Substation and Transmission Lines Earthing System Design under Substation Fault

High-voltage substations are fed by transmission lines with the earthing system solidly bonded to the substation earth grid. Under substation fault, both the substation earth grid and the pole grid resistance are exposed to voltage rise. This voltage rise could reach unacceptable and dangerous levels. Earthing system design ensures safety compliance for both the substation and transmission lines under fault conditions. This article analyses the relation between the substation earth potential rise and the transmission pole earth potential rises. The analysis shows that the poles located within the finite length from the substation form a solid input to the substation earth potential rise. The article reviews the existing literature and develops the formulas to assist the designer to compute the substation earth potential rise from the pole earth potential rise and vice versa. The article proposes modifications to IEEE earthing design block diagram. This modification ensures that the transmission line earthing system is always compliant to allowable safety limits under substation fault. Furthermore, the article shows the method to estimate the substation earth potential rise by measuring the pole earth potential rise with a case study.     

Hard machining of hardened bearing steel using cubic boron nitride tool

In many cases, hard machining remains an economic alternative for bearing parts fabrication using hardened steels. The aim of this experimental investigation is to establish the behaviour of a CBN tool during hard turning of 100Cr6-tempered steel. Initially, a series of long-duration wear tests is planned to elucidate the cutting speed effects on the various tool wear forms. Then, a second set of experiments is devoted to the study of surface roughness, cutting forces and temperature changes in both the chip and the workpiece. The results show that CBN tool offers a good wear resistance despite the aggressiveness of the 100Cr6 at 60HRC. The major part of the heat generated during machining is mainly dissipated through the chip. Beyond 280 m/min, the machining system becomes unstable and produces significant sparks and vibrations after only a few minutes of work. The optimal productivity of machined chip was recorded at a speed of 120 m/min for an acceptable tool flank wear below 0.4 mm. Beyond this limiting speed, roughness (R_a) is stabilized because of a reduction in the cutting forces at high speeds leading to a stability of the machining system. The controlling parameter over roughness, in such hard turning cases, remains tool advance although ideal models do not describe this effect rationally. Surface quality obtained with CBN tool significantly compared with that of grinding despite an increase in the advance by a factor of 2.5. A relationship between flank wear (VB) and roughness (R_a) is deduced from parametric analysis based on extensive experimental data.     

Characteristics of Rb40 steel superficial layer under ball and roller burnishing

Both ball and roller burnishing processes are largely considered in industrial cases in order to ameliorate surface characteristics. Usually, roughness and hardness are sought to measure surface integrity. The aim of this study is to develop a device for mechanical plastic deformation of structural Rb40 steel using ball and roller burnishing and to investigate the evolution of associated roughness, hardness and wear resistance. It was found that roller burnishing provides optimal roughness results, particularly when initial surface quality is close to 3 μm whereas in terms of hardness, ball burnishing becomes interesting. Optimum roughness and hardness are obtained for a specific operating regime in which decisive parameters are the applied force as well as the number of passes. When considering roughness criterion, it is recommended to limit the number of passes to two while three passes are advised for a hardness basis. Rb40 steel superficial layers treated by either roller or ball burnishing behave as a grinded surface with an appreciable wear resistance.     

Season's Variation Impact on Citrus aurantium Leaves Essential Oil: Chemical Composition and Biological Activities

Citrus aurantium leaves' essential oils (EOs) were evaluated for chemical composition and antioxidant and antibacterial activities. The vegetable material, taken 5 times during the year, has undergone the hydrodistillation to prepare EO. Chemical characterization by gas chromatography/mass spectrometry and GC/flame ionization detection allowed the identification of 46 compounds, and a notable quantitative and qualitative differences between the different Petitgrain samples according to the harvest time. Linalool (43.2% to 65.97%), linalyl acetate (0.77% to 24.77%), and α-terpineol (9.29% to 12.12%) were the main components. The most important number of components was registered for summer EOs (July and September). The 5 EOs submitted biological activities screening, namely, antioxidant and antimicrobial activities. Weak antioxidant activities (IC(50) values >10000 mg/L) were registered by both 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azinobis-3-ethylbenzothiazoline-6-sulphonate assays, mostly because the weak amount of phenols in EOs. Antibacterial activities (12 microorganisms) were registered against Gram-positive bacteria [Bacillus subtilis (MIC = 2.7 mg/mL), Staphylococcus aureus (4.8 mg/mL)], and moderated ones against yeasts [Saccharomyces cerevisiae (9.2 mg/mL)] and fungi [Mucor ramannianus (5 mg/mL)]. Positive correlations between the identified compounds and the antimicrobial activities were noted. Many compounds were correlated to antimicrobial activity mainly caryophyllene oxide against Escherichia coli (R(2) = 0.99), S. cerevisiae (R(2) = 0.99), and Fusarium culmorum (R(2) = 0.99).     

Wind Farm Earthing System Design Using Clustering Technique

Abstract—A wind farm consists of large number of turbines, the earth grids of which are connected together. Under fault condition at one turbine, only limited numbers of turbines are impacted. This article analyzes the fault current distributions between wind turbine earth grids under fault conditions. Furthermore, it introduces the clustering technique, which limits the simulation requirements for the wind farm, thus reducing the cost and time of the design process. A case study is also included to validate the analyses.     

Work hardening of mild steel within dynamic strain ageing temperatures

An investigation has been performed on the plastic behaviour of a mild steel within the region of dynamic strain ageing. For this purpose tension tests have been performed on annealed XC18 steel within a range of temperatures, from 305–776 K, and a range of strain rates, from 1.0×10^–4–1.85×10^–1s^–1. An analysis of experimental results is presented using a model for plastic deformation based on dislocation multiplications.