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Analysis of Residual Current in Low-Voltage Bipolar DC System and Improved Residual Current Protection Scheme

Residual current analysis and measurement of low-voltage direct current (LVdc) is the key technology for its applications in civil architectures. The residual current expressions of positive and negative electric shock of LVdc under constant impedance load (CIL) and constant power load (CPL) are derived, respectively. On this basis, the effects of electric shock position and human equivalent impedance on residual current are analyzed. Subsequently, the residual current when the neutral line has unknown grounding is studied, and the difference between it and the neutral line of electric shock is analyzed. Meanwhile, the overlap interval of these two residual currents is investigated. For the meshed bipolar LVdc grid, the circulating currents caused by the asymmetry of line parameters as well as its influences on residual current measurement are analyzed. Moreover, these expressions are simplified for engineering applications. Finally, an improved residual current protection (RCP) scheme with a communication system is proposed. A simulation platform of MATLAB/Simulink and a low-voltage experimental platform are built to verify the deduced residual current expression and protection scheme.