Page:The steam turbine, the Rede lecture 1911 (IA steamturbinerede00parsrich).pdf/31

DYNAMO FOR TURBINE DRIVE 19 from 80,000 to 120,000 or more. With the first figure a loss of efficiency of about 10 per cent. below the highest attainable is accepted, and with the latter figure the deficit is only about 3 per cent.

The construction of a suitable dynamo to run with the turbine involved nearly as much trouble as the turbine itself: the chief features were the adoption of very low magnetic densities in the armature core and small diameters and means to resist the great centrifugal forces as shown in the views on page 18. The dynamo was also mounted in elastic bearings. Now that the turbine has found its most suitable field in large powers to which we always looked forward and as the speed of revolution has been consequently reduced, elasticity in the bearings is less essential, and in large land plants and in marine work rigid bearings are universal. There are many forms of turbines on the market. It is only necessary, however, for us here to consider the four chief types which are:— 2-2