The insulation performance of enameled wire is related to temperature!
Let me first talk about the state of polymer materials-the paint film of enameled wire is a polymer material:
As the temperature rises, polymers will experience three material states: glassy, highly elastic, and viscous fluid states. The physical properties of the three states are as follows:
Glassy state: rigid solid solid
High elasticity: rubber-like solid with good elasticity
Viscous flow state: fluid with fluidity
In the test of enameled wire, there is a performance called softening breakdown (a similar test in the United States is called thermoplastic flow), which is mainly to assess the high temperature that the enameled wire paint film can withstand. If it exceeds a certain temperature, the paint film will soften into a viscous fluid state-it can flow like syrup.
After the enameled wire is used (winding into a motor or transformer, etc.), there is a certain stress or pressure between the wire and the wire. If the temperature of the varnish film is very high, causing the varnish film to be in a viscous state, one of the pressure enameled wires The paint film between the paint film will be forced to flow in other directions due to pressure, resulting in the thinning of the insulating layer, resulting in a decrease in insulation performance.
If the temperature drops again, the paint film will drop from the viscous flow state to the high elastic state, and then return to the glass state, so as to restore better insulation performance. However, there may also be a certain decrease. The main reason is that the pressure has caused the paint film to flow, which causes the paint film to be eccentric and the insulation thickness becomes thinner.
Another premise is that the insulation is not damaged under high temperature conditions, that is to say, there is no breakdown. If the insulation has been damaged, the damage point is still irreversible after the temperature drops.
Enameled wire for motor (among them: B; F grade commonly used)
1. Acetal enameled wire; Class E
2. Polyester enameled wire: Class B
3. Modified polyester enameled wire: Class F
4. Modified polyester imine enameled wire: Class H
5. Amide-imide enameled wire: Class C
Different insulation grades represent different insulation materials of the motor, and the difference in heat resistance is also the allowable temperature rise. For example: Class B temperature rise allows 80K; Class F allows 100K; Class H allows 125K (all measured by resistance method). At present, the A.E level has basically been eliminated.