High voltage generator insulation

The insulation of high voltage stator windings for electric utility generators must have a very high order of reliability. Machines of this category have always been of extreme importance because of their size with the accompanying high capital investment and the dependence of so many things in our society upon their continuous and uninterrupted operation. Lately, the size of these machines, particularly steam driven turbine generators, has increased tremendously, so that units are now being produced with ratings of 500 MVA and more on single shafts. Waterwheel generators are approaching a size of 300 MVA. These sizes will continue to increase in the future and it is almost a certainty that turbine generators will soon approach 1000 MVA, possibly within 5 years. This means that extremely large blocks of power are dependent upon the insulation. Figure 1 is a view in a winding aisle showing parts of a typical waterwheel generator and a turbine generator of the types employed by electric utilities.