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Universities Power Engineering Conference (UPEC), 2012 47th International

Date 4-7 Sept. 2012

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Displaying Results 1 - 25 of 207
  • [Title page]

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  • Defining the role of wide area adaptive protection in future networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    Recent increases in generation diversity, use of renewable energy resources and HVDC, as well as the increasing electricity demand may act to push power systems closer to their operating limits, not to mention the increasing likelihood of hidden failures or severe contingencies. It has never been easy for conventional protection with fixed relay settings to deal with such complicated scenarios. That, inevitably, led to some protection performance issues, including sensitivity and coordination issues. Accordingly, to maintain a reliable and robust power system, a protection system which is potentially immune to changes and aforementioned challenges plays an important role in future networks. Adaptive protection, capable of real-time signal processing and timely adjustment of relay settings for the prevailing system conditions, is seen as a potential approach to cope with these system issues. This paper will define wide area adaptive protection (WAAP) and discuss why and how adaptive protection can be best utilized to improve protection performance, particularly during system-level disturbances. The potential challenges and drawbacks of WAAP are also analysed. View full abstract»

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  • Studies on parallelism of feeders for automatic reconfiguration of distribution networks

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    The parallelism of distribution networks can be used to transfer loads between feeders without the need of disconnection of consumers during the maneuvers. In the context of the Smart Grids, the parallelism of feeders can be used in automatic reconfiguration of networks for the improvement of power quality and voltage levels, and reduction of energy losses. However, the maneuvers for parallelism must be preceded by studies to verify their technical and operational feasibility. This paper presents a study that discusses aspects of loading, protection, and voltage levels related to parallelism of networks, in transient and steady-state analysis. The validation of the developed methodology was carried out by comparison of simulation results with the ATP program. The study aims to be suitable for real-time application in reconfiguration of distribution networks. Integration with remote controlled switches, so that the network reconfiguration can be done automatically, is one of the differentials of the work. The tests here presented are made in a real model of a distribution network of a power utility. The developed algorithm has as main result a reliable indication of the technical feasibility of connecting feeders in parallel. View full abstract»

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  • Using H to design robust POD controllers for wind power plants

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB) |  | HTML iconHTML  

    Large wind power plants (WPPs) can help to improve small signal stability by increasing the damping of electromechanical modes of oscillation. This can be done by adding a power system oscillation damping (POD) controller to the wind power plants, similar to power system stabilizer (PSS) controllers on conventional generation. Here two different design methods are evaluated for their suitability in producing a robust power system oscillation damping controller for wind power plants with full-load converter wind turbine generators (WTGs). Controllers are designed using classic PSS design and H methods and the designed controllers evaluated on both performance and robustness. It is found that the choice of control signal has a large influence on the robustness of the controllers, and the best performance and robustness is found when the converter active power command is used as control signal. It is found that the classically designed controllers have fairly good robustness, but that H controllers can provide better robustness. View full abstract»

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  • Effects on Transmission Capacity with wind power participation

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    The use of wind power to generate electricity is probably the most widely used renewable energy sources around the globe. The major reason may well be of its well developed technology in comparison with other form of renewable. The percentage of wind power installation with respect to the total power generation, also known as the penetration factor, is increasing rapidly year by year in many countries. As wind speed varies randomly and which means that the output of wind generators is intermittent. When a wind farm is connected to a transmission network its effects on the network can be quite different from that of connecting a conventional power station even when connected at the same point. When analyzing the effects of the conventional generator on the network under different load profiles the operator can assume that the generator operates at its maximum capacity. In the case of wind power the situation is more complex as the output of the generator is intermittent. The analysis could be even more complex when more than one wind farm is connected at more than one location. In this paper a method is proposed to analyze the effects of wind power on transmission network. In the study the Weibull Distribution Function is used to represent the stochastic wind speed distribution. The method of Monte Carlo simulation will also be introduced to solve the problem of wind turbine output calculation and the system reliability studies. To estimate the reserve capacity of the transmission line when wind power participated, Monte Carlo Simulation method will be used a second time. The results of the calculation are then used to estimate an Economic Transmission Capacity on transmission lines affected after wind power is introduced. This can be used for transmission lines reinforcement implementation. The IEEE-9bus system will be used an example. The study will include 3 scenarios and will consist of 1 and 2 wind farms participation. View full abstract»

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  • Modeling of a hybrid system of photovoltaic and fuel cell for operational strategy in residential use

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (426 KB) |  | HTML iconHTML  

    In our country, a photovoltaic solar energy system has been widely utilized as an alternative energy source to fossil fuel at a residential area. The output of photovoltaic cell sharply changes according to weather conditions. Therefore, a certain power storage device is required to smooth the output and to meet electricity demand equivalent to a household load. A fuel cell is a promising candidate for long term energy system because hydrogen is supplied stably. This paper presents the modeling and operational strategy of a hybrid system of photovoltaic (PV) and fuel cell. The proposed system is consists of PV array, fuel cell stack, electrolyzer (EL), hydrogen storage tank, and power conversion devices. If the photovoltaic system is not able to supply power to the household load, the fuel cell system compensates a power shortage together with the utility grid. In case that surplus power occurs from the PV system, the EL system consumes it to generate hydrogen from pure water. The behavior of the proposed hybrid system is verified by numerical simulation using MATLAB/Simulink. View full abstract»

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  • Multi-objective optimization techniques and applications in electric power systems

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB) |  | HTML iconHTML  

    Efficient operation and planning of power systems is important for a reliable and sustainable electricity supply. Therefore, optimization techniques have been applied to several optimization problems in power systems in order to achieve technical and economic efficiency. This paper presents an overview of existing optimization techniques and applications in power systems, with a special focus on multi-objective optimization in power system planning. Power system planning is by its nature a very complex multi-objective optimization problem involving perspectives of different stakeholders. Besides, a single stakeholder can also have various objectives that need to be optimized at the same time. This paper provides a review of the state-of-the-art in multi-objective evolutionary algorithms applied to power systems planning problems. View full abstract»

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  • A congestion management method with demand elasticity and PTDF approach

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (393 KB) |  | HTML iconHTML  

    The deregulation of electricity market has brought more challenges to the system operator to handle system contingencies. In the deregulated market, congestions are encountered with higher frequency than before. Congestion can lead to price volatility and system instability, which can deteriorate the electricity market operation. Therefore proper congestion management methods should be developed to meet the criterion of the new electricity trading mechanism. Most of published researches on congestion management were investigated without considering the demand elasticity of the load. A congestion management approach taking the demand elasticity into account is proposed in this paper. The Optimal Power Flow tool is used to determine the congestion relief action and the power transfer distribution factor matrix is introduced with the demand elasticity. A case study on IEEE 14-Bus system is presented to illustrate the application of the proposed method. View full abstract»

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  • An automatic transient detection system which can be incorporated into an algorithm to accurately determine the fault level in networks with DG

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (569 KB) |  | HTML iconHTML  

    The use of distributed generation is on the increase within the United Kingdom and the Distribution Network Operators (DNO's) require a novel approach of assessing potential fault levels in near “real-time” to assist with network planning and design. The short circuit current is the current expected to flow into a short circuit fault at a known point on the system, and therefore, the fault level is the product of the open circuit voltage and short circuit current. Recent techniques used by the industry involve power system software that calculates the fault level in accordance with BS EN 60909, however, this frequently provides a conservative answer and possibly this will be a factor restricting future connections of distributed generation. This paper will describe the initial stages of the development of an algorithm which can be used alongside a digital signal controller (a Texas Instruments TMS320F28335) to calculate in near “real-time” the fault level at a specified point on the distribution network. Matlab & Simulink are utilised to both simulate source faults and to create the initial elements of the algorithm which are analysed utilsing the test program. The implementation of a Short Time Fourier Transform (STFT) to determine when a fault occurs is discussed. Finally the results from these simulations are examined and presented alongside a discussion of future work. View full abstract»

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  • Ensuring energy-market liquidity through adequate imbalance settlement

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB) |  | HTML iconHTML  

    In this paper we assess the influence of different imbalance settlement systems on the strategic behavior of Balance Responsible Units. We therefore apply a continuous action agent-based approach in a representative test-system. The investigation points to the effects of one-/two price settlement systems as well as to the impacts of different capacity remuneration schemes. Further, we take transmission capacity limits into account and evaluate the effects of varying pricing on the energy market (with consideration of congestion) and the imbalance settlement (without consideration of congestion). View full abstract»

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  • Experimental investigation of DC corona on stranded conductors under variable air density

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    Knowledge on the effects of air density on corona discharge is of great importance for many practical applications, including overhead transmission lines. In the present study the salient characteristics of both positive and negative DC corona on 7-stranded conductors, namely the corona inception voltage, corona current and the associated power losses, are experimentally investigated in the coaxial cylindrical electrode arrangement under variable air density. Theoretical predictions of the corona current and losses are in good agreement with experimental values for an ion mobility decreasing with relative air density according to a power law, the rate of decrease being higher for negative than positive ions. Irregularity factors for the 7-stranded conductors have been obtained based on electric field simulations and Peek's formula for smooth conductors. Logarithmic expressions, describing well the dependence of the irregularity factor on the product of relative air density and conductor radius, allow for a satisfactory estimation of the corona inception field strength of 7-stranded conductors. View full abstract»

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  • PV plants for voltage regulation in distribution networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (326 KB) |  | HTML iconHTML  

    This paper deals with the development of a centralized nonlinear auto-adaptive controller able to optimize the network voltage profile by managing the reactive power supplied by PV inverters. The control design is based on a realtime optimization procedure involving the sensitivity theory in conjunction with the Lyapunov function and produces the control laws that must be sent to local controllers of PV-inverters. The derived controller is implemented and tested on a MV distribution network. View full abstract»

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  • The modelling of electric field, capacitance and dissipation factor of a high voltage bushing over varying frequency

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (534 KB) |  | HTML iconHTML  

    Within a high voltage substation, power transformer bushings are key components and an assessment of their condition is important to ensure operational reliability. Bushings represent a large proportion of transformer failures, where most issues are as a result of moisture ingress. Moisture ingress affects the distribution of the electric field and changes the capacitance and dissipation factor (tanδ) of the insulation. In this paper, a numerical model is built for an oil impregnated paper (OIP) condenser bushing. The simulated dielectric frequency response (DFR) dependence of transformer oil and OIP with varying moisture content is given. Simulations are made of the AC and very low frequency (approximated to DC) potential and electric field distributions. Furthermore, the capacitance and dissipation factor over a frequency range of between 1mHz to 1kHz is presented. The results are found to be consistent with typical bushing manufacturers' data. View full abstract»

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  • UK electricity market modeling using combined Conjectural Variation equilibrium method and hierarchical optimization algorithm

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (541 KB) |  | HTML iconHTML  

    Various methods such as equilibrium models are introduced to manage the risks of participating in the electricity market. Especially in those electricity markets with specific structures, such as BETTA (British Electricity Transmission and Trading Agreement), based on bilateral trading, the usage of this modeling becomes more significant. This paper proposes a novel Conjectural Variation (CV) equilibrium model for bilateral electricity markets, such as BETTA, to reduce the market participants' exposure to risk. Through an iterative coordination algorithm, consisting of a conjectural variations equilibrium model of an oligopolistic set of generators with a corresponding oligopsonistic equilibrium model of a set of supply companies, the `match' of both quantity and price between these two models can be obtained. This match can be found by a hierarchical optimization approach, using the Matlab Direct-Search optimization method. View full abstract»

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  • Influence of inductive voltage transformers on the measurement of switching transients

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB) |  | HTML iconHTML  

    The inductive voltage transformers (VTs) used on the power system are primarily designed for protection or metering at 50Hz. The leakage inductance of the VT windings and stray capacitances can form a resonant circuit. When subjected to AC voltages at frequencies well below resonance, the VT can be assumed to behave linearly giving accurate measurements. The resonance of the VT limits the bandwidth over which it may be used to provide accurate measurements. This is of particular importance when taking harmonic and transient measurements. This paper reviews the different kinds of VT model available. A model is selected for transient simulation in EMTP, and the influence of the VT model on switching transients is examined. A key observation is that when the inductive VT model is subjected to a step change in voltage, a voltage ripple is introduced at the VT's resonant frequency to its secondary winding. The aim of this work is to quantify the influence of the inductive VTs on measured transient voltage waveforms. View full abstract»

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  • Comparison voltage across insulator strings of 69 kV and 24 kV lines due to lightning strokes to top pole and mid span

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    This paper analyzes the effects of the voltage across insulator of 69 kV and 24 kV lines installed on the same pole. The case studies illustrated the lightning strike to direct top pole and mid span of ground wire using the Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP). The results found that when lightning strike the voltage across the 69 kV line insulator at mid span is 1.55 times and 1.34 times higher than at top pole when the front time is 0.25/100 μs and 10/350 μs, respectively. When lightning strike the voltage across the 24 kV line at mid span is 1.04 times and 0.64 times higher than at top pole when the front time is 0.25/100 μs and 10/350 μs, respectively. So the effect of lightning strike is more severe at mid span than at the direct top pole, especially for the 69 kV insulator. View full abstract»

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  • Electrical load pattern for LV consumers. A Romanian case

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    Current structure of the main electric distribution utility in Romania consists in three areas, which cover the center and north areas of Country. Starting from the analysis of small users and users on the distribution utility subsidiaries and ways of building load profiles used in other countries and presented in the literature, are proposed following categories representative of non-dispatched users. Theoretical development of the specific mathematical model based on collecting data measured at each user was generated. The study was performed for consumers which do not have implemented the proper metering devices within each distribution subsidiary and clustering them into categories. The identified clusters were pre-evaluated from variability of consumption, in order to ease the overall load pattern identification process. View full abstract»

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  • Investigation of simultaneity in distribution networks for the assessment of DA feasibility

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB) |  | HTML iconHTML  

    Implementation of distribution automation into medium and low voltage grids is gaining more and more support amongst distribution grid operators. In order to assess the feasibility and usefulness of dynamic network reconfiguration for the purpose of reducing losses and increasing available network capacity, it is necessary to know to what extent simultaneity amongst MV/LV transformers within distribution networks occurs. Measurements have been done in parts of the distribution network of Enexis, one of the largest distribution network operators in the Netherlands. For a full year, in 30 MV/LV substations the transformer and all outgoing low voltage feeders have been measured. In this paper the measurement data is being analyzed in order to determine the degree of simultaneity in low voltage distribution grids, both seen from the low- and the medium-voltage level. The results of this analysis will be used to assess the feasibility of power flow optimization by using distribution automation. Furthermore, an example of a field application will be simulated and discussed. View full abstract»

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  • Investigation on the interaction between inertial response and droop control from variable speed wind turbines under changing wind conditions

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (449 KB) |  | HTML iconHTML  

    As wind power penetration into power systems increases, it poses a growing challenge to power system operation and stability. This is partly because wind power is highly time variable and cannot inherently contribute to power system frequency regulation. The provision of frequency support from wind turbines under changing wind conditions is examined in this paper. A simplified variable speed wind turbine model is developed. A modified turbine controller to deliver inertial and droop response is proposed. The interaction between inertial and droop response from wind turbines is examined under varying wind. View full abstract»

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  • Small wind turbines applied to rural areas for independent power supply

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (945 KB) |  | HTML iconHTML  

    Electricity generation based on wind energy has seen rapid growth in the last years in Germany due to a favourable regulatory framework. But in contrast to the large-scale wind power market, the small wind power sector is still in its infancy. Current research at the South Westphalia University of Applied Sciences will focus on the development and construction of small wind turbines mainly usable for the supply of single buildings in rural areas in the South Westphalian region which are not necessarily connected to any larger electrical system. First results of pre investigations are presented in this paper. View full abstract»

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  • Impact of the ULTC on the dynamic voltage collapse of an electric power system with large scale of wind generation

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (343 KB) |  | HTML iconHTML  

    Voltage stability is predominantly a load stability phenomenon and solutions to voltage stability can be found by control of the load as seen from the bulk power network. A delay of the load restoration gives time for other corrective actions. The load restoration may be delayed and/or limited by certain countermeasures, such as blocking of Under Load Tap Changers (ULTC). In this paper it was studied the impact of the ULTC on the dynamic voltage collapse of an electric power system with large scale wind generation. It is used the Cigré Electric Power Network with 32 bus and three wind farms equipped with wind turbines, including pitch control coupled with a Fixed Speed Induction Generator (FSIG) and a shunt capacitor bank. The automatic voltage regulators (AVR) of the generating units and the turbine speed governors were modelled. Different load models were used and the ULTC were taken into account. Several significant disturbances were simulated in the test power network, such as the increase of the wind speed, the tripping of an overhead transmission line and three-phase short-circuits. The simulation results were obtained using the EUROSTAG software package. Finally, some conclusions that provide a better understanding of the ULTC effect on the dynamic voltage stability in a system with a large amount of wind power generation are pointed out. View full abstract»

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  • A congestion index considering the characteristics of generators & networks

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    The connection of renewable generation into transmission network contributes a lot to provide green electricity and ensure energy security. However, the current congestion management schemes and related cost allocation methods fail to fairly treat different types of generators, such as wind farms with low load factor and conventional thermal plants with high load factor. In this paper, a congestion index which is defined as the annual congestion cost of unit transmission line, Annual Congestion Unit Cost (ACUC), is first introduced. ACUC identify different generators with their installed capacity, load factor and electricity price. Moreover, the calculation of ACUC learns from the idea of MW·km and the congestion cost is allocated by Power Transmission Distribution Factor (PTDF). Therefore, ACUC consider the characteristic of both generators and networks. The application of ACUC is demonstrated by DC Optimal Power Flow. The case studies based on a three-bus power system & an eight-bus power system are undertaken in this paper. Simulation results show that ACUC can effectively locate the congested transmission branches and with the reinforcement of these branches, the total congestion cost can be extremely reduced. View full abstract»

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  • Adaptive NeuroFuzzy Legendre based damping control paradigm for SSSC

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (621 KB) |  | HTML iconHTML  

    The controllable series injected voltage can be used to damp low frequency power and rotor angle oscillations. Conventional linear and NeuroFuzzy control schemes perform well only for a specific operating condition, or in the vicinity of the tuned operating point of highly nonlinear power system, due to their fixed parameters architecture. To improve the performance of the damping control, nonlinear behavior of power system must be incorporated via some nonlinear control scheme. This work presents an online adaptive nonlinear control paradigm by incorporating Legendre polynomial NNs in the consequent part of the conventional TSK structure. The proposed control scheme is successfully applied to damp local and inter-area modes of oscillations for different contingencies and operating conditions. The robustness of the proposed control scheme is validated using comparative analysis based on nonlinear time domain simulations and different performance indices. View full abstract»

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  • Investigation of open standards to enable interoperable wide area monitoring for transmission systems

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (437 KB) |  | HTML iconHTML  

    Nowadays, power systems face more challenging network wide issues with regard to ensuring secure and reliable operation. Therefore, having a wide area monitoring system is a vital need in order to detect problems and react on them as quickly as possible. An important component when providing wide area monitoring and control for transmission networks is the SCADA system, which connects the substations to the control center by polling data from Remote Terminal Units (RTUs). However, due to data rate limitations, the monitoring is relatively static and therefore infrequent. By using Phasor Measurement Units (PMUs) data can be provided in higher rates and with higher accuracy. Since different manufacturers exist in the market, standardization is the key for advancement of the connectivity and interoperability within the system. In the past, utilities used to employ proprietary protocols, which were specified by the product vendors. Gradually, it was decided to move towards open standards to provide an interoperable environment and improve modelling capabilities. Apart from PMU standards, in a typical power system several communication protocols exist and are required for transferring data and each of them covering certain domains and specific groups of data. The objective of this paper is to investigate the adoption, development and performance of the most common open standards to enable interoperable wide area monitoring systems. View full abstract»

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