With the rapid development of the national economy, the supply of electricity resources in China has become increasingly tight. The electricity supply department has formulated different time period electricity pricing policies to regulate electricity supply. The underground drainage in mines is mainly done by high-power water pumps, which account for about 20% of the electricity consumption in mining production. According to the peak and valley electricity prices in various regions, the peak electricity price is about 4.25 times that of the valley electricity price. If an intelligent control system is used for off peak drainage, it can save about 40% of the electricity cost of underground drainage projects.

The automatic control system can automatically control the start and stop of the water pump based on the level and time period of the water tank, and can also monitor various operating parameters of the water pump in real time, reducing the failure rate of the water pump and lowering the operating costs of the mine.

The current situation of automatic control system for mine drainage in China

At present, many underground main drainage systems in mines still use manual control, and the start stop and switching of water pumps need to be completed manually, relying entirely on the sense of responsibility of workers and unable to predict the growth rate of water level in the water tank. A very small number of large mines have installed partial remote control systems, but they only achieve remote start stop of water pumps, which cannot automatically start and stop water pumps during peak and off periods of electricity consumption based on water level and other parameters. This will seriously affect the level of automation management and economic benefits of mines, and also easily cause safety hazards due to human factors.

Structural Design of System 2

The pump room automation system control has three working modes: automatic, semi-automatic, and maintenance. During automatic operation, the PLC detects water level, pressure, and related signals to automatically complete the operation of each water pump without the need for manual intervention; In semi-automatic working mode, the staff remotely or locally selects one or several pump units to be put into operation, and the PLC automatically completes the start stop and monitoring work of the selected pump units; The maintenance method is used for troubleshooting and on-site testing. When a certain water pump and its ancillary equipment fail, the water pump will automatically shut down without affecting the normal operation of other water pumps.

The entire control system includes PLC control part, on-site input and output equipment, transmission equipment, etc.

The PLC control part mainly consists of programmable controllers, signal transmitters, intermediate relays, etc. It mainly completes the reception, transformation, and amplification of signals, and sends out various control signals through PLC calculation and judgment to monitor the operating conditions of the water pump and achieve unmanned operation of the water pump room.

The on-site input and output equipment consists of a field control box, sensors, and solenoid valves. The on-site control box consists of buttons, indicator lights, etc. Sensors include ultrasonic water level gauges, flow sensors, electrical sensors, temperature sensors, etc. The parameters detected mainly include water level in the water tank, water pump shaft temperature, motor temperature, and equipment working status. All types of solenoid valves and electric ball valves are manually and automatically integrated, enabling manual or automatic control of the opening and closing of related pipelines.

The transmission equipment includes Ethernet control modules, network switches, servers, and transmission fibers. The PLC controller is connected to the industrial Ethernet through the Ethernet module to achieve the sharing of monitoring information between the automatic control subsystem of the water pump and the "six major systems" for safety avoidance in the entire mine.

Signal acquisition of 3 systems

Water level signal acquisition in the water tank: The PLC needs to control the operation of the water pump based on changes in water level. To ensure accurate acquisition of water level signals in the pool, the system is equipped with two sets of ultrasonic water level sensors and transmits data to the PLC through RS485 signals.

Vacuum status signal detection: To ensure accurate detection, in addition to installing a vacuum degree sensor on the suction port of each water pump, a flow switch should also be installed at the outlet of the vacuum pump to confirm the vacuum degree by detecting whether there is water flow at the outlet of the vacuum pump.

Collection of motor power parameters: By collecting the three-phase voltage and current signals of each water pump motor, the operating status of the system can be accurately determined. By accurately detecting the working status of the motor, timely or even early warning of faults can be given, which facilitates maintenance personnel to detect faults in advance and take preventive measures.

Collection of operating status parameters: System parameters include the cumulative and instantaneous flow rates of two main drainage pipes, the operating time of each pump, and the status of various valves. These parameters are not only necessary basis for starting and stopping the water pump, but also important basis for statistical analysis and querying of the system.

Collection of fault state parameters: The precursor of mechanical failure in a water pump is often manifested as an abnormal increase in the temperature of the pump body and an increase in the amplitude of the transverse vibration of the front axle. In order to avoid major production safety accidents caused by major accidents during the operation of the water pump and to avoid huge economic losses, the system monitors the temperature of the motor stator, the temperature and vibration of the front axle of the water pump, and the pressure at the water outlet of the water pump pipe.

Design of Control Software for System 4

The operating software for the main monitoring system is Windows 7 Professional, the programming software is Siemens STEP7 V5.3SP9, the configuration software is Siemens WINCC, and the database software is Microsoft SQLserver 2012 version.

The system software strategy mainly focuses on peak shaving, valley filling, and uniform wear and tear. The system uses the water level in the water tank as the basic condition for starting and stopping the water pump, and then implements the start and stop of the water pump according to the predetermined software strategy, provided that this condition is met. Set four water level limits: minimum water level L1, low limit water level L2, alarm water level L3, and over limit water level L4. In the absence of any water pump start-up, the system first detects the water level in the water tank. When the water level reaches L3, it first monitors the peak and valley times of the power grid. If it is in the electricity valley or flat section, the lowest frequency water pump is immediately started. If the selected water pump is in maintenance status, the second lowest frequency water pump is started; If it is in the peak power consumption period, the startup will be temporarily suspended. When the water level continues to rise beyond the limit, regardless of the peak and valley times of the power grid, the water pump must be immediately started. If the water level continues to rise, turn on the second and third pumps in sequence. When multiple water pumps are running and the water level drops to (L2+L3)/2, the pumps can be stopped in sequence according to the principle of high or low usage frequency, until the water level drops to the lower limit water level and the last pump is stopped.

5 Conclusion

The design of an automatic control system for the underground mine water pump room using PLC and power peak valley control principles not only enables unmanned operation of the entire water pump room, saving labor costs and improving the intrinsic safety of the mine, but also achieves economical and efficient drainage, with very ideal application effects.

References

[1] State Administration of Work Safety. Safety Regulations for Metal and Non Metal Mines GB16423-2006 [Z]. 2006

[2] Liu Changsheng, Xuan Zongqiang. Concise Manual and Application Circuit of Sensors [M]. Xi'an: Xi'an Electronic University Press, 2005

[3] Sun Zhenqiang. Principles and Applications of Programmable Logic Controllers [M]. Beijing: Tsinghua University Press, 2012

Author's affiliation

Shandong Zhengyuan Yeda Technology Development Co., Ltd. Jinan City, Shandong Province 250014