Pan Shanxian 7 Summary
(Department of Production Technology, Longzhou Sugar Factory, Longzhou Nanhua Sugar Industry Co., Ltd., Longzhou 532400, China)
ã€Abstract】Compared with the composition, technical parameters, production capacity, unit energy consumption, maintenance and maintenance of the digital AC/DC speed regulation method of the sugar mill scraper centrifuge, the digital AC speed control method is more digital than the digital DC speed. The speed control method has more advantages.
[Keywords] scraper centrifuge; digital AC and DC speed regulation; comparison
[Chinese Library Classification Number] TQ051.8 [Document Identification Code] A [Article Number] 1003-2673 (2009) 07-41-02
1 Introduction
In the industrial field, the electric drive system is a basic power system and is widely used. For the electric drive system that needs speed regulation, according to the motor current form, it is often divided into two types: DC speed control system and AC speed control system. The DC speed regulation system is the most widely used automatic speed control system in the field of electric power drag. It can smoothly adjust speed within a certain range and has good static and dynamic performance. Due to the good running performance and control characteristics of DC motors, DC speed control systems have always occupied a monopoly position. In recent years, the AC speed control system has developed rapidly. The AC motor has the advantages of simple structure, convenient manufacture and maintenance, and low price, which is sufficient to compete with the DC motor. Especially with the continuous improvement of computer technology, power electronics technology and automation control technology, it provides a strong technical support for the development of AC speed regulation, making AC speed control system completely replace DC speed control system in some engineering applications. may. Since the digital AC and DC speed control systems have their own characteristics, it is very common in the engineering practice that these two speed control systems are applied to the same equipment.
Centrifuges are one of the important production facilities for sugar mills. In recent years, domestic large-scale sugar companies have gradually eliminated old-fashioned centrifuges with backward technology and installed digital AC speed-regulating or digital DC-speed adjustable blade centrifuges with large capacity, high efficiency, energy saving and intelligence. In 2007, our factory installed three XG-1500AT digital AC speed-adjusting scraper centrifuges and one XG-1500AT-Z digital DC speed-adjusting scraper in the second production line of the 14000t/d technical transformation project. Machines, these two different speed control centrifuges have different performances in production operation. This article compares the application of these two digital speed control methods in the sugar mill scraper centrifuge.
2 speed control system
The composition of the XG-1500AT digital AC speed control scraper centrifuge system is shown in Figure 1. The speed control device adopts Siemens 6SE7133-7EF61-5BA0-Z, input 3AC380~460V, 370A, 50/60Hz, output 3AC0~460V, 370A, 0~500Hz, maximum output 503A; the traction motor selects ABB three-phase asynchronous frequency conversion speed regulation The motor, model number QABP355L8A, has Pe=200kW, Ue=380V, Ie=399A. The Siemens 10.4 inch color large-screen touch screen and Siemens S7-200 series PLC are used to form a monitoring management system to control the program of the centrifuge. The XG-1500AT-Z digital DC speed control scraper centrifuge system is shown in Figure 2. The speed control device adopts Siemens 6RA7085-6DV62-0, armature input 3AC400V, 498A, 50/60Hz, output DC±420V, 600A; excitation input 2AC400V, 25A, 50/60Hz, output DC325V, 25A; AC current 403A; select Z4 -280-22 DC motor drag, its Pe=250kW, Ue=400V, Ie=685A, excitation voltage 180V, excitation current 16A, speed 1355rpm. As with the AC speed regulation, Siemens' 10.4-inch color large-screen touch screen and Siemens S7-200 series PLC are used to form a monitoring management system for program control of the centrifuge.
3. Main technical parameters
The main technical parameters of the two centrifuges (see Table 1).
The parameters listed in Table 1 are the same except for the maximum basket speed and motor power. From the maximum speed of the basket, another important parameter of the two centrifuges, the separation factor fc, can be calculated.
The separation factor refers to the ratio of centrifugal force to gravity, that is, the ratio of centrifugal acceleration to gravity acceleration. which is:
Fc=F/mg=mRn2/mg×100≈Rn2/900
In the above formula, R is the radius and n is the rotation speed. The larger the separation factor fc, the higher the separation capacity of the centrifuge, the faster the separation process, and the better the separation effect. Substituting the parameters in Table 1 into the above equations, the separation factor fc of the two centrifuges is obtained as follows:
XG-1500AT separation factor fc=0.75×11402/900=1083 XG-1500AT-Z separation factor fc=0.75×10502/900≈918 Obviously, the XG-1500AT separation factor fc is larger than the XG-1500AT-Z separation factor fc.
4 production capacity
According to the actual size of the sugar paste in the production, the operating parameters of the centrifuge as shown in Table 2 were set on the touch screen at the same sugar paste density.
In the automatic control mode, the programmable controller PLC of the centrifuge speed control system starts to receive the signals sent by the on-site command signal and the speed detecting unit and the position switch, performs logic judgment, and then controls the processes according to the prepared commands. The motor speed and the actuators operate to achieve automatic cycle operation. According to the real-time running data of the centrifuge displayed on the touch screen, the drawing speed curve is shown in Figure 3.
As can be seen from the speed graph, the acceleration/deceleration response of the digital AC speed control device is faster, when the centrifuge starts to increase to the highest separation speed (accelerated from 180 rpm to 1140 rpm) and the maximum separation speed is reduced to the discharge speed (from 1140 rpm) When the speed is reduced to 60 rpm), it is much faster than the digital DC converter. It is shown on the touch screen that the XG-1500AT centrifuge uses 210s for one cycle, while the XG-1500AT-Z centrifuge uses 250s.
According to the cycle time, the maximum number of hours and the maximum hourly production capacity of the two centrifuges are calculated as follows.
XG-1500AT centrifuge
Maximum number of cycles: 3600÷210≈17(h-)1
Maximum production capacity: 1.5 × 17 = 25.5 (t · h -) 1
XG-1500AT-Z centrifuge
Maximum number of cycles: 3600 ÷ 250 ≈ 14 (h-) 1
Maximum production capacity: 1.5 × 14 = 21 (t · h -) 1
From the above calculations, the XG-1500AT centrifuge has a larger production capacity than the XG-1500AT-Z centrifuge.
5 unit energy consumption
XG-1500AT scraper centrifuge and XG-1500AT-Z scraper centrifuge are both high-efficiency, low-energy, fully automatic modern sugar-making equipment. The difference between the two is electric drive. The former uses a digital AC variable frequency speed control system, while the latter uses a digital DC speed control system. In the work, the two speed control systems can realize stepless adjustment within the set range, the speed conversion is stable, no impact phenomenon, and the speed adjustment requirements of each stage of the sugar paste honey separation are satisfied to the utmost. Both speed control systems use regenerative braking. When the speed is increased, the speed regulating device converts the electrical energy of the power grid into mechanical energy to drive the centrifuge to work; when the speed is reduced, the speed regulating device converts the mechanical energy of the centrifuge into electric energy, brakes the centrifuge, and feeds the electric energy back to the power grid. Both centrifuges reduce energy consumption by more than 50% compared to older centrifuges that use both energy-consuming brakes and mechanical brakes.
Because the speed control system is different, the power of the drag motor is different, and the time consumption of each work cycle is different, so the power consumption of the centrifuge is not the same. In order to truly reflect the unit energy consumption of the centrifuge, the two types of centrifuges are separately measured on the side of the AC power distribution cabinet using the energy meter. The measured data are shown in Table 3.
It can be seen from the data in Table 3 that the energy consumption per ton of sugar of the digital AC speed regulating blade centrifuge XG-1500AT is less than that of the digital DC speed regulating blade centrifuge XG-1500AT-Z.
6 Maintenance and care
6.1 Motor section
The AC motor is the electric-mechanical energy conversion device of the digital AC speed control system, which generates the required torque and speed by controlling the motor. The main advantages of the AC motor are: no brush and commutator, simple structure, reliable operation, long service life, suitable for on-site use in harsh working conditions. During the season of production, it is only necessary to keep the AC motor of the XG-1500AT scraper centrifuge well ventilated, regularly clean the air inlet of the air inlet to prevent overheating, and it is convenient and simple to maintain and maintain.
The electric-mechanical energy conversion device of the digital DC speed control system is a direct current motor. Due to the special structure of the DC motor and the high temperature and humidity of the sugar factory, the harsh environment with strong vibration determines the maintenance and maintenance requirements are much more complicated than the AC motor, especially for the DC motor commutator and The maintenance of brushes is more important. During the season of production, in addition to maintaining good ventilation of the DC motor of the XG-1500AT-Z scraper centrifuge, regularly clean the air inlet of the air inlet to prevent overheating, and pay attention to the daily maintenance of the commutator and brush.
(1) Keep the surface of the commutator clean, periodically purge and clean, and do not use any liquid solvent, including industrial alcohol, to prevent the ablation of materials such as commutator surfaces and mica.
(2) If there are slight streaks or grooves on the surface of the commutator, the surface should be cleaned with a clean silk cloth after grinding or polishing to facilitate the formation and protection of the oxide film.
(3) Always check the wear of the brush, keep the brush and the commutator in good contact, pay attention to the level of the brush spark, and replace the excessively worn brush in time. Only the perseverance of daily maintenance and maintenance can maintain the performance of DC motors, reduce the failure rate and extend the service life.
6.2 Electrical control cabinet section
The maintenance and maintenance methods of the electric control cabinets of these two types of scraper centrifuges are the same, mainly the following:
(1) Frequently clean the dust of the electric control cabinet and keep all parts of the electrical clean. (2) The electric control room should maintain a good ventilation and heat dissipation condition to prevent overheating and keep the room dry. (3) Always check and tighten the terminals to maintain good electrical insulation and prevent malfunction. (4) Check the ablation of the contactors of each contactor. For the ablation, the abrasive cloth can be polished to make the contact surface flat; if it is serious, it should be replaced to prevent accidents. (5) Check whether the work of each relay is normal. If there is any abnormality, replace it in time. (6) In daily operation, always pay attention to the correct position of each actuator of the machine, and whether the running program and parameters are normal. When the vehicle is suddenly powered off and then restarted, it is necessary to re-check and check each operation data. If the program and data are wrong or deviated, it should be corrected and adjusted in time, and then put into use after the empty vehicle test run.
In summary, the digital AC speed-adjusting blade centrifuge XG-1500AT has the following advantages over the digital-type DC speed-regulating blade centrifuge XG-1500AT-Z:
(1) Digital AC speed-adjusting scraper centrifuge XG-1500AT has high separation ability, rapid separation process and good separation effect. (2) Digital AC speed-adjusting scraper centrifuge XG-1500AT has a short working cycle and a large production capacity. (3) The digital AC speed-adjusting blade centrifuge XG-1500AT has high efficiency and remarkable energy saving effect. (4) Digital AC speed control scraper centrifuge XG-1500AT is convenient and simple to maintain and maintain.
Therefore, the advantage of the digital AC speed control system is that the digital DC speed control system cannot be compared to the sugar mill scraper centrifuge which only needs speed control and is not very important for the starting performance and torque adjustment requirements.
references
[1] Su Shi Group Suspension Centrifuge XG-1500AT Instruction Manual.
[2] Chen Weizhen, Xu Sixin et al. Sucrose crystallization and sugar formation [M]. Beijing: China Light Industry Press, 2001.