978-1-5090-0169-9/15/$31.00 ©2015 IEEE Study of Power Quality with changing customer loads in an urban distribution network Tareq Aziz Department of Electrical & Electronic Engineering Ahsanullah University of Science & Technology, Dhaka, Bangladesh. Email: aziz.tareq@gmail.com, taziz@ieee.org Sanjib Kumar Nandi, Md. Siddikur Rahman, Ridown Rashid Riadh American International University-Bangladesh, Dhaka, Bangladesh. Email: sanjib.eee.aiub@gmail.com, rahman.siddikur286@gmail.com, rashidridown@gmail.com. Abstract— Power quality is one of the most significant current discussions in electric energy distribution systems. The issue of harmonics has been a controversial and much disputed subject within the field of power quality. Harmonic current originates from all types of nonlinear loads. This paper attempts to show the impacts of rapidly increasing share of nonlinear loads on harmonic distortion of urban distribution feeders. The recommendations of IEEE Std. 519-1992 and Bangladesh Grid Code are considered carefully. Simulations have been carried out to find out how far the existing distribution system can accommodate non-linear loads. Results show that though the connected load is not hampering power quality of test distribution at present, an increase of nonlinear load share above 30% would cause Total Harmonic Distortion (THD) go beyond tolerable limit and result in poor power quality. Keywords-Power Quality, Distribution System, Harmonic Sources, Nonlinear Load, Total Harmonic Distortion (THD) I. INTRODUCTION The term power quality is the assurance of proper power in power distribution system [1, 2]. The purpose of the electric utility is to provide sinusoidal voltage at properly sustained scale all over their system. In real scenario, it is quite impractical to attain this kind of state. When a sinusoidal voltage is applied to a certain type of load, the current drawn by the load is determined by the voltage and impedance. Loads that cause the current to vary disproportionately with the voltage during each cyclic period are classified as nonlinear loads. Nonlinear loads create harmonics by drawing current in abrupt short pulses rather than in a smooth sinusoidal manner. Since harmonic distortion is caused by nonlinear elements connected to power system, any appliance/ equipment that has non-linear characteristics will cause harmonic distortion. The influence of harmonic currents on power system is a fairly- investigated topic at present. High harmonic currents cause fuse blowing in capacitor banks resulting in a loss of reactive power supply to the system. Harmonic voltage distortion may cause equipment insulation stress particularly in capacitors. Keeping low THD values on a system ensures proper operation and longer life span of equipments. However, in recent years, a substantial increase of non-linear loads has been noticed across all types of feeders in recent years. Along with residential and commercial feeders, industrial feeders having metal factories are also facing similar situations [3, 4, 5]. Research work has been conducted on load behavior and harmonic contribution in various sectors of power system. The influence of load model on behavior of electrical power system is examined in [6]. Experimental determination of nonlinear loads in power systems have been carried out in [7]. The sources of harmonic distortion and the propagation of the distortion in the power system and their effects are observed in [8, 9, 10]. However, very few papers have investigated the detail impact of nonlinear load along with the ultimate limit of its inclusion in test feeders. The goal of this paper is to investigate harmonic distortion in an urban distribution network due to changing load pattern. A practical urban system has been taken as test system where the ultimate inclusion limit of non-linear load has been sorted out. This paper is organized as follows: Section II presents a brief overview of sources of harmonics and their measurement index in distribution feeders. A detail account of recent changes in customer load pattern has been presented in section III. Simulation results along with analysis have been discussed in section IV. Finally section V concludes the work highlighting the major contributions. II. HARMONIC SOURCES AND MEASUREMENT In an ideal power system voltage and current waveforms are purely sinusoidal. In a simple circuit containing only linear circuit elements (resistance, inductance and capacitance), the current which flows is proportional to the applied voltage. So that it results in a sinusoidal current flow. In practice, non- sinusoidal currents result when the current flowing through the load is nonlinearly related to the applied voltage [5]. This section identifies the common sources of harmonic along with the measurement index of harmonic contents. A. Harmonic Sources Industrial, commercial, and residential facilities are exposed to various sources of harmonics. In general, sources of harmonics are divided into: (a) Domestic loads (b) Industrial loads (c) Control devices [11]. Figure 1 depicts this classification.