250 HYDRAULIC EQUIPMENT 



thereby causing danger of collapse, or permitting increases of 

 pressure beyond the strength of the penstock. 



The duration of the momentary variation between the first 

 departure of the speed from normal and its complete restoration to 

 steady speed should also be a minimum. It is governed by the 

 energy contained in the water column as well as the flywheel 

 effect. By increasing the flywheel capacity the speed variation 

 can be reduced, and thus a plant with a moderate length of pen- 

 stock and a small flywheel capacity will give a large momentary 

 variation over a short interval of time, while the same plant with 

 a larger flywheel capacity will give a comparatively small varia- 

 tion over a longer time interval. The latter is, however, more 

 favorable from an operating standpoint. 



The speed regulation of a number of 10,000-H.P. recently 

 installed reaction turbines, operating under a 96-foot head, at 

 185 R.P.M., is given in the following. It is based on a total fly- 

 wheel effect (WR 2 ) of 1,700,000, a pipe line diameter of 11 feet, 

 and a pipe length of 190 feet. 



Load change, per cent 10 25 50 100 



Speed change, per cent 0.9 2.1 3.5 16 



These governors were furthermore guaranteed to restore the 

 speed oAhe units to within 0.5 per cent of normal from any change 

 in load, and will begin to act before the speed has changed more 

 than 0.5 per cent from normal. 



An unnecessarily close regulation should not be required when 

 considering such extreme conditions as full load thrown suddenly 

 on or off a unit, conditions which seldom occur in a plant, and 

 when they do occur it is usually due to a short circuit or a dropping 

 of load under circumstances in which regulation ceases to be a 

 consideration. 



Pipe-line Pressure Caused by Governor Action. In order to 

 arrive at the maximum pressure developed in the pipe lines by the 

 governor action, the following formula may be used with sufficient 



aCCUraCy: P _0.027XLX. 



f 



where P maximum pressure change in pounds per square inch; 

 L = length of water column in feet; 

 v = velocity in feet per second ; 

 7 T =time in which water column is stopped in seconds. 



