Generator Stator Coils Research Articles

Breakdown strength-enhancing study on anti-corona nonlinear material for high-voltage generator stator coils

Breakdown strength-enhancing study on anti-corona nonlinear material for high-voltage generator stator coils

Trend in Insulation Technology for Turbin Generator Stator Coil

Trend in Insulation Technology for Turbin Generator Stator Coil

発電機固定子コイルの直流耐電圧及び超低周波耐電圧試験法の検討

発電機固定子コイルの直流耐電圧及び超低周波耐電圧試験法の検討

Aging Properties of Mica Insulation Systems Impregnated with Solventless Resin for Generator Stator Coils

In these days, the solventless resin-impregnated mica insulation systems are extensively adopted to the large powergenerator stator-coil insulation systems as a result of rapid development of synthetic resin in recent years. Various destructive and nondestructive tests with these samples were made. The electrical properties were compared between the initial coils (which were measured by the electrical properties at the acceptance test) and the used coils (which were taken out from the generator winding that was used for about ten years). It is said that the winding insulation systems will change during long running times because of a number of factors such as thermal, mechanical, and electrical. Studies by the present authors show that used coils were not deteriorated by mechanical stress because electrical breakdown voltages did not decline in comparison with those of the initial coils, and also they were not deteriorated by electrical stress because the breakdown voltages of coils at the line side were lower than at the earth side. Therefore, some changes of the electrical properties in the nondestructive test seemed to result from thermal effects. As mentioned above, it is proved that solventless resin-impregnated mica insulation systems have kept good electrical properties in service for over ten years.

A matching network for discharge measurements at high voltages in unscreened test areas

A bridge network is described, which can attenuate bus-bar noise by factors ranging from 300 to 500 when making discharge measurements at very high voltages with an ERA discharge detector. Also it gives sufficient attenuation of noise from discharges on the guard ring of test samples, so that discharge measurements on samples of generator stator or motor coils with the ERA detector becomes possible. The performance of the bridge network as a filter is independent of the bandwidth of the detector and hence it can be used with either model 2 or model 3 ERA detectors.

Pyrolysis of Stator Coil Insulation in Air and Hydrogen

The study of changing properties of generator stator coil insulation on long-time exposure at elevated temperature is an accepted part of insulation development. This aging, however, has usually been done in air, while the windings of modem turbine generators operate in hydrogen atmosphere. Samples of synthetic resin bonded insulation were pyrolyzed in air and hydrogen at 200°C and one atmosphere. The gaseous, liquid, and residual products were analyzed by chromatography and infrared spectroscopy. Heated in air, the gases contained C3, C4, and C5 straight chain hydrocarbons, but the products in hydrogen contained, in addition, cyclohexane. The liquid and residual products indicate the sample pyrolyzed in air degrades by depolymerization and oxidation, while the sample in hydrogen depolymerizes, followed by some degree of hydrogenation.

Unique system cools generator stator coils

Unique system cools generator stator coils

Stator insulation for H-V inner-cooled generators

Inner-cooling of high-voltage generator stator coils has made possible greatly increased ratings for the magnetic and conductor materials in large hydrogen-cooled machines. This has required modification in some insulation design practices and application methods.