Simulation and emulation of rapid transit DC short circuit current

In this paper we present an integrated tool for DC short circuit current simulation and current waveform emulation for rapid transit traction power system protection applications. The current simulation program has the capability of including the characteristics of rectifier voltage regulation and frequency dependence of track impedance. Current profiles obtained from the simulation program can be directly output from a notebook computer through a D/A (digital to analog) interface card to generate waveform signals similar to those from current sensing instrument. The system is inherently portable, making it not only suitable for off-line relay parameter setting but also mobile for on-site relay function testing purposes. Moreover, it can be applied to adjust relay settings easily should there be modifications in transit line traction power system configuration.