Copyright © IFAC Power Plants and Power Systems Control, Seoul. Korea, 2003 ELSEVIER IFAC PUBLICATIONS www.elsevier.com/localelifac INTERACTION AND COORDINATION OF TWO STATIC VAr COMPENSATORS IN CLOSE ELECTRICAL PROXIMITY Raymond S. C. Chokelal and Jin Jiang Department ofElectrical and Computer Engineering The University of Western Ontario, London, Ontario N6A 5B9, Canada Phone: (519) 661-2111 ext. 88320, Fax: 519-661-3488, Email:jjiang@uwo.ca Abstract: Flexible AC Transmission Systems (FACTS) and Custom Power Devices have proven to be very useful in improving power system stability and transmission capability. However, the potential interaction among multiple FACTS devices in close electrical proximity is still an open issue. This paper presents a case study to investigate the interaction and lack of coordination between two FACTS in a distribution network through computer simulations. The system consists of two Static YAr Compensators (SYCs). One of them is installed on the load bus by an industrial customer to improve the power quality and the voltage profile, and the other is used by the utility to increase the voltage stability on a relatively weak feeder line. The emphasis of the paper is on the interaction of these two devices and their effects on the voltage profile of the distribution system. After the preliminary studies, it is shown that the interaction does exist, and one of the effective ways to reduce such an interaction is through coordinating control. The performance of the system with a simple coordinating controller is illustrated. It is shown that such control strategies are quite effective. Copyright © 2003 IFAC Keywords: Flexible AC Transmission System, FACTS, Custom Power, Static YAr Compensator (SYC), and Distribution. 1. INTRODUCTION The rapid de-regulation of world electric market calls for tighter control over the power flows on the grid at transmission level, while the increasing use of large scale transient inducing loads has lead to poor power quality at the distribution level. Such phenomenon can best be characterized by frequent occurrence of voltage sags or swells. In addition to improving the transmission capability of existing transmission lines, another application of Flexible AC Transmission System (FACTS) devices is to improve the voltage profile by injecting or absorbing reactive power (Kundur, 1994). Such devices could be located in a transmission network or at a distribution bus point. When used at distribution level, such devices are often known as Custom Power devices. For heavy industrial customers, it is possible that they would like use such a device at their service entrance to mitigate the effects of potential poor power quality or simply to ensure that sags/swells do not affect their own equipment. However, use of such a device could potentially interact with other FACTS devices on the transmission network installed elsewhere by the utility company. The interaction could even result in more serious 529 consequences. The objective of this paper is to investigate such issues and to determine whether there is a need for a coordination control for multiple FACTS devices. If so, what are the strategies in such a coordinating controller? The findings from this study can form a basis for further investigation in the design of such a coordinating controller. Specifically in this paper, we will investigate the above issues in a realistic distribution network of a heavy industrial user located in Sarina, Ontario, Canada, where two Static YAr Compensators (SYCs) have been installed. Since most of industrial loads are inductive in nature, with no exception to this particular industrial customer, the voltage profiles considered herein pertain to large induction loads. The issues on the placement of FACTS devices on transmission networks have been documented and their interaction at the transmission voltage class have also been extensively studied (Mathur and Yarma, 2002). However the problems associated with the use of FACTS technology at a distribution voltage level have not received the same level of attention. There are several special issues when one has to consider for the problem at the distribution level. One of them is that percentage of voltage