Application of frequency converter in underground belt conveyor

The belt conveyor transmission system is an important part of the underground coal mine transportation system, and is also the main component of coal mining enterprises' energy consumption. In recent years, with the country's increased efforts in energy conservation and emission reduction, the maturity of inverter technology and automatic control technology, inverters are widely used in belt conveyor system energy conservation and emission reduction and technical improvement.

1. Introduction

Most of the existing belt conveyors in coal mines in China generally use industrial frequency dragging, and rarely use inverter drive. Due to the long-term industrial frequency operation of the motor and the efficiency of the hydraulic coupler, the operation of the belt conveyor is very uneconomical; at the same time, since the motor cannot use soft start and soft stop, it produces severe impact on the machine and accelerates the wear of the machine; in addition, the wear and maintenance of the belt and hydraulic coupler will bring a large amount of expenses to the enterprise. The above problems can be improved by the application of INVT GD3000 inverter.

2. Application site equipment and operating conditions analysis

2.1 Project Introduction

Baodian Coal Mine belongs to Yanzhou Coal Mining Group Co., Ltd. It is a large-scale fully mechanized mine with an annual output of 3 million tons designed and constructed by my country. The newly built 1701 working face chute belt of the mine is a down-conveying belt driven by an asynchronous motor, equipped with INVT GD3000 series four-quadrant inverter, with a total belt length of 2.4km.

2.2 Field equipment parameters

2.3 On-site working conditions

The site includes a control box, and the controlled equipment is 4 BPJ-630/1140 mining explosion-proof and intrinsically safe inverters (using INVT GD3000-11-630G-12 inverter movement), which are controlled by the belt protection box. It is applied to the chute belt of the 1701 working face of Baodian Coal Mine to achieve synchronous operation and centralized management of 4 inverters and monitoring of the belt control system.

The control box uses Siemens S7-300 series PLC to communicate with four inverters via DP. It can monitor the inverter status in real time and change the parameter settings of the inverter master and slave through the control box.

The four four-quadrant inverters are placed in parallel lanes near the machine head, and the LCL reactor cabinet and the transfer transformer are placed in a vertical lane, about 30 meters apart (as shown in Figure 3). The 1# and 2# inverters drive the coaxially connected rollers (both can be used as hosts), and the 3# and 4# inverters drive two rollers respectively as slaves. The 1# to 4# rollers are driven by belts. The host receives the start and stop control signal from the Huaning control box and gives the slave frequency setting through CAN communication. In addition, the 1# and 2# inverters share the 1# transfer transformer as the input power supply, and the 3# and 4# inverters share the 2# transfer transformer as the input power supply.

Figure Layout of the on-site LCL reactor cabinet, four-quadrant inverter and belt conveyor head

2.4 On-site electrical parameters

Table 1. Environmental parameters

Table 2. Motor parameters

Table 3. Inverter parameters

3. Inverter Configuration Scheme

3.1 GD3000 Series Medium Voltage Inverter Features

(1) Novel technology

Goodrive3000 series inverter is a high-performance general-purpose vector inverter, which adopts three-level hardware topology, is compatible with two-quadrant and four-quadrant, and can be used to control AC asynchronous induction motors and permanent magnet synchronous motors, and can meet the working modes of different motors. The product adopts the current internationally leading vector control technology, with more optimized functions, more flexible applications and more stable performance.

(2) The output waveform is closer to a sine wave

The motor runs more smoothly, reducing mechanical vibration caused by non-sine output waveform and extending the life of the motor. The output harmonics are significantly reduced, greatly suppressing the conduction and radiation interference caused by the inverter, and having excellent EMC characteristics.

(3) The output voltage change rate (du/dt) is low, reducing damage to motor insulation

Reduce the impact voltage applied to the electric shaft, effectively protect the motor insulation; alleviate the electrical corrosion of the motor bearings caused by the shaft current, and extend the life of the motor; reduce the system leakage current, and the system runs safely and reliably.

3.2 DP control scheme

Configure the EC-TX103 communication card to connect the inverter to the PROFIBUS network. On the PROFIBUS network, the inverter is a slave device. The following functions can be completed through the EC-TX103 communication card:

* Issue control commands (start, stop, fault) to the inverter.

* Send speed or torque reference signal to the inverter.

* Read status and actual values ​​from the inverter.

* Modify the inverter parameter value.

PROFIBUS-DP bus allows fast data exchange between the master station and the inverter device. PROFIBUS transmits messages periodically, and the messages are transmitted in 16 words. The PZD area of ​​the communication message is designed for controlling and detecting the inverter.

For example, the PZD address of inverter No. 1 in the PLC is 200~211, and inverter PZD2 is set to output current. The inverter current can be read by reading PIW202.

3.3 Inverter selection

Combined with the actual situation on site, our company selected the following:

4. Specific use effect on customer site

4.1 On-site use effect

* The four inverters in Baodian Coal Mine use our GD3000 series products. They have been debugged and are running safely and reliably.

* From the test results, the use of variable frequency speed regulation has completely realized the soft start and soft stop operation mode of the belt conveyor, greatly improving the power factor and system efficiency of the system;

* The system can automatically adjust the output frequency and output torque according to the load changes, changing the previous mode of constant speed operation of the motor at industrial frequency, thus saving electric energy to a great extent;

* Compared with the original relay protection, it has more protection functions and is more sensitive, greatly enhancing the protection of the motor;

* Perfectly solves the problem of synchronous output of multiple motors;

* The withdrawal of hydraulic coupling saves more maintenance and repair costs of equipment.

* Since it was put into operation, the system has high reliability, simple operation, and can be connected with the mine automation system to improve production efficiency.

4.2 On-site photos

On-site measured equipment operation waveform

Figure 1. On-site monitoring (coal belt for production shift) The current of 4 inverters is relatively stable.

V. Conclusion

In summary, the GD3000 series medium voltage inverter drives asynchronous motors to fully meet the load control requirements of the coal mine underground belt conveyor system. In the belt conveyor application, it shows good speed regulation performance, high reliability, high starting torque, good power balance, extremely low maintenance and maintenance costs, etc., which improves the automation level of the coal mine underground transportation system. At the same time, in the environment where the country vigorously advocates energy conservation and emission reduction, vigorously promoting the application of inverters in belt conveyors has positive social and practical significance.