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Application of SAFESAVE frequency converter in constant pressure water supply

Mar 26, 2021

Application of SAFESAVE frequency converter in constant pressure water supply

Abstract: This article analyzes the energy-saving principle of applying frequency converters to water pumps in the process of water supply treatment, and proposes a design scheme that uses SAFESAVE frequency converters as water pump frequency converter components. After SAFESAVE frequency converters are used, the water supply system runs stably.

Under normal circumstances, the water pump is driven by a constant-speed AC motor, but the water consumption is variable. In order to ensure the normal water supply of the pool, workers must frequently adjust the baffle or valve opening on the spot to control the pumping volume of the water pump, or Drain the unused water in the pool in vain. This not only increases the labor intensity of the workers, but also a large amount of electric energy is wasted on the loss of the resistance of the pump valve. Therefore, the water pump is required to operate under variable working conditions. If the frequency converter is used to adjust the speed, the method of adjusting the motor speed instead of adjusting the baffle or valve can not only reduce the labor intensity of the workers, but also achieve the purpose of saving electric energy, which will improve the economy of the enterprise. Benefits are of great significance.


   Water pump inverter control energy-saving principle


  1, water pump characteristic analysis


  According to the relevant formula of the characteristic curve of the centrifugal pump:


  P=K1Qh (1)


  Q=K2n (2)


  H=K3n2 (3)


   From (1), (2), (3) formulas:


  P=k4n3 (4)


  P/Q=K5n2 (5)


   where: K1, K2, K3, K4, K5 are constants:


  P is the pump shaft power;


  Q is the flow of the pump;


  H is the pump head;


  N is the speed of the pump.


(1) The formula shows that under the same shaft power, if the flow rate of the pump is adjusted through the outlet valve, it will cause the corresponding change of the pump head. The smaller the flow, the greater the head. However, in actual pumping, because the head is basic Invariable, more surplus head will be generated from this.


   (4) formula shows that the pump shaft power is proportional to the cube of the speed. If you try to reduce the speed, you can reduce the pump shaft power. From (1), we can see that the flow or head can be adjusted freely.


   (5) formula shows that the energy consumption per m3 of water discharged per unit of time (ie, power consumption) is proportional to the cube of the rotation speed, which shows that the lower the rotation speed, the lower the power consumption under the premise of reaching the actual water supply flow.


  2, motor characteristic analysis


  According to the working principle of AC motor:


  N=60p.f(I-s)(6)


   Where: f is the power frequency of the motor;


  P is the number of pole pairs of the motor;


  S is the slip rate.


  Since the S and P of the motor are constants, the formula (6) shows that the speed of the motor has a fixed proportional relationship with the frequency of the power supply.


  3, the principle of energy saving


It can be seen from the analysis of the characteristics of the motor that evenly changing the power supply frequency F of the motor can smoothly change the speed of the motor, thereby changing the speed of the pump; combined with the analysis of the characteristics of the pump, reducing the motor speed will reduce the input power of the motor. The power is reduced accordingly. This is the energy-saving principle of the inverter controlled water pump.


In addition, the sudden twisting of the water pump when starting and the water hammer phenomenon when suddenly stopping are often easy to cause the pipeline to loosen or rupture, and the serious may cause damage to the motor. After the water pump adopts the frequency converter to adjust the speed, the pump can be realized according to the needs of the process. Soft start and soft stop, so that the phenomenon of sudden twist and water hammer can be solved. Moreover, when the water consumption is not large, the speed of the pump can be reduced, which not only avoids the premature aging of the motor caused by the long-term full-load state of the pump, but also the soft start of the frequency converter greatly reduces the time when the pump starts. The impact on machinery also has the effect of energy saving, and its power saving rate is generally about 15%-40%.


   Water pump frequency conversion control design


   Inverter selects SAFESAVE inverter as the execution unit of the frequency control system. SAFESAVE inverter is a general-purpose inverter with high-performance space voltage vector control.


 It has the following characteristics:


   32-bit DSP motor control dedicated microprocessor, high-precision frequency output.


  The novel power accumulation function makes it more intuitive and convenient to observe the energy-saving effect.


  Unique time accumulation function, which can display the running time of a single power-on and the accumulated running time.


  Built-in RS-485 interface, which can be controlled by computer network. Multi-signal input, built-in simple PLC, automatic control is more convenient.


  Parameter interactive function, easy to set.


   The carrier frequency is adjustable, and it runs silently.


   The control method is diversified and has strong versatility.


  Built-in PID adjustment function, simple closed-loop control.


   Low-speed rated torque output, stable operation.


  The keyboard is easy to operate, and the relevant parameters can be adjusted and set online during operation


  Built-in brake unit, quick stop.


  The running status of the fan can be controlled, making scheduling and operation easier and more convenient.


  Various display of inverter operating status parameters, clear to the control signal and load related conditions.


The controlled object of the system is a 30KW water pump motor. The original power frequency starting unit of the motor is retained, and the frequency conversion control is added. The two are mechanically and electrically interlocked, which not only ensures the normal operation of the pump, but also facilitates the maintenance of the system. The measuring transmitter is used to measure the liquid level of the pool, and convert the liquid level signal into a 4-20mA standard electric signal, which is supplied to the SAFESAVE inverter.


When the water consumption of the factory increases, the water level of the pool will drop accordingly, and the post-liquid measuring transmitter will transmit the drop of the liquid level to the SAFESAVE pool water supply inverter in the form of an electrical signal, so that the output frequency of the SAFESAVE inverter will increase accordingly, and the water pump The rotation speed of the motor increases, and the water supply is increased accordingly, thus maintaining the relative stability of the pool liquid level. On the contrary, the output frequency of the inverter is reduced to keep the water level of the pool no longer rising.


  4 Conclusion


After the water pump is controlled by the SAFESAVE inverter, it not only eliminates many tedious manual operations, reduces the hidden dangers of insecurity, but also keeps the system running in an energy-saving state, prolongs the service life of the equipment, and reduces the maintenance workload. The maintenance frequency can also realize the soft start of the motor, reduce the starting voltage, reduce the impact of large current on the power grid, and better meet the needs of production. Moreover, SAFESAVE inverter has rich internal control functions, which can easily realize closed-loop automatic control with other control systems. Therefore, the use of frequency converters in the water supply treatment process has very good application value and promotion value.