Electric Power Systems Research 127 (2015) 271–279 Contents lists available at ScienceDirect Electric Power Systems Research j o ur na l ho mepage: www.elsevier.com/locate/epsr Unbalance and harmonic distortion assessment in an experimental distribution network Aranzazu D. Martin a , Reyes S. Herrera a , Jesus R. Vazquez a,* , Paul Crolla b , Graeme M. Burt b a University of Huelva, Spain b University of Strathclyde, Glasgow, Scotland a r t i c l e i n f o Article history: Received 2 September 2014 Received in revised form 18 May 2015 Accepted 7 June 2015 Available online 26 June 2015 Keywords: Harmonic distortion source Distribution networks Non-linear loads Unbalance a b s t r a c t The identification of voltage and current harmonic distortion and voltage unbalance sources is one of the main problems in electric distribution systems. In order to overcome it, in this paper the use of two novel indices is proposed. On the one hand, the Load Characterization Index (LCI) is suggested to calculate the harmonic distortion introduced by the load. This index identifies linear and non-linear loads in the power systems. On the other hand, the Unbalance Current Ratio (UCR) is suggested to assign the responsibility for system unbalance to load and source sides. Both indices can be calculated only from the measurement of the current at the input of the load and the voltage at the Point of Common Connection (PCC). The main objective of this paper is to test the performance of these two indices on an experimental three-phase electrical network. In order to do that, several experimental tests have been considered. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Nowadays,the assessment of electric power quality is becoming increasingly important due to the widespread use of non-linear and time-varying loads. Otherwise, the uneven distribution of single- phase loads in the low voltage distribution system, among other causes, makes the voltage unbalance a problem in the power sys- tem. In this way, the IEEE Standard establishes the procedure to assess the voltage and current distortion and unbalance in the electric network PCC, [1,2]. Power monitoring equipment is fre- quently used to do that, [3–7]. However, the Standard does not regulate the procedure to assign the responsibility for the net- work harmonic distortion and/or unbalance to the different agents in the electric power system. This is a requirement to decrease these non-conformities, i.e., knowing the cause of the distortion and/or unbalance, the best location of the compensation systems is guaranteed and the most suitable procedure to mitigate them is established [8]. There are many proposals in technical papers to establish the responsibility of each agent for the harmonic distortion in power distribution networks [9–19]. One of the most significant methods is based on the sign of the harmonic active power. It can be used * Corresponding author. Tel.: +34 959217579; fax: +34 959217304. E-mail address: vazquez@uhu.es (J.R. Vazquez). with measurements in a single-point, [10,11], or with distributed measurements systems, [12–15]. This method is based on the fact that the harmonic active power flows from source to load if the load is linear, whereas it flows in the opposite direction when it is a distorting load. One of the indices based on this concept is the Harmonic Global Index, HGI, which will be considered in the experimental results assessment. Other methods are those based on the representation of load and source sides by means of their corresponding Norton circuits, [16]. There is a further technique called the critical impedance method, [17]. The drawback of these methods is the necessity of knowing the network and consumer harmonic impedances. Numeric techniques have also been used to establish each agent responsibility for the harmonic distortion in the electric network, for example, neural networks, [18]. Finally, there is another set of methods in the literature based on the current decomposition, [9,20,21,28]; among them, the Non- Colinear Index (NCI), [21], and the Non-Linear Index (NLI), [20], these will be used in the experimental results assessment in this paper. Another of those methods is the Load Characterization Index (LCI), [9], proposed by Herrera and Salmerón, which is based on the decomposition of current at the input of the load into two compo- nents: a current component which introduces harmonic distortion into the system and a second current component which does not introduce harmonic distortion, and whose harmonic distortion is the same as that of the voltage. http://dx.doi.org/10.1016/j.epsr.2015.06.005 0378-7796/© 2015 Elsevier B.V. All rights reserved.