The arithmetic sequences optimised by genetic algorithms have been applied in the lifetime estimation and diagnosis of cross-linked polyethylene (XLPE) high-voltage insulation under thermal ageing. To know an idea of the cable capacity to work without failure, it is necessary to predict the future state of the electrical insulation. If the estimation is very good, the authors can start to schedule maintenance tasks of electrical system and find preventive solutions in early time. A large amount of money can be saved if they take appropriate actions. The developed model gives results in good agreement with the experimental results, with an acceptable error margin. The authors also applied the same models in the diagnosis of the high-voltage insulation to plan the preventive maintenance actions. The decision is taken from the carried out previous experimental measurements of XLPE properties. The developed approaches are able to make the diagnosis and the classification of the insulation state. The results of modelling, prediction and diagnosis presented in this work demonstrate the effectiveness of the used method.

Microgrids are used widely in electric power systems for enhancing the power system operation in both grid-connected and island modes. One of the main problems with microgrid operations in power systems is maintaining the microgrid voltage and frequency within permissible ranges and sharing microgrid loads among participating distribution generations (DGs) in an island mode. The droop control method will pose a degraded performance when feeder impedances of DGs are different. In this study, a new control method based on the virtual impedance and the compensating voltage is proposed and the simulation results show that this method combined with the droop control will offer a balanced power sharing among DGs with negligible voltage and frequency drops. Here both single-bus and multi-bus microgrids with distributed loads have been considered. The simulation results are based on the MATLAB Simulink which shows that the proposed method has a good load sharing performance among DGs with varying feeder impedances and droop gains.

This study proposes a novel non-invasive method for estimating the utility harmonic impedance. Since the major concern about non-invasive methods is the dependency of the accuracy of the results on background harmonic fluctuations, proper measured samples are selected using a three-point data selection technique to increase the method accuracy. Then, a new non-invasive method for the evaluation of the utility harmonic impedance at a point of common coupling (PCC) based on fuzzy logic is presented. In the proposed method, fuzzy logic is applied to the constrained recursive least squares algorithm (CRLS) by designing a set of fuzzy if-then rules. Due to the changes in the quantities at a PCC because of the changes in the utility and customer sides, these rules are used to determine the magnitude of the forgetting factor of the CRLS in order to estimate the utility harmonic impedance. Analysis of the simulation and real field test results for different cases show that the proposed method is effective in reducing the harmonic impedance calculation error caused by the fluctuations of the background harmonic.

In a deregulated energy market, voltage security (VS) is one of the major concerns, as it improves the loadability limits, loading profiles while concurrently reducing power loss. Further, voltage dependent loads can operate at high efficiency at rated voltage. Therefore, power utilities have to explore options of reconfiguration to secure the voltage level under frequently changing operating conditions. In this study, an efficient heuristic and meta-heuristic (harmony search) approach for reconfiguration is proposed by imposing VS. Two indices namely node voltage security index (NVSI) and node voltage quality index are developed for aggregated improvement in node voltages. Moreover, efficient methodologies for identification of new tie-lines, network radiality and the load flow solution are also presented. The effectiveness of the proposed index and the methodology is tested for reconfiguration of various distribution systems and the results are obtained with reduced computational efforts.

Alpha plane (α-plane)-based differential relay protecting a transmission line uses the ratio of the current phasors of both ends and has numerous advantages. Such an approach either uses phase or sequence components of currents. For a normal operating condition and external fault, the ratio remains within restraining region in the α-plane. During high resistance internal fault, the computed ratio at times lies inside the restraining region resulting misoperation of the technique. The scheme which uses sequence components of the currents has limited performance for single pole tripping and line impedance unbalance conditions. In this study, two features: phase angle between voltage and current and magnitude of change in currents of both ends of the line supplement the relay in identifying an internal fault. This improves the performance of phase current-based α-plane relay. The proposed method is tested for Western Electricity Coordinating Council (WSCC) 9-bus and two source equivalent system and results for various cases show improved performance.

This study proposes a novel protection scheme for residual current devices (RCDs) based on the theory of skewness and the least squares-support vector machine (LS-SVM). The skewness of the residual current is applied to detect the electric shock fault time, and the LS-SVM regression technique is used to perform touch current identification. The experimental test results indicate that the protection scheme can not only detect the electric shock fault time correctly and rapidly but also effectively recognise the circulation through the animal's current. Moreover, the proposed protection technique can provide valuable information for developing new generations of RCDs.

This study presents the combined model of automatic load frequency control (ALFC) and automatic voltage regulator (AVR) of a multisource multi-area system for control of voltage, frequency and tie-line power. Each area comprises of a solar thermal, thermal and diesel plant. A more realistic system is studied by considering generation rate constraint and governor dead band (GDB) for the thermal plant. Integral (I)-double derivative (DD) controller with derivative (D) filter (IDDF) is proposed for the combined ALFC and AVR model by considering 1% step load perturbation in area1. The controller parameters are optimised using lightning search algorithm (LSA). The performance of proposed controller is compared with other conventional controllers such as proportional–I (PI), I–D and PI–D. The analysis reveals that the proposed controller outperforms the others in terms of settling time and peak deviations. The comparative performance of various performance indices shows that integral squared error is better than others. Analysis of the effect of GDB with IDDF controller and LSA indicates that the presence of GDB leads to more oscillations in the system dynamics. The sensitivity analysis against the change in magnitude and position of disturbance derived the robustness of the IDDF controller parameters obtained at nominal condition.

An improved electromagnetic time-reversal (EMTR)-based method is proposed for fault-location of voltage-source converter multi-terminal high-voltage direct current systems (VSC-MTDC) transmission lines in this study. After a brief description of the EMTR, its application to lossless transmission line is mathematically demonstrated. Assuming that the DC faults are isolated by AC breakers, a window of adequate transients is used. If the protection has identified the faulted line correctly, only the recorded measurements at both ends of the faulted line should be time-reversed and further calculated. To eliminate the influence from AC side, the 0/1-mode observed currents and high-pass elliptic filter are adopted. After the processed signals are set as current sources, the current effective value at each pre-set fault position is calculated, with the peak value at the real fault-location. The simulation test cases are based on a five-terminal VSCHVDC modified from the China Nanau demonstration project. The results show that the improved method has good performance to deal DC line faults with high resistance and different types. Besides,, the results are not affected by measurement errors. Compared with the travelling wave-based method, the proposed method does not need to employ high sampling rates and precise fault-occurred time; meanwhile, it can achieve more precise results.

This study investigates the winding mechanical defects of power transformers including radial deformation and axial displacement of windings. The effects of these defects on performance of differential protection of the transformer will be investigated by modelling these mechanical defects using the detailed model in EMTP software. The inrush current phenomenon and internal electrical faults including turn-to-turn short circuit and terminal fault are investigated. Then, the differential and restraint currents, obtained using EMTP simulations, are analysed by MATLAB software. Using the statistical methods and extracting various indexes in MATLAB environment, these disturbances are discriminated and classified. Both the experimental and simulation results show that some winding mechanical defects affect the performance of the differential protection and the proposed statistical indexes are able to discriminate among mechanical faults, external faults, inrush currents and internal faults.

The worldwide needs to increase the reliability of the electrical grids and to reduce energy not supplied (ENS) are the major goals in traditional grids. Smart grids have key features such as intelligence, adaption and flexibility abilities, to reduce the effects of outages in society. This study proposes an optimised operational strategy which increases the robustness of smart grid against outages caused by bad weather conditions. The proposed method takes advantage of dynamic economic dispatch and hourly forecasted weather information. Intelligent scheduling of demand response programs and energy storage system, are formulated as a multi-objective optimisation problem considering consumer interruption costs. In this study, the objective functions consist of benefit maximisation of the distribution companies, benefit of the distributed generation and energy storage owners (DGO). In the proposed approach, line interruption rates are affected by weather conditions and consequently the ENS cost will be influenced in each time interval. DisCohas the ability to modify energy cost to overcome bad weather conditions and reduce ENS in different time periods. Simulation results show that the presented method reduces the real operation and ENS cost for DisCo. In addition, DisCo increases the benefits of DGO.

The passive fluctuation of the node voltage (NVPF) and the active fluctuation of node voltage (NVAF) are defined to analyse the dynamic coupling characteristic between the source, the network and the load. The NVPF indicates how the effect of come from by other nodes or regions, and the NVAF indicates the voltage impact on other nodes or region. Their combination can comprehensively reflect the coupling characteristic relationship of each part which is closely related to the power flow and the electrical connection. A method in non-analytical complex domain is proposed to find this relationship. Finally, the method is validated by the simulations on a three-bus system, the IEEE39-bus system and an actual system.

This study describes a loadability analysis in power systems based on short-circuit power (S _SC) at a load bus as a parameter space. This analysis determines the maximum loadability based on a proposed voltage stability indicator called voltage-power stability indicator (VPSI). VPSI is calculated by processing two consecutive sets of voltage magnitude and power measurements, both recorded at the same bus of a power system. By maximising VPSI under load changes, one can obtain information concerning the S _SC. Then, the loadability value can be calculated based upon S _SC. The results demonstrate that a simple relation between the S _SC and power load can be used to determine the loadability of the power system. This work highlights the advantage of obtaining the loadability in S _SC parameter space because system changes or load changes produce the same effect into the S _SC domain, allowing better determination of the maximum loadability.

This study proposes an efficient and accurate method for updating measurements weight in a distributed multi-area power system state estimation. In general, a power system state estimation is formulated in a weighted least squares (WLS) problem where the selection of weights for various types of measurements is one of the key factors for maintaining the accuracy of state estimation. The authors develop a weight updating algorithm based on the proposed scheme in a distributed state estimation. In the proposed scheme, which includes pseudo measurements to enhance the measurement redundancy at the local and the global levels, the developed weight update approach along with the weight adjustment equations for pseudo measurements can improve the accuracy and convergence speed of the measurements weight updating. A simulation study is performed in the IEEE 30-bus and 118-bus systems, and the results demonstrate the advantages of the proposed approach over the conventional approach in terms of the capability for bad data detection as well as the accuracy of the updated weight and estimation solution and the convergence speed.

This study introduces a quick, highly efficient and a single sensor based maximum power point (MPP) tracking (MPPT) for partially shaded solar photovoltaic (PV) system. For this purpose, a novel ‘human psychology optimisation’ (HPO) algorithm is proposed, which is based on psychological and mental states of an ambitious person. The main objective of the HPO algorithm is the maximum extraction of the power from PV panel and efficiently supplying it to the load (battery). In this study, a single (current) sensor based MPPT for battery charging, by using HPO and some recent state-of-the-art MPPT algorithms, is tested on MATLAB simulation and verified on a developed prototype of the partially shaded solar PV system. The efficient battery charging and quickly reaching the MPP by HPO w.r.t. all other algorithms, in steady-state as well as in dynamic conditions, show the superiority over all the recent state-of-the-art control methods. Moreover, due to the single sensor, the cost of the MPPT system is reduced, as well as due to HPO the computational burden is very less, so it can be easily implemented on the low-cost microcontroller.

One major concern in using over current relays (OCRs) is their coordination in power system protection to decrease the pressure of electrical equipment and avoid mal-trip in the primary and backup relays. The issue has recently become more challenging with the increasing use of distributed generation (DG). This study proposes the use of firefly algorithm (FA) to achieve an optimised coordination of OCRs in power system protection when DG is present in the system. Typically, the FA is done by selecting plug setting and time setting multiplier parameters. However, the algorithm associated with such method requires a long convergence time and has the risk of getting trapped in local optima. Therefore, an adaptive modified FA (AMFA) has been developed to overcome these issues and obtain the optimised coordination of OCRs. The AMFA is tested in five case studies of a power system with DG whose results are then compared with those obtained from the conventional and FA methods. The results demonstrate that the proposed AMFA is able to achieve the optimised coordination of OCRs in all test cases with significant improvement in time reduction reaching 40.446%.

This study presents calculation of fundamental frequency-based per phase digital impedance pilot relaying (DIPR) scheme for static synchronous compensator (STATCOM) compensated transmission line (TL) using two end synchronised measurement. DIPR involves computation of absolute value of ratio of estimated phasor sum of voltages to the phasor sum of currents of both ends. DIPR inherently differentiate between internal and external faults on the line. For all internal faults, computed value of DIPR ratio is equivalent to system and TL impedance value whereas for external faults, it is equal to line capacitance impedance value. This novel pilot relaying scheme is easy to set once the system parameters are estimated and has the ability to detect all types of faults and correctly classify faulty phase with mid-point connected STATCOM on TL. This scheme is immune to effect of STATCOM compensation mode, level of injection and its dynamic response. Also it is not affected by line charging capacitive current and fault transient resistance. The fault distance is estimated using the STATCOM current injection information for various types of fault with high accuracy, considering maximum fault resistance of 20 Ω. Accuracy and effectiveness of this scheme is evaluated in EMTDC/PSCAD simulation for 230 kV, 300 km, mid-point STATCOM compensated TL and in hardware setup with mid-point STATCOM on 100 V supply voltage having 200 km TL in offline mode. Results bring out the robustness, reliability and superiority of proposed novel pilot relaying scheme with fault location algorithm.

This study presents an iterative algorithm for modelling the mean-risk model with the conditional value at risk (CVaR). The algorithm is based on the Lagrangian relaxation decomposition, and its main advantage is that it allows removing the coupling between the scenarios due to the constraints used to model the risk. At each stage of the algorithm, a risk-neutral stochastic optimisation problem is solved with the risk-adjusted probabilities that substitute the original ones. The study presents the application of the proposed iterative CVaR algorithm to two different short-term problems where the decision makers are exposed to a high volatility of electricity spot market prices. In the first problem, a time horizon of 1 week is taken into account and a future physical contract is employed as a hedging mechanism. The second problem includes a very detailed formulation of the unit commitment problem. The numerical application is based on realistic data of the Iberian electricity market, where the algorithm has shown a good performance in terms of accuracy and computational time. In addition, this study provides a criterion for selecting the value of the parameters used to implement the CVaR model.

Day-ahead market clearing is usually executed by independent system operator to determine the accepted energy and reserve bids and their payments. In this study, an effective multi-objective stochastic framework is presented for joint energy and reserves market clearing problem considering the power system security. To this end, the 24 h scenarios are generated using the Monte Carlo simulation (MCS). Besides, a scenario reduction technique is also presented to reduce the computational burden of the proposed stochastic market clearing procedure. A new validation method based on MCS which is called MCVM method is proposed to verify the proposed strategy against the deterministic model. Direction scalarisation method (DSM) is proposed to solve the proposed multi-objective problem. A new method as the combination of gravitational search algorithm and primal-dual interior point method is employed to solve the proposed single-objective optimisation problem obtained by the DSM. IEEE 24-bus test system is used to address the effectiveness of the proposed framework.

Multiple-circuit transmission lines combining different voltage levels in one tower present extra challenges when setting a protection philosophy, as faults between voltage levels are possible. This study presents a detailed theoretical analysis of such combined faults, including the development of a formula for estimating the magnitude of the short-circuit current. It is demonstrated that if the faulted phase from the higher voltage level leads the faulted phase from the lower voltage level, a distance relay at the higher voltage level sees the fault in the forward direction, whereas a distance relay at the lower voltage level sees the fault in the reverse direction. The opposite happens if the lower voltage level leads the higher voltage level. It is also demonstrated that the magnitude of fault currents of combined faults is normally slightly larger than of equivalent single-phase-to-ground fault at the higher voltage level. Part II will continue the research work and focus in the fault loop impedance RX diagrams.

Multiple-circuit transmission lines combining different voltage levels in one tower present extra challenges when setting a protection philosophy, as faults between voltage levels are possible. In this study, the fault loop impedance of combined faults is compared with the fault loop impedance of single-phase-to-ground faults and it is demonstrated that they are similar for high short-circuit powers; however, the fault loop impedance of a combined fault may increase substantially as the short-circuit power of the system decreases, a behaviour that is less noticeable for single-phase-to-ground faults. It is also demonstrated that the fault loop impedance of combined faults is more resistive, when compared with equivalent single-phase-to-ground faults. It is concluded that the settings used to protect a line against single-phase-to-ground faults are capable of protecting the line against combined faults, being advised to increase the resistive limit of the protection zone, if the network has lower short-circuit power. It is recommended to assure that the fault can only happen for cases where the faulted phase from the higher voltage level leads the faulted phase from the lower voltage level, if the length of the line at lower voltage level is smaller than of the line at higher voltage level.

This study presents a market model that procures energy and performance-based regulation services simultaneously considering the participation of energy storage devices. The correlations of energy, regulation capacity, and regulation mileage are explicitly demonstrated. The proposed market model determines the energy schedule of generation units, charging and discharging profiles of energy storage devices, and the schedule of regulation services. Market clearing prices for energy, regulation capacity, and regulation mileage are derived and decomposed through Lagrange multiplier analysis. The relationships between the clearing prices of different market products are analysed. The proposed market model is tested and verified with the IEEE 30-bus system.

This research work introduces a new hybrid technique called quasi-Newton back-propagation based icosϕ control algorithm. Its structure is constructed on the concept of biological features like input neuron, target neuron, weight correction and more attractive due to its parallel computing, learning capability behaviour. Systematic step-by-step procedures are represented by mathematical equations in the MATLAB/Simulink platform. The fundamental weighted values of active and reactive power components of load currents are extracted using the proposed control technique to generate the reference source currents. Further, the reference source currents are used to generate switching pulses for voltage source converter (VSC) of the distributed static compensator (DSTATCOM). It is capable enough to perform several functions such as harmonic mitigation, power factor correction, load balancing and voltage regulation which further reduce the DC link voltage across the self-supported capacitor of the VSC. Simulation and experimental validation demonstrates better performance of the suggested algorithm for operation of the DSTATCOM at different loading conditions.

Since the power system is actually a continuous-discrete hybrid system jointly driven by continuous time and random discrete events, a Markovian switching model of AC/DC power system is established to reflect the operating state of the system. Based on the model, a novel non-linear DC modulation control with time-delay compensation is derived to improve the transient rotor-angle stability of the entire AC/DC power system. The main contributions are: (i) the external events are described as Markovian jumps in system model parameters to reflect the random discrete characteristic of system operating. Meanwhile, the Markovian state transition rates are replaced by the outage rates and repair rates, which avoids expensive computation when the numbers of system operating modes are large; (ii) The time delays are regarded as a kind of bounded disturbance depending on system state and input. By a robust compensation control, the negative influence of time delay disturbance can be eliminated. Simulation performed on a dual-infeed AC/DC system shows the effectiveness of the proposed method in improving the transient stability of the power system.

This article has been withdrawn as the incorrect text was uploaded due to a technical error.

In this study, a sliding mode controller (SMC) is designed to regulate rotor speed, and therefore generated power of a doubly-fed induction generator-based wind turbine. The designed controller is able to compensate for the uncertainty arising from non-linear and un-modelled dynamics, reject wind turbulence disturbance, and effectively keep the rotor speed and produced power close to a nominal value. Since the chattering phenomenon increases the control activities and excites unwanted high-frequency dynamics of a system and even in some cases, causes system instability; therefore, a fixed boundary layer is used to avoid the chattering. The simulation results show the considerable superiority of the designed SMC in comparison with the conventional proportional–integral (PI) controller and the PI controller calculated through optimal control method. Improving dynamic characteristics, reducing the maximum amplitude of oscillations, and increasing the convergence speed of the states are achieved in this research.

This study proposes a distributed model predictive control (DMPC) scheme for the load frequency control (LFC) problem of the multi-area interconnected power system in the presence of wind turbines (WTs). The distributed model predictive controller is designed by formulating the LFC problem as disturbance attenuation problem in the presence of both external disturbances and constraints which represent load reference setpoint, generation rate constraint (GRC) and control input constraints of the WT, respectively. The frequency response model of three-area power system concerning the aggregated WT model is introduced, in which the WT model is integrated into the interconnected power system to participate in LFC as a part of the power system. Simulation and analysis results for the three-area interconnected power system with WTs indicate possible system performance improvements, while satisfying the physical hard constraints.

Mathematical analysis indicates that stator output power of doubly fed induction generator (DFIG) could be directly controlled by the output voltage of rotor-side converter (RSC). Thus, a direct stator-power controller (DPC) could be induced. Furthermore, rotor speed can be directly controlled by RSC with direct rotor-speed controller (DSC). When the rotor speed is selected as a feedback of RSC controller, the equivalent impedance of RSC could be decreased sharply. Under this condition, DFIG will supply little energy for series resonance caused by fixed series compensation. This results in that DFIG with DSC is insusceptible to subsynchronous control interaction (SSCI). Updating DLP into DSC could be selected as a solution of existing SSCI. Eigenvalue analysis and time-domain simulations prove the effectiveness of DSC in mitigating SSCI.

This study proposes an improved coupled single-port method for the assessment of voltage stability based on phasor measurement unit (PMU) data. The impedance matching condition, i.e. the condition that the local load impedance and the Thévenin equivalent impedance are equal in magnitude at the loadability limit point, has been a fundamental assumption of many existing studies on voltage stability assessment. However, it is shown in this study that the impedance matching can happen either before or after the loadability limit point in certain cases. The authors have proven that the inaccuracy of the conventional impedance matching condition is due to the time-varying equivalent parameters of a power system. To deal with the dynamic nature of grid equivalence, they propose an innovative method to improve the conventional coupled single-port method. In the new method, voltage magnitude-to-load consumption sensitivity is used to adjust the equivalent parameters calculated by the coupled single-port method. Compared to conventional methods, the proposed method requires fewer PMU measurements and provides more accurate margin estimates. Case studies on extensive test systems validate the accuracy of the proposed method. The comparison between the conventional coupled single-port method and the developed method is also provided to demonstrate the effectiveness of the new method.

The rationalisation of the territorial resources leads to consider carefully the possibilities of using motorway and railway infrastructures (existing or planned ones) for cable line installation within them. The full compatibility of such synergy ‘transport – electrical power transmission’ involves different branches of engineering. The study provides an overview of the research undertaken for a fully reliable use of this combination. The manuscript aims at highlighting a procedural approach that should be followed in order to analyse all the key elements involved in the safe operation of power transmission lines hosted in transport infrastructures. First, the geometrical compatibility between different types of power transmission technologies, (i.e. gas insulated lines and high-voltage direct/alternating current insulated cable lines), and transport infrastructures (i.e. motorway galleries, railway galleries and railway prospection tunnels) is considered. Subsequently, the behaviour and magnitude of the magnetic field generated by the different power transmission technologies inside the transport infrastructures are presented. Moreover, the study analyses the effects of a phase-to-screen short circuit that could occur inside the hosting facility. Finally, an analysis of the reliability of the synergy between power transmission systems and transport infrastructures is discussed.

One of the most important tools for condition monitoring is the gas chromatography test of transformer oil, which is known as dissolved gas analysis (DGA). In this research, the DGA results of >3000 power transformers operating in Iran's power grid were carefully studied and from among them, the results related to transformers suspicious of being faulty were used to validate the fault detection accuracy of the presented fuzzy inference system (FIS). In most of the previously published papers, the detection and isolation of transformer faults has been based on one or two of the following parameters: absolute concentrations of free and dissolved gases in transformer oil, total dissolved combustible gases, total combustible gases, ratios of some gases to each other, and the rates of gas increase. However, in this research, most of these parameters have been used for fault detection and isolation, according to the IEC 60599 standards. Also, no attempt has been previously made to detect the decomposition of insulation papers of transformers; but the presented FIS is able to detect this fault as well. The overall performance accuracy of the presented system is F1 = 91.2%, which seems to be a suitable value.