Principle of transformer core demagnetization

The two key conditions for demagnetization are: alternating magnetic poles and decreasing magnetic field strength. To demagnetize a ferromagnetic material, the uniformity of its magnetic domain alignment must be disrupted, making the arrangement of the magnetic domains completely random so that no magnetism is exhibited externally.

1. Methods for alternating magnetic poles:
Using alternating current (AC) for measurement; alternately reversing the direction of direct current (DC); or changing the orientation of the test piece within the magnetic field.

2. Methods for decreasing magnetic field strength:
Gradually moving the test piece away from the magnetic field (or vice versa); or controlling current decay/step-down reduction via the power supply. Demagnetization involves placing the workpiece in an alternating magnetic field to generate a hysteresis loop. As the amplitude of the alternating magnetic field gradually decreases, the trajectory of the hysteresis loop becomes progressively smaller. When the magnetic field strength drops to zero, the residual magnetism (Br) remaining in the workpiece approaches zero. During demagnetization, the changes in the direction and magnitude of the current and magnetic field must involve "simultaneous reversal and attenuation."