US2175875A - Turbine protective arrangement - Google Patents

Description

' Oct. 10, 1939.

R. J. CAUGHEY 2,175,875 TURBINE rnorzcuvfi ARRANGEMENT Filed July 30-, 19,38 2 Sheets-Sheet 1 0 A9 v m...

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Reedlcaughey HI' S ZttQPney Patented Oct. 10, 1939 UNITED STATES PATENT OFFICE Reed J. Caughey, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 30, 1938, Serial No. 222,239

15 Claims.

The present invention relates to protective. means for elastic fluid power plants and more particularly to arrangements for preventing overheating of superposed, back pressure turbines 5 connected to electric current generators.

In enlarging older designed central stations, additional boiler capacity is usually provided which supplies steam or other elastic fluid at relatively high pressure to one or more super- 10 posed turbines which in turn exhaust to the existing lower pressure header supplying operating fluid to one or more lower pressure turbines. The generators driven by the various turbines are usually connected together in parallel through 15 the station buses to supply power to a network or other load.

Upon the occurrence of certain abnormal conditions, the flow of steam through the high pres sure turbine may be reduced below that required 20 for driving it full speed at no load. The lower pressure units may continue in operation at full or partial load either from the reduced flow of steam through the high pressure unit or from the steam supplied from the lower pressure boil- 5 ers. With the generators connected together, the direction of power flow will reverse through the generator of the high pressure unit to drive it as a motor and in turn drive the high pressure turbine at substantially full speed. It has been 30 found that if a high pressure turbine is rotated at such a speed with a flow of steam being supplied thereto materially less than that normally required for driving it at no load, the internal temperature of the turbine will rise to a danger- 35 ously high value due primarily to the windage losses of the rotor.

Among the more common occurrences which may result in the motoring of a superposed high pressure turbine through the generator are 4 these:

(1) An accidental tripping of the high pressure emergency stop valve or failure of the governor control valve resulting in no flow of steam to the turbine and with the generator left con- 45 nected to the line.

(2) An abnormal rise in back pressure to the high pressure turbine due either to an increase in the output of the low pressure boilers or faulty operation of the reducing valve by-passing the 50 high pressure turbine. This increase in back pressure, operating on the back pressure regulator of the high pressure turbine, greatly decreases the steam flow through the high pressure turbine until the flow therethrough may reach 55 a dangerous minimum value.

(3) A loss of station load with the high and lower pressure turbine generators connected together. The no load flow of steam, as determined by the requirements of the low pressure turbines, would be materially less than the no 5 load flow of the high pressure turbine and hence may be insuflicient to prevent the overheating thereof.

(4) A sudden shut down of the high pressure boiler resulting in no ifow of steam through the high pressure turbine but leaving the high pressure turbine generator electrically connected to the buses.

Because of the problems inherently involved in obtaining accurate indications of the rotor temperature and because of the relatively slow rate of thermal conduction through the turbine casing, means other than temperature indicating devices must be resorted to for preventing damage to the turbine blading upon the occurrence of any abnormal conditions, such as those listed, likely to cause excessive heating.

It is an object of this invention to provide a new and improved arrangement for safeguarding a superposed high pressure turbine against overheating when being driven by its generator by disconnecting the high pressure turbine generator from the line in response to a predetermined minimum flow of elastic fluid through the turbine. 80

It is a further object of this invention to provide a new and improved arrangement for protecting a turbine against overheating due to windage losses by maintaining a predetermined minimum flow of elastic fluid therethrough during the continuance of the abnormal conditions causing the turbine to be driven by its generator.

For a consideration of what I believe to be novel and my invention, attention is directed to the following specification and the claims ap- 0 pended thereto taken in connection with the accompanying drawings.

In the drawings, Fig. 1 discloses a typical superposed turbine power plant provided with one form of protective means according to my invention, and Figs. 2, 3, and 4 disclose turbine power plants of the type shown in Fig. 1 provided with protective means according to further modifications of my invention.

Referring to Fig. 1 of the drawings, i0 is a superposed back pressure turbine supplied with elastic fluid from the high pressure boiler ll. Suitable control valves, such as the emergency stop valve 12 and the throttle or admission valve I3, are provided in the conduit I4 supplying elastic fluid from the high pressure boiler H to the turbine. The exhaust from the high pressure turbine is conducted as by conduit l5, having a suitable check valve iii therein, to the header ii to which may be connected one or more lower pressure turbines It, or other elastic fluid consumers, through branch feeders 59. Additional elastic fluid may be supplied to the header II from one or more lower pressure boilers 20 through conduit 25. A connection, such as 22, having an automatic pressure reducing valve 23 therein, is also usually provided for supplying fluid from the high pressure boiler to the header ll when the high pressure turbine is shut down. Means are usually provided in turbine installations of the class described for maintaining substantially constant the back pressure on the high pressure turbine it or, in other words, the pressure in the header II. This may be accomplished by means of a back pressure regulator of a wellknown form (not shown) for augmenting the regulation of the admission valve l3. The high and lower pressure turbines, Ml and I8, are connected to generators 24 and 25 which during normal operation supply power to the bus lines in parallel connection through the feeders 2i and 28, respectively. Suitable circuit breakers and 38 are provided in the leads 27 and 28 respectively, the circuit breaker 29 being illustrated as being of the latched closed type having a suitable closing operator 3! and latch releasing device 32.

According to my invention, means are provided for disconnecting the high pressure turbine generator 24 from the station buses 26 in accordance with a predetermined minimum flow of elastic fluid through the high pressure turbine iii. A measurement of the actual elastic fluid flow therethrough may be made by any suitable means such as by the difierential pressure responsive means 33 arranged across a given number of turbine diaphragms. As indicated in the drawings, a pair of suitable pressure responsive devices 35 and 35 may be connected across a given number of turbine diaphragms by connections 35 and 317 respectively and arranged for differentially actuating a lever 38. The lever 38, pivoted to a stationary part 39, is provided on its outer end with a movable contact it adapted to engage with a stationary contact to close a circuit for energizing the circuit breaker tripping solenoid 32 from a suitable source of supply 42. An interlock 43 provided on the operating mechanism of the switch 29 may be arranged in the circuit for deenergizing the tripping solenoid following actuation of the circuit breaker to the open position. Suitable adjusting means 44 may be provided in connection with the flow responsive device 33 whereby the tripping operation may be selectively controlled in accordance with a predetermined minimum flow of elastic fluid through the turbine. Thus, if for any reason, such as upon the occurrence of one of the above listed abnormal conditions, the flow of elastic fluid through the turbine should be reduced to the point where it would be driven by its generator, the generator will be disconnected from the line before the turbine is seriously overheated.

In central station operation, it is often undesirable to disconnect the generators from the station buses except in cases of absolute necessity. In a second modification of my invention shown in Fig. 2, an arrangement is provided which will effect a readjustment of the governor control means for the elastic fluid admission valves to the high pressure turbine so as to permit a sufiicient flow of fluid through the turbine upon the occurrence of certain predetermined abnormal conditions which conditions might otherwise cause overheating of this turbine. In Fig. 2 is shown a power plant of the same type as shown in Fig. 1, like reference characters being applied to indicate elements previously described in connection with Fig. l. The low pressure portion of the power plant including turbine l8 and generator 25 has been deleted in Fig. 2, it being understood that such elements may be connected to the header H. In this modification the elastic fluid admission valve it for the high pressure turbine lil is shown connected to a suitable hydraulic operating motor 45 which is in turn controlled by the pilot valve lii. The admission valve operating motor and pilot valve are normally regulated in a well-known manner as by a speed governor 4'! which is shown as being driven through gearing 48 from the turbine shaft 9. The flyweights of the governor may be connected by link 5%] to the governor beam 5! which is stationarily pivoted as at 52. Movements of the governor beam may be transmitted through link 53 to the floating lever 54 connected in the wellknown manner to the stems of the pilot valve and of the operating motor.

Assume a normal condition of station operation during which the high pressure turbine is operating at partial load and at least one lower pressure turbine is operating under full load, the latter turbine receiving operating fluid exhausted by the high pressure unit. Now assuming a loss of station load, due to some extraneous reason, both turbines will tend to rise in speed. Since the high pressure turbine governor will close its admission valves by only a partial stroke, while a full stroke will be necessary to close the valves of the low pressure turbine, a slight increase of speed will normally close the valves of the high pressure unit whereas the same increase of speed will only partly close the lower pressure turbine valves. Upon the resultant decrease of pressure in the header H, the automatic by-pass valve 23 will open to pass operating fluid into the low pressure header, permitting the lower pressure turbine to continue to run. The high pressure turbine will then be motored by a reversal of power flow to its generator from the lower pressure turbine generator. With little or no flow of elastic fluid through the high pressure turbine, it would rapidly overheat due to windage losses therein as explained above.

According to this modification of my invention, r

means are provided for biasing the high pressure turbine governor beam 46 against valve closing movements in response to a predetermined minimum flow of elastic fluid through the turbine l0. Such biasing of the governor beam may be accomplished by suitable control of the usual governor synchronizing spring, or by separate biasing means. As shown, the spring 55, normally inactive, is arranged for adjustment into a biasing position against the beam. 5| to oppose the valve closing movements of the governor 4'! by means of a suitable motor 55 and gearing 57. The motor circuit is adapted to be energized from a suitable source of supply 58 through contacts 40 and H of the flow measuring device 33 and interlock 43 associated with the circuit breaker 529. The interlock 43 is provided for deenergizing the circuit 65 upon the opening of the circuit breaker 29, such as upon shut down of the high pressure unit. Any suitable means (not shown) may be provided for limiting the duration of operation of the motor 56, or for restoring the biasing means to the normal inactive position upon the resumption of normal station load conditions. By the arrangement shown, the motor 56 is energized upon a predetermined decrease in the flow of elastic fluid through the turbine III to exert a biasing force upon the governor beam 5I in opposition to the governor 41 so that the admission valve I3 will be maintained at least in the opened no load position. With this quantity of elastic fluid passing through the turbine excessive heating thereof due to energy losses will be precluded. The quantity of elastic fluid exhausted into the header II in excess of that required by the low pressure turbines connected thereto may be passed oil to atmosphere through the usual relief valve such as 59.

In Fig. 3 is shown a further modification similar in its function to that shown in Fig. 2. In this modification a by-pass connection 60 is provided extending around the emergency stop valve I2 and the governor controlled admission valve I3 between the high pressure boiler and the turbine I0. The by-pass connection is provided with a suitable valve 6| which is normally retained in its closed position as by spring means 62 connected to the valve operating lever 63. The valve may be opened by means of an electro-magnetic device 64, the circuit 65 of which may be energized from a suitable source of supply 66 through contacts and M of the flow measuring device 33 and through the interlock 43 associated with the circuit breaker 29. By this arrangement upon the loss of station load and the resultant closure of the governor controlled admission valve I 3, as described above, the flow measuring device 33 will close the contacts 40 and H to energize the electro-magnetic operator 64 for opening the by-pass valve 6|. The by-pass connection may be of such size so that it will pass an amount of elastic fluid to the turbine I0 substantially equal to the no load flow required for keeping the turbine sufliciently cool. It will be noted that this arrangement will also protect the high pressure turbine against overheating upon the occurrence of conditions (1) and (2) as well as (3), as described.

In Fig. 4 is shown a further modification in which a flow, of cooling elastic fluid is allowed to pass through the turbine I0 in the reverse direction upon the occurrence of one of the conditions outlined above. An exhaust connection Ill extending from the first stage shell is provided with a valve II normally retained in the closed position by such means as the spring I2 connected to the operating arm I3. The valve is actuable to the open position by the electro-magnetic actuating means I4 connected to the valve operating arm "I3. The normally unidirectional or check valve I6 in this instance is provided with an operating arm I5 to which is connected an electro-magnetic actuating device I6 for holding the valve open so as to allow fluid flow therethrough in the reverse direction. The electromagnetic devices 14 and I6 may be connected in parallel and arranged for simultaneous energization from a suitable source of supply 11 through the contacts 40 and 4| of the flow measuring device 33. By this arrangement, upon the occurrence of any abnormal condition resulting in the closure of either of the valves I2 or I3, or upon the failure of the boiler II, with the generator left connected to the buses, a suflicient flow of elastic fluid for maintaining the temperature of the turbine l0 within safe limits may be circulated through the turbine in the reverse direction from the header I'I.

Having described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

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

1. In a superposed power plant system, the combination including a source of relatively high pressure elastic fluid, a high pressure turbine connected to said source, a source of relatively low pressure elastic fluid including the exhaust of said high pressure turbine, a low pressure turbine connected to said last-mentioned source, generators coupled to said turbines and arranged for parallel operation, means for preventing overheating of said high pressure turbine upon said high pressure turbine being driven by its generator, said means including means responsive to a predetermined flow of elastic fluid through said high pressure turbine.

2. In a superposed power plant system having a source of relatively high pressure elastic fluid, a high pressure turbine connected to said source, a source of relatively low pressure elastic fluid, a low pressure turbine connected to said lastmentioned source, generators driven by said turbines and normally electrically connected togethor for parallel operation, means for preventing overheating of said high pressure turbine due to windage losses caused by said high pressure turbine being driven by its generator supplied with energy from said low pressure turbine generator, said means including means responsive to a predetermined minimum flow of elastic fluid through said high pressure turbine.

3. In a superposed power plant system comprising high and low pressure turbines for normally driving parallel connected generators, the combination including governor means for normally regulating the supply of elastic fluid to said high pressure turbine, means responsive to a predetermined minimum flow of elastic fluid through said high pressure turbine, and valve means responsive to the actuation of said flow responsive means for admitting elastic fluid to said high pressure turbine independently of said governor means.

4. In an elastic fluid power plant, a turbine, a generator normally driven by said turbine for supplying power to station buses, means for preventing overheating of said turbine upon its being driven by a reversal of power flow from said buses to said generator, said means comprising a device responsive to a predetermined minimum flow of elastic fluid through said turbine, and valve means responsive to the operation of said device for admitting an increased flow of elastic fluid to said turbine.

5. In a power plant system having a source of relatively high pressure elastic fluid, a high pressure turbine connected to said source, a relatively low pressure turbine connected for receiving the exhaust from said first turbine and electric generators driven by said turbine normally electrically connected to common buses for parallel operation, a circuit breaker for disconnecting said high pressure turbine generator from said buses, tripping means for said circuit breaker, and a device responsive to a predetermined minimum flow of elastic fluid through said high pressure turbine for energizing said tripping means.

6. In a superposed power plant system having a source of relatively high pressure elastic fluid, a high pressure turbine connected to said source, a relatively low pressure turbine connected for receiving the exhaust of said first turbine, electric generators driven by said turbines normally electrically connected together through common buses for parallel operation, means for preventing overheating of said high pressure turbine due to windage losses occasioned by said high pressure turbine being motored by its generator supplied with energy from said low pressure turbine generator, said means including a device responsive to a predetermined minimum flow of elastic fluid through said high pressure turbine for disconnecting said high pressure turbine generator from said low pressure turbine generator.

7. In a superposed power plant system comprising sources of relatively high and low pressure elastic fluid, a high pressure turbine arranged between said two sources, a generator normally driven by said turbine and supplying power to station buses, a device responsive to a predetermined minimum flow of elastic fluid through said turbine, and means responsive to said de vice for admitting elastic fluid from said low pressure source to said turbine.

8. In a superposed power plant system comprising sources of relatively high and low pressure elastic fluid, a turbine arranged between said sources, a generator normally driven by said turbine and supplying power to station buses, means responsive to a predetermined flow of elastic fluid through said turbine, and valve means responsive to the actuation of said flow responsive means for admitting elastic fluid from said low pressure source through said turbine.

9. In a power plant, a high pressure header, a low pressure header, a high pressure elastic fluid turbine arranged between said headers, a generator normally driven by said turbine and supplying power to station buses, a normally unidirectional valve for precluding the flow of elastic fluid from said low pressure header to said turbine, conduit means including a normally closed auxiliary exhaust valve in communication with the inlet chamber of said high pressure turbine, a device responsive to a predetermined minimum flow of elastic fluid through said turbine for initiating the opening of said unidirectional valve and said auxiliary exhaust valve whereby elastic fluid is permitted to flow from said low pressure header through said high pressure turbine.

10. In combination, an elastic fluid turbine, an electric generator normally driven by said turbine connected to station buses, valve means for controlling the admission of elastic fluid to said turbine, a governor driven by said turbine for normally regulating said valve means, and means responsive to a predetermined minimum flow of elastic fluid through said turbine for effecting an increase in the supply of elastic fluid to said turbine irrespective of the position of adjustment of said governor for preventing overheating of said turbine upon said turbine being motored by a reversal of power flow from the station buses to said generator.

11. In combination, an elastic fluid turbine, governor controlled means for normally regulating the supply of elastic fluid to said turbine, an electric generator normally driven by said turbine, means for normally connecting said generator to station buses, means for preventing overheating of said turbine upon said turbine being motored by said generator, said means comprising a device responsive to a predetermined minimum flow of elastic fluid through said turbine, and means controlled by said device for adjusting said governor controlled means for increasing the supply of elastic fluid to said turbine.

12. In combination, an elastic fluid turbine, an elastic fluid admission valve for said turbine, governor means driven by said turbine for normally regulating said valve, and means responsive to a predetermined minimum flow of elastic fluid through said turbine for increasing the supply of elastic fluid to said turbine irrespective of the condition of operation of said governor means.

13. In combination, an elastic fluid turbine, an electric generator normally driven by said turbine, means for normally connecting said generator to station buses, and means responsive to a predetermined minimum flow of elastic fluid through said turbine for effecting the disconnection of said generator from said buses.

14. In combination. a source of relatively high pressure elastic fluid, a turbine normally receiving elastic fluid from said source, a source of relatively low pressure elastic fluid, a header supplied with elastic fluid from said low pressure source, conduit means for normally conducting the exhaust fluid from said turbine to said header, a unidirectional valve in said conduit means for normally precluding a reversal of elastic fluid flow from said header to said turbine, means responsive to a predetermined minimum flow of elastic fluid through said turbine, and means controlled by said last mentioned means for permitting a circulation of elastic fluid from said header through said turbine.

15. In combination, a source of relatively high pressure elastic fluid, a turbine normally receiving elastic fluid from said source, a source of relatively low pressure elastic fluid, a header supplied with elastic fluid irom said low pressure source, conduit means for normally conducting the exhaust fluid from said turbine to said header, a unidirectional valve in said conduit means for normally precluding a reversal of elastic fluid flow from said header to said turbine, means responsive to a predetermined minimum flow of elastic fluid through said turbine for permitting a reverse fluid flow from said header through said conduit means to said turbine, and normally closed valve means operable upon actuation of said flow responsive means for permitting the discharge of said reverse fluid flow from said turbine.

REED J. CAUGHEY.

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