There are many types of rotating motors. According to their functions, they are divided into generators and motors, DC motors and AC motors according to their voltage properties, and synchronous motors and asynchronous motors according to their structure. Asynchronous motors can be divided into three-phase asynchronous motors and single-phase asynchronous motors according to the number of phases; According to its different rotor structures, it can be divided into cage type and wound rotor type. Among them, cage type three-phase asynchronous motors are widely used and in greatest demand in various motors due to their simple structure, convenient manufacturing, cheap price, and reliable operation. The lightning protection of rotating motors (generators, condensers, large motors, etc.) is much more difficult than that of transformers, and the lightning accident rate is often higher than that of transformers. This is because rotating motors have some unique characteristics in terms of insulation structure, performance, and insulation coordination compared to transformers. (1) Among electrical equipment of the same voltage level, the insulation of rotating motors has the lowest impulse withstand voltage level. The reason is that: ① the motor has a high-speed rotating rotor, so it can only use solid media, and cannot use a combination of solid liquid (transformer oil) media for insulation like a transformer. During the manufacturing process, the solid media is easily damaged, and voids or gaps are prone to appear in the insulation. Therefore, partial discharge is prone to occur during operation, leading to insulation degradation; ② The operating conditions of motor insulation are the most severe, subject to the combined effects of heat, mechanical vibration, moisture in the air, pollution, electromagnetic stress, and other factors, resulting in a faster aging rate; ③ The electric field of the motor insulation structure is relatively uniform, and its impact coefficient is close to 1. The electrical strength under overvoltage is the weakest link. Therefore, the rated voltage and insulation level of the motor cannot be too high. (2) The residual voltage of the lightning arrester used for protecting rotating motors is very close to the impulse withstand voltage value of the motor, and the insulation margin is very small. If the factory impulse withstand voltage test value of the generator is only 25% to 30% higher than the 3kA residual voltage value of the zinc oxide lightning arrester, the margin of the magnetic blowing lightning arrester is smaller, and the insulation margin will be lower with the operation of the generator. Therefore, relying solely on lightning arresters for motor protection is not enough, and it must also be combined with capacitors, reactors, cable sections, etc. for protection. (3) Interturn insulation requires strict restrictions on the steepness of the intrusion wave. Due to the small and discontinuous inter turn capacitance of the motor winding, overvoltage waves can only propagate along the winding conductor after entering the motor winding. The length of each turn of the winding is much larger than that of the transformer winding, and the overvoltage acting between adjacent two turns is directly proportional to the steepness of the intrusion wave. In order to protect the inter turn insulation of the motor, it is necessary to strictly limit the steepness of the intrusion wave. In short, the lightning protection requirements for rotating motors are high and difficult, and it is necessary to comprehensively consider the protection requirements for the main insulation, inter turn insulation, and neutral point insulation of the windings