Summary: This article introduces the application of the mine high-voltage power cable insulation fault monitoring system. It analyzes the special requirements of the high-voltage power supply system in coal mines, a high-risk industry. The on-line monitoring of the insulation status of high-voltage cables in the power supply system, achieving early warnings, fault localization, and grounding selection functions, is an important technical means for power supply management. It elaborates on the system's characteristics and advancement. Practice has shown that the application of the system has improved the regulatory level of the power system for enterprise electromechanical management personnel, as well as the economic and social benefits of the enterprise.
Keywords: Cable Insulation; Early Warning; Fault Location; Grounding Wire Selection
Shendong Baode Coal Mine, a large-scale coal production base of the Shendong Coal Group Company of the National Energy Group, is located in Shanxi Province. It was integrated through the technical transformation of the original Baode County Dongguan Town Coal Mine and Qiaotou Coal Mine. The mine field extends 14.0km from north to south and 5.7km from east to west, covering an area of 55.898km2. Due to the characteristics of the production system, a large number of high-voltage power cables are used above and below the ground, and the operation of the cables directly affects the coal mine's production. A cable failure would inevitably lead to accidents in mining production, mine ventilation, drainage, and compressed air systems, resulting in significant production losses, casualties, and secondary disasters. Currently, the cable partial discharge and withstand voltage tests conducted annually have the following issues: first, they fail to truly reflect the actual insulation level of the cables; second, the withstand voltage test is a destructive test that also damages the cable insulation; and third, with the increasing demand for power supply reliability in the mine, long-term online monitoring is not feasible.
The application of low-current grounding systems and insulation monitoring devices in the high-voltage power supply systems of coal mines has not resolved the aforementioned issues, which have been a persistent pain point in coal mine power supply. In response, the Baode Coal Mine has undergone an automated transformation of its power supply equipment. The mine has always hoped to provide an alarm before a high-voltage cable fault occurs in the power supply system, forming a warning system to take preemptive measures and eliminate potential hazards, thus preventing sudden short circuits from causing widespread power outages. Additionally, it should be able to quickly and accurately trace the fault location. Below is the design plan for the Baode Coal Mine's high-voltage power cable insulation fault system.
High-voltage Power Cable Insulation Fault System Design
The Baode Coal Mine High-Voltage Power Cable Fault Early Warning Monitoring System primarily includes: a ground remote host (cloud-based service), system collection units, and various monitoring devices (including high-frequency sensors), as shown in Figure 1 for the system structure.
Figure 1: System Architecture Diagram
1.1 Ground Remote Host
The ground remote host is set up at the mine dispatching and command center, where a control station is also established. The control station is used to centrally control and monitor all related equipment of the high-voltage cable system underground. The control station is divided into two parts: hardware and software.
Hardware Equipment: Industrial Control Computers, Monitors, etc.
② Software: Monitoring and control configuration software.
The on-site remote host employs a system management software based on the B/S architecture, communicating with monitoring devices via a local area network to configure device parameters and provide remote services through host communication. The system also includes cloud access functionality, allowing users to view the operation status of the cable online monitoring system, equipment performance, and line alarm information from any connected computer. The high-voltage power cable insulation fault monitoring system for coal mines utilizes a fully networked design, assigning a unique IP address to each device, enabling one device to simultaneously online detect up to 16 cross-linked polyethylene or rubber sheathed high-voltage power cables. The system can continuously monitor and record the number of "recoverable faults" in the measured power cables and the intensity and shape of instantaneous electromagnetic transient signals within a set time period, serving as specific criteria for fault early warning, cable selection, and distance measurement.
1.2 System Technical Specifications
① Current signal sampling frequency: 10MHz x 16 channels; ② Voltage signal sampling frequency: 100kHz x 4 channels; ③ Current single-ended fault location range: ≤17km ( customizable); ④ System positioning accuracy: ±4.25m; ⑤ Synchronization time accuracy: 10ns; ⑥ Test blind zone: ≤10m; ⑦ Cable fault early warning accuracy: ≥95%; ⑧ Cable fault selection accuracy: ≥99%; ⑨ Communication with cloud: Wireless 4G, 5G; ⑩ System device communication method: Network port; 11 Cloud server: Free 3A cloud service; 12 System upper computer: Brand industrial computer; 13 System expansion: Supports networking up to 253 monitoring units; 14 Power supply method: AC 127V ±10%; 15 Operating temperature range: -25~+70℃; 16 Online system operation: >80,000 hours.
1. System Data Collection Unit
PowerDee Coal Mine selects online monitoring for 15 busbars and their three-core cables at six substations: No. 1 Central Substation, No. 2 Substation, San (Lower) Pumping Room Substation, Kangsun 62 Lane Substation, No. 5 Pumping Room Substation at the Bottom of the Shaft, and Concentrated Alley Substation. The system employs on-site centralized monitoring. On the low-voltage side of the substations, a suitable location is chosen to install an explosion-proof and intrinsic safety type high-voltage power cable insulation fault analysis host. On the high-voltage side, a suitable location is selected to install an intrinsic safety type current collector for mining use.
4 GPC Electromagnetic Acoustic Transducer Probe
GPC current probe is installed on the grounding line of the metallic shielding layer of the monitored cross-linked polyethylene cable, responsible for monitoring transient electromagnetic wave signals of the cable under test. The probe is fixed on the cable shielding line according to the arrow direction. Note that insulation treatment must be carried out before installing the probe on the shielding line. The probe is connected to the explosion-proof electromagnetic wave collector for mining use via a multi-core coaxial cable.
1. 5 GPD Electromagnetic Wave Probe
The GPD electric wave probe is installed on the monitored rubber sheathed cable, responsible for monitoring the transient electric wave signals of the measured cable. The probe is connected to the mine-safe electric wave collector via a multi-core shielded cable.
1. June 6th Communication Network
The main station of the system communicates internally via internal Ethernet channels or fiber optic channels; the main station connects to the system cloud using the Baode Coal Mine Comprehensive Substation's 5G fiber optic network.
1. Key Features of the 7 System
① Fault Warning: Implements yellow, orange, and red level warnings for insulation faults in high-voltage cables, junction boxes, and power supply and distribution equipment, which is part of the major equipment perception content in coal mines and a foundation for the construction of smart mines; ② Fault Selection: Based on the traveling wave principle, achieves grounding fault selection, reliably implements the selective single-phase grounding protection as stipulated in Article 453 of the "Coal Mine Regulations," and is an upgraded and replaced product for low-current grounding fault selection devices; ③ Fault Distance Measurement: Utilizes the A-type distance measurement principle to achieve fault point distance measurement, providing a basis for rapid fault handling and preventing secondary disasters and expanding accidents; ④ System Cloud Service: Provides sufficient user space, allowing users to access the on-site system monitoring at any time and place through a browser, system historical data storage for convenient historical review; ⑤ Local Function: The system backend is installed within the main station, configured with a single-line system diagram, and achieves fault warning, selection, and distance measurement functions, with real-time display of bus voltage, flickering of fault lines on the single-line system diagram, pop-up alarms, and audio alarms; ⑥ Electronic Duty: Achieves unattended operation, with alarm information and working status sent via text messages or APP notifications to relevant personnel; ⑦ Remote Technical Support: 7x24-hour remote service, enabling auxiliary analysis of fault waveforms and remote upgrading of system programs; ⑧ Historical Storage: Achieves real-time information storage, allowing for query of historical data, etc.
2 High-voltage Power Cable Insulation Fault System Application
The Baode Coal Mine employs a coal mine high-voltage power cable fault early warning monitoring system, which includes high-voltage power supply fault early warning, grounding selector, fault distance measurement, etc., to prevent major power supply accidents and avoid accidents caused by high-voltage power supply.
The occurrence of major mine disasters such as water, fire, and gas has resolved the long-standing challenges in the maintenance and management of the power supply system [2]. The system offers the following benefits:
Enhanced the automation level of the mine power supply system, proactively implemented measures in advance, ensuring the safe operation of mining equipment, guaranteed reliable power supply to the grid, and avoided economic losses due to sudden power outages.
② Automation in fault selection and early warning significantly enhances the efficiency of power operation personnel. Previously, manually identifying fault points was time-consuming and labor-intensive. By installing a cable online monitoring system that automatically warns of cable faults, a substantial amount of time and manpower is saved, thereby improving work efficiency.
③By monitoring the cable's operational status in real-time, early warnings of cable failures are issued, allowing for timely repairs or switches before the fault occurs. This extends the cable's lifespan and reduces production and operation costs. The lifespan of a 20A cable might be extended to 25A or even longer, significantly cutting down on raw material costs.
④ The system features a compact structure, easy construction and installation, and can continuously monitor key stations, equipment, and abnormal equipment with flexible configuration. It does not alter the operation or structure of the cables, occupies no existing system resources, and installs high-frequency sensors on the cable grounding conductors, ensuring safety and reliability.
⑤ Employing the traveling wave fault location measurement method, the insulation weakness points in the cable are accurately located with a precision of ±4.25m. This significantly reduces the time required to locate power supply faults. Utilizing a high-performance FPGA processor, it achieves high-speed sampling and storage with a 100Msps sampling rate and 14-bit resolution.
The successful application of the system has achieved early warning of faults in high-voltage power cables, such as cross-linked polyethylene and rubber-sheathed cables. It meets technical requirements in aspects like fault early warning, fault selection, and fault distance measurement, enhancing power supply reliability and improving the efficiency of maintenance personnel. Real-time monitoring of cable operation status ensures timely handling before faults occur, extending cable lifespan and saving production and operation costs. The system raises the level of automation in power line monitoring, ensuring reliable power supply to the grid and avoiding economic losses due to sudden power outages. The system software platform is deployed on cloud servers, allowing operators easy access without time or location constraints, enabling real-time viewing of line operation for convenient management. With a short response time, the system can transmit fault signals collected by high-frequency sensors to the host software via network communication and display fault lines and waveforms within 5 seconds after transient faults in cables, facilitating rapid analysis and handling by on-duty personnel.
3. Utilizing Fault System Analysis to Resolve Insulation Faults in High-Voltage Power Cables
3.1 Inspection of High-Voltage Cables
In the high-voltage power system of coal mines, there are critical components such as switches and protective electrical appliances. The function of the switchgear is to ensure the normal operation of the entire circuit in the high-voltage power system of coal mines, and to protect the system by opening and closing the switchgear when there are obvious abnormalities.
3.2 Inspecting the Transformer of the Coal Mine High-Voltage Power System
An electric transformer is a device that utilizes the principle of electromagnetic induction to alter alternating voltage, primarily consisting of the main winding, secondary winding, and core. Currently, transformers are widely used, with many in high-voltage power systems of coal mines. The operation and accident handling of transformers are crucial topics.
During the operation of high-voltage power systems in coal mines, sudden shutdowns can occur, often due to transformer issues. Transformers are used to alter the voltage of high-voltage power systems in coal mines, reducing losses during power transmission. However, improper modifications can affect the transformer's heat dissipation function. Some workers, in an attempt to keep the high-voltage power system running for longer periods, make unscientific modifications to the transformers. These changes do not seem to meet the requirements. While voltage increases do lower losses, heat is produced more rapidly, leading to higher cable temperatures. During fault troubleshooting, it is essential to check if the cable overheating is caused by improper transformer operation, and further investigate the fault. Additionally, to address issues with high-voltage power systems in coal mines, it is crucial to enhance the promotion of maintenance knowledge, encouraging users to gain a deeper understanding and inspection of common faults. The internal components of high-voltage power systems in coal mines are relatively fragile and require timely repair in case of failure. Generally, if the core components of the high-voltage power system are not problematic, other issues can be resolved effectively. Once the core equipment malfunctions, it takes a significant amount of time to identify the faulty component, and the replacement and repair process becomes more complex, severely impacting user experience. To this end, we utilize knowledge of high-voltage power systems and fault diagnosis techniques, ensuring thorough inspection of transformers to promptly identify potential faults.
3.3 Inspecting the operational status of the high-voltage power cable insulation fault detection system
The insulation fault system and fault handling for high-voltage power cables are also urgent issues to be addressed in the maintenance of high-voltage power systems in coal mines at present. With the advent of the big data era, nearly all industries are striving to integrate intelligent technology into their operations, and China's high-voltage power systems in coal mines are no exception. There is significant room for the application of intelligent control technology. Firstly, through intelligent control, the switching of motors can be automated, reducing manual operation, allowing systems to cease work without executing tasks, thereby saving electricity. Secondly, the intelligent control system can adjust the power of the motor, avoiding the various noises and harmful substances produced during high-power operation, reducing safety hazards and negative impacts. Of course, intelligent systems are also very beneficial in handling faults. In the high-voltage power systems of coal mines, the fault system is a critical component. Firstly, increased funding is needed to ensure the normal operation of the fault system; resources have already been allocated to the fault system. However, currently, China still does not place enough emphasis on the fault system in high-voltage power systems in coal mines, and there are many issues in the installation, use, maintenance, and management of the fault system. Many systems and devices are not tested before installation and are not used for routine maintenance. Additionally, to better handle accidents in high-voltage power systems in coal mines, the state should also increase investment and policy support in this area. With sufficient funding and strong policy support, the relevant departments should vigorously promote the high-voltage power cable insulation fault system, increase support for the system, and ensure the construction of related high-voltage power systems in coal mines. Conduct fault diagnosis for transformer equipment in high-voltage power systems in coal mines, address certain fault phenomena, improve the reliability of the high-voltage power systems, ensure power supply, and create greater benefits for the high-voltage power systems in coal mines.
Insulation Monitoring and Insulation Fault Location Products
4.1 Insulation Monitoring and Insulation Fault Location Products
AIM-T Series Industrial Insulation Monitoring Instruments
The AIM-T series insulation monitors are primarily used in industrial IT power distribution systems, including the AIM-T300, AIM-T500, and AIMT500L models, which are all suitable for systems operating on pure AC, pure DC, and AC-DC mixed systems.
The AIM-T300 is suitable for AC, DC, and AC-DC hybrid systems below 450V, while the AIM-T500 is designed for systems up to 800V AC, DC, and AC-DC hybrid. The AIM-T500L adds the insulation fault location feature compared to the AIM-T500.
4.2 Insulation Fault Location Product
Industrial insulation fault location products, when used with the AIM-T500L insulation monitor, include the ASG200 test signal generator, the AIL200-12 insulation fault locator, and the AKH-0.66L series current transformers. These are suitable for IT power distribution systems with numerous outgoing circuit loops.
4.3 Insulation Monitoring Coupling Instrument
The Insulation Monitoring Coupling Instruments, when used in conjunction with the AIM-T500 Insulation Monitoring Instrument, include the ACPD100 and ACPD200 models. They are suitable for IT distribution systems with AC voltages above 690V and DC voltages above 800V.
Technical Specifications
5.1 Insulation Monitor Technical Specifications
5.2 Test Signal Generator Technical Parameters
5.3 Insulation Fault Locating Instrument Technical Parameters
5.4 AKH-0.66L Series Current Transformer Technical Specifications
5.5 Insulation Monitoring Coupling Instrument Technical Specifications
6. Conclusion
The successful application of the Baode Coal Mine's high-voltage power cable insulation fault monitoring system is one method for condition-based maintenance. The system detects the insulation status of the cables under operating voltage, accurately reflecting the cable's insulation level. In the automatic continuous monitoring mode, based on a large amount of data and numerical analysis of criteria, the monitoring system utilizes cloud services to upload cable fault early warning information to a multi-user cloud space. Equipment managers can remotely monitor, allowing the mine's electrical and mechanical supervisor to实时 obtain information on the cable operation within the substation, determine the cable operation status, and implement real-time early warning, cable selection, and distance measurement before a fault occurs, achieving condition-based maintenance of the cables, significantly reducing manual inspections. This improves the level of supervision over the power system by mine electrical and mechanical managers, enhancing both the economic and social benefits of the enterprise.
Reference:
Wang Xiaobiao. Analysis of Fault Diagnosis and Detection Technology for Power Cables[J]. Electronic Manufacturing, 2016(18).
Yu Yang, Yang Yixuan. Fault Diagnosis and Detection Technology for Power Cables[J]. Heilongjiang Science and Technology Information, 2015(36).
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