Application of DANFOSS Soft Starter in Low Pressure High Power Reservoir Pumping Station

I. INTRODUCTION: Reservoir pumping stations in urban water supply systems are generally equipped with several high-power reservoir pumps and booster pumps. Their good and stable operation provides a reliable guarantee for the domestic water for urban residents and the socialist industrial and agricultural production. 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. Soft starter Shanghai Municipal Water Company Shibei pumping station under the management of true North pumping station 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 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: 1. Control Principle 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. Soft starter wiring At present, the domestic and foreign motor soft starter control system are generally used a soft starter with a motor control program, in order to save investment, after multiple proofs, and the Shanghai Jin letter Drive Technology Co., Ltd. Experts conducted a 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. The main equipment selection: the water supply system to tens of thousands of households, the system design and equipment selection to consider its reliability and product manufacturers credit, the system under normal working conditions, as far as possible be foolproof. 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. Soft starter wiring 2.1 PLC selection PLC is one of the key components of the control system, in addition to the selection of the above requirements to be met, but also to consider the future maintenance and expansion and other pumps Station to maintain a unified communication interface for the future to connect PC monitoring to prepare. After comprehensive consideration, decided to adopt SLC500 series PLC of ROCKWELL. 2.2 The selection of soft starter: Denmark Danfoss Industrial Co., Ltd. selected MCD3000-type industrial soft starter, the product has the following advantages: 1. There are dedicated bypass terminals, there is current monitoring in the bypass, can For overload protection; 2. Danfoss soft starter has more than 1 with the special features, especially for this transformation; 3. Danfoss soft starter has a built-in soft stop function; 4. Danfoss soft starter is the real constant current Closed-loop control, can set the starting current value for the fastest start, start the completion of the logical discriminant is more reasonable. Soft-start 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. Third, the program design using ROCKWELL company RSLOGIX500 programming software, the block diagram below: Click here to view all news photos Fourth, installation and commissioning Notes: On-site installation and commissioning are carried out without affecting the normal water supply of the entire pumping station, so beforehand we must develop a detailed construction plans, requirements engineering company has: - a strong technical strength - the ability to coordinate a large number of materials, equipment ordering, shipping and stock issues - there are design and construction experience in the corresponding project - with 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 retrofit of booster pump station and reservoir pump station in the future urban water supply system: 1. Since the full start-up and soft stop of the pump motor can be realized by using the soft starter, Pump outlet valve can be completely canceled; 2. High-power soft starter "a multi-" successful application of the future, making the multi-pump station motor starting control system costs dropped significantly; 3. Soft-start itself with voltage and current protection Function, and has an inherent zero-current switching characteristics, making the motor protection has been strengthened, while greatly reducing the loss of contactor; 4. Such a system because of the PLC as the main controller, the future can be further expanded functionality. Sixth, the conclusion: As a result of the advanced PLC and motor soft starter, making the original electrical control has been successfully transformed, the entire pumping 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.