US1751667A - Hydraulic apparatus - Google Patents

Description

March 25, 1930.

H. B. TAYLOR HYDRAULIC APPARATUS 4Sheets-Sheet l Original Filed Dec. 4, 1919 ll Illllllll hull/Ill March 25, 1930. H. B. TAYLOR HYDRAULIC APPARATUS Original Filed Dec. 4, 9 4 Sheets-Sheet A 2 March 25, 1930. H. B. TAYLOR HYDRAULIC APPARATUS Original Fil ed Dec. 4, 1919 4 sheeisrsheet lfimammxm wmm March 25,1930. H. B. TAYLOR 1,751,667

HYDRAULIC APPARATUS Original Filed Dec. 4, 1919 4 Sheets-Sheet 4 i .5; (Hz) i H F HE. o H 20:: ELEVATION OF mm no 1. A T D'SCHARGE ABOVETALWATER TO TAILWATER I IO H Fe: HEAD H 4-0 FT- Snmc Dnscwxzaa L RUNNER BELOW HEADHZN Ft AL TNLWATER EFFICIENCY go :mcxeucy CaeeEcTlu 70 H Fa: H w H= 6Q For: Manse m s Qwrrncw L955 Z A 6 100 ml Ml 30A 2? v H =5ncn=1c Spica ATTANABLE BY luczeAsmq Patented Mar. 25, 1930 UMTED stares PAT HARVEY BIRCHARD TAYLOR, OF PI-I I LADELPI-IIA, PENNSYLVANIA, ASSIG-NOR, BY

MESNE ASSIGNMENTS, TO I; P. MORRIS CORPORATION, A CORIOBATION OF DELA- WARE HYDRAULIC APPARATUS Original application filed December 4, 1919, Serial No. 342,383. Divided and this application filed February This invention relates to hydraulic power plants and particularly to such plants where the available water supply is under small and moderate heads. In such plants. it is necessary to use a large flow of water to develop power in commercial quantity. In order to keep the turbines and power house required to handle these great quantities of water from being prohibitively large and expensive it is desirable to increase the velocity of the water as much as possible particularly where it passes through the turbines and at discharge from the runners; and in order to keep the electrical generators from being unduly large, it is desirable to obtain the high est possible rotary speed for the turbines. This high speed is also advantageous in making it possible to use standard electric machinery in many installations where otherwise large special machines would be necessary. When the velocity in the water passages is increased beyond a certain amount, however, the corresponding drop in pressure, according to hydraulic principles hereinafter explained, permits the pressure to approach the point at which the water will vaporize and if carried too far allows the'continuity of the water column to be broken causing loss ofhead and danger of surges and,

other disturbances. Even before actual break in the water column therewill be danger of rapid corrosion of exposed metal SUI"? faces so that a margin of safety mustbe al-.

lowed above the point of vaporization.

This is particularly the case at the turbine runners, where velocities are usually highest,- and with turbines located as heretofore at a considerable elevation above the tail water there has been a limitation on the permissible velocity in the water passages which has so increased the size of the turbines for the power developed as to make thefirst cost of turbines and power house prohibitive.

The objectof this invention is to provide a hydraulic power system for such low and moderate head conditions which will not re-v quire such large and expensive apparatus and in which high velocities of flow may be safely used without danger of interrupting thecontinuity of the water column. In the Serial No. 251,156.

the points of maximum velocity and, therefore, any velocity may be used within the limits of the opposing pressure head. To supply this opposing pressure head the tur-v bines or other parts of maximum velocity are in the system of this invention placed at an elevation with respect to the level of the tail water corresponding to the desired velocity and the pressure head necessary. to counterbalance the reduction in pressure resulting therefrom, departing fromthe customary practice of limiting the runner to positions above the tail water level. a

. In the accompanying drawings illustrating specific applications of the principle of the invention A Fig. 1 is a vertical sectional view of a power plant'showing one embodiment of the invention; Fig. 2 is a Vertical sectional View of a modification; Fig. 3 is a plan view of the same; Fig. 4 is a partial plan view of the same, and Figs 5 and 6 are diagrams i1lustrating the principles hereinafter explained.

In the embodiment of the invention illustrated in Fig. 1 a power house 8 has the head water 9 in the usual forebay or liquid basin on one sideand tail water 10 in the usual forebay or liquid basin on the other. A vertical pit 11, is provided for the verticalshaftturbine 12 having arunner 13 below and shaft 14 driving generator 15 in'thepowerhouse above; The inflow to the turbine runner is provided by passage 16 from. head water 9 and controlled 'by gate 17 and at the runner this intake 16 has the form of a spiral or volute of progressively decreasing section delivering the water tothe runner blades with a combined radial and circumferential flow. The turbine 13 is of-the high speed type and is positioned below the level even of the tail race 10 and the supply head H between the runner and the surface of the head water '9 is greater than the not head difference H between this headwater and the tail race sur face so that the water at the turbine is under relatively great static head; the absolute ENT OFFICE values of the hydraulic pressures being however determined by the conditions of flow and the effect of the relatively high velocities desired at these points. lVith the turbine runner under a certain initial head H above the runner discharge, and having an absolute pressure hp at the runner discharge then the head H on the turbine proper, between intake and discharge, will be expressed by the following formula H =H +h h g; (a)

where h is the head corresponding to atmospheric pressure.

It is proposed according to this invention to place the runner at such an elevation (here assumed below tail water) that the turbine proper can operate under a head H considerably greater than the head on the system H. Toaccomplish this, the velocity head at the runner discharge must" be so related to the atmospheric pressure and the heightof tailwater above the section that k the static pressure head at the runner discharge, has a value safely in excess of that at whichthe water will tend to vaporize and the continuity of the water column in the draft tube will be in danger of being broken' The relation is as follows Here H denotes the height of tailwater above the runner discharge; e denotes absolute velocity of discharge from-therunner;

L the loss of head in the draft'tube; o the velocity of final discharge from the draft tube; Z, the percentage of velocity head lost in, and'at final discharge from, the draft tube; and e the eiiiciency of the draft tube,

-In Well designed draft tubes e be assumed to be in the neighborhood of in the case of large units. If Hg and (consequently) H are made large in comparison 2 with H, and g with the above formula (keeping h w1th1n a range'of say from 5 to 10 ft. as a proper margin, to allowfor variations in velocity, etc.) then a value of H, can be securedconsiderably in excess of -H.

increased in accordance the latter by (1+ GCZCLOSH' If N is the specific speed of a runner computed 1n the usual manner from the formula,

N5 Hi2 in which HP is horsepower and if H, is the head on the turbine proper corresponding to the H upon which this value of N is based,

let Nfg be the N, for the turbine proper, based on H that is:

p In other words, in a turbine having a discharge velocity head from the runner of (sometimes called the outflow loss 2,,H which We may denoteby Q expressed asa percentage of the head H 100) and a draft tube efficiency of e the specific speed of the turbine proper can be found from the specific speed of the complete turbine by dividing For example, in a turbine of 100 specific speed, having an outflow loss of 25%,- and draft tube efficiency of speed of the turbine proper lid remain the same, but the effective specific 7 speed of the complete'turbine will be s s,( di d y v in which is the new value of the outflow loss. 1 Continuingthe above example, if the tur bine of N is placed 7 ft. below the surface of tailwater and is altered so as to-in crease its outflow loss to take advantage of this location, its outflow Velocity head willbe v H +.h h- 7 +34-6 from 25% t0220 will reduce theefiiciency, Increased to ,1, f due to draft tube losses alone, to

as it, a value of h s of 6 ft. being provided.

If the actual net head H on the system is 20ft. the outflow loss will be 1 20H 20 .20 (220%) The specific speedof the complete turbine will then be:

The change in the location of the turbine, accompanied by the increase in the outflow loss which, is thus permitted, has therefore made possible an increase in the specific speed from to 285, which would give a corresponding increase in the actual speed of the unit. 1

It should be understood that the increase in specific speeds madepossible by this method involves a certain sacrifice, which in this problem takes the form of a possible'loss in efiiciency. .If a turbine having an original outflow loss of 3d and efficiency of e is altered so as to increase its outflow lossto @61 the additional direct loss caused by this change to this will be:

i It is probable that there will also as a rule be an accompanying increase inithe other losses in the turbine, although this will-n'ot be as great. If all thev losses 1ncrease-d 1n the same ratio as the outflow less we shouldhave-z velocity as well as tlie meridian components;

this makes it possibleto reduce the relative velocities at the runner discharge and to minimize the losses within the runner by giving the absolute discharge velocity a. considerable whirl component. Moreover. high speed turbines are continually being improved and higher efiiciencies secured.

In the example just considered, the efiect upon the eficiency of the great increase in speed which we have found to be possible will be as follows :Assuining the original efliciency of the 100 N turbine to be 90%, and the eiiiciency of the draft tubeto be 80% as already used, the increase in outflow loss sure head at the outflow 21.

' each other.

This result is largely dependent on the draft tube efficiency which it may be possible to realize. In the structure shown in Fig. 1 the turbine 13 discharges downward with axial and whirling motion and the draft tube 20 is designed to have the greatest possible efficiency in converting-the velocity head at the runner discharge into pressure head'at the outflow 21 into thetail race. Draft tube 20 is of the spreading conical type suited to so progressively increasing in cross section and further converting velocity head into pres- With such a draft tube the expected efficiency of=conversion may be as high as 90%. If this value is applied in the above example theefliciency J resulting from an increase in outflow loss from 25% to 220 would be :1

.195 .705 or 70.5%. It may be pointed out that in the example discussed above a head on the plant of only 20 ft. was considered. The increase of head on the turbine proper consisted in this example largely of the"atmosphericpressure, the distance at which the turbine was assumed to be placed .below' tailwater being only 7 ft. orjust about sutiicient to supplythe absolute pressure head whichhas beenprovided at the point of discharge from the runner. If a case had. been cons'ideredin which the not head on the plant had been higher it would have been found-necessary to locate the turbine at an increased 'distance below the tailwater SUIfZiCGlIl OI'ClEl. cto-, real ze,,any

such increase in specific speed as was: found possible in the example considered.

The relations expressed bythe-preceding formulae may be morereadily grasped if presented graphically the variationsof some of the factors-upon This diagram is based-on the same data as was assumedin the example given above, namely: y a;

The specific speed. of turbine proper, N 0

. Turbine efficiency, e=.90

Draft tube'eificiency,e =.80

The curves plotted in the diagram show the manner of variation of the efficiency-in Figure 5 is therefore 1 given, forthe purposeof showingthe effect of Cal relation to the specific speed when the specific speed is increased by increasing the outflow loss from the runner. The elevation at which the turbine must be placed with respect to tailwater in order to obtain the increased values of specific speed are shown for three different values of the net head H on the plant, namely, for 20, and ft. It will be noted, for example, that in order to obtain a specific speed of 167 when the net head on the plant is 60 ft. it will be necessary to depress the turbine 20 ft. below tailwater, and this increase in specific speed will reduce the efliciency to With the turbine of this invention, the velocity of discharge from the turbine runner can be increased to the point where the pressurehead against which the turbine is discharging is reduced to within a small margin of absolute zero, and the turbine will then operate under an efiective head represented by the entire gross head on the intake side, including the atmospheric pressure acting on the head water surface; This head in low head plants may be several times the net head measured from head water to tail water so that the turbine can be operated at a speed corresponding to the gross intake head, and will be correspondingly reduced in dimensions and cost and the electrical generator or other driven machine also reduced in size and cost.

In .the system shown in Fig. 1 a discharge gate 25 may be closed to exclude the tail race water 10 and with the inflow gate 17 also closed the turbine passages may be pumped out to give clear access to the turbine parts. In the modification of the invention shown in Fig. 2 the draft tube 20 is continued from the core surface immediately below the axial portion of the tube leading from the runner, in a vertical passage 30 which curves in a vertical plane to pass over a'crest 31 which is placed at an elevation slightly higher than the maximum tailwater elevation. The tube thenpasses downward, toprovide a curtain wall, and is completely enclosed to a depth slightly below the lowest tailwater elevation to which the plant would be subjected. The passage thus formed will act as a siphon enabling the turbine dis-- charge to take place below the tailwater surface while at the same time providing a protecting wall or crest to protect the turbine from submergence by tailwater whenever the siphon and draft tube passages are unwatered. This un watering would be efi'ected by shutting down the turbine, closing the head gates 17, admitting air to the top of the siphon through the air valve 82, and pumping out the water in the draft tube to a point sufiiciently beneath the turbine to provide convenient access. The air valve 32 at the top of the siphon can also be used for the attachment of a hydraulic ejector or pump to-draw out any air which may collect at that point during operation. It is, however, proposed in general to provide sulficient velocities in the draft tube to sweep out any air which might have a tendency to collect. A. curved baflie plate 33 is, shown than are used in present practice. Present practice is based on the erroneous assumption that the degree of'specific speed which can be used depends upon the net head on the plant. This is only true whenthe practice is adhered to of placing the runner at an arbitrary height above tailwater. The

method now in use by hydraulic engineers for determining the leading factors in a "power plant design is to plot a curve, based on accepted practice, between specific speed and net head on the plant, and as soon as the available net head is known for any new development, to select from such a curve the specific speed to be used. Such a curveas described. however, does not represent any true relation, since it is plotted between two variables which are not necessarily functions of each other. The permissible specific speed does not depend on the net head on a plant, but upon the pressure-head hpd beneath the runner. As long as this pressure-head is not allowed to fall to within an unduly small margin of absolute zero, the runner may be as safely used under higher heads as under low. As much margin inpressure (h may 'be provided in any case as may be considered desirable by placing the runner at a sufficient- 1y low elevation with respect to tailwater, the distance required being computed by solving Formula (72) for H Toillustrate this point, let us consider the use of a runner of N =82 having 30% outflow loss, when applied to various heads. Present practice would confine the use of such a runner to heads lower than about 50 ft The possibilities opened up by this invention in the case of such a turbine are shown in the diagram (Fig. 6) which gives the elevation H of the runner discharge with respect to tailwater which would enable the same turbine to be used under a wide range of heads. This curve is plotted from Formula (6) V transposed:

2 ad at+ Pa "(9) Theassumed values are as follows 6d O-; d=0.30; hat 3tt ft. hpd has been increased so as to allow greater margin for higher heads,'10 ft. being provided at 100 ft. and 15 ft. at 200 ft. This has been, done to take care of greater variations in pressure when the velocitiesare higher,

andtogive additional insurance against cor rosion of the metal of the turbine undertlfie t e 5 higher heads. The formulwfrom which curves have been plotted are: i 1 f i Q and or H w To compare the possibilities indicated by these curveswith present practice, consider the. turbine represented as applied to a head of-200 ft. .By placing the runner29 ft. below 410,000 H. P. under 200 ft. head, the speed inaccordance with present practice wouldyv be limited to 150 revolutions per minute',but by 30 the method hereioutlined can be raised to 300.

R. P. M. .or higher. This will very greatly reduce the cost of both the turbine and'electrical generator and will effect economies in carrying out a power development. The increase in speed just outlined need not involve any sacrifice in efficiency. n x

Referring to Formula (0) it will be noted that the'velocitywith which the runner dis-1 charges into the draft tube is properly a funcnet. .head. The velocity which can; be em.- ployed at the discharge from the runneris therefore independent of lthenet head on'the turbine, and for a given atmospheric. pres-.-

sure. andiaf given allowance forthe absolute pressure in the draft tube, this velocity is dependent only on the location of the runner with respect to tailwater. It shouldalso be noted that the actual location of the turbine for by Formula (g) from the elevationof low tailwater in a plant in which the tailwater level is subject to variation at different stages of the river and under different conditions of operation of the plant. It will therefore be necessary in some cases to place the runner at a somewhat greater de th below normal tailwater than the value ca led for by the formula. Whenever a siphon draft tube is used it will also be necessary in plants subject to variations in tailwater level to place the lower wall of the siphon at its crest at an elevation equal to or slightly higher than the highest tailwater expected for the plant, and the discharge end of "the siphon must be carried a tion.of1I-I ,and is not afunction of H, the

runner should be fixed by measuring H called 7 sutficient distance below the lowtailwater level to insure the siphon remaining sealedunder all; conditions of operation.

In'some cases and particularly with the inverted form of turbine the draft tube may have a straight tapered portion interposed I between the runner discharge and the spread portion to axially elongate the tube'and ac commodate a deeper settingof the runner. B the system of this invention a wide range 0 speeds is available for theturbine and by I the adoption of increased speeds, the entire installation may be reduced insize and'cost.

In many llow-head developments this first cost is the really determinative consideration; the" problem is not to. develop the greatest amount of power possible from the full flow of the river, but is to develop some power as" economically as possible. In many such cases,

it will pay to allow some water to go to waste, if the rest can be utilized economically.v In

many cases, efiiciency will not be a ruling con sideration ifn'rotary speeds for'the turbines andgenerators can'be increased to values which will-enable cheaper machines to be' used. In'such cases the systemof this invention affords a direct and practicable solution; of the problem andmakes available power hitherto altogether lost. A

In this specification, tailwater means the elevation. of the surface of the tailrace. Static discharge head means the difference in height of tailwater and point of discharge of.r unner;'(I-I plus the head corresponding to the pressure of the atmosphere. Discharge pressure.- and discharge pressure head means the absolute pressureand pres-v surefhead at the point of discharge of the runnerwith reference to absolute vacuum as zero. By cont nuity of the water column,

ismeant that the intake, turbine and draft tube passages during operation remain filled with. water forming a continuous columnthrough "these passages, from head; water to tailwaterwithout interruption at any section.

I claim;: v I

.. .1. The combination with a turbine of a downward flow draft tube and; a water sealed 2. The eombinationwith a turbine having the waterinthe tail race.

e combination with a turbine having a downward 'fiow draft tube ofavacuum chamber into which said tube extends, thedischarge' area of said chamber increasing upwardly fora portion of its height. 1

The combination with a turbinehaving a-downwardly extending draft tube ofa -vacuum; chamber, and means to exhaust the air,

from said chamber whenever necessary. 1

Th. combi ation w h et rb n havin 'm bha t i to which the draft tube discharges. r

a downwardly extending i draft tube increas{ ing in diameterdownwardly, of a .vacuum chamber having a curtain walle'xtendiiig-be low the level of the water in the tail race into which the draft tube extends, and means to exhaust the air from the vacuum chamber whenever necessary. D

6. The combination with a turbine having a downwardly extending draft tube of a 'vacuum chamber extending above the level of the bottom of the drafttube, the discharge downwardlyextending draft tube of a vacuum chamber, said chamber extending upwa'rdly from the bottom of the draft tube and being of increasing cross-sectional area from its lower portion to an intermediate portion thereof, and means to exhaust the air from said chamber when necessary.

8. The combination in a hydraulic turbine comprising a downward-flow drafttube having a portion leading axially from the tur b ine, means forming 'a surface immediately below said axial portion, a conduit leading from said draft tube and having a curved portion therein,-and a horizontal baflle member disposed in said conduit and also being spaced and separate from the axial portion of said draft tube and said surface imme diately below said axial portion.

9. The'combination in a hydraulic turbine comprising a draft tube having a portion leading axially from the turbine and means forming a surface immediately below said axial portion, a conduit leading therefrom, and a transverse bafile disposed in said conduit and spaced from the opposite wallsthere of and'also being spaced and separate from said draft tube and surface. i I

10. The combination in a hydraulicdra'ft tube comprising a downward-flow spreading draft tube, and a water-sealed vacuum chamber into which the draft tube discharges.

11. The combination in a hydraulic turbine comprising a downward-flow draft tube which flares at its lower end, a coneextending upwardly into said draft tube for cooperation with the flaring portion thereof, and a water-sealed vacuum passage into which the draft tube discharges.

12. The combination in a hydraulic turbine comprising a downward-flow draft tube,

' and a water-sealed vacuum passage into which the draft tube discharges, said passage extending upwardly above the uppermost portion of said draft tube.

13. The combination ina hydraulic turbine comprising a downward-flow draft tube, and a water-sealed vacuum passage into which the draft tube discharges, said passage extending upwardly above the uppermost portion of said draft tube, and then extending downwardly to discharge into a liquid basin.

tarta passage leading upwardly therefrom and to one side thereof,' a'nd then turningdownward ly-toa liquid basin; to form a liquid-sealed passage. 7

15. The combination ina hydraulic turbine comprising a downward-flow draft tube and. a water-sealed passage into which the draft tube discharges, said passage having upwardly and downwardly extending portions which.

are connected bya relatively smooth curving upper surface." *1? '16. The combination in a hydraulic turbine comprising a downward-flow draft tube and a water-sealed passage intowhich the draft tube discharges, said passage having upward.- ly and downwardly extending portions which are connected by a relatively smooth curving upper surface of large radius. f

17. The combination in a hydraulic turbine comprising a downward flow draft tube, and a water-sealed passage extending upwardly and then downwardly and into which said draft tube discharges, the downwardly-extending portion of said draft tube being flared in the direction of flowtherethrough.

18. The combination in a hydraulic turbine comprising a downward-flow draft tube, and a water-sealed passage extending upwardly and downwardly and into whichthe draft tube discharges, the upwardly-extending por-' tion of said passage having walls contracting in the direction of flow through said passage.

19. I The combination in a hydraulic turbine comprising a downward-flow draft tube, and a watei sealed passage extending upwardly and then downwardly and into which said the downwardly-extending portion "of said passage has walls diverging'in the direction offlow.

HARVEY BIRGHARD TAYLOR.

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