The Analysis Of Contact Force Between The Pantograph And Contact Line In Electrified Railway Via Signal Processing Methods

The fluctuation of the contact force has already been regarded as an index that evaluates the contact line unevenness degree and the current collection performance between the pantograph and the catenary. In recent years, constructing catenary spectrum has become a new idea to evaluate the overall dynamic performance of catenary and pantograph system. In the paper, the contact force signals are analyzed with the modern signal processing methods.For the stationarity of contact force and the statistics characteristic in time domain and frequency domain, the work is listed as follows:1) Testing the stationarity of the random signal is an important preprocessing step before studying its statistical feature. Firstly, the methods on testing the stationarity of the signals are fully summarized. Then based on the data of Beijing-Guangzhou line and Shanghai-Kunming line(two data points sampled per mile), the stationarity of contact force is analyzed by both using the methods in frequency domain, which compares the time-frequency spectrum similarity of the signal, such as surrogates-based test and spectrum-based test, and using the methods in time domain, such as the run test and a series of unit root tests. The testing results show that, whether the contact force signal can be considered as stationary, relatively to a given observation scale. From a longer observation scale (sample distance is over1000m), the contact force sections can be consider as stationary; from a small observation scale (sample distance is below500m), the dynamic contact force appears obvious non-stationary. At last, a non-stationarity index is proposed as a quantitative tool to assess the fluctuations of the contact force.2) The contact force is analyzed by the time domain indexes which are applied to initially evaluate the unevenness degree of the contact line and monitor the state of pantograph and contact lines.3) Based on wavelet transform theory and empirical mode decomposition, the contact force wavelength identification procedure is presented. As a result, the wavelength composition in normal sections and abnormal sections are identified and located. Firstly, the contact force is pretreated by using EMD and the signal concluding the wavelength ranging from lm to100m is obtained. Secondly, the pretreated contact force is decomposed into multilayer detail signals and approximation signals via the wavelet transform, then the long and short wavelength ingredients are separated. Lastly, the detail signals and the approximation signals are respectively analyzed in the frequency domain and time-frequency domain. The result implies that the combination of EMD and the wavelet transform could identify the natural wavelength and mutation wavelength effectively and accurately; the contact force detail signal time-frequency spectrum may be as a reference to evaluate the performance of the current collection and the contact line fault identified.4) Based on the data of Beijing-Guangzhou line and Shanghai-Kunming line, the spectral kurtosis based on wavelet transform are applied to the contact force signal processing. The results show that, the spectrum kurtosis based on wavelet transform has the ability of detecting the local mutation in the contact force, which may be as a reference to evaluate the current collection performance; the idea that testing the stationarity of the contact force via the spectral kurtosis based wavelet transform is proposed.