Figure 2.

Equivalent circuit model: a three-phase control cable with a soft fault and a motor of the robot joint. A soft fault is induced in phase a. $Z_c$ is the characteristic impedance of the wire. $C_i$ and $R_i$ in parallel represent the insulator. $i_{res}$ and $i_{cap}$ are the leakage current and the current flowing through the capacitance of the insulator $C_i$, respectively. $V_n$ is the neutral voltage of the motor.