US1792240A - Control mechanism - Google Patents

Description

Feb. 10,1931. J. L. RAY 1,792,240

CONTROL uacmmrs u 7 Filed July so. 1929 4WITNESS INVENTOR 3 BY J. L. RAY.

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ATTORNEY Patented Feb. 10, 1931 UNITED STATES PATENT}, OFFICE JAMES L. BAY, OF SWARTHMORE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CONTROL MECHANISM Application filed July 30, 1929. Serial No. 382,235.

.My invention relates to a control mechanism for a prime mover, more particularly to a load-responsive control for a prime mover, and it has for its object to provide a mech- 5 anism of this character which will minimize the increase in speed upon a sudden removal or decrease in the load thereof.

My invention is adapted, more particularly, to a steam turbine of large capacity driving an electric enerator. While carrying full or a heavy oad, the quantity of steam in the casing is very great and the admission valve or valves are fully open, or nearly so and admit large quantities of steam. In the event that the circuit breaker for the generator opens, the entire load on the turbinegenerator unit is removed, and the speed thereof is increased by the large quantity of steam in the turbine casing and by the steam being admitted through the open admission valves. A short but appreciable period of time is required, after such event, for the speed to accelerate to the point at which the governor acts to close the admission valves, during which period of time the admission valves remain open and admit an amount of steam, which, together with the steam in the casing at the moment of load removal, is sufficient to produce an over-speed great enough to effect operation of the auto-stop governor. It is desirable to avoid operation of the auto stop governor, as this requires resetting thereof, and also manual operation of the massive throttle valve before the unit can be restarted.

The steam in the casing at the moment of load drop may be sufficient to increase the speed somewhat above the normal operating speed, but it is not enough to increase the speed sufficiently to operate the auto-stop governor. A control mechanism, therefore, which effects closing of the admission valve during the interval of time between'the moment of load drop and the increase in speed to the point where the governor will shut the admission valves, will avoid operation of the auto-stop governor.

In accordance with my invention, I provide a control mechanism including a device for closingfthe admission valve upon a predetermined low load on the turbine, and further including means controlled b the adjustment of the governor for ren ering the device inoperative while the governor is adjusted for a light load. Thus the closing device does not interfere with operation of the prime mover While carrying no load or a light load, at which time the functioning of the closing device is not needed as the quantities of steam within the casing and steam being admitted are not sufiicient to cause objectionable overspeeding.

The above and other objects are effected by my invention, as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a diagrammatic view showing my novel control mechanism applied to a prime mover driving an electric generator; and,

Fig. 2 is a detail of a modified portion of the control mechanism.

Referring to the drawing more in detail, I show a turbine-generator unit including an elastic fluid turbine driving an electric generator 11. The generator 11 delivers electric current to a power line 12 through leads 13, in which is disposed a circuit break or 14.

The turbine 10 is supplied with motive fluid from a conduit 15, through a valve 16 which controls the admission thereof to the turbine. The valve 16 is controlled by a speed responsive governor 17 through a fluid pressure relay mechanism 18. The relay mechanism 18 includes a motor device 19 connected to the valve 16 by a rod 16 and controlled by a pilot valve 20.

The latter is operated by a lever 22, which is connected, intermediate its ends, to the same is well known in the art, one suitable form being fully described in Patent No. 1,151,522, issued August 24, 1915, to Francis Hodglrinson. For the purpose of the present description, the lever 22 may be considered as if fulcrumed at 23.

The governor 17 may be of any suitable construction and is here shown as of the centrifugal flyball type. It is 'pivotally connected at 23 to a lever24 tulcrumed on a stationary part at 25, and biases the same upwardly by a force varying with the speed oi. the turbine, said force increasing with increased speed.

The lever 24 is pivoted at 26' to a lever 27. which in turn is pivoted to the lever 22 at 28. At itsothe'r end the lever 24 is connected to a speed changer mechanism 29; the connection including a lever 31, tulcruined intermediate its ends, as at 32, and connected tofthe other end of the lever 24 by means of a short link 33.

The speed changer mechanism 29 includes a spring 34 connected at its upper end to the lever '31 and-at its lower end to a spring holding'member 35. The spring holding member 35 is attached to the upper end oi a screw threaded stem36, whose vertical position is controlled by a worm gear 37 actuated by a speed changer motor 38.

The apparatus so far described is old and well known, and operates briefly as follows:

Upon a decrease in load on the generator 11 andan increase in speed, the governor 17 moves the right hand end of the leverv 4 upwardly against the force of the spring 34, thereby moving. the lefthand end of the lever 22 upwardly through the lever 27. The relay mechanism thereupon moves the valve 16 in closing direction to decrease the admission of motive fluid.

Upon increase in load and decrease in speed, theright hand end of the lever 24 is moved downwardly and the admission valve 16 is moved in opening direction.

To raise the speed setting of the governor, the speed changer motor 38 is operated to lower the stem 36 by means ofthe gear 37, As will be apparent from the drawing, this operation effects. through the connecting levers, an increased opening oi the admission valve, whereupon the speed increases until the increased force of the governor effect-s an increased deflection of the spring 34. To lower the'speed setting, the speed changer motor 38 is operated to raise the stem 36.

To the above described apparatus, I add my novel control mechanism which includes an electrical circuit 39. In this circuit is interposed a switch 41, whichis normally biased to open position by a spring 42, and adapted to be closed by a low-load device 43. The latter is any device responsive to the load on the generator 11, such as a wattmeter or ammeter device responsive to the current flowing through the leads 13.

in the illustrated embodiment, this device includes a solenoid 44 and a core 45 therein which operates the switch 41. FJ hen the load on the generator is of a pr determined amount, the solenoid 44 raises the core to open the switch 41. When the load is less than this amount, however, the core 45 drops by gravity and closes the switch 41. The device 43 is preferably provided with suitable adjusting means, such as arheostat 46,

to setthesame to any desired predetermined load.

The circuit-39 further includes a second switch 47 having a contact member 48. The latteris disposed in the path of a second contact member 49 attached to the speed changer stem 36 which contacts withthe member 48 to close the switch when lowered to a sufiicient extent in raising the speed setting.

The circuit 39 further includes a solenoid 51, which operates the valve 21, when the circuit is completed, to effect complete closinn; of the admission valve 16. A suitable source-oi electrical current, such as a battery 52, is provided for the circuit.

The operation of the above described embodiment is as follows:

As is understood in the art, the speed changer is operated in accordance with the load carried on the turbine, that is, as the load increases the speed setting is raised in order to obtain the increased admission valve opening without a change of speed. This is more particularly, true where the turbine drives a synchronous generator electrically connected to other generators in a system so that all the generators must run at the same speed. Here, the load on any one generator can be changed only by changing the speed setting. The position 01 the speed changer stem 36 may, therefore, be taken as a function of the load for which the admission valve is set to provide the necessary motive fluid admission. 7 V

The contact member 49 and the contact member, 48 are so disposed as to close the switch 47 only when the speed changer is set for a load at which the switch 41 is open, preferably a load slightly above the predetermined load above which the switch 41 is opened, and to open the same when set for lowerloads. Thus, the turbine and generator may be controlled at low loads by the speed governor, without interference of the control mechanism.

When the load on the generator 11 is removed or decreased to a load below theprelie determined load, while the speed changer is set to close the Switch '47, as by opening of the circuit breaker 14, the switch 41 is closed. The circuit 39 is thus completed,

and the solenoid 51 is energized to operate the valve 21. The latter controls the motor device 19 to effect immediate and rapid closing of the admission valve 16.

Thus, upon a load drop while the unit is carrying a heavy load, the admission of motive fluid is promptly shut ofl' without waiting for the speed to accelerate, and an excessive overs eed thereof is accordingly avoided. Bef ere the circuit breaker 14 can again be closed, the speed of the unit must be brought exactly to synchronous speed, that is, the speed at which the alternations of the current of the generator 11 are in synchronism with the alternations of the current in the line 12. This operation is commonly known in the art as synchronizing, and is effected by lowering the speed setting to the point at which the no-load speed corresponds to the synchronous speed or frequency in the line 12. As above described,

when the speed setting is lowered sufliciently, the switch 47 is opened, rendering the governor 17 fully operative to control the admission of motive fluid to the turbine.

The switch 47 enables the unit to be operated, when desired, at low loads at which the switch 41 is open. Should a load drop occur while thus operating, the speed can be adequately limited by the speed governor, due to the fact that the m'otivefluid within the turbine casing and that being admitted by the admission valve 16 are of lesser amounts.

In Fig. 2, I show a modification of my control mechanism which is similar to that shown in Fig.1, the only difference being that the contact member 49 for operating the switch 47 is carried on the lever 27 instead of the speed changer stem 36.

The operation of this embodiment is substantially the same as that of Fig. 1. The

position of the lever 27 controls, normally, the admission valve 16. Hence the position of this lever may be used to open the circuit 39 while carrying light loads.

At light loads, the lever 27 moves upwardly and the switch 49 is opened. When the lever moves downwardly to admit an amount of motive fluid to carry a load greater than the predetermined load at which the switch 41 1 opens, the contact member 49 engages the contact member 48 and closes the switch 47 The circuit may thus be completed by the switch 41 to effect closing of the admission valve in case of load drop.

From the above description it will be seen that I have provided a novel control mechanism which effects immediate closing of the admission valve in the event of load drop while carrying heavy load, thus minimizing overspeeding at such time. The necessity of resetting the automatic stop governor (not shown) and reopening the throttle valve (not shown) is eliminated,-it being only necessary to change thespeedsetting to render the governor operative and to restore the unit to the line.

. While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth inthe appended claims.

What I claim is: g

1. The combination with a prime mover having a speed governor and an admission valve normally controlled by the overnor, of meansfor varying the setting of t e governor, means for effecting closing movement of the admission valve independently of the governor action upon a minimum load on the prime mover, and means controlled by the governor setting for rendering the last-mentioned means inoperative.

2. The combination with a prime mover having means responsive to the speed thereof for normally controlling the admission of motive fluid thereto, of means for shutting ofl the admission of motive fluid upon a predetermined low load on the prime mover, and means controlled by the first-mentioned means for rendering the last-mentioned 1 means inoperative.

3. The combination with a prime mover having a speed governor and an admission valve normally controlled by the governor, of means for varying the setting of the governor, means responsive to a predetermined 10w load on the prime mover for shutting ofl the admission of motive fluid thereto, and means for rendering the last-mentioned means inoperative while the governor is set for light load.

4. The combination with a prime mover having means responsive to the speed thereof for normally controlling the admission of motive fluid thereto, of a control mechanism including an electric circuit having therein a plurality of switches in series, means responsive to a predetermined low load on the prime mover for closing one of the switches, means controlled by the first-mentioned means and operative when positioned to admit motive fluid for carrying a predetermined minimum load to open another of said switches, and means controlled by said circuit and efiective when the same is closed to shut off the admission of motive fluid to the prime mover.

5. The combination with a prime mover having a speed governor and an admission valve controlled by the governor, of a speed changer for varying the setting of the governor, and a control mechanism including an electric circuit having therein a plurality of switches in series, means controlled by the load on the prime mover for operating one of the switches and efiective to close the same upon a predetermined minimum load, means controlled by the speed changer for operating another switch and effective to open the same While the governor is set for carrying a load 10 less than said predetermined minimum load, and means operative upon closing of the elec-, tric circuit for closing said admission Valve.

In testimony whereof, I have hereunto subscribed my name this th day of July, 1929.

JAMES L. RAY.

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