Electricity Distribution Network Operators Research Articles

Optimal Capacitor Bank Allocation in Electricity Distribution Networks Using Metaheuristic Algorithms

Energy losses and bus voltage levels are key parameters in the operation of electricity distribution networks (EDN), in traditional operating conditions or in modern microgrids with renewable and distributed generation sources. Smart grids are set to bring hardware and software tools to improve the operation of electrical networks, using state-of the art demand management at home or system level and advanced network reconfiguration tools. However, for economic reasons, many network operators will still have to resort to low-cost management solutions, such as bus reactive power compensation using optimally placed capacitor banks. This paper approaches the problem of power and energy loss minimization by optimal allocation of capacitor banks (CB) in medium voltage (MV) EDN buses. A comparison is made between five metaheuristic algorithms used for this purpose: the well-established Genetic Algorithm (GA); Particle Swarm Optimization (PSO); and three newer metaheuristics, the Bat Optimization Algorithm (BOA), the Whale Optimization Algorithm (WOA) and the Sperm-Whale Algorithm (SWA). The algorithms are tested on the IEEE 33-bus system and on a real 215-bus EDN from Romania. The newest SWA algorithm gives the best results, for both test systems.

Distribution System Voltage Control Under Uncertainties Using Tractable Chance Constraints

Voltage control plays an important role in the operation of electricity distribution networks, especially with high penetration of distributed energy resources. These resources introduce significant and fast varying uncertainties. In this paper, we focus on reactive power compensation to control voltage in the presence of uncertainties. We adopt a chance constraint approach that accounts for arbitrary correlations between renewable resources at each of the buses. We show how the problem can be solved efficiently using historical samples analogously to the stochastic quasi-gradient methods. We also show that this optimization problem is convex for a wide variety of probabilistic distributions. Compared to conventional per-bus chance constraints, our formulation is more robust to uncertainty and more computationally tractable. We illustrate the results using standard IEEE distribution test feeders.

Risk Assessment of Distribution Networks Integrating Large-Scale Distributed Photovoltaics

Risk impacts on the operation of electric power distribution networks, when large amounts of distributed photovoltaics (PVs) are included, are gradually increasing to become a critical consideration for distribution networks' operations. In this paper, a risk assessment method is proposed which considers large-scale distributed PV feeding into distribution networks. Cluster partitioning is used to group large-scale distributed PV, to more accurately calculate the operational risk indicators for distribution networks with large-scale distributed PV compared to traditional risk assessment methods. A copula function is used to describe the correlation between the PV output and the load, in order to more accurately calculate power flow information compared to the traditional independent model of output and load. Node voltages over-limits and branch power flows outside boundaries are selected as the risk indicators, and a comprehensive risk indicator is introduced to more comprehensively and meaningfully evaluate the risk of distribution networks' operation. Also, the effects on the operational risk of the distribution network of load fluctuations, and, PV quantity, capacity, and location are analyzed and discussed. Finally, the IEEE34-bus system was simulated, and the results for different scenarios were calculated and analyzed. The simulation results demonstrate the effectiveness of the proposed method.

An Analysis of the Systematic Error of a Remote Method for a Wattmeter Adjustment Gain Estimation in Smart Grids

Smart energy meters supporting bidirectional data communication enable novel remote error monitoring applications. This research targets characterization of the systematic worst-case error of the previously published remote watthour meter’s gain estimation method based on the comparison of synchronous measurements by the reference and meter under test. To achieve the research aim a methodology based on global maximization of the systematic error objective function assuming the typical low voltage electrical distribution network operation parameters ranges as defined by the standard recommendations for network design. To cross verify the reliability of the assessed solutions the suggested error analysis methodology was implemented utilizing two stochastic global extremum search techniques (genetic algorithms, pattern search) and the third one utilizing nonlinear programming solver. It was determined that the wattmeter adjustment gain worst-case error does not exceed 0.5% if the remote wattmeter monitored load power factor is larger than 0.1 and a network is designed according to the recommendation of the acceptable voltage drop less than 5%. For a load exhibiting power factor larger than cos φ = 0.9 the worst-case error was found to be less than 0.1%. It is concluded therefore that considering the systematic worst-case error the previously suggested remote wattmeter adjustment gain estimation method is suitable for remote error monitoring of Class 2 and Class 1 wattmeters.

Multi-Criteria Optimization of the Functionning of a Distribution Network in Normal Operating Regime

The growth of loads on distribution networks and the delay in investment in energy field are driving power systems operators to operate their power grids beyond allowed limits. This mode of operation of the networks generates more distribution losses and violations of the normative voltage ranges. This paper presents the multi-objective optimization of electrical distribution network operation under operational and safety constraints. Since load-flow analysis is the basis for any optimization and planning, and given that radial topology of distribution networks are characterized by high R/X ratio and imbalances, are not adapted and converge with difficulty. An algorithm based on the backward – forward sweep principle is developed in MATLAB environment for permanent network regime computation and is tested on a IEEE 33-bus network before it is applied to a 41-bus network of the Beninese Society of Electrical Energy (SBEE). The genetic algorithm (NSGA II) is implemented to optimize the operation of distribution network and the proposed model implemented in MATLAB made it possible, from the reference data of the SBEE test network, to minimize the losses and to reduce the voltage drops under thermal constraints of the conductors.

Unbalanced current-based tariff

The voltage and current unbalances are serious power quality problems with interaction on each other and mainly affecting low-voltage electricity distribution three-phase systems. In a three-phase system, the current unbalance is due to load unbalance, while it is considered as the main cause of voltage unbalance. The electricity utilities and distribution network operators are responsible for providing of symmetrical voltages system at the point of common coupling between distribution gird and customers' internal network. The duty of current balancing is solidarity of both of electricity suppliers and customers. The utilities must do it for voltage balancing by equally distribution of single-phase customers between three phases, while three-phase customers have no responsibility for doing it for their single-phase loads. According to this paper, the power quality penalty and unbalanced current-based tariff are innovated for encouraging them to do it like as utilities.

Towards the modernisation of the supervisory control and data acquisition systems of the Hellenic electricity distribution network operator: considerations and steps forward

Currently, Hellenic Electricity Distribution Network Operator (HEDNO) undergoes an upgrade of its supervisory control and data acquisition systems. As part of this, the information and communication technology (ICT) infrastructure of the organisation will undergo a respective change towards data harmonisation and smooth interoperation between the heterogeneous ICT systems it consists of. This work presents the current state of the most important of HEDNO ICT systems, in an attempt to point out the diversity and complexity of the ICT infrastructure of such a large organisation, and, then, it proposes the implementation of the enterprise service bus approach as a means to achieve the desired integration, interoperability and data harmonisation between the various ICT systems of HEDNO.

Sizing of energy storage systems considering uncertainty on demand and generation

Abstract Over recent years there has been a general consensus about the necessary changes towards modernizing the existing power grid to meet environmental and socio-economic objectives. The adoption of low carbon technologies is a milestone in this process. On the other hand, the massive and uncoordinated connection of distributed generators (e.g. solar or wind) is making the operation of electrical distribution networks more challenging, e.g. causing energy balancing problems or voltage violations. Energy storage systems represent a possible means to cope with these issues. In this paper, we consider the problem of sizing the energy storage systems installed in a low voltage network with the aim of preventing voltage violations along the feeders. Since the problem is solved at the planning stage, when future realizations of demand and generation are unknown, we adopt a two-stage stochastic formulation where daily demand and generation profiles are modelled as random processes. The cost function to be minimized takes into account installation and operation costs related to storage use. By taking a scenario-based approach, the two-stage problem is approximated via a multi-scenario optimal power flow. To reduce the computational burden of the latter problem, a heuristic strategy consisting of solving separately a sizing problem for each scenario, and then combining the solutions of the single problems through a worst-case criterion, is proposed. The multi-scenario approach and the heuristic strategy are compared in terms of both computation time and quality of the solution using real data from an Italian low voltage network with photovoltaic generation.

Multi-Objective Optimization of Electrical Distribution Network Operation Considering Reconfiguration and Soft Open Points

High penetration levels of Distributed Generations (DG) significantly affect the operations of electrical distribution networks. In this paper, Distribution Network Reconfiguration (DNR), and the implementation of Soft Open Point (SOP) – a distribution-level power electronic device are investigated as effective solutions to facilitate large DG penetrations while meeting network operational constraints. DNR is developed based on the ant colony optimization, and the optimal SOP outputs are determined using the Taxi-cab algorithm after determining the network configuration. Both optimization problems are formulated within a multi-objective framework using the Pareto optimality. The performances of DNR and SOP to improve network operations are demonstrated on a modified 33-bus distribution system with various DG penetrations.

Net Metering in Brazil: regulation, opportunities and challenges

Net metering schemes have been used in many countries to push distributed generation (mainly solar photovoltaic) development. In Brazil, regulation came into effect in 2012 but recent update has made substantial changes in the regulatory framework in order to reduce barriers and provide more favorable conditions for the development of small scale renewable energy based distributed generation in the country. However, because it is a new subject, which requires in-depth studies and an adjustment period, many questions arise regarding its operation. Thus, this paper presents an analysis of the different net metering schemes possibilities in Brazil and its insertion in the national regulatory background. Results show that Brazilian net metering scheme has great potential for encouraging small scale solar photovoltaic in Brazil, providing great business opportunities and low payback time. However, challenges such as electricity taxation and distribution network operators' revenue have to be addressed smartly in the near future in order to push market development without compromising distributed generation viability.

Investigations on Dielectric Properties of Nano SiO2-Mineral Oil for Transformer Insulation Applications

Successful operation of electric power transmission and distribution network depends on the consistency of power transformers. Any unscheduled outage due to a faulty transformer leads to expensive and time consuming repair work and affects the entire power system reliability. Majority of the power transformer faults occur due to aging and degradation of oil insulation. Mineral oil is being used as a liquid dielectric in transformers for a longer period of time. In general, periodic monitoring of electrical, physical and chemical properties will certainly give information about the aging and deterioration of insulating oil. In recent times, advancements in nanotechnology has given scope for the development of nano-dielectrics for transformer insulation applications. Many research works are being carried out to understand the dielectric performance enhancements in nano-modified insulating oils for high voltage applications. In the present work, dielectric properties of nano-SiO2 modified mineral oil is investigated. Detailed reports on the characteristics of nano SiO2-modified mineral oil such as breakdown strength, loss factor, volume resistivity, viscosity, flash point and fire point are scanty. Hence, this paper attempts to investigate the above mentioned characteristics of SiO2 nanofiller added mineral oil at different %wt concentrations of nanofiller material. Results clearly show that addition of SiO2 nanofiller material in the base mineral oil enhances dielectric performance of mineral oil. These results will be useful for electrical utilities in improving the design aspects, identifying the root cause of insulation failures and carrying out the preventive maintenance activities of transformers.

Distributed Generation Placement in Distribution Network Based on Power-Flow Relations

Installing Distributed Generation (DG) influences distribution network stability and losses. The aim of the Distributed Generation placement (DGP) is to provide the best locations and sizes of DG units to optimize electrical distribution network operation and planning taking into account DG capacity constraints. In this paper a really formula based on Power flow for obtaining DGP and sizing to improve the performance of the distribution network is offered. The aim of this really formula is to eliminate complex and time-consuming algorithms in solving DGP problems. Using the proposed method, one can easily and without complex calculations obtains the size and location of DG units on the network. The proposed method has been tested on several networks and the test results show its effectiveness. The benefit of the proposed method is its low computational burden as well as its simplicity of implementation.

Benefits analysis of Soft Open Points for electrical distribution network operation

Soft Open Points (SOPs) are power electronic devices installed in place of normally-open points in electrical power distribution networks. They are able to provide active power flow control, reactive power compensation and voltage regulation under normal network operating conditions, as well as fast fault isolation and supply restoration under abnormal conditions. A steady state analysis framework was developed to quantify the operational benefits of a distribution network with SOPs under normal network operating conditions. A generic power injection model was developed and used to determine the optimal SOP operation using an improved Powell’s Direct Set method. Physical limits and power losses of the SOP device (based on back to back voltage-source converters) were considered in the model. Distribution network reconfiguration algorithms, with and without SOPs, were developed and used to identify the benefits of using SOPs. Test results on a 33-bus distribution network compared the benefits of using SOPs, traditional network reconfiguration and the combination of both. The results showed that using only one SOP achieved a similar improvement in network operation compared to the case of using network reconfiguration with all branches equipped with remotely controlled switches. A combination of SOP control and network reconfiguration provided the optimal network operation.

Operating principle of Soft Open Points for electrical distribution network operation

Soft Open Points (SOPs) are power electronic devices installed in place of normally-open points in electrical power distribution networks. They are able to provide active power flow control, reactive power compensation and voltage regulation under normal network operating conditions, as well as fast fault isolation and supply restoration under abnormal conditions. Two control modes were developed for the operation of an SOP, using back-to-back voltage-source converters (VSCs). A power flow control mode with current control provides independent control of real and reactive power. A supply restoration mode with a voltage controller enables power supply to isolated loads due to network faults. The operating principle of the back-to-back VSCs based SOP was investigated under both normal and abnormal network operating conditions. Studies on a two-feeder medium-voltage distribution network showed the performance of the SOP under different network-operating conditions: normal, during a fault and post-fault supply restoration. During the change of network operating conditions, a mode switch method based on the phase locked loop controller was used to achieve the transitions between the two control modes. Hard transitions by a direct mode switching were noticed unfavourable, but seamless transitions were obtained by deploying a soft cold load pickup and voltage synchronization process.

Identify Resonant Frequencies in AC Distribution Networks – A Numerical Example Part II – The State Matrix Method

One of the most important issues regarding the operation of electrical distribution networks which is harmonic polluted is to avoid parallel resonance frequencies of relatively high harmonic currents, that are present in the network. For this is absolutely necessary to know the frequency response of the network or its harmonic impedance, more exactly, the frequencies which can produce parallel harmonic resonance. This article is the second part of the paper which presents two methods of calculating the parallel resonance frequencies corresponding to peaks (poles) harmonic impedance seen in the buses: harmonic nodal admittance matrix method (in the first part), respectively that state matrix method (in the second part). The results obtained by the two methods are compared and a qualitative and quantitative analysis is done.

Electrical distribution network operation with a presence of distributed generation units in a Pre Smart Grid environment using a clustering-based methodology

Technical planning methodologies applied to electrical distribution networks presented in the literature generally consider that the distributed generation units (DGs) are operating in their standard operation mode, i.e., the distribution network operators (DNOs) have no control over the active power dispatched by DGs and there is no injection of reactive power into the electrical distribution network. Furthermore, such methodologies generally consider only balanced loads connected to electrical distribution networks. Some others methodologies that have control over the power dispatched by DGs consider that the Smart Grid philosophy is completely implemented. However, it is a distant prospect in many developing countries. In that ideal scenario, there is a constant and online communication between DGs and DNOs control centers. In this paper, the authors propose a new technical planning methodology, based on a clustering method, that considers the occurrence of unbalanced electrical distribution loads, the absence of DNO control over the active power dispatched by DGs and the absence of online communications between DGs and DNOs. The proposed methodology can be implemented in a short and medium term (called Pre Smart Grid). In that period of time, the Smart Grid philosophy will not be completely implemented.

High resolution modelling of multi-energy domestic demand profiles

Increasing interest in low carbon electro-thermal heating technologies, such as electric heat pumps and combined heat and power units, may in the near future significantly change the character of domestic electricity and gas demand profiles. To understand the impact of adoption of such technologies it is necessary to appreciate fully the multi-energy aspects of such technologies, and indeed of any other domestic energy service demands. Such holistic treatment is necessary to fully capture the effects of coincidence in various energy service demands within and across dwellings. To that end this paper introduces and details a high resolution domestic multi-energy model comprised of physically based space heating, domestic hot water (DHW), cooking and electrical appliance models. Given the potential for thermal storage in the heating system and building elements particular attention is given to the space heating model, which includes building, heat emitter, buffer tank and heating unit models, capturing the relevant inter-temporal dependencies, heat transfer rates and system inertia. The power and interest of the presented model is demonstrated through exploration of a selection of various possible applications, including amongst others: effect of input energy/heating technology substitution on consumption profiles of different energy vectors, effect of thermal inertia, and investigation of dwelling diversity. Additionally the importance of high granularity modelling is demonstrated. The presented model can be utilised by many actors involved in energy systems for various purposes. For example electricity distribution network operators for modelling of network peak demand, demand aggregators for estimation of potential demand side flexibility, government agencies for assessing incentive scheme costs, electricity retailers for understanding the impact of electro-thermal technology adoption upon their demand portfolio or potential heat network operators for understanding the demand for heat in an area.

Application of the Co-Evolutionary Algorithm with Memory at the Population Level for Optimisation of the Operation of Real Electric Power Distribution Networks

A solution of the optimisation problem of complex power electric networks post-fault configuration has been proposed. The analysed problem of search for optimal configurations of electric power distribution networks for changing loadings of network elements and for malfunction conditions is a multi-criteria optimisation problem. In this case the sought-after solution is the collection of Pareto-optimal solutions. Scientific methods belonging to the class of artificial intelligence methods (evolutionary algorithms and classifier system) have been used in the paper. Scientific work of the author is presented the co-evolutionary algorithm using memory at the level of organised populations in the form of five subpopulations, the composition of which is changed and organised according to classifying systems’ procedures. The process of creating a collection of classifiers describing the substitute network configuration was performed by the author supported by the theoretical genetic basics of self-teaching system. Cooperation of the evolutionary algorithm with the classifier system enables significant reduction of the classification time, reduces the iterative calculation process on average by 40 %. The calculations performed for the mapped real system of the medium voltage municipal distribution network have given satisfactory results, confirming the adequate direction of the research. The method presented in the article enables effective search of optimal configurations of distribution networks for various network loadings and also network malfunction conditions

Definition of information uncertainty in energy

The approach to solving the problem of initial information uncertainty using the fuzzy-set theory is given in the paper. The features of using the fuzzy approach to solving the problems in the design and operation of electrical distribution networks are considered. It is shown that, in the design, the main forms of initial information uncertainty are ambiguity, intervality, randomness. The method of defining these uncertainty forms using the fuzzy-set theory is given. The method of converting standard design tasks into the fuzzy form is given.In the operation of electrical distribution networks, one of the tasks is ensuring the required electricity quality. In solving this task, there is the problem of defining linguistic uncertainty and randomness. The method of uncertainty definition in the fuzzy-set theory is given. The given approach uses achievements of deterministic and stochastic approaches, summarizes them within the single mathematical apparatus. In addition, it allows formalizing the linguistically uncertain concepts and on this basis forming new generalizing forms of analysis.

Managing the asset time bomb: a system dynamics approach

For organisations responsible for managing the UK's national infrastructure, particularly those that are tightly regulated, a major challenge today is how to maintain performance of their infrastructure assets within the constraints of both limited budgets and externally set performance targets. This problem becomes more acute when significant members of an asset base approach an end-of life state at the same time. Resolving this problem has often proved difficult as it doesn't readily lend itself to exploration with traditional analytical and forecasting tools. This paper discusses how system dynamics methods and tools have been successfully used to develop a new approach to asset and infrastructure planning which builds simulation models that both give insight into the nature of the asset time bomb threat but, more importantly, enable the development of asset management polices and strategies that will eliminate the threat. The paper includes a description of system dynamics showing the detailed structure of the models developed. A case study of a leading European electricity distribution network operator who used system dynamics to understand and solve the asset time bomb threat is described including the outcome which resulting in a fundamental change in asset management strategy.