For any motor product, DC resistance, insulation resistance, and grounding resistance are important parameters characterizing its quality and performance. This is a topic that technicians and skilled workers who directly work with motors are quite familiar with, but it may be difficult for other people. This special explanation was given in response to a question from a netizen.
DC resistance is a parameter relative to the motor winding itself. The resistance is directly related to the winding design. However, the purity of the magnet material and the uniformity of wire drawing directly affect the resistance. For the motor winding itself, the correct number of turns and the tightness of the winding process both affect the coil resistance. For three-phase motors, the balance of the three-phase windings is also involved. Especially during winding manufacturing, the welding quality at joints also affects the resistance and balance. Simply put, DC resistance testing is a parameter for evaluating the quality of the winding itself, directly related to the winding design, and unrelated to the motor's rated voltage, insulation structure, or magnet type.
Insulation resistance is one of the parameters for evaluating the insulation structure characteristics of motor windings. Insulation resistance includes the insulation between the winding conductors and the casing, and between phases of a three-phase motor winding. Generally, the insulation resistance of materials decreases with increasing ambient temperature and humidity. When measuring insulation resistance, the temperature and humidity at which the sample and the environment reach equilibrium must be specified. The insulation resistance control requirements for motors are directly related to the motor's rated voltage and rated power. GB/T 14711 is a general safety requirement standard for small and medium-sized rotating electrical machines, specifying the lower limit values of insulation resistance under cold and thermally stable conditions. From a safety perspective, higher insulation resistance is better; cold-state insulation resistance should be greater than hot-state insulation resistance.
Grounding resistance refers to the resistance encountered when current flows from a grounding device into the earth, then through the earth to another grounding body, or diffuses to a distance. The grounding resistance value reflects the degree of good contact between the electrical device and the "ground". From a safety perspective, the lower the grounding resistance, the better. GB/T 14711 specifies that the upper limit of the resistance value of the motor grounding path is 0.1 ohms.
