A traction motor drive system includes a plurality of armatures arranged in parallel with each other and a plurality of field circuits arranged in series with one another. The plurality of field circuits is arranged in parallel with the armatures. The traction motor drive system also includes a field isolation system including a shunt circuit associated with at least one field circuit. The field isolation system includes a first field switch arranged in series with the plurality of field circuits and configured to switch between a first terminal of the shunt circuit and a first field terminal of at least one field circuit. The field isolation system includes a second field switch, arranged in series with the plurality of field circuits and configured to switch between a second terminal of the shunt circuit and a second field terminal of at least one field circuit.