A critical review on soil ionisation modelling for grounding electrodes

Grounding electrode resistance non-linearly changes under impulse conditions due to soil ionisation phenomenon. Several models have been proposed to model soil ionisation for grounding electrodes applications. However, to date, there is yet an attempt made to compile all these works into a comprehensive review article. Therefore, this paper is written with the objective of summarizing all related works in this field as a one- stop reference. With reference to the literature, this paper is written to summarize the working principles of the soil ionisation models as well as the accuracy and performance analysis of the models. This paper, particularly highlights the deficiencies of the available models in terms of accuracy and performance. This knowledge will contribute to the development of a new accurate and efficient soil ionisation model

Short circuit fault transient studies of power distribution systems including dispersed generation

Nowadays, there is a great interest in installation of dispersed generation systems in low voltage or medium voltage distribution systems, all over the world. Some standards suggest that all dispersed generation systems should be disconnected from the power system as an earth fault has occurred in the distribution system which can lead to an ineffective solution due to disconnection of a huge number of units. In this paper, the connection of dispersed generation systems to the power distribution system at short circuit faults are studied and the results of the connected or disconnected units are investigated. The simulations done with ATP-EMTP prove the capability of handling the power system stability with standard voltage and current characteristics when a fault has occurred in the power distribution system

Lightning and switching transient overvoltages in power distribution systems feeding DC electrified railways

Control and reduction of the voltage transients in power distribution systems feeding electrified railways are a significant issue. Theref ore, it is necessary to study how and why the voltage transi ents are injected to the system and how they can be reduced. In this paper, the switching and lightning overvoltage transients of DC electrified railways are studi ed and investigated and the selection of qualified DC su rge arresters and their best point of connection to the electric system are recommended. Later on, through the simulation results done with PSCAD/EMTDC the e fficiency of the selected and installed surge arresters with the proposed characteristics is verified

Electrical Energy Management of Virtual Power Plants in Distribution Networks with Renewable Energy Resources and Energy Storage Systems

Abstract: Production of energy in centralized power plants and transmitted via transmission lines tothe customers is always with high power losses. Distributed generation (DG) especially renewableenergy resources (RES) and energy storage systems (ESS) through distributed system are very costsaving and sometimes inevitable. If these small DGs want to connect to power system and participatein energy market directly, both distribution and energy market would have many problems withcontrol such a high amount of information and small supplies of DGs. Application of virtual powerplant (VPP) as an aggregation of some DGs with own local energy management system and some fixand variable loads is a suitable solution for DGs and networks problems. VPP has a main energymanagement too. So they can be in contact with distribution system operator and each local energymanagement systems of each DGs via main energy management system, so the VPP can makedecisions when and which and how much each DGs supply. In the other hand random type ofelectrical productions of RESs and also shortage of energy at peak load times and necessity of energystorage make electrical energy management more complicated. All energy managements in virtualpower plants were without RESs and ESSs so in this publication electrical energy management for aVPP with considering some RESs and ESSs will be done via three different scenarios and MA TLABtools was applied to evaluate the units control dispatch to the optimal system configuration.Key Words: Electrical Energy Management, Virtual Power Plant, Renewable Energy Sources,EnergyStorage Systems, Local Management System, MainManagement System5 Halama

Combined design of VSC-HVDC and PSS controllers for LFO damping enhancement

The purpose of this paper is to present a novel combined design of the voltage source converter–high voltage direct current (VSC-HVDC) and the power system stabilizer (PSS) controllers to obtain a better dynamical response. The proposed technique is applied to enhance the damping of the power system low-frequency oscillations (LFOs) and results are compared with traditional design. A fuzzy logic controller is designed for PSS (FPSS). Then, a chaotic optimization algorithm, which has a strong ability for finding the most optimistic results, is employed, in presence of FPSS, to search for optimal VSC-HVDC output feedback controller parameters. Moreover, a singular value decomposition method is utilized to select the most effective damping control signal of the VSC-HVDC output feedback controllers. The novel proposed controllers are evaluated on an AC/DC power system. The simulation results demonstrate that the combined controllers have an excellent capability for damping power system LFOs and greatly enhance the dynamic stability of the power system. Also, the system performance analysis under different operating conditions and some performance indices show the effectiveness of the proposed controllers. The benefit of the suggested procedure is greatly improving the dynamic response of the system. In addition, the overshoots, undershoots and the settling times are dramatically reduced by applying the proposed method

Optimum regulation of DC sources in cascaded multi-level inverters

Purpose:\ud The purpose of this paper is to introduce a new concept in selecting the values of the DC source voltages in cascaded multi-level inverters in order to improve the output voltage THD.\ud \ud Design/methodology/approach:\ud In cascaded multi-level inverters, it is usually assumed that the DC sources have the same constant voltage and output harmonics minimization is accomplished by applying proper switching angles. Employing different DC voltages with proper ratios can result in further reduction of the harmonics. After formulation of the system, i.e. describing the inverter's output voltage components in terms of the switching angles and unequal DC source voltages, a rule is applied to obtain the step heights of the staircase output waveform (DC source voltages), so that the output waveform becomes as close to the required fundamental sine wave as possible. Substituting the obtained DC source voltages into the harmonics elimination equations results in a set of equations, which are functions of switching angles only. Solving these equations leads to proper switching angles, which, regardless of the fundamental component's value, provide the specified harmonic conditions. The output voltage is then controlled by DC sources voltage regulation.\ud \ud Findings:\ud Computer simulations show that employing the proposed concept results in substantial improvement in the harmonic minimization, as well as, extending the operating range of the inverter, compared to the conventional methods with equal DC source voltage multi-level inverters.\ud \ud Originality/value:\ud The proposed concept according to which the ratio of the DC source voltages are determined, is original