Research On Electrical Field Distribution In Insulation Structures Of Stator Bar In HV Generators

The reliability and stability of high voltage generators depend on theirdesign and manufacturing level. For current gigawatt generators, theinsulation issue has become an important issue in the design andmanufacture of these generators because of their higher rated voltage.Insulation structure of stator bar, plays a very important role in the wholeinsulation system in a generator, as its technology level influence theinsulating ability of the entire generator. Therefore, it is necessary forinsulation structure research about the stator bar.The design and research of insulation structure of the stator bar inhigh voltage generators take into account electrical, thermal, mechanicalfactors and so on. But discharge problems caused by large electrical fieldin some areas are the leading cause of insulation damage, so electricalfactors are the primary consideration in the research. Three areas of statorslots, inner shielding and end of bar, where corona discharge usuallyappears, should be researched.Based on numerical method, anti-corona structures of semi-conductorpad, corrugated pad in slots, inner shielding inside the bar and threeanti-corona layers at the bar end were established in COMSOLMultiphysics to be computed and analyzed for electrical field distributionin this paper. And the influence on electrical field distribution from theparameters of materials and structures was also studied.The results showed, in insulation structures of semi-conductor pads,the highest potentials on the anti-corona layers were usually on the middlesurface between the gaps and the anti-corona layers, and the potentialswere nearly in direct proportion to the surface resistivity of anti-corona layers,the rated voltage of the bars and the square of the size of gap lengthbetween two semi-conductor pads; in corrugated pad structures,the highestpotentials were also on the middle surface of anti-corona layer beside thegap, and were lower than potentials on the anti-corona layers in structuresof semi-conductor pads; for inner shielding structure, the maximalelectrical field in the structure in the type of semi-conductor of lowresistivity and copper, was smaller than other structures such as the type ofputty insulation, electric conduction putty and Siemens binding type; in theend of the bar, the potential would be higher when the location on theanti-corona layers was further away from the rabbet of stator, and thepotential was lower on the low resistivity belt than the potential on highresistivity; the maximum field was in the main-insulation adjoiningrabbet,where it should be focused in the measures for anti-corona.