The DC residual current sensor has a small excitation current in the primary circuit and operates under a weak magnetic field. For a residual current protection device with a rated residual operating current of 0.006 A, the working magnetic field strength is only about 0.080 A/m. During operation, the main circuit is often subjected to several hundred amps to thousands of amps of starting current or tens of thousands of amps of short-circuit current, and the residual current transformer is in extreme saturation. under these circumstances. The transformer cannot affect the operating characteristics due to the residual magnetism generated by the inrush current. Therefore, the core material of the residual current transformer generally adopts an iron-nickel soft magnetic alloy material having high initial permeability, high magnetic permeability and low coercivity. The iron-nickel soft magnetic alloy material has extremely high initial permeability and magnetic permeability, extremely low coercive force, low saturation magnetic flux density, and good temperature stability.
The DC residual current sensor core is manufactured by winding into a ring shape and an annular punching film. The material of the wound core is generally selected from a cold-rolled strip having a thickness of 0.10 to 0.20 mm, and the material of the punched core is generally selected to have a thickness of 0.3 to 1.00. Cold rolled strip.
In addition to the iron-nickel soft magnetic alloy, a residual current transformer core is also fabricated using a soft or ultra-fine crystalline soft magnetic alloy material. Amorphous and ultra-microcrystalline soft magnetic alloys have the advantages of simple manufacturing process and heat treatment process, low cost, high magnetic permeability and high saturation magnetic flux density.