US2407454A - Automatic speed limiting device for hydraulic turbine rotors - Google Patents

Description

Sept. 10,1946. P. w; SEEWER AUTOMATIC SPEED LIMITING DEVICE FOR HYDRAULIC TURBINE ROTORS Filed Dec. 28; 1942 3 sheets sheet l 2 7 4 m U 0 o I a?! v 2 fi v- 1. l m .6 3 HQ 1.

P ,VP. W.SEEWER 2,407,454

AUTOMATIC SPEED'LIMI'IING DEVICE FOR HYDRAULIC TURBINEROTORS Filed 06 28, 1942 a Sheets-Sheet 2 Sept. 10, P. WER AUTOMATIC SPEED LIMITING DEVICE FOR HYDRAULIC TURBINE ROTORS Fil ed Dec. 28, '1942 :s Sheets-Sheet s Patented Sept. 1Q, 1946 AUTOMATIC SPEED LIMITING DEVICE FOR HYDRAULIC TURBINE ROTORS Paul Werner Seewer, Rugby, England, assignor to The English Electric, Company Limited, London, England, a British company Application December 28, 1942, Serial No. 470,396 In Great Britain January 12, 1942 screams. (01. 253-7443) This invention relates to hydraulic turbines and has for its object to prevent automatically excessive runaway speeds. Although of general application it is of particular value when applied to turbines having swivelling propeller type blades since as is Well known the problem of guarding against runaway of such turbines is particularly difficult.

The invention consists in speed-limiting means mounted on the turbine rotor and adapted, if a predetermined speed be exceeded, to project into the stream and limit the speed of the rotor by exerting a braking torque thereon or by diverting or otherwise disturbing the water on its way to the driving blades or by having a combination of these effects.

Preferably, the device according to the invention consists of a speed-limiting unit in the form of a ring fastened tothe hub of the turbine rotor adjacent to and preferably above the turbine blades. Hinged or slidably mounted on or within this ring are braking or deflecting vanes or like members normally retained against the action of centrifugal force and held out of the stream. When a certain speed is exceeded centrifugal force causes these members to project into the stream.

One form of the invention is .illustrated by Figures 1-4 and Figures 6 and '7 ofthe accompanying drawings, of which Figure 1 is the left hand half of a vertical cross-section through a complete hydraulic turbine of the swivelling propeller bladed type incorporating the invention; Figure 2 is an enlargement of apart of the upper end of the turbine shown in Figure 1; Figure 3 is an enlargement of the pivoted braking vane shown in Figure 1; Figure 4 is a perspective view-showing the swivelling blades and a ring of braking vanes of part of the rotor of the turbine shown in Figure 1, the vanes projecting in the fully operative position; Figur 5 is a view corresponding to Figure 3 of a slightly modified form ofv braking vane; and, Figures 6 and '7 are inclined views of a detail of Figure 2, but to a larger scale than Figure 2.

' In Fig. 1 the turbine is of conventional swivelling propeller bladed type. The stator includes the enveloping turbine casing I from which the incoming water flows through the spaces between the pivoted shutters 2 on its way to the rotor blades. The shutters are operated in the usual manner by the lever and link mechanism indicated at 3 under the automatic control of the turbine speed governor. The rotor comprises the a 2 vertical shaft 4 terminating in the hollow hub 5 carrying the swivelling blades 6.

Secured to the hub immediately above the blades 6 is the ring 1 incorporating the automatic speed-limiting device according to the invention. Within thi ring are mounted a number of braking vanes 8 each of which is hinged as shown in Figs. 1 and 3 about a hinge pin 9 ,with its axis in a plane transverse to the rotor axis. Normally each of the vanes 8 is retained in the position shown in full lines so as to be exactly flushwith the curved circumferential surface of the ring 1 which is a smooth continuation of the surface of the hub 5. vWhen under the action of centrifugal force these vanes turn about their pivot pins 9 the water vpressureas soon as the tips of the vane emerge-assists the vanes to fly out. In their outer position, the vanes 8 create a disturbing action on the incoming stream therebyreducing the driving torque exerted by the water on the turbine driving blades while at the same time these vanes 8 can exercise a powerful braking torque on the rotor by reason of their having to act against the incoming water stream.

Although the device is efiective if the vanes 8 be parallel to the rotor axis, the drawings show the axe of the hing pins 9 in planes which, although transverse to the rotor axis, are not horizontal but inclined at an angle other than 90 to the rotor axis whereby the vanes 8, when they swing out, are not parallel to but are inclined to the rotor axis oppositely to the direction of the blades 6, as shown in Fig. 4, their surfaces thus having a more marked tendency to divert the incoming water on its way to the driving blades 6. It will beappreciated, however, that th axes of the hinge pins could be either horizontal or vertical and the surfaces of the vanes either vertical or specially shaped to divert the water.

Hinged vanes 8 are counter-balanced by portions such as in Fig. 3 to reduce the effect of centrifugal force, thereby allowing of the use of weaker retaining means.

The vanes are provided with means normally retaining them flush with the ring 1 until a certain centrifugal force and hence a certain speed is exceeded. These retaining means may be springs; alternatively they may be breaking links which are snapped by the action of centrifugal force, or they may be a combination of springs and breaking links as shown in Figs. 1 and 2.

As shown in Figs. 1, 2 and 3 each vane 8 is connected by a flexible cable l9-e. g. a steel wire ropepassing over an adjacent pulley ll on the 3 rotor and vertically along a groove formed between the vertical shaft 4 and the usual protective sleeve l2 thereon (see Fig. 1) to the retaining means at the upper end of the shaft shown in the enlarged view Fig. 2. The upper end of the cable NJ is coiled around and anchored to the drum l3 mounted on one of a number of bearings 2! carried by the rotor. Turning with the drum I3 is another drum l4 while coiled around and anchored to the latter is another cable l5 directly attached to a link rod [6, the upper end l6a of which is of such reduced cross section as to snap when the desired pull is applied to the link which thus serves as a breaking link for releasing the associated vane 8 under the ac-.

tion of a predetermined centrifugal force. In the arrangement shown the drum I4 is of smaller diameter than the drum l3 so that the combination forms a reducing arrangement whereby the movement of the broken link rod l6-when the associated vane flies out -is less than the movement of the cable Ill, but it will be understood that these drums could, if desired, be both of the same diameter or that the cable 10 could be directly connected to the link rod IS.

The link rod l6 slides through a guide sleeve 57 carried by the rotor and carries towards its upper end a collar [8. Surrounding the sleeve 51 and the collar it between the flanges thereon is the coiled compression spring I9 which is a comparatively light spring exerting on the cable l0 only sufficient force to retain the associated Vane at a comparatively low speed of the rotor.

The described retaining devices-one for each of the vanes 8are arranged in a ring around the shaft and all are normally held up by the engagement of the upper end of each link rod IS with a latchZil' which can be released in known manner by the ordinarily provided overspeed trip device. The well-known form of operating member for this devicecomprising the tappet pin 22 which, under the action of centrifugal force, can slide (against the action of the spring 23) radially outwards in the sleeve portion 24a forming part of the annular structure 24 secured to and carried around by the shaft 4--can be seen in Figs. 2 and 6. The tappet 22, when it moves out, engages and moves the operating lever 21 of the Well-known complementary part of the trip device attached to a fixed portion of the turbine casing, which part sets in motion valve means to cut off the supply of water to the rotor blades of the turbine, as already mentioned. The upper end of the said operating lever 21 which can be seen at 26 in Figures 2, 6 and 7 is then in a position to engage the end of each latch 29 as they are moved in succession past the lever 27 by the rotation of the shaft. Each latch is shown as being movable clear of the underside of the head of link rod part ltd by turning about the vertical pivot pin secured on and carried around with the said annular structure 24, and will be so moved by the engagement with the end 26 of lever 21.

Figure 6 shows the tappet 22 in its normal position when it is just passing the lever 21, while Figure '7 shows one of the latches 20 just passing the upper part 26 of the lever 21; the chain lines in Figure 7 show the position of part 26 when the tappet 22, in response to excessive overspeed, has engaged lever 21, in which position part 26 can engage and move latch 29 as the turbine rotor rotates.

On a predetermined speed being exceeded, the latch device 20 is released by the overspeed trip 4 device, thus releasing the link rod 16. At this speed the centrifugal force acting on the vane 8 causes a pull on the upper cable is which while insufiicient to snap the reduced portion Ilia of the breaking link 16 is more than suflioient to overcome the upward forc of the spring 19. Accordingly on the release of the latch device, all the vanes fly out substantially simultaneously under the action of centrifugal force aided by the action of the water once the vanes have started to move. In the unlikely event of any latches 20 not releasing, the individual breaking links l6 will snap under the action of the centrifugal force at a slightl higher speed and so allow each vane to fly out. When the turbine rotor has subsequently been brought substantially to a standstill, the springs H can pull up the cables l5 and Ill to their normal position. and. withdraw the vanes into the ring 1.

Operation of the speed limiting device can be seen since the latch 28 visible and downward movement of the link rods !5 can be observed.

To facilitate this observation, markings la may be provided on the shaft adjacent to the flange oi" the collar 58 which moves down with the link 16. Failure of any one of the retaining devices-womprising the combination or" breaking link l6 and spring i9-to retain or withdraw its associated vane 8 can also be seen. In the unlikely event of breakage of any one of the cables [0 or E5, the associated spring is will force the free upper end of the link rod it above its normal position and this again can be seen. The retaining means, being outside the water, are readily available for adjustment 'or replacement of the springs l9 and for replacement of the breaking links it after snapping.

A modification is shown in Fig. 5 which is a section through one vane and an end View of another vane of a ring of retarding vanes 8 each slidably mounted within the ring 7 but with its surface shaped for diverting the incoming water, as can be seen from the said end View. The sliding vane 8 (shown in its outer position by the chain lines) takes the place of the pivoted vane B of Fig. 3 and is connected by the flexible cable Ii] to retaining means exactly as already described with reference to Figs. 2 and 3; it will be clear that this sliding vane will tend to move out into the stream under the action of centrifugal force just as does the hinged vane previously described.

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

1. In combination, a hydraulic turbine rotor, driving blades mounted on the rotor, a ring of speed-limiting vanes mounted on the rotor and free to move outwardly under the action of centrifugal force into the water stream to limit the speed of the rotor, a flexible cord attached to each of said vanes and extending along the rotor to an exposed position above the water stream, guide pulleys for said cords and means holding the ends of said cords at the said position above the water stream to retain said speed-limiting vanes out of the water stream until centrifugal force corresponding to a predetermined safe rotor overspeed is exceeded.

2. In combination, a hydraulic turbine rotor, driving blades mounted on the rotor, a ring of speed-limiting vanes mounted on the rotor and movable under the action of centrifugal force into the Water stream to limit the speed of the rotor, operative connections between said vanes and an exposed position above the water stream,

links at that position holding the ends of said operative connections, said links being proportioned to snap under the action of centrifugal force on the vanes (transmitted through the operative connections) at a predetermined excessive rotor speed, springs exerting on said operative connections a vane-retaining force but so proportioned as to be overcome by centrifugal force at a comparatively low rotor speed, a latch device retaining each of said links (together with the said springs) and latch-releasing means responsive to an excessive rotor speed below that speed at which the links are proportioned to break.

3. In combination, a hydraulic turbine rotor, driving blades mounted on the rotor, speed-limiting vanes mounted on the rotor and movable under the action of centrifugal forc into the water stream to limit the speed of the rotor and means retaining said vanes out of the Water stream, said retaining means having a weakened part proportioned to break when the force thereon due to a predetermined safe overspeed of the 10 turbine is exceeded.

PAUL WERNER SEEWER.

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