Journal of electricity, power, and gas . he de-flecting nozzle is used only on the impulse type ofwater wheel, and so arranged that the water is de-flected from the runner blades. Draft Tubes and Tail Races. When the water leaves the turbine runners andproceeds through the draft chest into the draft tube,it ordinarily has a considerable velocity head whichshould be gradually converted into pressure head byso shaping the draft passages that the velocity is uni-formly decreased to a minimum. It is readily appre-ciated that the above would only be accomplished byeliminating any sudden changes in
Journal of electricity, power, and gas . he de-flecting nozzle is used only on the impulse type ofwater wheel, and so arranged that the water is de-flected from the runner blades. Draft Tubes and Tail Races. When the water leaves the turbine runners andproceeds through the draft chest into the draft tube,it ordinarily has a considerable velocity head whichshould be gradually converted into pressure head byso shaping the draft passages that the velocity is uni-formly decreased to a minimum. It is readily appre-ciated that the above would only be accomplished byeliminating any sudden changes in the direction ofthe water. The plant should be so located with respect to thetail race that full advantage is taken of whatever drafteffect there may be available. In general, tail raceshould consist of as unrestricted a water passage asconditions will permit. Electrical Control. In designing a hydroelectric plant, care should begiven to the subject of electrical control. If possible,the switchboard should be, for the sake of convenient. Electrically Operated Heaclgates. operation, compactly arranged. In most cases theswitchboard is located in full view of the plant andreadily accessible to the various parts of it. All re-mote controlled motors and solenoids on auxiliary ap-paratus should preferably be possible of operation froma point adjacent to the switchboard. A plant so de-signed will be more economical to operate than a plantin which the control devices are installed at variouspoints, because the operator can accomplish more atthe time when his services are most required. Electrically operated headgates are used exten-sively, resulting in a saving of labor and acting as aprotection to the plant in case of trouble. All modernplants are equipped with remote controlled governors,so that the speed may be varied by the switchboardoperator for purposes of synchronizing and as a meansof load adjustment when the machine is operating onthe system. Remote electrical control in case
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