Numerical Analysis of Power System Electromechanical and Electromagnetic Transients based on the Finite Element Technique

This paper presents a novel technique for numerical analysis of electromagnetic transients and electromechanical oscillations in a power system. The proposed method is based on the finite element method (FEM). The finite element technique so far used for numerical analysis of continuum field problems here has been adopted to analyse electromagnetic and electromechanical transients in a power system. According to the finite element technique in the field problem, where the region of interest is divided into finite elements, in the proposed method power system is also divided into electric power system (finite) elements. Each finite element (generator, transformer, transmission line, load etc.) is characterized by a system of governing differential equations. Using generalized trapezoidal rule, also known as thetamethod for time integration, the system of differential equations of each electric power system (finite) element can be transformed to the system of algebraic equations for every time step. Once when a system of algebraic equations of each electric power system element is obtained, assembly procedure has to be done. The main contribution of the proposed approach is in an assembly procedure. With the proposed approach, in case of any disturbances in power system or in a part of power system, nodal voltage and branch currents will be obtained, as well as all other interesting variables. The proposed method will be tested on the example of the single-phase short circuit in the power system

Distribution and dispersal of two invasive crayfish species in the Drava River basin, Croatia

The aim of this work is to explore the current distribution and dispersal rates of two nonindigenous crayfish species (NICS) recorded in Croatia: the signal crayfish (Pacifastacus leniusculus) and spiny-cheek crayfish(Orconectes limosus). Both NICS have been recorded in the Drava River basin, with signal crayfish spreading downstream from the north-west along the Drava’s tributary the Mura River, and spiny-cheek crayfish spreading upstream from the east from the Danube River throughout the Drava River. Signal crayfish distribution in the Mura River has been recorded up to 3 km from the confluence with the Drava River. Based on literature data and the current recorded distribution front, the downstream dispersal rate was between 18 and 24.4 km·yr−1. Spiny-cheek crayfish distribution has been recorded 15 km upstream of the Drava River mouth into the Danube River. Its upstream dispersal in the Drava River has been calculated at 2.5 km·yr −1. Both NICS could have an impact on native crayfish populations recorded within the Drava River basin in Croatia: the noble crayfish (Astacus astacus) and the narrow-clawed crayfish (Astacus leptodactylus). In the Mura River no noble crayfish have been recorded since 2007, and the watercourse is at the moment dominated by the signal crayfish. Spiny-cheek crayfish populations have been found in coexistence with narrow-clawed crayfish populations, with O. limosus dominating by 16:1