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Due to intermittent renewable energy and fluctuating load demand, distribution networks with renewable distributed generation (DG) installations are more likely to suffer voltage issues and significant power losses. The performance of conservation voltage regulation (CVR) schemes may be adversely affected by the undesirable voltage profile at specific nodes. This paper aims to reduce power losses in CVR‐implemented networks by optimally planning new renewable DGs without changing the existing ones. A scenario‐based optimal renewable DG planning model is proposed with a novel scenario formation method. The uncertainties of load demand and renewables are captured jointly and formed into a finite number of scenarios based on a multivariate Gaussian mixture model (MultiGMM). The locations and capacities of different types of new renewable DGs are optimally planned for CVR performance improvements on power loss saving by aggregating the operation status and probabilities of the scenarios using mixed‐integer non‐linear programming (MINLP). A time‐series simulation is formulated for accuracy verification. The results of case studies show that the proposed model can significantly reduce power losses, active load demand, and reactive load demand. The accuracy of the planning results can be guaranteed with fewer scenarios compared to a widely used classical scenario‐based planning method. [ABSTRACT FROM AUTHOR]

With an increased focus on renewable power generation, dynamic thermal ratings of various power equipment are being investigated to connect the new intermittent generation to the grid without needing to replace existing infrastructure. Previous research is mainly focused on a dynamic thermal rating for overhead lines. End‐of‐line equipment are also restricted by a thermal limit. This paper combines the thermal model for overhead lines with the transformer thermal model, to investigate the impact of environmental conditions on both. A wind farm case study is used to determine the potential increase in capacity using a combined thermal model. The impact of a higher thermal limit on the loss of life of the transformer is compared to the amount of curtailed wind and the potential revenue from the added wind farm. This analysis serves to provide a method to analyse the risks of using a higher transformer thermal limit, compared to the benefits of increased wind penetration and additional revenue. [ABSTRACT FROM AUTHOR]

Estimation of harmonic impedances and harmonic contributions is beneficial to harmonic control, and harmonic phasors data is necessary for the existing estimation methods. However, the phase angles of harmonic phasors are not recorded in some of current power quality measuring instruments (such as Fluke 1760 etc.), which makes the existing methods unavailable. To solve this problem, the Norton equivalent circuit model under harmonic frequency is improved and a new model composed of harmonic complex power sources and harmonic impedances is proposed. Based on the model, the harmonic impedance and harmonic contribution can be estimated by using independent component analysis algorithm, and the harmonic phasor data is no longer required. The superiority of the proposed model is verified through simulation and field cases. [ABSTRACT FROM AUTHOR]

With the increasing distribution network accidents caused by typhoon disasters, risk management in typhoon scenarios is necessary. A risk management framework for power distribution networks (PDNs) undergoing a typhoon disaster is proposed. First, a risk prediction model of the PDN under typhoon conditions based on the Batts model is developed to predict the loss of load risk (LLR) index and economic loss risk (ELR) index of the PDN before the typhoon lands. Then, a vulnerability index of overhead lines, considering the failure frequency of specific overhead lines and their load importance, is introduced for use in a weak link identification model to identify weak links in the PDN. Finally, a two‐time‐step risk relief model based on typhoon forecast information and the identified weak links is developed to allocate PDN relief materials to reduce the LLR and ELR during a typhoon disaster. An IEEE RBTS BUS6 system is employed as a test system to verify the risk management strategy. The vulnerability index proposed by the strategy considers both the importance of load and line failure. The risk management strategy adopts a two‐time‐step model, which reduces the impact of meteorological forecast errors and enables more efficient use of materials. The results show that the proposed framework can take more effective use of relief materials to reduce the loss of PDNs compared with the traditional strategy. [ABSTRACT FROM AUTHOR]

Proposed to be the critical enabling component for future distribution networks, solid‐state transformers (SSTs) have drawn much attention lately. They have a massive potential to help reduce size and weight, improve efficiency, integrate microgrids, renewables and energy storages in distribution systems, and can fulfil multiple grid functions such as bidirectional power flow control, fault isolation, system reconfiguration, and post‐fault restoration. The introduction of these power electronics devices in distribution systems, however, also brings new challenges to the grid. Extra levels of electromagnetic interference, stray current, and personnel safety are among the most prominent practical issues that proper grounding arrangements can address. In this paper, considerations that should be factored into the grounding scheme design for SST ports with different voltage forms and levels are thoroughly reviewed and summarised. The characteristics of various grounding schemes used in AC and DC distribution systems are evaluated and compared in detail from different perspectives. Based on the comprehensive review, several combinations of grounding schemes are recommended for typical SSTs. In addition, the inclusion of new relay protection devices in the SST grounding scheme design, considering their characteristics and unique requirements, to enhance protection and reliability is also discussed. [ABSTRACT FROM AUTHOR]

A method of capacity value evaluation for wind farms considering the correlation between wind power and load is presented. The paper starts with defining the metric of capacity value called capacity credit, and its basic evaluation process. Then the core part of capacity credit evaluation, which is the reliability assessment of power systems, is focused on. In this core part, two limitations of the frequently used cross entropy based importance sampling method are analysed. To solve the problems, an improved method is proposed by using truncated Gaussian mixture model as the proposal distribution of the cross entropy based importance sampling methods. This improved method is adopted to speed up the reliability assessment of composite power systems in the capacity credit evaluation. Finally, several numerical tests are designed and performed on the IEEE‐RTS 79 and IEEE‐RTS 96 test systems. The results show that the improved method is faster than traditional cross entropy based importance sampling methods when assessing the reliability of power system. Besides, the efficiency of the improved method is almost impervious to the correlation of load and wind power output, which ensures its applicability in different scenarios. [ABSTRACT FROM AUTHOR]

This study presents a differential protection scheme based on ensemble empirical mode decomposition (EEMD) for AC microgrid. The fault current level is significantly lower during the islanded operation of a microgrid, which leads to the malfunction of the traditional over-current protection scheme. The proposed differential protection scheme uses the spectral differential energy of the first intrinsic mode function extracted from the decomposition of the current signal using EEMD for effective fault detection in the AC microgrid. The proposed EEMD-based differential protection scheme is validated on 10 bus and modified IEEE 34-bus AC microgrid test systems during various shunt faults. Moreover, the performance of the proposed EEMD-based differential protection scheme is evaluated under high fault impedance scenarios. The simulation results reveal that the proposed differential protection scheme can effectively detect the faulty line in an AC microgrid during seamless islanded and grid-tied operations. [ABSTRACT FROM AUTHOR]

To relieve congestion due to open‐access feature in competitive power system framework, utilities plan flexible alternating current transmission systems (FACTS), ensuring improved utilization and performance of the transmission infrastructure. However, high‐investment cost restricts implementation to single type of FACTS' planning in a time. Therefore, successive planning of another FACTS to delay transmission expansion results in multi‐type FACTS planning. Consequently, to optimise performance, subsequent planning must coordinate with existing FACTS. The main objective of this study is to implement coordination of multi‐type FACTS for available transfer capability (ATC) enhancement. A hybrid real power flow performance index (PI) and particle swarm optimisation (PSO), coordinate thyristor control series compensator (TCSC) in the first planning horizon with static synchronous series compensator (SSSC) and unified power flow controller (UPFC), in the second horizon. The PI–PSO‐based multi‐type FACTS coordination improves ATC of multilateral power transfers in a standard 9‐buses test network. Results show that multi‐type FACTS achieved higher ATC; such that enhanced ATC by TCSC–SSSC ranges between 8.06–69.34% while the TCSC–UPFC ranges between 11.85–71.59% for various power transfer transactions. A comparison of the three coordination schemes shows that the scheme with more decision parameters provides superior loadability and transfer capability improvement. [ABSTRACT FROM AUTHOR]

The surge in the uptake of harmonic producing loads in 21st-century smart distribution networks has necessitated that robust data-driven approaches for harmonic assessment be developed. Moreover, there exists abundant harmonic data which can be leveraged on for the construction of this harmonic assessment tool. This is the objective of this study. Large volumes of time-stamped data acquired from a practical distribution network in Edmonton, Canada, have been used to construct a time-dependent cross-coupled harmonic model that has been combined with a formulated iterative time-dependent robust extended computer-aided harmonic power flows. The constructed harmonic power flow formulation also considered the constraints relating to the power conservation principle at the fundamental frequency. Practical network conditions including untransposed lines, load unbalance and skin effects of conductors have been thoroughly modelled. The proposed method has been applied to practical radial and weakly meshed medium voltage distribution networks and it demonstrated robustness to initialisation of the iterative procedure. Moreover, findings from this detailed data-driven technique reveal that harmonic impacts in the distribution networks depend on the quantum of harmonic levels, type of network and location of the harmonic sources. [ABSTRACT FROM AUTHOR]

The surge in the uptake of harmonic producing loads in 21st‐century smart distribution networks has necessitated that robust data‐driven approaches for harmonic assessment be developed. Moreover, there exists abundant harmonic data which can be leveraged on for the construction of this harmonic assessment tool. This is the objective of this study. Large volumes of time‐stamped data acquired from a practical distribution network in Edmonton, Canada, have been used to construct a time‐dependent cross‐coupled harmonic model that has been combined with a formulated iterative time‐dependent robust extended computer‐aided harmonic power flows. The constructed harmonic power flow formulation also considered the constraints relating to the power conservation principle at the fundamental frequency. Practical network conditions including untransposed lines, load unbalance and skin effects of conductors have been thoroughly modelled. The proposed method has been applied to practical radial and weakly meshed medium voltage distribution networks and it demonstrated robustness to initialisation of the iterative procedure. Moreover, findings from this detailed data‐driven technique reveal that harmonic impacts in the distribution networks depend on the quantum of harmonic levels, type of network and location of the harmonic sources. [ABSTRACT FROM AUTHOR]

This work assesses the financial viability of a wind farm where turbines are equipped to provide frequency services. Two control strategies are compared: the former enables the frequency response provision by operating the turbines part loaded, the latter employs the kinetic energy stored in the turbines' rotating masses. The analysis accounts for typical factors affecting the wind farm operation, the wake effect and the forecast errors on wind availability. A two‐stage optimisation model determines the day‐ahead and (close to) real‐time operation of the turbines, which profit from selling energy at the wholesale market (including subsidies), receiving availability payments for frequency services, while facing imbalance costs due to mismatches between forecasted and available wind. The two control strategies are applied to the Teesside Offshore Farm and the economic and financial performance are evaluated against a base case where the turbines do not provide frequency response service. Under current settings, the added value from frequency response capability is marginal. Changes to the market value of frequency services would favour the strategy based on part‐load operation of the turbines. The scheme based on the deployment of kinetic energy becomes profitable when the duration of time window for frequency response reduces. [ABSTRACT FROM AUTHOR]

The reliability of transmission lines (TLs) has great influences on the safe operation of power systems. Random failures from TLs can be caused by multiple uncertainties such as the high load current. In this study, a multi‐stage risk‐based dispatch model is proposed to minimise the sum of generation cost and risk cost. Impacts of natural ageing, load current, health condition and disaster weather on the short‐term reliability of TLs are studied. For ensuring the operation security of power systems in the post‐contingency stage, the dynamic thermal rating (DTR) technology is implemented to improve capacities of TLs for coping with the potential overload. In order to solve this non‐linear optimiation problem caused by load current‐dependent failure probabilities and thermal rating constraints, a double‐iteration solving strategy is proposed. In exterior iterations, the sequential linear programming is applied to decouple bilinear terms of the risk cost and locally linearise failure probabilities. Meanwhile, in interior iterations, the Benders decomposition is utilised to further divide the model into the main problem and the sub‐problem for coordinating the preventive and corrective control and checking the feasibility of DTR, respectively. Proposed approaches are validated on a modified IEEE 24‐bus test system. [ABSTRACT FROM AUTHOR]

The adoption of low-voltage DC microgrid at a large scale is hindered by the lack of an effective protection scheme. This work proposes a dedicated protection scheme based on multi-threshold current values, which enhances the security of the system by avoiding the risk of false tripping. This is achieved in a few milliseconds without losing the deadline of critical fault clearing time post, which the voltage sources converter interfaced power sources may get disrupted leading to de-energisation of the system. The algorithm relies upon the transient response of the series resistor–inductor–capacitor (R–L–C) equivalent circuit having initially charged filter capacitors. The threshold values of the fault current for each protection device at every network node are set locally by considering the weakest fault criterion. The extensive simulation study has been performed on MATLAB/Simulink for validating the reliability of the proposed algorithm under heavy load transient, at different fault locations, and with high fault resistance. [ABSTRACT FROM AUTHOR]

The adoption of low‐voltage DC microgrid at a large scale is hindered by the lack of an effective protection scheme. This work proposes a dedicated protection scheme based on multi‐threshold current values, which enhances the security of the system by avoiding the risk of false tripping. This is achieved in a few milliseconds without losing the deadline of critical fault clearing time post, which the voltage sources converter interfaced power sources may get disrupted leading to de‐energisation of the system. The algorithm relies upon the transient response of the series resistor–inductor–capacitor (R–L–C) equivalent circuit having initially charged filter capacitors. The threshold values of the fault current for each protection device at every network node are set locally by considering the weakest fault criterion. The extensive simulation study has been performed on MATLAB/Simulink for validating the reliability of the proposed algorithm under heavy load transient, at different fault locations, and with high fault resistance. [ABSTRACT FROM AUTHOR]

This study investigates the impact of embedded voltage source converter‐based high voltage direct current (VSC‐HVDC) links on AC grids transient stability. Firstly, using transient energy functions, it is demonstrated that VSC‐HVDC links controlled to track constant power references, do not inherently improve transient stability of the surrounding AC grid as an AC line naturally does. Then, a control law using the feedback linearisation technique on a simple but representative power system is derived. The control law highlights and combines the three main actions the VSC‐HVDC link can offer to enhance rotor angle stability: fast power reallocation, injection of synchronising power and injection of damping power. The control law is implemented and validated in EMT simulation. It is then shown that an HVDC link can assure the synchronisation of different AC areas even if no AC transmission lines interconnect them. Through another case study, it is shown how the HVDC link can help to share dynamic frequency reserves to not jeopardise the stability of the system. The last example investigates the effect of a DC fault on AC transient stability and how the control can help improving the system response. [ABSTRACT FROM AUTHOR]

In this study, a new method for utility harmonic impedance measurement based on robust independent component analysis (RICA) and bootstrap check is proposed. The RICA approach which adopts exact line search to seek the optimal step‐size in iteration has better performance for short data records. At the same time, a bootstrap check technique to remove the singular solutions of this sort of independent component analyses methods is presented as well. This verification technique is performed through judging the dispersion degree of the estimates of the bootstrap samples which is quantified by the coefficient of variation. Based on the results of computer simulation and filed test, it is proved that the combination of the RICA approach with the bootstrap check technique can reduce the adverse impact of the background harmonic fluctuation and the singular solutions on impedance estimation effectively, and satisfactory measurement results can be acquired. [ABSTRACT FROM AUTHOR]

The integration of the various types of distributed generators in low‐voltage (LV) distribution networks becomes a great concern, especially the rooftop photovoltaic (PV) systems. The negative impacts of the rooftop PVs on the distribution feeder buses' voltage include voltage rise and voltage unbalance (VU). Such a voltage‐violation condition depends mainly on the PVs ratings and the network unbalance percentage. This study presents a review for different techniques used to mitigate the voltage violation resulting from PVs integration in a typical three‐phase four‐wire LV distribution network case study. The voltage‐violation mitigation techniques studied in this study are enhancement of the feeder, on‐load tap changer, demand‐side management, active power curtailment, a reactive power control, static transfer switch, energy storage systems and hybrid strategies. The LV distribution network case study was modelled based on constant power model method using MATLAB software environment. The simulation results demonstrate both voltage regulation and alleviating VU capabilities of each technique. [ABSTRACT FROM AUTHOR]

Different from conventional low-rise buildings, in high-rise buildings, the gas pressure can easily exceed the safe limit, and the hot water cannot be easily transported to the higher floors owing to the effect of gravity. Therefore, overcoming these problems to supply heating for high-rise buildings remains a great challenge. Accordingly, gas-hanging stoves are introduced in this study as a provision for decentralised heating supply. To analyse the influence of gas hanging stoves on high-rise buildings and on the entire urban micro integrated energy system (UMIES), two models were developed: a scenario-based two-stage stochastic model for optimal scheduling of the UMIES and a gas overpressure model taking both additional overpressures caused by the frictional resistance and gravity into account. Numerical experiments based on two microgrid test systems show the efficiency of gas hanging stoves with regard to reducing operation costs of the UMIES; moreover, the gas pressure in highrise buildings becomes more uniform and concentrated. Thus, the supply of gas and heat to high-rise buildings can be significantly improved. [ABSTRACT FROM AUTHOR]

Predictions of the spatiotemporal distribution of fault events help the management planning and the maintenance scheduling in power transmission systems. To this end, this study proposes an early warning system based on the exploration of cause-attribute relationships. A comprehensive assessment of all the fault causes is conducted by incorporating entire available environmental attributes in the investigated system as inputs. To cope with the rarely occurred fault causes and environmental elements, a procedure of the weighted association rule mining is established. Then, a risk evaluation model is employed in evaluating the prediction performance and the risks of possible false predictions. Three requirements for the uncertainty are taken into account when this framework is applied in real use: technical reliability, internal reliability, and factitious effectiveness. An empirical study is conducted in a real power transmission system to verify the feasibility of the proposed framework, and the results prove that a flexible and robust prediction can be generated consequently. [ABSTRACT FROM AUTHOR]

This study proposes a new method to detect and locate the fault in a DC distribution system in the presence of distributed generators. As the mesh-type network provides good continuity of service during faults and the bipolar system transmits high power at low-voltage level to the end user, the proposed scheme has utilised 1200 V mesh-type bipolar DC microgrid network. The proposed scheme detects a fault by comparing the calculated value of fault current and pole-to-pole voltage with the pre-defined threshold values and then distinguishes internal or external fault based on an estimation of line parameters. In case of an internal fault, the estimated parameters yield the exact location of the fault. The modelling of the aforementioned DC microgrid network has been carried out in PSCAD/EMTDC environment and various faults involving pole and ground have been performed with variable fault resistance and location. The simulation results clearly indicate that the proposed technique is not only capable to detect the fault rapidly but also able to disconnect the faulty section speedily (around 1.25 ms). As the proposed method detects fault by utilising local voltages and currents, its reliability is better than the previous algorithms. [ABSTRACT FROM AUTHOR]

Line protection is of great challenge for Voltage Source Converter‐Direct Current (VSC‐DC) distribution systems because the protection scheme must selectively identify the fault section as fast as possible. This study proposes a full‐current‐based directional pilot protection to meet the above requirements. The proposed protection utilises the full‐current (the measured current). The theoretical analyses, which have considered the influence of the VSC blocking, have proved that the full‐current has a certain direction during a pole‐to‐pole short‐circuit fault. Therefore, the protection is robust to the non‐linearity of the DC system. The theoretical analyses have also pointed out that the protection is immune to the line‐distributed capacitance. Both experimental and simulation results have demonstrated the analyses. The proposed protection can trip in <2 ms at a 1.6 kHz sampling rate in the experiments and within 1 ms at a 10 kHz sampling rate in the simulations. It can also correctly operate with 20 dB white noise and 20 Ω fault resistance. There is also no strict synchronisation requirement for the measurements of both the terminals. These features make the protection feasible for industry application. [ABSTRACT FROM AUTHOR]

This study proposes a new method to detect and locate the fault in a DC distribution system in the presence of distributed generators. As the mesh‐type network provides good continuity of service during faults and the bipolar system transmits high power at low‐voltage level to the end user, the proposed scheme has utilised 1200 V mesh‐type bipolar DC microgrid network. The proposed scheme detects a fault by comparing the calculated value of fault current and pole‐to‐pole voltage with the pre‐defined threshold values and then distinguishes internal or external fault based on an estimation of line parameters. In case of an internal fault, the estimated parameters yield the exact location of the fault. The modelling of the aforementioned DC microgrid network has been carried out in PSCAD/EMTDC environment and various faults involving pole and ground have been performed with variable fault resistance and location. The simulation results clearly indicate that the proposed technique is not only capable to detect the fault rapidly but also able to disconnect the faulty section speedily (around 1.25 ms). As the proposed method detects fault by utilising local voltages and currents, its reliability is better than the previous algorithms. [ABSTRACT FROM AUTHOR]

Meeting electricity demand in remote communities and non‐electrified regions in the poor developing world is a challenge. Power generation is in shortage compared to electricity demand. Electric utilities either would enforce grid's zonal load curtailment or not electrify regions. Controlling electricity demand can play a vital role in enabling electricity access; however, weather uncertainty drives electricity demand variability. This article provides an overview of current demand‐side management research, identify research gaps, and propose a more promising approach to enable electricity access. Also, it proposes manipulating appliances models to fit their operation in applications where power supply shortage is an issue. The proposed work considers the effect of the probabilistic nature of weather and meeting AC grid codes of operation. [ABSTRACT FROM AUTHOR]

One of the effective methods to reduce the risk of load shedding and its subsequent blackout is to evaluate the risk of cascading outages and detection of key links in a power system. This risk assessment is getting more complicated considering the plans for integration of high wind energy. Therefore, in this study, a new sequential time approach has been proposed to evaluate risk of cascading outages considering the high penetration of correlated wind farms. The cascading processes are investigated using the extended OPA model using the graph traversal algorithm. Therefore, the problem of non‐convergence situations caused by the island formation is resolved. To deal with the future wind farms integration, a correlation is defined between them by a proposed method based on the Copula theory. The numerical results confirm that in evaluation of risk, the limited scenarios cannot always be reliable. The extended OPA model is then compared with a simple OPA to confirm the importance of islanding detection in the cascade simulation. Different aspects of cascading outages, i.e. fractional load shedding, cascade propagation level and number of line interruptions have been investigated. Finally, the impact of wind penetration and correlation of wind farms on results have been presented. [ABSTRACT FROM AUTHOR]

There is a growth of distributed generation (DG) impacting the network. There are several studies which focus on defining the location and size of DG to optimise network performance. However, this approach is only possible in a market regulation where utilities can control the DG. Otherwise, this information depends on the consumer and not on the utilities. In this case, the optimisation studies do not make sense anymore. This work aims to identify if the distribution network expansion planning (DNEP) will be changed by the DG integration in a scenario where DG is not controlled by the utilities. The method consists of performing load flows in the feeder considering the load growth during the planning horizon to calculate voltage levels, currents and technical losses. Then, the procedures are repeated considering DG integration in many penetration levels, after that, the results are compared. The results showed that, for the feeder under study, the critical hours do not necessarily occur at the period of peak load, but in the moments with greater generation and smaller load. Therefore, the focus of the DNEP should be changed when considering DG integration. [ABSTRACT FROM AUTHOR]

This study proposes a multi-stage restoration strategy to solve the service restoration problem in distribution systems considering the uncertainty of outage duration. Furthermore, it also proposes a restoration index defined in terms of (i) priority of the load restored, (ii) number of switching operations, and (iii) estimated likelihood of the restoration solution to assist the utility in enhanced decision-making. Service restoration is formulated as a single objective optimisation problem considering the maximising of the restoration index as the only objective. A decentralised multi-agent system method is developed to solve the service restoration problem considering controlled islanding of distributed generators. The uncertainty of outage duration is estimated using the maximum entropy principle-based on the cause of the fault. Exhaustive case studies are implemented on a small 38 bus and a large 119 bus test distribution system to demonstrate the effectiveness of the proposed multi-stage restoration strategy to restore the system under outage duration uncertainty. [ABSTRACT FROM AUTHOR]

Renewable energy sources provide an important means of reducing reliance on conventional fuels. However, some renewable energy resources such as wind and solar energies are intermittent, and their uncertainty threatens the operating security of the power grid. To solve this problem, this study proposes the use of intervals to model the power output of renewable energy resources and the power load demand, and accordingly develops an interval voltage control model, i.e. interval reactive power optimisation model. The proposed model considers the control modes of renewable energy power generators and can safeguard the security of power grids by ensuring that the voltages reside within established limits. An adaptive genetic algorithm is employed to solve the proposed model, where a newly developed interval power-flow (IPF) calculation is used to solve the IPF equations, and penalty functions are applied to express inequality constraints. The proposed method is introduced in detail, and simulation results are presented to demonstrate its performance in comparison with a previously proposed interval voltage control method, as well as its applicability to large systems with various fluctuations of input data. The proposed approach provides robust convergence, obtains lower system power losses, and substantially reduces the computation time. [ABSTRACT FROM AUTHOR]

This study proposes a multi‐stage restoration strategy to solve the service restoration problem in distribution systems considering the uncertainty of outage duration. Furthermore, it also proposes a restoration index defined in terms of (i) priority of the load restored, (ii) number of switching operations, and (iii) estimated likelihood of the restoration solution to assist the utility in enhanced decision‐making. Service restoration is formulated as a single objective optimisation problem considering the maximising of the restoration index as the only objective. A decentralised multi‐agent system method is developed to solve the service restoration problem considering controlled islanding of distributed generators. The uncertainty of outage duration is estimated using the maximum entropy principle‐based on the cause of the fault. Exhaustive case studies are implemented on a small 38 bus and a large 119 bus test distribution system to demonstrate the effectiveness of the proposed multi‐stage restoration strategy to restore the system under outage duration uncertainty. [ABSTRACT FROM AUTHOR]

Renewable energy sources provide an important means of reducing reliance on conventional fuels. However, some renewable energy resources such as wind and solar energies are intermittent, and their uncertainty threatens the operating security of the power grid. To solve this problem, this study proposes the use of intervals to model the power output of renewable energy resources and the power load demand, and accordingly develops an interval voltage control model, i.e. interval reactive power optimisation model. The proposed model considers the control modes of renewable energy power generators and can safeguard the security of power grids by ensuring that the voltages reside within established limits. An adaptive genetic algorithm is employed to solve the proposed model, where a newly developed interval power‐flow (IPF) calculation is used to solve the IPF equations, and penalty functions are applied to express inequality constraints. The proposed method is introduced in detail, and simulation results are presented to demonstrate its performance in comparison with a previously proposed interval voltage control method, as well as its applicability to large systems with various fluctuations of input data. The proposed approach provides robust convergence, obtains lower system power losses, and substantially reduces the computation time. [ABSTRACT FROM AUTHOR]

Electric distribution utilities are required to continuously deliver reliable electric power to their customers. Regulatory utility commissions often practise reward and penalty schemes to regulate reliability performance of utility companies annually with respect to a desired performance targets. However, the conventional regulation procedures are commonly found based on the customer‐based standard reliability indices, which are not able to discern the service characteristics behind the electric meters and, hence, fail to holistically characterise the actual impact of electricity interruption. This study proposes a new method to evaluate the load‐based reliability indices in power distribution systems using advanced metering infrastructure data. Furthermore, the authors introduce a reward/penalty regulation scheme for utility regulators to provide a reliability oversight using the proposed load‐based reliability metrics. The new load‐based reliability metric and the reward/penalty scheme proposed bring about superior advantages as the distribution grids become further complex with a high penetration of distributed energy resources and enabled microgrid flexibilities. Numerical analyses on different settings with and without microgrid considerations reveal the applicability and effectiveness of the proposed approach in real‐world scenarios. [ABSTRACT FROM AUTHOR]

Quick fault detection and isolation of faulty section are desired in DC microgrid due to the presence of power electronic converters and low cable impedances. Owing to need of fast disconnection, limited time and data are available for online fault distance estimation. Some of the existing techniques consider source capacitors connected at only one end of the cable; therefore, assume that the fault current is contributed by only one end of the cable. This may not be true in the case of multi‐source DC microgrids, where fault current would be supplied from both the ends. Further, existing communication‐based techniques require either data synchronisation or fast communication network. To address these issues, this study proposes an online fault location method for multi‐source DC microgrid without using communication. The mathematical model of faulted cable section connected to sources at both the ends is derived. This model is used along with the measurements to determine the fault distance. The model consistency with the measurements is quantified using the confidence level based on the residual analysis. A ring‐type multi‐source DC microgrid system is considered and simulated on real‐time digital simulator to demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Detection of shorted DC faults and high‐resistance faults on ring type low‐voltage DC (LVDC) micro‐grids imposes an elusive challenge. This research work proposes an efficient and reliable protection scheme for DC system in order to boost up LVDC system adoption on large scale, despite lack of proper standards and mature experience in DC system protection. In order to ameliorate these deficiencies, a wavelet transform‐based fast fault protection scheme using local measurements has been proposed for eliminating threat to voltage source converters during fault. The features extracted using wavelet coefficients are utilised as key indicators to identify the fault with wide variations in operating conditions. The LVDC micro‐grid system has been simulated using real‐time digital simulator and the test results studied show a great potential ability in performing DC fault detection and classification task efficiently. Furthermore, the robustness of the proposed protection scheme is capable of fault line identification and setting up desired relay selectivity in the LVDC distribution system. [ABSTRACT FROM AUTHOR]

Recently, diverse technologies and apparatus are launched to enhance service reliability in the distribution level. In this regard, remote controlled switches (RCSs) can play a prominent role in declining interruption durations and costs. The stochastic nature of contingencies, however, imposes considerable uncertainty on the achievements of RCS deployment. This study presents a model to consider the financial risk induced by the uncertainty in an RCS placement problem. The risk awareness of distribution companies is scrutinised through an effective risk measure, i.e. conditional value at risk. In the model, the number and location of RCSs are determined such that the system expected cost is minimised and the risk is managed. The model is treated as a multi‐objective problem with two conflicting objectives. The problem is then solved via a non‐dominated sorting genetic algorithm II. This algorithm results in a set of non‐dominated solutions. Finally, a fuzzy decision making method is applied to select the best placement strategy from the set. The presented model is applied on RBTS‐Bus4, where the findings reveal the importance of considering the risk in an RCS placement problem as well as the capability of the method in doing so. [ABSTRACT FROM AUTHOR]

The potential benefits of direct current (DC) network in low‐voltage system promote smart grids and facilitate increasing penetration of distributed generation (DG). Correct identification of faulted section of a distribution network by an automation system reduces power outage time and improves reliability indices of such systems. With the onset of a fault in a DC distribution system, data recorded at an outage management system are used to identify the faulted section. With DG units active in a distribution system, there will be bidirectional power flow and faulted section identification becomes challenging. Using voltage and current data from consumer‐end smart meters and the substation, a method is proposed to identify the faulted section in DC distribution system. The Hadamard product of fault‐affected sections (obtained from network topology and voltage status matrices) is used to identify the faulted section correctly. Using power systems computer‐aided design/electro‐magnetic transient design and control simulation, the accuracy of the proposed method is verified for different fault situations including simultaneous faults, fault close to a bus and with rooftop photovoltaic integration to a DC distribution system. The method has the capability to provide information on the fault segment that connects feeder pillar to the consumer end also. [ABSTRACT FROM AUTHOR]

Evaluation of available transfer capability (ATC) is a complicated process involving the determination of the total transfer capability (TTC) and the existing transfer commitments (ETC). Considering the uncertain renewable generation such as wind power will bring more challenge to this process. Previously the uncertainty of wind power is considered either in the ED model or the following TTC calculation, but not included in two process simultaneously. Therefore, the ATC output may not be accurate since the uncertainty impact two problem simultaneously. To consider the uncertainty and correlation of wind power in both ISO's ED and ATC evaluation, this paper proposes a bi‐level optimization framework in which the ATC evaluation is formulated as the upper level problem and the ED is the lower level. The bi‐level model is first converted to a mathematic program with equilibrium constraints (MPEC) by recasting the lower level problem as its Karush‐Kuhn‐Tucker (KKT) optimality conditions, and then transformed to a mixed‐integer linear programming (MILP) problem which can be solved by existing optimization tools. Case studies on the PJM 5‐bus and IEEE 118‐bus systems are presented to verify the proposed methodology and the impacts of correlation of wind power on ATC are analysed. [ABSTRACT FROM AUTHOR]

Transient stability‐constrained optimal power flow is an important emerging problem with power systems pushed to the limits for economic benefits, dense and larger interconnected systems, and reduced inertia due to expected proliferation of renewable energy resources. In this study, two more approaches: single machine equivalent and computational intelligence are presented. Also discussed are various application areas, and future directions in this research area. A comprehensive resource for the available literature, publicly available test systems, and relevant numerical libraries is also provided. [ABSTRACT FROM AUTHOR]

This study presents a combined electro‐thermal overhead line (OHL) model for power flow and time‐domain power system simulations. It originally enables the combined dynamic simulation of thermal as well as electrical characteristics of OHLs. The thermal behaviour of OHLs is replicated according to IEEE Std.738‐2012 considering time‐varying weather variables and is incorporated as controllable resistance into a traditional electrical OHL model. Therewith, simulating the dynamic influence of conductor temperatures on electrical quantities is enabled. The impact of the electro‐thermal OHL model is evaluated based on the analysis of bus voltages, line currents, losses, reactive power flows, cumulated generation and consumption in a small radial as well as in a meshed power system. Therefore, a method for estimating line lengths from given system data and a process for the calculation of mutually depending initial line conductor temperatures for power flow and time‐domain simulations is presented. The results show high deviations in active power line losses (up to 33.34%) and reactive power flows (up to 11.43%) compared with the traditional electrical OHL modelling approach. Thus, the relevance for considering electro‐thermal line models in power system simulations with special emphasis on the assessment of line losses and reactive power flows is demonstrated. [ABSTRACT FROM AUTHOR]

A distributed population games algorithm is proposed to solve the dispatch problem in microgrids to respond dynamically to the requirements of the system. This study extends the distributed replicator dynamics (RD) algorithm, it has four main contributions. First, the authors apply the distributed RD to a distributed generator dispatch over a communication topology in a microgrid test system. Second, they consider power losses of the networked microgrid on the distributed RD. Third, they propose an algorithm to estimate robust loss coefficients of the network considering different demand patterns through a combination of two heuristic optimisation algorithms. Finally, the uncertainties of wind power are considered as a renewable generation integration case. The simulation results show that the proposed distributed control algorithm of a microgrid is able to integrate the economic dispatch problem with frequency control considering the entire network topology. [ABSTRACT FROM AUTHOR]

The increased complexity of the modern distribution system caused by the installation of a large number of distributed energy resources, dictates the necessity for novel, decentralised schemes for the grid operation. In this study, a fully distributed method for the economic dispatch (ED) problem is proposed that takes into account distribution losses. The solution is reached using only local computations and exchange of messages between adjacent nodes without the need of a central coordinating entity. The algorithm presents plug-and-play capabilities and is self-triggered. More specifically, the ED is formulated as a resource allocation problem and a fully distributed algorithm is employed to acquire the solution that is based on the replicator equation model. It takes into account the technical constraints of the generators and it is extended in order to integrate the distributed calculation of active power losses using distributed estimation of the loss penalty factors. Guarantees for the convergence and optimality of the proposed algorithm are provided along with numerical results that demonstrate the effectiveness and efficiency of the algorithm. [ABSTRACT FROM AUTHOR]

Efficient and well-timed investment in distributed generation (DG) in distribution networks in the electricity market environment presents a big challenge for distribution companies. In this study, a real option valuation framework is proposed to determine the optimal investment strategies for DG including the investment location, size, and timing. Within the proposed framework, the profit from investing in DG is modelled, where the benefits include the operation cost savings and capacity update deferral benefit compared with a no-DG-investment scenario over the study period. Future power demands and electricity prices are modelled as stochastic variables. The candidate DG investment plans are considered as multiple mutually exclusive options, and the corresponding managerial flexibility for seizing opportunities and mitigating risk of loss upon an unfavourable unfolding of future uncertainties is assessed with real option analysis using the extended least square Monte Carlo method. The distribution of future investment strategies and optimal initial investment threshold levels under various scenarios are analysed in a case study to demonstrate the characteristics of the proposed framework and methodology. [ABSTRACT FROM AUTHOR]

The integration of Distributed Generation (DG) units in the existing power system has made the reliable operation of the system more complex. This has necessitated a comprehensive approach in planning the expansion of the system with the incorporation of DG units for effective and reliable operation of the system. In this study, a robust Hybrid Islanding Detection Technique (HIDT) has been proposed for identifying the islanding event early and accurately in the distribution networks with DGs installed by a two-step Genetic Algorithm (GA) process. As the reliability of power supply to the customer is of utmost importance, a priority-based load shedding scheme is proposed. The proposed load shedding scheme sheds only the vulnerable loads in the island for regaining the frequency and voltage stabilities. By the proposed methods, a comprehensive solution for system planning and emergency control actions can be obtained for effective operation of the system with DG units. The proposed methods are investigated on standard IEEE 33 and 69 bus distribution systems under different loading conditions. The results obtained show that the proposed methods are able to identify the islanding event more effectively and also regain the stability in the island with less amount of load shedding. [ABSTRACT FROM AUTHOR]

The increased complexity of the modern distribution system caused by the installation of a large number of distributed energy resources, dictates the necessity for novel, decentralised schemes for the grid operation. In this study, a fully distributed method for the economic dispatch (ED) problem is proposed that takes into account distribution losses. The solution is reached using only local computations and exchange of messages between adjacent nodes without the need of a central coordinating entity. The algorithm presents plug‐and‐play capabilities and is self‐triggered. More specifically, the ED is formulated as a resource allocation problem and a fully distributed algorithm is employed to acquire the solution that is based on the replicator equation model. It takes into account the technical constraints of the generators and it is extended in order to integrate the distributed calculation of active power losses using distributed estimation of the loss penalty factors. Guarantees for the convergence and optimality of the proposed algorithm are provided along with numerical results that demonstrate the effectiveness and efficiency of the algorithm. [ABSTRACT FROM AUTHOR]

Efficient and well‐timed investment in distributed generation (DG) in distribution networks in the electricity market environment presents a big challenge for distribution companies. In this study, a real option valuation framework is proposed to determine the optimal investment strategies for DG including the investment location, size, and timing. Within the proposed framework, the profit from investing in DG is modelled, where the benefits include the operation cost savings and capacity update deferral benefit compared with a no‐DG‐investment scenario over the study period. Future power demands and electricity prices are modelled as stochastic variables. The candidate DG investment plans are considered as multiple mutually exclusive options, and the corresponding managerial flexibility for seizing opportunities and mitigating risk of loss upon an unfavourable unfolding of future uncertainties is assessed with real option analysis using the extended least square Monte Carlo method. The distribution of future investment strategies and optimal initial investment threshold levels under various scenarios are analysed in a case study to demonstrate the characteristics of the proposed framework and methodology. [ABSTRACT FROM AUTHOR]

The integration of Distributed Generation (DG) units in the existing power system has made the reliable operation of the system more complex. This has necessitated a comprehensive approach in planning the expansion of the system with the incorporation of DG units for effective and reliable operation of the system. In this study, a robust Hybrid Islanding Detection Technique (HIDT) has been proposed for identifying the islanding event early and accurately in the distribution networks with DGs installed by a two‐step Genetic Algorithm (GA) process. As the reliability of power supply to the customer is of utmost importance, a priority‐based load shedding scheme is proposed. The proposed load shedding scheme sheds only the vulnerable loads in the island for regaining the frequency and voltage stabilities. By the proposed methods, a comprehensive solution for system planning and emergency control actions can be obtained for effective operation of the system with DG units. The proposed methods are investigated on standard IEEE 33 and 69 bus distribution systems under different loading conditions. The results obtained show that the proposed methods are able to identify the islanding event more effectively and also regain the stability in the island with less amount of load shedding. [ABSTRACT FROM AUTHOR]

Voltage source converters (VSCs) are highly vulnerable to DC fault current; thus, protection is one of the most important concerns associated with the implementation of multi‐terminal VSC‐based DC networks. This study proposes a protection strategy for medium voltage DC distribution systems. The strategy consists of a communication‐assisted fault location method and a fault isolation scheme that provides an economic, fast and selective protection by means of using the minimum number of DC circuit breakers. This study also introduces a backup protection which is activated if communication network fails. The effectiveness of the proposed protection strategy is analysed through real‐time simulation studies by use of the hardware‐in‐the‐loop approach. Furthermore, the effects of fault isolation process on the connected loads are also investigated. The results show that the proposed strategy can effectively protect multi‐terminal DC distribution networks and VSC stations against different types of faults. [ABSTRACT FROM AUTHOR]

Power economic studies are challenging because of growing system sizes, the advance of smart grids, and economic, technical, and policy unknowns. Consequently, system models must be simplified so that they can be solved with many scenarios of renewable output, load, and long-run uncertainties. Scenario reduction, network aggregation, and DC linearisation are three common simplifications. The authors compare their errors and computation times for optimal power flow (OPF) and stochastic unit commitment (SUC), using the IEEE 14-, 30-, and 118-bus test systems, and also briefly discuss impacts on generation and transmission planning. The authors find that the most appropriate simplification depends on the study type, and there are no consistent results concerning which simplification is most distorting. The following example conclusions apply to these cases, but not universally; nonetheless, the findings provide information about what simplifications can matter, which is a helpful starting point for practicing modellers. The authors find that linearisation's disregarding of losses distorts total costs in OPFs, but it causes relatively little error in SUC. Scenario reduction reduces OPF computational times with little distortion but is less effective for SUC. Network aggregation decreases computation effort more than linearisation in OPF, but causes little error unless there are few scenarios. [ABSTRACT FROM AUTHOR]

Power economic studies are challenging because of growing system sizes, the advance of smart grids, and economic, technical, and policy unknowns. Consequently, system models must be simplified so that they can be solved with many scenarios of renewable output, load, and long‐run uncertainties. Scenario reduction, network aggregation, and DC linearisation are three common simplifications. The authors compare their errors and computation times for optimal power flow (OPF) and stochastic unit commitment (SUC), using the IEEE 14‐, 30‐, and 118‐bus test systems, and also briefly discuss impacts on generation and transmission planning. The authors find that the most appropriate simplification depends on the study type, and there are no consistent results concerning which simplification is most distorting. The following example conclusions apply to these cases, but not universally; nonetheless, the findings provide information about what simplifications can matter, which is a helpful starting point for practicing modellers. The authors find that linearisation's disregarding of losses distorts total costs in OPFs, but it causes relatively little error in SUC. Scenario reduction reduces OPF computational times with little distortion but is less effective for SUC. Network aggregation decreases computation effort more than linearisation in OPF, but causes little error unless there are few scenarios. [ABSTRACT FROM AUTHOR]

This study presents an efficient power flow method for analysing distribution systems. The proposed method utilises efficient quadratic‐based (QB) models for various components of distribution systems. The power flow problem is formulated and solved by a backward/forward sweep (BFS) algorithm. The proposed QBBFS method accommodates multi‐phase laterals, different load types, capacitors, distribution transformers, and distributed generation. The advantageous feature of the proposed method is robust convergence characteristics against ill conditions, guaranteeing lower iteration numbers than the existing BFS methods. The proposed method is tested and validated on several distribution test systems. The accuracy is verified using OpenDSS. Comparisons are made with other commonly used BFS methods. The results confirm the effectiveness and robustness of the proposed QBBFS at different conditions. [ABSTRACT FROM AUTHOR]

The use of electrical energy storage (EES) and demand response (DR) to support system capacity is attracting increasing attention. However, little work has been done to investigate the capability of EES/DR to displace generation while providing prescribed levels of system reliability. In this context, this study extends the generation‐oriented concept of capacity credit (CC) to EES/DR, with the aim of assessing their contribution to adequacy of supply. A comprehensive framework and relevant numerical algorithms are proposed for the evaluation of EES/DR CC, with different 'traditional' generation‐oriented CC metrics being extended and a new CC metric defined to formally quantify the capability of EES/DR to displace conventional generation for different applications (system expansion, reliability increase etc.). In particular, specific technology‐agnostic models have been developed to illustrate the implications of energy capacity, power ratings, and efficiency of EES, as well as payback characteristics and customer flexibility (that often also depend on different forms of storage available to customers) of DR. Case studies are performed on the IEEE RTS to demonstrate how the different characteristics of EES/DR can impact on their CC. The framework developed can thus support the important debates on the role of EES/DR for smart grid planning and market development. [ABSTRACT FROM AUTHOR]

This study analyses the coordinated actions of modern wind power plants for improving the transient and smallsignal stability in power systems. Supplementary controls on wind farms are considered, and specific modifications on the controllers are tailored to increase the grid-support services. The proposal is analysed and validated in a practical power system based on the Argentine electrical network. The wind farm supplementary controls use active and reactive power control loops as well as local and remote measurements. Local controls can rapidly respond decelerating the system frequency in the first instants of a fault, consequently reducing the transient angle separations and improving the firstswing stability. On the other hand, remote controls using global information are able to increase the damping of lowfrequency inter-area oscillations. Structures combining centralised and decentralised control approaches will become more common in the near future. With this aim, the integration of fast local controls with remote controls is thoroughly studied using non-linear time-domain simulations and eigenvalue analyses. A robustness evaluation is also performed to validate the proposal over a wide range of operating conditions. [ABSTRACT FROM AUTHOR]