Shutting Down
When shutting down the turbine the load may be taken off before closing the throttle; or, as in the case of a generator operating on an independent load, the throttle may be closed first, allowing the load to act as a brake, bringing the turbine to rest quickly. In most cases, however, the former method will have to be used, as the turbine generally will have been operating in parallel with one or more other generators. When this is the case, partially close the throttle just before the load is to be thrown off, and if the turbine is to run without load for some time, shut off the steam almost entirely in order to prevent any chance of the turbine running away. There is no danger of this unless the main valve has been damaged by the water when wet steam has been used, or held open by some foreign substance, when, in either case, there may be sufficient leakage to run the turbine above speed, while running light. At the same time, danger is well guarded against by the automatic stop valve, but it is always well to avoid a possible danger. As soon as the throttle is shut, stop the condenser, or, in the case where one condenser is used for two or more turbines, close the valve between the turbine and the condenser. Also open the drains from the steam strainer, etc. This will considerably reduce the time the turbine requires to come to rest. Still more time may be saved by leaving the field current on the generator.
Care should be taken, when the vacuum falls and the turbine slows down, to see that the water is shut off from the glands for fear it may leak out to such an extent as to let the water into the bearings and impair the lubricating qualities of the oil.