The operation and the behaviour of grounding systems are defined by some fundamental parameters: the rate of change in soil resistivity, the type and the size of grounding systems. The continuous improvement in designing these systems guarantees the maximum safety of people and electrical facilities. In the last decades, the usage of ground enhancing compounds (GECs) for soil alleviation and decreasing the ground resistance value becomes more and more popular in engineering field, particularly in electric power systems (transmission and distribution facilities) and in electric railway. This study provides an overview of the past and recent research, carried out on GECs, based on published scientific work during several decades. It includes computational and experimental work on these materials, both at steady-state operation and under impulse conditions, from all over the world, and cites the most distinguish applications on grounding systems. It also refers to international standards that specify the requirements and tests for GECs producing low resistance of a ground termination system. This work aspires to be a useful guide to engineers and researchers who study, design and construct grounding systems using such materials for the optimisation of their operational performance.

Under frequency load shedding (UFLS) as a special protection scheme is executed to arrest declining frequency. The setting parameters of a multi-stage load shedding plan are determined using a discretised model of dynamic system frequency response considering uncertainty of generation loss. The proposed probabilistic UFLS plan is formulated as a mixed integer linear programming optimisation problem to minimise the expected amount of load curtailment. The uncertainty of the proposed discretised dynamic load shedding plan is modelled using the point estimate method, and the obtained results are compared with those of the Monte-Carlo simulation method (MCSM). The utilised point estimate technique converts the continuous probability distribution functions of the uncertain parameter (i.e. the generation loss) to discrete statistical moments. The proposed probabilistic UFLS is solved using the BONMIN solver. The performance of the proposed dynamic UFLS plan is investigated for the IEEE 39-bus test system.

Optimal capacitor placement in distribution systems has been studied for many reasons such as the improvement of voltage profile, mitigation of total harmonic distortion, and reduction of power losses. In this study, a new approach is presented for capacitor placement in the presence of harmonic distortion along with a proposed resonance index (RI). In this approach, a sensitivity analysis is first applied to find candidate buses. After that, the size and location of capacitors are optimised by a proposed fitness function. The fitness function includes a fuzzy membership function of annual net benefit, maximum THD of voltage, maximum voltage deviation, and a resonance constraint. This procedure supports different load levels employing fixed and switched capacitors. Also, a new RI is presented to prevent resonance conditions. Finally, the approach is tested on an IEEE 18-bus and an IEEE 69-bus system using the multi-swarm particle swarm optimisation algorithm. The simulation results show the efficiency of the method in comparison with the other methods.

This study presents a new function-based modulation control technique for modular multilevel converters (MMCs). The main contribution of this study is the formulation of two new modulation functions for the required switching signals of the MMC's upper and lower sub-modules, respectively. The output and circulating current equations of the converter are employed to attain the arm's currents which are utilised for the proposed modulation functions, which have two important features: (i) it is much less complex compared to the existing control methods of MMC; and (ii) the proposed controller can be regulated properly to deal with parameter variations in a bid to ensure stable and accurate performance. In this controller, the MMC output current magnitude and phase angle required for special active and reactive power sharing can be easily applied to the modulation functions. Also, the equivalent capacitors of upper and lower sub-modules are discussed based on the proposed modulation functions. Finally, simulations are performed in Matlab/Simulink environment to evaluate the performance of the proposed control technique in both the dynamic conditions of load as well as varying parameters.

This study reports on investigations aiming to determine by numerical simulation the effect of space charges on the electrical and electromechanical constraints in microcavities contained in high-voltage cables insulation. The simulation is based on the numerical resolution of the Poisson equation by the finite element method. The authors calculate the electric field and they determine the electrostatical pressure for various space-charge density values. The elongation of microcavities is calculated for appreciating the effect of the electrostatical pressure on the walls of the cavity. The role of homocharges and heterocharges on constrains is studied and results of the simulation are in agreement with published technical literature.

In AC–DC parallel systems, line-commutated-converter (LCC)-based high-voltage direct-current (HVDC) emergency control strategy can improve the stability of the power system. This study proposes an LCC HVDC emergency control strategy that utilises the global information measured by wide-area measurement systems. The design of the proposed LCC HVDC emergency control strategy takes advantage of dynamic surface control and adaptive control. The Lyapunov stability analysis is used to prove that the AC–DC parallel system is uniformly ultimately bounded in the presence of the uncertainties. A two-area four-generator AC–DC parallel system is developed in PSCAD/EMTDC to verify the effectiveness and correctness of the proposed strategy. Simulation results show that the proposed LCC HVDC emergency control strategy can improve the stability of an AC–DC parallel system and is robust. Its superiority is demonstrated by comparing the proposed method with controllers designed using backstepping technique and pole placement technique.

As the large-scale wind power penetration and distributed generation become popular in modern power systems, the governing control of pumped storage unit has attracted many attentions in recent years for its flexible power adjustment capability. To provide a research platform for dynamic analysis of the hybrid power system, a micro-grid mainly including a pumped storage unit and a wind power plant is introduced in detail and taken as the system plant. Refined mathematical models of pump turbine, synchronous generator and wind turbine generator have been established considering the complicated non-linear dynamic characteristics of the multi-energy power system. Furthermore, a novel chaotic grey wolf optimiser algorithm is proposed to select the optimal control parameters of the pump turbine governing system for the sake of maintaining frequency stability and enhancing control performances under the complicated operating conditions. Simulation experiments have been conducted in the micro-grid under representative operating conditions to validate the effectiveness of the proposed control method and its preponderance in comparison with traditional ones.

In this research article, a maiden approach of hybrid adaptive ‘gbest’ guided gravitational search and pattern search (hGGSA-PS) optimization method are proposed for load frequency control (LFC) of multi-area interconnected power system considering the nonlinear effect of generation rate constraint (GRC). At first, the two area single stage thermal–thermal power system with conventional proportional integral derivative (PID) controller is analyzed and the parameters of the PID controller are optimized by the proposed technique. Initially, the ‘gbest’ guided gravitational search algorithm (GGSA) using integral time absolute error (ITAE) fitness function is used and then pattern search (PS) technique is employed to fine-tune the obtained best solution from the GGSA. The supremacy of the hGGSA-PS optimized PID controller is presented by comparing its results with other modern soft computing techniques. Later in order to demonstrate the robustness of the proposed controller, the sensitive analysis is performed. Finally, the proposed technique is extended to a two area multi-source power system. The parameters of the controller for each area are optimized using the novel hGGSA-PS technique. From the simulation results, it can be seen that the proposed technique has superior performance than the prior results with lesser settling time and different performance index values.

Due to the gradual exhaustion of petroleum-based energy resources and severe concern for environmental protection, renewable energy (RE) resources and demand response (DR) techniques have been wide deployed in power network. However, the insufficient management as well as technology bottleneck becomes the major obstacle in their further development. Based on the uniform clearing of electricity market, a centralised dispatch model of virtual power plant (VPP) is introduced to improve the competitiveness of distributed energy resources in electricity market. To neutralise the side effect of RE penetration, a bidding strategy optimisation model considering DR and the uncertainty of RE for VPP is proposed and numerical analysis is conducted to prove its applicability. In addition, scenario analysis method is applied to deal with the influence of elastic demand and potential risk, which are associated with utility users’ consumption patterns and VPP's bidding preference, respectively. The application of distributed algorithm into multi-players’ strategy optimisation problem accelerated the convergence of bidding procedure, which verifies the applicability and effectiveness of the proposed models. Furthermore, numerical case studies demonstrate the distinctive superiority of VPP in the integration and management of RE and DR resources, which in turn contribute to its advantage position in electricity market.

In this study, a Pelton turbine and governor system dynamic model with deflector control was developed. The Pelton turbine established reasonable parameters for the deflector control model to effectively restrain unit frequency rise, which played the role of a similar thermal power overspeed protection. Since a Pelton turbine typically contains multiple needles, the concept of average needle opening was employed in the model. An improved orthogonal learning biogeography-based optimisation (IOLBBO) algorithm, which adopted good point set to initialise habitat, elites to maintain the tactics, and an orthogonal learning strategy to improve global search capabilities, was developed. The parameters were identified with the IOLBBO algorithm based on measured data. To develop the model in this study, various types of Pelton turbine and governor system models with different refinement degrees were analysed. Large fluctuations, like a load rejection process, verified the validity of the established deflector control model. Additionally, digital deflector control characteristics were achieved by computer programming. The non-linear Pelton turbine and water diversion system model with an elastic water hammer model that considered a non-linear relationship between the average needle opening and mechanical power developed in this study demonstrated superior simulation results in power system stability analysis.

This study presents a variational mode decomposition (VMD)-based approach to analyse wide-area (WA) measurements based signals. The commonly used empirical mode decomposition (EMD) has limitations such as sensitivity to noise and sampling rate. However, VMD is an entirely non-recursive algorithm, where the modes are extracted concurrently. These modes help in extracting dynamic patterns of different power system disturbances. The performance of the proposed scheme is extensively validated on the IEEE-39 bus New England test system. The modes generated and the frequency deviation contours of the disturbances including generation loss, fault and line outage are assessed using VMD and the results provide improved performance in terms of decomposition quality compared with the existing EMD technique. Furthermore, a data-mining model known as decision tree is used to classify different power system disturbances based on intrinsic mode functions generated through VMD. The suggested method shows improved decomposition quality and classification accuracy. Thus, the proposed scheme is a potential candidate for improving WA situational awareness along with a post-mortem analysis of real events occurring in a power system.

In this study, a novel fuzzy logic control scheme is investigated for the frequency and power control of an isolated hybrid power system (HPS) (IHPS) and HPS-based two-area power system. The studied IHPS comprises of various autonomous generation systems such as wind energy, diesel engine generator and an energy storage device (i.e. capacitor energy storage device). A novel fractional order (FO) fuzzy proportional-integral-derivative (PID) (FO-F-PID) controller scheme is deployed and the various tunable parameters of the studied model are tuned by quasi-oppositional harmony search (HS) (QOHS) algorithm for improved performance. The QOHS algorithm (based on standard HS algorithm) accelerates the convergence speed by combining the concept of quasi-opposition in the basic HS framework. This FO-F-PID controller shows better performance over the integer order-PID and F-PID controller in both linear and non-linear operating regimes. The proposed FO-F-PID controller also shows stronger robustness properties against loading mismatch and different rate constraint non-linarites than other controller structures.

A novel unified power flow controller (UPFC)-based line overload control is presented in this study for power system security enhancement. The line loads of the transmission lines are monitored in real-time operation and are controlled within their thermal limits through a feedback dynamic control of the UPFC. Firstly, the relationship between the line load of a transmission line and the active power setting of the UPFC is deduced. Secondly, the control law of the line overload control is developed, which adjusts the active power setting of the UPFC intelligently in case of line overloads. Thirdly, the implementations of the above control law are also provided. Using PSS/E, the case study is run in the Nanjing Western Power Grid, where the world's first modular multilevel converter-based UPFC project, the Nanjing UPFC project, is located. The validity of the proposed line overload control is proved by the case study. The case study also indicates that the proposed line overload control is still valid with a 0.2 s delay, which further confirms the feasibility of the line overload control in practical engineering.

This study addresses the impact of ultra-capacitor (UC) on load frequency control of a restructured two-area multi-source system, incorporating conventional thermal and solar thermal power plant (STPP). The thermal system consists of single reheat turbine, appropriate generation rate constraint and governor dead band. Two generating companies and distribution companies are considered in each area. Maiden attempt has been made to use a cascade combination of integer-order (IO) proportional–integral–derivative with filter and fractional-order proportional–derivative (PIDN-FOPD) controller. Performance comparison of some commonly used IO controllers with proposed PIDN-FOPD controller reveals superiority of the latter in terms of peak deviations and settling time in policy schemes like poolco, bilateral and contract violation. A more recent optimisation technique called Whale optimisation algorithm (WOA) is successfully used for simultaneous optimisation of above controllers. Effect of UC using PIDN-FOPD has been studied for above policy schemes and analysis explores that use of UC improves the system dynamics. Sensitivity analysis reveals that WOA optimised PIDN-FOPD gains and system parameters are robust. It is also proved that PIDN-FOPD parameters obtained at nominal distribution companies participation matrix (DPM) are fit enough and parameters need not be optimised for change in DPMs.

Comprehensively considering the operation cost and safety constraints of nuclear power, an optimal operation scheme of large-scale nuclear power plant participating in peak load regulation of power system is proposed. After quantitatively analysing the peak load regulation cost of nuclear power, the optimal objective is set to minimise the total operation cost including the fuel cost, the start–stop cost, and the peak load regulation cost. On the basis of the normal constraints of power scheduling, safety constraints of the nuclear power unit's daily output performance and power characteristic constraints of the pumped storage unit are considered. The mixed integer programming method is used to achieve the solution of the optimal operation scheme. Simulation results from a regional power system show that the proposed optimal operation scheme can effectively reflect the real characteristic of nuclear power and apply to power dispatching analysis under the background of the large-scale access of nuclear power. In comparison to other two typical schemes of peak load regulation, the proposed optimal operation scheme of peak load regulation is more economic and efficient.

To take advantage of line commutated converter (LCC) and voltage source converter high-voltage, direct current (HVDC) technologies a hybrid multi-terminal HVDC (MTDC) is designed to exploit the power from renewable resources. A previous study showed that the voltage dependent current order limiter (VDCOL), an emergency function to reduce the current order of an HVDC converter station when voltage is depressed, should be installed in all of the LCC stations of the hybrid MTDC. This study presents a design for a master self-tuning VDCOL function implemented in a hybrid multi-terminal HVDC system. This controller aims to generate an adaptive current reference for each LCC station of the VDCOL in a low-voltage condition. The parameter of this adaptive VDCOL can be chosen according to the summary table of practical experiences; therefore, no tuning technique is required. The developed HVDC control algorithm is implemented on the simplified South East (SE) Australian 14 generator system using DIgSILENT PowerFactory. The simulation results demonstrate the effectiveness of the proposed control function in reducing the complexity of the control system and operation along with improving system transient stability.

It has been decades since automation was introduced to electrical networks, yet it has not found its right place in the distribution level. One of the main obstacles in the path of automating electricity distribution system is the amount of investments needed for its implementation. This study presents a novel idea for distribution automation (DA) implementation planning, in which the sequence and timings of installing automatic switches are optimised, to exploit periodical savings and to minimise the total externally financed investment. The planning optimisation problem is formulated and solved in a mixed-integer non-linear form. The monetary value of periodical savings depends on several factors including network size, type of the distribution system operator, local regulations etc. To include all these factors, a scenario-based method is developed to test the proposed method. Finally, the method proposed is tested on parts of the network covered by Tehran Vicinity Electricity Distribution Company as well as bus number four of Roy Billinton test system. The results show that a considerable part of investments needed for DA can be financed through exploiting periodical savings of DA, in a reasonable time, thus a partial self-sufficiency can be reached for DA project financing.

Power transformer optimal design (PTOD) is a complex multi-objective optimisation problem. Due to large variables search space, most optimisation methods proposed in literature for PTOD are prone to find local minimum instead of the global one. To prevail over the aforementioned problem, this study aims to propose a new heuristic algorithm combined with mixed-integer non-linear programming (MINLP), and also, some modifications to conventional PTOD procedure. Some promising features of the proposed method in comparison to the previously proposed methods are (i) it considers more design variables as a gene for transformer constructing chromosome (TCC), (ii) before building the main TCC, it divides the PTOD algorithm into some sub-algorithms and starts to construct some sub-chromosomes with lower number of genes as parts of the main TCC, which allows us to detect improper genes based on a sensitivity analysis and design constraints, (iii) not only it considers technical and consumer constrains, but it also take manufacturing constraints into account, (iv) MINLP is used to find global optimum point, and (v) the validity of obtained optimal solution is further assessed by presenting comprehensive finite-element method (FEM) and experimental result.

In this study, a new method using graph theory and analytical hierarchy process (AHP)-based multi-criteria decision making approach has been proposed to solve optimal phasor measurement unit (PMU) placement (OPP) problem for complete network observability. The proposed approach assures maximum measurement redundancy too. A decision matrix is formed with some unique criteria from the concept of network graph theory and this helps to formulate priority vertex ranking using AHP. Candidate vertex search technique is used to enumerate the candidate PMU placement vertices from priority vertex ranking. The contribution of zero injection buses (ZIBs) in PMU placement problem has been considered. The proposed technique is further analysed for complete observability under single PMU loss or line outage cases. The proposed approach is tested on IEEE 14-bus, 24-bus, 30-bus, 57-bus, 118-bus, and New England 39-bus systems. To verify the computational efficiency and higher redundancy of solutions of the proposed method, the results are compared with some well-established methods reported in the literature. The proposed method is further applied to IEEE 300-bus, Polish 2383-bus and 3120-bus system to show the efficacy of the proposed approach in solving OPP in large scale power systems.

The penetration of large-scale renewable generation leads to a shortage of primary frequency regulation resources as well as increasing regulation demand. By exploiting the thermal capacity of buildings, the authors achieve linear power–frequency characteristics comparable to turbine droop control via clustering a number of air-conditioning units (ACs) to participate in primary frequency regulation without affecting indoor comfort. Due to the bandwidth limitations and latency in communication, the real-time centralised control method face great challenges. This study proposes a two-level coordinated state-estimation method to reduce the coordination burden, in which a central coordinator and local controller for each AC are involved. The central coordinator periodically gathers the working state of every AC and estimated thermal parameters individually, then broadcasts this identified model parameters – the coordination information – to each local controller. Resorting to a state-estimation method considering the coordinated information and local measurements, local controller determines whether to toggle the state of local AC to realise a fast frequency response. Simulation results show that the approach can effectively manage a large number of ACs with heterogeneous parameters to provide a primary frequency regulation service without inducing a rebound effect.

Recent trends have shown that the power quality has been adversely affected due to increased power electronics based devices at the utility grid in the distribution system. Suppression of harmonics and reactive power current compensation at point of common coupling (PCC) improve the power quality using distribution static compensator (DSTATCOM). The development of new control algorithm based on adaptive Volterra second-order filter (AVSF) for DSTATCOM to extract the fundamental power current components from the polluted load current of non-linear load in distribution system is presented in this study. The AVSF is a combination of linear and non-linear functions of the input signals. Both linear and quadratic functions optimise filter coefficients with fast convergence, which is quite important in the success of an adaptive solution. The proposed algorithm is also related to autocorrelation matrix and step size, which are used for rapid convergence. The performance of proposed algorithm for DSTATCOM is validated through experimental results for unity power factor of AC source and zero voltage regulation of the terminal voltage at PCC.

This study presents the performances of two discretisation schemes which are implemented in a novel multilevel Monte Carlo (MLMC) method for reliability calculation of power distribution systems. The motivation of using the proposed approach is to reduce the computational effort of standard Monte Carlo simulation (MCS) and accelerate the overall distribution system reliability evaluation process. The MLMC methods are implemented through solving the stochastic differential equations (SDEs) of random variables related to the reliability indices. The SDE can be solved using different discretisation schemes. Two different discretisation schemes, namely Euler–Maruyama (EM) and Milstein are utilised in this study. For this reason, the proposed MLMC methods are named as EM-MLMC and Milstein MLMC. The reliability evaluation efficiency of the methods is analysed and compared based on accuracy and computational time saving for basic reliability assessment of Roy Billinton test system. Numerical results show that both methods reduce the computational time required to estimate the reliability indices compared with the same discretisation schemes used in MCS and maintain satisfactory accuracy levels.

This study presents synchrophasor assisted protection scheme for the protection of long transmission line compensated with shunt flexible AC transmission system (FACTS) device. With the advancement in synchrophasor technology, data communication medium, and wide area measurement system for transmission line protection, the differential protection scheme is a most suited scheme over the over-current, distance and directional protection schemes. The proposed scheme discriminate between internal and external fault using the time synchronised voltages and currents of both the terminal of the transmission line. The performance of proposed scheme has been evaluated on IEEE 12 bus FACTS benchmark power system model implemented in PSCAD/EMTDC. The measured voltage & current signals are pre-processed and phasors are estimated through DFT algorithm in MATLAB. The performance remains unaffected during wide variation in fault and system parameters including different line length and static var compensator rating. The test results confirm the selective, simplicity, high speed, sensitivity, and robustness of the proposed protection scheme. This scheme is also able to distinguish the faulty phase(s) from healthy phases, which enables the single-pole tripping option. Finally, comparative evaluation of the proposed technique with the existing protection schemes clearly shows its superiority.

A transactive energy framework can provide an integral management scheme that facilitates power delivery with high efficiency and reliability. To close the gap between wholesale and retail markets, this study presents a two-stage optimal scheduling model for distributed energy resources in the form of a virtual power plant (VPP) participating in the day-ahead (DA) and real-time (RT) markets. In the first stage, the hourly scheduling strategy of the VPP is optimised, in order to maximise the total profit in the DA market. In the second stage, the outputs of the VPP are optimally adjusted, in order to minimise the imbalance cost in the RT market. The conditional-value-at-risk is used to assess the risk of profit variability due to the presence of uncertainties. Furthermore, formulated two-stage models are solved by the enhanced particle swarm optimisation algorithm and a commercial solver. Case study results show that the proposed approach can identify optimal and accurate scheduling results, and is a useful decision-making tool.

The problem of large disturbance attenuation in the single-machine infinite-bus system with a static synchronous compensator (STATCOM) is proposed to be alleviated by an improved robust backstepping algorithm, which utilises error compensation and sliding mode variable structure control methods to achieve stability. For STATCOM systems with internal and external disturbances, the adaptive backstepping method is used to construct the storage function, and a non-linear gain interference rejection controller and parameter substitution law are applied simultaneously. The improved method differs from the traditional adaptive backstepping design in terms of error-compensation design methodology, in order to ensure robustness and insensitivity to large disturbances of the STATCOM system, and furthermore, preserving useful non-linearities and the real-time estimation of uncertain parameters. Finally, a simulation demonstrates that the improved method is more efficient than traditional adaptive backstepping with respect to the speed of adaptation and the response of the STATCOM system. Hence, the effectiveness and practicality of the proposed control method is demonstrated by engineers in applications.