1. Introduction
As shown in Figure 1, the Shazhangtu Mine is a mine under construction under the Shandong Energy Xinwen Mining Bureau, with a designed production capacity of 5 million tons per year. The auxiliary vertical shaft is responsible for the lifting and lowering of personnel, equipment, and large components (hydraulic supports), the lowering of long materials, cement, and sand, and the hoisting of gangue. The shaft entrance rail surface elevation is +1248m, the main shaft bottom rail surface elevation is +550m, and the hoisting height is 698m. It adopts a non-standard design with 1.5t mine cars in a double-layer, four-car cage, one wide and one narrow design.
Figure 1 Shazhangtu Auxiliary Well
The auxiliary shaft hoisting system of this coal mine is equipped with a ground-mounted multi-rope friction hoist, with a drum diameter of 5 meters, a DC motor power of 2000 kW, and a maximum hoisting speed of 9.95 m/s. The electrical control system of the hoisting equipment is a low-speed DC motor drive system powered by a thyristor converter. The electrical control system adopts dual PLC control, with key components monitoring and backing up each other.
2. Basic requirements of the electrical control system
(1) All electrical equipment must be able to operate safely and reliably in the mining industrial environment.
(2) The static and dynamic performance indicators of the electrical control device meet the requirements of the hoist's four-quadrant operation and meet certain overload capacity and safety factor.
(3) Electronic cards for adjustment, monitoring, detection, and control must be standard plug-ins for easy replacement.
(4) The control, regulation, monitoring and safety circuit systems should have high reliability. The safety circuit and other key circuits adopt a redundant structure design.
(5) A variable frequency speed control device is installed in the main motor cooling fan circuit. The cooling air volume can be automatically or manually adjusted on site according to the heating of the main motor, ambient temperature, seasonal changes, etc., to avoid the impact of mechanical air adjustment on the fan equipment, improve the service life of the fan equipment, and save energy.
(6) The electrical control device is equipped with cabinet lighting, its transmission device is equipped with a cooling fan, and ventilation monitoring is provided.
(7) The well shaft and downhole electrical equipment shall meet the relevant waterproof or explosion-proof requirements, and the protection level shall not be lower than IP65.
(8) The electrical control system adopts full digital control, and the key equipment such as the transmission regulator and PLC are original imported products from ABB and Siemens, and can be easily connected to the mine management network.
3. Main circuit structure of the electronic control system
As shown in Figure 2.
Figure 2 Main circuit of the electrical control system
4. Specific Implementation of the Electronic Control System
The auxiliary shaft hoisting room requires dual 10kV power supplies, using YJV22-8.7/103×70mm² cross-linked polyethylene insulated power cables, sourced from different busbar sections on the 10kV side of the 35/10kV substation. The voltage is 10kV ±5%, 50Hz, and the neutral point is ungrounded. The auxiliary shaft hoisting room also requires dual 380V power supplies. One circuit is sourced from the auxiliary transformer of this substation, and the other uses YJV22-0.6/13×35+1×16mm² cross-linked polyethylene insulated power cables, sourced from the 380V side busbar section of the 10/0.4kV substation at the shaft entrance. The voltage is 380V, 50Hz, and the neutral point is grounded, with an allowable fluctuation range of ±7% (short-term voltage fluctuations of +10% to -15%). The underground power supply voltage is ~660V/127V, 50Hz, and is a neutral point ungrounded system. The voltage is drawn from the corresponding power supply network at the bottom of the well, and the allowable voltage fluctuation range is ±7% (with short-term voltage fluctuations of +10% and -15%).
Figure 3 Electrical Control Room
(1) High-voltage switchgear
The high-voltage switchgear is the KYN28A-12 type metal-armored withdrawable high-voltage vacuum switchgear. The power supply system is a single busbar connection, used for 10kV high-voltage power distribution and protection. It includes: incoming line cabinets (2 units, electrically interlocked with each other); stator circuit rectifier transformer cabinets (2 units); voltage transformer cabinets (measuring); and auxiliary transformer cabinets.
The switchgear can operate safely under maximum short-circuit fault conditions and can withstand the resulting electrical and mechanical stresses. Each device inside the cabinet can operate continuously, with an IP41 protection rating and "five protections" (preventing the pushing and pulling of removable parts under load, preventing accidental opening/closing of circuit breakers, preventing the closing of grounding switches while energized, preventing the grounding switch from being energized while in the grounding position, and preventing accidental entry into energized compartments). The cabinet also has an anti-condensation space heater.
High-voltage switchgear has protection functions such as overcurrent, undervoltage, short circuit and grounding insulation detection, as well as measuring instruments and transmitters for active power, reactive power, current and voltage, and can input the above-mentioned switching quantities and analog voltage and current signals to the monitoring system.
The high-voltage switchgear is equipped with an intelligent control device for switchgear status. This device has functions such as circuit simulation diagram, live display, automatic heating and dehumidification controller, circuit breaker opening and closing status indication, grounding switch indication and spring energy storage status indication. It can also perform remote/local operation switching and circuit breaker opening and closing control operations on its operation panel. It is also equipped with energy storage power switch, heating power switch and lighting.
(2) Main rectifier transformer
The rectifier transformer is an epoxy resin cast dry-type transformer that supplies power to the rectifier cabinet. It meets the phase requirement of 12 pulses, has H-class insulation, IP00 protection level, and connection group: D/D-6, DY-5.
The rectifier transformer can withstand changes in cyclic load and the electrodynamic forces generated by a short circuit on the secondary side of the transformer. Temperature sensors are embedded in the transformer windings, and a digital temperature detector monitors and displays the temperature at each measuring point. It provides audible and visual alarms for the upper temperature limit and participates in the interlocking of the hoist control system.
(3) Fully digital regulating and rectifying cabinet
The regulating and rectifying cabinet should be able to adapt to various working conditions of the hoist, and according to the predetermined speed diagram and hoisting requirements, be able to achieve accurate and smooth start-up, operation, deceleration, braking, and stopping within four quadrants. Throughout the entire cycle, it should be able to effectively limit or eliminate the elastic vibration of the hoisting wire rope, ensuring accurate stopping accuracy with an error not exceeding ±2cm.
(4) Excitation transformer
The excitation transformer is an epoxy resin cast dry-type transformer that supplies power to the excitation rectifier cabinet. It has H-class insulation and IP00 protection rating.
(5) DC fast switch
The DS series DC fast-acting switch is used for overcurrent protection of DC circuits to protect motors and thyristors and prevent peak currents. Its mechanical response time di/dt ≤ 2kA/ms.
(6) Reactor
It employs an iron-core reactor, which is unsaturated at twice the rated current. It is used in the armature circuit to smooth out voltage fluctuations.
(7) Power transformer (Δ/Y)
It adopts an H-class dry-type transformer, with a pre-embedded temperature measuring resistor to detect the temperature of the iron core, and is equipped with a temperature control instrument. The alarm temperature value is 85℃, and the tripping temperature is 115℃; the rated impedance is 4%; and the cooling method is air self-cooling.
(8) Low-voltage auxiliary power supply cabinet
It adopts a dual-circuit power supply method to provide 380V/220V three-phase power to auxiliary equipment of the electrical control system, auxiliary equipment of the hoist (hydraulic station, lubrication station), and auxiliary facilities of the machine room (including lighting 5kW, air conditioning 4kW, crane, cooling fan, etc.). Protection rating IP44.
The low-voltage auxiliary power supply cabinet is equipped with remote I/O, which transmits the status of each circuit to the main and auxiliary PLCs via bus for processing and interlocking, effectively reducing the number of cables. The panel of the low-voltage auxiliary power supply cabinet is equipped with operating and fault indicators for each circuit. The low-voltage auxiliary power supply cabinet is also equipped with a UPS to provide uninterrupted power to some critical control equipment and PLCs, ensuring reliable safe braking and data retention of the hoist in the event of a low-voltage power failure.
(9) Main control PLC cabinet
The main control PLC cabinet employs three-line multi-layer protection for key signals of the hoist operation (such as speed, container position, safety protection, deceleration, overwind, speed limit, hydraulic brake feedback, etc.), with each signal monitoring the others.
(10) Supervisory control computer
The supervisory control computer and the control PLC communicate via cable. All alarm and operation signals are fed into the hoisting control system controller for processing. These signals can be displayed on a color monitor and printed at any time. During actual operation, the system monitors the dynamic and static parameters of the hoist and equipment that may endanger its normal operation. It features a fully Chinese-language interface and graphical display, diagnoses and saves information on minor and major faults in the hoisting system, and provides comprehensive backup protection. Accident records are kept for at least 10 days. The system can display and print the location, time, cause, and relevant data parameters before the fault occurred. It displays and records real-time values of depth and speed, hoisting type, and signal status, functioning as a "black box" to provide strong support for maintenance personnel to quickly locate and troubleshoot faults.
5. Debugging Results
The PLC monitoring diagrams for heavy-load lifting and heavy-load decentralization are as follows:
(1) Heavy load lifting curve
(1) Heavy load reduction curve
6. Advantages of the electronic control system
(1) An ABB original DCS800 series fully digital speed control device is adopted. The transmission system scheme is an armature reversible 12-pulse parallel connection, constant magnetic field control, DC output voltage matching the main motor voltage, rated output current meeting the speed diagram and force diagram requirements of the hoist under various operating conditions, dual excitation, full load and full speed configuration. The AC side incoming line voltage is matched with the secondary side voltage of the rectifier transformer. Its static and dynamic performance indicators fully meet the requirements of the hoist's four-quadrant operation, and meet the overload capacity and safety factor required by the hoisting process. Static accuracy ≤0.1%, dynamic tracking error less than 5%, speed regulation range greater than 100:1, speed indication accuracy 0.1m/s.
The regulating system is used for closed-loop regulation of the transmission device and has the following functions:
① Generate various required reference signals and measurement signals;
② It can control the electromechanical resonance that may be generated in the system and the coupled oscillations generated on both sides of the converter;
③ It has comprehensive electronic protection measures;
④ Control of the setpoint for manual, semi-automatic, and manual maintenance operation speeds;
⑤ Start-up anti-shock control, lifting wire rope anti-vibration function ("S" type speed curve given, acceleration change rate da/dt=0.4m/s3), adjustable slope acceleration and deceleration setpoint setting;
⑥ Fully digital dual closed-loop control of speed and current;
⑦ The pre-set starting torque is reliably locked with the oil pressure of the hydraulic braking system to prevent the container from tipping over;
⑧ Grounding insulation testing and overvoltage protection.
(2) The main control PLC operating system uses two Siemens S7-400 series programmable controllers, with hot standby redundancy. One PLC operating system can complete all control requirements of various operating modes of the hoist, such as manual, semi-automatic, maintenance and fault start-up, and complete the control functions of various equipment of the hoist, various operating process requirements and signal interlock requirements, various safety protections of the hoist and handling of special working conditions, etc. The other PLC completes real-time monitoring of the control PLC. When the control PLC fails, it can automatically switch to the other PLC. Either PLC can independently complete the control of the hoist. Both PLCs use dual field control bus communication, and the communication is hot standby redundancy.
The PLC can also perform functions such as setting the travel position of the hoist, performing the functions of a digital monitor and corresponding protection, monitoring and protecting the safety circuit, realizing network communication, monitoring important signals such as speed, position, and shaft switches, and providing redundant control for depth displays, various operating elements, shaft switches, etc.; the PLC has no less than 20% of spare DI/DO and AI/AO.
Two or more safety circuits (software and hardware redundancy): Field safety accident signals are isolated by relays before entering the PLC. Multiple safety protections are formed by combining the PLC's internal safety circuits and external relay safety circuits. Multiple protection circuits should also be set up within the PLC to achieve comprehensive judgment of various faults.
A communication interface is reserved for use with the wellhead control equipment.
(3) Gate control system: The working gate is controlled by a PLC and can be adjusted automatically or manually. In manual mode, the brake oil pressure is adjusted by the gate control handle; in automatic mode, the transmission torque is coordinated, and the command provides control signals for releasing the brake, pre-applying the brake pads, and applying the brake. The gate control system has an oil pressure feedback signal, which participates in the command control.
This electrical control system features networked control, modular components, and a combined cabinet structure to minimize external wiring. It represents a significant reform and innovation compared to older hoist electrical control systems, achieving near-automatic control. Furthermore, the system incorporates both hardware and software safety protections, greatly enhancing its safety factor.
7. Conclusion
The auxiliary shaft hoist control system adopts fully digital control, which can be easily connected to the mine management network and has remote diagnostic functions. Technical personnel can check the working status of the equipment on site through the computer network without being on site, help solve problems quickly, provide corresponding solutions, shorten maintenance time, ensure the safe operation of the hoist, and improve the economic benefits of mine production.
