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In this paper, a novel hybrid phasor particle swarm optimization and gravitational search algorithm, namely the hybrid PPSOGSA algorithm, is proposed to find the optimal size and location of shunt capacitors in distribution systems with non-linear loads. The performance of PPSOGSA are studied and evaluated using the IEEE 9- and 85-bus test systems with the objective of minimizing the total annual cost of the system. The procedure is conducted taking into account effects of harmonic distortion and discrete size of capacitors available in the market. Simulation results are compared with those obtained by other optimization techniques, and verified using the Electrical Transient Analysis Program (ETAP). It was established that that the hybrid PPSOGSA algorithm provides better solutions in terms of convergence and accuracy.

This paper considers the problem of determination of optimum locations and sizes of capacitor banks (CB) for reactive power compensation in distribution systems to reduce harmonic distortion and improve voltage profile. Genetic Algorithm (GA) was used for solving this non-linear multi-objective optimization problem with constraints. A detailed methodology was presented for solving the power flow problem at fundamental and higher harmonic frequencies of interest and models of network components in harmonic analysis. The proposed procedure was successfully tested on the standard IEEE 33-bus test system for three different objective functions. Calculations showed the efficiency of GA for solving this complex problem.

This paper considers the problem of the determination of the optimum values for dimensions of cable trench and cable bedding, interaxial spacings between power cables in trefoil formation and cable ampacities. This non-linear multi-objective optimization problem with constraints is solved by using the gravitational search algorithm (GSA). The procedure used in this paper has allowed the simultaneous inclusion of all control variables into the optimization process and the determination of an optimal solution in accordance with specified optimization criteria. in the present case, the optimal solution is obtained based on the following optimization criteria: (i) minimization of the total installation cost for cable line, (ii) maximization of the cable ampacity and (iii) a simultaneous application of the minimization of the total installation cost for cable line and the maximization of the cable ampacity. The constraints on control variables are introduced through penalty factors which expand the objective function, it is also assumed that the cable ampacity corresponds to a load factor of 0.8. The procedure is carried out with respect to the drying out effect in the soil surrounding the cables.

It is well-known that there is no PLAN-DO-CHECK-ACT (PDCA) approach that is used by electricity distribution network operators and asset managers of power cable systems. Accordingly, this paper proposes a novel application of the PDCA approach to thermal aging management of underground power cables in electricity distribution networks. Another novelty of the proposed approach is that the finite element method (FEM) is used in combination with the traditional Arrhenius model to calculate the unknown temperature of cable conductors under service conditions. In particular, this means that the FEM-based Arrhenius model can involve the effects of other heat sources, wind, solar irradiation, etc., in procedures for qualification of underground power cables. The Arrhenius model is applied to an actual hot spot of a 110 kV underground cable line of most importance to reliable operation of the electricity distribution network of the city of Belgrade. In the hot spot, the 110 kV cable line is installed in parallel with the group of 35 kV cables and crosses an underground heating pipe-line. The proposed approach is successfully validated using the existing experimental data on cross-linked polyethylene insulation. Finally, it is found that the hot spot effect can shorten the expected total service lifespan of the 110 kV cables in the hot spot area by 36.84%, as well as that the largest consumption of total thermal lifespan occurs in the presence of all the existing thermal effects. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a Backward/Forward Sweep (BFS) power flow method in the frequency domain for the analysis of the harmonic distortion in radial distribution systems with distributed generation (DG) units. A detailed procedure for solving the power flow problem at fundamental and harmonic frequencies and the models of distribution system elements in harmonic analysis are presented. In addition, the effects of converter‐based and nonconverter‐based DG units on voltage profile, power losses, and power quality are carried out. Performance of the proposed method is tested and evaluated on the standard IEEE distribution systems. Simulation results, obtained using the proposed BFS method, are compared with those obtained using the Decoupled Harmonic Power Flow (DHPF) method, Harmonic Analysis module of the ETAP program, and Full Harmonic Solution module of the PCFLO program. It is shown that the BFS method provides effective, robust, and high‐quality solutions. Besides that, the proposed method has better computational performance than the commonly used DHPF method, since the bus admittance matrix inverse employed by the DHPF method is not necessary in the solution procedure. [ABSTRACT FROM AUTHOR]

This paper proposes a thermal model for calculating the temperature of open-rack mounted photovoltaic (PV) modules taking into account the meteorological conditions, position (i. e. the inclination of one PV module and the angle between its surface and wind direction) and technical characteristics of the PV modules. The present model is valid for the steady-state operation and is based on the energy balance equation in which the forced convection is modelled by the new empirical correlations. The possibility of occurrence of the flow separation along the surfaces of the PV modules is included in these correlations. The effect of the angle between the wind direction and the PV module plane, which is usually ignored in the modelling of forced convection, is also taken into consideration. In this manner, it is possible to estimate the temperature of PV modules more precisely, as well as to determine the power and efficiency which depend on the temperature. For four particular PV modules, it is found that the temperatures, obtained using the proposed thermal model, are in good agreement with the corresponding measured temperatures. Compared with the other models commonly used for thermal analysis of PV modules (SNL and NOCT-based correlations), this model yielded better results. The deviation of the PV module temperature calculated using the proposed thermal model from the measured one is up to 2 °C, and the deviations of the PV module temperatures calculated using the SNL and NOCT-based correlations from the measured ones amount up to 5 °C and 20 °C, respectively, depending on the PV module type and ambient conditions. [ABSTRACT FROM AUTHOR]

This paper shows how the pavement surface radiation properties can be used to control the thermal environment of 110 kV underground cables in order to increase their ampacity. It is assumed that the ampacity is additionally affected by the cable bedding size and an underground heating pipeline. Thanks to an experimental apparatus, some useful data were collected for the validation of two different finite element method based models that predict the effect of the pavement surface radiation properties on the cable ampacity. The first model corresponds to the experimental apparatus and actual indoor conditions, while the second one corresponds to the theoretical case and assumed outdoor conditions (taking into account the thermal effects of solar radiation, cable bedding size, and heating pipeline). This paper examines two possible cases of outdoor conditions, one corresponding to summer period (the most unfavorable ambient conditions) and another one corresponding to winter period (the most common winter conditions in Serbia). This proposed new method is based on the experimental data and generalized using the finite element method in COMSOL. It is found that the ampacity of the considered 110 kV cable line can be increased up to 25.4 % for the most unfavorable ambient conditions and up to 8 % for the most common winter conditions. [ABSTRACT FROM AUTHOR]

This study takes into consideration a problem that commonly occurs at the design stage of underground cable lines and that relates to the manner of determining the optimal values for dimensions of cable trench and bedding, interaxial spacings between power cables in flat formation and cable ampacities. The problem is formulated as a non‐linear optimisation problem with constraints. The gravitational search algorithm, simulated annealing algorithm and generalised pattern search algorithm are used to solve the problem. The optimal solutions are obtained based on the following three optimisation criteria: (i) minimisation of the total installation costs, i.e. the total costs for producing the cable trench, laying the bedding material, laying the backfill material and installing the cables, (ii) maximisation of the cable ampacity and (iii) a simultaneous application of the minimisation of the total installation costs and the maximisation of the cable ampacity. The constraints on design and control variables are introduced through penalty factors by means of which the objective function is expanded. The procedure is conducted taking into account the effect of drying out of the soil surrounding the cables. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to show how the inclination angle affects natural convection from a flat-plate photovoltaic module which is mounted on the ground surface. In order to model this effect, novel correlations for natural convection from isothermal flat plates are developed by using the fundamental dimensionless number. On the basis of the available experimental and numerical results, it is shown that the natural convection correlations correspond well with the existing empirical correlations for vertical, inclined, and horizontal plates. Five additional correlations for the critical Grashof number are derived from the available data, three indicating the onset of transitional flow regime and two indicating the onset offlow separation. The proposed correlations cover the entire range of inclination angles and the entire range of Prandtl numbers. This paper also provides two worked examples, one for natural convection combined with radiation and one for natural convection combined with forced convection and radiation. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to propose an algorithm for the determination of the allowable ampacities of single rectangular-section bus bars without the occurrence of correction factors. Without correction factors, the ampacity computation of the copper and aluminum bus bars is fully automatized. The analytical algorithm has been implemented in a computer program code that along with the allowable ampacity can compute the bus bar temperature and the individual heat transfer coefficient for each side of the bus bar, as well as their corresponding power losses. Natural and forced convection correlations for rectangular bus bars are applied. Effects of the solar radiation and radiation heat losses from the bus bar surface are taken into consideration as well. The finite element method has been used for the linear/non-linear steady-state thermal analysis, i. e. for validation of the analytical algorithm. All finite element method based numerical computations were carried out using the COMSOL heat transfer module. [ABSTRACT FROM AUTHOR]

This paper shows the roots of the unsuccessful transitional justice in Serbia. From Milosevic to Kostunica, Djindjic and Tadic their approach to transitional justice was only to change the stylization of carefully selected political statements. The author gives a critical review of the role of "democratic" leaders during the 2000s and their often forgotten contribution to the "blurring of reality". Despite the more or less harsh rhetoric transitional justice had the same path and follows the same pattern. Transitional justice processes were monitored by relation analysis of other powerful (non)- state actors such as the Universities, school textbooks in which the young generations are nurtured, catalytic role of the media and intellectual elites, and above all politicized Serbian Academy of Sciences and Arts, led by "father of the nation" - Dobrica Cosic. This paper shows that deeply established nationalism had the major role in the unsuccessful transitional justice in Serbia. [ABSTRACT FROM AUTHOR]