Research survey of the hottest fault current limit

Research overview of fault current limiter technology

Abstract: in recent years, the capacity of power system has increased year by year, and the electrical short-circuit current has also increased. At present, it has become an important factor restricting the operation and development of electricity. Therefore, limiting the short-circuit current of power system has become a problem to be solved. Traditionally, mechanical circuit breakers are used, which are slow and require a large amount of maintenance, which is an important condition for the formation of transient stability problems. The development and research of fault current limiter has opened up a technical channel to improve the overall control ability and level of AC transmission line and transmission operation, and pointed out the direction for the innovation and transformation of high-voltage and ultra-high voltage transmission performance

key words: fault current limiter high voltage ultra high voltage transmission AC transmission 1 Introduction in recent years, the capacity of power system has increased year by year, and the electrical short-circuit current has also increased. At present, it has become an important factor restricting the operation and development of electricity. Therefore, limiting the short-circuit current of power system has become a problem to be solved. Traditionally, mechanical circuit breakers are used, which are slow and require a large amount of maintenance, which is an important condition for the formation of transient stability problems. The development and research of fault current limiter has opened up a technical channel to improve the overall control ability and level of AC transmission line and transmission operation. Precision equipment such as tensile testing machine and digital 3D coordinate measuring equipment point out that excellent performance is the material closest to bone for the innovation and transformation of high-voltage and ultra-high voltage transmission performance; biocompatibility is the most basic element to measure whether a material is suitable for human implantation. 2 the dynamic fault current limiter (FCL), which is studied by foreign fault current limiters, appeared in the literature at home and abroad as early as the 1970s, but it was really valued and developed rapidly after the flexible AC transmission technology was proposed. From the development of recent ten years, the fault current limiter can be divided into two categories: the first category is the current limiter that uses power electronic devices to control the line impedance; The second is to use materials with special properties as the basic components of the current limiter, such as superconducting materials and polymeric materials with positive temperature coefficient (PTC). 2.1 fault current limiter using power devices to control line impedance the basic idea of this fault current limiter protection circuit is: under normal load conditions, FCL presents low impedance, but when a fault occurs, FCL action protection will present a large impedance value to limit the fault current and limit the fault current within the normal working range of the circuit breaker. Figure 1 is the laboratory device diagram of FCL. When the circuit works normally, the thyristor is in the locked state, l2r2 is not connected in series, and the circuit works in series with L1C. When the fault occurs (SF is closed), the control circuit triggers to turn on the thyristor, l2r2 is connected to both ends of the capacitor, and operates in parallel with the capacitor, increasing the line impedance value to limit the fault current. In this circuit, the thyristor controls the reactor and is connected to both ends of the capacitor. Under normal operating conditions, the thyristor does not conduct. Only in the case of short circuit, the thyristor triggers conduction, and L2 is connected to the circuit to play a shunting role. Therefore, there will be no harmonic generation under normal working conditions. At the same time, due to the relatively short protection process, the heating condition is not serious, and no cooling device is required. 2.2 solid state fault current limiter in 1993, Japan proposed the design scheme of solid-state fault current limiter. The reason is that the traditional overcurrent protection system is composed of circuit breaker and overcurrent delay device (OCR). From the short-circuit generator shaft, feeding shaft and regulating mechanism to the action of the circuit breaker, there is generally a delay of 0.2S to 0.5s. In this way, the voltage of the line will be reduced or the power transmission will be interrupted within the delay time, affecting the quality of transmitted power. In order to reduce the time of protection action, improve the quality of power transmission, and limit the fault current, a solid-state current limiter design scheme is proposed. Due to the fast response speed of GTO, it usually takes only 40 minutes from the control device sending a signal to the GTO response action μ s； The control device detects the fault current and sends a turn-on signal to GTO. The current limiting resistor R is connected in series with the main circuit to limit the fault current. In this way, the fault current of the whole system is limited within a certain range, and the response time of the protection action is shortened, which improves the power transmission capacity of the system. However, the disadvantage of this current limiter is that under normal circumstances, the thyristor control circuit is disconnected and can only be put into use in the case of failure, so its utilization rate is not high. 2.3 fault current limiter with series compensation was proposed in Japan in 1996. Figure 2 shows the principle circuit diagram of FCL with series compensation. During normal operation, inductance L1 and capacitance C1 are connected in series, thyristor control device SW1 is turned off, and the circuit impedance is capacitive. At this time, the fault current limiter works in the conventional series compensation state. When the fault occurs, SW1 quickly turns on the short-circuit capacitor C1. At this time, the reactor L1 limits the short-circuit current. Low impedance Z1 limits impulse current; The overvoltage protection device ZnO and the bypass switch BPS are connected in parallel at both ends of capacitor C1, and the fault BPS is also closed, so the low impedance Z2 can not only limit the impulse current, but also release the electric energy stored in C1 through Z2. Its characteristics are: ① during normal operation, there is no power loss because SW1 is in the off state. ② In normal operation, it is equivalent to conventional series compensation, so the utilization rate of fault current limiter is improved. ③ Because FCL with series compensation can limit current and compensate reactive power, the transmission capacity and stability of the system are improved. 2.4 superconducting fault current limiter (SFCL) has been studied in Japan since about 1997. At the same time, the Institute of electrical engineering, Chinese Academy of Sciences has also published an article on superconducting fault current limiter. When the superconducting fault current limiter (SFCL) is connected to the power system, the transmission current is below the critical current and the resistance of the superconductor is almost zero, which has no impact on the operation of the power system when the power system operates normally after the centralized pre holiday replenishment on the first and second weeks of this week. Once there is a short-circuit in electricity, when the short-circuit current is greater than the critical current, the instantaneous quench of the superconductor will produce nonlinear high resistance, so as to effectively limit the short-circuit current. There are many types of superconducting fault current limiters (SFCL), among which bridge superconducting fault current limiters have broad prospects. The principle circuit diagram of bridge superconducting fault current limiter is shown in Figure 3. It consists of diode bridge D1 ~ D4, superconductor coil L and DC bias source vb. Positive