Petar Sarajcev

Power Loss Computation in High-current Generator Bus Ducts of Rectangular Cross-section

Abstract Due to the medium voltage level of generator terminals and very high-current output, generator connection to the step-up transformer is often carried out with a so-called high-current air-insulated bus duct system. Due to these high currents, during normal generator operation, accompanying Joule power losses are often very high, which in turn, results in excessive (and even non-permissive) heating of the bus duct system. The solution to the mentioned power loss problem involves a determination of currents in phase conductors and in the shield of the metal-enclosed bus duct system. A bus duct transmission line consists of either a segregated or a non-segregated air-insulated three-phase system. Phase conductors and metal enclosures are both rectangular in cross-section. Here, the developed computation model is based on the conductor filament method with application of the geometric mean distance method. It takes into account both skin effect and proximity effects, as well as complete electromagnetic coupling between phase conductors and metal enclosure.

Potential distribution for a harmonic current point source in horizontally stratified multilayer medium

Purpose – This paper aims to describe a numerical procedure for approximating the potential distribution for a harmonic current point source, which is either buried in horizontally stratified multilayer earth, or positioned in the air. The procedure is very efficient and general. The total number of layers and the source position in relation to the medium model layers are completely arbitrary.Design/methodology/approach – The efficiency of the computation procedure is based on the successful application of the numerical approximation of two kernel functions of the integral expression for the potential distribution within an arbitrarily chosen layer of the medium model. Each kernel function of the observed layer is approximated using a linear combination of 15 real exponential functions. Using these approximations and the analytical integration based on the Weber integral, a simple expression for numerical approximation of potential distribution within boundaries of the observed medium layer is given. Pote...

Time-harmonic current distribution on conductor grid in horizontally stratified multilayer medium

This paper presents a novel time-harmonic electromag- netic model for determining the current distribution on conductor grids in horizontally stratifled multilayer medium. This model could be seen as a basis of the wider electromagnetic model for the frequency-domain transient analysis of conductor grids in multilayer medium. The total number of layers and the total number of conductors are completely arbitrary. The model is based on applying the flnite element technique to an integral equation formulation. Each conductor is subdivided into segments with satisfying the thin-wire approximation. Complete elec- tromagnetic coupling between segments is taken into account. The computation of Sommerfeld integrals is avoided through an efiective approximation of the attenuation and phase shift efiects. Computation procedure for the horizontally stratifled multilayer medium is based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer, which is caused by a point source of time-harmonic cur- rent. Extension from the point source to a segment of the earthing grid conductors is accomplished through integrating the potential con- tribution due to the line of time-harmonic current source along the segments axis.

Mathematical model of lightning stroke development

This paper presents a mathematical model of the lightning stroke path development. Any lightning model is a mathematical construct design to reproduce certain aspects of the physical process involved in the lightning discharge. This mathematical model resides on the underlying observed physical properties of the lightning stroke development. It uses Monte Carlo based algorithm in order to simulate stochastic and dynamic movement of the lightning stroke stepped leader descent. Influence of the lightning stroke current amplitude on the path development is also taken into account. Two examples of the lightning stroke stepped leader propagation paths are presented.

Computation of the overhead power line electromagnetic field

This paper presents a novel computational algorithm for the determination of the overhead power line electromagnetic fields. Algorithm is based on the separation of the phase conductor currents into its longitudinal and transversal components and application of the Biot-Savart law for the computing of the magnetic field. Longitudinal component of the electric field is computed from vector magnetic potential, while two other components of the electric field are computed from the transversal currents, which are obtained by the average potential method. Typical example of the 110 kV overhead power line is also considered.

PV power forecast error simulation model

Presence of solar energy driven power sources has been increasing with remarkable trends in recent years. Such growth is mostly related to photovoltaic generation and it is a direct consequence of significant fall in costs for this technology. Such generation, together with load and wind power, requires forecasting in day-ahead operation planning. Furthermore, in power system studies, it is often necessary to simulate performance of such forecasts. This paper presents models for PV power forecast error simulation based on the stochastic process simulation methods. Specificities of PV power forecast error, autocorrelation, correlation and dependence of standard deviation on forecasting horizon, can be reproduced with this model. Furthermore, two distinct models are presented in this paper. First model simulates and superposes forecast error on known PV production time series. Second model is a further improvement of the first model incorporating PV production simulation for purpose of applications in the planning phase when actual data on production is unavailable. Proposed models provide an efficient solution for studies requiring PV power forecast error time series.

Application of Gaussian copulas in describing station impinging lightning overvoltages

This paper presents an application of the bivariate Gaussian copulas in describing - by means of a statistical distribution function - station impinging lightning overvoltages, which could be subsequently employed in the statistical and semi-statistical methods of station insulation coordination. The proposed method further employs a state-of-the-art transmission line model for lightning-surge transient analysis, constructed within the EMTP software. It also makes use of the electrogeometric model of lightning attachment to transmission lines in order to estimate the shielding failure and backflashover rates. The proposed method efficiently generates random lightning currents from these non-normal and correlated bivariate statistical probability distributions and employs them in the Monte-Carlo simulation for the purpose of station equipment insulation coordination.

Analysis of Electromagnetic Influences Concerning Two Adjacent Parallel High-current Bus Ducts

Abstract Due to the medium-voltage level of generator terminals and very high current output, generator connection to the step-up transformer is often accomplished by means of high-current air-insulated bus duct systems. These high currents during normal generator operation produce accompanying power losses, which could result in excessive heating of the bus duct system. Additionally, the associated electromagnetic fields could have adverse effects on the performance of the neighboring equipment. Problems are further exacerbated by the fact that there are often two parallel adjacent systems, often equal in cross-sectional geometry, which interact through the electromagnetic coupling. The starting point for the analysis of the aforementioned problems involves a determination of current distribution in phase conductors and in the shields of the metal-enclosed bus duct systems. This article presents a computation model for the mentioned analysis, which is based on the mesh-current method, with the application of the geometric mean distance method in combination with the conductor filament method. It takes into account both skin effect and proximity effects, as well as the complete electromagnetic coupling between phase conductors and metal enclosures of two mutually parallel and adjacent high-current bus duct systems having equal cross-sectional geometry.

Optimal reconfiguration of distribution network using cycle-break/genetic algorithm

This paper presents novel approach for optimal distribution network reconfiguration using the combination of cycle-break algorithm and genetic algorithms. Significant improvements are introduced in the phases of initial population generation as well as other general operations inside genetic algorithm. These improvements lead to better convergence rate and computational time reduction. Even though genetic algorithms are widely used, problems related to inapplicability for real-size are often present. These problems are related to the high individual rejection rate due to violation of system constraints and distribution network radial structure requirements. Utilization of combined cycle-break algorithm and genetic algorithm solves these issues and allow real-size network application. Acknowledging this fact, algorithm described in the paper is used to find optimal distribution network topology while fulfilling system constraints and maintaining radial network requirements in all solution steps. The proposed algorithm for optimal distribution network reconfiguration is tested on several standard IEEE test cases. Optimal distribution network reconfiguration can be found under minimum network loss or optimal network loading framework.

Energy and reserve co-optimization in power system with wind and PV power

Due to increase in renewable generation presence in power systems worldwide, current practices in day-ahead or hour-ahead operation planning require revision. Both wind and solar energy governed power sources require forecasting similar to load forecasts performed in traditional power systems. When such stochastic generation reaches significant amounts, traditional day-ahead or hour-ahead operation planning is not suitable, and a novel approach is required in order to ensure reliable and economically efficient generation scheduling. This paper presents an optimization procedure for energy and reserve co-optimization accounting for uncertainty in both wind and solar power forecasting. Problem formulation is based on two-stage stochastic programming where energy and capacity procurement is performed in the first stage, while balancing power or curtailments and load losses are performed in the second stage.