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The purpose of this paper is to present a practical method for computing contingency‐based reliability and quality indices in power systems and to answer questions related to how much the system is reliable, how robust it is in surviving random contingencies, how much it is costing to maintain appropriate system security and reliability levels and, finally, to what extent the desired balance is maintained between generation facilities, transmission capabilities and consumer demand levels in various zones of the electric power system.

The methodology adopted in this paper is based on a combined contingency analysis/reliability evaluation scheme. A three‐component system model is utilized, which can be used effectively for evaluation and sensitivity analysis of reliability and quality in power systems. The model is a reduced (equivalent) system representation that comprises generation, transmission and load components with multi‐state values. The computational scheme presented in the paper integrates both the contingency effect and its probability of occurrence into one routine of analysis while reducing the power system around the region of interest.

The computational scheme presented in the paper can effectively assess both service reliability and system quality. The practical applications presented demonstrated that lower service reliability levels would jeopardize energy supply continuity and increase the likelihood of additional maintenance and restoration costs due to the resulting higher rate of system outages. Poor system quality levels, on the other hand, imply either deficiency or excess in the overall system capabilities as designed by its planners.

The work of this paper contributes to the solution of the reliability and quality assessment problem in practical power systems. As part of the present work, an advanced computerized scheme for fast composite system reliability and quality assessment was developed and then applied to an equivalent system model of the Saudi electricity system. The results obtained are claimed to have far‐reaching implications on various planning and operation aspects of the power system.

Classic models for distribution systems design have usually considered only basic aspects such as power capacity limits, power demand requirements and the minimization of a single‐objective function that represents the total system expansion cost. However, multiobjective design models include aspects such as reliability evaluations, the optimal voltage profile in the network, social amenity values and geographical conditions of the study area, as well as the basic design aspects. In this paper, a multiobjective model is presented for optimal design of distribution systems by finding the best reliability of the network and the least expensive system expansion simultaneously. A multiobjective method used in applications of the model to practical distribution systems design problems is outlined. The computer results indicate that multiobjective models achieve satisfactory solutions, which consider multiple objectives simultaneously. These solutions, preferred by the planner, are advantageous compared with the classic design solutions.

Multiobjective planning models for electric power distribution system planning can include multiple aspects such as community amenity values, geographical conditions of the study area, reliability evaluations (mainly in terms of service continuity), or the optimal voltage profile in the network, as well as the basic planning aspects: power demand requirements, power capacity limits and the minimization of the total system expansion costs. On the other hand, classical single objective planning models have usually considered only the basic aspects. This paper describes a multiobjective model to find the optimal voltage profile and to look for the least cost system expansion simultaneously. Furthermore, two multiobjective techniques for the application of the model to distribution system expansion problems are outlined. The computer results have shown that multiobjective models are able to find solutions which include multiple planning objectives simultaneously, and that these solutions are advantageous compared with the ones from classical single objective models.

An annual substation equipment failure report says 3/7 capacitive voltage transformer (CVT) got damaged because of ferroresonance overvoltage. The conventional mitigation circuit fails to protect the transformer as the overvoltage may fall in the range between 2 and 4 per unit. It is necessary to develop a device to suppress the overvoltage as well as overcurrent of the CVT. This study aims to propose the suitability of memristor emulator as a mitigation circuit for ferroresonance.

The literature implies that a nonlinear circuit can protect the transformer against ferroresonance. An attempt is made with a memristor emulator using Operational Amplifier (OPAMP) for the mitigation of ferroresonance in a prototype transformer. The circuit is simulated using PSpice and validated for its ideal characteristics using hardware implementation. The nonlinear memductance is designed which is required to mitigate the ferroresonance. The mitigation performance has been compared with conventional method along with fast Fourier transform (FFT) analysis.

While the linear resistor recovers the secondary voltage by 74.1%, the memristor emulator does it by 82.05% during ferroresonance. Also, the total harmonic distortion (THD) of ferroresonance signal found to be 22.06% got improved as 2.56% using memristor emulator.

The suitability of memristor emulator as a mitigation circuit for ferroresonance is proposed in this paper. As ferroresonance occurs in instrument transformers which have extra high voltage (EHV) rated primary windings and (110 V/[110 V/1.732]) rated secondary windings, the mitigation device is proposed to be connected as a nonlinear load across the secondary windings of the transformer. This paper discusses the preliminary work of ferroresonance mitigation in a prototype transformer. The mitigation circuit may have memristor or meminductor for ferroresonance mitigation when they are commercially available in future.

The electronic component-based memristor emulator may not work at 110 V practically as they may be rated at low power. Hence, chemical component-based memristor emulator was developed to do the same. The authors like to clarify that the memristor will be a solution for ferroresonance in future not the memristor emulator circuit.

With the real form of memristor, the transistor world will be replaced by it and may have a revolution in the field of electronics, VLSI, etc. This contribution attempts to project the use of memristor in a smaller scale in high-voltage engineering.

The electronic component-based memristor emulator is proposed as a mitigation circuit for ferroresonance. The hypothesis has been verified successfully in a prototype transformer. Testing circuit of memristor emulator involves transformer, practically. The mitigation performance has been compared with conventional method technically and justified with FFT analysis.

This paper aims at building a discharge model for the power cable bellows based on plasma energy deposition and analyzing the discharge ablation problem.

Aiming at the multiphysical mechanism of the discharge ablation process, a multiphysical field model based on plasma energy deposition is established to analyze the discharge characteristics of the power cable bellows. The electrostatic field, plasma characteristics, energy deposition and temperature field are analyzed. The discharge experiment is also carried out for result validation.

The physical mechanism of the bellows ablative effect caused by partial discharge is studied. The results show that the electric field intensity between the aluminum sheath and the buffer layer easily exceeds the pressure resistance value of air breakdown. On the plasma surface of the buffer layer, the electron density is about 4 × 1,019/m³, and the average temperature of electrons is about 3.5 eV. The energy deposition analysis using the Monte Carlo method shows that the electron range in the plasma is very short. The release will complete within 10 nm, and it only takes 0.1 s to increase the maximum temperature of the buffer layer to more than 1,000 K, thus causing various thermal effects.

Its physical process involves the distortion of electric field, formation of plasma, energy deposition of electrons, and abrupt change of temperature field.

This study aims to summarize the effects of minor addition of Ho REE on the structure, mechanical strength and thermal stability of binary Sn- Ag solder alloys for high-performance applications.

This study investigates the effect of a small amount of holmium addition on the microstructure, thermal stability, mechanical behaviour and wettability of environmentally friendly eutectic melt-spun process Sn – Ag solder alloys. Dynamic resonance technique, X-ray diffraction (XRD) and scanning electron microscopy were carried to study stiffness, identification of the phases and the morphology features of the solder. Structure and microstructure analysis indicated that presence of rhombohedral ß-Sn phase in addition to orthorhombic IMC Ag₃Sn phase dispersed in Sn-matrix. Also, the results showed that Ho rare earth addition at a small trace amount into Sn-Ag system reduces and improves the particle size of both rhombohedral ß-Sn and orthorhombic IMC Ag₃Sn based on the adsorption effect of the active RE element. The adsorption of Ho at grain boundaries resulted in Ag₃Sn more uniform needle-like which is distributed in the ß-Sn matrix. The fine and uniform microstructure leads to improvement of mechanical strength. The microstructure refinement is due to the high surface free energy of IMC Ag₃Sn grains, and it prevents the dislocation slipping. This maybe enhance the micro-hardness and micro-creep hence delays the breaking point of the solder. Ho (RE) trace addition could enhance the melting temperature and contact angle up to 215°C and 31°, Respectively, compared with plain solder. All results showed that Ho trace addition element has an effective method to enhance new solder joints.

Effect of rare earth element Ho particles on the microstructure and mechanical behavior of eutectic Sn-3.5Ag solder alloy was studied. Some important conclusions are summarized in the following: microstructure investigations revealed that the addition of Ho particles to eutectic Sn-3.5Ag inhibited in reducing and refines the crystallite size as well as the Ag3Sn IMC which reinforced the strength of plain solder alloy. The mechanical properties values such as Young’s modulus, Vickers microhardness of Sn-3.5Ag solder alloy can be significantly improved by adding a trace amount of Ho particles compared with plain solder due to the existence of finer and higher volume fraction of Ag3SnIMC. These variations can be understood by considering the plastic deformation. The strengthening mechanism of the Sn-3.5Ag-Ho solder alloy could be explained in terms of Ho harden particles and finer IMC, which are distributed within eutectic regions because they act as pinning centres which inhibited the mobility of dislocation that concentrated around the grain boundaries. The results show that the best creep resistance is obtained when the addition of Ho 0.5 is compared to plain solder. The addition of Ho on Sn-3.5Ag lead-free solder alloy decreases the melting temperature to few degrees.

Development of holmium-doped eutectic Sn-Ag lead-free solder for electronic packaging.

This study aims to study the impact of intermetallic compound on microstructure, mechanical characteristics and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder.

In this paper, a new group of lead-free high-temperature Pb-free solder bearing alloys with five weight percentages of different silver additions, Bi-Ag_x (x = 3.0, 3.5, 4.0, 4.5 and 5.0 Wt.%) have been developed by rapidly solidification processing (RSP) using melt-spun technique as a promising candidate for the replacement of conventional Sn-37Pb common solder. The effect of the addition of a small amount of Ag on the structure, microstructure, thermal and properties of Bi-Ag solder was analyzed by means of X-ray diffractometer, scanning electron microscopy, differential scanning calorimetry and Vickers hardness technique. Applying the RSP commonly results in departures from conventional microstructures, giving an improvement of grain refinement. Furthermore, the grain size of rhombohedral hexagonal phase Bi solid solution and cubic IMC Bi_0.97Ag_0.03 phase is refined by Ag addition. Microstructure analysis of the as soldered revealed that relatively uniform distribution, equiaxed refined grains of secondary IMC Bi_0.97Ag_0.03 particles about 10 µm for Bi-Ag_4.5 dispersed in a Bi matrix. The addition of trace Ag led to a decrease in the solidus and liquidus temperatures of solder, meanwhile, the mushy zone is about 11.4°C and the melting of Sn-Ag_4.5 solder was found to be 261.42°C which is lower compared with the Sn-Ag₃ solder 263.60°C. This means that the silver additions into Bi enhance the melting point. The results indicate that an obvious change in electrical resistivity (?) at room temperature was noticed by the Ag addition. It was also observed that the Vickers microhardness (H_v) was increased with Ag increasing from 118 to 152 MPa. This study recommended the use of the Bi-Ag lead-free solder alloys for higher temperature applications.

Silver content is very important for the soldering process and solder joint reliability. Based on the present investigations described in this study, several conclusions were found regarding an evaluation of microstructural and mechanical deformation behavior of various Bi-Ag solders. The effect of Ag and rapid solidification on the melting characteristics, and microstructure of Bi-Ag alloys were studied. In addition, the mechanical properties of Bi with different low silver were investigated. From the present experimental study, the following conclusions can be drawn. The addition of Ag had a marked effect on the melting temperature of the lead-free solder alloys, it decreases the melting temperature of the alloy from 263.6 to 261.42°C. Bi-Ag solders are comprised of rhombohedral Hex. Bi solid solution and cubic Ag_0.97Bi_0.03 IMC is formed in the Bi matrix. The alloying of Ag could refine the primary Bi phase and the Bi_0.97Ag_0.03 IMC. With increasing Ag content, the microstructure of the Bi-Ag gradually changes from large dimples into tiny dimple-like structures. The refinement of IMC grains was restrained after silver particles were added into the matrix. The inhibition effect on the growth of IMC grains was most conspicuous when solder was doped with Ag particles. As a result, the Vickers microhardness of the Bi-Ag lead-free solder alloys was enhanced by more than 100% ranging from 118.34 to 252.95 MPa. Bi-Ag high-temperature lead-free solders are a potential candidate for replacing the tin-lead solder (Sn-37Pb) materials which are toxic to human and the environment and has already been banned.

This study recommended the use of the Bi-Ag lead-free solder alloys for high-temperature applications.

Low power devices with switched-mode power supply represent harmonic generating apparatus in widespread use nowadays. The influence of personal computers (PCs), which affect the supply voltage, is considered. Harmonic level due to simultaneous PC operation is quantified by the total harmonic distortion of input current (THD _I). The purpose of this paper is to propose a multi-parameter mathematical model for the THD _I calculation. The model is convenient for practical engineering application.

The model is derived using the measured and simulated data. The model coefficients are obtained in the least squares sense.

Mathematical modeling of THD _I is the least expensive and the most convenient solution for engineering application. The models proposed in the literature have many drawbacks, which motivated the authors to develop a more comprehensive solution. Grid stiffness, capacitance of PC power supply unit and PC cluster size represent the major parameters that affect THD _I, and as such they are taken into account in the proposed model. The influence of other existing parameters from both line and load side is also discussed and the reasons for their omitting from the model are explained. The model considers various PC configurations within the cluster and it enables the THD _I calculation for an arbitrary PC cluster size.

Due to its comprehensiveness and mathematical simplicity, the model is suitable for practical use, and its accuracy is verified through conducted measurements presented in the paper.

The proposed model is more comprehensive than the existing ones, and it overcomes their shortcomings. The THD _I calculation is simplified to the level of applying basic arithmetic operations only, without jeopardizing the accuracy. The validity of the model is supported by additional measurements carried out in sites characterized by grid conditions quite different from that used for model developing.

This paper presents the second part of the investigation on resistance to elevated temperatures of a proposed hybrid composite concrete (NCSF-Crete) mix. The composite including nano metakaolin (NC) and steel fibers (SF) in addition to regular concrete components has proven -in the first published part-earlier promoted fresh concrete behavior, and to have reduced loss in compressive strength after exposure to a wide range of elevated temperatures. This presented work evaluates another two critical mechanical characteristics for the proposed composite -namely- splitting and bond strengths.

A modified formula correlating splitting and compressive strength (28 days) based on experiments results for NCSF is proposed and compared to formulas derived for regular concrete in different design codes. Finally, both spitting and bond strengths are evaluated pre- and post-exposure to elevated temperatures reaching 600 °C for two hours.

The proposed NCSF-Crete shows remarkable fire endurance, especially in promoting bond strength as after 600 °C heat exposure tests, it maintained strength equivalent to 70% of a regular concrete control mix at room temperature. Improving residual splitting strength was very significant up to 450 °C exposure.

Obvious deterioration is monitored in splitting resistance for all concretes at 600 °C.

This proposed composite improved elevated heats resistance of the most significant concrete mechanical properties.

Using a more green and sustainable constituents in the composite.

The proposed composite gathers the merits of using NC and SF, each has been investigated separately as an addition to concrete mixes.

Series capacitive compensation in electrical power systems is generally recognized as a very economical and powerful means for increasing the transmission capability of long‐distance transmission lines, resulting in relevant technical advantages in power system behavior: increased steady‐state and transient stability margins, reduced voltage drop in receiving systems during occurrence of severe contingencies and reduction of transmission losses. In this paper, a general method for choosing the series compensation degree is proposed, focusing the attention on the transient stability aspect. The approach, based upon a probabilistic framework, allows to properly select – at the design stage – the optimal degree of series compensation in order to contain the instability risk at an acceptable value. The transient stability problem is formulated by using the transient energy function method. In order to show the feasibility of the proposed approach, a numerical application to the Cigre test network is performed in the final part of the paper.