This paper uses transport-line theory to construct equivalent model of jointless track circuit under shunted state and analyses the principle of track induced circuit in the disconnection fault of compensation capacitor based on the model. At the same time, according to the work principle of cab signal and the consistent changes relationship between cab signal induced voltage and short-circuit current of the track circuit, the induced voltage recorded by cab signal is denoised by DBWT (discrete binary wavelet transform), and then the instantaneous frequency of the signal is extracted by WR (wavelet ridge), finally by detecting the changes of instantaneous frequency to diagnose the disconnection fault of compensation capacitor. This method is verified that it can detect the location of fault capacitor when there is only one capacitor is fault, in addition, it largely overcomes the disadvantages existed in recent detection methods: high cost, bad detection timeliness and influence on railway transportation.

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