit and an active one. It also describes a mathematical simulation for determining the induced voltages by the active circuit into the disconnected one. The measurements are compared with those obtained through calculations in order to validate the mathematical model, becoming a useful tool for professionals in electric high voltage overhead power lines.

Keywords: Electromagnetic interference, high voltage, induced voltage, electric capacity, mutual inductivity.

Title of the Paper:  Optimized Fuzzy Variable Structure for a Three-Phase Rectifier with Power Factor Correction


Authors: Alberto Berzoy, Miguel Strefezza

Abstract: This paper presents optimized fuzzy variable structure control design in a three phase rectifier to correct the power factor. This control strategy combines fuzzy and sliding mode control algorithms. Few fuzzy rules are used for this scheme. The parameters of the fuzzy controller are adjusted by using the VSC for a better response and robustness. To improve the behavior of the system is applied a gradient optimized method to find better matrix rule values. The simulations of the three-phase rectifier with controlled current are carried out on a DSP. The control scheme presented here offer higher robustness and it is easier to adjust and implement.

Keywords: Three-phase Rectifier, Fuzzy Control, Variable Structure Controller, Optimization

Issue 9, Volume 4, September 2009

Title of the Paper:  The Transient Current Distributions in a Vertical Electrode and the Ground


Authors: Y. Beck, A. Braunsteiny

Abstract: This paper presents a model for calculating the transient space-time current distributions in vertical electrodes and to the surrounding ground. The model is based on the electromagnetic field theory for calculations of the step function wave-pair response. The method takes into account the parameters of the electrode, such as: the radius and the length of the electrode. Furthermore, the conductivity, permittivity and the propagation velocity of the currents in the ground are also considered. In the analysis, the electrode is divided into finite sections. Thereafter, the "Compensating Currents", ground leakage currents and the current in the electrode in each section are calculated at all times. The model is applied by a MATLAB code for the calculations of the above-mentioned currents' distributions. The results show that for soils of high conductivity values, relative short electrodes are needed for dissipating transient currents such as lightning currents. Furthermore, soil conductivity is a more sensitive parameter compared to the radius of the electrode and the permittivity of the ground.

Keywords: Current distribution, Grounding electrodes Lightning, Transient response, vertical electrodes

Title of the Paper:  Using the Frequency Response Analysis (FRA) in Transformers Internal Fault Detection


Authors: Jalal Abdallah

Abstract: This paper deals with diagnostic methods of the internal faults in power transformers. The diagnostic process uses some of the current diagnosis methods (e.g. oil test, dissolved gases analysis (DGA), partial discharge (PD), etc.) to determine the condition of the transformer. In this process, the most frequent diagnostic methods were listed and applied practically to be compared. A conventional faulty oil-immersed transformer 400 V / 10 kV, 100 kVA was diagnosed and tested with different methods. The parameters and results were compared with a normal working transformer with the same parameters and age. After that an opening of the transformer was performed to approve and to make a visual verification of the diagnostic methods and the used devices. Among the applied methods, the frequency response analysis FRA reflects the real situation of the internal faults such as short circuits, mechanical displacement and deformation of the transformer windings.

Keywords: Transformer Fault Diagnosis, Case Study, Frequency Response Analysis (FRA), Polarization and Depolarization Current (PDC)

Title of the Paper:  Control of an Hybrid Solar-Wind System with Acid Battery for Storage


Authors: Nazih Moubayed, Ali El-Ali, Rachid Outbib

Abstract: In the context of renewable energy, this study treats the functioning of a hybrid system containing two sources: solar panels and wind turbine. In fact, the conversion of solar energy and of wind energy to electrical one is non pollutant. The studied system is connected to a lead acid battery. The modeling of solar panel and its functioning in charging the used battery is discussed in this paper. Same analysis is applied on the wind turbine connected to the lead acid battery. Then, the functioning of the hybrid system combined with the used battery is treated. Finally, a control strategy of the global system is proposed.

Keywords: Renewable energy, solar energy, wind energy, lead acid battery, modeling, control

Issue 10, Volume 4, October 2009

Title of the Paper:  Fault Induced Voltage Sag Mitigation using Dynamic Voltage Restorer


Authors: N. R. Patne, K. L. Thakre

Abstract: In this paper aim is to study the effectiveness of Dynamic Voltage Restorer (DVR) in mitigating the voltage sag due to different types of faults at every point of the power network under study. The comparative study is done with conventional DVR along with series insertion transformer and proposed DVR at the tertiary winding of already existing step down transformer in the system at the load point. The effectiveness of DVR is studied in terms of critical fault length. It is observed that there is reduction in critical fault length with DVR in the system. Further the study shows that the voltage sag compensation with transformer tertiary winding DVR is effective. But the conventional DVR are more effective to compensate fault induced voltage sag at the cost of additional insertion transformer. The system considered is simulated in PSCAD/EMTDC to do the required study.

Keywords: Voltage sag, faults, DVR, critical fault length

Title of the Paper:  Improved Control Strategy for Fuel Cell and Photovoltaic Inverters in a Microgrid


Authors: A. A. Salam, A. Mohamed, M. A. Hannan

Abstract: This paper presents an improved control strategy for parallel inverters so as to better manage power sharing among the distributed generation units in a microgrid. The proposed control strategy combines both power and voltage control schemes implemented on the voltage source inverters which are used as power electronics interface systems for conversion of power generated by fuel cell and photovoltaic generation units. Dynamic models of the fuel cell and photovoltaic systems available in the PSCAD/EMTDC simulation software are used as distributed generation units present in the microgrid. To evaluate the effectiveness of the developed control strategy, the microgrid is operated in grid connected, islanding and transition modes of operation.

Keywords: Distributed generation, microgrid, fuel cell, photovoltaic, inverter

Issue 11, Volume 4, November 2009

Title of the Paper:  Optimum Time Coordination of Overcurrent Relays in Distribution System Using Big-M (Penalty) Method


Authors: Prashant P. Bedekar, Sudhir R. Bhide, Vijay S. Kale

Abstract: This paper presents big-M (penalty) method for optimum time coordination of overcurrent (OC) relays. The method is based on the simplex algorithm which is used to find optimum solution of linear programming problem (LPP). The method introduces artificial variables in the objective function to get an initial basic feasible solution (IBFS). Artificial variables are removed using iterative process which also leads to an optimum solution. The OC relays are the major protection devices in a distribution system. To reduce the power outages, mal-operation of the backup relays should be avoided, and therefore, OC relay time coordination in power distribution network is a major concern of protection engineer. The OC relay time coordination in ring fed distribution networks is a highly constrained optimization problem. The purpose is to find an optimum relay setting to minimize the time of operation of relays and at the same time, to avoid the mal-operation of relays. Big-M simplex technique for optimum time coordination of OC relays in a ring fed distribution system is presented in this paper.

Keywords: Backup protection, Big-M method, Constrained optimization, Overcurrent relay, Ring fed system, Time coordination

Title of the Paper:  A New Monitoring Spectral Technique for Subsynchronous Electrical Torque Frequencies


Authors: Jose A. Castillo J., Daniel Olguin S., Carlos A, Rivera S., David Sebastian B.

Abstract: The modern protection schemes are designed to protect against the negative effects that has the Subsynchronous Resonance (SSR) in the turbo-generators mechanical system damping. The studies which have been done with torsional monitoring data allows to propose the maintenance and inspection planning to mitigate the damages and overcome with this expensive repairs, this is because very few monitoring equipment is designed to capture transitory sporadic oscillations with torsional phenomenon characteristic. In this work, it is proposed a new monitoring technique through the torsional behavior modes forms based on a spectral analysis of the electrical subsynchronous torque component to detect its associated frequencies and to establish the coincidence with the mechanical turbo-generator torsional oscillation subsynchronous frequencies, transient load model is included indicating results of utmost importance in their modes damping

Keywords: Subsynchronous Resonance, Electrical Torque, Subsynchronous component, Prony, Torsional Modes Forms

Issue 12, Volume 4, December 2009

Title of the Paper:  Modeling Subharmonic and Chaotic Ferroresonance with Transformer Core Model Including Magnetic Hysteresis Effects


Authors: Paul Moses, Mohammad Masoum

Abstract: Ferroresonance is a highly destructive power quality phenomenon caused by complex oscillations generated by nonlinear magnetizing inductances in ferromagnetic materials and capacitive elements in power systems. In an effort to better understand ferroresonance and predict bifurcations and responses, an improved nonlinear transformer model for dynamic and steady-state operating conditions is developed which includes magnetic hysteresis nonlinearities of the transformer core. The model expands on Tellinen’s scalar hysteresis approach which includes major and minor hysteresis loop effects. This paper carries out an investigation into single-phase transformer ferroresonance initiated by switching transients using the developed model. A range of ferroresonance modes (e.g., subharmonic and chaotic) initiated by switching transients is identified with the transformer core model. The model is used to compute time-domain waveforms of transformer flux, voltage and magnetizing current for several ferroresonance modes. Furthermore, Poincar/e and phase-plane portraits are used to examine the stability domain of observed ferroresonance modes. The main contribution of this work is a new analysis into ferroresonance through an improved transformer model which incorporates magnetic hysteresis effects.

Keywords: Chaos, ferroresonance, hysteresis model, nonlinear dynamics, Poincar/e, power quality, transformer

Title of the Paper:  Proposed Techniques for Identifying Open and Short Circuit Sections in Distribution Networks


Authors: Wael Al-Hasawi, Mahmoud Gilany

Abstract: This paper presents novel solutions for three problems encountered in the closed loop distribution systems. The first problem is how to identify a faulty section after being successfully isolated by the protection system. The second problem is how to identify a section affected with undetected open-circuit fault. A novel circuit is suggested in this paper to solve these two problems. The third problem addressed in the paper is how to deal with undetected faults in the 11 KV part of a 132/11 KV network which may result in a complete shut down problems. An effective modification in the trip circuit of the relays protecting the main feeders of the closed loops is suggested to avoid this problem. The validity of the proposed circuits is examined using ASPEN-OneLiner simulation program applied to a real part of Kuwait power distribution network. It is also checked against the specifications of the available equipment used in the real network. The proposed circuits provide fault detection capabilities normally achieved by the advanced and expensive Distribution Automation System (DAS) but with minimal cost.

Keywords: Distribution networks, open-circuit faults, Undetected faults, Ring systems, Fault identification, Fault detection

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