Compared with windings of standard-brand motors, the coil manufacturing process for SIMO high-voltage motors is more complex: several layers of mica tape must be wrapped around formed coils, followed by additional low-resistance and high-resistance tapes. Mica tape wrapping can be performed manually, semi-automatically, or fully automatically—three methods in total. During mica tape wrapping, basic requirements—including uniform wrapping thickness, consistent tension, and absence of damage—must be met. In practice, fully automatic wrapping delivers the best results, eliminating interference from human factors; by contrast, semi-automatic and manual operations inevitably introduce uncertainties—both in lap consistency and tension control.

During the tape-wrapping process of SIMO high-voltage motors, maximum conformity between the wrapping tape and the winding, as well as between adjacent tape layers, must be ensured to prevent air gaps from forming—otherwise, final varnish impregnation and curing performance will be compromised, and partial discharge may even occur, directly impairing motor performance. It must also be emphasized that the low-resistance tape wrapped on the straight section of the coil and the high-resistance tape wrapped at the slot opening jointly reinforce insulation and suppress corona generation; therefore, tape integrity—i.e., freedom from damage—is mandatory.

1、High-voltage motorCharacteristics of coil corrosion

Under normal circumstances, high-voltage motor coils rarely exhibit quality issues; however, after sufficient operating time and under the influence of internal and external environmental factors, insulation corrosion and aging may still occur. Based on observed main insulation breakdown phenomena in high-voltage motor stator winding coils, corrosion-induced damage to the main insulation falls broadly into two categories: one originates externally and progresses inward—commonly termed “external corrosion”; the other originates internally and progresses outward—commonly termed “internal corrosion”.

2. Introduction to external corrosion damage

    During motor operation, electromagnetic forces cause vibration in the end-winding section, resulting in insecure fixation of coils within the stator core slots. This leads to loosening or detachment of slot wedges, inter-layer spacers, end-spacing blocks, and binding ropes. Friction then arises among coils, binding ropes, and spacing blocks, damaging anti-corona semiconductive paint and tape and triggering corona corrosion—ultimately causing main insulation breakdown in both slot and end-winding regions.

    Conductive foreign matter (e.g., iron filings) inside the stator core becomes magnetically attracted to the coil’s main insulation surface during motor operation. Under electromagnetic induction and electromagnetic force, such magnetic debris rotates, gradually wearing away the coil’s main insulation.

    Oil contamination infiltrating the winding from the operating environment causes delamination between insulation and conductor, reducing overall coil insulation strength. Prolonged operation under such conditions may lead to stator winding faults including phase-to-phase short circuits and ground faults.

    During stator core stacking, misaligned silicon steel laminations—or poor clamping of stator core ventilation duct steel plates and end pressure fingers—can induce motor vibration during operation, leading to insulation wear and eventual main insulation breakdown of the coils.

3. Characteristics of internal coil corrosion

Internal corrosion first manifests as whitening of the coil’s internal insulation, progressively expanding in area; subsequently, insulation burns and forms pits, accumulating substantial green powder—accelerating inter-strand conductor and main insulation corrosion until main insulation breakdown occurs. Additionally, thermal aging caused by excessive temperature is another significant factor contributing to internal corrosion.