US2141260A - Governing mechanism for elastic fluid turbines - Google Patents

Description

Dec. 27, 1938. 4 R. J. CAUGHEY 2,141,260

GOVERNING MECHANISM FOR ELASTIC FLUID TURBINES Filed Nov. 6/1936 Inventor:

Reed J. (laugh g,

"His A torneg.

Patented Dec. 27, 1938 PATENT OFFICE GOVERNING MECHANISM FOR- ELASTIC FLUID TURBINES Reed J. Caughey, Schenectady, Y., assignor to New York General Electric Com pany, a corporation of Application November 6, 1936, Serial No. 109,454

4 Claims.

In the operation of steam plants and especially those of public utilities, it is becoming more and more important to provide accurate and sensi tive governing mechanisms for the steam turbines which drive the generators that supply electric current to distribution systems. This is particularly true of those systems where the total load is apportioned from time to time by load dispatchers between two or more generating stations upon some predetermined plan and where the frequency of the currentof the several generators must be maintained alike. The construction and operation of steam throttle valves of the commonly accepted type are such that so long as the pressure on the outlet side of the valve is less than approximately one-half the pressure on the inlet side, a condition commonly referred to as the critical, equal movements of the valve result in equal increments of steam passing therethrough. However, when the valve is further opened, the critical relation no longer exists and it becomes necessary to move the valve a substantially greater distance for the same added increments of steam flow. For

2;") example, with the valve wide open and a presvsure drop ofonly one and one-half per. cent across it, there is required approximately four times as much area to pass the same quantity of steam as is required when the pressure drop 30 is less than the critical. Asa result of this, when turbine driven generators areconnected in multiple to the same system of distribution and are deliveringdifferent amounts of power thereto, the positions of the governing mecha- 35 nisms thereof will be dissimilar in certain respects. This is due to the fact that steam flow 'when plotted against the travel or stroke of the valve no longer has a straight line function after the valve has been opened to a position 40 above its critical.

My invention has for its object the provision of an improved governing mechanism for elastic fluid turbines having means operating on the controlling valve or valves in such manner 5 that for equal increments of speed equal increments of elastic fluid are supplied to the turbine, thereby producing a straight line function of steam flow. 4

For a consideration of what I believe to be 50 novel and my invention, attention -is directed to the accompanying description and the claims appended thereto.

In the drawing is illustrated an embodiment of my invention applied to a steam turbine.

5 l indicates a multistage steam or other elastic fluid turbine of any known or suitable construction. Secured to the casing in any suitable manner is a valve chest 2 having a fluid inlet conduit 3. Inside of the chest may be one or more valves 4 each having a seat 5. Since all of the 5 valves are similar, a description of one of .them will sufiice. To the valve is attached a stem 6 and the latter is moved by a lever 1. In order to impart to the valve a greater movement for a given increment of steam after the valve has 10 passed its critical, a cam 8 is provided, the radial dimension of which increases rather rapidly after the valve'has begun its movement from its seat. The lever has an antifriction roller at one end for engagement with the cam, and a compres- 15 sion spring 9 is provided to cause the valve to close as the cam permits the free end of the lever'to be lowered.

Mounted on the shaft l0 of the cam is a gear H which meshes with a rack i 2 which is actue 20 ated by an hydraulic ,or other motor and forms a continuation of its piston rod. The motor comprises a piston l3 and cylinder M. The motoris controlled by a pilot valve having heads l5 and I6 which normally cover the cylinder ports communicating with the conduits I! and i8 leading to the motor. Fluid under pressure enters the valve casing through the conduit I 9 and escapes therefrom either through the conduits 20 or 2|, depending upon the position of the pilot valve. After each movement of the motor, the pilot valve is returned to the position shown, which has the effect of holding the piston of the motor in a definite position as determined by the speed governor.

The speed governor as usual comprises centrifugally acting weights 22 and an opposing spring 23. The governor is driven by a shaft 24 which in turn is driven by the main shaft 25 of the turbine in the usual manner. 'The weights act 40 on the governor lever 26 to raise and lower its outer or free end as the speed changes. To the outer end of the lever is connected a floating lever 21 through thelink 28. The floating lever is .pivotally connected to the stem 29 of the pilot valve. The floating levers of governors and motors of the character described, as ordinarily constructed, are pivotally connected to the piston rod of the motor. My construction differs therefrom so that a modification of the movements of the valve 4 for a givenmovement of the governor lever may be obtained. To accomplish this, a rack 30 is mounted on the piston rod with which meshes a gear 3| rigidly mounted on a shaft 32. On said shaft is also 56 as a pivot.

rigidly mounted a cam 33 so shaped that its radial dimension rapidly increases from the low point to the high point. The right-hand end of the floating lever which ordinarily would be pivotally attached to the piston rod is provided with an antifriction roller 34 which engages the peripheral surface of the cam and is held in governor raises the free end of the governor lever and by means of the link 28 the left-hand end of the floating lever is raised about the roller 34 This has the effect of raising the pilot valve and admitting fluid through conduit ,l'i to the cylinder space above the piston l3. As the piston moves downward, it turns the gear H and cam 8 in an anticlockwise direction with the result of further opening the main steam valve 4. The same downward movement of the motor piston turns the gear 3| and cam 33 in a clockwise direction with the result of changing the position, of the roller or pivot 34 by permitting the spring 35 to raise itv by a limited amount determined by the position of the cam 33. This action has the effect of somewhat delaying the restoration of the pilot valve to its neutral position, where it closes the ports of the motor. This delay in closing of theports means that for a given upward movement of the outer end of the governorlever 26, the main valvehas a greater opening movement than would be the case if the floating lever were pivotally attached to the piston rod as usual. Conversely, when the speed of the turbine rises due to decrease of load, the pilot valve is depressed and the piston l3 rises and the gear H and cam 8 turn clockwise and permit the main valve-4 to move toward its seat under the action of the compression spring 9. At the same time, gear 3| and cam 33 are turned anticlockwise, which has theeffect of depressing the roller 34 more quickly than would be the case if the floating lever was directly connected to the piston rod, as in former constructions, and the pilot valve is restored more quickly to its neutral position than would otherwise be the case. The ultimate effect of the cams 8 and 33 with their associated parts is to impart to the main steam valve 4, a straight line function over its entire range of movement where equal increments of speed result in equal increments of steam, thereby increasing the accuracy of operation of the mechanism and a closer regulation of the turbine obtained. Where more than a single valve 4 for admitting steam to the turbine is employed, the cam 33 will have as many cam faces as there are valves.

What I claim as new and desire to secure by Letters Patent of the United States is:

'1. An elastic fluid turbine in combination with a speed governor driven thereby, a controlling valve for admitting fluid to the turbine, a fluid actuated motor comprising a piston and cylinder,

a quick lift cam and lever actuated by the motor for moving the valve from its seat, a pilot valve moved by the governor for controlling the action of the motor, a follow-up device for restoring the pilot valve to its neutral position after each movement thereof which includes a floating lever connected at one end to the governor and a quick acting cam moved by the motor and acting on the other end of the floating lever, the action of said cams resulting in a straight line function of steam flow.

2. An elastic fluid turbine in combination with a speed governor driven thereby, a controlling valve for admitting fluid to the turbine, a fluid actuated motor comprising a piston and cylinder, a quick lift cam and lever, gearing actuated by the motor for turning the cam to move the valve by the lever from its seat, a pilot valve moved by the governor for controlling the action of the motor, a follow-up devicefor restoring the pilot valve to its neutral position after each movement thereof, which includes a floating lever connected at one end to the governor, a quick acting cam acting on the other end of the lever, and gearing actuated by the motor as it moves the controlling valve for turning the lastmentioned cam, the action of said cams resulting in a straight line function of steam flow.

3. An elastic fluid turbine in combination with a speed governor driven thereby, a controlling valve for admitting fluid to the turbine, a fluid actuated motor comprising a piston and cylinder, a first cam, a lever actuated by the cam for opening the valve, gearing actuated by the motor for turning the cam to cause the lever to open the valve, a pilot valve moved by the governor for controlling the action of the motor, a follow-up device for restoring the pilot valve to its neutral position after each movement thereof, which includes a floating lever connected at one end to the governor, a second cam upon which the other end of the floating lever is fulcrumed, and gearing actuated by the motor as it moves the controlling valve for turning the last mentioned cam, the motor turning the first and second cams in opposite directions for each of its movements.

4. An elastic fluid turbine in combination with a speed governor driven thereby, a throttle valve movable through a critical position for controlling the admission of motor fluid to the turbine in accordance with changes in speed thereof, a

fluid actuated motor comprising a piston and cylinder for moving the valve from and toward its seat, a pilot valve having neutral and oper-- ative positions for controlling the action of the motor, a follow-up device including a floating lever for moving the pilot valve, one end of the lever being moved by the governor, and a cam moved by the motor acting as a fulcrum for the floating lever, the cam being shaped to delay the restoration of the pilot valve to its neutral position by changing the position of the fulcrum when the throttle valve is moved in one direction from its critical position and to accelerate the restoration of the pilot valve to its neutral position by again changing the position of the fulcrum but in the opposite sense when the throttle valve is moved in the opposite direction from said critical position, the shape of the cam resulting in a straight line function of steam flow.

' REED J. CAUGI-IEY.

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