Summary
Opposite to a slot Partial Discharges (PD), Vibration Sparking (VS) or “spark erosion” is to some extent scarcely known even though it is a fast deterioration mechanism and service failure in a relatively short time – just a few years of operation - have been reported. It is driven by the airgap flux in the core and can occur at any point of the winding, including at the neutral side. Vibration sparking requires 2 fundamental conditions to be generated: (i) the presence of an induced parasitic current flowing along the conductive slot coating of the bar/coil because the coating is much more conductive than “normal”; (ii) vibration of that bar/coil within the slot because the bar/coil must be loose in the slot and vibrating under the magnetic forces. VS is generated from repeated interruption of the parasitic current under the bar/coil vibration.
Read more Read lessA relatively simple methodology, based on electric circuit theory, which allows designers and owners/operators to assess the risk that sparking vibration will occur on a given large electric machine. The lower the surface resistance of the OCP/CAT is, the higher the risk of VS sparking. On the other hand, if the surface resistance is too high its function to prevent (slot)
PD will be jeopardized. Hydrogenerators usually have relatively low induced voltage per unit length and short cores. Therefore, an OCP/CAT surface resistance in the range of 1000 Ω/∎ to 10.000 Ω/∎ is quite suitable to prevent Vibration Sparking and (slot) Partial Discharges.
Additional informations
| Publication type | Session Materials |
|---|---|
| Reference | A1_10787_2026 |
| Publication year | |
| Publisher | CIGRE |
| Country | Brazil |
| Study committees | |
| File size | 831 KB |
| Price for non member | 30 € |
| Price for member | 30 € |
Authors
HILDINGER Thomas - Voith Hydro Brazil
Keywords
Vibration sparking, spark erosion, slot coating resistance, electrical degradation
