Abstract: This paper introduces the application of soft starter in low pressure high power reservoir pump station, gives the system electrical schematic diagram, the main parameters of the soft starter set value, a soft starter to drive multiple motor soft start and stop Solutions and debugging to pay attention to the main problems. Keywords: city water pump soft starter soft start soft stop I. Introduction: Urban water supply system of the reservoir pumping stations are generally equipped with high-power reservoir pumps and booster pump several units, the good and stable operation of urban residents living water and socialist industrial and agricultural production to bring a reliable guarantee. At present, many existing equipment has become aging, daily maintenance workload, the control principle is relatively backward. How to reform the existing equipment rationally without increasing the large amount of investment so as to exert the highest work efficiency is the key issue to be solved now. Shanghai North Water Works Corporation under the North Pump Station Zhenbei pump station under a total of three 280kW booster pump and three 280kW reservoir pump. Start the cabinet are used to start the auto-start, start current, and with the long-term use of equipment, switching components and the outlet valve is more serious loss. In order to reduce operating costs, reduce equipment losses, improve management, decided to adopt PLC automatic control system and motor soft starter to transform the original equipment. Second, the working principle and transformation programs: Control principle The motor starter decided to use the soft starter. The basic principle of soft starter shown in Figure 1, by controlling the conduction angle of the SCR to control the output voltage. Therefore, the soft starter is essentially an automatic control of the step-down starter, due to be able to adjust the output voltage, the current closed-loop control, and thus than the traditional step-down start mode (such as string resistance start, auto transformer start Etc.) have more advantages. For example full load wind turbine pump and other variable torque load, the motor soft stop, applied to the pump can completely eliminate the water hammer effect. At present, the domestic and foreign motor soft starter control systems generally use a soft starter with a motor control program, in order to save investment, after multiple proofs, and Shanghai Jin letter inverter Co., Ltd. with the technical experts Simulation test, the final decision to use a soft starter with multiple motors program. In the meantime, in order to guarantee the trouble-free continuous operation of the equipment to the maximum extent, the original self-starting cabinet has been transformed to retain all the functions of the original auto-start and utilize the original operation contactor in the self-coupling cabinet as the soft starter Bypass contactor, bypassing the soft starter after it has been started, so that the soft starter can continue to control other motors. Soft stop control strategy is exactly the opposite, first of all to disconnect the original operating contactor in the cabinet, the motor switch to the soft starter control, and then start the soft starter soft stop function, and gradually reduce the output voltage, the motor Slowly stop, finally soft starter exit, waiting for the next start or stop operation. 2 system block diagram: Figure 2 for the single main line wiring diagram 3. The main equipment selection: The water supply system is connected to millions of households. The design of the system and the equipment selection should be based on their reliability and product manufacturer's creditworthiness so that the system can be as foolproof as possible under normal working conditions. At the same time, we must also take into account the economy of the system. Therefore, we should select domestic and international high-quality products as far as possible for the key equipment in the equipment, and we can choose the products with good quality and low price for the auxiliary equipment that does not affect system performance and reliability. To improve the overall system cost. 3.1 programmable logic controller (PLC) selection PLC is one of the key components of the control system, in addition to the selection of the above requirements to meet the above, but also to take into account the future maintenance and expansion and maintain a unified communication interface with other pumping stations for the future to connect PC monitoring well Ready to wait. After comprehensive consideration, decided to adopt SLC500 series PLC of ROCKWELL. 3.2 Soft starter selection: Selection Danfoss Danmark Industrial Co., Ltd. MCD3000-type industrial soft starter, the product has the following advantages: 1. A dedicated bypass terminal, in the bypass current monitoring, overload protection can be made; 2. Danfoss soft starter has more than 1 with the special features, especially for this transformation; Danfoss soft starter has a built-in soft stop function; 4. Danfoss soft starter is a true constant current closed-loop control, to set the starting current value for the fastest start, start the completion of the logical discrimination is more reasonable. Pump motor model JS137-6, 280kW, 493A, 983rpm. Pumping station by two high-voltage incoming power supply, each with 3 motor. Therefore decided to use two 300kW soft starter (model MCD3300), each power supply connected to a soft starter, each soft starter is responsible for three soft-start and soft stop motor. The start control principle, see Figure 3, the start-up is completely closed-loop control of the current, until the motor accelerates to rated speed, the current also dropped to the rated current, thyristor fully open enough, and finally the soft starter sends operating signals. Â Third , the program design Using ROCKWELL's RSLOGIX500 programming software, the program block diagram is as follows: Fourth, installation and commissioning Note: Site installation and commissioning does not affect the normal water supply throughout the pumping station under the circumstances, so in advance must develop a detailed construction plan, requiring engineering companies have: - Strong technical strength - Ability to coordinate large quantities of materials, equipment orders, shipping and purchase issues - Have the corresponding engineering design and construction experience - Have a good management system This construction is carried out by pump after full coordination with the schedule. Debugging is also the case, the first election in a certain way on the power of the three pumps are not when the soft starter on this road for debugging; then choose to be controlled by the pump, the pump will be selected outlet valve completely closed to Mian tune test work affect the pipe network; and then start the official debugging action, pay attention to when the pump is playing boring, the best time not to exceed 1 minute; and so on these debugging work are passed, you can open the outlet valve, Start the soft stop test, then because it is full load so the soft start time will be longer than when no load, so the parameters of the soft starter to have a certain margin; the final test, summarize the data, come to the best Control methods and control parameters, you can put into trial operation. In addition low-voltage high-power motor power distribution is more compact, so most of the debugging should be done under simulated conditions, in order to reduce the chance of formal debugging failure. Fifth, the operation effect and significance: This set of control system has been officially put into operation in Zhenbei pumping station. Six water pump outlet valve is fully open, under normal circumstances they no longer operate. Soft starter start-up current is set to 330%, the start-up time is about 5-6 seconds, the starting system withstand current surge current and start with the autotransformer when the same; soft stop current maximum does not exceed 170%, soft stop time about 7 seconds, there is no impact on the check valve. The system has been operating normally since it was put into use. The successful application of this system will bring far-reaching significance to the design and renovation of booster pump stations and reservoir pumping stations in the future urban water supply system: 1. Since the use of soft starters have been able to achieve full load pump motor start and soft stop, the water pump outlet valve can be completely canceled; 2. High-power soft-start "a multi-area" successful application, making the future of multi-pump station motor starting control system costs dropped significantly; 3. Soft-start itself has voltage and current protection, and has inherent zero-current switching characteristics, making the motor protection has been strengthened, while large Greatly reduce the contactor loss; 4. Such a system because PLC as the main controller, the future can be further expanded functionality. Six, concluding remark: As a result of the advanced PLC and motor soft starter, the original electrical control has been successfully transformed, the entire pump station electrical control and management level to a new level. With the constant updating of power electronics technology at home and abroad and the continuous development of automation control theory, I believe there will be more and better solutions in the future.