GOVERNORS 249 



For installations with long penstocks the regulation becomes 

 much more serious and is difficult to calculate accurately due to 

 the many variable factors involved, such as the length of the pipe 

 line, the effective head and velocity of flow, time of governor 

 action, flywheel effect and effect of standpipes, etc. 



The final speed after a load change will be that due to the 

 initial kinetic energy of the rotating parts and the excess or 

 deficiency above or below the load requirements during the time 

 of gate adjustment. This excess or deficient energy is due to the 

 excess or deficiency in the quantity of water during the change in 

 addition to that of the energy required to accelerate or retard the 

 water column in the penstock. 



The effect of a standpipe must also be considered in absorbing 

 the excess power. When such a structure of sufficient size is 

 installed close to the wheels, the conditions will approach those of 

 an open flume, while, if located some distance from the plant, 

 they become similar to those of a closed penstock of a Jength equal 

 to the distance from the draft-tube to the standpipe. 



Action of Governor. The obvious tendency of a governor, as 

 explained above, is to permit the speed to oscillate above and below 

 normal. A successful governor must, therefore, anticipate the 

 effect of any gate movement, and in order to overcome the effect 

 of the pressure change in the penstock the governor must move 

 the gate slightly beyond the final position, in order to restore the 

 speed to normal; the final motion of the gate being a slow move- 

 ment back to the final position. This last slow movement is con- 

 trolled by the compensation device as explained. The percentage 

 variation in speed which will occur before the governor begins to 

 move the gate, or the limits within which the governor is inopera- 

 tive, should be a minimum. This is generally realized with 

 hydraulic governors where it varies from practically nothing to 

 0.75 per cent. 



The speed with which the governor moves the gate is a most 

 essential element of a good governor. No general rule can be 

 given of the rate at which the governors should open or close the 

 gates. It can be more rapid the shorter the penstock and the 

 lower the velocity of the water. The effect of both rapid opening 

 and closing of the gates should be investigated in every projected 

 plant, in order to guard against drawing down the pressure at 

 critical points in the penstock below that of the atmosphere, and 



