US1726561A

US1726561A - Power plant

Info

Publication number: US1726561A
Application number: US749267A
Authority: US
Inventors: Hodgkinson Francis; Robert C Allen
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1924-11-11
Filing date: 1924-11-11
Publication date: 1929-09-03
Anticipated expiration: 1946-09-03

Description

5Pt3, 1929. v F. HoDGKINsoN ET A1.M l 1,726,561

POWER PLANT l I Filed N0v 11, 1924 2 Sheets-Sheet l RLNenw F. HodqkiNsoN `INVENTORS. 4

ATTORNEY et.- 3, 1929. F. HoDGKlNsoN ET Ax. 1,726,561

POWER PLANT Filed Now-11, 1924 2 Sheets-Sheet 2 ATTORN EY Patented Sept. 3, 1929.

UNITED STATES 1,726,561 PATENTl OFFICE.

FRANCIS I-IO'DGKINSON AND ROBERT C. ALLEN, 0F SWARTHMORE, PENNSYLVANIA,

ASSIGNOR-S 'I'O WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A COR- PORATION OF IENNSYLVANIA.v

POWER PLANT;

Application filed November 11, 192,4. Serial No. 749,267.

Our invention relates to power plants, particularly to power plants in which motive fluid having a relatively high pressure 1s employed and it has for an object to provide apparatus of the character designated which shall operate efliciently and reliably for extended periods of time. It has fora further object to embody in the power plant means for automatically controlling theflow of the u) motive fluid to and the flow of the exhaust fluid from the prime moversand for automatically continuing the circulation of the motive fluid through the pressure generating apparatus upon a stoppage of the prime i5 mover.

These and other objects which will be made apparent throughout the further description of the invention7 may be attained by the employment of the apparatus hereinafter described and illustrated in the accompanying drawings in which Fig. 1 is a diagrammatic illustration of a power plant arrangedin accordance with my invention and Fig. 2 is a detailed view of the auto stop mechanisms associated with the high pressure and the low pressure turbine elements.

In power plants employing kmotive fluid having a relatively high pressure and temperature, and in which the fiuid exhausted by the high pressure turbine element is conveyed to the inlet of a low pressure turbine element, it is advisable in the interests of efficiency to reheat, or, to again superheat thefluid prior to its entrance into the' low pressure turbine element. Furthermore, it is customary to associate with the respective turbine elements, means responsive to their speed for governing the admission of motive fluid thereto,

thereby avoidingr the possibility of serious injury to the turbine element from overspeeding. The restriction of the supplyof motive fluid to the high pressure or the" low pressure turbine elements by their respective 'governors may result in the rapid accumulation of excess pressure within the fluid pressure generating device, namely, the boiler, and the superheater and reheater elements ass'o ciated therewith. As it is customary to pro'- vide the boiler and the superheater with a safety valve, any excess fluid` pressure which may accumulate therein is automatically relieved to the atmosphere or to a condenser. However, such a condition resultsV inl a total absence of. circulation of fluid through the reheater which, because of the high operating `temperatures normally prevailing therein,

may be ruined or burnt out in a comparatively short time. While it has been known to provide manually-operated' means for circulating'a cooling Huid through the reheater in such an emergency, nevertheless this method is extremely hazardous inasmuch as the safety of the reheater is solely dependent upon the degree of vigilance exercised by the operating personnel.

Furthermore, in installations wherein the high lpressure turbine element exhausts through 'a reheater to a low pressure turbine element, the closing` of the fluid admission valve of' the high pressure turbine element by its governing mechanism results in the immediate generation of an excessive pressure Within the reheater because of the total absence of proper circulation. Such a condition may create excessive pressures within the low pressure turbine element and result in serious damage to the same. In this case, manuallyoperated means have also been provided heretofore for closing the admission valve of the low pressure vturbine element and for directing the uid pressure generated within the reheater'directly to the condenser. Here again, however, the safety of the low pressure turbine element is solely dependent upon the degree of vigilance exercised 'by the operating personnel. The latter practice is extremely dangerous, inasmuch as the operating temperatures, pressures and velocities usually employed in power plants of this type are relatively high and may result in serious damage being -incurred almost momentarily.

We have entirely overcome the above diiiiculties by incorporating in the power plant novel automatic devices by means of which the lif'e of the apparatus ris continually safeguarded. This is accomplished by providing means for conveying the Huid discharged by the boiler and the superheater safety valve to the inlet of the reheater, whereby the excess fluid pressure `accumulating within the boiler and the superheater element, upon a closure of the fluid admission valve associated with the high pressure turbine ele ment, is conveyed to the reheater and is circulated therethrough as cooling fluid. Furthermore, we associate with the high pressure turbine element and also with the low pressure turbine element, a mechanismV fer sistemati# l turbine element.

cally diverting, upon an overspeeding of either turbine or upon an abnormal fluctuation in the speed of the high pressure turbine, the motive fluid from the inlet of the low pressure turbine and for redirecting it to the condenser.

With the above arrangement, a closure of the high pressure admission valve by its governor results in conveying the fluid pressure, relieved by the consequent opening of the boiler and superheater safety valve, to the reheater. Upon being circulated therethrough it is conveyed by an automatic device .directly to the' condenser andnot to the. low pressure turbine thereby preventing the accumulation of any excess of pressure or temperature Within the reheater or the loW pressure turbine element. Our apparatus is so yarranged that the latter condition is effected coincident with an overspeeding of either the high pressure or the low pressure turbine elements, or upon an abnormal fluctuation in the speed of the high pressure The possibility of injury to the several elements comprising the power plant from numerous causes such as a sudden dropping of the electrical load or an unusual fluctuation in the pressure of the motive fluid is consequently reduced to a minimum, thereby increasing the reliability of the entire plant and, because of the reduced operating personnel required and the absence of serious damage repairs, effecting a considerable economy in the operating costs.

Referring to the drawings for a more detailed description of our invention, We show in Fig. 1 a boiler 10 comprising a Water drum 11, a steam 'drum 12, and a heating element 13. Provided in the Water drum 11 is an inlet connection 14 for the admission of feed Water and provided in the steam drum 12 is an outlet connection 15 for the discharge of saturated steam. The saturated steam is conveyed by means of a conduit 16 to a superheater 17, usually associated With the boiler in the same furnace structure. The superheater 17 is provided with an inlet header 18, an outlet header 19, and a heating element 20. Provided in the outlet header 19 are outlet nozzles 21 and 22 for the discharge of superheated steam and for the reception of a safety valve 30. The superheated steam discharged through the nozzle 21 is conveyed by means of a conduit 23, ay control valve 24, a regulator valve 25 and a conduit 26 to an inlet connection 27 of a high pressure turbine element v28.

The motive fluid exhausted by the high pressure turbine element 28 is discharged through an outlet nozzle 29 to a conduit 31 Which conveys it to a reheater 32. This reheater, if desired, may be associated With the boiler and the superheater in the same furnace structure. It is provided With an inlet header 33 and a discharge header 34 from which the reheated fluid is conveyed by means of a conduit 35 to a T fitting 36. Disposed on opposite sides ofthe T fitting 36 are

valves

37 and 38 Which are automatically actuated in a manner to be hereinafter described. The valve 37 may convey the reheated fluid by means of a conduit 39 to an inlet connection 41 of a low pressure turbine element 42. The fluid exhausted by the loT pressure turbine element 42 is conveyed by means of an exhaust trunk 43 to a condenser 44. .The condenser 44 is provided with an inlet nozzle 45 for `receiving the reheated fluid which may be conveyed through the valve 38. A conduit 46 connects the valve 38 Vand the inlet connection 45 of the condenser, and it is customary to provide this conduit With a relief valve 47 for prevent.- ing the creation of an excessive pressure Within the condenser, should the supply of cooling Water fail.

The safety valve 30, Which is associated with the superheater 17, is of a type especially adapted for use with motive fluids having high temperatures and pressures and which is disclosed in a copending application of Robert C. Allen, Serial No. 749,288, filed November 11, 1924, and assigned to the Westinghouse Electric and Manufacturing Company. While We have illustrated this one form of safety valve, it is to be understood that our invention is not so' limited and that We may readily employ any of the Well-known types of safety valves generally employed in 'this art. Briefly speaking, the safety valve 30 comprises a body portion 51 having disposed therein tvvo valve discs arranged in series, a disc 52 for regulating the flow of the motive fluid escaping from the superheater and the boiler, and a valve disc 53 for controlling the floW of the fluid. The valve discs 52 and 53 are actuated by a servo-motor 54 of Welllnown type, the movements of which are controlled by a pressure-responsive mechanism 55. The movements of the pressure-responsive mechanism 55 are in turn controlled by the pressure prevailing Within the boiler 10 and the superheater 17. We therefore provide a conduit 56 Which communicates With the pressure-responsive mechanism 55 and With the Water drum 11 of the boiler 10. We have found from actual practice that the cutting or erosive action of high temperature steam upon the pistons of pressure-responsive mechanisms isexcessive and We, therefore, illustrate a novel method of transmitting the pressure prevailing Within the boiler and the superheater to the pressure-responsive mechanism in such manner as not to convey the prevailing high temperatures thereto'. This may be accomplished by tapping into the Water drum 11 and by trapping or arranging a U-shaped portion 57 in the conduit 56. In this manner, relatively cold Water acts upon the piston of the pressure-responsive mechanism and the life of the apparatus is consequently prolonged. The excess fluid discharged by the safety valve 3() is conveyed by means of a conduit 58 to the inlet header 33 of the reheater 32.

The regulator valve 25 is provided with a spring 61 for biasing the valve to a closed position. The valve is actuated through suitable levers by a servo-motor 62, of well-known construction. Theservo-motor 62 is in turn controlled by any speed-responsive device such as a centrifugal governor 63 actuated by the rotations of a rotor shaft 64, provided in the high pressure turbine element 28. In addition to controlling the movements of the regulator valve 25, the centrifugal governor 63 actuates the

valves

37 and 38 for controlling the flow of the motive fluid .discharged by the reheater 32. This is'accomplished in a novel manner by providing a lever 65 which has suspended from the end remotely disposed 'from the turbine rotor shaft 64, a piston rod 66 and a piston 67. The piston 67 is disposed in a floating cylinder 68 provided with a passage 69 for maintaining communication betweenthe opposite sides of the piston 67. Any suitable liquid, such as oil, may be placed within the cylinder 68l and this oil is conveyer back and forth through the passage 69 by the movements of the piston with respect to the cylinder 68. A handoperated needle valve 71 is disposed in the passage 69 for accurately regulating the flow of the oil therethrough. A spring 72 is provided within the floating cylinder 68 for. returning the cylinder to its median position.

The floating cylinder 68 is connected by means of

suitable levers

73, 74, and 75 to a pilot valve 76 associated with. a power cylinder 77. The pilot valve 76 is disposed Within a suitable cylindrical chamber 78 provided with a fluid inlet connection 79 and

fluid outlet connections

80 and 81. The cylindrical chamber for the pilot valve 76 communicates, by means of a plurality of passages 82 to 86, inclusive, with a cylindrical chamber 87 for housing a secondary pilot valve 88. The secondary pilot valve 88 is actuated by means of a power cylinder 89 in a manner to be hereinafter described. The cylindrical chamber 87 in turn communicates with the power cylinder 77 through suitable ports 91 and 92. Pivotally connected to the lever 75 by a piston rod 93 is a piston 94 which is disposed-within the power cylinder 77 and which in turn is connected by means of a rod 95 and lever 96 to valve stems 97 and 98-

ofthe valves

37 and 38 respectively.

The low pressure turbine element 42 is provided withv a rotor shaft 111 which has associated therewith an auto stop mechanism 112, shown to a larger scale in Fig. 2. The auto stop mechanism 112 is ofr a type well-,known in the art and, as shown in Fig. 2, includes an eccentrically Weighted member 113 which, when displaced by a predetermined overspeeding of the turbine element, moves a latch 114 to trip a lever 115. Associated with thelever 115 is a pilot valve 116 disposed in a suitable chamber 117 having a fluid inlet port 118 and a fluid outlet port 119. The lever 115 normally holds the pilot valve 116 in the position illustrated but `upon a tripping of this lever by the eccentrically weighted member 113, a spring 121`is provided for moving the pilot valve/116 to shut off the communication normally provided between the inlet port 118 and the outlet port 119.

A similar auto stop mechanism 122 is associated with the rotor shaft 64 of the high pressure turbine element 28. The fluid outlet connection 119 of the auto stop mechanism 122 communicates, through a conduit 123, with the inlet connection 118 of the auto stop mechanism 112 which is associated with Athe low pressure turbine element 42. The outlet port 119 of the latter communicates, through a conduit 124 and

branch conduits

125 and 126, with a power cylinder 127 associated with the control valve 24 and the power cylin.- der 89 associated with the secondary pilot valve 88. The powercylinder` 127 has disposed therein a piston 128 which actuates, through a rod 129, the control valve 24.` A

spring 130 is provided for biasing the valve to a closed position. The power cylinder 89 is provided with a piston 131 which is connected through a rod 132 to the secondary pilot valve 88. The piston 131 may be made a rather loose fit within the cylinder 89 in order to further insure reliability of operation. A leak-off connection 133 is therefore provided for discharging the liquid which continually leaks between the periphery of the piston 131 and the inner walls of the cylinder 89. We believe it to be advisable to employ such construction in all of the power cylinders employed. A spring 134 is provided for actuating the secondary pilot valve 88 upon a failure of the oil pressure.

While we have illustrated, in the above embodiment of our invention, two independent prime moversor turbine elements connected in series, it is to be understood that our invention may be readily employed with any number of turbine elements and with various arrangements of turbine elements as well as with a single turbine having a plurality of pressure stages.

The operation of the above embodiment is as follows: Feed water is injected into the boiler 10 through the inlet connection 14 in the usual manner, and the saturated steam generated is discharged through the outlet connection 15 and the conduit 16 to the inlet header 18 of the superheater 17. The superheated steam is thence discharged throug the conduit 23, control valve 24, regulator valve 25 and conduit 26 to the inlet connection 27 of the high pressure turbine element 28. The steam is thereafter exhausted by the high pressure turbine elementat a relatively lower pressure and at substantially the temperature of saturation It is thence conveyed, by means of the conduit 31, to the inlet header 33 of the reheater 32, and is again superheated after which it is conveyed, by means of the conduit 35, to the 'l' fitting 36. Under normal operating conditions, the valve 37 is maintained in an open position while the valve 38 is maintained in a closed position and the reheated steam is therefore conveyed through the conduit 39 to the inlet connection 41 of the low pressure turbine element 42. Upon being discharged therefrom, it is finally conveyed to the condenser 44.

The speed of the high pressure turbine element 28 is maintained substantially constant by means of the centrifugal. governor 63 which actuates the servo-motor 62 to control the movements of the regulator valve 25 in a manner well known in the art. Should the speed of the high pressure turbine element exceed a predetermined amount, the centrifugal governor 63 moves to substantially close the regulator valve 25 to reduce the amount of motive fluid admitted to the turbine. Such a reduction in the flow of the motive fluid results in a rapid accumulation of excess fiuid pressure within the boiler 10 and the superheater 17, which excessive pressure is ccnveyed by means of the conduit 56 to the pressure responsive mechanism 55. The pressure responsive mechanism consequently actuates the servo-motor 54 to open the safety valve 30, permitting the excess fluid to escape through the conduit 58 to the inlet header 33 of the reheater 32.

Assuming the high pressure turbine element 28 to be operating in a normal manner, the fluctuations in its speed are naturally confined within rather narrow limits by the centrifugal governor 63, and the extent of the movements imparted by the latter to the lever 65 and the piston 67 is consequently rather limited. These relatively slow reciprocatory movements of the piston 67 by-pass the liquid or oil which is present in the floating cylinder 68 through the restricted passage 69 to each end of the cylinder alternatively. In this manner,the movements of the lever 65 and of the centrifugal governor 63 are not transmitted to the lever 73 upon normal fluctuations in the speed of the turbine.

Should, however, the speed of the turbine element grow excessive, or, should there be a sudden increase in the speed of the turbine element from any cause whatsoever, the flow area through the passage 69 being restricted by the needle valve 71, is not sufficient for permitting the rapid displacement of the oil and the floating cylinder 68 is therefore drawn upwardly, moving the lever 73. The movement of the lever 73 is imparted, by .means of the

levers

74 and 75, to the pilot valve 76.

The pilot valve 76 is normally maintained in the position illustrated, as is the secondary pilot valve 88. Any extraneous fluid under pressure, such as oil, may besupplied to the fluid inlet connection 79 from whence it is conveyed by the passage 83 and the port 91 to the upper portion of thefpower cylinder 77. This oil pressure is normally maintained upon the upper face of the piston 94, holding the valve 38 in a closed position and the valve 37 in van open position. Upon a downward movement of the pilot valve 76, the oil under pressure is conveyed through the passage 85 and the port 92 to the lower portion of the power cylinder 77. and moves the piston 94 upwardly. The upward movement of the piston 94 opens the valve 38 and closes the valve 37, thereby shutting off the supply of reheated steam to the low pressure turbine element and conveying it directly to the condenser. VVith an arrangement such .as this, the low pressure turbine element is not subjected to sudden surges occuring in the motive fluid exhausted by the high pressure turbine element and, in addition, the circulation of fluid through the reheater is not interrupted.

Should the above-mentioned overspeeding f or sudden increase in speed reach such an eX- tent as to cause the centrifugal governor 63 to substantially close the regulator valve 25 momentarily, the safety valve 30, being preferably of the very sensitive type illustrated, discharges the excess fluid pressure accumulating within the boiler and the superheater through the conduit 58 to the reheater from whence it is conveyed to the'condenser. Upon the high pressure turbine element returning to its designed operating speed, the centrifugal governor actuates the various control mechanisms in a reverse manner to return the fluid-controlling means to their norm al operating positions. The arrangement of a power plant as above described reduces to a minimum the possibility of serious damage being incurred by its several elements upon very sudden changes in load, etc., thereby providing a longer life for the apparatus and insuring an absence of serious shut-downs.

Should the centrifugal. governing device be rendered inoperative for any reasons whatsoever, permitting the high pressure turbine element 28 or the low pressure turbine element 42 to attain an excessive speed, the

auto stop mechanisms

112 and 122 are adapted to close the fluid inlet to the high pressure turbine element 28 and to convey the steam discharged from the reheater 32 directly to the condenser 44. This is accomplished as follows: Any fluid under pressure, such as oil, is supplied to the inlet 118 of the auto stop mechanism 122, which is normally .held

in the position illustrated in Fig. 2, and isy conveyed through the outlet port 119 and con-4 24 and the upper side ofthe piston 131 asso.

ciated with the secondary pilot valve 88.

Attention is directed to the fact that should this oil pressure fail for any reason whatsoever, the apparatus is so constructed that the f spring 130, which the pressure of the oil maintains under compression, moves the piston 128 to close the control valve 24, thereby shutting off' the supply of motive fluid to the high pressure turbine element. This failure of t e oil supply also permits the spring 134, which is held under compression by the pressure of the oil, to move the piston 131 and the secondary pilot valve 88 upwardly. This upward movement allows the oil under pressure, which is normally present in the passage 84, to be conveyed through the port 92 to the lower portion of the power cylinder 77 and permits the oil, which is present in the upper portion of the cylinder, to be discharged through the port 91 and the passage 82 tothe outlet connection 80. The vresultant upward` movement of the piston 94 opens the valve 38 and closes the valve 37, thereby shutting off the supply of motive fluid to the low .pressure turbine and conveying the fluid discharged from the reheater directly to the condenser 44. The apparatus is thereforenotsuscepticle to damage upon afailure of the oil supply.

Should either the high `pressure turbine element 28 or the low pressure turbine element 42 attain an abnormally high speed, the eccentrically Vweighted member 113 is thrown outwardly by the action of centrifugalforce, moving the latch 114 to trip the lever .115, thereby permitting the spring 121 to move the pilot valve 116 to shut olf communication between the inlet port 118 and the outlet port 119 of whichever auto stop mechanism is 1associated with the over-speeding turbine. Such a movement of either auto stop mechanism causes a failure of the oil pressure and this failure of oil pressure acts in a manner simi lar to that heretofore described, to `shut `olf the supply of steam to the high `pressure andl low pressure turbine elements, and to convey the steam circulated through the reheater by the safety valve to be discharged to the con-` denser. A hand resetting of 'the 'auto .stop

mechanism is necessary before .resuming operation. u

`While we have shown our invention 1n but one form, it will be 'obvious to thoseskilled' fications, without departing from the spirit thereof, and we desire, therefore, that only such limitations shall `bey placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

n What we claim is:

I1. In a power plant, the combination of a prime mover, .a generating device for supplying motive fluid to the prime mover, a heater for increasing the temperature of the Huid exhausted by the prime mover, and automatic means for maintaining a circulation of motive fiuid frornthe generating device through the heater upon a stoppage ofthe prime mover.

2. In a power plant, the combination of a prime mover, a generating device for supplying motive Huid to the prime mover, a heater for increasing the temperature of the fluid exhausted by the prime mover, and means responsive to changes in the `pressure of the fluid within the generating device, as affected by a stoppage of the prime mover,

for conveying fiuid'from the generating de` plying motive fluid under pressure to the` prime mover, speed responsive 4means associated with the prime lmover for controlling the flow of theimotivegfluid thereto, `a heater for increasing theV temperature of the ffiuid exhausted 'by the prime mover, and meansv for `conveyingfiuid from the generating device to the heater uponashutting off, b the speed responsive fmeans, of `a supply o mo- 'tive fluid to the prime mover.

5. In a power plant, the combination of a prime mover, a boiler for supplying motive fluid to the prime mover,a heater for increasing the temperature of the fluid exhausted by the prime mover, means associatedwitli the prime mover for controlling the flow of the fluid from the boiler to the lprime mover, a safety valve associated with the boiler for permitting the discharge of surplus fluid therefrom upon a shutting of of the supply of motive 4Huid to the prime mover, and means for conveying the fluid discharged by the safety valve to the heater.`

`6. In a power plant, the combination of a prime mover, a boiler `for .supplying motive uid under pressure to the1 prime mover, a

[heater for increasing the temperature of the fluid discharged .bytheprime mover, a safety valve associated with the boiler, and communicating means provided between the safety Cil valve and the heater, whereby motive fluid under pressure is discharged from the boiler to the heater upon a stoppage of the supply of motive fluid to the prime mover. f

7 In 4a power plant, the combination of a prime mover, a boiler for supplying motive fluid under pressure to the prime mover, a heater for increasing the temperature of the iotive fluid exhausted by the prime mover, a relief valve for theboiler, communicating meansprovided between the relief valve and the heater, and fluid pressure means controlled by the 'pressure prevailing within the boiler for causing the relief valve to discharge motive fluid to the heater' upon a predetermined maximum pressure within the boiler'. 1

8. In a power plant, the combination of a prime mover, a boiler for supplying motive fluid under pressure to the prime mover, a heater for receiving the exhaust fluid from the prime mover, a relief valve associated with the boiler, communicating means provided between the relief valve and the heater, a fluidvpressure device for actuating the relief valve, a pressure responsive mechanism for controlling the movements of the fluid pressure actuating device, and a conduit, communicating with `thepressure responsive mechanism yand with the liquid containing portion ofthe boiler.

9. In a power plant, the combination of a high pressure turbine element receiving motive fluid, a rlow pressure turbine element receiving the motive' fluid exhausted by the high pressure turbine elementi, means for heating the motive fluid passing from' the high pressure tothe low pressure turbine element, and automatic meansfor controlling the flow of motive` ,fluidlfrom the heating means to the low pressure `element in response to an operating condition of one' of said turbine elements. i f 10. In a power plant, the combination of a high pressurerturbine element having fluid inlet means, a vlow pressure turbine element receiving the fluid exhausted by the high pressure turbine element, means for heating the fluid passing from the high pressure tur- Vbineelement to the 'low pressure turbine element, and speed responsive means associated with the high pressure turbine element for shutting off the supply of fluid from the heating means to the low pressure turbine element `Y yupon an abnormal fluctuationin the speed of the high pressure turbine element.

11. `In a power plant, the combination of a high pressure turbine element having fluid inlet means, a low pressure turbine element having fluid inlet means, means for condensing the fluid exhausted by the turbine elements, and means associated with one of the turbine elements for directing'the fluid exhausted by the high pressure turbine element "to the inlet of the low pressure turbine element during normal fluctuations in the speed of the one said turbine element and for directing the fluid` exhausted by the high Apressure turbine element to the condenser upon an abnormal fluctuation in the speed of the one said turbine element.

12. In a power plant, the combination of a high pressure turbine element having fluid inlet means, a low pressure turbine element having fluid inlet means, means for heating 'the fiuidexhausted bythe high pressure turbine element, means for condensing the fluid exhausted by the low pressure turbine element, and automatic means associated with the high pressure turbine element for directing fluid discharged from the heating means to the inlet meansof the low pressure turbine element during normal fluctuations in the speed of the high pressure turbine element and to the condensing means upon an abnormal fluctuation in the speed `of the high pressure turbine element.

13. In a power plant, the combination of a high pressure turbine element having motive fluid inlet means, a low pressure turbine element for receiving the fluid exhausted by the high pressure turbine element, means for heating the fluid prior to its entrance intov the low pressure turbine element, means for condensing the fluid exhausted by the turbine elements, and governing means associated with the high pressure turbine elementy for directing the flow of motive fluid from the heating means to the low pressure turbine element-during normalconditions of operation-and to the condensing means during` abnormal conditions of operation.

14. In a power plant, the combination of a high pressure turbine element having fluid inlet means, a low pressure turbine element having fluid inlet means, a condenser, means fer connecting the condenser to the exhaust portion of the low ,pressure turbine element, means for heating the fluid exhausted by the high pressure turbine element, communicating means provided between the heater and the inlet means of the low pressure turbine element and between the heater and the condenser, and speed responsive means associated with the high pressure turbine element for regulating the flow-of motive fluid thereto and for directing the flow of fluid 'from the heating means to either the inlet of the low pressure turbine element or to the condenser.

15. In a power plant, the combination of a high pressure turbine element having fluid inlet means, a generating device foi' supplying motive fluid to the high .pressure turbine element, a heater for increasing the temperature of the Huid exhausted by the high pressure turbine element, a low pressure turbine element having fluid inlet means communicating with the heater, a condenser having inlet means communicating with the exhaust portion of the low pressure turbine element,

means for connecting the condenser with the heater, a speed responsive device for regulating the flow of the fluid from the generating device to the high pressure turbine element and for directing the flow of the fluid from the heater to the low pressureturbineelement under normal conditions of operation and to the condenser under abnormal conditions of operation, and a safety valve associated with the pressure generating device and having communicating means connected with the heater, for discharging fluid to the heater under abnormal conditions of operation. i

16. ln a power plant, the combination of a prime mover having a valve means for the admission of motive fluid and means for exhausting the motive fluid, two power plant elements adapted for receiving the motive fluid exhausted by the prime mover, means including a valve for normally directing the fluid exhausted by the prime mover to one of the power plant elements, a second means including a valve for directing the fluid exhausted by the prime mover to the second power plant element and governing means associated with the prime mover for controlling the movements ofthe admission valve and for closing the first-mentioned exhaust valve and opening said second exhaust valve upon an abnormal fluctuation in the speed of the prime mover.

17. In a power plant, the combination of a prime mover having valve means for the .admission of motive fluid and means for exhausting the motive fluid,two power plant elements adapted for receiving the motive fluid exhausted by the prime mover, means including a valve for normally directing the fluid exhausted by the prime mover to one of the power plant elements, a second means including a valve for directing the fluid exhausted by the prime mover to the second power plant element, governing means associated with the prime mover for regulating the admission of fluid during normal fluctuations in the speed of the prime mover and for closing the firstmentioned exhaust valve and for opening said second exhaust valve upon an abnormal fluctuation in the speed of the prime mover, and an auto stop mechanism associated with the prime mover for closing the admission valve and the first-mentioned exhaust valve and for opening said second exhaust valve upon an overspeeding of' the prime mover.

18. In a power plant, the combination of a high pressure turbine element having valve means forthe admission of condensible motive fluid and means for exhausting the motive fluid, a heater for increasing the temperature of the fluid exhausted by the high pressure turbine, a low pressure turbine element having motive fluid inlet and exhaust means, means communicating with the exhaust portion of the low pressure turbine element for condensing the fluid exhausted therefrom,

means including a valve for normally directing the fluid discharged from the heater to the inlet of the low pressure turbine element, a second means including a valve for directing the fluid discharged from the heater to the condenser, an auto stop mechanism associated With one of the turbine elements for closing the admission valve of the high pressure turbine element and the valve for conveying the heated fluid to the low pressure turbine element and for opening the valve for conveying the heated fluid to the condenser upon an overspeeding of' one of the turbine elements, and additional means for supplyingcondensible fluid to the heater.

19. In a power plant, the combination with a high pressure turbine element having a valve for controlling the admission of motive fluid, a valve for regulating the flow of the motive fluid thereto and motive fluid exhaust means, of a low pressure turbine element having fluid inlet and exhaust means, means for condensing the fluid exhausted by the low pressure turbine element, means including a valve for normally directing the fluid exhausted by the high pressure turbine element to the inlet of the low pressure turbine element, a second means including a valve for directing the fluid exhausted by the high pressure turbine element to the condensing means, a speed responsive device associated with one of the turbine elements for actuating the regulating valve of the high pressure turbine element and for closing the valve for directing the fluid exhausted by the high pressure turbine element to the inlet of the low pressure turbine element and for opening the valve for redirecting said exhaust fluid to the condenser upon an abnormal fluctuation in the speed of its associated turbine element, and auto stop mechanisms associated with each turbine element for closing the fluid control valve of the high pressure turbine element and the valve for directing fluid to the inlet of the low pressure turbine element and for opening the valve for redirecting said fluid to the condensing means upon an overspeeding of one of the turbine elements.

20. In a power lant, the combination of a high pressure tur ine element having valve means for the admission of condensible motive fluid and means for exhausting the motive fluid, a generating device for supplying motive fluid to the high pressure turbine element, a heater for increasing temperature of the fluid exhausted by the high pressure turbine element, a low pressure turbine element having motive fluid inlet and exhaust means, means communicating with the exhaust portion of the low pressure turbine element for condensing the fluid exhausted therefrom, means including a valve for normally directing the fluid discharged from the heater to the inlet of the low pressure turbine element,

a second means including a Valve for directing a fluid discharged from the heater to the Condenser, an auto stop mechanism associated with one of the turbine element-s for closing the admission valve of the high pressure turbine element and the valve for conveying heated iiuid to the low pressure turbine element and for opening the valve for conveying heated fluid to the condenser upon an overspeeding of one of the turbine elements, and means providing communication between the generating device and the heater upon excessive pressure in the generating device.

21.y In a power plant, the combination of a motive-fluid generating device7 a high pressure turbine element, a reheater for reheating the motive fluid exhausted by the high pressure turbine element, a low pressure turbine element7 a condenser, means for passing motive fluid through theaforementioned ele-` ments in the order named during the normal operation of the turbine elements, means for passing motive fluid from the generating de vice to the reheater upon excessive pressure in the generating device, and means responsive to overspeeding of a turbine element for preventing passage of motive fluid to the turbine elements and for passing fluid trom the reheater to the condenser.

In testimony whereof, We have hereunto subscribed our names this twenty-seventh day of October, 1924.

FRANCISV HODGKINSON. ROBERT C. ALLEN.