Lubrication of the four bearings, which are of the self-adjusting, ball and socket pattern, is effected by supplying an abundance of oil to the middle of each bearing and allowing it to flow out at the ends. The oil is passed through a tubular cooler, having water circulation, and pumped back to the bearings. Fig. [33] shows the entire arrangement graphically and much more clearly than can be explained in words. The oil is circulated by a pump directly operated from the turbine, except where the power-house is provided with a central oiling system. Particular stress is laid by the builders upon the fact that it is not necessary to supply the bearings with oil under pressure, but only at a head sufficient to enable it to run to and through the bearings; this head never exceeding a few feet. With each turbine is installed a separate direct-acting steam pump for circulating oil for starting up. This will be referred to again under the head of operating.
Generator
The turbo-generator, which constitutes the electrical end of this unit, is totally enclosed to provide for noiseless operation, and forced ventilation is secured by means of a small fan carried by the shaft on each end of the rotor. The air is taken in at the ends of the generator, passes through the fans and is discharged over the end connections of the armature coils into the bottom of the machine, whence it passes through the ventilating ducts of the core to an opening at the top. The field core is, according to size, built up either of steel disks, each in one piece, or of steel forgings, so as to give high magnetic permeability and great strength. The coils are placed in radial slots, thereby avoiding side pressure on the slot insulation and the complex stresses resulting from centrifugal force, which, in these rotors, acts normal to the flat surface of the strip windings.
Operation
As practically no adjustments are necessary when these units are in operation, the greater part of the attention required by them is involved in starting up and shutting down, which may be described in detail as follows:
To Start Up
First, the auxiliary oil pump is set going, and this is speeded up until the oil pressure shows a hight sufficient to lift the inlet valve and oil is flowing steadily at the vents on all bearings. The oil pressure then shows about 20 to 25 pounds on the "Relay Oil" gage, and 2 to 4 pounds on the "Bearing Oil" gage. Next the throttle is opened, without admitting sufficient steam to the turbine to cause the spindle to turn, and it is seen that the steam exhausts freely into the atmosphere, also that the high-pressure end of the turbine expands freely in its guides. Water having been allowed to blow out through the steam-chest drains, the drains are closed and steam is permitted to continue flowing through the turbine not less than a half an hour (unless the turbine is warm to start with, when this period may be reduced) still without turning the spindle. After this it is advisable to shut off steam and let the turbine stand ten minutes, so as to warm thoroughly, during which time the governor parts may be oiled and any air which may have accumulated in the oil cylinder above the inlet valve blown off. Then the throttle should be opened sufficiently to start the turbine spindle to revolving very slowly and the machine allowed to run in this way for five minutes.