Determination of Flicker Propagation Direction in Power Systems with Arc Furnace Loads Arash Kiyoumarsi, Behzad Mirzaeian Dehkordi, Pegah Hamedani, Department of Electrical Engineering, Faculty of Engineering, University of Isfahan, Isfahan, Iran *corresponding author: E-mail: mirzaeian@eng.ui.ac.ir Abstract- The daily increase of various flicker source loads in power systems, has a lot of disadvantages like malfunctioning of electrical instruments and light flickers of the loads. Therefore, it is hardly demanded to determine the direction of flicker propagation that in turn helps to locate the flicker compensators. This paper has used an algorithm [1] for determining the flicker source direction. This method has been tested on a case study with two arc furnaces that are the main source of voltage flicker generation. The algorithm performance has been validated by the simulation results. Index terms- Arc furnace, Flicker Direction, Flicker Power, Power Quality I. INTRODUCTION Each phenomenon that changes the voltage rms value can be considered as a source of flicker generation. Inter- harmonics can cause voltage fluctuations or voltage source changes. Loads which cyclically change the active and reactive power, are considered as flicker sources. These cyclical changes cause cyclical voltage drops over the source impedance and thereby changes in the voltage amplitude. Even rather small voltage fluctuations (less than 1 percent) can cause a quite annoying flickering light. It is of mutual interest for both the utility and its costumers to find the flicker source [1]. In this paper a new algorithm is proposed for determining the flicker propagation direction. The performance of this algorithm is based on the sampling of voltage and current signals. They have developed their work in [2]. So far a lot of works have been done to measure the intensity of voltage flicker, so far. In [3-5] by using the IEC flickermeter, the intensity of flicker caused by flicker source loads has been evaluated. In [6] a frequency domain method based on the frequency component propagation of a power network is proposed for determining the flicker direction. In [7] a method for studying flicker propagation based on frequency domain and interharmonics is described. According to the IEC 61000-4-15 standards [8], low frequency fluctuations in voltage and current are recovered from the input signals by demodulation and are passed through a proper bandpass filter. Based on the output of these two bandpass filters, a new quantity -flicker power- is defined. The direction of a flicker source is obtained from the sign of this flicker power. Motivated by the previous discussion, this paper will apply the latter flicker direction algorithm to a case study with two arc furnaces which are the main flicker source loads in power networks. The performance of the utilized algorithm will be verified by means of simulations. The case study is simulated using PSCAD/EMTDC software [9]. II. VOLTAGE FLUCTUATIONS AND LIGHT FLICKER [1] Voltage fluctuations originate from fluctuations in load current. It can be explained by examining the one-line diagram in Fig. 1 representing a small power network consisting of a source voltage , a source impedance , one flicker load , and one static load . Voltage fluctuations at occur due to changes in (i.e., changes in load current). The voltage fluctuations lead to fluctuations in the light intensity of lamps. Slow changes in light intensity are experienced by the human observer simply as changes in light intensity or often not noticed at all. Very fast light intensity variations are not noticed due to the time constant of the lamp as well as the human eye- brain combination inability to observe very fast phenomena. Light-intensity fluctuations in a transition region are observed as light flicker. If this light flicker becomes too severe or lasts too long, it will become annoying or even lead to a headache. Annoying light flicker due to voltage fluctuations is also referred to as “voltage flicker”. Voltage fluctuations may also affect the performance of motors and other electronic devices but the main concern is their effect on lighting sources. Fig. 1. One-line diagram with flicker load 1 Z and static load 2 Z Fig. 2 shows the human being sensitivity curves for voltage fluctuations as described in the flicker- meter standard IEC 61000-4-15. The diagram gives the border lines for flicker perception as magnitude of the fluctuations with respect to the frequency of the variations (the solid