Various types of insulators in operation may be damaged due to various reasons such as AC arc, malicious damage, and others. B-type insulators (see Chapter 4 of GB/T1001.1-2003 "Insulators for overhead lines with a nominal voltage above 1000 V - Part I: Definitions, test methods, and judgment criteria for ceramic or glass insulator units used in AC systems"), such as the insulation part of disc suspension insulators, may also be damaged due to electrical breakdown. IEC - Publication 383 does not include tests for checking residual strength. As long as the insulator is not completely damaged, its residual mechanical strength is definitely important. This standard only considers disc suspension tempered glass and porcelain insulators, as well as long rod porcelain insulators. These three types of insulators have different actual damage and residual performance. Therefore, when discussing residual strength and residual strength tests, it is necessary to consider each type of insulator separately, even if these three types of insulators are also used as insulator string components for overhead lines. The degree of damage to disc suspension porcelain insulators varies depending on the type of mechanical collision and the magnitude of the force. The damage to porcelain insulators can lead to a decrease in their mechanical strength. For disc suspension tempered glass insulators, any damage will cause all glass bodies, including the inner part of the cap, to immediately break into small pieces, and the decrease in mechanical strength of the insulator is imaginable. The degree of damage to long rod shaped porcelain insulators varies greatly. It may be due to micro cracks in the umbrella skirt or overall damage. The damage to the rod body will reduce its mechanical strength. It is still not possible to specify residual strength tests for long rod porcelain insulators, as representative sample preparation methods cannot be specified, and the relationship between the degree of damage and the decrease in mechanical strength cannot be found (see Appendix A.1 for more detailed information on the residual strength of long rod porcelain insulators). It has been found that the residual strength of disc suspension tempered glass and porcelain insulators depends on the design of the insulator, and is not closely related to manufacturing, material selection, and degree of damage (the latter factor only applies to porcelain insulators)