Shell-type transformers use an anti-ymchwydd coil with high dielectric strength to resist the influence of pulse foltedd. Since shell-type transformers use coils with large surface area, the series capacitance between coils is large. When a ymchwydd is applied, it can Distributing the foltedd reasonably, the surge coil is a non-oscillating winding, which can suppress the voltage oscillation caused by the pulse voltage.