Variable frequency control belt conveyor heavy load starting method

Abstract

The application provides a heavy-load starting method of a belt conveyor with frequency conversion control, and belongs to the technical field of conveying belts. The method is applied to a heavy-load starting system of a belt conveyor with frequency conversion control. The heavy-load starting system of the belt conveyor with frequency conversion control comprises a frequency converter and a belt motor. The frequency converter is electrically connected with the belt motor. The method comprises the following steps: the frequency converter is powered on to perform self-checking; when the self-checking state of the frequency converter is normal, light-load starting is performed; after the frequency converter is started, the frequency converter will be raised to a preset frequency to operate, and the belt conveyor operates at a set speed; when the belt conveyor is stopped under abnormal conditions, the frequency converter is switched to heavy-load starting; the belt conveyor operates at a low speed, but the starting torque is increased, so that a great impact on the starting of the belt motor is avoided; the starting time, voltage and frequency of the belt motor are optimized through the frequency converter; the frequency converter is preset with two starting programs, i.e., light-load starting and heavy-load starting, so that the operation safety of the belt motor and the belt conveyor is ensured when the frequency converter is started under heavy load.

Description

Technical Field

[0001] This invention relates to the field of conveyor belt technology, specifically to a method for heavy-load starting of a belt conveyor controlled by frequency conversion. Background Technology

[0002] Circulating fluidized bed (CFB) power plants have good combustion performance and low requirements for coal quality, capable of burning low-quality coal such as coal slime. The initial conveyor belts for coal slime are mostly small 380V conveyor belts with relatively small planned conveying capacities, and most lack corresponding soft-start devices. With increasingly stringent environmental requirements, the amount of coal slime co-combusted has increased year by year, pushing the conveyor belt loads close to their limits. Due to the sticky nature of coal slime, after a coal slime conveyor belt trips, it is inevitable that it will restart under load or even heavy load. Excessive starting current frequently leads to burnt-out motor terminals, startup failures, and even damage to the motor itself. This forces the system to shut down for extended periods, severely reducing the power plant's fuel economy. The paper "An Example of Inverter Starting of Asynchronous Motors" (Science and Technology Wind, Zhang Yujun, Weifang Shengteng Pharmaceutical Co., Ltd., August 2017) illustrates the starting scheme of asynchronous motors under heavy load conditions through an example, namely, starting with an inverter. After starting, the inverter is taken out of operation, and the device switches the motor to power frequency operation. This starting method can effectively solve the impact of motor starting process on the power grid. The whole process is controlled by PLC and the operation is reliable.

[0003] After the conveyor belt is shut down under heavy load, operators need to manually shovel the coal sludge off the belt. Once the belt is restarted and running normally, the coal sludge is shoveled back onto the belt. This not only consumes a lot of manpower and is extremely inefficient, but also makes it easy for workers to cause safety accidents by working next to the running belt. In emergency situations where heavy load restart is required, it can also easily cause belt motor failure and damage. Each equipment repair costs tens of thousands of yuan, and the normal coal sludge co-firing of the boiler cannot be guaranteed during equipment repair, making it extremely uneconomical. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to design a starting method to ensure the safety of belt conveyors and belt motors during heavy-load starting.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0006] A method for heavy-load starting of a belt conveyor controlled by a frequency converter is provided. The method is applied to a belt conveyor heavy-load starting system controlled by a frequency converter. The belt conveyor heavy-load starting system controlled by a frequency converter includes: a frequency converter and a belt motor, wherein the frequency converter and the belt motor are electrically connected.

[0007] The method includes the following steps:

[0008] S1. The frequency converter performs a self-test upon power-up.

[0009] S2. The inverter self-test status is normal. Perform a light load start. After the inverter starts, it will run at the preset frequency and the belt conveyor will run at the set speed.

[0010] S3. When the belt conveyor stops under abnormal conditions, switch the frequency converter to heavy load start. The belt conveyor will run at low speed, but the increased starting torque will not cause a large impact on the starting of the belt motor.

[0011] Beneficial Effects: This invention uses a variable frequency speed control device to control the starting of the belt motor. The frequency converter optimizes parameters such as starting time, voltage, and frequency of the belt motor, improving its starting characteristics. Based on the typical operating conditions of the belt motor, two starting programs, one for light load and one for heavy load, are preset for the frequency converter, with speed ramp rates set for each. This ensures the safe operation of the belt motor and conveyor under heavy load starting, while allowing the conveyor to reach its rated operating speed quickly under light load conditions, improving work efficiency. The conveyor now possesses heavy load starting capability, reducing the labor intensity of personnel operating the coal slurry system (eliminating the need to remove coal slurry accumulated on the belt after it stops), and significantly improving production efficiency and safety. Using a frequency-controlled belt conveyor heavy load starting system greatly reduces the failure rate of the belt motor. The reliability of the conveyor system is improved by using a frequency converter, reducing mechanical system losses, minimizing maintenance, and resulting in significant energy savings. Promoting the application of variable frequency drive technology is of great significance to implementing the national energy conservation and emission reduction policy. Apart from adding a frequency converter, this invention does not increase the additional cost or workload. The construction method only requires adding a frequency converter cabinet, and the operation is simple.

[0012] Furthermore, the frequency converter-controlled belt conveyor heavy-load starting system also includes: frequency converter circuit breaker QF1, power frequency circuit breaker QF2, and power bypass. Frequency converter circuit breaker QF1 is located on the line between the frequency converter and the power supply, the power bypass is connected in parallel across the two ends of the frequency converter, and power frequency circuit breaker QF2 is located on the power bypass.

[0013] Beneficial effect: By connecting a power supply bypass in parallel across the inverter, when the inverter fails or is under maintenance, the power supply bypasses the power supply to the belt motor, ensuring the continuous and normal operation of the belt motor.

[0014] Furthermore, the frequency converter-controlled belt conveyor heavy-load starting system also includes a contactor KM1, which is located on the line between the frequency converter and the belt motor.

[0015] Furthermore, the frequency converter-controlled belt conveyor heavy-load starting system also includes: a cooling fan, and a power frequency circuit breaker QF3, a contactor KM2, and an overload relay KH2 on the line between the cooling fan and the power supply.

[0016] Furthermore, step S1 also includes: checking that the power frequency circuit breaker QF2 on the power bypass is in the open state, the frequency converter circuit breaker QF1 is closed, the frequency converter is powered on and performs a self-test. If the frequency converter self-test is normal, the frequency converter operation start contact XR012 and the frequency converter operation start contact XR013 will be automatically connected. If the frequency converter has a fault, the frequency converter operation start contact XR012 and the frequency converter operation start contact XR013 will not be connected.

[0017] Furthermore, the frequency converter-controlled belt conveyor heavy-load starting system also includes a transformer, a second power supply, and a relay control unit. The power supply outputs the second power supply through the transformer. The relay control unit includes: an intermediate relay KA1, a frequency converter start-allowing relay KA4, a heavy-load / light-load changeover switch SA, and a frequency converter closing button SF. The coil of the intermediate relay KA1, the frequency converter running start contact XR012, the frequency converter running start contact XR013, the frequency converter closing button SF, and the heavy-load / light-load changeover switch SA are connected in series to the second power supply. The two ends of the normally open contact of A1 are connected in parallel to the two ends of the frequency converter closing button SF. The normally open contact of the intermediate relay KA1 and the normally closed contact of the overload relay KH2 are connected in series between the frequency converter start contact XD244 and the frequency converter start contact XDI1. The normally closed contact of the frequency converter start relay KA4 and the normally open contact of the intermediate relay KA1 are connected in series between the frequency converter constant speed contact XD242 and the frequency converter constant speed contact XDI5. The frequency converter constant speed contact XD242 is connected to the frequency converter start contact XD244.

[0018] Further, step S2 also includes: adjusting the heavy load / light load changeover switch SA to the light load position, pressing the frequency converter closing button SF, energizing the coil of contactor KM1, causing contactor KM1 to engage, energizing the coil of intermediate relay KA1, closing the normally open contact of intermediate relay KA1 connected in parallel across the two ends of the frequency converter closing button SF, forming a self-holding circuit, closing the normally open contact of intermediate relay KA1 connected in series with the normally closed contact of overload relay KH2, connecting the frequency converter start contact XD244 and frequency converter start contact XDI1, receiving a start signal from the frequency converter, closing the normally open contact of intermediate relay KA1 connected in series with the normally closed contact of frequency converter start-allowing relay KA4, connecting the frequency converter constant speed contact XD242 and frequency converter constant speed contact XDI5, and after the frequency converter starts, it will run at the preset frequency, and the belt conveyor will run at the set speed.

[0019] Furthermore, the frequency converter controlled belt conveyor heavy-load starting system also includes a frequency converter start relay KA4, a frequency converter speed control knob WR, the coil of the frequency converter start relay KA4 is connected in series with the heavy-load / light-load changeover switch SA and then connected to the second power supply, one end of the normally open contact of the frequency converter start relay KA4 is connected to the frequency converter closing button SF, the other end of the normally open contact of the frequency converter start relay KA4 is connected to the coil of the frequency converter start relay KA4, and the frequency converter speed control knob WR is connected to the three input terminals XAI1, XAI3, and XAI4 of the frequency converter.

[0020] Furthermore, step S3 also includes: first, adjusting the inverter speed control knob WR to a relatively low speed state, adjusting the heavy load / light load switch SA to the heavy load position, energizing the coil of the inverter start relay KA4, closing the normally open contact of the inverter start relay KA4, energizing the coil of the intermediate relay KA1, closing the normally open contact of the intermediate relay KA1 connected in series with the normally closed contact of the overload relay KH2, connecting the inverter start contact XD244 and the inverter start contact XDI1, receiving the start signal, opening the normally closed contact of the inverter start relay KA4, interrupting the circuit of the inverter constant speed contact XD242 and the inverter constant speed contact XDI5, at this time the inverter constant speed state will not be triggered, and the inverter will run according to the command of the inverter speed control knob WR.

[0021] Furthermore, the frequency converter controlled belt conveyor heavy-load starting system also includes: frequency converter fault relay KA2 and frequency converter running relay KA3. The coil of frequency converter fault relay KA2 is connected in series with frequency converter fault contacts XR032 and XR033 and then connected to the second power supply. The normally open contact of frequency converter fault relay KA2 is connected in series with frequency converter fault indicator YG and then connected to the second power supply. The coil of frequency converter running relay KA3 is connected in series with frequency converter running contacts XR022 and XR023 and then connected to the second power supply. The normally closed contact of frequency converter running relay KA3 is connected in series with frequency converter stop indicator GG and then connected to the second power supply. The normally open contact of frequency converter running relay KA3 is connected in series with frequency converter running indicator RG and then connected to the second power supply.

[0022] Furthermore, the frequency converter-controlled belt conveyor heavy-load starting system also includes: cooling fans, with two cooling fans connected in series with the normally open contact of a frequency converter running relay KA3 and then connected to a second power supply.

[0023] Compared with the prior art, the present invention provides a variable frequency controlled belt conveyor heavy-load start-up method, which has the following beneficial effects:

[0024] 1. This invention uses a variable frequency speed control device to control the starting of the belt motor. The frequency converter optimizes the starting time, voltage, frequency, and other parameters of the belt motor, improving its starting characteristics. Based on the typical operating conditions of the belt motor, two starting programs, one for light load and one for heavy load, are preset for the frequency converter, with speed ramp rates set for each. This ensures the safe operation of the belt motor and conveyor under heavy load starting, while allowing the conveyor to reach its rated operating speed quickly under light load conditions, improving work efficiency. The conveyor now possesses heavy load starting capability, reducing the labor intensity of personnel operating the coal slurry system (eliminating the need to remove coal slurry accumulated on the belt after it stops), and significantly improving production efficiency and safety. Using a frequency converter-controlled heavy load starting system for the conveyor can greatly reduce the failure rate of the belt motor. The reliability of the conveyor system is improved by using a frequency converter, reducing mechanical system losses, decreasing maintenance, and resulting in significant energy savings. Promoting the application of variable frequency drive technology is of great significance to implementing the national energy conservation and emission reduction policy. Apart from adding a frequency converter, this invention does not increase the additional cost or workload. The construction method only requires adding a frequency converter control cabinet, and the operation is simple.

[0025] 2. By connecting a power supply bypass in parallel across the inverter, when the inverter fails or is under maintenance, the power supply bypasses the power supply to the belt motor, ensuring the continuous and normal operation of the belt motor.

[0026] 3. A variable frequency drive (VFD) is used to control the starting belt motor. The VFD optimizes the starting time, voltage, frequency, and other parameters of the belt motor, improving its starting characteristics. The "vector control" function of the VFD enables the belt motor to achieve a low-speed, high-torque starting method, reducing impact on mechanical components and the motor itself. Simultaneously, by modifying the local control cabinet, local control of the belt motor is achieved, enabling local speed adjustment. Furthermore, optimized VFD parameters perfectly match the conveyor belt's stall protection features.

[0027] 4. The motor air cooling device has been changed from coaxial air cooling to an independent cooling fan. The operation and stop of the fan are controlled by the start contact of the frequency converter. That is, when the frequency converter sends a start signal, the cooling fan starts and reaches the rated speed, ensuring sufficient cooling capacity and preventing the belt motor from overheating. This is used for heat dissipation of the belt motor.

[0028] 5. The starting method of the frequency converter of the present invention is set to manual start after power-on. That is, after the power distribution room switch is closed and the frequency converter is energized, the operator still needs to manually start the frequency converter from the frequency converter control cabinet. This can solve the problem that the frequency converter can only be started remotely and avoid the occurrence of accidental starting of belt motor. Attached Figure Description

[0029] Figure 1 This is a primary wiring diagram of the frequency converter controlled belt conveyor heavy-load starting system of the present invention;

[0030] Figure 2 This is a wiring diagram of the relay control unit of the frequency converter-controlled belt conveyor heavy-load starting system of the present invention;

[0031] Figure 3 This is a schematic diagram of the control wiring of the frequency converter in the frequency-controlled belt conveyor heavy-load starting system of the present invention;

[0032] In the diagram: 1. Inverter, 2. Power bypass, 3. Belt motor, 4. Cooling fan, 5. Radiator fan. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains. The terms “upper,” “lower,” “left,” “right,” “front,” “back,” etc., used in this patent application specification and claims are only used to indicate relative positional relationships, and these relative positional relationships change accordingly when the absolute position of the described object changes; terms such as “connected” or “linked” are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0036] like Figure 1As shown, a variable frequency drive (VFD) controlled heavy-load starting method for a belt conveyor is applied to a VFD controlled heavy-load starting system. The VFD controlled heavy-load starting system includes: a VFD control cabinet, a VFD 1, a power bypass 2, a belt motor 3, and a motor cooling device. The belt motor 3 drives the belt conveyor. The VFD control cabinet is located inside the belt conveyor's trestle, and the VFD 1 is located inside the VFD control cabinet. The VFD control cabinet has an operation panel that displays the switching, starting, stopping, and running status of the VFD 1 under light and heavy loads. The VFD control cabinet also includes a cooling fan, an anti-condensation heater, and a temperature controller. The VFD control cabinet has an IP65 protection rating, providing protection for the VFD 1 and other components. The control circuit is powered by a second power source, which can be connected from the mains power source or set separately. The second power source in this invention is a 220V AC power source, which is drawn from the 380V AC power source of phases A and B of the switch and converted into 220V AC power source through transformer T. The line between the 380V AC power source and transformer T is connected to the upper-level switch QF of the transformer.

[0037] like Figure 1 As shown, the R, S, and T terminals of inverter 1 are connected to a 380V AC power supply via lines and cable distribution boxes, respectively. The U, V, and W terminals of inverter 1 are connected to the belt motor 3 via lines. A contactor KM1 is also installed on the line between inverter 1 and belt motor 3. The main contacts of contactor KM1 are located on the line between inverter 1 and belt motor 3 and are used to control the operation of belt motor 3. For details, please refer to... Figure 2 One end of the coil of contactor KM1 is connected to the live wire L of the 220V AC power supply, and the other end of the coil of contactor KM1 is connected to the neutral wire N of the 220V AC power supply. When the upper-level switch QF of the transformer is closed and the frequency converter / power frequency conversion switch SA1 is closed, the coil of contactor KM1 is energized and contactor KM1 is engaged.

[0038] like Figure 1As shown, a frequency converter circuit breaker QF1 is installed on the line between frequency converter 1 and the 380V AC power supply to prevent backfeeding from the output of frequency converter 1 and avoid short circuits in the equipment power supply. Power bypass 2 is arranged in parallel with frequency converter 1, and a power frequency circuit breaker QF2 is installed on power bypass 2. The main function of power bypass 2 is to supply power to the belt motor 3 through the 380V AC power supply during frequency converter 1 failure or maintenance, ensuring the continuous normal operation of the belt motor 3. The AC power supply in this invention uses the original three-phase 380V AC power supply of the belt motor. This invention can add a frequency converter drive circuit without changing the original motor drive circuit system. Only a frequency converter control cabinet needs to be added near the belt motor 3, using the original drive circuit as the power supply for the frequency converter circuit. The original control circuit controls the power-on of the frequency converter system, and after power-on, the frequency converter 1 starts to drive the belt motor 3. Apart from adding a frequency converter, there was basically no additional cost or workload. The construction method only requires adding a frequency converter control cabinet, and the operation is simple.

[0039] In practical applications, it is strictly forbidden to close the frequency converter circuit breaker QF1 and the power frequency circuit breaker QF2 simultaneously. When starting the belt motor 3, if using frequency converter 1, turn the frequency converter / power frequency conversion switch SA1 on the operation panel of the frequency converter control cabinet to the "frequency converter" position. The frequency converter circuit breaker QF1 will close. At this time, check that the power frequency circuit breaker QF2 is in the open position, i.e., the power frequency circuit breaker QF2 on the power bypass 2 is open. Contact the coal slurry central control room to close the coal slurry belt power switch. The transformer upstream switch QF will close, the coil of contactor KM1 will be energized, and contactor KM1 will engage. Check that the energized indicator light on the operation panel of the frequency converter control cabinet is lit. Close the frequency converter closing button SF of the frequency converter control cabinet to give the frequency converter 1 a start signal. The frequency converter 1 will drive the belt motor 3 to start, and the coal slurry belt will start. The power frequency operation of the coal slurry belt is an emergency start method in case of frequency converter failure. When the frequency converter malfunctions, manually disconnect the frequency converter circuit breaker QF1, adjust the frequency converter / power frequency conversion switch SA1 to the power frequency position, de-energize the contactor KM1 coil, release the contactor KM1, remotely disconnect the upstream power supply of the coal slurry conveyor, and then close the power frequency circuit breaker QF2. After the on-site operators inspect and clean the residual coal slurry on the coal slurry conveyor, contact the central control room to remotely close the upstream power supply of the coal slurry conveyor. At this time, the coal slurry conveyor will operate in power frequency mode.

[0040] When inverter 1 starts, it drives the belt motor 3 during startup. As inverter 1 accelerates, the voltage of the belt motor 3 gradually increases, and its power consumption also gradually increases. At this time, the starting current is very small, within the rated current of the belt motor 3. After startup, inverter 1 exits operation and switches to mains frequency operation. This ensures that the starting current does not impact the power grid, and that inverter 1 exits operation after startup to reduce losses, shorten its operating time, and extend its service life.

[0041] Based on the calculation and performance comparison of the actual load of belt motor 3, this invention selects the ABB ACS880-01-145A-3 direct torque control frequency converter. This frequency converter has an output power of 75kW and 55kW under light and heavy load applications, respectively. It can not only fully meet the current operating conditions of belt motor 3, but also reserve some space for future technical upgrades (replacing with a larger motor). The starting method of frequency converter 1 is set to manual start after power-on. That is, after the switch in the power distribution room is closed and frequency converter 1 is energized, the operator still needs to manually start frequency converter 1 from the frequency converter closing button SF. This can solve the problem that frequency converter 1 can only be started remotely and avoid the accidental start of belt motor 3. Based on the typical operating conditions of the belt motor 3, two start-up programs, one for light load and one for heavy load, are preset for the frequency converter 1. The speed ramp rate is set for each program. This ensures the safe operation of the belt motor 3 and the belt conveyor when the frequency converter 1 starts under heavy load, and allows the belt conveyor to reach the rated operating speed as quickly as possible under light load conditions, thus improving work efficiency. The normal operating mode of the frequency converter 1 is set to constant current output.

[0042] The motor cooling system has been changed from coaxial air cooling to an independent cooling fan 4. Cooling fan 4 is connected to a 380V AC power supply via a circuit. A power frequency circuit breaker QF3, contactor KM2, and overload relay KH2 are installed on the circuit between cooling fan 4 and the 380V AC power supply. The main contacts of contactor KM2 are located on the circuit between cooling fan 4 and the 380V AC power supply and are used to control the operation of cooling fan 4. For details, please refer to... Figure 2 One end of the coil of contactor KM2 is connected to the live wire L of the 220V AC power supply, and the other end is connected to the neutral wire N of the 220V AC power supply. When the power frequency circuit breaker QF3 is closed, the coil of contactor KM2 is energized, contactor KM2 engages, and cooling fan 4 starts. The operation and stop of the fan are controlled by the transformer upstream switch QF. When the transformer upstream switch QF is closed and the power frequency circuit breaker QF3 is closed, the cooling fan starts and reaches its rated speed to ensure sufficient cooling and prevent the belt motor 3 from overheating, thus providing heat dissipation for the belt motor 3.

[0043] The frequency converter-controlled belt heavy-load starting system also includes a relay control unit. Figure 2 The wiring diagram for the relay control unit of this invention is shown below. The power supply for the relay control unit is drawn from the 380V AC power supply of phases A and B of the switch, which is converted to 220V AC power supply via transformer T via the neutral line N and live line L. The relay control unit includes: intermediate relay KA1, inverter fault relay KA2, inverter running relay KA3, and inverter start-up relay KA4. The inverter running start contact XR012 is connected in series with the coil of intermediate relay KA1, the normally closed contact of inverter fault relay KA2, inverter closing button SF, inverter opening button SS, and heavy / light load transfer switch SA, and then connected to the 220V live line L output by transformer T. The inverter running start contact XR013 is connected to the 220V live line L output by transformer T. Between the 20V neutral line N, the 220V live line L output from transformer T, and the heavy / light load transfer switch SA, there is a frequency converter / power frequency transfer switch SA1 and a fuse FU. The coil of the frequency converter start relay KA4 is connected in series with the heavy / light load transfer switch SA and then connected between the neutral line N and the live line L of the 220V AC power supply output from transformer T. One end of the normally open contact of the frequency converter start relay KA4 is connected to one end of the normally closed contact of the frequency converter fault relay KA2 through a line, and the other end of the normally open contact of the frequency converter start relay KA4 is connected to the coil of the frequency converter start relay KA4 through a line. The two ends of the normally open contact of the intermediate relay KA1 are connected in parallel to the two ends of the frequency converter closing button SF through a line. The heavy / light load transfer switch SA has an interlocking function.

[0044] One end of the coil of inverter running relay KA3 is connected to the inverter running contact XR023, and the other end of the coil of inverter running relay KA3 is connected to the neutral wire N of the 220V output of transformer T. The inverter running contact XR022 is connected to the live wire L of the 220V AC power output of transformer T. The normally closed contact of inverter running relay KA3 is connected in series with the transformer stop indicator light GG between the neutral wire N and the live wire L of the 220V AC power output of transformer T. The normally open contact of inverter running relay KA3 is connected to the inverter running indicator light RG. After being connected in series between the neutral wire N and the live wire L of the 220V AC power output from transformer T, after inverter 1 starts running, inverter running contacts XR022 and XR023 automatically conduct, the coil of inverter running relay KA3 is energized, the normally closed contact of inverter running relay KA3 connected in series with inverter stop indicator GG opens, inverter stop indicator GG does not light up, and the normally open contact of inverter running relay KA3 connected in series with inverter running indicator RG closes, inverter running indicator RG lights up, indicating that inverter 1 is operating normally.

[0045] One end of the coil of inverter fault relay KA2 is connected to inverter fault contact XR033, and the other end of the coil of inverter fault relay KA2 is connected to the neutral line N of the 220V output of transformer T. Inverter fault contact XR032 is connected to the live line L of the 220V output of transformer T. The normally open contact of inverter fault relay KA2 is connected in series with inverter fault indicator YG between the neutral line N and the live line L of the 220V AC power supply output of transformer T. When inverter 1 malfunctions, inverter fault contact XR032 and inverter fault contact XR033 automatically conduct, inverter fault relay KA2 is energized, the normally closed contact of inverter fault relay KA2 connected in series with intermediate relay KA1 opens, and the normally open contact of inverter fault relay KA2 connected in series with inverter fault indicator YG closes, and inverter fault indicator YG lights up, indicating that inverter 1 is faulty.

[0046] There is a cooling fan 5 on each side of the inverter control cabinet. The two cooling fans 5 are connected in series with the normally open contact of the inverter running relay KA3 and then connected between the neutral line N and the live line L of the 220V AC power output from transformer T. After the inverter 1 starts running, the inverter running contacts XR022 and XR023 are automatically turned on, the coil of the inverter running relay KA3 is energized, and the normally open contact of the inverter running relay KA3 connected in series with the cooling fan 5 closes. The cooling fans on both sides of the inverter control cabinet start automatically, ensuring that the inverter 1 will not be damaged due to excessive temperature during operation.

[0047] Figure 3 The diagram shows the control wiring of the frequency converter of the present invention. The speed control knob WR of the frequency converter is connected to the input terminals XAT1, XAT3 and XAT4 of the frequency converter 1. The frequency converter start contact XD244 is connected in series with the normally open contact of the intermediate relay KA1, the normally closed contact of the overload relay KH2 and the frequency converter start contact XDI1. The frequency converter constant speed contact XD242 is connected in series with the normally closed contact of the frequency converter start-allowing relay KA4, the normally open contact of the intermediate relay KA1 and the frequency converter constant speed contact XDI5. The frequency converter constant speed contact XD242 of the frequency converter 1 is connected to the frequency converter start contact XD244.

[0048] The method includes the following steps:

[0049] Step 1: Inverter 1 is powered on and performs a self-test. Specifically, check that the power frequency circuit breaker QF2 on the power bypass 2 is in the open state. Turn the inverter / power frequency conversion switch SA1 to the inverter position. The inverter circuit breaker QF1 will close. If the inverter has no fault, the inverter's self-test status is normal, and the inverter's operation start contact XR012 and inverter's operation start contact XR013 will automatically conduct. If inverter 1 has a fault, the inverter's operation start contact XR012 and inverter's operation start contact XR013 will not conduct.

[0050] Step 2: If the frequency converter's self-test status is normal, perform a light-load start. After starting, frequency converter 1 will run at the preset frequency, and the coal slurry conveyor belt will run at the set speed. Specifically, contact the coal slurry control room to close the coal slurry conveyor belt power switch, close the transformer upstream switch QF, adjust the heavy-load / light-load transfer switch SA to the light-load position, press the frequency converter closing button SF, the coil of contactor KM1 is energized, contactor KM1 is energized, the coil of intermediate relay KA1 is energized, the normally open contact of intermediate relay KA1 connected in parallel across the two ends of the frequency converter closing button SF closes, forming a self-holding circuit, the normally open contact of intermediate relay KA1 connected in series with the normally closed contact of overload relay KH2 closes, the frequency converter start contact XD244 and frequency converter start contact XDI1 are connected, and frequency converter 1 receives the start signal. At the same time, the normally open contact of the intermediate relay KA1, which is connected in series with the normally closed contact of the inverter start relay KA4, closes, and the inverter constant speed contact XD242 and the inverter constant speed contact XDI5 are turned on. After the inverter 1 starts, it will run at the preset frequency, and the coal slurry belt conveyor will run at the set speed.

[0051] Step 3: When the coal slurry conveyor belt stops under abnormal conditions, resulting in residual coal slurry on the belt, switch inverter 1 to heavy-load start. Specifically, first adjust the inverter speed control knob WR to a relatively low speed state, and adjust the heavy-load / light-load switch SA to the heavy-load position. The coil of the inverter start relay KA4 is energized, and the normally open contact of the inverter start relay KA4 closes. The coil of the intermediate relay KA1 is energized, and the normally open contact of the intermediate relay KA1, which is connected in series with the normally closed contact of the overload relay KH2, closes. The inverter start contacts XD244 and XDI1 are connected, and inverter 1 receives a start signal. At the same time, the normally closed contact of the inverter start relay KA4 opens, and the circuit of the inverter constant speed contacts XD242 and XDI5 is interrupted. At this time, the constant speed state of inverter 1 will not be triggered, and inverter 1 will run according to the command of the inverter speed control knob WR.

[0052] Working Principle: The variable frequency drive (VFD) belt heavy-load starting system of this invention has two starting modes: light-load start and heavy-load start. When the VFD 1 is in a normal self-test state and has no faults, the VFD running start contact XR012 and VFD running start contact XR013 automatically conduct, contacting the coal slurry control room to close the coal slurry belt power switch, closing the transformer upstream switch QF, adjusting the heavy-load / light-load transfer switch SA to the light-load position, pressing the VFD closing button SF, energizing the coil of intermediate relay KA1, closing the normally open contact of intermediate relay KA1 connected in parallel across the VFD closing button SF, forming a self-holding circuit, closing the normally open contact of intermediate relay KA1 connected in series with the normally closed contact of overload relay KH2, and conducting the VFD starting contact XD244 and VFD starting contact XDI1, thus receiving the start signal for VFD 1. At the same time, the normally open contact of the intermediate relay KA1, which is connected in series with the normally closed contact of the inverter start relay KA4, closes, and the inverter constant speed contact XD242 and the inverter constant speed contact XDI5 are turned on. After the inverter 1 starts, it will run at the preset frequency, and the coal slurry belt conveyor will run at the set speed.

[0053] When a coal sludge conveyor belt stops under abnormal conditions, resulting in residual coal sludge on the belt, a heavy-load start-up of the frequency converter is required. First, adjust the frequency converter speed control knob WR to a relatively low speed position. Then, set the heavy-load / light-load switch SA to the heavy-load position. This energizes the coil of the frequency converter's start relay KA4, closing its normally open contact. This energizes the coil of the intermediate relay KA1, closing its normally open contact, which is connected in series with the normally closed contact of the overload relay KH2. This connects the frequency converter's start contacts XD244 and XDI1, and frequency converter 1 receives a start signal. Simultaneously, the normally closed contact of the start relay KA4 opens, interrupting the circuit between the frequency converter's constant-speed contacts XD242 and XDI5. At this point, the constant-speed state of frequency converter 1 will not be triggered, and frequency converter 1 will operate according to the commands of the frequency converter speed control knob WR. At this time, the coal slurry conveyor belt will run at low speed, but the increased starting torque will not cause a large impact on the starting of the belt motor.

[0054] A variable frequency drive (VFD) is used to control the starting belt motor. The VFD optimizes the motor's starting time, voltage, frequency, and other parameters, improving its starting characteristics. The VFD's "vector control" function enables a low-speed, high-torque starting method, reducing impact on mechanical components and the motor itself. Local control of the belt motor is achieved by modifying the local control cabinet, allowing for local speed adjustment. Optimized VFD parameters perfectly match the conveyor belt's stall protection features. An independent cooling fan ensures sufficient cooling for the belt motor at low speeds, preventing overheating.

[0055] After a belt conveyor is shut down under heavy load, operators need to manually remove the coal sludge from the belt. Once the belt is restarted and running normally, the coal sludge is then removed back onto the belt. This process is not only labor-intensive and inefficient, but also poses a safety risk due to workers operating near the belt. In emergency situations requiring heavy-load restarts, it can also cause damage to the belt motor. Each equipment repair costs tens of thousands of yuan, and the boiler cannot be guaranteed to continue co-firing coal sludge during equipment repairs, making it extremely uneconomical.

[0056] After the modification, the belt conveyor gained heavy-load starting capability, reducing the labor intensity of coal slurry system operators (eliminating the need to remove coal slurry accumulated on the belt after shutdown), and greatly improving production efficiency and safety. The use of a frequency converter-controlled belt conveyor heavy-load starting system significantly reduces the failure rate of the belt motor. The modification improves the reliability of the conveying system by using a frequency converter, reducing mechanical system losses, minimizing maintenance, and resulting in significant energy savings. Promoting the application of frequency converter-controlled drive technology is of great significance in implementing national energy conservation and emission reduction policies. This invention, apart from adding a frequency converter, requires virtually no additional cost or workload; the construction method only requires adding a frequency converter cabinet, making operation simple.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for heavy-load starting of a belt conveyor controlled by frequency converter, characterized in that, The method is applied to a frequency converter-controlled belt conveyor heavy-load starting system. The frequency converter-controlled belt conveyor heavy-load starting system includes: a frequency converter (1), a belt motor (3), a relay control unit, and a frequency converter speed control knob WR. The frequency converter (1) is electrically connected to the belt motor (3), and the power supply outputs a second power supply through a transformer. The relay control unit includes: an intermediate relay KA1, a frequency converter start-up relay KA4, a heavy-load / light-load changeover switch SA, and a frequency converter closing button SF. The coil of the intermediate relay KA1, the frequency converter running start contact XR012, the frequency converter running start contact XR013, the frequency converter closing button SF, and the heavy-load / light-load changeover switch SA are connected in series to the second power supply. The coil of the frequency converter start-up relay KA4 is connected in series with the heavy-load / light-load changeover switch SA and then connected to the second power supply. The normally open contact of the frequency converter start-up relay KA4 is connected in series with the heavy-load / light-load changeover switch SA. One end is connected to the frequency converter closing button SF. The other end of the normally open contact of the frequency converter start relay KA4 is connected to the coil of the frequency converter start relay KA4. The two ends of the normally open contact of the intermediate relay KA1 are connected in parallel to the two ends of the frequency converter closing button SF through the line. The normally open contact of the intermediate relay KA1 is connected in series with the normally closed contact of the overload relay KH2 and then connected between the frequency converter start contact XD244 and the frequency converter start contact XDI1. The normally closed contact of the frequency converter start relay KA4 is connected in series with the normally open contact of the intermediate relay KA1 and then connected between the frequency converter constant speed contact XD242 and the frequency converter constant speed contact XDI5. The frequency converter constant speed contact XD242 of the frequency converter (1) is connected to the frequency converter start contact XD244. The frequency converter speed control knob WR is connected to the three input terminals XAI1, XAI3, and XAI4 of the frequency converter (1). The method includes the following steps: S1. The frequency converter (1) is powered on and performs a self-test; S2. When the inverter (1) is in normal self-test status, start it under light load. Adjust the heavy load / light load switch SA to the light load position and press the inverter closing button SF. The coil of contactor KM1 is energized and contactor KM1 is energized. The coil of intermediate relay KA1 is energized and the normally open contact of intermediate relay KA1 connected in parallel to the two ends of the inverter closing button SF is closed, forming a self-holding circuit. The normally open contact of intermediate relay KA1 connected in series with the normally closed contact of overload relay KH2 is closed. The inverter start contact XD244 and inverter start contact XDI1 are connected. The inverter (1) receives the start signal. The normally open contact of intermediate relay KA1 connected in series with the normally closed contact of inverter start relay KA4 is closed. The inverter constant speed contact XD242 and inverter constant speed contact XDI5 are connected. After the inverter (1) starts, it will run at the preset frequency and the belt conveyor will run at the set speed. S3. When the belt conveyor stops under abnormal conditions, switch the inverter (1) to heavy load start. First, adjust the inverter speed control knob WR to low speed, and adjust the heavy load / light load switch SA to heavy load position. The coil of the inverter start relay KA4 is energized, the normally open contact of the inverter start relay KA4 is closed, the coil of the intermediate relay KA1 is energized, and the normally open contact of the intermediate relay KA1, which is connected in series with the normally closed contact of the overload relay KH2, is closed, and the inverter starts. When contact XD244 and inverter start contact XDI1 are connected, inverter (1) receives a start signal. The normally closed contact of inverter start relay KA4 is opened, and the circuit of inverter constant speed contact XD242 and inverter constant speed contact XDI5 is interrupted. At this time, the constant speed state of inverter (1) will not be triggered. Inverter (1) will run according to the command of inverter speed control knob WR. The belt conveyor will run at low speed, but the starting torque will increase and will not cause a large impact on the start of belt motor (3).

2. The method for heavy-load starting of a belt conveyor with frequency conversion control according to claim 1, characterized in that, The frequency converter-controlled belt conveyor heavy-load starting system also includes: frequency converter circuit breaker QF1, power frequency circuit breaker QF2, and power bypass (2). The frequency converter circuit breaker QF1 is located on the line between the frequency converter (1) and the power supply. The power bypass (2) is connected in parallel across the two ends of the frequency converter (1). The power frequency circuit breaker QF2 is located on the power bypass (2).

3. The method for heavy-load starting of a belt conveyor with frequency conversion control according to claim 2, characterized in that, The frequency converter-controlled belt conveyor heavy-load starting system also includes: contactor KM1, which is located on the line between the frequency converter (1) and the belt motor (3).

4. The method for heavy-load starting of a belt conveyor with frequency conversion control according to claim 3, characterized in that, The frequency converter-controlled belt conveyor heavy-load starting system also includes: a cooling fan (4), and a power frequency circuit breaker QF3, a contactor KM2, and an overload relay KH2 on the line between the cooling fan (4) and the power supply.

5. The method for heavy-load starting of a belt conveyor with frequency conversion control according to claim 2, characterized in that, Step S1 also includes: checking that the power frequency circuit breaker QF2 on the power bypass (2) is in the open state, the frequency converter circuit breaker QF1 is closed, the frequency converter (1) is powered on and performs a self-test. If the frequency converter (1) performs a normal self-test, the frequency converter operation start contact XR012 and the frequency converter operation start contact XR013 will be automatically connected. If the frequency converter (1) has a fault, the frequency converter operation start contact XR012 and the frequency converter operation start contact XR013 will not be connected.

6. The method for heavy-load starting of a belt conveyor with frequency conversion control according to claim 1, characterized in that, The frequency converter controlled belt conveyor heavy-load starting system also includes: frequency converter fault relay KA2 and frequency converter running relay KA3. The coil of frequency converter fault relay KA2 is connected in series with frequency converter fault contacts XR032 and XR033 and then connected to the second power supply. The normally open contact of frequency converter fault relay KA2 is connected in series with frequency converter fault indicator YG and then connected to the second power supply. The coil of frequency converter running relay KA3 is connected in series with frequency converter running contacts XR022 and XR023 and then connected to the second power supply. The normally closed contact of frequency converter running relay KA3 is connected in series with frequency converter stop indicator GG and then connected to the second power supply. The normally open contact of frequency converter running relay KA3 is connected in series with frequency converter running indicator RG and then connected to the second power supply.

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