Researchs On The Novel High Temperature Superconducting Fault Current Limiter

Development of electrical power systems is accompanied by a constant increase in short circuit breaking capacity and fault currents, these impose enhanced electrodynamical and thermal stability requirements to be met by electrotechnical device components. This in turn leads to a significant increase in size, weight and cost of electrical power equipment. As a consequence, exorbitant short current would pose threat to the power equipments and their operators. In order to cut the short-current to the lower level when the control equipment of power system can break, during the last few years, a number of programs have been sponsored to investigate various techniques and devices applicable to limit fault currents in power systems. One method for fault current reduction is the application of fault current limiting devices having nonlinear characteristics: low impedance in normal operating conditions. the most ideal one of such devices is the superconducting fault current limiting devices. In a normal work condition, it is a good conductor with no influence on power system. However, in the case of short-circuiting, its impedance abruptly increase to limit short current and short circuit breaking capacity. It works naturally and is self-examination, self-triggered, self-operation and self-restore. If we can make its products more applicable, it can not only upgrade the capability of the existing electrical transmission system, but also can exalt the safey and dependability of the power system and power supply quantity.This paper introduced superconductor's basic characteristic and its theory, discussed its application. Then it reviewed the development of the superconducting fault current 1imiter, mainly about their principles, configurations and characteristics of SCFCL. The system requirements for the current 1imiting devices have been proposed and potential installation locations and benefits for user resulting from the effective fault current 1imiter have been shown. Analyzed quantitatively the economic benefit of SCFCL, and expatiated the technique benefits of HTSCFCL from the dependable with lower system insulate 1evel. Later, the magnetic-shield inductive HTSCFCL, the hybrid HTSCFCL and the rectifier bridge type HTSCFCL are studied and improved.firstly, our aim is to analyze the magnetic shielding type high temperature superconducting fault current limiter(HTSCFCL) in this context, the magnetic shielding type HTSCFCL, the improved magnetic shielding type HTSCFCL and the novel magnetic shielding type HTSCFCL are discussed as following:The magnetic shielding type HTSCFCL mainly consists of a primary copper coil, a high-Tc superconducting cylinder ring as the secondary winding, an iron core and a sub-cooled nitrogen cryostat with a cryocooler, the principle of the device's operation is based on a rapid rise of the device's impedance at the transition of the ring from the superconducting to the normal state. The operating theory of the fault current limiter is discussed deeply. The effect of parameters variety of the magnetic shielding type HTSCFCL is analyzed for limiting fault current.An improved magnetic shielding type HTSCFCL with a control ring and an air gap is developed and analysized, it can effectively avoid the reduction of a limiting impedance in the HTSCFCL under the higher current with an effective air gap and shorten recovery time by using a copper ring.A novel magnetic shielding type HTSCFCL is proposed for three-phase power system. The model of an inductive current-limiting device consists of a primary high-Tc superconducting coil, a high-Tc superconducting cylinder ring as the secondary winding, an iron core and a sub-cooled nitrogen cryostat with a cryocooler. The principle of the device's operation is based on a rapid rise of the device's impedance at the transition of the winding and the ring from the superconducting to the normal state.The results of simulation demonstrate that the three type magnetic shielding type HTSCFCL can reduce both the transient and the steady-state fault current significantly, the devices are of great benefit in improving transient stability and enhancing the electrical energy quality of power system.Secondly, based on studying of the working principle of hybrid type dc high temperature superconducting fault current limiter and dc S/N transition rectifier bridge type high temperature superconducting fault current limiter, the concept of a hybrid fault current limiter is introduced. A novel single-phase hybrid type dc high temperature superconducting fault current limiter is proposed, which is based on a novel fast-acting IGBT to control the protection resistor within 100μs after fault detection. The new design method by MATLAB simulation that we put forward in this paper is an effective approach for the accurate design parameters and its promise limiting-current results.Then a novel rectifier type high temperature super conducting fault current limiter for a three-phase power system is developed. When normal operating, no current limiting mode occurs through the application of DC bias current to the bridge, and at the time of fault, the fault current limiting capability decrease due to the bias DC current. An idea is to put a resistor in series with the superconducting coil for absorbing the incoming energy into the coil, and turn the switch on and off to disconnect the DC bias voltage source from the rectifier in order to control the fault current in a pre-set region. The operating theory of the new fault current limiter is discussed, and the effect of parameters variety of HTSCFCL is analyzed on limiting fault current. The simulation and experimental results show that the device is of good limiting and re-closing capability, and demonstrates that the device can reduce both the transient and the steady-state fault current significantly. The device is of great benefit in improving transient stability and enhancing the electrical energy quality of power system.Finally, in this paper, current lead, power loss, stability and protection method, low temperature insulation of SCFCL and winding superconductor technique are studied. All works above not only in terms of theory and experiment demonstrate the feasibilities and advantages of SCFCL, but also make fundamental effort for following exploration of the products baed on SCFCL.