井下金属结构近场耦合大环发射天线电磁波能量安全性分析

Analysis of electromagnetic wave energy safety of underground metal structure near-field coupled large loop transmitting antenna

当井下巷道内分布的金属结构处于大环发射天线近场时,会耦合大环发射天线的电磁波能量。一旦金属结构存在断点并发生刮擦,可能会以刮擦放电的形式产生放电火花并点燃瓦斯气体,对煤矿井下安全造成威胁。针对该问题,从近场耦合危险系数及安全距离2个方面分析了井下金属结构近场耦合大环发射天线电磁波能量的安全性。通过建立金属结构近场耦合大环发射天线电磁波能量等效电路,推导出近场耦合危险系数表达式和金属结构与大环发射天线之间的安全距离的表达式。分析了大环发射天线半径、金属结构等效接收线圈半径、刮擦放电火花负载、金属结构与大环发射天线之间的距离对近场耦合危险系数和安全距离的影响。仿真结果表明:近场耦合危险系数随大环发射天线半径的增大先稍增大再稍减小或一直增大;刮擦放电火花负载在一定条件下可使近场耦合危险系数达到峰值,当大环发射天线半径大于等于金属结构等效接收线圈半径时,峰值处的近场耦合危险系数有可能超过近场耦合危险系数临界值0.46,可能会造成危险;当大环发射天线半径小于金属结构等效接收线圈半径时,峰值处的近场耦合危险系数大部分情况下小于临界值0.46,造成危险的可能性较小;环发射天线半径在一定条件下可使近场耦合危险系数达到峰值,峰值处的近场耦合危险系数随金属结构等效接收线圈半径的增大先增大后减小,超过近场耦合危险系数临界值0.46的可能性较大,这种耦合在瓦斯气体环境中很可能造成危险。安全距离随大环发射天线半径的增大而增大,即刮擦放电火花负载上电磁波能量的安全性随大环发射天线半径的增大而降低;当大环发射天线半径大于等于金属结构等效接收线圈半径时,安全距离随金属结构等效接收线圈半径的增大而增大,即刮擦放电火花负载上电磁波能量的安全性随金属结构等效接收线圈半径的增大而降低;当大环发射天线半径小于金属结构等效接收线圈半径时,安全距离随金属结构等效接收线圈半径的增大先缓慢增大再减小,即刮擦放电火花负载上电磁波能量的安全性随金属结构等效接收线圈半径的增大先降低再升高。

When the metal structures distributed in the underground roadway are in the near-field of the large loop transmitting antenna, they will couple the electromagnetic wave energy of the large loop transmitting antenna. Once the metal structure has a breakpoint and friction occurs, it may produce friction discharge spark and ignite gas. This poses a threat to the safety of coal mine. In order to solve this problem, the safety of electromagnetic wave energy of underground metal structure near-field coupled large loop transmitting antenna is analyzed from two aspects of near-field coupling risk coefficient and safe distance. By establishing the equivalent circuit of electromagnetic wave energy of metal structure near-field coupled large loop transmitting antenna, the expressions of near-field coupling risk coefficient and safe distance between metal structure and large loop transmitting antenna are derived. The influence of the radius of the large loop transmitting antenna, the radius of the equivalent receiving coil of the metal structure, the friction discharge spark load and the distance between the metal structure and the large loop transmitting antenna on the near-field coupling risk coefficient and the safe distance are analyzed. The simulation results show that the near-field coupling risk coefficient increases slightly at first and then decreases slightly or increases all the time with the increase of the radius of the large loop transmitting antenna. Under certain conditions, the friction discharge spark load can make the near-field coupling risk coefficient reach the peak value. When the radius of the large loop transmitting antenna is greater than or equal to the radius of the equivalent receiving coil of the metal structure, the near-field coupling risk coefficient at the peak value may exceed the critical value 0.46 of the near-field coupling risk coefficient. This may cause danger. When the radius of the large loop transmitting antenna is smaller than the radius of equivalent receiving coil of the metal structure, the near-field coupling risk coefficient at the peak value is less than the critical value0.46 in most cases. This will not cause danger in most cases. Under certain conditions, the radius of the large loop transmitting antenna can make the near-field coupling risk coefficient reach the peak value. The near-field coupling risk coefficient at the peak value first increases and then decreases with the increase of the radius of equivalent receiving coil of the metal structure. It is more likely to exceed the critical value 0.46 of the near-field coupling risk coefficient, which is likely to cause danger in the gas environment. The safe distance increases with the increase of the radius of the large loop transmitting antenna. The safety of the electromagnetic wave energy on the friction discharge spark load decreases with the increase of the radius of the large loop transmitting antenna.When the radius of the large loop transmitting antenna is greater than or equal to the radius of the equivalent receiving coil of the metal structure, the safe distance increases with the increase of the radius of the equivalent receiving coil of the metal structure. The safety of the electromagnetic wave energy on the friction discharge spark load decreases with the increase of the radius of the equivalent receiving coil of the metal structure. When the radius of the large loop transmitting antenna is smaller than the radius of the equivalent receiving coil of the metal structure, the safe distance first increases slowly and then decreases with the increase of the radius of the equivalent receiving coil of the metal structure. The safety of the electromagnetic wave energy on the friction discharge spark load first decreases and then increases with the increase of the radius of the equivalent receiving coil of the metal structure.