The excitation coil of DC voltage electromagnet is supplied by DC constant voltage source (U unchanged). When the coil parameters are constant (the number of turns and the resistance remain unchanged), both the excitation current and the magnetic potential remain unchanged, and the type of constant magnetic potential is the type of constant magnetic potential.

   If the armature does not pull in after the coil is electrified, the working parts driven by the armature will not move, which will affect the normal operation of the equipment. However, if ∵ u does not increase, the excitation current will not increase, and ∵ has no effect on the electromagnet itself.