Sensitivity of Cable Model Parameters for Traveling Wave Differential Protections in MTDC Systems

Multi-terminal HVDC systems equipped with multiple DC breakers require a protection system that selectively detects faults within a few milliseconds. In the development and application of such protection algorithms, time-domain simulation studies of various faults are essential when determining the setting and verifying the performance. However, when such protections are applied in practice, it should be expected that the models will not perfectly represent the behavior of the real system or transmission line, thereby possibly causing protections to operate unreliably. This paper presents a simulation process that evaluates the consequences for a protection algorithm when the transmission line parameters are varied. More specifically, the false differential current due to cable model parameter errors is evaluated in a traveling-wave differential protection applied in a multi-terminal HVDC system during an external fault. The purpose is to identify the most critical parameters and evaluate how inaccuracies influence the protection performance when applied in practice. It is shown that the parameters which significantly influence the propagation delay are critical for achieving the ideal performance - a strictly zero differential current during external faults.