The level of advancement in technological culture primarily depends on the development of energy sources for the needs of man. The use of steam and particularly electricity over the last one hundred years brought industrial rrevolution and grave a tremendous impetus to the development of society. In the last few decades worldwide production of electric energy has increased a hundredfold. The electric power of generating plants has grown to 2700 mln kw. If the rates of growth of generated energy remain the same, in 50 years from now the output of energy will reach 0.2% of the total energy the earth receives from the sum. Electric generators produce almost all the electric energy used, two-thirds of which is fed to electric motors to be converted to mechanical energy. Each year industry turns out tens of millions of electric machines and trasformers. In serial production now are turbine-driven generators of 500, 800, and 12000 MW, hydroelectric generators of 700 MW, and transformers rated at 1000 MVA. Today, motors and generators are an essential part of the fabriv of living, serving diverse purposes in industry, agriculture, and in the home.