Causes and preventive measures of the burning of t

The reasons and preventive measures for the burning of three-phase asynchronous motors

the reasons for the burning of motors can be roughly divided into rich experience: A. burning due to lack of phase operation; B. burning due to overload operation and mechanical failure. The specific symptoms are as follows: lack of phase is that some windings turn black, and when overloaded, all three-phase windings turn black. Mechanical failure often shows that a group of windings are open circuited but not black

1 causes and measures of motor burning due to lack of phase operation

when the motor is normally started or operated, the three-phase load is symmetrical load, and the three-phase current is equal, less than or equal to the rated value. The phenomenon that any phase in the three-phase winding is disconnected is called phase failure (phase loss). When one phase is disconnected, the three-phase current will be unbalanced or too large. The lack of phase of the motor will increase the vibration, have abnormal sound, increase the temperature, decrease the speed, increase the current, and the current between windings will inevitably exceed the rated current, which will heat the motor shell and burn the motor after long-term operation. Open phase operation is very harmful to squirrel cage asynchronous motors that operate for a long time. 60% - 70% of the accidents in which such motors are burned are caused by open phase operation. Therefore, it is very important to protect the motor from phase failure

1.1 phase loss during starting. If the motor cannot be started, its winding current is 4 ~ 7 times of the rated current. The heating capacity is 16 ~ 49 times of the normal temperature rise, which quickly exceeds the allowable temperature rise and burns the motor

1.2 phase loss during operation. When the phase is missing at full load, the motor is in the over-current state, that is, the current exceeds the rated current, which effectively improves the friction life and fatigue life of the mechanical mechanism. The electric machine fully meets the mechanical standard of pipe inspection, and the opportunity changes from fatigue to locked rotor. The line current without phase interruption increases more, causing the motor to burn out rapidly. When the motor operates under light load with phase failure, the winding current without phase failure increases rapidly, causing this phase winding to be burned due to excessive temperature rise. There is no harm to the motor due to the lack of two-phase open phase, the rotating magnetic field cannot be established in the motor and it cannot be started. The battery box on Wang Yong's hand, which caused the lack of phase, is still intact. The main reasons are: the fuse is open circuit or the contactor contact is not in good contact, the contactor contact is deformed and stuck by heating, or the main contact is burned, the wire connector is loose or a wire is broken, etc. For phase loss caused by fuse fusing, the capacity of the melt should be correctly selected, the fuse melt and the fuse base must be in good contact, and the contact pressure between the melt and the fuse base should be frequently checked and adjusted. Avoid damaging the fuse during wiring, fasten it properly, and add spring washers at the wiring. For phase loss caused by contactor failure, a more suitable contactor should be selected to keep the dynamic and static contacts of the contactor in good contact. If the contactor is selected improperly, the arc extinguishing capacity of the contact is small, which will make the dynamic and static contacts stick together, and the action of the three-phase contacts is not synchronized, resulting in phase failure operation. The contactor shall be inspected irregularly. When the contactor contact is seriously worn and the surface is uneven, the contact pressure will be insufficient and phase failure operation will be caused. It is also necessary to determine a reasonable inspection and maintenance cycle and carry out strict and careful maintenance work according to the actual situation. When the operating environment is bad, such as humidity, vibration, corrosive gas and poor heat dissipation conditions, it will cause contact damage or wiring oxidation, poor contact and phase loss operation. Select electrical components that meet environmental requirements, take appropriate protective measures, forcibly improve the surrounding environment, and regularly replace components