Creepage distance is the shortest path between two conductive parts, or between a conductive part and the protective interface of an equipment, measured along an insulating surface. In other words, under different usage conditions, the insulating material surrounding the conductor becomes electrically charged due to polarization.
Electrical clearance refers to the shortest spatial distance measured between two conductive components or between a conductive component and the protective interface of equipment. In other words, it is the shortest distance that can achieve insulation through air while ensuring stable and safe electrical performance.
For motor products, the stator winding, rotor winding of wound-rotor motor, stator and rotor terminals, connecting plates, etc., all involve creepage distance and clearance issues.
Different rated voltages and different operating conditions will have different requirements. For these requirements, compliance and safety design and evaluation will be carried out during the design stage of motor products. Therefore, they cannot be changed or substituted at will during the production process and later use of the product. Moreover, it must be ensured that there are no conductive foreign objects in the space where the live parts are located, especially dusty conductive materials. Otherwise, electrical failures or safety accidents may occur in the motor.
Expanding knowledge about electric motors
1. Regarding creepage distance and clearance
Creepage distance and clearance are actually two related parameters, both related to electrical insulation. Especially in the selection of industrial control products such as relays and switches, it is necessary to comply with relevant standards and also set appropriate creepage distances and clearances according to the actual operating environment requirements (such as air pressure, pollution, etc.) to ensure safety and stable electrical performance.
Creepage distance refers to the path of leakage current that forms on the surface of an insulating material. If these leakage current paths constitute a conductive path, surface flashover or breakdown will occur. This change in the insulating material takes time and is caused by the operating voltage applied to the device for an extended period. Pollution in the surrounding environment can accelerate this change. Therefore, when determining the creepage distance of terminals, the magnitude of the operating voltage, the pollution level, and the creepage resistance characteristics of the insulating material used must be considered.
The size of an electrical clearance is unrelated to aging. Electrical clearances can withstand very high overvoltages, but once the overvoltage exceeds a certain critical value, it will quickly cause electrical breakdown. Therefore, the size of the electrical clearance must be determined based on the maximum internal and external overvoltages (pulse withstand voltage) that the equipment may experience. The magnitude of overvoltages will vary depending on the application of the same electrical equipment or the use of overvoltage protectors in different situations.
2. Creepage distance and clearance of motor products
GB14711 stipulates that in low-voltage motors, the creepage distance and clearance shall conform to the following table: (1) through the surface and space of the insulating material; (2) between exposed live parts of different voltages or different polarities; (3) between exposed live parts (including electromagnetic wires) and parts that are grounded (or may be grounded) when the motor is operating.
For motors with a rated voltage of 1000V and above, the electrical clearances and creepage distances between different exposed live parts or parts of different polarities inside the junction box, as well as between exposed live parts (including: electromagnetic wires) and non-current-carrying metal or movable metal casings, shall not be less than those specified in Table 5 below.
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