Earlier, we posted a tweet about the surface coating of motor rotors, which received heated discussion among netizens. Today, we will have a brief discussion with you on this issue again.

Rust prevention is the most basic purpose of rotor surface coating. For rotors without special requirements, rust prevention is sufficient. However, for some special types of motors, the rotor surface coating requirements have other functions and effects.

For low-voltage ordinary series motors, the main purpose of rotor surface coating is to prevent rust, and it is also a way or means to distinguish and beautify parts from different manufacturers.

For the rotors of high-voltage motors, variable-frequency motors and explosion-proof motors, the coating material on the rotor surface must have anti-corona properties. Anti-corona paint is a semi-conductive paint with a surface resistivity between 103 and 1011 ohms. It is mainly used for anti-corona of high-voltage motor windings. That is, a layer of such paint will be coated on the surface of the high-voltage motor winding and the rotor surface. Its color is mostly red.

In addition to high-voltage motors, most variable-frequency motors also have corona problems. For this reason, many motor manufacturers will coat the rotor surface of such motors with anti-corona paint. There are also many motor manufacturers who do not take measures on the rotor surface of the motor, but use anti-corona electromagnetic wire for the motor stator winding.

For explosion-proof motors, whether high voltage, low voltage, or variable frequency motors, in order to further prevent explosion accidents, a safer measure is adopted to coat the rotor surface and even the stator winding surface with anti-corona paint.

Semi-conductive paint is divided into low-resistance semi-conductive anti-corona paint and high-resistance semi-conductive anti-corona paint according to its resistivity. High-resistance semi-conductive anti-corona paint is mainly used for coating the winding ends of high-voltage motors to make the surface electric field distribution of the winding ends uniform and increase the corona initiation voltage of the winding ends.

Low-resistance semi-conductive anti-corona paint is generally directly applied to the surface of the winding slot, or the glass ribbon is first dipped in anti-corona paint and then wrapped around the surface of the slot winding to improve the electric field distribution at the ventilation slot of the motor and ground the surface of the slot winding, reduce the surface potential of the slot winding, and prevent corona discharge between the winding and the slot wall. For the convenience of production, most manufacturers use high-low resistance insulation tape instead of anti-corona paint.