60 PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 8/2012 Robert ZIEMBA Rzeszow University of Technology Computer Simulation of Fast Transients in Railway Systems Abstract. The railway installations are particularly endangered by the direct lightning discharges in the supplying system or equipment and indirect lightning strike. Lightning overvoltages are the most unfavorable voltage stresses for the railway traction. The objective of paper is to develop modeling and digital simulations involving fast front waveforms. The creation of digital models for the analysis of work of the equipment (power system, rails, induced voltage, traction tower etc.) requires the knowledge of data organizing file and declarations used by simulation programs. The paper comprises results of calculations of overvoltages in the railway traction, performed using software package a EMTP-RV simulation software. Streszczenie. Symulacje komputerowe pełnią ważną rolę w badaniach oddziaływania elektromagnetycznego urządzeń elektroenergetycznych. Wykorzystując w symulacjach sprawdzone modele matematyczne urządzeń i zjawisk fizycznych z powodzeniem można uzupełniać badania laboratoryjne i „poligonowe” rzeczywistych układów. W referacie przedstawiono wyniki modelowania komputerowego sieci trakcyjnych przy wymuszeniach szybkozmiennymi impulsami prądowymi reprezentującymi impulsy pochodzenia atmosferycznego lub łączeniowego (Symulacje komputerowe szybkozmiennych stanów nieustalonych w sieci trakcyjnej). Keywords: railway systems, transients modelling, transmission line. Słowa kluczowe: siec trakcyjna, modelowanie szybkozmiennych przebiegów, linia transmisyjna. Introduction Lightning overvoltages are the most unfavourable voltage stresses for the railway traction. These threats cause interference in the equipment services and signal transmission system. The creation of digital models for the analysis of work of the equipment (power system, rails, induced voltage, traction tower etc.) requires the knowledge of data organizing file and declarations used by simulation programs. The paper comprises results of calculations of overvoltages in the railway traction, performed using software package a EMTP-RV simulation software. The overhead lines are represented by multi-phase models considering the distributed nature of the line parameters due to the range of frequencies involved. A possibility of the transient analysis of examples of dynamic characteristics of the selected model is presented. The equivalent model of the rail, interpolation methods and the rail conductor are presented. They will be utilized in future work during estimation of impedance of the track circuits based on the current obtained results and recognized possibility. Surge transients In Polish standards [1, 2] there are presented general requirements and research regarding electromagnetic compatibility (EMC) of devices, sets of devices and systems destined for automation and measurement. The range of applying these standards encompasses: designing, production, technical acceptance, installation and exploitation of the devices destined for automation and measurement. They define a group of standard surge tests waveforms. Traditionally, the 1.2/50 μs voltage waveform was used for testing the basic impulse level of insulation (BIL). The 8/20 μs current waveform was used to inject large currents into surge-protective devices. Mathematical representations of the nominal waveforms would be convenient for engineers who wish to perform computer simulations of transient protection circuits are given by equations: (1)   t t m e e U A t u         ) ( (2)  t m e t I A t i     3 ) ( where: A - correction factor; , , - time constants. These equations are useful for designing surge generators and for simulations of surge performance on computers. In the group of standards regarding railway applications, for the network compatible with PN-EN 50163 [3], the PN-EN 50124-2 [4] standard introduces, apart from the abovementioned 1.2/50 μs and 8/20 μs surges, impulses for testing the basic impulse level of insulation. It is 4/10 μs current surge defined in the PN-EN 60099-1 and –4 standard [5, 6] and in PN-EN 50123-5 [7]. Moreover, the PN-EN 60099-4 standard also suggests applying 30/80 μs current surge with the peak value equal 40 kA for testing surge arresters in the AC networks. In Fig. 1 there are presented the waveforms of 4/10 μs and 30/80 μs current impulses. The parameters of approximating those impulses with double exponential functions defined by (1) are A = 8.067 =0.21•10 6 μs;  = 0.295•10 6 μs – for 4/10 μs impulse and A = 10.96;  = 0.029•10 6 μs;  = 0.038•10 6 μs; – for the 30/80 μs impulse. Fig. 1. Waveforms of the current surges 4/10 s and 30/80 s Frequency spectrum of surge impulses Frequency analysis of any signal involves the transformation of a time-domain signal into its frequency components. The need for describing a signal in frequency domain exists because signal processing is generally accomplished using systems that are described in terms of frequency response.