Today's electrical equipment types are diverse, different types of electrical equipment in our lives are widely used, electrical equipment overvoltage use will have what harm? Today, we will analyze the harm of overvoltage with you, and look at the specific role and form of overvoltage of the flow overtemperature thermal protector. Below to understand! Transient high voltage or overvoltage caused by lightning strike is often coupled or transferred to network equipment through network lines, resulting in equipment damage. For the graded insulated transformer with ungrounded neutral point, when the lightning wave penetrates the substation from the line to the transformer neutral point, the system is single-phase grounded, non-full-phase operation, especially the transformer excitation inductance and line capacitance resonance, it will produce higher lightning overvoltage or power frequency overvoltage, which poses a threat to the graded insulated transformer neutral, and even causes insulation damage. The lightning current generated by lightning discharge is as high as tens or even hundreds of thousands of amps, which will cause huge electromagnetic effects, mechanical effects and thermal effects, and can be protected by overvoltage protectors. Overvoltage protectors must be integrated use of discharge (shard), voltage equalization (equipotential), shielding (isolation), grounding, limiting voltage (clamp) protection and other technologies, overvoltage protectors in accordance with the principles of external and internal lightning protection, according to the characteristics of the protected object, flexible application, take specific measures to form a complete protection system. The main forms of overvoltage in substations are: lightning overvoltage, power frequency overvoltage and resonant overvoltage, operating overvoltage, etc. These overvoltages form dangerous overvoltages on lines and equipment by conducting or electromagnetic induction, especially lightning overvoltages. When lightning strikes substations, it will produce strong inductive overvoltages in low-voltage power supply systems and weak current systems. This article mainly introduces the harm of overvoltage, generally caused by lightning strikes, and knows the working form and characteristics of overvoltage protectors.