The Earth’s magnetosphere acts as a protective shield against the solar wind—a stream of charged particles from the Sun. This interaction results in a large-scale electric field in the magnetosphere, known as a dawn-dusk convection electric field, playing a crucial role in disturbances such as the storm-time ring current and substorms. We explored the quasi-steady large-scale electric fields and the role of space charge in the magnetosphere by using global magnetohydrodynamics (MHD) simulations. When the interplanetary magnetic field is southward, a substorm growth phase begins. The large-scale electric field is in a relatively stable condition, in particular, on the dayside. In the MHD simulation, the positive space charge dominates the duskside magnetosphere, while the negative space charge dominates the dawnside. If the electric field is purely caused by the space charge deposited in the magnetosphere, the direction of the electric field will be in the dusk-dawn direction. However, the dawn-dusk electric field is established in the magnetosphere due to continued plasma motion interacting with the magnetic field. It is suggested that the magnetosphere maintains dynamic equilibrium through a balance of energy flow from the solar wind to the ionosphere. These insights improve our understanding of magnetospheric convection and the magnetospheric system.