Development of magnetospheric substorms is controlled by variations of two components of the magnetospheric electric field: a potential field (E^p_m) and a vortex one (E^v_m). It is shown that the motion of auroral arcs located at closed magnetic field lines is determined by the E^p_m, field only, while the motion of arcs located at the field lines passing the reconnection (neutral) line in the plasma sheet is determined by the E^v_m, field only. The regularities of the auroral arc motion at various phases of the substorm are studied, and the energy budget of magnetospheric substorms is discussed.