What is the difference between the withstand voltage requirements of loose embedded windings and formed windings?
Due to the possibility of direct contact between the first and last turns of loosely embedded round wire windings, the insulation of the wires should still be higher than the operating voltage (power frequency drive) or overshoot voltage (IGBT drive) at the end of life. Then when designing, the initial breakdown voltage that needs to be considered should be ten times higher than the operating voltage. For IGBT driven motors, this working voltage should use the overshoot voltage.
For flat wire forming windings, such as the currently commonly used "hairpin" windings, the currents among multiple wires of the same phase in the same slot all enter and exit at the same time. There is no voltage drop problem between turns. The voltage drop mainly exists in the slot. The voltage difference between the 2 phases (phase-to-phase voltage) and the voltage difference between the conductor and the core (voltage to ground). If the slot insulation and phase insulation are reinforced by methods such as insulating paper, the enameled rectangular wire can use a very thin coating thickness.

For windings without slot insulation and phase-to-phase insulation (development trend), the phase-to-phase insulation is provided by the paint film on both sides of the wire, and the insulation against the ground is a single-side paint film. Under the same voltage conditions, priority is given to the resistance to the ground voltage. Ability to withstand. Therefore, when designing, the insulation capacity data should be based on the measurement results of the paint film on one side. If the overshoot voltage can be controlled at 1.5 times the rated voltage, for an 800V system, the overshoot voltage is 1200V, and one side of the flat wire is required. The paint film's voltage resistance exceeds 12,000V.


Linear relationship between PDIV and breakdown voltage

Comparing the breakdown voltage and PDIV of enameled wire, there is a certain linear relationship. The corona-resistant enameled round wire with a film thickness of 0.1mm (both sides) has a PDIV value of about 820V, but its breakdown voltage is as high as 12KV, and its breakdown voltage at the end of its 20,000-hour aging life at 220°C is higher than 1,200V. The PDIV value of a corona-resistant flat wire with a film thickness of 0.13mm is about 900V, and the back-to-back breakdown voltage is as high as 14KV. Theoretically, as the insulation withstand voltage capability decreases, its PDIV value will also decrease accordingly. When the PDIV resistance value drops below the overshoot voltage, partial discharge will occur, resulting in accelerated aging of the insulation. Therefore, when using a high PDIV solution, how to slow down the aging of the insulation becomes very important.
When slot insulation is eliminated and a high PDIV solution is adopted, the 800V system requires a single-side PDIV of 1200V. According to the current enameled wire materials and manufacturing levels, there are still many difficulties to overcome for ultra-thick insulated enameled flat wires, which cannot meet such requirements. High PDIV requirements require compound extruded PEEK coating on the enameled coating.