Application of the hottest soft starter in low vol

Application of soft starter in low-voltage high-power reservoir pump station

Abstract: This paper introduces the application of soft starter in low-voltage high-power reservoir pump station, and gives the system electrical schematic diagram, the main parameter setting values of soft starter, the solution of soft start and soft stop of multiple motors driven by one soft starter, and the main problems that should be paid attention to in debugging

key words: urban water supply pump soft starter soft start soft stop

I. Introduction:

the reservoir pump station of urban water supply system is generally equipped with several high-power reservoir pumps and booster pumps, whose good and stable operation brings a reliable guarantee for urban residents' domestic water and socialist industrial and agricultural production. At present, many existing equipment has become aging, the daily maintenance workload is heavy, and the control principle is relatively backward. How to reasonably transform the existing equipment without increasing a large amount of investment in order to give full play to the highest work efficiency is the key problem to be solved at present

Zhenbei pump station under Shibei pump station management office of Shanghai water supply company has three 280KW booster pumps and three 280KW reservoir pumps. The auto coupling starting cabinet is used for starting, and the starting current is large. With the long-term use of the equipment, the loss of switching elements and water outlet valves is relatively serious. In order to reduce operating costs, reduce equipment losses and improve management level, it is decided to adopt PLC automatic control system and motor soft starter to transform the original equipment

II. Working principle and transformation scheme:

1 Control principle

motor starter decides to use soft starter. The basic principle of the soft starter is shown in Figure 1. The output voltage is controlled by controlling the conduction angle of the thyristor. Therefore, the soft starter is essentially a step-down starter that can be automatically controlled. Because it can arbitrarily adjust the output voltage for current closed-loop control, it has more advantages than the traditional step-down starting methods (such as series resistance starting, autotransformer starting, etc.). For example, starting the variable torque load such as fan and water pump at full load, realizing the soft stop of motor, and completely eliminating the water hammer effect when applied to water pump

at present, the control system of motor soft starter at home and abroad generally adopts the control scheme of one soft starter with one motor. In order to save investment, the lack of understanding of steel structure has been demonstrated by many parties, and the simulation test has been carried out with the technical experts of Shanghai Jinxin frequency converter Co., Ltd., and finally the scheme of one soft starter with multiple motors has been decided. At the same time, in order to ensure the fault free continuous operation of the equipment to the greatest extent, the original self coupling starting cabinet is reformed to retain all the functions of the original self coupling starting, and the operation contactor in the original self coupling cabinet is used as the bypass contactor of the soft starter, which is bypassed after the soft starter is started, so that the soft starter can continue to control other motors. The soft stop control strategy is just the opposite. First, disconnect the running contactor in the original autotransformer cabinet, switch the motor to be controlled by the soft starter, then start the soft stop function of the soft starter, gradually reduce the output voltage, and slowly stop the motor. Finally, the soft starter exits, waiting to accept the next start or stop operation

2. System composition block diagram:

Figure 2 is the main circuit wiring diagram of single incoming line

Figure 2

3 Selection of main equipment:

the water supply system is related to thousands of households. The reliability of the system and the credit of the product manufacturer should be considered in the design and selection of equipment, so that the system can be as safe as possible under normal working conditions. But at the same time, we should also take into account the economy of the system. Therefore, in terms of equipment allocation, we should choose high-quality products at home and abroad as far as possible for the main key equipment. For some auxiliary equipment that does not affect the performance and reliability of the system, we can choose products with low price and good quality to improve the performance price ratio of the whole system

3.1 selection of programmable controller (PLC)

PLC is one of the key components of the control system. In addition to meeting the above requirements, the selection also takes into account the future maintenance and expansion, as well as maintaining a unified communication interface with other pump stations, so as to prepare for the future connection of upper computer monitoring, etc. After comprehensive consideration, it is decided to adopt Rockwell SLC500 series PLC

3.2 type selection of soft starter:

mcd3000 industrial soft starter produced by Danfoss Industry Co., Ltd. in Denmark is selected. This product has the following advantages:

1 There is a special bypass terminal, and there is current monitoring during bypass, which can be used for overload protection

2. Danfoss soft starter has more than one exclusive function, which is especially suitable for this transformation

3. Danfoss soft starter has built-in soft stop function

4. Danfoss soft starter is a real constant current closed-loop control, which can make the fastest start with the set starting current value, and the logical discrimination of starting completion is also more reasonable

the model of water pump motor is JS, 280KW, 493a, 983rpm. The pump station is powered by two high-voltage incoming lines, each with three motors. Therefore, it is decided to adopt two 300kW soft starters (model mcd3300), each power supply is connected with one soft starter, and each soft starter is responsible for the soft start and soft stop of three motors. The starting control principle is shown in Figure 3. When starting, it is completely current closed-loop control. When the motor accelerates to the rated speed, the current also decreases to the rated current, the thyristor is fully opened, and finally the soft starter sends a running signal

Figure 3

parameter setting

Fourth, the program design

adopts the rslogix500 programming software of Rockwell company, and the program block diagram is as follows:

Figure 4

v. precautions for installation and commissioning:

the on-site installation and commissioning are carried out without affecting the normal water supply of the whole pump station, so a detailed construction plan must be formulated in advance, The engineering company is required to have:

- strong technical strength

- ability to coordinate a large number of materials, equipment ordering, transportation and purchase problems

- corresponding engineering design and construction experience

- low price and good management system

this construction is carried out pump by pump after full coordination with the dispatcher. The same is true during commissioning. First, when the three pumps on a certain power supply are not used, debug the soft starter of this circuit; Then select the controlled water pump and completely close the outlet valve of the selected water pump to avoid the impact of commissioning work on the pipe; Then start the formal commissioning action. Note that the water pump is blocking water at this time, and the running time should not exceed 1 minute; After these commissioning works are successfully passed, the water outlet valve can be opened for full load soft start and soft stop test. At this time, because it is full load, the soft start time will be longer than that under no-load, so the parameter setting of the soft starter must have a certain margin; Finally, through the test, summarize the data, get the best control mode and control parameters, and then it can be put into trial operation

in addition, the power distribution of low-voltage high-power motors is relatively compact, so most debugging should be completed under simulated conditions as far as possible to reduce the chance of failure during formal debugging

VI. operation effect and significance:

this set of control system has been officially put into operation in Zhenbei pump station. The outlet valves of the six water pumps are fully opened, and they are usually no longer operated. The starting current of the soft starter is set to 330%, and the starting time is about seconds. The starting impulse current borne by the power supply system is similar to that when starting with an autotransformer; The maximum current during soft stop shall not exceed 170%, and the soft stop time is about 7 seconds, without any impact on the check valve. The system has been running normally since it was put into use

the successful application of this system will bring far-reaching significance to the design and transformation of booster pump stations and reservoir pump stations of urban water supply system in the future:

1 Since the full load start and soft stop of the pump motor can be realized by using the soft starter, the outlet valve of the pump can be completely cancelled

2. The successful application of high-power soft starter "one belt and more" has greatly reduced the cost of motor starting control system in multi pump pump pump stations in the future

3. The soft starter has voltage and current protection functions, and has internal zero current switching characteristics, which strengthens the protection of the motor and greatly reduces the loss of the contactor

4. Because this kind of system has PLC as the main controller, it can further expand its functions in the future

VII. Conclusion:

due to the use of advanced PLC and motor soft starter, the original electrical control has been successfully transformed, and the electrical control and management level of the whole pump station has reached a new level. With the continuous updating of power electronics technology at home and abroad and the continuous development of automation control theory, I believe that there will be more and better solutions in the future

this article is for peer reference and correction. If there is anything unknown, please contact us

VIII. References:

[1. Principles of electrical automation, Chen Boshi;

[2 with the soaring price of raw materials. Mcd3000 user manual, Danfoss Co., Ltd., Denmark