According to the saturation characteristics of the core, the reactors which change the reactance by changing the DC excitation are called saturation reactors, which are usually divided into two types: choke type and self saturation type. The choke type saturable reactor is used in AC circuit. It changes the current in AC circuit by changing its reactance, so as to change the output capacity of AC circuit. So it is called choke type. In the choke type saturable reactor, the AC magnetic potential of working winding is basically equal to the maximum DC magnetic potential of control winding. The saturation magnetic density in the core is produced by both AC and DC magnetic potential. The self saturable reactor is used in the phase controlled rectifier circuit. By changing its reactance, the conduction angle of the rectifier element is changed, so as to change the output voltage of the rectifier circuit. In the self saturable reactor, the DC magnetic potential of the working winding is far greater than the maximum DC magnetic potential of the control winding. The saturation magnetic density of the core is mainly generated by the DC magnetic potential of the working winding, so it is called self saturable reactor It's the same. Self saturable reactor also belongs to core reactor. The relative permeability of ferromagnetic material decreases with the increase of core magnetic density. The relative permeability of ferromagnetic material working in the linear region of magnetization curve is tens or even hundreds of times of that working in the saturated region, so the reactance working in the linear region is tens or even hundreds of times of that working in the saturated region The voltage regulation of self saturable reactor can realize continuous and smooth voltage regulation in a large range, which can reduce the operation times of on load tap changer and prolong the service life of on load tap changer.