At both ends of the high-voltage winding that has not been treated with corona protection, the leakage current on the surface of the winding coil ends increases from the nose end to the stator core slot, so the voltage drop on the insulation surface at the slot is the largest and the axial field strength is also the highest. This is also the most important part of the main insulation and corona protection treatment. The winding coil of the high-voltage winding 6kV voltage level motor is already in a critical state of corona initiation. Therefore, the national explosion-proof standard stipulates that winding coils of voltage levels of 6kV and above must be protected against corona.
The end of the high-voltage winding can be treated with constant resistivity or nonlinear resistivity to prevent corona from occurring at the straight part and end of the winding coil.
Analyzing from the voltage distribution characteristic curve along the end direction from the notch, if the resistivity of the anti-corona layer is too large, the voltage distribution will be too steep, and the starting end will corona first; if the resistivity of the anti-corona layer is too low, the outer side of the end of the anti-corona layer will corona first. Therefore, the electric field distribution of the same level of constant voltage resistivity anti-corona layer is still not uniform enough.
If the resistivity increases from the slot outlet to the end, a more ideal and uniform electric field distribution can be obtained. For motors with higher rated voltages, three-level anti-corona protection with increasing low resistivity, medium resistivity, and high resistivity can be used; generally, two-level anti-corona treatment with increasing low resistivity and high resistivity can be used.
The difference between high-resistance tape and low-resistance tape
The insulating tape on the high-voltage coil of the motor is divided into high-resistance tape and low-resistance tape. The high-resistance tape is made of alkali-free glass fiber tape dipped in semiconductor high-resistance paint and is used for the end of the wire rod. The low-resistance tape mainly includes iron-containing asbestos tape and alkali-free glass fiber tape dipped in semiconductor low-resistance paint. Iron asbestos tape is woven from asbestos fiber yarn; low-resistance tape is used for the wire rod and wire slot part.
1. Low resistance materials. The main materials are acetylene black, which is carbon precipitated when gaseous, liquid or solid organic matter is not completely burned, and is used as a conductive base for anti-corona paint. In addition, there is graphite, which is a crystal of carbon.
2. High resistance materials. The main materials are silicon carbide, which is used to prepare high resistance nonlinear paint. Silicon carbide has nonlinear resistance characteristics, and its resistivity decreases with the external applied field strength, that is, it has the ability to adjust the field strength so that the surface potential of the wire rod at the end of the slot is evenly distributed. For the silicon carbide coating used at the end, the medium resistance is prepared with 320-400 mesh silicon carbide, and the high resistance is prepared with 1600-1800 mesh silicon carbide. Why should the outside of the coil be wrapped with high resistance and low resistance bands?
The manufacture of coils for high-voltage motor products is a very tedious task, which requires winding, molding, gelling, wrapping with mica tape, wrapping with high resistance bands and low resistance bands. Ms. Can will mainly talk to you about the role of high resistance and low resistance bands today. The insulation of the high-voltage motor winding is all on the coil. The iron core adopts an open slot. After the coil is placed in the slot, the slot wedge is finally covered. According to the specific requirements of the motor, most high-voltage motors use magnetic slot wedges.
Electro motor, low voltage alternator, asynchronous electric motor
