US1792241A - Control mechanism - Google Patents

Description

Feb. 10, 1931. J R 1,792,241

CONTROL MECHANISM Filed July 30, 1929 WITNESS INVENTOR 6.1 I J. L. RAY. BY

ATTORNEY Patented Eel 10, 1931 UNITED- s'ra'ras PATENT OFFICE JAMES L. BAY, OF SWABTHMOBE, PENNSYLVANIA, ASBIGNOB '10. WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CONTROL MECHANISM Y Application filed July 30,

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 mechanism 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 generator. While carry, ing full or a heavy load, the quantity of steam in the casing is very great and the admission valve or valves are, fully 0 en, or

nearly so and admit large quantities o steam.

' In the event that the c1rcuit breaker for the generator opens, the entire load on the turbine generator unit is removed, and the speed thereof is increased by the large quantity of steam inthe turbine casing and by the no steam being admitted through the open ad mission valves. A short but appreciable eriod 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 .30 great enough to effect operation of the autostop 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 sufiicient to increase the speed somewhat above the normal operating speed, but it is not enough to increase the speed sufliciently 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 oint where the governor will shut the 8111111881011 valves, will avoid operation of the auto-stop governor.

In accordance with my invention, I provide, in addition to the usual speed governor, a mechanism which is responsive to the 1929. Serial No. 382,286.

load on the prime mover, and which effects immediate closing of the admission valve, independently of the governor action, upon decrease in'load by a predetermined amount below the load for which the overning mechanism is positioned to admit motive fluid. In other words, the minimum load below which the control mechanism efl'ccts closing of the admission valve is varied by the position of a part of the governor mechanism, as by the adjustment of the speed changer.

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 drawin s, forming a part of this application, in Whic The figure is a diagrammatic view showing my novel control mechanism applied to a prime mover driving an electric generator.

Referring to the drawing more in detail, I show a turbine-generator unit including an elastic fluid turbine 10 driving a synchronous alternating current generator 11. The generator 11 delivers electric current to a power line 12 through leads 13, in which is disposed a circuit breaker 14.

The turbine 10 is supplied with motive fluid from a conduit. 15, through a valve 16 which controlsthe 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 valve 20. The latter is operated by a lever 22, which is connected, intermediate its ends, to the pilot valve, as indicated at 23', and at one end to the rod 16. It also includes an auxiliary pilot valve 21 adapted to control the motor device 19'to elfect complete closin of the valve '16 regardless of the action 0 thepilot valve 20. The relay mechanism is not shown in detail for the reason that 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 Hodgkinson. For the purpose of the present description, the lever 22 may be considered as fulcrumed at 23.

The governor 17 may be of any suitable construction and is here shown as of the flyball type. It is pivotally connected to a lever 24, fulcrumed on a stationary part at 25,

' At its other end, the lever 24 is connected to a speed changer mechanism 29, the connection including a lever 31, fulcrumed intermediate its ends, as at '32, and connected to the 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 of a screw threaded stem 36, 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 and an increase in speed, the governor 17 moves the right hand end of the lever 24 upwardly against the force of the spring 34, thereby.moving the left-hand end of the lever 22 upwardly. The relay mechanism thereupon moves the'valve 16in closing direction td decrease theadmissionof motive Upon increase in load and decrease in speed, the right-hand end of the lever 24 is moved downwardly and the admission valve 16 ismoved 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 of the gear 37.

As will be a parent from'the drawing, this operation e ects, through the connecting levers, an increased opening of the admis- S1011 valve, whereupon the speed increases until the increased force of the governor effects 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 actuates the auxiliary pilot valve 21 ofthe relay mechanism 18. This control mechanism includes a circuit 39, in which is interposed a solenoid 51 for operating the auxiliary pilot'valve 21. Any suitable means, such as a battery 52, may be provided forsupplying electric current to the circuit, and the clos ng of the circuit is controlled by a switch 41, normally biased to open position by a spring 42.

The switch 41 is adapted to be .closed by a device 43, which is responsive to the load on the generator 11 and is adapted to close the switch 41 upon suflicient decrease in load. The device 43 preferably includes a solenoid 44, which is energized in accordance with the flow of current through the leads 13 in any suitable manner, as by the current transformer coil 53 arranged in circuit with the solenoid 44. Disposed within the solenoid 44 is a core 45 which is adapted to drop by gravity to close the switch 41 when the core is insufliciently energized, and to be raised by the solenoid 44 to open the switch 41 when the solenoid 44 is sufficiently energized.

In accordance with my invention, the auxiliary pilot valve 21 is operated by my novel control mechanism when the load on the generator is a predetermined amount less than that for which the governor 17 is positioned and accordingly the setting of the load-responsive device 43 is controlled by some part of the governing mechanism whose position corresponds to the amount of motive fluid being admitted by the valve 16. In the present embodiment, this is accomplished by suspending the core 45 from the stem 36 of the speed changer mechanism through a spring 47. Suitable adjusting means for varying the setting of the load-responsive devlce for a givenspeed setting of the governor is preferably provided such as a screwthreaded connection 50 between the spring 47 and the core 45. r

The operation of the above described em bodiment is as follows: t

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, theload on any one generator can be changed only by changing the speed setting. The position of the speed changer stem 36 may, therefore, be taken as a function of the load on the unit.

The core 45 is biased downwardly by gravity. It is biased upwardly by the spring 47 and further b the magnetic effect of the solenoid 44, w ich varies with the load on the turbine. The adjusting means 50 is set so that when the generator 11 is carrying the load corresponding to the adjustment of the speed changer as determined by the position of the stem 36, the switch 41 is open.

When the load decreases, however, a prcdetermined amount below said corresponding load, the solenoid 44 permits the core to close the switch 41. The circuit 39 is thus completed and the solenoid "51 operates the auxiliary valve 21. The latter controls the motor device 19 to efiiect complete closing of spring force for a given amount of necessary to close t cordance with the load corresponding to that for which the speed changer is set.- As the speed setting is raised for increased load, by. lowering the stem 36, the deflection of the spring 47 is decreased. Hence, the generator must carr a greater load to hold the core 45 a ainst c osing the switch 41. Conversely, w on the s eed setting is lowered for de creased 'loa by raising the stem 36, the deflection of the spring 36 is increased, and the low load on the generator at which the switch 41 closes, is decreased. As the speed setting is lowered to some suitable light load at Which the speed governor can satisfactorily restrict the speed in case of load drop, the force of the s ring 47 alone becomes suflicient to hold t e core 45 against closing the switch 41; thus at lightloads, the control mechanism is not operative.

The amount which'the load on the generator must decrease, below the load corresponding tothe adjustment of the speed changer, to close the switch 41, may be the same for all settings. This is done by adjusting the rheostat so that the solenoid 44 effects a change in'bias equal to the chan e in load change. The amount of the necessary decrease may then be varied by the adjustment 5(). On the other hand, the rheostat 46 may be adjusted to var ing amounts of decrease he switch 41 with varying adjustments of the speed changer. While the unit is carrying a substantial load, i. e. a load as great as the amount of decrease necessary to close the switch 41, it

I the load on the enerator be removed, as by opening of the circuit breaker 14, the admission valve 16 is promptly brought to completely closed position. Before 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 1.1 are in synchronism with the alternations of the current in the line 12. This operation is commonlv known in the art as synchronizing, and is effected by lowerin the s p setting to the point at which t e nocad speed corresponds to the synchronous speed or frequency in the line 12. As above described, when the speed setting is lowered suificiently, the switch 41 is opened independentl of the load on the generator, reno erative to derin t e governor 17 full g y uid to the control the admission of motive turbine.

During normal operation, the load on the generator does not vary greatly from that corresponding to 'the setting of the speed changer, and control of the admission valve by the speed governor 17 is not interfered .with.

It will thus be seen that I hav e provided a novel control mechanism which permits thespeed governor to control the admission valve at all loads during normal operation, but effects immediate closing of the admission valve if a substantial load is removed from the generator. Thus overspeeding' in case-of load drop due to o ning of the circuit breaker' is avoided. y avoiding overspeeding, the necessity of resetting the automatic sto governor (not shown) ,and reopening the throttle valve (not shown) 15 eliminated, it being only necessary to change the speed'setting to render the governor operative and to permit the unit to be restored to the line. V

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications, without departing from the spirit thereof,

and I desire, therefore, that only such limi-H tations shall be placed thereupon as are imposed b the prior art or asare specifically set fort in the appended clalms. I

What I claim 1s: a 1 g.

1. The combination with a prime mover having a speed governor and a. speed ,changer for the governor, of means responsive to the load on the rime mover and -o rative to shut off the admission of motive flu1d to the operative stages thereof upon decrease below a predetermmed minimum load, and means conand means controlled by the position of the,

speed changer mechanism for adjustin the first-mentioned means to vary the pre etermined minimum load.

3. The combination with a prime mover having an admission valve and an electric generator driven thereby, of a governor mechanism for normally controlling the admission valve and including a speed-responsive governor, means efi'ectmg complete closing of the admission valve, independently of the action of the governor, upon decrease inload on the generator below a predetermined minimum load, and means controlled biy'the governing mechanism for changing t e setting of the last-mentioned means tovary said predetermined-minimum load with changes in the load to which the governing mechanismis ositioned.

4. The com ination with a prime mover and an electric generator driven thereb of a governor responsive to the speed c the prime mover for normally oontrolling the admission of motive fluid to the prime mover and having a part whose position varies in acoordance with the admission of motive fluid, means responsive to the electric load on the generator for effecting closing movement of the admission valve, independently of the governor action, upon decrease below a predetermined minimum' load, and means controlled by the position of said governor part for adjustin the first-mentioned means to vary the pre etermined minimum load.

5. The combination with a prime mover having'an admission valve and an electric generator driven thereby, of a governor responsive to the speed of the prime mover for normally controlling the admission of motive fluid thereto, and having a part whose position normally varies with the amount of motive fluid admission determined byv the governor,a relay for operating the admission valve, said relay havin a pilot valve controlled by the governor or normally controlling the admission valve and' an auxiliary pilot valve adapted to effect closing of thet admission'valve independently of the action of the first-mentioned ilot valve, and means for operating the aux iary pilot valve upon decrease in load on the generator by a predetermined amount below the load corresponding to the position of said governor part.

a governing mechanism responsive to the speed of the 823119 mover. for normall controlling the a ssion of motive fluid t ereto and having a part whose position normally varies in accordance with the admission of motive fluid, means responsive to the load on the prime mover for com letely shutting oil? the admission of motive uid, independently of the speed-responsive action of the govern-' ing mechanism, upon decrease below a predetermined minimum load, and means controlled by the position of said governor part for adjusting the load-responsive means to vary the predetermined minimum load.

In testimony whereof, I have hereunto subscribed my name to this 25th day of July,

'- 1 JAMES L. RAY.

6. The combination with aprime mover, of

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