The insulation performance of Enameled Wire is related to temperature. First, the state of polymer data. The paint film of enameled wire is a polymer. Polymers will experience three material states with the increase of temperature: glassy state, highly elastic state and viscous state. The physical properties of the three states are as follows:
Vitreous State: rigid consolidated solid
Highly elastic: a solid with good elasticity similar to rubber.
Viscous fluid state: fluid with mobility
There is a performance called softening breakdown in the insulation test of enameled wire, which is mainly to assess the acceptable high-temperature level of the enameled wire paint film. If it goes beyond a certain temperature, the paint film will soften into a viscous fluid state and move like syrup.
After the enameled wire is used (wound into a motor or transformer, etc.), there is certainly stress or pressure between the wires. If the paint film is at a high temperature, causing the paint film to be in viscous flow state, the paint film between the enameled wires under pressure will cause the paint film to be squeezed to move in other directions due to pressure, causing the insulation layer to become thinner, thus causing the insulation performance of the enameled wire to drop.
If the temperature drops again, the paint film will drop again from the viscous state to a highly elastic state and then to a glassy state, thus recovering better insulation performance. However, there may also be a certain drop. The main reason is that the paint film was formed under pressure, resulting in eccentric paint film and thinner insulation thickness.
In the high-temperature state, the insulation has not been damaged, that is to say, there is no breakdown. If the insulation has been damaged, the damage point is still irreversible after the temperature drops.