The formation of a discrete auroral arc is studied in the framework of the arc energization system, which includes the energy source, the acceleration region for the auroral electrons, and the electromotive force for the field-aligned currents connected to the arc. The kinetic energy of an earthward plasma flow shock is proposed as a possible mechanism for generating V-shaped electric equipotential contours in the energization system which can accelerate the auroral electrons and, at the same time, drive the arc field-aligned current. It is shown that the shock must be located in the plasma sheet in order to drive the observed arc field-aligned current with a field-aligned potential jump of ~10 kV for a plasma flow having a speed of a few hundred kilometers per second. The auroral electron beam is generated in the shock in the plasma sheet and then is modified by wave-particle interaction processes in the topside ionosphere.