Improvement of unbalanced current capability of large turbine generators

This paper deals with the influence of unbalanced currents on the design and operation of large turbine generators. With the demand for electric power doubling every decade, generator ratings are growing very rapidly, and at the same time reliability and availability are becoming major considerations. It is necessary to raise the capability of unbalanced loading by introducing components that can reduce the eddy current loss of rotor surfaces, keeping the local temperature rise within a reasonable value, since the surface loss density increases with electromagnetic loading in large machines. Conclusions deduced from analysis, factory model tests, factory unbalanced current tests and operating experiences show num. erically that full-length amortisseurs, particularly those with several bars in the pole faces, are highly effective in reducing the surface temperature and in satisfying the required degree of reliability and availability in the unbalanced current operation of large generators.