Pump loads widely used in metallurgy, chemical industry, electric power, municipal water supply, mining and other industries account for about 40% of the energy consumption of the entire electrical equipment, and electricity charges in water plants even account for 50% of the water production cost. This is because: on the one hand, equipment is usually designed with a certain margin; On the other hand, due to the change of working conditions, the pump needs to output different flows. With the development of market economy and automation, manufacturers have begun to use high-voltage converters to control the speed of pump loads. However, with the introduction of permanent magnet drive technology into China and its continuous improvement, more and more manufacturers choose to use permanent magnet speed regulators instead of high-voltage converters. Let's make a simple comparison between the two from the aspects of principle, later use and maintenance, and adaptability to the operating environment.
working principle
Permanent magnet governor:
The permanent magnet speed governor transmits the torque from the motor to the load through the air gap between the copper conductor and the permanent magnet. This technology realizes that there is no mechanical link between the drive (motor) side and the driven (load) side. Its working principle is that the rare metal oxide NdFeB permanent magnet at one end interacts with the induced magnetic field at the other end to generate torque. The transmitted torque can be controlled by adjusting the air gap between the permanent magnet and the conductor, so as to achieve load speed regulation. Permanent magnet speed governor is mainly composed of conductor rotor, permanent magnet rotor and controller. During operation, the output torque on the load shaft can be changed by adjusting the air gap between the permanent magnet and the conductor, so that the load speed can be changed.
Frequency converter：
Frequency converter is a power control device that uses the on-off function of power semiconductor devices to convert power frequency power supply to another frequency. The frequency converter mainly adopts the AC-DC-AC mode (VVVF frequency conversion or vector control frequency conversion). First, convert the power frequency AC power supply into DC power supply through the rectifier, and then convert the DC power supply into AC power supply with controllable frequency and voltage to supply the motor, so as to change the speed of the motor.
Wuhu Huadian slurry circulating pump permanent magnet governor project
Permanent magnet speed governor is achieved by transmitting torque between magnetic field and conductor through space, and speed is regulated by air gap distance; The frequency converter realizes speed regulation by changing the frequency and other parameters of the motor. Therefore, compared with the frequency converter, the permanent magnet speed governor has more advantages in mechanical characteristics, such as complete off load startup without accurate centering.
Impact on other equipment in the system
Permanent magnet governor：
Since the main part of the permanent magnet speed regulator is a mechanical speed regulator, it is almost independent of power and will not generate harmonics, so it will not affect other equipment in the system. When the power quality is very poor, such as voltage fluctuation, power harmonic, flicker, drop, short interruption, lightning stroke, surge, etc., these factors are often fatal to electronic or electrical speed regulating devices, but have no impact on permanent magnet speed regulators. Permanent magnet speed governor will not be damaged due to power quality.
Frequency converter：
Because the AC-DC-AC circuit of the frequency converter is mainly composed of electronic components, a large number of high-order harmonics will be generated during operation. Power harmonics are serious pollution of the power grid. A large number of harmonic currents and voltages can cause heat loss of electrical components, or even equipment malfunction, resulting in power factor compensation capacitor burning, fuse fusing, air or circuit breaker switch tripping.
Datang Foshan Thermal Power Vertical Condensate Pump Permanent Magnet Governor Project
Permanent magnet speed governor is mechanical, which is safer and more reliable. For industrial users, these are the safety guarantees for continuous production operation.
Operation and maintenance
Permanent magnet governor：
Because it is pure mechanical equipment, there is no complex electronic equipment; After simple training, the staff will quickly determine the cause of the failure and solve the failure by themselves, without having to ask the professional company to repair. Its service life can reach 30 years. The main cause of motor system failure is vibration, which will lead to accelerated wear of bearings, oil seals, etc., as well as looseness, fracture or damage of bases, pipe joints, fasteners, etc., and strong noise. Because the permanent magnet speed governor uses air gap to transmit torque, there is no rigid connection between the motor and the load equipment, and it can buffer through slip during mechanical impact, so it greatly reduces vibration and noise, and also reduces the maintenance workload of the motor.
Frequency converter：
Frequency converter is a complex electronic equipment, and the installation environment is required to be - 5 ℃~40 ℃. A large number of studies show that the failure rate of high-voltage frequency converter increases exponentially with the increase of temperature, and the service life decreases exponentially with the increase of temperature. The ambient temperature increases by 10 ℃, and the service life of high-voltage frequency converter will be halved. Summer is a frequent period for high-voltage frequency converter failures. In addition, whether the high-voltage inverter operates well depends on the degree of environmental cleanliness. Therefore, the high-voltage inverter is generally installed in an independent air conditioning room, which requires regular maintenance. If there is no guidance or fine training from the manufacturer, once a fault occurs, it will be difficult for the staff to quickly determine the cause of the fault, and involve the replacement of spare parts. It is impossible to quickly solve the fault by themselves. Only the inverter manufacturer or professional company can send someone to repair it, which is difficult to ensure rapid repair and does not affect production. The service life of frequency converter is generally about 8-10 years.
Transformation Project of Permanent Magnet Governor for Desulfurization Circulating Slurry Pump of Boiler # 7 in Guodian Jingmen Power Plant
Considering the initial investment, the life cycle cost of the permanent magnet governor is only about 1/3 of that of the frequency converter. With the life cycle maintenance cost included, the annual service cost of the permanent magnet governor is far lower than that of the frequency converter.
Economic security
Permanent magnet governor：
Since the permanent magnet speed governor does not need to lay cables, build a special air conditioning room and install air conditioners, the initial investment of the permanent magnet speed governor is lower than that of the frequency converter; As the main part is a mechanical part, it is safe and reliable to use, requires less maintenance, has a much longer mean time between failures than the frequency converter, and has a long service life. The service life of the same permanent magnet speed regulator is equivalent to the total life of 4-6 frequency converters; In addition, there is no need for a large number of expensive spare parts, which saves a lot of costs.
Frequency converter：
When the inverter is put into operation at the initial stage, it is necessary to purchase the host machine, and also consider the cost of laying cables, building a special air conditioning room, and installing air conditioners. Therefore, the initial investment is higher than that of the permanent magnet governor; During later use, regular dedusting and other special maintenance are required; At the same time, because the frequency converter is composed of a large number of electronic devices, the corresponding failure rate is high, and even explosion occurs in serious cases, delaying production and causing property losses; In order to deal with the problem of high failure rate of frequency converter, it is necessary to prepare corresponding spare parts during operation, and the use cost is high.
High voltage inverter explosion and burning site
It can be seen from the above comparison that the permanent magnet speed governor has many advantages over the frequency converter, and can be applied to various harsh environments, including corrosion, explosion, humidity and high dust. The use of permanent magnet speed governor can significantly improve the safety and stability of system operation and reduce economic losses. The permanent magnet speed regulation can further optimize the system, improve the energy saving effect, increase the energy efficiency and reduce the operation and maintenance costs.
According to the conversion of 0.4kg standard coal consumption per kilowatt hour and 0.997kg carbon emission per kilowatt hour, and 8000 hours of normal annual operation of industrial motors, it is equivalent to saving 64-160 tons of standard coal and reducing 160000-400000 kg carbon dioxide per 100KW of electrical equipment. At present, the company has an annual capacity of 500 sets, and the average function of a single set is about 1000KW, which is equivalent to reducing 800000-200000 tons of carbon dioxide emissions for the whole society every year, with remarkable ecological benefits.
By contrast, the permanent magnet speed governor has overwhelming advantages in terms of the service cost of the whole life cycle, the maintenance of its entire shafting equipment, the vibration of the system, the quality of the power grid, etc.