System Overview
In recent years, with breakthroughs in computer control and communication technologies and the maturity of coal mine safety monitoring technologies, underground coal mine power supply has begun to see increasingly widespread application of remote computer monitoring systems, making them a powerful guarantee for safe and efficient production. Simultaneously, to strengthen supervision of coal mine safety, coal management departments require their affiliated mines to monitor safety production and management in a timely manner, and to understand and query on-site safety monitoring information in real time. In 2005, the National Development and Reform Commission, the State Administration of Work Safety, and the State Coal Mine Safety Administration jointly issued document No. 457 of 2005, Article 44 of which requires real-time monitoring of coal mine power supply systems to reduce unplanned power outages and ventilation stoppages, effectively curb gas accumulation, and ensure safe coal mine production.
A sudden power outage in the entire mine will cause the main ventilation fans to stop operating. The lack of ventilation underground will cause gas to accumulate. If power is restored indiscriminately, it could lead to a gas explosion. A power outage will prevent water pumps from draining water in time, and if it lasts too long, it could cause a mine flooding accident. In mines with enclosed fire zones, a power outage may cause CO and gas to leak, resulting in poisoning or suffocation accidents.
System Composition
The underground power grid safety monitoring system in coal mines adopts an industrial Ethernet plus fieldbus mode. The backbone channel is a fiber optic Ethernet ring network connecting to each substation. Fieldbuses from each power substation are connected to the system via switches and PROFIBUS bus conversion gateways. A distributed fieldbus control system is used within the substations. The integrated protection devices of each switch are connected to the power substations via MODBUS-PROFIBUS to PROFIBUS gateways and RS485-PROFIBUS to PROFIBUS bridges. The system consists of four parts:
- Comprehensive protection for high-voltage explosion-proof switches: one comprehensive protector is installed for each high-voltage explosion-proof switch.
- Measurement and control substations, substations and working faces.
- The main monitoring station of the surface mine dispatch center.
- The mine leadership and relevant electromechanical management departments monitor and control the equipment.
One problem that needs to be solved in power substations is connecting integrated protectors without PROFIBUS interfaces to the PROFIBUS bus system. In the power substation of the underground power grid safety monitoring system in a coal mine in Jixi, the PLC used is a Siemens S7300 series 315-2DP, and the integrated protector is a product of Tianjin Tiankuang. Tianjin Tiankuang's integrated protector products do not have PROFIBUS communication interfaces, only RS485 communication interfaces, therefore they cannot be directly connected to the Siemens PLC. Using the MODBUS to PROFIBUS gateway and RS485 to PROFIBUS bridge from Beijing Microhard Innovation Technology Co., Ltd., the Tianjin Tiankuang integrated protector is connected to the PROFIBUS bus. The system diagram is as follows:
The measurement and control substation is connected to the ground monitoring master station via optical fiber, forming a dual-ring self-healing fiber optic Ethernet. This fiber optic Ethernet has multiple spare Ethernet ports to facilitate other service channels. The substation's video and audio systems can also be connected to this Ethernet system. The mine dispatch center's monitoring master station is connected to the monitoring and control equipment of mine leaders and relevant electromechanical management departments via existing optical fiber.
Technical features
This project enables the display and recording of all data from the 6kV sections of each substation at the ground dispatch center. It facilitates remote measurement, control, signaling, and adjustment of underground substations, thereby achieving unmanned operation of the substations, significantly improving the safety and reliability of mine power supply, and establishing an automated information platform for coal mine safety production, thus enhancing the overall information automation level of the coal mine. The system features are as follows:
(1) It has strong anti-interference ability. When a serious error occurs in a node of the system, it has the function of automatically shutting down the output of the node and cutting off the connection between the node and the bus, so that other nodes on the bus and communication are not affected.
(2) The system has a time-of-use electricity recording function, which facilitates electricity management.
(3) Monitoring of all electrical quantities, monitoring of signal quantities, control of switch opening and closing, setting of set values, etc. can be realized on the ground, and the substation can be unmanned.
(4) The high-performance undervoltage protection can distinguish between voltage fluctuations and bus undervoltage. In the event of a power outage at the entire station, the undervoltage protection will accurately and promptly trip the switch, completely avoiding the trouble of large-scale power outages in the mine caused by voltage flicker in the past.
(5) The protection device is digitalized, with high protection action accuracy, fast action and high reliability, completely eliminating the protection maloperation and over-level tripping caused by the drift of old protection action values and poor action sensitivity.
(6) The accurate event sequence recording and fault recording function helps to quickly find faults, greatly shorten the substation power outage time and power restoration time, and completely avoid the trouble of the top-level switch tripping again after the fault is tested and closed.
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