Four-phase transmission lines have been recently proposed and studied as an alternative to the traditional three-phase lines. The identification of the best transformer typology to link the three-phase and four-phase system sections is still an open problem, despite some specific solutions were proposed. However, these solutions were not included in a general framework yet. Resorting to the classic Parton's theory of phase transformation and to a rigorous mathematical approach, this study provides a general framework for the specific problem in study. After having recalled the underlying principles of the Parton's theory of phase transformation, by formulating proper optimisation problems and solving them using a rigorous mathematical procedure, this study derives several solutions for three-to-four phase transformation, some of which were never proposed yet. This way, both traditional solutions (T-connection, Leblanc connection, Scott connection) and more recent proposals are described together with the new solutions within one common framework.

Crete is the largest autonomous power system in Greece. Thera is a small island in the Aegean Sea, widely known as Santorini. This study tackles with the potential impact in case of interconnection of these two island systems. The impact on the economic operation of both power systems, the expected flow between these two power systems and the fuel savings resulting from their interconnection are presented as a part of a preliminary techno-economic study that can be also used for investigation of further interconnections in the area. In addition, some insight on the transmission losses and the level of interconnection voltage is provided.

This study presents a tie line planning and its effects on the operating cost and environmental issues of power systems via a novel multi-area active–reactive optimal power flow (MA-AROPF) model. In this study, the authors focus on the significant role of tie line planning on power system operation. To select an appropriate tie line, a modified sensitivity index is used, which not only reduces the operating cost and emissions, but also enhances the voltage stability of individual areas and the entire power system. These benefits are obtained by increasing the degree of freedom of the power system through providing uniform economic and emission dispatch. Moreover, in this study, to address the drawbacks of commonly used decomposition methods for solving MA-AROPF, an integrated model is proposed. An AROPF that considers the environmental effects is a highly non-linear problem, and the multi-area consideration of such problems via tie line planning makes it an even more complicated and exceedingly non-linear problem. For didactic purposes and to verify the model, a small two-area system is considered in detail, while to show the effectiveness of the proposed approach, a three-area system consisting of 14-, 30-, and 118-bus IEEE test systems is conducted.

In this study, a new model for participating in market is presented in which each generation company (GENCO), considering nodal price limitation, defines a risk index. Using a linear combination, it determines its proposed bid based on energy prices of other buses. Since each participant in power market needs reference points to decide, concept of sensitivity factors is introduced initially. Consequently, using these factors, potential points are obtained. To model price uncertainty, risk concept is cooperated into sensitivity factors. After that, using regulation factors, new derated sensitivity factors (DSFs) are defined. Applying these factors, each player’s model in the market is divided into two parts. In the first part, modelling its rival’s behaviour, a player proposes its bid in such a way that obtained nodal price becomes equal to estimated nodal price. In the second part, computing DSFs and using potential bus prices, linear combination of regulation factors are utilized to modify GENCO’s offer. Player’s profit function would be average of both parts. GAMS software is executed to solve this problem. Different scenarios are considered to cover nodal electricity and fuel price uncertainties. A 30-bus system with six GENCOs is used to verify the proposed model.

This study presents a closed-loop coordination mode and model between generation maintenance scheduling (GMS) and long-term security-constrained unit commitment (SCUC) considering energy constraints and N − 1 contingencies that aims at improving the security and economy of power system operations. Given the calculation complexity, this study employs constraint transformation techniques and an efficient approach termed the relaxation induced method, which is based on the solution of the relaxed mixed-integer programming (MIP) model. The proposed approach can quickly obtain a near-optimal solution. If the near-optimal solution is not acceptable for system operators, it can be used to warm-start the solution of the original MIP problem. The modified IEEE 30-bus test system and a provincial power system in China are employed to demonstrate the effectiveness of the proposed model and algorithm.

This study presents the modelling of transformers for voltage disturbances. The focus in this study is on the security of the power supply for sensitive loads, for instance, the auxiliary systems for a nuclear power station feeding, for instance, pumps for emergency systems. Both steady-state operation as well as transient conditions have been analysed. A five-limb as well as a three-limb 4 kVA transformer was designed in order to verify theoretical assumptions with experimental results. The results show that the theoretical models provided results in conformity to the actual experiments with an average discrepancy of 3%. Moreover, it is shown that a five-limb transformer gives lower inrush currents, especially in the highly saturated region. In addition, it was demonstrated that an inductive load gives much higher inrush currents compared with a resistive load. A final observation was that the current drawn by the two transformers in their saturated state differ severely depending on the topology of the core.

The safe and continuous operation of power systems necessitates the implementation of special protection schemes (SPSs) against severe disturbances that may lead to a system breakdown. This study proposes a new SPS to mitigate voltage collapse against predetermined contingencies that can significantly lessen the voltage stability margin (VSM) of the system. The proposed SPS is based on an effective load shedding scheme that uses a multi-objective optimisation framework including the objectives of load cut, VSM and the integral of the deviation from nominal voltage. Moreover, a new diversely distributed multi-objective fuzzy-based theta gravitational search algorithm is proposed to solve the optimisation problem. Khorasan area of Iran's power system in 2014 peak load time is used as a test case for the suggested SPS. Effectiveness of the proposed approach is shown by comparing its simulation results with the results of the current SPS and other solution approaches.

To prevent atmospheric ice on optical fibre composite overhead ground wire (OPGW) from affecting the safe and stable operation of power system, applying the direct current (DC) ice-melting technology to remove ice from OPGW is a feasible option. If the selection of DC ice-melting current is unreasonable, the temperature of optical fibre can be extremely high which may shorten its operating life or even cause it to burn. Therefore, based on the finite element method, the ice-melting process of OPGW under glaze icing condition is simulated by COMSOL and MATLAB. The ice-melting time and temperature variations of optical fibre for ice-covered OPGW under different environmental conditions are obtained. Then, a series of ice-melting tests are carried out in an artificial climate chamber to verify the calculation results. Results show that the ice-melting and temperature increase of optical fibre gradually slow down during the entire DC ice-melting process. When ice sheds from the OPGW, the temperature of optical fibre reaches its maximum value. The ice-melting time is closely related to the ice-melting current, ambient temperature, wind speed, ice thickness and type of OPGW. The maximum temperature of optical fibre is significantly influenced by ice thickness and ice-melting current.

With the wind generation increasingly penetrating the power grids, there is a growing interest in developing new risk-based assessments for the grids security analysis. This study develops one kind of such risk tools to evaluate the security risks of power grids under certain amount of wind generation in a short period of time. First of all, a very short-term uncertainty model of wind generation is introduced. Then the conditional value-at-risk is used to design a safety distance (S-D), revealing the tail risks of operating states. Based on S-D, four new indices are defined to highlight the risks in a near future with considerable change of wind power output. The overall security assessment tool is compared with the conventional method both on a benchmark test system and a real power system in China. The results demonstrate the effectiveness and some advantages of this new risk-based tool.

In this study, the economic benefits of using a probabilistic-dynamic approach (PDA) in the quantification of operating reserves are investigated and compared with more traditional quantification rules in power systems with high penetration levels of wind power. To do this, a comprehensive methodology to quantify different operating reserves categories within the real-time system operation is proposed. The quantification is based on an iterative process where the total costs of the system are minimised, that is the sum of the operating costs (including the additional costs of partially loading generating units due to operating reserves) and the costs of the expected energy not supplied. The PDA considers conventional generation outages; load and wind forecast uncertainty on an hourly basis as well as load and wind variability in a 10 min time frame. The authors use the Chilean power system to demonstrate the efficiency and advantages of the proposed reserve quantification approach.

This study investigates two common types of stator winding faults in doubly fed induction generators (DFIGs) including inter-turn short-circuit fault (ITSCF) and winding resistive asymmetrical fault (WRAF), and compares them with the operation of DFIGs underpower grid voltage unbalance conditions. A complete magnetic equivalent circuit model has been used to model ITSCF and WRAF in the stator windings of DFIG. The aim of this investigation is to discriminate between these types of faults using the rotor-reference-voltage signals inside the rotor-side-converter control system. A new fault diagnostic index (FDI) is proposed based on normalised energy evaluation of the given signal using the discrete wavelet transform. The accuracy of the proposed FDI has been evaluated by simulation of DFIG performances with Matlab/Simulink software under low number of stator shorted turns conditions, different severities of winding resistive asymmetrical faults, various levels of grid voltage unbalance, various rotor speeds, and various output active powers. Analysis of the simulation results confirms that the proposed FDI can accurately discriminate between ITSCF even with minor shorted turns, WRAF or unbalanced voltages except for the cases with minor asymmetry and healthy conditions of stator winding.

In high-impedance grounded distribution networks which are common in many countries, single line-to-ground (SLG) fault diagnosis is difficult due to weak fault characteristics, noise interference, three-phase unbalanced operation's influence and so on. Upon thorough analysis on the space-time characteristics of SLG fault, this study applies signal processing and analysis techniques to do SLG fault location detection. First, finite impulse response (FIR) filter is applied to effectively strain out interference factors and extract pure fault characteristics for each line. Afterwards, hierarchical clustering is used to classify lines based on the extracted fault characteristics. According to the clustering result, the fault line could be determined. If there are monitoring terminals distributed in the fault line, the fault section could also be further identified. Simulation shows that the proposed method works well under various fault conditions and has a higher reliability compared with wavelet analysis. Besides, this method makes full use of the existing hardware conditions in the grid and the cost is low, hence it has high practical value.

As the rapid development in power electronic devices, the harmonic pollution becomes one of principle power quality problems in power system. The fast Fourier transform (FFT) is widely used for analysing and measuring power system harmonics. However, the limitation of the FFT such as an aliasing effect, spectrum leakage picket-fence effect, would contribute to inaccuracy results. Furthermore, the real power system harmonic is actually a non-stationary signal while FFT is a tool for stable signal. This study focuses on a novel FFT based method for time-varying power system harmonic measurement. The harmonic signal is preprocessed by infinite impulse response filter bank and Teager–Kaiser energy operator for fast detection of instability onset time. Then an adaptive Kaiser self-convolution window-based interpolated FFT algorithm is used to estimate each harmonic component. The results of both simulation and practical implementation show that the proposed method is suitable to deal with time-varying harmonic and achieves a higher accuracy compared with the traditional FFT-based techniques.

This study proposes a dual three-leg voltage source inverter (VSI)-based distribution static compensator to compensate unbalanced and non-linear loads in three-phase four-wire distribution systems. The proposed topology uses two three-leg inverters having common dc link with single dc capacitor and an additional small rating ac capacitor connected from the negative terminal of VSI to the system neutral. The proposed scheme with associated control algorithm has capability to compensate unbalanced non-linear load and hence makes source current as balanced sinusoidal and at desired power factor. The control algorithm also ensures the proper sharing of reactive, harmonics and unbalanced powers between two VSIs and controls the grid current total harmonic distortion level even in the presence of unbalanced and distorted voltages. The performance of the proposed scheme has been verified using simulation and experimental studies under different voltage conditions and detailed results are presented.

Implicit Z-bus distribution power flow method may encounter divergence problems when applied to distribution systems with distributed generators modelled as P-V nodes. In this study, analysis of divergence problems associated with the implicit Z-bus method is performed. Physical insights toward the divergence problem are also provided. To this end, the iterative map of the implicit Z-bus method is first derived. Then the fix-point theorem and the non-linear discrete stability theorem are applied to perform convergence/divergence analysis of the implicit Z-bus power flow method. The authors apply the derived analytical results to conduct divergence analysis of the IEEE 13-bus, and a practical 1101-node distribution networks.

This study proposes a novel algorithm for fast and accurate measurement of fundamental, harmonics, sub- and inter-harmonic parameters of a distorted current signal with additive noise. A novel hybrid technique called adaptive linear neural network and filtered-x least mean square (ADALINE-FXLMS) algorithm is employed for amplitude and phase estimation. The ADALINE-FXLMS algorithm is the advancement of ADALINE least mean square (ADALINE-LMS) algorithm. With the help of this proposed algorithm, the adaptive step-size parameter is expanded up to the upper-bound limit that results in further improvement of system stability. The convergence behaviour of the mean square errors for the noisy input signal is derived in details. By applying the proposed algorithm, the dynamic and steady-state response are analysed with different signal-to-noise ratio values. The simulated results obtained from the proposed algorithm are compared with the results generated by the variable step-size ADALINE-LMS algorithm in order to demonstrate the tracking capability. Finally, a laboratory prototype model is developed to justify the efficacy of the analytical results. The motivation of applying the proposed hybrid algorithm is due to its successful implementation in a real-time environment, faster convergence and simplicity structure.

Observations of contamination tests showed that, the contamination distribution of insulators is usually uneven. In this study, the solid layer method was used to imitate different non-uniform pollution conditions and the AC pollution flashover tests of 7-unit insulators were carried out. The results indicate that the increase of uneven pollution degree J from 1 to 15 will give a 39% raise of U ₅₀ under non-uniform pollution on top and bottom surfaces, a 23% decrease for fan-shaped non-uniform pollution and a 21% higher U ₅₀ with ring-shaped non-uniform pollution. A higher occupation ratio (k) of leeward side will reduce U ₅₀ under fan-shaped non-uniform pollution and a bigger radius R of heavy polluted area has certain effect on U ₅₀ for ring-shaped non-uniform pollution. The U ₅₀ and salt deposit density still can be expressed by the negative power function, and non-uniform pollution conditions and J have great effect on a, but less impact on n. The correction equations of different non-uniform pollution conditions are obtained and the relative errors are acceptable. The research has certain reference significance for the design and selection of AC transmission line external insulation.

This study presents an optimisation control strategy for the power control of voltage source converter-based high-voltage direct current transmission under unbalanced grid voltage conditions. To facilitate simple implementation and flexible operation, the current references are derived and synthesised into one generalised equation that introduces two individually adaptable parameters. The two parameters can be adapted to eliminate the oscillations of instantaneous active and reactive power, as well as the currents at the grid side under unbalanced grid voltage conditions. The optimisation method based on particle swarm optimisation algorithm is presented to determine the two parameters. The simulation is conducted with PSCAD/EMTDC. The results show that the proposed strategy is effective and feasible.

Massive amounts of data generated in large-scale grids poses a formidable challenge for real-time monitoring of power systems. Dynamic state estimation which is a prerequisite for normal operation of power systems involves the time-constrained solution of a large set of equations which requires significant computational resources. In this study, an efficient and accurate relaxation-based parallel processing technique is proposed in the presence of phasor measurement units. A combination of different types of parallelism is used on both single and multiple graphic processing units to accelerate large-scale joint dynamic state estimation simulation. The estimation results for both generator and network states verify that proper massive-thread parallel programming makes the entire implementation scalable and efficient with high accuracy.

This study presents an innovative design for a wave energy converter (WEC). The system is based on a novel mechanical power take-off (PTO) device that can absorb wave energy by converting the bidirectional motion of an ocean wave into the one-way rotation of an electric generator. First, the PTO mechanism and configuration are described in detail. A coupled mechanical and hydrodynamic time-domain simulation of a hemispherical floating buoy connected to a bidirectional gearbox and torque generation device under regular waves were modelled in MATLAB^®/Simulink^®. The hydrodynamic forces acting on the semi-submerged floating buoy are calculated by employing linear potential wave theory. The friction behaviour in the PTO system is modelled by using Brian Armstrong's method. Next, an average wave energy and absorbed energy calculation was applied to investigate the conversion efficiency of the WEC. Finally, the experimental setup is carried out in a water tank under various conditions to evaluate the performance of WEC and validate the modelling. The results indicate that high-energy conversion efficiency of generating electricity from waves is approachable, thanks to the high efficiency of the proposed device.

In this study, the calculations of flexible AC transmission system (FACTS) devices energy function and corrected transient energy function (CTEF) in presence of FACTS are formulated. The most versatile FACTS devices are modelled for transient-stability assessment using CTEF. Furthermore, the effects of FACTS devices on the corrected transient margin are evaluated by considering the corrected transient energy margin (CTEM), corrected transient kinetic energy (CTKE), and fault critical clearing time (CCT). The proven formulations are applied and compared on three different networks, 3-bus, 39-bus, and 145-bus test systems. All evaluations are compared with each other in the presence and absence of the FACTS devices, and the results of simulation and direct method are investigated. It is proven that by using the energy functions of static VAr compensator, thyristor-controlled series capacitor, and unified power flow controller, the results of the direct method and the simulation method are almost equal. Also, the efficient criteria in identifying first swing stability behavior are developed for the hybrid method to evaluate the CTEM. Test results do not show any irregular non-linearity on the variations of CTEM, CTKE, and CCT for both plant and inter-area mode disturbances.

Communication systems serve as the key element in the smart grid as it supports observability and controllability of electric power systems. However, communication failures can lead to an electric power grid operating in an abnormal state causing cascading failures. It is therefore crucial to study adverse effects of communication system failures on power system operation. In this study, a vulnerability assessment framework is proposed to evaluate the role of communication networks on wide-area power system operation, in which the reliability is evaluated probabilistically considering both latency and communication interruptions; and impact of communication service interruption is evaluated using a multi-level analytic hierarchy process method. A case study of integrated power and communication systems is used to demonstrate the usefulness of the proposed framework. The proposed method can be used to evaluate the vulnerability of communication systems for electric power grids in both static and dynamic states.

In an oligopoly electricity market, generation companies (GenCos) are often able to exercise market power through capacity withholding. This study proposes a comprehensive approach for evaluating the capacity withholding of GenCos in the presence of network constraints in electricity markets. The Cournot-Nash equilibrium model for GenCos is considered, and then various scenarios in terms of network constraints and GenCos parameters are analysed. The purpose of this study is to propose and examine a set of comparison indices for capacity withholding assessment in transmission-constrained electricity markets. In the proposed indices, three types of electricity markets are considered: oligopoly market, perfectly competitive market, and perfectly competitive market with the nodal prices of oligopoly market. The effectiveness of the proposed indices is shown based on IEEE 30-bus and IEEE 118-bus test systems. The results demonstrate that GenCos' capacity withholding can be influenced by their parameters, network constraints, and demand elasticity.

This study connects several modular multilevel converters to form multi-pole voltage source converter high-voltage dc (VSC-HVDC) links which are suited for bulk power evacuation, with increased resiliency to ac and dc network faults. The proposed arrangements resemble symmetrical and asymmetrical HVDC links that can be used for bulk power transfer over long distances with reduced transmission losses, and for the creation of multi-terminal super-grids currently being promoted for transitional dc grids in Europe. The technical feasibility of the proposed systems is assessed using simulations on symmetrical and asymmetrical tri-pole VSC-HVDC links, including the case of permanent pole-to-ground dc faults.

The fault identification process in transmission systems involves three functions: discrimination, classification and phase selection. The current study classifies the methods that applied for each function. Moreover, this study introduces criticism and assessment study that helps the power system protection engineer to choose the best fault identification scheme at responsible indices. Investigated solutions for the drawbacks appeared with the previous methods are suggested. This study also proposes sensitive and automated fault identification scheme to solve the existing challenges such as high-impedance faults (HIFs), non-linear modelling of arcing etc. Several simulation studies are employed using alternative transients program/electromagnetic transient program (ATP/EMTP) package on a sample 500 kV test system to ensure the performances of the proposed scheme compared with the previous methods. Simulation results concluded that: the proposed identification scheme has the ability to discriminate correctly between HIF and low-impedance faults using current signal captured from one end only. Moreover, the proposed scheme alleviates perfectly the problems associated with load variations by adaptive threshold settings and reduces the impacts on the environmental and external phenomena.

This study proposes a novel method based on mathematical morphology (MM) for islanding detection in micro-grid integrated with distributed generation (DG). The method uses basic MM operators like dilate erode difference filter (DEDF) to operate on three-phase voltage and current signals on target DG location. These filter output values are fed to a new operator defined as the average of the difference between maximum and minimum value of DEDF at each structuring element called K _V and K _I . Accordingly, a new operator called the MM ratio index (MM RI) of K _I to K _V is derived. The MM RI computed is used to track the islanding condition from non-islanding condition. Additionally, to further aid the islanding detection, a mathematical morphological operator close open difference filter on negative sequence voltage is computed, which is passed through a difference operator D. The proposed method is analysed extensively to efficiently detect islanding in electrical power distribution network integrated with DG.

This study presents a new method for determining the harmonic contributions (HCs) of utility and consumer at the point of common coupling (PCC). The proposed method is based on a well-known statistical signal processing technique, the so-called complex independent component analysis (ICA). The complex ICA technique is applied to the harmonic voltage and current measured at the PCC to estimate the parameters of the Northon equivalent circuit model. Then, the HCs of utility and consumer are calculated through quantitative indices defined by the superposition method. The proposed method is robust against the background harmonic disturbances and works well in resonance condition. Moreover, the impact of consumer harmonic impedance is appropriately considered in calculations. The effectiveness of the proposed method is verified through the computer simulation and the real case study.

Low voltage feeders (LVFs) experience several voltage quality (VQ) issues such as voltage drop at network peak periods, voltage rise at middays when high number of rooftop photovoltaic cells (PVs) are existing in the feeder, rapid voltage fluctuations as the results of the clouds effects on the power generation of PVs, and voltage unbalance due to the inherent random characteristics of the single-phase loads and PVs. This study addresses these problems by proposing the concept of coupling the neighbouring LVFs. Based on this concept, two or more LVFs of the same distribution transformer or different distribution transformers are interconnected to support each other and minimise the VQ problems. First, the performance of LVFs in the existing form is discussed and three approaches of coupling the LVFs are presented. Among the presented techniques, coupling of LVFs through a distribution static compensator (DSTATCOM) at the end of the feeder is proposed and focused as an effective technique with minimal side effects such as power losses and cost. Proper dynamic control methods are also proposed for the DSTATCOM and the performance of such a system is investigated under steady-state and dynamic conditions via numerical analysis and simulation studies in MATLAB and PSCAD/EMTDC.

Fault current limiters are playing an ever more important role in today's power systems and many of their different types have now reached maturity. Owing to the progress in superconducting technology, the superconducting fault current limiter (SFCL) has attracted increasing attentions. To investigate the efficacy of SFCL devices from a system point of view, the fault current limiting impedance is of great importance. This study proposed an improved structure of flux-lock type of SFCL and compares the current limiting impedance of different layouts. It focuses on the impacts of iron core shape on primary winding inductance. The analyses include simulations based on finite element method carried out in the simulation software ANAlysis SYStem (ANSYS). This study shows that an E–E-shaped core with an air gap is better than a closed core when being used for an SFCL. It is also found that for an iron core SFCL with fixed size, its rated fault current limiting impedance can be adjusted by changing the cross-sectional area of the iron core centre leg and the length of the air gap.

Phasor measurement units (PMUs) play an important role in the wide-area monitoring and protection of modern power systems. Historically, their deployment was limited by the prohibitive cost of the device itself. Therefore, the objective of the conventional optimal PMU placement problem was to find minimum number of devices, which when carefully placed throughout the network, maximised observability subject to different constraints. Due to improvements in relay technology, digital relays can now serve as both relays and PMUs. Under such circumstances, the substation installations consume the largest portion of the deployment cost, and not the devices themselves. Thus, for minimising cost of synchrophasor deployment, number of substation installations must be minimised. This study uses binary particle swarm optimisation to minimise number of substations in which installations must be performed for making all voltage levels observable, while being subject to various practical constraints. Standard IEEE systems have been used to explain the technique. Finally, a large-scale network of Dominion Virginia Power is used as the test bed for implementation.