静电平衡和静电屏蔽是电磁学中的重要知识点，其关键在于导体中存在大量自由电子，在外加电场作用下形成新的电荷分布，由此产生的附加电场抵消外加场使得导体内部电场处处为零. 那么如果持续增大外加电场，静电平衡和静电屏蔽是否能一直实现？静电平衡和静电屏蔽是否有极限？本文分析了静电平衡在外加电场逐渐增强下，从开始被打破的临界状态到完全被打破的极限状态的变化过程，并以铁质外壳为例分析了静电屏蔽被打破所需要的场强和电势差. 

 Electrostatic equilibrium and electrostatic shielding are important knowledge points in electromagnetics. The key point is that there are a large number of free electrons in the conductor, which are form a new charge distribution under an external electric field. The resulting additional electric field offsets the external field and makes the electric field inside the conductor zero everywhere. Then, if the external electric field continues to increase, can electrostatic equilibrium and electrostatic shielding be realized all the time? Are there limits to electrostatic equilibrium and electrostatic shielding? This paper analyzes the process of electrostatic balance from the