Rectifier arc-back study on the analogue computer

ONE OF the most difficult problems encountered in the application of power rectifiers is the calculation of arc-back currents. Arc back is the term which refers to conduction of current through the rectifier in the reverse direction, i.e., from cathode to anode. It provides, simultaneously, a short circuit on the rectifier transformer low-voltage winding and paths for the flow of direct current from the d-c bus. Consequently, arc-back currents are nearly always higher than currents resulting from a 3-phase short circuit on the rectifier transformer. Knowledge of the magnitude of arc-back current is important because the resulting stresses may damage the rectifier or associated transformer and switchgear.1‾³ The magnitude of arc-back current can be obtained from the curves presented in this paper without restoring to the use of complicated mathematics. In addition, the curves provide a way to evaluate readily the effect of a change in circuit constants, a consideration which is important when reactors must be installed to limit stresses on the equipment.