Abstract: This paper briefly introduces the current status of the original electrical control system of the main shaft hoist in Wangcun Coal Mine, proposes and implements a digital and networked electrical control system upgrade plan. Through in-depth analysis and performance comparison of the old and new systems, the safety, reliability, and efficiency of the new system are demonstrated. Keywords: coal mine hoist, system transformation [b][align=center]Transformation of Electric Control System of Wangcun Coal Mine's Shaft Hoist Zhang Yu-he, LI Wei[/align][/b] Abstract: This paper briefly introduces the situation of the original electric control system of Wangcun Coal Mine hoist. It puts forward the transformation project of the digital network electric control system and implements it. It analyzes and compares both the new and old systems, which shows the security, reliability, and efficiency of the new system. Keywords: coal mine hoist, system transformation 1 Overview The main shaft hoist of Chenghe Mining Co., Ltd. is a JKMD-3.5×4 type low-speed direct-drive floor-mounted multi-rope friction wheel hoist designed by Xi'an Coal Mine Design Institute, manufactured by Shanghai Metallurgical Mining Machinery Plant, and equipped with electric control by Shanghai Electric Complete Set Plant. The hoist's electric control part consists of a DC motor, synchronous machine, DC generator set, lubricating oil cooling system, forced ventilation system, DC electric control and AC auxiliary unit, etc. The system adopts a generator and motor DC drive system, i.e., FD system. As the service life and raw coal production continue to increase, the shortcomings of the original electrical control system are becoming increasingly apparent. The speed control system adopts a two-stage amplification process—a dual-stage magnetic amplifier and a motor amplifier—forming a closed-loop speed control system. The given signal from the integrator is applied to the given winding of the dual-stage magnetic amplifier, amplified, and then supplied to the given winding of the motor amplifier. After further amplification, it is supplied to the excitation winding of the DC generator. The generator and the DC motor form an FD drive system. The given signal uses a time-based, stroke-corrected method (i.e., setting a second deceleration point at a certain stroke). The disadvantage of this method is that it cannot guarantee accurate operation according to the speed diagram requirements, especially in the deceleration section. Due to its integral effect, it may produce a large distance-speed deviation, either entering the creep speed prematurely or causing the final stopping speed to be too high, potentially exceeding the safe allowable 2 m/s. This is even more pronounced in the operation of the auxiliary winch, thus having an extremely adverse impact on hoisting safety. The main principle of the travel setting section is to utilize the main shaft of the hoist to drive a series of levers and cam bridges via changing sprockets, lever shafts, and cam shafts. These levers interact to push a series of switches, providing position signals such as the first deceleration point, second deceleration point, stop point, and overwind protection during hoist operation for control and protection. Because this method uses mechanical transmission and the cam bridges collide with the switches, mechanical wear and unreliable switch operation frequently occur in actual operation. Especially when the deceleration point signal cannot be accurately issued, it can result in no deceleration during the deceleration phase. The speed feedback signal of the speed control system is obtained through a tachogenerator rigidly connected to the hoist. This signal is applied to the speed feedback winding of the magnetic amplifier, connected in a negative feedback configuration, and compared with the given signal to form a speed negative feedback loop. Based on years of operational experience, it has been found that some resistors in the speed feedback control circuit frequently experience resistance changes (more pronounced in summer), and the control relays are prone to poor contact due to environmental factors. This leads to unstable speed and current during hoisting, and even overspeeding. More seriously, there have been instances where the polyurethane drive wheel of the tachogenerator slipped or delaminated, causing the hoist to "run away." Secondly, the hoist's synchronous machine and generator unit use a 6KV low-oil circuit breaker with series reactor for reduced-voltage starting. Due to frequent starting, this causes significant stress on the power grid and equipment (starting current exceeds 400A), requiring frequent disassembly, inspection, and replacement of contacts, transformer oil, or even the entire circuit breaker assembly. Since its commissioning in December 1988, the hoist's electrical control system, while generally meeting production needs, still suffers from low efficiency, high power consumption, poor safety performance, low reliability, high noise levels, and excessive maintenance. Annual maintenance costs amount to tens of thousands of yuan, and significant amounts of overhaul time are required. In particular, the generator rotor windings have experienced numerous incidents of solder detachment and burnt-out at the riser joint and parallel head sleeve during its fifteen years of operation, directly impacting mine safety and causing substantial economic losses. The old system can no longer meet the mine's normal production and safety requirements; therefore, an upgrade and renovation are necessary. 2. Digital Networked Electrical Control System Upgrade Scheme The digital DC hoist electrical control system consists of a PROFIBUS-DP fieldbus network structure. Its main components include: a transmission system composed of an ABB DCS600 fully digital thyristor rectifier control unit; a host computer, an Advantech industrial PC, running WinCC V6.0 industrial control configuration software as monitoring software; main control and line control are handled by one Siemens S7-300 PLC, with another S7-300 PLC handling monitoring tasks. Other components include a touchscreen, operator console, relay safety circuits, high and low voltage power distribution systems, transformers, reactors, DC fast circuit breakers, and shaft encoders. See Figure 1 for the specific system configuration. [align=center]Figure 1. Hoist Electromechanical Control Network Structure Diagram[/align] The speed control unit of the fully digital control system uses ABB's DCS600 fully digital DC drive control unit. This control unit is a new generation of fully digital products with high intelligence and excellent static and dynamic performance, high reliability, and convenient debugging and maintenance. Its main features are: It adopts a 16-bit microprocessor and 12-bit A/D and D/A chips, possessing fast signal processing and software management capabilities, high precision in adjustment and calculation, and strong engineering adaptability. Automatic adjustment and control of armature current, excitation current, and speed ensure excellent control performance. It has current adaptive and speed adaptive functions, allowing preset speed reference values, current limit values, and other parameters, and can limit the impact during acceleration, ensuring good system stability and accuracy. It has electromechanical resonance suppression function and multiple compensation functions. It has multiple fault self-diagnosis and fault sequential memory and fault nature memory functions, facilitating maintenance and troubleshooting. The monitoring and protection functions include main voltage overvoltage, undervoltage, phase sequence error, armature overcurrent, overvoltage, large armature current fluctuation, excitation overcurrent, overvoltage, underexcitation, motor overload, stall, etc. All control parameters can be set, modified, stored, or recalled online or offline via computer or control panel, and the system can prevent accidental changes to the set parameters. The system has multiple communication interfaces and a user-friendly human-machine interface and full-screen display software control structure, making debugging and parameter setting very intuitive and convenient. It has multiple input and output ports, allowing users to measure and control system operation through programmable I/O ports. The fully digital DC speed control device also includes a thyristor rectifier, and its matching DC motor, armature rectifier transformer, excitation rectifier transformer, DC fast switch, reactor, etc., forming a constant magnetic field, reversible armature, and a series 12-pulse drive mode, which can switch between 12-pulse and 6-pulse operation to achieve full-load half-speed operation. The control section of the digital networked hoist electrical control system mainly consists of two Siemens S7-300 PLCs, remote I/O, and control electrical components. It performs functions such as hoist stroke speed control, system operation, monitoring, and protection. It coordinates the control of speed regulating devices, braking equipment, and auxiliary units to ensure the hoist operates normally according to various working conditions. Simultaneously, it monitors the status and faults of the hoist and system equipment, identifies faults and their types, provides alarms and displays, and implements corresponding controls based on the fault type. Hoist stroke speed control is mainly implemented by the travel control PLC, which performs S-curve speed control with stroke as the variable, and forms a two-line monitoring and protection system with the monitoring PLC. The sensors use incremental shaft encoders manufactured by the Italian company ELTRA, offering high control accuracy. A 5-digit decimal KP value is used for stroke calculation and correction, ensuring a stroke measurement accuracy of ≤±0.01m. This guarantees that the hoist operates accurately according to the speed diagram requirements, whether under no-load or heavy-load conditions. The safety control circuit of the electrical control system is implemented by two PLCs, forming a two-wire safety circuit. Simultaneously, critical faults such as overwind, power failure, and speed control device failure are directly incorporated into relay safety circuits, thus creating multiple safety protections. Based on the nature and severity of the faults, they are divided into four categories: Category 1 faults: An audible and visual alarm is triggered, and the system immediately applies the safety brake, stopping the machine. Category 2 faults: An audible and visual alarm is triggered, and the system immediately applies the electrical brake, decelerating at the electrical braking deceleration rate. When the speed drops to 1 m/s, the safety brake is applied, stopping the machine. Category 3 faults: An audible and visual alarm is triggered, allowing the machine to stop only after one lifting cycle is completed, and locking the machine from restarting. Category 4 faults: Only an alarm is triggered. The system equipment, operating status, and faults are displayed by indicator lights on the control panel and on the host computer's display screen. An alarm is installed in the control panel to sound an alarm during faults. Monitoring of the system equipment's operating status is also achieved by the two PLCs and the speed control unit, forming multiple safety monitoring systems. The system employs various measurement and sensor sources to generate monitoring signals. These signals are converted and isolated before being input to the main control PLC1, while safety-related signals are simultaneously input to the monitoring PLC2. Both PLCs use specially programmed monitoring functions to memorize equipment and operational status faults, collect initial fault data, and implement alarms and displays. To ensure system reliability and improve power supply performance, a 2KVA isolation transformer powers the control system, and a 2KVA uninterruptible power supply (UPS) powers critical control units. In the event of a main power failure, the UPS automatically switches to ensure uninterrupted power supply, unaffected by external interference, until the hoist stops and the brakes engage. Furthermore, the system incorporates comprehensive anti-interference measures in control power, input/output signals, and data communication. Its electromagnetic compatibility design is reasonable, and its structural layout is meticulous and reliable, ensuring system reliability. The system's operational states can be categorized as: coal hoisting, personnel hoisting, special material unloading, maintenance, and emergency response. The control methods can be divided into: automatic control, semi-automatic control, manual control, maintenance operation control, slow operation control, emergency operation control, parking point bypass operation control, overwind bypass operation control, gate adjustment control (adjusting the hydraulic station or gate gap), gate test control function, and 6-pulse emergency operation control. The system uses an industrial control computer and communication components to form a host computer monitoring system, using WinCC monitoring software to monitor the operation of the hoist and other equipment, displaying and storing status and parameters for convenient use, maintenance, fault handling, and system management. Considering the importance of the hoist electrical control system in coal mine production, the old system is retained, and a conversion device is designed. The old and new systems can switch between shared DC motors, hydraulic stations, ventilation fans, and other auxiliary equipment and signal systems through this device to ensure mutual backup. The conversion includes main circuit conversion, auxiliary unit conversion, and control and monitoring signal conversion. The high-voltage power distribution system uses two KYGC-Z type high-voltage switchgear units. The circuit breakers are vacuum circuit breakers with electric operating mechanisms, which are convenient to operate and have minimal impact on the power grid. The switchgear has overcurrent, short circuit, and grounding protection, and has "five protection" functions. 3 Conclusion Since the system was commissioned and put into production 8 months ago, it has been running smoothly and reliably, with good speed regulation performance, high lifting efficiency, sensitive and reliable protection, and significantly reduced maintenance. After doing a good job in daily equipment inspection and maintenance and keeping the equipment clean, no abnormalities have occurred so far. In particular, the energy-saving effect of the new system is particularly significant. According to statistics, as of the end of August this year, compared with the old system, a total of more than 400,000 kWh of electricity has been saved, achieving good economic benefits. References: [1] Wang Zhaohui, Wang Anshan. New technologies and equipment for mine hoisting systems. Coal Industry Press. 1999, 3