Abstract:The requirement for reliable electrical energy supply increases continuously because of its vital role in our lives. However, events due to various factors in the power grid can cause energy supply to be interrupted. One of these factors is human error and thus human reliability analysis is a serious element in the industry. The first step is to identify the roots of human error, on which there has been limited research in this area. In this paper, the potential and actual causes of human error in maintenance teams of power transmission system protection are identified and predicted within a framework of human factors analysis and classification system method. Then, human error factors are ranked to help improve human reliability. The proposed method is implemented in the Fars Electricity Maintenance Company.

Abstract:The electric vehicle (EV) charging station is a critical part of the infrastructure for the wide adoption of EVs. Real- time simulation of an EV station plays an essential role in testing its operation under different operating modes. However, the large numbers of high-frequency power electronic switches contained in EV chargers pose great challenges for real-time simulation. This paper proposes a compact electromagnetic transient program (C-EMTP) algorithm for FPGA-based real-time simulation of an EV station with multiple high-frequency chargers. The C-EMTP algorithm transforms the traditional EMTP algorithm into two parallel sub-tasks only consisting of simple matrix operations, to fully utilize the high parallelism of FPGA. The simulation time step can be greatly reduced compared with that of the traditional EMTP algorithm, and so the simulation accuracy for high-frequency power electronics is improved. The EV chargers can be decoupled with each other and simulated in parallel. A CPU-FPGA-based real- time simulation platform is developed and the proposed simulation of the EV station is implemented. The control strategy is simulated in a CPU with 100μs time-step, while the EV station circuit topology is simulated in a single FPGA with a 250 ns time-step. In the case studies, the EV station consists of a two-level rectifier and five dual-active bridge (DAB) EV chargers. It is tested under different scenarios, and the real-time simulation results are validated using PSCAD/EMTDC.

Abstract:Phasor measurement units (PMUs) are preferred for installation at weak buses in a power network. Therefore, the weak buses need to be located and the strategic locations of PMUs identified to ensure network observability. Thus, the primary aim of this work is to identify the placements of the maximum number of PMUs installed at the weak buses in the electrical network. The voltage collapse proximity indicator, line stability index, fast voltage stability index, and a new voltage stability indicator utilizing load flow measurement are used to determine the weak buses. A novel deterministic methodology based on a binary-integer linear programming model is then proposed to determine the optimal locations of PMUs. The effect of a single PMU outage considering the weak buses is also demonstrated. The effectiveness of the developed approach is tested and validated on the standard IEEE 14-, 118-, 300-, and New England 39-bus systems. The obtained results are also compared to those using different weak bus methodologies.

Abstract:For AC transmission lines connected to an LCC-HVDC inverter station, commutation failure can lead to the wrong operation of traditional protection. To solve the problem, this paper proposes a fast protection scheme using transient information from one end of the AC line. The boundary frequency characteristics of the AC line connected to LCC-HVDC inverter are analyzed first. This reveals the existence of significant attenuation on both high frequency signals and some specific frequency signals. Based on the boundary characteristics, a novel boundary protection principle utilizing a backward traveling wave is then proposed. A PSCAD/EMTDC simulation model of a±800 kV LCC-HVDC and 500 kV AC transmission system is established, and different fault cases are simulated. The simulation results prove that the novel protection principle is immune to commutation failure, fault resistance and fault type.

Abstract:Large interconnected power systems are usually subjected to natural oscillation (NO) and forced oscillation (FO). NO occurs due to system transient response and is characterized by several oscillation modes, while FO occurs due to external perturbations driving generation sources. Compared to NO, FO is considered a more severe threat to the safe and reliable operation of power systems. Therefore, it is important to locate the source of FO so corrective actions can be taken to ensure stable power system operation. In this paper, a novel approach based on two-step signal processing is proposed to characterize FO in terms of its frequency components, duration, nature, and the location of the source. Data recorded by the Phasor Measurement Units (PMUs) in a Wide Area Monitoring System (WAMS) is utilized for analysis. As PMU data usually contains white noise and appears as multi-frequency oscillatory signal, the first step is to de-noise the raw PMU data by decomposing it into a series of intrinsic mode functions (IMF) using Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (ICEEMDAN) technique. The most appropriate IMF containing the vital information is selected using the correlation technique. The second step involves various signal processing and statistical analysis tools such as segmented Power Spectrum Density (PSD), excess kurtosis, cross PSD etc. to achieve the desired objectives. The analysis performed on the simulated two-area four-machine system, reduced WECC-179 bus 29 machine system, and the real-time power system PMU data set from ISO New England, demonstrates the accuracy of the proposed method. The proposed approach is independent of complex network topologies and their characteristics, and is also robust against measurement noise usually contained in PMU data.

Abstract:Optimal reactive power dispatch (ORPD) is a complex and non-linear problem, and is one of the sub-problems of optimal power flow (OPF) in a power system. ORPD is formulated as a single-objective problem to minimize the active power loss in a transmission system. In this work, power from distributed generation (DG) is integrated into a conventional power system and the ORPD problem is solved to minimize transmission line power loss. It proves that the application of DG not only contributes to power loss minimization and improvement of system stability but also reduces energy consumption from the conventional sources. A recently proposed meta-heuristic algorithm known as the JAYA algorithm is applied to the standard IEEE 14, 30, 57 and 118 bus systems to solve the newly developed ORPD problem with the incorporation of DG. The simulation results prove the superiority of the JAYA algorithm over others. The respective optimal values of DG power that should be injected into the four IEEE test systems to obtain the minimum transmission line power losses are also provided.

Abstract:Non-renewable fuel sources have been the predominant energy sources and a significant source of foreign exchange income for Nigeria, while at the same time there is a severe problem of electricity inconsistency and persistent power blackouts in Nigeria. The research aims to end the concern for deficient energy use, and to encourage energy efficiency and sustainability. Nigeria has not maximized the advantages of renewable energy after the denationalisation of its electricity industry despite the current transformation in the power industry and the rising demand for renewable energy supply. The research adopts a doctrinal legal approach with a library-based legal research technique with a comparative legal method. It reveals that the absence of a comprehensible legal regime with encouragement for the use of renewable energy is the fundamental element causing the slow utilization of renewable energy as a substitute source of energy in Nigeria. It is suggested that, among other reforms, there is a need for a comprehensible legal regime on renewable energy and the encouragement of strict implementation of energy regulatory strategies and policies with incentives for the application of renewable energy sources in Nigeria.

Abstract:Large integration of doubly-fed induction generator (DFIG) based wind turbines (WTs) into power networks can have significant consequences for power system operation and the quality of the energy supplied due to their excessive sensitivity towards grid disturbances. Under voltage dips, the resulting overcurrent and overvoltage in the rotor circuit and the DC link of a DFIG, could lead to the activation of the protection system and WT disconnection. This potentially results in sudden loss of several tens/hundreds of MWs of energy, and consequently intensifying the severity of the fault. This paper aims to combine the use of a crowbar protection circuit and a robust backstepping control strategy that takes into consideration of the dynamics of the magnetic flux, to improve DFIG’s Low-Voltage Ride Through capability and fulfill the latest grid code requirements. While the power electronic interfaces are protected, the WTs also provide large reactive power during the fault to assist system voltage recovery. Simulation results using Matlab/Simulink demonstrate the effectiveness of the proposed strategy in terms of dynamic response and robustness against parametric variations.