Application Case in Steel Industry
Case I
Transformation Application of SB70 Inverters in Winding of Stainless Steel Sheets
Nitrogen bright annealing furnace – Put the stainless steel sheets into the nitrogen bright annealing furnace for high-temperature treatment to soften the sheets before subsequent processing series to form finished product. This procedure is of crucial importance in its impact on quality of the products, and therefore has high requirement. It generally consists of several components: unwinding motor, before the pressure roller motor, S club motor, winding motor, etc. The unwinding motor, front roller motor, S roller motor has power of 5.5 kW and the winding motor has power of 30 kW. Operation process of system – A roll of stainless steel sheet is led by the unwinding motor into the annealing furnace through the front roller; after high-temperature heating treatment, and then led by S roller motor, and wound by winding motor. During the work process, the constant linear speed of each part is constant, which has important effect on the subsequent processing of the products. It is shown as follows:
Fig. 1Schematic Wiring Diagram of Winding Stainless Steel Sheets
Before the transformation, traditional inverter synchronization method is previously used for control. However, frequency conversion control can only guarantee synchronization of S roller motor and winding motor in speed. For the winding motor part, with the increase of winding turns, the outer diameter is gradually enlarged, and its linear speed is required to be unchanged; therefore, it is actually constant tension between the two. To maintain a constant speed, the operator must always measure the linear speeds of S roller motor and winding motor, and according to the difference of the measured speeds, manually change the frequency of S roller inverter and winding inverter to adjust the linear speeds of the two in order to achieve consistent linear speeds. As it is difficult for manual operation, which cannot achieve constant tension control or constant linear speed control for winding stainless steel sheets, and thus cannot maintain a constant tension, the excessive large tension and tautly deformed steel sheets or excessive small tension and loosely deformed steel sheets are often the results, affecting the quality of the products. Moreover, the previous winding system has the following drawbacks: 1. As each power point receives non-uniform force, the system can not run in the same linear speed; 2. S roller motor is liable to slip at low speeds; 3. Overload and stalling often occur to the winding motor; 4. In material feeding and discharge, it is difficult to control.
Under the existing conditions, for the winding motor, with the increase in volume diameter, as long as the S roller motor and winding motor can always maintain constant linear speed (i.e., constant tension), the technological requirements of the winding system is satisfied. For this, in the original system, frequency-conversion speed regulation is adopted for transformation. As the unwinding motor is at the front stage, the requirement in tension control is not high; therefore, transformation will only be made on the S roller motor and the winding motor. The S roller motor of the system will adopt SB70G5.5 kW. Between the S roller motor and winding motor, there is a flexible connection for stainless steel sheets. If the winding motor has linear speed higher than that of S roller motor, the S roller motor will be in power generation state, and therefore, the inverter needs to be provided with external braking resistor. Winding motor adopts SB70G30KW, while the inverter adopts vector control without PG and uses the rich arithmetic logic unit of SB70, and through connection of internal computing unit, to increase torque limitation on the basis of the speed control. Torque limitation value is given directly by the internal arithmetic unit, based on 100% of the 2.5 times of the motor rated torque.
The analog output frequency of S roller SB70G5.5 kW is used as the given value of the linear speed to supply the winding motor, and by regulating the gain and offsetting of corresponding input signals of the inverter as linear speed signal, to carry out the calculation, limitation of the torque, in order to achieve constant linear speeds of the S roller motor and winding motor. The schematic wiring diagram of the inverter is shown in Figure 2:
Fig. 2Schematic Wiring Diagram of Tension Control Inverter
For S roller inverter, the setting is relatively simple. For frequency setting, the potentiometer setting and external control starting is configured. Emergency stop button that has combined movement with the winding motor is provided in case of emergency stop. In just starting the winding motor, inching function is needed, and therefore, inching function is provided. In inching, torque limitation is switched by the analog switch in the inverter to make the torque limitation to be 100% in inching.
The scheme has been used to make transformation for winding of the four nitrogen bright annealing furnace and has been successfully applied. After transformation, with the constant-tension winding, the precision of processing is high, and the product quality is greatly improved. It is safe, reliable and of stable performance, and improves production efficiency. The system is not provided with tension sensor. The speed encoder realizes the control of linear speeds and constant tension of S roller and winding motors, which has won favorable praise from the users who have expressed high recognition and satisfaction of the excellent and powerful function of SB70 inverters.
Case II
Application of SB70 Inverter in Position Control
In the speed regulation system of motor, there is a need to control the load position or angle. Simple position control is to align the target position at stop, while higher level position control requires high dynamic tracking function.
The built-in general function modules, rich programmable units and flexible interfaces of SB70 series inverters provide a basis for realizing position control. Point-to-point position control and position control with pulse frequency as given value have been developed. SB70 inverter has two counters, both of which can realize high-speed orthogonal counting function, and for input of increasement counting of the Counter #2, electronic gear is provided to facilitate use of zooming of given position.
A steel plant requires trolley to move forward and backward in the range of 0～8m and stop at 8m and then return in steel production. To facilitate use by users, inching function is added and the function that proximity switch at position 0 can remove accumulated error of Counter #2 is added, and multi-speed 1 as crawling speed can improve positioning accuracy.The run diagram of trolley is shown in Fig. 3:
Fig. 3Trolley Run Diagram
This scheme uses the high-speed orthogonal counting function of the counter, that is, making increasement counting for Channels A and B of the orthogonal encoder with increasement counting for positive turning and decreasement counting for reverse turning. When the counting direction is not consistent with the positive and reverse turning, the wiring of Channels A and B can be changed, or change can be made through parameter Fd-03 “PG Direction Selection”.
The main concept is to make the travel distance of the trolley is fixed and reproducible.
The proximity switch at the starting position is used to make the counter preset or clear, to eliminate the accumulated error of the trolley in traveling.
The preset value of the counter is about the count value of the trolley from 0m to the preset proximity switch.
What needs to be pointed is that F9-14 "set count value" is about 5% greater that the count value at 8m, such as 36000.
In positive turning, through the regulation of F9-15 "Designated Count Value", F4-18 "Multi-Band Frequency 1", FE-03 "Comparator #1 Number Setting", make the trolley stop at the required position, such as 8m; the setting that F9-15/F9-14 must be less than FE-03 must be met. For example, if FE-03 = 95%, then F9-15 = 90% × 36000 = 32400.
In reverse turning, contrary to the above, Fd-20 "Designation Count Value #2" should be less than the number set in Comparator #2. For example, if FE-08 "Comparator #2 Number Setting" = 10%, then Fd -20 = 5% × 36000 = 1800.
The multi-band frequency is set as 15Hz and can be changed in actual use.
The process of running is as follows:
When the trolley is at 0, the count value is small with counter percentage <95%. If the positive turning terminal FWD is valid, the output of Counter #1 is 1, and the starting motor turns positively and accelerates to the frequency set in F0-00 with count value increased; when the count value rises to "Designated Count Value", number output "Designated Count Value Reached" decelerates the motor by the Logic Unit #3 and Counter #4, and it crawls at the speed of "multi-band frequency #1"; when the count value continues to increase, and the percentage of the count value ≥ 95%, the output of Comparator #1 is 0, causing the output of Counter #1 is 0 and the internal virtual FWD terminal is invalid, the motor decelerates until stop. Adjustment of the comparison value of Comparator #1 can stop the motor at the required position.
The condition of reverse turning is the reverse process of positive turning.
The commissioning on site and users’ reflection shows that it meets the requirement of actual production and has high-level position accuracy and repeatability.
Case III
Application of Senlan SB70 Series Inverter in Speed Raising Transformation of Slag Conveying Belt
1.Existing Problems and Countermeasures
TYNA method is used by iron smelting plant in treating slag for blast furnace. The slag, after granulation and dehydration, is transported by belt to a train wagon. As the equipment has small design capacity, especially the small conveying capacity of slag belt, a large quantity of slag can not be carried away in time, and the belt is often buried by slag. Once accident occurs to the slag equipment, the opening of the blast furnace will be blocked, resulting in uncompleted tapping of slag iron and even reduced air, which will bring about a great negative impact to operation of blast furnace. To solve the problem of small belt conveyor capacity, raising of belt speed by frequency conversion transformation is a feasible approach.
2.Speed Raising Scheme
There are also two methods to raise the speed of belt. One is to perform frequency conversion transformation to increase the output frequency of the inverter to above 50Hz with the speed ratio of speed reducer unchanged, and the other is to reduce speed ratio of speed reducer to raise speed and then adjust the output frequency of the inverter. Our plant select the latter after comparison. The gear ratio is previously 31.5, and changed to 25 after transformation, so that in the condition of maintaining the previous power supply frequency, the conveying capacity of the belt can be increased by about 30%.
3.Selection of Motor and Inverter
By Comparison, our plant decides to select SB70 Series Inverter manufactured by SenLan Science & Technology Holding Corp., Ltd. According to the actual condition, we finally select SB70G75KW General Inverter.
4.Inverter Control Scheme and Parameters Debugging
The inverter control schematic diagram is shown in Fig. 4. The inverter adopts external control FWD and CM terminal for starting and stopping control, and utilizes 4-20mA current signal to control the output frequency of the inverter. Relay output terminal Y1 acts as inverter running signal output.
Fig. 4 Inverter Control Schematic Diagram
5.Transformation Effect
①After speed raising transformation of lag belt, the conveying capacity of the belt has been greatly enhanced. If the frequency is 50Hz, the conveying capacity can be increased by 30%, and if it is 60Hz, the conveying capacity can be increased by 50%.
②The previous control system adopts thermal relay for thermal protection with low accuracy, which is likely to burn to the motor. After it is changed to frequency conversion control, the protection function is improved, which can effectively protect the motor.
③Before transformation, the motor can only run at 50Hz, regardless of the amount of slag. After transformation, the speed can be regulated according to the amount of slag, especially when the belt has no slag to convey, the frequency can be very low by setting to achieve the energy-saving effect.
Case IV
Application of Senlan Inverter in Water Supply of Baogang Group
I.Introduction
In plant water supply and domestic water supply, the flow rate, pressure, lift and other parameters always change with the change of working conditions. In the past, due to limitation of technical level, there is no appropriate speed regulation method to solve the negative effect brought by the variables. Therefore, manual switchover of pump is low in regulation precision and will cause electric energy waste. Switchover of pump has great impact of the entire pipe network, and pumps and motors have always been running at high speed, which will reduce the normal service life of the mechanical system and electrical system.
Practice proves that in the fan and pump type loads, the application of frequency conversion control can save electric energy of 20% to 50%, and its application can bring the following benefits :
1.It has obvious energy saving effect.
2.It realizes soft start and soft stop for motor. It solves the dripping, leakage and overflow caused by impact of direct starting of motor to pumps and pipe network. There is no impact to the electric grid in starting of motor.
3.It realizes protection functions for the motor, such as motor overload, over-voltage, under-voltage, overheating, earthing, power supply phase failure, etc.
4.The whole production process realizes automation to maintain stable pressure of the pipe network.
5.It extends the service life of the pump and motor. The inverter can automatically regulate the running frequency to mitigate wear of the pump and aging of the motor.
IIFrequency Conversion Transformation Scheme for Constant-Pressure Water Supply System
The system mainly consists of three pumps, one Senlan SB200 Inverter, pressure transmitter, PLC and other components Steel enterprises have large water consumption, large pump capacity, and correspondingly large diameter of pipe network. Therefore, in switchover of the pump, valve should be controlled. Switch-on of the pump shall follow the principle of "switch pump before opening valve", while switch-off of pump shall follow the principle of “close the pump before stopping the pump". In this time, PLC should be used for control. The system control schematic diagram is shown in Fig. 5.
Fig. 5Schematic Diagram of Water Supply System under Frequency Conversion and Constant Pressure
In Fig. 5, the given value of pressure is set by keyboard of the inverter, while the feedback value of the pipe network pressure is sent by the pressure transmitter. The built-in PID controller of the inverter compare the given value with the feedback value from the pressure transmitter, to control the number of pumps in operation, and the frequency-conversion also regulates the speed to achieve constant pressure of the pipe network. If small-capacity pumps are used, no PLC control valve is required, and multi-pump switchover functions can use the built-in expansion unit of Senlan inverter to realize control. Its application is simple and maintenance is convenient.
IIIEnergy Saving
To adapt to the change of actual water consumption, manual switchover of the number of station pumps was adopted in the past to regulate the water pressure and flow rate of the pipe network. This would cause pressure change (sometimes over-pressure and sometimes under-pressure) at different outlets of the pipe network. Application of frequency-conversion speed regulation technology for pump unit is to change the speed of pump by regulating the frequency of the input motor power supply. Centrifugal pump has load of square torque characteristics. The power consumption of the motor is proportional to the cube of its speed. After frequency-conversion speed regulation, a lot of electric energy can be saved to achieve the objective of energy saving and efficiency improvement.
Case V
Frequency Conversion Transformation for Fan of Steel Industry
The drive motor for the blast furnace fan of Guangzhou Steel Plant is 315kW. It adopts self-coupling step-down startup mode. After startup, the fan motor runs at 50Hz with air volume regulated by throttling and controlled by opening of the valve. The air volume used is about 78% of the rated air volume. The electric power consumed by the fan motor can be calculated by empirical equation:
=[0.45+0.55（0.78）2]315=247.16(kW)
To save energy, frequency-conversion speed regulation is adopted for the fan. When the valve is fully open, the frequency is so adjusted that the air volume output of the fan is 78%, whereby the energy saving rate can be calculated based on energy saving rate equation:
The energy saving rate is 40%. The investment will pay itself off in one year and three months.
Case VI
Frequency Conversion Transformation for Fan of Coke Plant
I.Current Situation:
The coke oven air blast cooling system of a coke plant has two fans of 400kW, one for service and one as standby, installed in front of the two primary coolers, that is a blast fan extracts coal gas from two primary coolers at the same time. To technologically ensure the maintenance of positive pressure of 120Pa in the primary cooler, speed of the blast fan needs regulation. The previous system adopted hydraulic coupler for speed regulation. In addition, it is required that both the positive pressures in the two primary coolers should be 120Pa. In the previous system, a manual operated valve is provided at the outlet of the cooler for manual adjustment. In the adjustment process, not only the valve opening should be adjusted, the oil pressure of the hydraulic coupler should also be adjusted to regulate the speed of the fan. As the valve and speed need to be adjusted and there is certain degree of coupling between the two, the case is often that the two cannot be attended at the same time, and it is difficult to meet the technological requirements. In addition, the hydraulic coupler is poor in speed regulation stability and inconvenient in speed regulation and low in efficiency. To meet the technological requirements and energy saving, transformation is needed.