Chapter 16. -AUXILIARY STEAM TURBINES 



arms which bear on a push rod assembly. The 

 push rod assembly is held down by a strong 

 spring. 



Because of centrifugal force, the position of 

 the flyweights is at all times a function of tur- 

 bine speed. As the turbine speed increases, the 

 flyweights move outward and lift the arms. As 

 the speed of the turbine approaches the speed 

 for which the governor is set, the arms lift 

 against the spring tension. If the turbine speed 

 begins to exceed the speed for which the governor 

 is set, the flyweights move even farther out, 

 thereby causing the governor valve to throttle 

 down on the steam. 



When the turbine slows down, as from an in- 

 crease in load, the centrifugal force on the fly- 

 weights is diminished and the governor push rod 

 spring acts to pull the flyweights inward. This 

 action rotates the lever about its pivot and opens 

 the governor valve, thus admitting more steam 

 to the turbine. The turbine speed increases until 

 normal operating speed is reached. 



The speed-limiting governor acts as a 

 constant- speed governor when the turbine is op- 

 erating at or near rated speed, although it 

 is designed only as a safety device to prevent 

 overspeeding. The governor has no effect on the 

 speed of the turbine at speeds below about 95 per- 

 cent of rated speed. 



Trips 



Several kinds of trips are used as safety de- 

 vices on auxiliary turbines. 



Overspeed trips are used on turbines that 

 have constant- speed governors. The overspeed 

 trip shuts off the supply of steam to the turbine 

 and thus stops the unit when a predetermined 

 speed has been reached. Overspeed trips are 

 usually set to trip out at about 110 percent of 

 normal operating speed. In the past overspeed 

 trips were used primarily on constant- speed tur- 

 bines and on some commercial-type variable- 

 speed units. Recent specifications require over- 

 speed trips onallnavalauxiliary turbines of over 

 100 horsepower. Figure 16-13 shows the con- 

 struction of an overspeed trip used on turbogen- 

 erator. 



Back-pressure trips are installed on turbo- 

 generators to protect the turbine by closing the 

 throttle automatically when the back pressure 

 (exhaust pressure) becomes too high. A back- 

 pressure trip is shown in figure 16-14. 



Emergency hand trips are installed on turbo- 

 generators to provide a means for closing the 

 throttle quickly, by hand, in case of damage to 



BELL CRANK HANDLE 



EMERGENCY GOVERNOR 

 DETAIL 



TRIP ROD 



OIL PIPE 



PLUNGER 



38.93 

 Figure 16-13. — Overspeed trip for turbogen- 

 erator. 



ADJUSTING 

 BUSHING 



LOCKNUT 



96.25 



Figure 16-14.— Back-pressure trip. 



435 



