With the acceleration of urbanization and the improvement of urban development speed, the total population of the city is increasing and traffic congestion is becoming more and more serious. In order to solve this problem better, cities are vigorously developing public transportation construction based on subway. This paper mainly discusses some problems in the application of ring network power supply technology in subway power supply system, and puts forward some opinions and suggestions, aiming at providing some reference for the practical application of ring network power supply technology in subway.
1 Overview of ring network power supply
The concept of (1) ring network power supply. The urban subway trunk line generally adopts loop line, which is a continuous distribution line and can form a closed loop. Its starting point and ending point are connected to the same group of buses. In order to increase the flexibility of operation, each part is usually equipped with its own circuit breaker. Usually, we divide the bus into two sections with sectional circuit breakers, and then connect the two ports at both ends of the line protector. Line protector is a kind of longitudinal differential protection circuit. When the line fails, this protector can isolate the faulty circuit from the main line through the protector without affecting the circuit work of other normal parts.
(2) Power supply mode. The ring network can be divided into open-loop operation and closed-loop operation, and the subway power supply system is mainly closed-loop operation. Only in this way can the characteristics of closed-loop power supply and uninterrupted power supply be brought into play. For relay protection devices, due to the difficulty of device setting, open-loop operation is usually adopted. If strictly in accordance with the regulations, the choice of open-loop point can only be determined through a series of calculations and designs. But in the actual work process, we choose the middle position of the ring network trunk line to set the open-loop point, so that the open-loop point can isolate the fault point well. At present, China's medium voltage (1 0~3 5kV) ring network adopts open-loop operation mode.
2 Common subway power supply methods
(1) adopts centralized power supply. Because the subway line is too long and its capacity is limited, it is necessary to establish a special power supply station in the subway station to supply power to the medium voltage ring network in the subway. The advantages of this power supply method are: power supply is not easily affected by external factors and has high reliability; Power supply all special on-load voltage regulating transformers can supply power for some special lines with good power supply quality; There is a strong degree of freedom in scheduling management. When there is an excellent dispatching management system, the efficiency and reliability of subway power supply station can be fully exerted. The maintenance work of this power supply mode is relatively simple, and the amount of construction work involved is relatively small, which is relatively easy to realize. However, the disadvantage is that the capital investment is relatively large, and the requirements for dispatching and coordination of the power supply system of the whole subway station are relatively high.
(2) Decentralized power supply is adopted. Because there are many urban power sources introduced along the subway, the substation in the area adopts direct voltage reduction to complete power supply. The advantage of this power supply mode is that the amount of investment is relatively small, which is convenient to realize the protocol planning and management of urban power grid. The existing defect is that the normal power supply process is easily influenced by other external factors. Because there are many connections with the urban power grid, it is difficult to plan and manage the urban power grid in a unified way, and it is difficult to obtain a more suitable solution in case of power supply failure; The rectifier will produce a large number of residual harmonics when it works, which will also have a great impact on the normal operation of urban power grid.
(3) Adopt hybrid power supply mode. The centralized power supply mode and decentralized power supply mode are effectively combined to form a brand-new power supply mode. There are two main forms: ① centralized and decentralized power supply modes are connected in parallel, and then in the' power supply network' of the whole subway loop, some of them use centralized power supply and some use decentralized power supply; ② Centralized power supply is mainly used for medium-voltage loop power supply in subway stations, and the centralized power supply station is changed into the power supply access point of decentralized power supply station, thus establishing a complete decentralized power supply station system.
Application of Three Ring Network Power Supply Technology in Metro Power Supply System
3. Connection of1ring network
The "N- 1 safety principle" we often say is a basic principle that the power grid must meet in the process of power supply. In practical work, we can complete the safe operation of the power grid by adjusting the wiring mode of the power grid and the operation rate of equipment. The traditional power grid connection mode is single loop network connection mode. In the case of line failure, this mode of power supply network must spend a lot of time and economy, manual switching and maintenance, and then restore power supply. Based on this, we can find that the stability of this power supply mode is relatively poor and cannot meet the basic needs of railway operation at this stage. After the subway power supply system adopts double-loop power supply network, because there are two independent parallel power supplies, even if one of them has problems, it will not affect the normal power supply of the other standby power supply. This connection mode of connecting two power supplies or different buses of one power supply in parallel can ensure the stability of the subway power supply system. When the whole power supply system works normally, all switches are in the off state. When there is a problem in a certain power supply line, the line load is immediately transferred to another power supply line through switch conversion to ensure the normal power supply system of the subway. It can be seen that the reliability of power supply can be greatly improved by controlling the line fault in a closed unit through combined switches without affecting the normal power supply of other sections. This connection mode of always reserving the spare line can ensure that when the working line has problems, the spare line can be used to complete the normal power supply task. In this way, the reliability of subway power supply has been improved to a new level, and the comprehensive utilization rate of the line has been improved.
3.2 Metro Medium Voltage AC Ring Network System
In order to achieve the purpose of convenient dispatching and stable operation, the following points should be done when designing the power supply network:
The connection of (1) line must be as simple as possible, and the operation process should be as flexible and reliable as possible with high economy;
(2) When designing the line capacity of the power supply network, a certain capacity space should be reserved;
(3) The lines of the subway power supply system should be designed according to the highest standards, and spare lines should be left;
(4) When the load in the power grid reaches the maximum, all equipment must work normally. When a line fails and the standby line carries the maximum load, the power supply system should also work normally. Generally speaking, when the traction substation fails, the main substation completes the power supply task of the whole power grid. Similarly, when the main power supply fails, there is a traction substation to complete the power supply. And if the traction substation or the main substation fails at the same time, it is necessary to ensure the normal power supply of the subway power supply system.
4 conclusion
In the whole subway ring network power supply system, each power point is connected with two power sources to form a ring network, which improves the reliability of power supply, helps to improve voltage overload and reduce circuit loss. At present, it is necessary to improve the manufacturing level of related products, develop a variety of products, and leave a lot of room for transformation in design, so as to promote the development and popularization of the whole ring network technology of subway power supply system.
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