From defect chemical considerations the sodium potential dependencies of the partial electronic conductivities of Na-beta-alumina are derived. As a result, relationships for the ionic transference number, the open-circuit voltage of a galvanic cell, the steady-state ionic current and the sodium potential profile across the electrolyte can be solved for. These relationships serve as a theoretical basis to determine and discuss the role of the partial electronic conductivities under defined operating conditions of the electrolyte.