Experimental analysis of a DC bucking motor blocking geomagnetically induced currents

An experimental study investigates the performance of a dc bucking motor for the blocking of geomagnetically induced currents (GICs) within a 3 kVA/ 416 V three-phase distribution feeder. This blocking method consists of connecting a separately excited dc motor between neutral and ground of a Y-grounded transformer consisting of a bank of three single-phase transformers. Losses and currents of the transformer and the blocking device are measured at no-load, rated-load, unbalanced-load. and line-to-neutral short circuit conditions without and with GICs. Thereafter, the dc ac and total λ-i characteristics of one single-phase transformer of the above mentioned transformer bank are simultaneously measured using an arbitrary waveform generator, a power amplifier and a digital data acquisition network. These λ-i characteristics -where the dc bias current is a parameter- are then used to model a single-phase transformer under dc bias current conditions (e.g., assumed Gles) and to calculate voltages and currents of a single-phase transformer when subjected to Gles. The simulated signals are then compared with measured time functions.