Electric dredge pump is a kind of hydraulic machinery and equipment that extracts the sand and slurry medium and transports them over long distance. Electric dredge pump units are more commonly used in In the working environment with convenient power supply in cities or suburbs, . The motor has the features of simple structure, low price and easy maintenance, but there is a problem that the instantaneous starting current is relatively large. Therefore, the soft start method is generally selected when starting. For how to choose the motor starting method, comprehensive consideration must be given to several aspects such as the torque characteristics of the mechanical load driven by the motor, the nature of the load on the start-up requirements, transformer capacity in the line, various start-up economic investments, etc.
1. Electric dredge pump motor starting method
a. Electric dredge pump motor full voltage direct start
When the grid capacity and load can be met, full voltage direct start can be considered. This starting method has the advantages of convenient operation and control, simple maintenance, and relatively cost effective. It is mainly used to start small-power motors below 10KW. If the power is greater than 10KW, Y-△ step-down starting should be considered to save costs.
b. Electric dredge pump motor auto-coupling decompression start
The motor auto-decompression start uses the autotransformer multi-tap to reduce the voltage, which can not only meet the needs of different loads, but also obtain a larger starting torque. It is often used to start a larger capacity motor. Its biggest advantage is that the starting torque is large. When the autotransformer winding tap is at 80%, the starting torque can reach 60% of the direct starting. And the starting torque can be adjusted through the winding tap.
c. Electric dredge pump motor star delta start
For a cage asynchronous motor whose stator windings are delta-connected in normal operation, if the stator windings are connected in a star shape when starting, and then connected into a delta after the start is completed, the starting current can be reduced to reduce the impact of current on power supply voltage during startup. This kind of starting method is called star-delta decompression starting, referred to as star-angle starting (Y-△ starting). When starting with a star angle, the starting current is only 1/3 of the direct start in the delta connection. If the starting current during direct start is calculated as 6~7 times the rated current, the starting current will only be 2~3 times the rated current during star-delta starting. Simply put, when the star-delta start is used, the starting torque is also reduced to 1/3 of the original direct start in the delta connection. It is suitable for equipment that is started at no load or light load. And compared with other decompression starters, it has the advantages of the simplest structure, more convenient maintenance, and the cheapest price.
d. Electric dredge pump motor soft starter
Soft start is an AC voltage regulator. It uses the phase shifting and voltage regulation principle of thyristor to realize the voltage regulation and start of the electric dredge pump motor. It is mainly used for the start control of the motor. It has the functions of overcurrent protection, motor overload, loss of voltage, over voltage, Phase failure, ground fault protection. The soft starter has a good start effect, but the cost is higher. The soft starter uses a single-chip microcomputer and high-power thyristor components, and the harmonic interference of the thyristor is large when it is working, which has a certain impact on the power grid. In addition, the fluctuation of the power grid will also affect the conduction of the thyristor components, especially when there are multiple thyristor devices in the same power grid. Therefore, the failure rate of thyristor components is relatively high. Because power electronics technology is involved, so the requirements for maintenance technicians are also relatively high.
e. Electric dredge pump motor inverter start
The frequency converter is used to adjust the working frequency of the electric dredge pump motor, reduce energy loss, smooth the starting equipment, and reduce the damage to the electric dredge pump motor caused by the large current generated when the equipment starts directly. At the same time comes with analog input (for speed control or feedback signal), PID control, pump switching control (for constant pressure), communication function, macro function (different parameter settings for different occasions), multi-speed, etc. .
The frequency converter is currently the motor control device with the highest technical content, the most complete control function, and the best control effect in the field of motor control. It adjusts the speed and torque of the motor by changing the frequency of the power supply. Because it involves power electronic technology and microcomputer technology, the cost is high, and the requirements for maintenance technicians are also high. Therefore, it is mainly used in fields that require speed regulation and high speed control requirements.
Among the above start control methods, star-delta start and auto-decompression start have low cost, and are easier to maintain than soft start and variable frequency control. They still occupy a large proportion in actual applications. But because it uses discrete electrical components to assemble the control circuit, so has more contacts, the failure rate is relatively high during its operation. The frequency conversion control has the best control effect. OCEAN PUMP will focus on the relevant information of the frequency conversion control cabinet when the electric dredge pump motor starts, for the reference of the majority of users.
2. Frequency conversion control concept
Frequency conversion control is mainly used to adjust the working frequency of the electric dredge pump, reduce energy consumption, can start the electric dredge pump smoothly, and reduce the damage to the motor caused by the large current generated when the electric dredge pump is directly started. The frequency conversion control cabinet product has multiple protection functions and complete status display such as overload, short circuit, lack of phase protection, pump body leakage, motor over temperature and leakage. It also has single electric dredge pump and multiple electric dredge pump control working modes, and multiple main and standby electric dredge pumps switching ways and various starting methods.
B. Frequency conversion control type
a. Liquid level. The control cabinet is equipped with a high-performance float switch, which automatically controls the on and off of the water supply and drainage pump according to the high and low changes of the liquid level.
b. Pressure control. An external electric contact pressure gauge or pressure controller can automatically turn on and off the electric dredge pump according to changes in the pressure of the pipe network. This model is widely used in domestic water supply and fire pressurization systems.
c. Temperature control. External temperature controller, according to the set temperature range to turn on or off the electric dredge pump, used in constant temperature, heat exchange system and other occasions requiring temperature control.
d. Time control. The chassis panel is equipped with a time setting button and a display. The user can control the opening and closing of the electric dredge pump according to the timing needs. It is suitable for the control of various timing or regular intermittent working modes.
3. Frequency conversion control characteristics
a. Energy saving. Compared with the traditionally controlled motor, the energy saving of the inverter controlled motor is the most practical. The motor operating conditions supplied according to the water injection and oil delivery requirements are economical operation conditions, which can save 48.8% of electricity.
b. Reduced operating costs. The operating cost of a traditional motor consists of three items: initial purchase cost, maintenance cost and energy cost. Among them, energy costs account for about 77% of the electric dredge pump motor operating costs. The energy cost is reduced by 44.3%, coupled with the reduction of the impact on the equipment after the frequency conversion start, the maintenance and repair volume will also be reduced, so the operating cost will be greatly reduced.
c. Improve pressure control accuracy. The frequency conversion control system has precise pressure control capability. Make the pressure output of the motor match the water injection volume required by the system. The output of the frequency conversion control motor changes with the change of the motor speed. Because the accuracy of the frequency conversion control motor speed is improved, it can keep the system pressure change of the pipe network within the range of 3pisg, that is, within the range of 0.2bar, which effectively improves the quality of the working conditions.
d. Extend the service life of the motor. The frequency converter starts the motor from 0HZ, and its starting acceleration time can be adjusted, thereby reducing the impact on the electrical and mechanical components of the motor when starting, enhancing the reliability of the system, and prolonging the service life of the motor. In addition, the frequency conversion control can reduce the current fluctuations when the electric dredge pump unit is started. This fluctuating current will affect the power consumption of the grid and other equipment. The frequency converter can effectively reduce the peak value of the starting current to a minimum.
e. Reduced the noise of the motor. According to the requirements of the motor’s working conditions, after the installation of frequency conversion speed regulation, the motor’s running speed is obviously slowed down, so the noise of the motor during operation is effectively reduced.
When the motor supporting the sand suction pump is used as the power, the starting methods are diversified, and each starting method has its own working principle and applicable environment. Customers can choose different startup methods according to actual needs. This article focuses on the principle and advantages of variable frequency start. During the sand suction operation of the electric dredge pump, the specific gravity and concentration of the sand medium change rapidly. The supporting motor is used as the power of the electric dredge pump. OCEAN PUMP recommends using frequency conversion control to start the motor. On the one hand, the power of the motor supporting the electric dredge pump is relatively large, the use of frequency conversion starting can greatly reduce the instantaneous starting current when the high-power motor starts, thereby reducing the requirements on the generator set or the transformer. Furthermore, the frequency of the motor can be adjusted according to the concentration of sand absorption, so as to achieve the purpose of high efficiency and energy saving. The advantages of frequency conversion control have been fully demonstrated during the use of the supporting motor of the electric dredge pump, and it has also saved a lot of costs for users and created higher economic benefits.
Tai’an Ocean Pump Co.,Ltd.(referred to as OCEAN PUMP) is a professional manufacturer and supplier of high-quality sand pump machine such as sand dredging pumps, sand pumps, slurry pumps, gravel pumps, submersible slurry pumps, simple sand pumps and sand dredgers. OCEAN PUMP integrates independent research and development, equipment manufacturing, pre-sales and after-sales services. The technical team has been engaged in the development, matching and application of sand pump machinery such as river dredging, sea reclamation, and tailing treatment since the 1990s. With more than 20 years experience, excellent technology, and thoughtful service, we has won the trust of users. We have focused on sand pumping equipment for more than 20 years. We not only provide high-quality products and overall solutions.
