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Reliability of Transmission and Distribution Networks (RTDN 2011), IET Conference on

Date 22-24 Nov. 2011

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  • Front cover

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (44 KB)  

    The following topics are dealt with: reliability; transmission networks; distribution networks; network protection & automation; network design and topology; and risk management. View full abstract»

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  • Contents

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  • Cost benefit analysis of redundancy levels of large, offshore windfarm equipment

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (403 KB)  

    The variability of the power generated by offshore windfarms provides an additional complexity to the assessment of reliability and appropriate redundancy levels of the primary equipment used to connect the windfarms to the transmission network. This paper will show the cost benefit of various redundancy levels of primary equipment such as transformers, cables and equipment associated with HVDC schemes and the configuration arrangements of the HVDC schemes. . View full abstract»

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  • Reliability assessment of offshore networks for connection of offshore windfarms

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    This paper discusses the reliability assessment for offshore windfarms which is applicable for various offshore network design configurations. The takes into account the overall risk associated with the offshore network and aims to calculate the availability level of the offshore network at one or multiple points of connections. View full abstract»

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  • Development of an optimization algorithm for simulation of medium voltage networks reliability performance

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The objective of this paper is to describe the main resources of the software developed to predictive analysis of some of the continuity indicators in distribution networks. This program deals with different information obtained directly from database to create a network modelling and to realize some simulations. All of the database access and the calculations are carried out automatically. View full abstract»

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  • Benchmarking of reliability indices for electricity distribution utilities: Approach and discussion

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    Reliability indices viz. System Average Interruption Duration Index (SAIDI), System Average Interruption Frequency Index (SAIFI), Average System Availability Index (ASAI) etc. are measures of system wide reliability provided by an electricity distribution utility. These indices also indirectly indicate the utility's Operations and Maintenance (O&M) efficiency, system's ability to transfer load to the neighbouring units in case of cable or equipment failures, response time to locate and isolate a fault and restoration time. A distribution utility would like to benchmark the indices and to investigate the cause of inferior indices, if any. Benchmarking of reliability indices is an important task to set the reference for a utility to improve upon it. A benchmarking model for reliability indices is presented using Data Envelopment Analysis (DEA). The model finds the best performing utility among the set of similar utilities based on the sets of inputs (Percentage of High Tension (HT) feeders, percentage of underground (UG) cables, load density and expected remaining life of transformers ) and outputs (SAIDI, SAIFI, ASAI). It has been observed that although benchmarking approach provides good inputs for improvement, further analysis is required to get a true rank of a utility in comparison to the best performing one. In the paper, a discussion on benchmarking of reliability indices is presented. View full abstract»

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  • Optimal location of spare transformers at distribution substations for reliability improvement

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (154 KB)  

    To ensure (n-1) reliability at distribution substations (DS) at 11 kV level, spare transformers are required at each DS. With no spare transformers at a DS, a failure of a transformer may result in loss of load connected to it. Spare transformer at each DS is very expensive. In a distribution system, where load transfer to the neighbouring units is not possible, the average time for unserved load could be 2-3 days. This loss of load would not be preferred by utility consumers. Also, this degrades the reliability indices of the utility. The paper proposes two methods to find out optimal location of spare transformers to provide maximum reliability. Optimal location for spare transformers has been found out via an Integer Linear Programming (ILP) problem with the objective of 1) minimization of the Value of Lost Load (VOLL), and 2) minimization of transformer failure probability. The proposed approaches are illustrated with a sample distribution company. View full abstract»

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  • Impacts of automatic loop restoration schemes on service reliability

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (370 KB)  

    Automatic loop restoration schemes are employed in electric power distribution systems to perform fault detection, isolation, and service restoration activities sequentially and automatically, so as to significantly reduce customer interruption time. This paper aims to quantitatively assess the impacts of employing an automatic loop restoration scheme, with and without a communication link, on the major attributes of the service reliability. In addition, the effect of the operational failure of communication facilities is taken into account. A typical Finnish urban distribution network is utilized in this paper for the quantitative reliability assessment studies. A powerful software package referred to as "Smart Grid Simulator" is used for directing the reliability studies. View full abstract»

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  • Case study: Application of wide-area, communications-assisted remedial action schemes improves transmission reliability

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (107 KB)  

    At Southern California Edison (SCE), remedial action schemes (RASs) are implemented to ensure reliable power system performance following outages on a transmission grid network. They include fast, automatic telecontrol actions (wide-area teleprotection) to mitigate thermal overloads and system instability upon the loss of one or more transmission lines. These communications-assisted RAS systems are intended to be used throughout the SCE area of operation, as well as at all interties to neighboring utilities to facilitate dynamic load shedding, generation tripping, and improved load management. With appropriately fast and deterministic communications, RAS systems are used in place of expensive alternative measures, which include reconductoring transmission lines, building new lines, and/or adding new transformers. Testing six years ago at SCE demonstrated the successful use of IEC 61850 Generic Object-Oriented Substation Event (GOOSE) messages over a distance up to 460 miles to collect analysis and arming data and transfer status and telecontrol. Devices designed to carefully manage teleprotection and GOOSE telecommunications are unaffected by the additional traffic of in-service installations with multiple devices networked together. However, subsequent research has shown that shared bandwidth Ethernet with typical substation traffic degrades the performance of GOOSE telecontrol within poorly designed IEDs from milliseconds to minutes. This paper focuses on the negative impact of Ethernet and Internet Protocol (IP) methods on mission-critical applications, why they are not widely recognized, and how to mitigate them. Research results and best practice recommendations of using Ethernet and time-division multiplexing (TDM) methods for telecontrol to solve transmission corridor stability issues are presented. View full abstract»

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  • Development of a predictive out of step relay using model based design

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Loss of synchronism can result in the blackout of a part or the whole system. Therefore it is essential that out of step condition in a power system is rapidly and reliably predicted and detected. A novel method of detecting out of step conditions is discussed in this paper. An out of step relay is implemented using model based design approach. The predictive out of step detection is based on fuzzy logic, which processes variables derived from the line voltages and currents measured by the relay. The effectiveness of the method is verified by simulated systems and waveforms recorded from real systems. Various system configurations are considered. Test results show that the relay can rapidly detect various out of step conditions while remain stable during normal conditions and faults. View full abstract»

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  • Application of measurement noise decoupling for a robust multiple models adaptive controller (RMMAC) to improve the damping of power system inter-area oscillation

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1030 KB)  

    The electric power system is a non-linear dynamic system, with continuous condition changes during normal operation. Therefore, it is required to have a special control strategy to cover different operating points. One of the proposed techniques to solve such problem is the use of a multiple model adaptive control (MMAC), allowing that the controller updating to represent the actual system properly. The use of a MMAC strategy is based on a physical system output measurement for system model estimation. So any noise from the output sensor measurement leads to a significant increase in the residual (the error in the output signal between the physical system and the designed model),[1]. So the weight computation block uses this residual to calculate the weights for all controllers in the controller bank. The highest residual model means that the model is far from the true system. Therefore, it is important to remove the noise from the residual calculations. In this work the new observer is installed to provide the full state estimation and noiseless output. So the effect of measurement noise is avoided and is independent of the type of noise. The system is tested by adding unknown noise to the system output measurement. The design of the local controller is based on different linear control techniques to achieve both local and global system stabilities. The damping improvements are verified using the Matlab software. View full abstract»

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  • Stochastic optimal power flow approach considering correlated probabilistic load and wind farm generation

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (257 KB)  

    This study presents a heuristic approach to solve the chance- constrained stochastic optimal power problem, considering Gaussian loads, non-Gaussian wind generations, as well as the correlation among these power injections. Such a heuristic approach starts from the result of a deterministic optimal power flow problem, then converts all the chance constraints into equivalent deterministic constraints through probabilistic power flow calculations, and further verifies the satisfaction of these equivalent constraints. If some violation happens, the corresponding constraint bounds are modified according to a heuristic strategy and an updated deterministic optimal power flow problem is solved again. This process is repetitively run until no violation of constraints exists. Case studies on a modified IEEE 118-bus system are presented and the results verify the effectiveness of the proposed heuristic stochastic optimal power flow approach. View full abstract»

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  • Modeling performance indices in distribution systems based on electrical network information, environmental variables and historical data

    Page(s): 1 - 5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (223 KB)  

    The performance indices of distribution systems are intended to quantify the frequency at which interrupts occur, as well as the time required for the restoration of the system. The aim of this paper is to present the way in which performance indicators are related to structural variables of distribution systems and with lightning variables in order to build an estimation model. Actual data were used in adjusting the estimation models and the results achieved are suitable for propositions related to improving the service of distribution of electricity. View full abstract»

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  • The application of reliability criteria to a railway power supply network

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (163 KB)  

    Power systems have evolved over decades with their main emphasis focused towards providing reliable and economic supply of electrical energy to their customers. Spare or redundant capacities in generation and network facilities can be built but the main question has been, "how much redundancy and at what cost?" economic concerns like these have been widely recognised and are part of the design, planning, and operating criteria for most power system operators. Techniques such as Reliability Assessment have been developed in an attempt to resolve and satisfy the dilemma between economic and reliability constraints. View full abstract»

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  • Optimal allocation of Wind Turbines in distribution systems based on social welfare evaluation

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    In this paper, a hybrid optimization method that combines Particle Swarm Optimization (PSO) and Optimal Power Flow (OPF) is proposed in order to allocate Wind Turbines (WTs) in distribution systems. The OPF is used to determine the optimal number of WTs in order to maximize the Social Welfare (SW) of the network while the PSO is used to choose the best type of WTs at each candidate bus. The OPF problem is solved using Step-Controlled Primal Dual Interior Point Method (SCPDIPM) considering network constraints. The effectiveness of the proposed method is verified on an 83-bus 11.4 kV radial distribution system. View full abstract»

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  • Large wind integrated bulk system reinforcement planning using the joint deterministic — Probabilistic method

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    The traditional methods used by system planners to maintain acceptable bulk system reliability are challenged by incorporating higher wind power penetration levels. This difficulty can be alleviated by combining deterministic considerations with probabilistic assessment in order to evaluate the quantitative system risk and conduct system development planning. This paper extends the joint deterministic-probabilistic approach to wind integrated bulk power system planning. This paper presents technical and economic assessments using probabilistic and the joint deterministic-probabilistic methods in large wind integrated bulk system planning. This paper also illustrates a comparison of the two methods for long-term bulk system planning. View full abstract»

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  • Incorporating health indices into a composite distribution network risk model to evaluate asset replacement major projects

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (127 KB)  

    The use of condition based risk management (CBRM) to prioritise asset replacement on electrical distribution networks has become widespread, typically through the calculation of health indices for each asset. A separate methodology has also been developed for evaluating network risk on both simple and complex EHV networks. By combining this risk methodology with CBRM techniques, a composite model has been developed to predict the consequences of replacing, or of not replacing, individual assets or combinations of assets. This model can be used to inform the distribution network operator's asset replacement decisions, enabling them to become more cost effective. The present paper describes the model, and applies it to regions of the actual distribution network in the North of England. View full abstract»

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  • Cyber attack impact on power system blackout

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    Information & Communication Technology (ICT) plays a key role in modern power system. Component failure and malicious attack of cyber system could trigger outage, and sometimes, catastrophic blackout in powers system. Previous research shows that self-organized criticality of blackout arise from cascade overload and cascade outage. Whereas, recently observation show the other factors, including malicious sabotage, could contribute to SOC of blackout along without cascade outage. Stuxnet worm, as a new paradigm of malicious software that can spread in the physical isolated network, could initiate coordinated attack and result in ultra large blackout than expected. The cyber security issues of power system should be revisited correspondingly. View full abstract»

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  • Challenges in high voltage and Ultra High voltage AC and DC field testing

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (118 KB)  

    One of the challenging issues with high voltage network connections, be it for off-shore windfarms, inter-network HVDC connections, or simply overhead line replacement is to test the complete connections before bringing them into service. Even if all components are individually tested before being brought onto the construction site the final assembly needs to tested as a complete system before it is put in service. There are currently several challenges in the area of testing 150KV and higher voltages: First for short length cables the cost of measurement is prohibitive due to the fact that most current testing equipment is designed for laboratory use, requires specialized and time consuming setup and is therefore uneconomical to use. Another challenging area is the testing of long cables completely assembled: Current testing technology requires multiple test systems to be interconnected, resulting in severe logistics and technical challenges and even then most time testing is done in sections. Furthermore for HVDC and voltages above 400kV testing is limited to laboratory tests mainly by lack of appropriate testing equipment and standards. A new technology development has promising capacities for these field testing needs: Differential Resonance Technology (DRT) is developed based on long years of experience in VLF field testing and before that specialised laboratory test equipment. Differential resonance technology, as the name describes uses the differential of 2 resonance circuits to create a high-voltage low frequency signal in the range from 0,1 Hz to 10Hz. In this way compact and powerful testing equipment for High and Ultra High voltage and DC can be constructed. Current status: the first prototype systems have been build, currently tested up to 200kV RMS, and the current product range goes from 100KV up to 400 View full abstract»

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  • Learning from success and failure in transformer fault gas analysis and interpretation

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    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (431 KB)  

    The importance of transformer fault gas analysis and interpretation is well recognised and documented. However, unlike the diagnosis of human blood where rules have been well established, the diagnosis of faults in transformer oil is not so clearly defined. Whilst some transformer faults are straightforward to diagnose, with dissolved gas analysis (DGA) results pointing to the type and severity of fault, in many other cases it is often difficult to diagnose what type of transformer fault is involved and even harder to determine the cause. In some cases the transformer may be damaged but this may not be obvious from DGA results. This paper introduces the causes of transformer faults and failure; presents an overview of development of DGA diagnostics and discusses the merits and limitation of DGA diagnostic method; and describes five case examples, showing that knowledge from forensic inspection of faults and failures in transformers are of vital importance in understanding results from DGA of oil samples, and an in-depth understanding of the transformer design and life-limiting faults enable better interpretation of DGA results. View full abstract»

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  • Energy capacity and economic viability assessment of the renewable hydrogen energy storage as a balancing mechanism in addressing the electric system integration issues inherent with variable renewable energy resources

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (313 KB)  

    Energy requirements continue increasing as the industrialisation spreads and the standards of living rise. Most of the world's power consumption is still generated from fossil fuels combustion which despite of its advanced development has only a maximum efficiency of about 50%, generates almost 35% of the greenhouse emissions, as well as becoming expensive and insecure with the recent instability of oil prices. Renewable energy sources such as wind, solar, micro-hydro, wave, geothermal, and biomass are potential solutions for clean energy problem, but still challenges exist. Britain's target to reduce carbon emissions by 32% by 2020 through producing up to 34% of electricity and 15% of all energy from renewables cannot be met unless the contribution of such intermittent energy sources becomes more effective. Storing energy harnessed from renewables using energy storage technologies allows integration of such intermittent weather dependent energy sources while balancing the grid. Hydrogen Energy storage technology is proposed here to enable the UK to utilise its vast, but intermittent renewable energy resources with increased reliance. The objective within this study is to evaluate this process which represents genuine energy carbon neutrality. Energy capacity and economic viability assessment of an existing wind/hydrogen energy system operating in conjunction with the grid is provided here as a case study. View full abstract»

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  • Extreme climate impact on periodicity of fault

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    In reliability analysis of power system, component failures are usually supposed to be independent from each other. Consequently, the number of component failure in given time interval should have exponential distribution and there should not be periodicity in the time series of component failure. In our previous work, it has been observed that component failure in distribution system follow power law distribution and have long term autocorrelation, i.e., it behave self organized criticality and there are phenomena like periodicity in time series of fault. The impact of extreme climate on power law distribution of fault has been identified, while the influence on periodicity of fault has not been reported. In the article, Hurst exponent, which denotes long term autocorrelation of a time series of data, is utilized to represent periodicity of power system fault. Fault data of Changsha distribution system in China is analyzed. It is found that the investigated system has long term autocorrelation. In order to investigate influence of extreme climate on periodicity in fault, the days with largest number of fault are removed and the Hurst exponent is calculated. Based on in-depth analysis of cause of removed fault data and variation of Hurst exponent, the factors contribute to periodicity of fault are identified. View full abstract»

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  • Optimal allocation of renewable energy resources for minimising emissions in distribution networks

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    Integration of renewable Distributed Generation (DG) into the distribution networks is one of the effective ways to ensure emission reduction with the added benefits of network support and transmission and distribution system expansion deferral. Emission reduction by renewable DGs mostly depends on the generation technology, size and type of DG units and curtailment of fossil fuel based grid energy. This paper proposes a strategy for evaluating the size and type of renewable DG and determining the best mix of different renewable DG technologies by minimising primary and operational emissions without violating network constraints. A methodology based on time sequential optimisation is proposed for maximising annual emission offset considering the time varying demand and generation with different penetration of renewable resources into distribution networks. The proposed technique is tested on a realistic distribution feeder with different scenarios and results are presented. View full abstract»

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  • Safety is critical to asset management in the GB electricity industry

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    The electricity industry in Great Britain has undergone significant change since privatisation in the 1990s. Asset managers are having to make critical decisions about network equipment. Whereas much of the database and work management is IT-driven, there is considerable need for human intervention at various stages. This paper considers the management of human assets that underpins safety as an integral part of an asset management process and suggests a new approach for this. View full abstract»

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  • Improving reliability, safety and resilience of overhead networks

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    The electricity industry has undergone significant change since privatisation in the 1990s. Asset managers are making critical decisions on investment to ensure the safe and reliable transmission and distribution of electricity. A significant number of asset management interventions are being made on asset data that is collected by people, stored in systems developed by people, translated from various databases into asset prioritisation models by people and ultimately planned and executed by people. This paper explores the link between safety leadership, world class asset management and the critical part played by people in collecting and using asset data. The concept of an emerging transformational asset management model is introduced. View full abstract»

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