1 Analysis of the characteristics of the domestic underground power grid system With the continuous improvement of the level of science and technology, the underground power grid system has developed rapidly in terms of safety protection performance, and can basically meet the safety protection requirements of the underground power grid. Its main performance characteristics are as follows:
1) The cables of the downhole protection system are selected and used in different types according to the use requirements of different environments. At present, underground cables mainly include plastic cables, armored cables, and rubber-sheathed flexible cables. Among them, the first two cables are mainly used for powering down equipment and main lines, while rubber-sheathed cables are mainly used for power supply of mobile equipment. , It has high safety protection performance as a whole. However, due to the harshness of the underground environment and the large amount of cables, many failures have also appeared during long-term use. Therefore, the correct selection of cable type and type is of great significance to improving the safety of the power grid.
2) In the power grid, the indirect grounding method is mainly used for grounding. When a contact accident occurs, if the indirect grounding method is used, the current flowing through the human body can be greatly reduced, and the personal injury of the personnel can be reduced. Probability; At the same time, the short-circuit phenomenon in the system is reduced, and the failure rate of transformers and power supply equipment is also greatly reduced. According to the relevant provisions of the “Coal Mine Safety Regulations”, the use of directly grounded transformers, motors and other equipment is not allowed to supply power to the underground.
3) At present, most of the protection systems in underground power grids have relatively complete functions, which can generate corresponding alarms for faults such as short circuit, overvoltage, and leakage of the power grid, and take effective measures in time to issue commands such as cutting off the power supply and switching switches. Operation ensures the normal operation of the underground power grid and the safety of underground operations. However, due to the harshness of the downhole environment and the often overloaded operation of downhole equipment, various failures of various equipment, cables, control switches, etc. often occur, and the stability of the entire power grid is relatively poor. Therefore, strengthening the comprehensive protection performance of the protection system in the underground power grid, effectively reducing or avoiding the occurrence of related faults and accidents, is essential for improving the safe operation capability of the underground power grid and the safety of underground operations.
2 The main functional requirements of the magnetic flap level gauge protection system refer to the relevant provisions of the “Coal Mine Safety Regulations”. The magnetic flap level gauge protection system during underground operations must meet certain functional requirements before it can be applied on site. The main functional requirements are as follows:
1) The protection system can conduct real-time data acquisition and detection of relevant parameters in the operation of the underground power grid, and convert them into corresponding electrical signals.
2) Equipped with control switches and monitoring ranges can be automated and remotely switched and controlled according to different operating states and needs of the power grid, reducing the labor intensity of personnel.
3) It is necessary to have the functions of integrating multiple protection functions such as current protection, grounding protection and leakage protection for the power grid. At the same time, in response to various faults in the power grid, it can promptly give fault signal instructions and accurately display the occurrence of faults. Location.
4) Real-time man-machine interface display of various signal parameters in power grid operation, and timely memory storage of data to form corresponding data recording files to facilitate later data search.
5) It can effectively shield other related interference signals underground to ensure that the data of the protection system is not interfered by the outside, so as to improve the control accuracy of the protection system.
3 Scheme design of protection system for magnetic flap level gauge
3. 1 Overall scheme design In view of some shortcomings in the use of the existing underground power grid, a more stable performance of the magnetic flap level gauge and protection system was designed. The system mainly includes analog input modules, CPU modules, current and voltage transmitters, fault storage modules, human-computer interaction interface units and other parts. Among them, the CPU main control unit adopts high-speed processing performance, integrated A/D signal conversion and other functions. The DSP chip TMS320F2812 can achieve a 32-bit, 150MIPS high-speed command processing speed, which overcomes the shortcomings of traditional calculations, slow response, and low accuracy; the fault storage module is mainly used to deal with fault signals such as short circuits and leakage in the power grid, and For real-time storage of these data, the overall framework of the protection system is shown in Figure 1. The working principle of the whole protection system is as follows: First, the relevant signals in the power grid are detected by the relevant detection equipment, and after the signal conversion of the current and voltage transmitters, they are sent to the CPU, and the CPU uses its own current A /D signal converter, which can convert the electrical signal into the corresponding digital signal, and process the signal through related calculation and judgment methods, and finally transmit it to the man-machine display interface for real-time display, and at the same time, cut off through the relevant control program Power supply, switch and other operations, in order to achieve the safety protection of the power grid. Compared with the traditional system, the system has higher response speed, more comprehensive protection functions, higher control accuracy and quick-action performance, and can better meet the needs of underground power grids.
3. 2 The design of the analog input module. Because the protection system needs to collect the current, voltage, zero sequence voltage signals and other signals in the underground power grid, and perform signal calculation and conversion through related control algorithms, thereby controlling the execution of related control programs The agency issues control instructions. The analog input, as the front-end module of the protection system’s signal acquisition and input, is very important to the entire protection system. Its structure is mainly composed of PT/CT, converter, low-pass filter, etc. Its working principle is shown in Figure 2. At the same time, because the voltage and voltage values collected by the module are all high voltage and large current values. It cannot be directly applied in the protection system. Therefore, it needs to be converted into low current and low voltage signals by relevant high-performance current and voltage transformers before being transmitted to the DSP chip for signal conversion and calculation judgment.
4 Protection system test analysis In order to further verify the comprehensive performance of the designed magnetic flap level gauge protection system, the system was tested on site in a mine.
4. 1 Short-circuit protection test analysis During the short-circuit test of the protection system, the software is mainly used to set the short-circuit fault to test. The specific method is: first set a short-circuit fault in the software, and then send it to the CPU to judge the short-circuit signal During the test, when the CPU received the short-circuit signal, it issued a trip command to the switch. At the same time, the circuit short-circuiter quickly issued a power-off command, and its action response time was only 80 ms. Therefore, it was verified The system has a better overall performance in terms of current short-circuit. 4. 2 Leakage protection test analysis In the leakage test of the protection system, the resistance value between the power grid and the ground is changed many times to simulate the leakage state. When the CPU detects that the resistance value exceeds the set threshold, it will send a message to the resistance relay Responsively cut off the power supply, so as to realize the protection of leakage faults in the protection system. After testing, the protection system can accurately and timely respond to leakage faults quickly and in real time, has high control accuracy, and can meet the current needs of underground power grids.
5 Conclusion Combined with the performance characteristics of the current domestic downhole power grid system, through the analysis of the functional requirements of the magnetic flap level gauge protection system, a set of downhole magnetic flap level gauge protection system with comprehensive functions, fast response speed and stable performance is designed. , Tests show that the system has high performance characteristics in terms of short-circuit protection, leakage protection, etc. The entire system is reliable in action and stable in performance, which is of great significance to improving the safety of underground power grids and underground operations.
Post time: 07-01-22