Analysis on the Fusion Technology of a Commercial Transformer and an SFCL
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O R I G I N A L PA P E R
Analysis on the Fusion Technology of a Commercial Transformer and an SFCL Yong-Sun Cho · Byung-Ik Jung · Hyo-Sang Choi
Received: 6 November 2012 / Accepted: 30 November 2012 / Published online: 20 December 2012 © Springer Science+Business Media New York 2012
Abstract In this study, a new concept is proposed on a combination device with functions of a commercial transformer and a superconducting fault current limiter (SFCL). This device serves as a transformer by stepping the voltage up or down in normal condition. When a transient phenomenon occurs in the power system, it serves as an SFCL to limit the fault current. The device quickly detects the line current using a current transformer (CT), and is based on the high-speed, silicon-controlled rectifier (SCR) interrupter operation. This is done by identifying the fault using an SCR switching control system. The test results showed that the fault current was limited by the impedance of the superconducting element a half cycle after a fault occurred. An SCR that initially had a normally open contact was turned on within a half cycle. However, an SCR with a normally close contact was turned off after a half cycle because the current dropped below the holding current after a half cycle. The voltage of the superconducting element was low in the step-down turn ratio condition of the transformer. This was because the secondary and tertiary windings were connected in series due to the SCR-1 turn-off condition, and the sum of voltages on each winding appeared on the superconducting element. By combining the existing power device technology and an SFCL technology, it is expected that the existing problems of an SFCL can be addressed to construct a smart power system. Keywords Commercial Transformer and SFCL · Step-down and up · SCR switch Y.-S. Cho · B.-I. Jung · H.-S. Choi () Department of Electrical Engineering, Chosun University, 501-759, 375 Seosuk-Dong, Gwangju, Korea e-mail: [email protected]
1 Introduction The power system sector has continued to develop in order to provide high-quality, large-volume electricity that meets the demand. To produce electricity for diverse demands, many advanced technologies are used to reduce the external effects and ensure accurate control and monitoring [1–4]. Of the surrounding environments, however, the lightning affects the power devices and customers by causing a large quantity of transient current in the power system [5, 6]. This is the biggest problem for the power system to have a large capacity. To prevent the over current due to the lightning, numerous researchers around the world are developing the SFCL [7–13]. Nonetheless, because of the characteristics of the SFCL, many parts that include the cryostat and superconducting element must be simultaneously developed. There are also many problems involved, including the thermal strength of the superconducting element, phase conductor lead, and cost competitiveness. In addition, there are also the secondary problems such as the space for the installa
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