1. Introduction
In various industrial fans and pumps, such as boiler drum, induced draft fan, deep well, centrifugal pump, most of them operate at rated power. The fan flow is designed according to the maximum air volume demand, and its adjustment mode is controlled by baffle, damper, reflux, start and stop motor, which can not form closed-loop control, and power saving is rarely considered; The design of pump flow is also the maximum flow, and the pressure can only be regulated by controlling the size of the valve and the start and stop of the motor. The electrical control adopts direct or Y △ start, which can not change the speed of the motor, can not have the function of soft start, has large mechanical impact, short service life of the transmission system, large vibration and noise, and low power factor.
2. Energy saving significance of variable frequency speed regulation
Variable frequency speed regulation is a new technology rising in recent years. It realizes speed regulation by changing the power frequency. It has been paid more and more attention because of its characteristics of stable speed regulation, high transient stability and energy saving. With the continuous maturity of variable frequency speed regulation technology, variable frequency speed regulation device is more and more widely used in fan and water pump equipment.
Using frequency converter to directly control the load of fans and pumps is the most scientific control method. The built-in PID adjustment software of the frequency converter is used to directly adjust the speed of the motor to maintain constant water and air pressure, so as to meet the pressure required by the system. Because the frequency converter can realize the soft stop and soft start of large motors, avoid the voltage impact during startup, reduce the motor failure rate, prolong the service life, reduce the capacity requirements and reactive power loss of the power grid, significantly improve the equipment operating conditions, improve the safety and reliability of the system and equipment utilization, and have a significant energy-saving effect.
3. Energy saving principle of variable frequency speed regulation of fan and water pump
According to the basic laws of fluid mechanics, fans and pumps belong to square torque load, and their speed n has the following relationship with flow Q, pressure h and shaft power P: Q ∝ N1, H ∝ N2, P ∝ N3; That is, the flow is directly proportional to the speed, the pressure is directly proportional to the square of the speed, and the shaft power is directly proportional to the cube of the speed.
Q2=Q1(n2／n1)
H2=H1(n2／n1)
P2=P1(n2／n1)
Therefore, ideally, there is the following relationship:
It can be seen from the above table that when the demand flow decreases, adjusting the speed can save a lot of energy. For example, when the motor operates at 80% of the rated speed, the power consumed is theoretically (80%) of the rated power, i.e. 51.2%. After removing the effects of mechanical loss, motor copper and iron loss, the energy-saving efficiency is close to 40%. At the same time, the closed-loop constant voltage control can also be realized, and the energy-saving efficiency will be further improved. If the traditional baffle and valve adjustment are adopted, although the energy consumption can be reduced accordingly, the saving effect is very different from that of frequency conversion.
4. Functions and features of qd800 series frequency conversion energy saving equipment:
·The speed of the motor is controlled by the ozhor frequency converter, the baffle and valve adjustment are cancelled, the failure rate of the equipment is reduced, and the power saving effect is remarkable.
·The soft start of the motor is realized, the service life of the equipment is prolonged, and the impact on the power grid is avoided.
·The motor will operate below the rated speed to reduce the impact of noise on the environment.
·It has automatic protection functions such as overload, overvoltage, overcurrent, undervoltage and power shortage.
·The operation status is flexible and diverse, which can be controlled manually or completely automatically, and can be electrically interlocked with other automatic control devices of the equipment to realize automatic protection and computer control of the equipment, so that the production will not be affected by accidents.
·During installation, the original power distribution facilities and environment can not be damaged and the production will not be affected.
·Just adjust the potentiometer knob to adjust the flow, which is convenient to operate.
5. Conclusion
Using frequency conversion speed regulation technology to realize energy-saving operation of fans, pumps and other equipment is a key promotion technology of energy conservation in China. It is listed as a general technology in Article 39 of the energy conservation law of the people's Republic of China. Practice has proved that the frequency converter has achieved remarkable power-saving effect when it is used in the driving and control of fans and pumps. It is an ideal speed regulation control mode. It not only improves the equipment efficiency, but also meets the production process requirements, greatly reduces the equipment maintenance and repair costs, but also reduces the shutdown cycle. The direct and indirect economic benefits are very obvious. The one-time investment in equipment can usually be fully recovered in 9 to 16 months of production.