Research On Time-Frequency Characteristics Of Electromagnetic Noise Radiated From Pantograph-Catenary Arc

The time-frequency characteristics of electromagnetic radiation noise(EMRN)produced by Pantograph-Catenary(PC)arc were researched in this paper,the physical characteristics of time domain waveform were analysed and mathematical model was established.Considering the frequency domain signal,analysis method was proposed and the range of EMRN was obtained,which laid the theoretical foundations for suppression of EMRN.The EMRN experiments under different conditions were carried out with the self-developed experimental system in anechoic chamber environment.The time domain waveform of EMRN is symmetrical and convergent.Its continuous time is shorter than 0.8 ?s.A mathematical model of the time domain waveform was established by using the leastsquare method.The performance of the model was evaluated by using determination coefficient,residual standard deviation,and correlation coefficient.The time domain waveform obtained from the model is almost the same as the waveform measured from experiments.Because the time domain signal of EMRN has some special features such as short duration,sudden change and so on,the Hilbert-Huang transform(HHT)was used to analyze the EMRN.The intrinsic mode function(IMF)components were got by using empirical mode decomposition(EMD)to the noise.The IMF with highest correlation and maximum variance was selected and calculated by using Hilbert transform.Then the instantaneous frequency of the noise under different conditions were obtained.With the increase of current,contact force and velocity,the RMS of instantaneous frequency of EMRN decreases obviously.The frequency's change with time of the electric field is faster than that of magnetic field noise.The second order forward difference was used to deal with the value of different frequency points of the waveforms of EMRN received by interference receiver,and the sum of difference was used to evaluate the change of frequency points.The top 10 frequency points of the sum of difference in descending order were statistically analyzed,and change rule of the waveforms of electromagnetic noise under different conditions was obtained.The low frequency and high frequency parts of magnetic field noise are bounded by 40 k Hz,and that of electric field noise are bounded approximately by 400 MHz.