Electric Power Systems Research 146 (2017) 218–227 Contents lists available at ScienceDirect Electric Power Systems Research journal homepage: www.elsevier.com/locate/epsr Modelling of three-phase electric arc furnace for estimation of voltage ﬂicker in power transmission network Ana Tomasovi ´ c Tekli ´ c a , Boˇ zidar Filipovi ´ c-Grˇ ci´ c b,∗ , Ivica Pavi ´ c b a Konˇ car Electrical Engineering Institute, 10000 Zagreb, Croatia b Faculty of Electrical Engineering and Computing, University of Zagreb, 10000 Zagreb, Croatia a r t i c l e i n f o Article history: Received 24 June 2016 Received in revised form 24 December 2016 Accepted 30 January 2017 Keywords: Electric arc furnace Voltage ﬂicker Matlab/Simulink Power quality Flickermeter a b s t r a c t This paper presents a dynamic model of an electric arc furnace (EAF) developed in Matlab/Simulink environment. Model is based on simulating varying resistance of the electric arc in time-domain while taking into account its stochastic behaviour. The model was applied for estimation of voltage ﬂicker in power transmission network at the point of common coupling caused by operation of EAF. Modelling and simulation of an International Eletrotechnical Commission (IEC) ﬂickermeter were also performed in order to calculate voltage ﬂicker from the simulated EAF voltage. In order to verify the developed EAF model, calculations of voltage ﬂicker were compared to measurements obtained from various operating conditions of the EAF such as boring, melting and reﬁning. Inﬂuence of short circuit power and switching operating condition of the transmission network on ﬂicker levels at point of common coupling was investigated. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Highly nonlinear time-varying loads, such as electric arc fur- naces (EAFs), are widely used in the steel-making industry. Due to the process of melting and reﬁning metals, mainly iron in the steel production, the EAF consumes large power which causes sig- niﬁcant power quality (PQ) disturbances, such as harmonics and voltage ﬂuctuations on the connected power network [1]. Distur- bances produced by EAFs in electrical networks can signiﬁcantly affect the voltage quality supplied by electrical power companies [2]. An EAF is a non-linear and time-varying load, which gives rise to harmonics, interharmonics and voltage ﬂuctuations (ﬂicker). The cause of harmonics is mainly related to the non-linear U–I charac- teristic of the electric arc, while the voltage ﬂuctuations are due to the arc length changes that occur during the melting of the scrap. The current and voltage harmonic distortion may cause sev- eral problems in electric power systems such as premature ageing of equipment, incorrect operation of devices and additional losses in both transmission and distribution networks. The ﬂicker phe- nomenon causes a physiological uneasiness in vision due to electric lightning ﬂux ﬂuctuations, which are particularly important with ∗ Corresponding author. Fax: +385 16129890. E-mail addresses: at.teklic@koncar-institut.hr (A.T. Tekli ´ c), bozidar.ﬁlipovic-grcic@fer.hr, bozoﬁlipovic@gmail.com (B. Filipovi ´ c-Grˇ ci´ c), ivica.pavic@fer.hr (I. Pavi ´ c). incandescent lamps. Therefore, it is of crucial importance to pre- dict the ﬂicker levels when an EAF is connected to a network or when an existing EAF is upgraded. In cases when ﬂicker emission limits are exceeded, mitigation techniques should be considered in order to correct such disturbances. An extensive research which enables practical application of static synchronous compensators for improving PQ in EAF and ﬂicker compensation applications was published in Ref. [3]. Obtaining an accurate model of EAF in time domain is thus important to study the impact of such load on the connected power system. For instance, the ﬂicker assessment of EAF loads has to be calculated to check the compliance with the regulated standards [4,5]. Therefore, it is crucial to model these nonlinear loads for the PQ studies and mitigation designs. Many models of the U–I characteristics have been proposed in the literature for both steady-state or dynamic operation of EAF. In Ref. [6] a controlled voltage source model for the EAF was proposed based on the piecewise linear approximation of the U–I characteristic. In Refs. [7,8] nonlinear time-varying resistance models for the EAF were proposed, where the arc length is domi- nated by periodic sinusoidal and band-limited white noise laws for ﬂicker compensation purpose. In Ref. [9] the conductance model of the EAF for harmonic studies was proposed based on Cassie equation representing the single-phase U–I characteristic during reﬁning stage. A time-varying resistance model was proposed in Ref. [10] for studying the early stage of melting cycle where the arc voltage is described by a linear function of arc length in random http://dx.doi.org/10.1016/j.epsr.2017.01.037 0378-7796/© 2017 Elsevier B.V. All rights reserved.