US2543129A - Reheat turbine control apparatus - Google Patents

Description

Feb. 27, 1951 H. R. REESE REHEAT TURBINE CONTROL APPARATUS Filed Nov. 4, 1949 2 Sheets-Sheet 1 INVENTOR R. Reese BY a vslcfi I Homer ATTORNEY Feb. 27, 1951 H. R. REESE REHEAT TURBINE CONTROL APPARATUS 2 Sheets-Sheet 2 Filed Nov. 4, 1949 NOE INVENTOR Homer R. Reese BY a KR ATTORNEY Patented Feb. 27, 1951 STATES "PATENT OFFICE REHEAT TURBINE CONTROL APPARATUS Application November 4, 1949, Serial No. 125,587

1 Claim.

The invention relates to the type of reheat turbine installation disclosed and claimed in the application of Franck, Serial No. 39,261, filed July 17, 1948, wherein high-pressure and intermediatepressure, unidirectional, axial-flow blading has th stationary blading carried by a single cylinder and wherein the cylinder has an interior partition sealed with respect to the rotor and separating the exhaust chamber of the high-pressure section from the inlet chamber of the intermediate-pressure section, superheated steam being supplied to the high-pressure blading and steam exhausting from the latter into the exhaust chamber being withdrawn, reheated and then supplied to the intermediate-pressure blading, and it has for an object, upon the attainment of a suflicient turbine speed, to close the interceptor valve in the passage supplying reheated steam to the intermediate-pressure blading and to open a leak-01f passag to conduct steam directly from the partition and rotor seal to the condenser in order to avoid overspeeding of the installation by entrapped steam leaking through the seal and driving the intermediate-pressure and low-pressure blading.

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

Fig. l is a diagrammatic view of a reheat turbine unit and control arrangement with the leakofi feature to avoid overspeeding incident to closing of the interceptor valve;

Fig. 2 is a sectional view of high and intermediate-turbine sections and showing the condenser leak-ofi for the separating seal; and

Fig. 3 is an enlarged detail view of the separating seal and its leak-off.

In the drawing, there is shown a turbine installation of the type disclosed in said Franck application. The cylinder and the rotor ll (Fig. 2) are provided with axial, unidirectional-flow blading including a high-pressure section, at 12, and an intermediate-pressur section, at M. Steam flows in series through the high-pressure and the intermediate-pressure sections and the low-pressure section or turbine (Fig. 1), arranged either in tandem or cross-compound relation.

The cylinder H! has an interior partition I! provided with an inner annular member l8 defining, with respect to the rotor ll sealing clearance H0. The partition separates the exhaust chamber of the high-pressure section from the inlet chamber 2! of the intermediate-pressure section. An annular leak-oft" chamber 22 communicates with the clearance l9 and sealing means 23 is arranged in the clearance at least at the downstream side of the leak-off chamber and preferably at both sides thereof.

A first conduit 25 supplies superheated steam to the high-pressure section 12; a second conduit 25 supplies steam from the exhaust chamber 20 to the reheater 25; and a third conduit 21 supplies reheated steam to the inlet chamber 2|.

The superheated steam conduit 24 has a throttle valve 28 and a governor valve 29 arranged downstream from the latter. A normally-open intercepting valve 3i is arranged in the reheated steam conduit .27.

The throttle, governor and intercepting valves are preferably operated by a speed-responsive governor arrangement, such as disclosed and claimed in the Bryant application, Serial No. 36,837, filed July 3, 1948, now Patent No. 2,504,640, the governing arrangement including main and auxiliary governors, at 32 and 33, an autostop governor, at 34, and operating devices or servos 35, 36 and 3'! for the throttle, governor and interceptor valves, respectively.

In normal operation, the throttle and interceptor valves 28 and 31 are open and the governor valve 23 is under control of the main governor, at 32. Upon sudden load drop and consequent increase in speed, when rated speed is exceeded a predetermined amount, the auxiliary governor, at 33, supersedes the main governor in control of the governing valve; and, because of its smaller speed droop, the auxiliary governor closes the governor valve at a lower speed than that at which it would be closed by the main governor. Upon increase in speed a small amount in excess of that required for the auxiliary governor to close the governor valve, such governor operates a trip device 38 to provide for closing of the interceptor valve. If, for any reason, the turbine overspeeds to the trip-ping point of the autostop governor, at 343, then the latter operates to trip both the throttle and the interceptor valves for closing.

Normally, the pressure drop across the partition seal 23, and determined by the piping resistance of the reheating flow path, is relatively small, being of the order of pounds; however, upon closing of the interceptor valve 3|, the pressure in the inlet chamber 2| of the intermediate-pressure section decreases rapidly due to the free passage therefrom through the intermediate-pressure and low-pressure turbine sections to the condenser 39, in consequence of which the pressure drop across the partition seal may increase greatly. For example, such pressure drop may increase from the order of 50 pounds to 400 pounds. As leakage through the seal from the high-pressure section exhaust chamber 20 to the intermediate pressure section inlet chamber 2! is a function of the pressure drop, upon closing of the interceptor valve, the pressure drop may become so great that the leakage of entrapped steam may be suflicient to drive the intermediatepressure and low-pressure sections to overspeed the installation. To guard against such overspeeding, in accordance with the present invention, the gland or seal has said leak-off space 22 communicating with the passage 40 formed in the cylinder structure and which passage communicates with a pipe 5! connected to the condenser, the passage and pipe forming a conduit, which, when open, provides for flow of steam directly from the leak-on space 22 to the condenser 39.

The leak-oft conduit is normally closed by a valve 42, the valve being biased to closing position by the spring 43. Upon the auxiliary governor taking control of the turbine, in addition to the auxiliary pressure tripping the interceptor valve for closing, such pressure acts on the piston 44 connected to the valve 32 to open the latter against the force of the spring. Therefore, when the auxiliary governor trips the interceptor valve to closed position, thereby, because of communication of the intermediate-pressure and low-pressure sections with the condenser, creating a condition of high-pressure drop across the partition gland, leakage of steam across the gland is limited because of opening of the leak-off passage from the gland to the condenser.

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.

What I claim is:

In a reheat turbine and condenser installation, a cylinder; a rotor; blading carried by the cylinder and by the rotor and including first and second unidirectional axial-flow blading sections; a reheater; an interior partition wall uni tary with the cylinder and separating the blading sections; said partition Wall including an inner annular member encompassin the rotor; a leak-off space in open communication with the clearance between such member and the rotor; means for sealing said clearance at least at the downstream side of the leak-off space; a first conduit for supplying superheated steam to the inlet of the first blading section; a second conduit for conducting steam from the exhaust chamber of the first blading section to the reheater; a third conduit for conducting reheated steam from the reheater to the inlet chamber of the second blading section; a fourth conduit for connecting the leak-off space to the condenser; a governor valve in the first conduit; an interceptor valve in the third conduit; a normally-closed stop valve in the leak-oi? conduit; and speed-responsive governor means operated by the turbine and operative, upon the attainment of a predetermined speed, to close the governor valve and thereafter, upon the attainment of a slightly higher speed to close the interceptor valve and to open said normally closed stop valve of the leak-oil conduit.

HOMER. R. REESE.

No references cited.

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