Manufacturing coils for high-voltage motors is a very complex process, involving winding, shaping, gelling, wrapping with mica tape, and wrapping with high-resistance and low-resistance tapes. Today, Ms. Can will mainly discuss the functions of high-resistance and low-resistance tapes.
Manufacturing coils for high-voltage motors is a very complex process, involving winding, shaping, gelling, wrapping with mica tape, and wrapping with high-resistance and low-resistance tapes. Today, Ms. Can will mainly discuss the functions of high-resistance and low-resistance tapes.
The insulation of a high-voltage motor winding is entirely on the coil. The iron core uses open slots. After the coil is placed into the slot, a slot wedge is finally added. According to the specific requirements of the motor, most high-voltage motors use magnetic slot wedges.
Today we'll discuss why high-resistance and low-resistance tapes are wrapped around the outside of coils. Along the straight edges of the motor coil, several layers of mica tape are wrapped according to process requirements, followed by a half-overlapping low-resistance tape. At the transition point between the straight edge and the end, a high-resistance tape is used. The purpose is to prevent corona damage to the windings, as the electric field strength is stronger at the core slot openings and winding ends than at the straight edges; therefore, high-resistance tapes are used in these areas.
During the winding process, it is important to prevent damage to the high and low resistance materials. In many motor manufacturers, the low resistance band on the straight edge is damaged or the slot is scratched during the winding process, which can significantly harm the motor performance.
Regarding high-resistivity and low-resistivity materials
The insulation tape on the high-voltage coil of an electric motor is divided into high-resistance tape and low-resistance tape. High-resistance tape is made of alkali-free glass fiber tape impregnated with a semiconductor high-resistance varnish and is used at the ends of the coil bars. Low-resistance tape mainly includes iron-containing asbestos tape and alkali-free glass fiber tape impregnated with a semiconductor low-resistance varnish. Iron-containing asbestos tape is woven from asbestos fiber yarn; low-resistance tape is used in the coil bar and groove sections.
(1) Low-resistivity materials. The main ones are acetylene black, which is carbon released during the incomplete combustion of gaseous, liquid or solid organic matter, and is used as the conductive base for anti-corona paint. In addition, there is graphite, which is a crystalline form of carbon.
(2) High-resistivity materials. Primarily silicon carbide, used to formulate high-resistivity nonlinear paints. Silicon carbide exhibits nonlinear resistivity, with its resistivity decreasing with the applied electric field strength. This means it has the ability to adjust the electric field strength, ensuring a uniform potential distribution on the surface of the wire rod at the outer end of the slot. For the silicon carbide coating used at the ends, 320–400 mesh silicon carbide is used for medium resistance coatings, while 1600–1800 mesh silicon carbide is used for high resistance coatings.
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