Research On Electromagnetic Detection System Of Goaf Under Transmission Line

Once the goaf of the transmission is collapsed,the non load stress may lead to the destruction of the tower structure,fracture,deformation and other accidents,which poses a major threat to the safe and stable operation of the transmission line.The reasonable exploration of goaf under transmission line can avoid the accident to a great extent.However,the electromagnetic environment of goaf under transmission line is complex,which makes the detection signal of conventional electromagnetic detection method easy to submerge in noise.If the signal-to-noise is increased only by increasing the transmitting power,it will cause the instrument to be bulky,which is not conducive to field detection.To solve the above problems,the spread spectrum coding signal is used as excitation,combined with the related detection algorithm,which can increase the signal-to-noise in the condition of small power transmission,and it has the advantages of high resolution,high accuracy,high efficiency and so on.Starting from the influence of goaf on transmission line,the existing detection methods in goaf are introduce.The two commonly used detection methods are discussed in detail:the principle,characteristics and development status of high density electrical method and transient electromagnetic method,and the possible problems in the detection of goaf under transmission line are pointed out respectively,so the spread spectrum coding electromagnetic detection method and the main research contents of this paper are proposed.The mathematical model of electromagnetic detection of goaf under transmission line is deduced.The influence of power tower on electromagnetic detection data and the working principle of the spread spectrum coding electromagnetic detection system are analyzed.The generation mode,correlation characteristics,identification effect and denoising ability of m sequence,Gold sequence and 2~n sequence are analyzed.Finally,m sequence is selected as the spread spectrum coding sequence in this paper.A spread spectrum coding electromagnetic detection system is studied and designed.In the emission system,the spread spectrum code is generated by the FPGA platform,through the optocoupler isolation circuit,the IGBT power tube in the high voltage main circuit is driven by it to achieve the required power level for launching.In the receiver system,the double T type notch filter is adopted to filter common power frequency interference.Meanwhile the two order Butterworth filter circuit is used to receive the signal within the required frequency range.The weak signal is amplified by a multiple adjustable amplifier circuit,and the synchronous acquisition circuit is used to realize the synchronous acquisition of the transmitted and received signals,so as to facilitate the data processing in the later stage.The feasibility of spread spectrum coding electromagnetic detection method is verified by resistance network experiment,the flume experiment results show that the system has good performance and noise suppression ability,the feasibility of the system in the outdoor environment is verified by the ground penetrating test,which show that the system has the advantages of high detection precision,strong anti-interference ability,stable and reliable operation,etc.