Fault Detection of the Medium-Voltage DC Cable by Using the Featured Modal Signals

The insulation of the medium-voltage direct current (MVdc) cable is prone to deterioration due to external and internal factors, which may lead to faults. Aiming to accommodate two different cable operation modes, in this article, the feasibility of decoupling transient measurements is first verified. An algorithm is presented for calculating the phase-mode transformation matrices used for signal decoupling. Then, the states of decoupled modal signals are analyzed to select the featured ones that reflect fault occurrence. A fault detection method is proposed based on the variation characteristics of featured modal signals. Finally, the experimental model of the MVdc cables is created using real-time digital simulation. The experimental results show that the method is independent of the fault condition, cable length, and operating mode. The average fault detection accuracy exceeds 99% with noises equal to or larger than 20 dB. The method applies to a wide range of fault resistances (1–3000 Ω).