Abstract: the power supply system in the metallurgical industry has its own particularity, which is very different from the ordinary power supply system. According to the analysis of the power supply system in the metallurgical industry, we have summarized the system characteristics of "six plus one special"
key words: Untitled Document of microcomputer relay protection in metallurgical industry
lecture: Hu Daliang, Shanghai Shenrui Power Automation Technology Co., Ltd.
finishing: Wang man, Shanghai Shenrui Power Automation Technology Co., Ltd. 1 differences between power supply system and power system in metallurgical industry. Power supply system in metallurgical industry has its own particularity, which is very different from ordinary power supply system. According to the analysis of the power supply system in the metallurgical industry, we have summarized the system characteristics of "six plus one special". There are many feeders. In general, only about ten feeders are connected to a bus in the power system, while many more feeders may be connected to the power supply system in the metallurgical industry. Therefore, bus management is relatively complex. There are many switching stations. Under the same voltage level, there are many switching stations, and the scale of each switching station is larger than that of the power system; There are many harmonics. There are many rectifying devices in the metallurgical industry, which will cause rich harmonics when running. There are many smart devices. There are microcomputer protection, rectifier equipment, PLC equipment, etc., and there are interface problems between these equipment. There are many motors and some synchronous motors. The impulse current of the motor is large and frequent, the starting current is large, and the load fluctuation is large. There are many bus sections. In the same voltage level, the power system is generally two to three sections of bus, while in the metallurgical industry, four, five and six sections will appear; Special requirements for standby automatic switching. There are many motors in the metallurgical industry. Zhang Xin said that they have high requirements for reliability. In addition, the structure of power supply system in metallurgical industry is complex, and the requirements for standby automatic switching are very special; After years of contact with metallurgical systems, our company has some experience in relay protection. This paper summarizes some problems encountered and introduces the solutions used. 2 problems encountered and solved in recent years 2.1 rapid protection of medium and low voltage ultra short lines
in the metallurgical system, short lines with low voltage levels can often be encountered, which vary in length from 500m-2km. Each line often has a switching post, and level protection needs to be installed from the low-voltage side of the substation to the final load point (generally, there are four levels of terminal, switching post, substation outgoing line, and main transformer backup),. See Figure 2.1 system diagram. Because the line is too short, there is no obvious change in fault current when the head and end are short circuited, and generally only time can meet the selectivity of protection. As a result, serious faults can not be quickly removed, which is easy to cause switch explosion, bus distortion, substation power failure, fire, etc. (the so-called "fire camp"), resulting in the expansion of the accident. For important short line protection, high-voltage power systems are often equipped with high-frequency locking directional protection, high-frequency distance protection or phase separation differential protection composed of optical cables. High frequency locking directional protection is composed of transceiver and high frequency directional protection; High frequency distance protection is composed of transceiver and distance protection; Split phase differential is composed of optical transceiver, optical cable and split phase differential protection. The principle of these protection devices is to exchange, compare and logically calculate the electricity at both ends, and finally decide whether to act. These protections are generally used as the main protection of high-voltage short lines, with high action selectivity and sensitivity. Generally, they do not need to cooperate with other levels of protection, but the cost is also very high
figure 2.1 system wiring diagram for low-voltage short lines of metallurgical power supply system, we believe that the requirements for time limit can be appropriately relaxed, but the cost should be low. In view of this, we have learned from the protection idea that the transformation and upgrading of high-frequency locking direction multifluoro has received a certain effect, and developed a pilot wire direction pilot protection device. See the schematic diagram in Figure 2.2
Figure 2.2 schematic diagram of longitudinal protection in the direction of guide wire. Short line directional longitudinal protection J1 and J2 are installed at both ends of the line, and the main protection is the directional protection on each side. When the directional protection detects the reverse fault on this side after starting, it sends a locking signal to this side, and after the relay is restarted, it is transmitted to the opposite side through the guide wire at the same time. After receiving the protection locking signal on both sides, it immediately locks the protection outlet logic; When the protection on both sides does not receive the locking signal, it is confirmed as a fault in the area after a short time delay, and the protection action cuts off the line. This protection configuration is completely different from the traditional lead longitudinal differential protection that needs to transmit comprehensive electric flow. Because the traditional lead longitudinal differential protection needs to transmit analog quantity to the opposite side, and the transmission of analog quantity involves the requirements of impedance matching, attenuation coefficient and anti-interference, it has high requirements for the specification and construction of lead cable. And the new guide wire direction we use will be a large number of innovative joint protection in the design, equipment and utilization of packaging materials in this k exhibition. Because only the high-voltage (AC220V or dc220v) digital switch is transmitted to the opposite side to help customers design, develop and produce better product lock signals of time testing machines in a faster and more economical way, there are no special requirements for the selection and construction of guide wires, Just lay an ordinary four core shielded cable between the two sides and ensure good contact. In case of fault in the area under single power supply or dual power supply, the system can ensure that the fault is removed within 0.1-0.15 seconds. In case of fault outside the zone, the protection on both sides can be locked in time by the reverse direction element, so that the protection will not act without selectivity. Because this protection configuration mode can remove short line faults in time, it can reduce the cooperation of primary protection in time, making it possible to quickly remove bus faults. In addition, in addition to the directional pilot protection as the main protection, the protection device also comes with a compound voltage locking overcurrent element that can be used as a backup protection. During operation, overcurrent components can also be selectively input. In other words, in addition to the traditional multi time limit and multi step coordination mode, the line with this protection mode has added the fast pilot protection as the main protection of the line. 2. Fast protection of low-voltage bus in 2
Large Metallurgical power supply system has many outgoing lines