A duality-based model of the controlled shunt compensator of transformer type (CSCT) Mohammad Tavakoli Bina ⇑ , Hosein Samsami, Hamed Valizadeh Haghi Faculty of Electrical and Computer Engineering, K.N. Toosi University of Technology, P.O. Box: 16315-1355, Tehran, Iran article info Article history: Received 24 March 2012 Received in revised form 29 July 2013 Accepted 25 November 2013 Keywords: CSCT Duality based model Parameter estimation Simulation abstract This paper discusses the structure of controlled shunt compensator of transformer type (CSCT) based on its operating principles. The modeling procedure of CSCT is further explored from a duality-based mod- eling viewpoint. Then, an experimental prototype is implemented and the results are measured up to the theory and simulation. Finally, the proposed model is used to simulate the interchanged reactive power between network and CSCT in order to demonstrate the capabilities of this compensator in both capac- itive and inductive modes of operation. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Transmission lines are bulky reactive power sources and often operate with surplus reactive power. This gives rise to several problems [1]; as a result, using reactive power compensation is indispensable. There is a variety of compensation techniques, con- trollers and devices, such as synchronous condensers, conventional shunt reactors, static VAR compensators (SVCs) and controllable reactors are developed to cater for such demand. By now, synchro- nous condensers nearly have been abandoned. Conventional shunt reactors cannot provide smooth power regulation, hence, cannot satisfy the requirements of excessively-high voltage long-distance networks. Owing to their complicated techniques, high manufac- ture cost and difficult maintenance, SVC are inapplicable for some countries which has lower semiconductor technique and economy level [2]. Hence, experts put up with some new kinds of controlla- ble reactors such as thyristor controlled reactor (TCR), also called the controllable reactors of transformer type (CRT) [3], and the magnetic controllable reactor (MCR) [4]. A MCR is developed on the principle of a magnetic magnifier. By controlling the angle of thyristor opening, the dc flux component in the core is regulated and thus the saturation of the core. By this means the purpose of automatic control of reactive power is real- ized. Unfortunately, there are two shortages inherent in MCRs [3]. First, due to the iron saturation, there is a high level of harmonics in the working currents. Then, the existence of the dc bias magne- tization gives rise to large electromagnetic Inertia, which results in low response. To get around the main defect of the MCRs, research- ers proposed CRTs in the late 20th century [3]. A CRT is equivalent to a multi-winding transformer with a net- work winding (NW) which is connected to the network high volt- age bus, and several control windings (CWs), in which a thyristor valve (TV) in parallel with a voltage circuit breaker, are connected across each of them. By controlling the TVs properly, CRT can real- ize the function of smooth stepwise power regulation from no load to nominal conditions, satisfying the current harmonic content constraints. In addition to those advantages of ordinary reactors, a CRT possesses other virtues such as low current harmonic con- tent, fast response, and small losses. Therefore, a CRT can be em- ployed to control reactive power of transmission networks [3]. However, in case there is strong inductive coupling among CWs, such negligence cannot render satisfactory results. It is noticed that the voltage of the network winding is the high voltage of the grid. Hence, when the short-circuited impedance between the NW and CW is less than 100%, current-limiting reactors (CLRs) are needed to limit the currents within the rated. When the regulation step number is more than two, the number of the windings for a CRT is larger than three. In this case, a precise calculation is very hard to obtain. This paper presents a controlled shunt compensator of trans- former type (CSCT) as a new kind of the CRTs, with only one control winding and too high short circuit reactance to solve the above problems. It provides sufficient response rate, very low total har- monic distortion (THD) and independently bidirectional reactive power injection. The controlled shunt compensator of transformer type (CSCT) is a new compensator which can be installed in high voltage 0142-0615/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijepes.2013.11.041 ⇑ Corresponding author. Tel.: +98 21 8406 2280; fax: +98 21 8846 2066. E-mail address: tavakoli_bina@ieee.org (M. Tavakoli Bina). Electrical Power and Energy Systems 57 (2014) 304–310 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes