Alignment of lamellar block copolymer microstructure in an electric field was studied. Two mechanisms of alignment are considered: selective electric-field-induced disordering and alignment through movement of defects. The latter mechanism is supported by the findings that, in an aligned sample, defect structures exbited a highly anisotropic arrangement and were spatially clumped. An analysis of field-induced forces on disclination lines and defect walls is presented. Also, defect interactions are considered. Through the interplay between these forces, the alignment process, the kinetics of alignment, and clumping of defects can be rationalized