Abstract--Power quality monitoring system is the cornerstone of power quality analysis, diagnosis and improvement. Power Quality (PQ) measurement concepts are evolving from instantaneous metering to continuous monitoring and recent developments in measurement technology make PQ monitoring system more powerful. That is, now it is possible to construct more flexible, reliable, fast and economical PQ monitoring system. So this paper presents an improved PQ monitoring system with central processing scheme. Proposed system basically consists of one PQ analyzer and multiple PQ meters. PQ meter only acts as raw data acquisition system and PQ analyzer performs all calculations and analysis algorithm. The proposed system is very economical especially for large-scale system because the price of PQ meter can be dramatically lowered in this scheme. PQ monitoring algorithms to catch steady-state trends and to detect PQ events are also proposed. The prototype of this system is constructed and real-time tests are performed using this system. Key words? analyzer, central processing, detection, Ethernet, event, measurement, meter, monitoring, power quality, PQ I. INTRODUCTION ower quality was the ability of utilities to provide electric power without interruption in the past. In recent years due to increase in critical load and electronic device, customers require high level power quality than ever before, so power quality has become an important concern to customers as well as utilities and facilities. Power quality is different from reliability in that it treats very short-duration events with a few cycles or seconds. New PQ problems such as sag, swell, harmonic distortion, unbalance, transient and flicker can impact customer operations, causing malfunctions and costs on lost production and downtime. To avoid these malfunctions and unnecessary costs, many facilities and large customers have been required to install PQ monitoring system[1-2]. The deregulation in power system (especially in Korea) is based on competition between the participants, who enter into contracts according to their own interests. In this case, electric This work was supported in part by the LG Industrial Systems Co., Ltd. Dong-Jun Won, Il-Yop Chung, Joong-Moon Kim and Seung-Il Moon are with the School of Electrical Engineering and Computer Science, Seoul National University, Seoul 151-742, Korea (e-mail: donjuan@ powerlab. snu.ac.kr). Jang-Cheol Seo and Jong-Woong Choe are with Electrotechnology R&D Center, LG Industrial Systems Co., Ltd., Cheong Ju, Korea (e-mail: jcseo@ lgis.com). power traded in market is considered as a product which has price and quality. As a matter of course, the quality of the electric power must be measured and evaluated. These facts also increase the need for PQ monitoring system[3]. Recent PQ monitoring systems show more high-tech functions than previous systems. Developments in electronic device and communication accelerate this tendency. Ethernet communication, graphic user interface (GUI) through web- browser and statistical analysis will be the basic functions for future monitoring systems[4]. And PQ monitoring system will be installed in large-scale for PQ analysis and diagnosis. In that case, conventional PQ monitoring system that calculates and processes raw data in one meter cannot have economic efficiency. Instead, the system in which several meters (PQ meter) only gather raw data and one central processing device (PQ analyzer) performs all calculations is more suitable and beneficial. So this paper presents the PQ monitoring system with central processing. The structure of this system is proposed and the advantages of this system are explained compared to the conventional system. PQ monitoring algorithm is also developed and implemented in this system. Prototype system is constructed and various power quality events are analyzed using this prototype. II. NEW TRENDS IN POWER QUALITY MONITORING A. Evolution from metering to monitoring As stated in introduction, it is the starting point to measure power quality to solve PQ problems. PQ measurement systems have many variations in their structure, price and function. Though it is somewhat difficult to classify all the PQ measurement systems into several groups according to their characteristics, they can be classified as Table I. TABLE I CLASSIFICATION OF PQ MEASUREMENT SYSTEM ACCORDING TO THEIR OBJECTIVES Group Objective Measurement Meter Instantaneous V, I, P etc. Analyzer Periodic, Reactive V, I, P, etc., Harmonics, Waveform, Event Monitor Continuous, Proactive Above contents + Statistics + Indices Development of Power Quality Monitoring System with Central Processing Scheme Dong-Jun Won, Il-Yop Chung, Joong-Moon Kim, Student Member, IEEE, Seung-Il Moon, Jang-Cheol Seo, Jong-Woong Choe, Member, IEEE P 0-7803-7519-X/02/$17.00 © 2002 IEEE 915