US3236498A

US3236498A - Hydraulic reaction turbines and pump turbines

Info

Publication number: US3236498A
Application number: US296539A
Authority: US
Inventors: Kerensky Gleb
Original assignee: English Electric Co Ltd
Current assignee: English Electric Co Ltd
Priority date: 1962-07-31
Filing date: 1963-07-22
Publication date: 1966-02-22
Anticipated expiration: 1983-02-22
Also published as: CH417505A; ES290401A1; GB1042509A

Description

Feb. 22, 1966 G. KERENSKY 3,236,498

HYDRAULIC REACTION TURBINES AND PUMP TURBINES Filed July 22, 1963 3 Sheets-Sheet 1 Feb. 22, 1966 5 Sheets-Sheet 2 Filed July 22, 1963 FIG.5

I I'm United States Patent 3,236,498 HYDRAULIC REACTION TURBINES AND PUMP TURBINES Gleb Kerensky, Netherton, England, assignor to The English Electric Company Limited, London, England, a British company Filed July 22, 1963, Ser. No. 296,539 Claims priority, application Great Britain, July 31, 1962, 29,414/ 62 9 Claims. (Cl. 253-24) This invention relates to hydraulic reaction turbines and pump turbines and to the control systems thereof.

In certain installations in which the hydraulic reaction turbine or reversible pump turbine is connected to an electric alternator to drive it, it is required to maintain the hydraulic turbine alternator set rotating, with the alternator synchronised with other generating units but without delivering any electrical energy. Such operation may have the purpose of improving the power factor of the electrical network connected to the alternator by using the latter as a synchronous condenser, or alternatively of enabling the hydraulic turbine alternator set to start delivering electrical power at very short notice in the event of the other alternators in the network experiencing a sudden overload. The latter condition of operation is known as spinning reserve. It will be apparent that it is desirable to be able to bring the hydraulic turbine alternator set on load in the shortest possible time. In the specification and claims, the word turbine includes a reversible pump turbine.

According to the present invention, there is provided a control system for a hydraulic reaction turbine alternator set, in which the maximum equivalent area of the main valve in the turbine penstock is at least twice the maximum equivalent area of the adjustable guide vanes, comprising means to maintain the spiral casing of the turbine, when the turbine alternator set is operating at synchronous speed with the main valve and the adjustable guide vanes closed and the turbine runner operating substantially in air, substantially full of water at a pressure which is only a small fraction of the normal working head of the turbine and means responsive to the extent of opening of the main valve and arranged to allow the adjustable guide vanes to begin to open in advance of complete opening of the main valve, the opening of the adjustable guide vanes being so limited that the equivalent area of the adjustable guide vanes at no time exceeds the equivalent area of the main valve.

One embodiment of hydraulic reaction turbine alternator set and its associated control system will now be described by way of example with reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic sectional elevation of a vertical-shaft hydraulic reaction turbine alternator set together with parts of the associated control system on the line 1-1 of FIG. 2,

FIG. 2 is a plan view of part of the hydraulic turbine alternator set of FIG. 1,

FIG. 3 is a diagram of the electrical connections of the control system of FIGS. 1 and 2,

FIG. 4 is a graph on which equivalent area is plotted against time,

FIG. 5 is a longitudinal section of a by-pass valve,

FIG. 6 is a longitudinal diagrammatic section of a valve in series with restricted orifices, and

FIG. 7 shows a modification of the system for making up the leakage of water.

Referring first to FIGS. 1, 2 and 3, the hydraulic reaction turbine comprises a runner 10 driving a shaft 11 connected to an alternator 12 which is linked to the electrical grid system.

Water is supplied to the runner 10, from a source of water (not shown) at a higher level, through a penstock 13 in which is provided a main valve 14, the penstock 13 being connected to a spiral casing 15 the outlet annulus 16 of which surrounds the inlet 17 of the turbine runner 10. The outlet annulus 16 is also provided with a ring of adjustable guide vanes 18. Below the outlet of the turbine runner 10 is provided a draft tube 19.

The shutter 21 of the main valve 14 is of well-known type and is moved from the closed position, as shown, to the open position by being rotated anti-clockwise through a right angle by means of a hydraulic servomotor 22 connected to a crank arm 23 secured on the shaft 24 of the valve.

A main -by-pass 26 having in it a valve 27 is provided between those parts of the penstock 13 respectively upstream and downstream of the main valve 14. There is also provided a secondary by-pass 28 having in it a valve 29, which is shown as being connected across the valve 27 of the main by-pass 26, but which may alternatively be connected from that part of the penstock 13 upstream of the main valve 14 to that part of the penstock downstream of the main valve.

A pipe 30 is provided through which cooling water may be supplied to the rim of the runner 10. Connected to the penstock 13 adjacent the spiral casing 15 is an automatic air release vent 31, through which any air trapped in the spiral casing 15 may be vented to atmosphere. When the penstock 13 and spiral casing 15 are full of water, the float 32 rises and seals oil the outlet of the release valve 31. There is also provided a low-level-indicating switch 33, in the form of a float valve connected to operate an audible or visual signal when the water in the spiral casing falls below a predetermined level. A pipe 34 is connected between the draft tube 19 and an air compressor or accumulator, or the pipe 3-4 may open to the surrounding air if the turbine tail-race level is sufiiciently low under all conditions of operation to allow air to flow into the draft tube through the pipe.

The adjustable guide vanes 18 are connected through lever arms 38 and links 39 to a control ring 40, which is, in turn, connected through rod 41 to a hydraulic servomotor 42 which is controlled by a load control device 43 which forms part of the turbine governor. A

pressure-sensitive switch 44 is provided which responds to the pressure of water within the spiral casing 15. A preferred construction of servomotor 42 and control device 43 is disclosed at 21 and A in FIG. 15 on page 29 of the National Electrical Manufacturers Association publication HT 1-1957, July 1957, and described on

pages

11 and 13 of the text of the publication.

In machines designed for operation at very high heads there maybe provided an over-flow pipe 45 (shown dotted in FIG. 1) connecting the penstock 13 or spiral casing 15 to the draft tube 19, and incorporating an isolating valve 46 and a regulating valve 47, which may be springloaded as shown at 48.

The shaft 24 of the main valve 14 is provided with a cam 50 arranged to close a switch 51'when the main valve 14 reaches a predetermined opening, at which its equivalent area is a predetermined percentage, referred to as x percent, of its maximum equivalent area. This predetermined percentage may be 25 percent. The equivalent area, at x percent, is, in the embodiment described, but not necessarily, greater than the maximum equivalent area of the adjustable guide vanes 18 (i.e. the equivalent area of the adjustable guide vanes when in the fully-open position). The equivalent area of the main valve 14 or of the adjustable guide vanes 18 is the area of an equivalent ideal orifice having no losses or contractions which would discharge the same flow of water under the same head as would the valve 14, or the adjustable guide vanes 18, respectively. The switch 51 is connected in an electrical circuit 52 (see FIG. 3), between the mains supply 53 and the load control device 43; the circuit 52 also comprises

switches

54, 55, and is so arranged that when either switch 54 or switch 55 is closed and switch 51 is closed, the load control device 43 is energised from mains 53 to operate the hydraulic servomotor 42 which controls the adjustable guide vanes 18.

The switch 54 is closed by the cam 50 on the shaft 24 of the main valve 14 when the latter reaches an opening at which the equivalent area is a predetermined percentage, referred to as y percent, of the maximum equivalent area. The predetermined percentage may be 50 percent. The switch 55 is opened by a cam 56 connected to the rod 41 when the adjustable guide vanes 18 reach an opening at which their equivalent area is a predetermined percentage, referred to as 2 percent, of their maximum opening. This predetermined percentage may be 50 percent.

Referring now to FIG. 5, there is shown a design of the secondary by-pass valve 29, in which the flow of water (in the direction of the arrow 60) is caused to change direction many times by a series of bafiles 61 so that the velocity is reduced and erosion or vibration of the valve is minimised. The valve obturator 62 closes onto a seating 63. Since the valve 29 is only required to be closed when the adjustable guide vanes 18 are closed, the valve 29 may be opened by oil pressure supplied to the cylinder space 64 from a point in the governor system where the pressure is cut off if the adjustable guide vanes 18 are closed; the valve is urged in the closing direction by a spring 65, so that when the pressure is cut off the valve 29 is closed.

As another variant, .a valve 29 which is without bafiles 61 may be provided with restricted orifices 66, 67 (FIG. 6) in the by-pass 28, to reduce erosion.

In operation, when the hydraulic turbine alternator set is rotating at synchronous speed with-out delivering energy to the associated electrical grid system, the main valve 14 will be closed, the adjustable guide vanes 18 will also be closed, and alternator 12 is driven as a synchronous motor. To minimise losses, the runner will be caused to rotate in air by the supply of compressed air, or (where the level of the tail-race is sufficiently low) by the supply of air at atmospheric pressure to the draft tube 19 through pipe 34.

The equivalent flow area of the penstock 13 and of the main valve 14 when fully open is preferably at least four times, and as shown in this example five times, the equivalent flow area of the adjustable guide vanes 18 when these are fully open; when the main valve 14 and adjustable guide vanes 18 are being opened the equivalent area of the main valve must never be reduced to a value less than that of the equivalent area of the adjustable guide vanes at any instant, and preferably not to less than twice the equivalent area of the adjustable guide vanes. In the present example the controls :are arranged not to permit a smaller ratio than 2.5 to 1. a

The valve 29 controlling the secondary by-pass 28 is open and supplies a sufiicient fiow of water to the spiral casing 15 to make up leakage of water from the spiral casing; for example, through the ring of adjustable guide vanes 18, which will not seal completely. The size of the water passage in valve 29 is so chosen or adjusted that the water in the spiral casing will be at a pressure only slightly greater than atmospheric, and substantially less than the pressure in the penstock 13 upstream of the main valve 14. Leakage through the adjustable guide vanes 18 is thus relatively small.

When it is required to bring the hydraulic turbine alternator set on load, the main by-pass valve 27 is opened to equalise the pressure in the penstock 13 and the spiral casing 15. When the pressure in the spiral casing is adequate, the switch 44 allows the opening of the main valve 14 to be initiated by supplying oil under pressure to the hydraulic servomotor 22. The opening of the main valve is plotted against time, as the upper curve 57 in FIG. 4, between zero and percent equivalent area.

When the valve 14 reaches the opening having an equivalent area of x percent, the cam 50 closes switch 51 and, since switch 55 will be closed when the adjustable guide vanes are closed, completes the circuit 52 and energises the load control device 43 which initiates operation of the hydraulic servomotor 42 to open the adjustable guide vanes 18. This is represented at time A in FIG. 4.

The opening of the adjustable guide vanes is plotted against time as the lower curve 57 in FIG. 4, between zero and 100 percent of their equivalent area. It will be seen that the maximum equivalent area of the main valve 14 is approximately five times the maximum equivalent area of the adjustable guide vanes.

When the adjustable guide vanes 18 have reached an opening corresponding to an equivalent area of z percent, represented at time B, cam 56 opens switch 55, and if switch 54 is also open the load control device 43 is deenergised and opening of the adjustable guide vanes ceases.

When the main valve 14 is opened to the extent of y percent of its equivalent area, the cam 50 closes the switch 54, represented at time C, and the load control device 43 is again energised, allowing the opening of the adjustable guide vanes to continue, until their opening is completed as represented at time D. If the main valve -14 reaches the necessary opening (y percent) so that switch 54 is closed, before the adjustable guide vanes reach 2 percent opening when switch 55 is opened, there is no dwell period from time B to C, but the adjustable guide vanes continue to open without pause. The opening of the main valve 14 meanwhile continues, until the valve is fully open as represented at time E. Irt this way, the turbine alternator set begins to generate well before the main valve is fully open, and is placed on full load rapidly without undesirable conditions occurring.

The equivalent area of the main valve 14 when x percent 0pen-when opening of the adjustable guide vanes is allowed to beginis in the preferred embodiment at least equal to the maximum equivalent area of the adjustable guide vanes. When the maximum equivalent area of the main valve 14 is five times the maximum equivalent area of the adjustable guide vanes, the minimum value of x is therefore 20 percent. Moreover, the equivalent area of the main valve 14 when y percent open is preferably equal to at least twice the maximum equivalent area of the adjustable guide vanes. Within these limitations, x, y and 2 may have any suitable values, as the conditions require; in the present example, even if the main valve fails to continue its opening movement at any time, the ratio of the equivalent area of the main valve to th'gtt of the adjustable guide vanes will never be less than 2. to l.

The control system may be so arranged, in accordance with the invention, that the adjustable guide vanes 18 are allowed to start opening before the equivalent area of; the main valve 14 exceeds the maximum equivalent area of the adjustable guide vanes, provided that the relation-v ship defined immediately below is satisfied at all times. This relationship implies that the equivalent area of the, main valve 14 is at all times greater than that of the adjustable guide vanes, Preferably the equivalent area of the main valve is at all times at least twice that of the adjustable guide vanes.

M is the maximum equivalent area of the main valve 14,

G is the maximum equivalent area of the adjustable guide vanes 18,

R is the percentage opening of the main valve 14 at any time t, and

S is the percentage opening of the adjustable guide vanes 18 at that time t,

then, in accordance with the invention,

RXM SXG 100 100 xXM In the present example x=25 percent, and 2:50 percent, and, since the maximum area of the main valve 14 is five times the maximum area of the adjustable guide vanes 18, we may write M :5 and G=l. Then:

Thus the relation is in fact satisfied.

Similarly switch 54, which closes when the main valve reaches an opening of percent, allows the adjustable guide vanes, in the embodiment described, to open to 100 percent of their maximum equivalent area. Thus, in accordance with the invention, at the moment when switch 54 closes, the following relation must be satisfied:

y M IOOXG 100 100 In the present example y=50 percent and M and G are as above; then:

Therefore this relation, too, is in fact satisfied.

It is also possible to have a greater number of switches so as to control the opening of the adjustable guide vanes in smaller steps, in a manner which will be evident to one skilled in the art. Moreover, as an alternative there may be provided a device which would correlate the opening of the adjustable guide vanes with that of the main valve throughout, which would be the equivalent of having an infinite number of switches, though such variants would not give much further advantage compared with the arrangement described.

In the example give the time from initiation of the main valve opening until the adjustable guide vanes are fully open is OD, and this is about half the time OE +AB+CD which would be necessary if the main valve were completely opened before opening of the adjustable guide vanes begins. To open the adjustable guide vanes fully at an earlier time, such as C, would not make it possible for the alternator to generate a large current correspondingly earlier because, with the main valve only half open, the turbine output would be severely limited by losses of energy occurring at the main valve.

In order to change from normal operation to spinning reserve or synchronous condenser operation, the adjustable guide vanes 18 are first closed, and the hydraulic servomotor 22 is next operated to close main valve 14. The main bypass valve 27 is next closed and the secondary by-pass valve 29 is opened. Air is next admitted to the draft tube 19 through pipe 34 in the manner already described.

The main by-pass 26 has an equivalent area so chosen that it is capable of filling the spiral casing 15 rapidly from empty; the secondary by-pass 28 has an equivalent area of the order of one tenth of that of the main by-pass.

Instead of the secondary by-pass 28, the leakage of water from the spiral casing may be made up, if desired, by using the main by-pass in the partly-open position, or by using water from an external source, in which latter case, a non-return valve 29' is inserted in line 28 which leads to the external source as illustrated in FIG. 7 so that water in the spiral casing under the full head does not enter the make-up water system.

In certain designs of turbines, where the centrifugal effect due to the runner opposes the through flow of cooling water from pipe 30 to the draft tube, the water flows through the adjustable guide vanes 18 into the spiral casing 15, and in this case the secondary by-pass 28 is unnecessary, but means should be provided for the escape of surplus water from the spiral casing; these may include the overflow pipe 45, isolating valve 46 and regulating valve 47. The valve 46 should be closed when the main valve 14 or valve 27 is open. The regulating valve 47 is preferably a relief valve which opens when the pressure in the spiral casing 15 rises slightly above atmospheric pressure.

The entry of air into the draft tube 19 through pipe 34 should be cut off (for example by means of a valve) when the turbine comes on load, the air in which the runner rotates under no-load conditions being swept out by the water as it flows through the runner.

When the spiral casing 15 is maintained full of water with the main valve 14, main by-pass valve 27, and adjustable guide vanes 18 all closed, the pressure is usually between 3 lbs/sq. in. and 20 lbs/sq. in. above atmospheric pressure. Normal pressure in the penstock 13 ranges from 30 lbs./sq. in. to 600 lbs/sq. in. according to the installation.

What I claim as my invention and desire to secure by Letters Patent is:

1. In a hydraulic reaction turbine alternator set comprising a supply of liquid, a penstock connected to said supply, a main valve in said penstock, first operating means connected to said main valve, a spiral casing connected to said penstock and having an outlet annular, a ring of adjustable guide vanes in said outlet annular, second operating means connected to said adjustable guide vanes, a turbine runner having its inlet within said ring of adjustable guide vanes, whereby liquid is supplied through said penstock, said main valve, said spiral casing and said ring of adjustable guide vanes to said turbine runner to drive it, an alternator having its rotor connected to said turbine runner to be driven thereby, and an electricity network connected to said alternator, characterised in that the maximum equivalent area as herein defined of said main valve is at least twice the maximum equivalent area of the adjustable guide vanes, a control system comprising means to supply liquid to said spiral casing at a pressure which is only a small fraction of the normal working head of the turbine, when the turbine alternator set is operating at synchronous speed and the main valve and the adjustable guide vanes are closed, whereby to maintain the spiral casing substantially full of water, said control system further comprising first position-responsive means responsive to the extent of opening of said adjustable guide vanes, power means for said second operating means, means to connect said power means to said second operating means under control of said first position-responsive means when the extent of opening of said main valve reaches a first predetermined value less than 100 percent, whereby to allow the adjustable guide vanes to begin to open in advance of complete opening of the main valve, means to disconnect said power means from said second operating means under control of said second position-responsive means when the equation R.M. S.G. 100 100 is not satisfied, where R is the percentage opening of the main valve at any time t, M is the maximum equivalent area of the main valve, S is the percentage opening of the adjustable guide vanes at that time t, and G is the maximum equivalent area of the adjustable guide vanes, and means to connect said power means to said second operating means under control of said first positionresponsive means when the equation R.M. S.G. 100 W is satisfied, whereby the opening of the adjustable guide vanes is so limited that the equivalent area of the adjustable guide vanes at no time exceeds the equivalent area of the main valve.

2. In a hydraulic reaction turbine having a main valve in a penstock and adjustable guide vanes in a casing, means to open said main valve, means to open said adjustable guide vanes, and means interlocking each of said means to prevent the equivalent area of the adjustable guide vanes exceeding that of the main valve.

3. In a hydro-electric power plant comprising a synchronous generator, a hydraulic reaction turbine drivingly connected to said generator, a penstock, a spiral casing connected to said penstock and connected to said turbine for delivering motive fluid to said turbine, a plurality of adjustable guide vanes interposed between said spiral casing and said turbine, a main valve in said penstock, first operating means for said main valve, and second operating means for said adjustable guide vanes; a control system comprising means to supply motive fluid to said spiral casing at low pressure when said main valve and said adjustable guide vanes are closed, whereby to maintain the spiral casing substantially full of water, said control system further comprising interlock means operative on opening of said main valve and of said adjustable guide vanes to prevent the equivalent area of the adjustable guide vanes exceeding that of the main valve.

4. In a hydro-electric power plant comprising a synchronous generator, a hydraulic reaction turbine drivingly connected to said generator, a penstock, a spiral casing connected to said turbine for delivering motive fluid to said turbine, a plurality of adjustable guide vanes interposed between said spiral casing and said turbine, a main valve in said penstock, first operating means for said main valve, and second operating means for said adjustable guide vanes; a control system comprising means to supply motive fluid to said spiral casing at low pressure when said main valve and said adjustable guide vanes are closed, whereby to maintain the spiral casing substantially full of water, said control system further comprising interlock means including electrical power supply means, an electric circuit connected between said electrical power supply means and said second operating means and including first switch means which is closed when the main valve reaches a first predetermined percentage opening (x percent) to complete said circuit whereby to allow said second Operating means to begin to open said adjustable guide vanes, said electric circuit also including second switch means which is opened when the adjustable guide vanes reach a predetermined percentage opening (z percent) to break said circuit, and said electric circuit also including third switch means which is closed when the main valve reaches a second predetermined percentage opening (y percent) to complete said circuit whereby to allow said operating means to continue to open said adjustable guide vanes.

5. In a hydraulic reaction turbine alternator set comprising a supply of liquid, a penstock connected to said supply, a main valve in said penstock, first operating means connected to said main valve, a spiral casing connected to said penstock and having an outlet annular, a ring of adjustable guide vanes in said outlet annular, second operating means connected to said adjustable guide vanes, a turbine runner having its inlet within said ring of adjustable guide vanes, whereby liquid is supplied through said penstock, said main valve, said spiral casing and said ring of adjustable guide vanes to said turbine runner to drive it, an alternator having its rotor connected to said turbine runner to be driven thereby, and an electricity network connected to said alternator, characterised in that the maximum equivalent area as herein defined of said main valve is at least four times the maximum equivalent area of the adjustable guide vanes, a control system comprising means to supply liquid to said spiral casing at a pressure which is only a small fraction of the normal working head of the turbine, when the turbine alternator set is operating at synchronous speed and the main valve and the adjustable guide vanes are closed, whereby to maintain the spiral casing substantially full of water, said control system further comprising first position-responsive means responsive to the extent of opening of said adjustable guide vanes, power means for said second operating means, means to connect said power means to said second operating means under control of said first position-responsive means when the extent of opening of said main valve reaches a first predetermined value less than percent, whereby to allow the adjustable guide vanes to begin to open in advance of complete opening of the main valve, means to disconnect said power means from said second operating means under control of said second position-responsive means when the equation is not satisfied, where R is the percentage opening of the main valve at any time t, M is the maximum equivalent area of the main valve, S is the percentage opening of the adjustable guide vanes at that time t, and G is the maximum equivalent area of the adjustable guide vanes, and means to connect said power means to said second operating means under control of said first position-responsive means when the equation is satisfied, whereby the opening of the adjustable guide vanes is so limited that the equivalent area of the adjustable guide vanes at no time exceeds the equivalent area of the main valve.

6. Control system as claimed in claim 1, including means to make up leakage of water from the spiral casing comprising a by-pass across said main valve, so arranged that the spiral casing is maintained substantially full of water at a pressure substantially lower than the full head of water in the penstock.

'7. Control system as claimed in claim 6, wherein said by-pass has an equivalent area between one fiftieth and one eighth of one percent of the maximum equivalent area of said main valve.

8. Control system as claimed in claim 1, including means to make up leakage of water from the spiral casing comprising an external source of water at low pressure connected to the spiral casing through conduit means, and a non-return valve is provided in the conduit means.

9. Control system as claimed in claim 6 for a hydraulic reaction turbine alternator set having a turbine 9 10 of very low specific speed design, wherein said means References Cited by the Examiner to make up leakage of Water from the spiral casing com- UNITED STATES PATENTS pnses means to supply cooling Water to the Uni of the turbine, the centrifugal efiect due to rotation of the tur- 1,706,812 3/1929 253-44 bine causing part at least of the cooling water to flow 5 2,713,643 7/1955 Rhemgans 253*97 past the adjustable guide vanes into the spiral casing and wherein means is provided for the escape of surplus MARK NEWMAN Pnmary Exammer' water from the spiral casing. JULIUS E. WEST, Examiner.

Claims

2. IN A HYDRAULIC REACTION TURBINE HAVING A MAIN VALVE IN A PENSTOCK AND ADJUSTABLE GUIDE VANES IN A CASING MEANS TO OPEN SAID MAIN VALVE, MEANS TO OPEN SAID ADJUSTABLE GUIDE VANES, AND MEANS INTERLOCKING EACH OF SAID MEANS TO PREVENT THE EQUIVALENT AREA OF THE ADJUSTABLE GUIDE VANES EXCEEDING THAT OF THE MAIN VALVE.