US3319422A - Speed governing systems for steam turbines - Google Patents

Description

May 16, 1967 w. G. WATSON SPEED GOVERNING SYSTEMS FOR STEAM TURBINES 2 Sheets-Sheet 1 Filed June 4, 1.965

mwwzwozoo OP H.

INVENTOR WILLIAM GEORGE WATSON BY of w 0 1 ATTORNEYS May 16, 1967 w. s. WATSON 3,319,422

SPEED GOVERNING SYSTEMS FOR STEAM TURBINES Filed June 4, 1965 2 Sheets-Sheet 2 TO RELAY OPERATED GOVERNOR VALVE F/GZ -1'o 'couneussa INVENTOR ATTORNEY -T0 STEAM LINE WILUAM GEORGE MTSON United States Patent 3,319,422 SPEED GOVERNING SYSTEMS FOR STEAM TURBINES William George Watson, Whitley Bay, England, assignor to C. A. Parsons & Company, Limited, Newcastle-upon- Tyne, England, a corporation of Great Britain Filed June 4, 1965, Ser. No. 461,304 Claims priority, application Great Britain, June 5, 1964, 23,494/ 64 9 Claims. (Cl. 60105) This invention relates to speed governing systems for steam turbines.

As is well known in the art, it is common practice to control the speed and load of a large steam turbine plant such as that used in large electrical power stations by means of governing systems which are basically hydraulic systems. In such systems a turbine driven governor controls the pressure of hydraulic fluid which is used to operate relays which in turn control the operation of the governor valves which control the supply of steam to the turbine. It is customary or usual to incorporate in such governing systems turbine unloading means operable in response to changes in one or more predetermined operating conditions. Such unloading means may, for example, incorporate devices sensitive to vacuum in the condenser or to the steam pressure at the main steam stop valve, or both types of device may be included. Any departure from predetermined values of vacuum or stop valve pressure is detected, and the load of the turbine is adjusted to meet the new conditions. The adjustment of the turbine load may be effected by altering the opening of the governor valves independently of the governor. Thus the turbine load is altered independently of any operation of the speed governor.

It is often desirable that the turbine be prevented from taking up load automatically on restoration of normal conditions in the condenser or at the stop valve. This automatic reloading of the turbine may take place because the adjustment of the turbine load as a result of the operation of the devices sensitive to vacuum or stop valve pressure is effected independently of the governor. The governor setting, therefore, remains at the setting which existed prior to the unloading of the turbine by the unloaders, and immediately upon the restoration of normal conditions of vacuum or stop valve pressure, the load on the turbine normally would return to its original value, the turbine speed then being controlled as before by the original setting of the speed governor.

It is an object of this invention to provide a speed governing system for a steam turbine which enable the turbine to be brought back to its original load at the discretion of the operator by adjustment of the governor setting following load shedding of the turbine as a result of the operation of the turbine unloading means.

More specifically, it is an object of this invention to provide such a system which provides for automatically adjusting the governor setting to correspond to the reduced load on the turbine when the unloader devices operate to reduce the load on the turbine, whereby the turbine will not automatically return to its loaded condition upon restoration of normal conditions, or when the unloader devices cease to operate or are restored partly or wholly to their original position.

It is a further object to provide such a system which incorporates a pressure converter so as to permit the use of different fluids in the hydraulic system.

The invention generally consists in a speed governing system for a steam turbine incorporating a governor operable in response to changes in turbine speed, a hydraulic system the pressure of hydraulic fluid in which is varied by changes in governor setting, a governor valve "ice controlling the flow of steam to the turbine in response to changes in pressure in the hydraulic system, and turbine unloading means operable in response to changes in one or more predetermined operating conditions to vary the pressure in the hydraulic system independently of any operation of the governor so as to reduce the steam flow to the turbine, the unloading means being adapted to automatically adjust the governor setting to correspond to reductions in turbine load produced by operation of the unloading means, whereby the turbine will not return to its loaded condition when the unloading means ceases to operate or is restored to its original setting, except under the control of the operator of the plant.

The invention further consists in a turbine speed governing system comprising a governor valve for controlling the flow of steam to a turbine, a governor hydraulic system for variably controlling the governor valve in accordance with the pressure of the governor hydraulic system, a governor for varying the pressure of the governor hydraulic system in response to changes in turbine speed, an unloader hydraulic system, means for varying the pressure in the unloader hydraulic system in response to changes in at least one predetermined operating condition of the turbine other than speed, and differential pressure means operable in response to a predetermined differential pressure between the governor hydraulic system and the unloader hydraulic system to adjust the governor setting so as to vary the pressure in the governor hydraulic system in the sense to reduce the opening of the governor valve, whereby when the pressure in the unloader hydraulic system is varied in response to changes in the predetermined condition to the extent that the predetermined pressure differential is reached, the turbine will be at least partially unloaded and the governor setting will be adjusted in accordance with the unloaded condition to remain in the adjusted setting should the pressure in the unloader hydraulic system return to its original level.

It is yet a further object of this invention to provide a system of the type originally described above wherein the hydraulic system comprises two separate circuits, a first circuit using a fire resistant fluid and incorporating the governor valve and the unloader means, and a second circuit incorporating the governor, a pressure converter connected with each circuit whereby changes in pressure in the second circuit produced by the governor effect changes of pressure in the fluid in the first circuit to operate the governor valve therein, electrical contacts associated with the pressure converter for closing when the pressure in the part of the second circuit in the converter 1 exceeds the pressure in the part of the first circuit in the converter by'a predetermined amount, and a motor connected to the governor and operable on closure of the electrical contacts to adjust the governor setting until the pressure difference in the converter between the first and second circuits is resorted to its original value, at which time the governor setting will not be adjusted further but rather will remain in its adjusted setting.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its operation, together with additional objects and advantages thereof, will best be understood from the following description when considered in connection with the accompanying drawings, wherein:

FIGURE 1 shows somewhat schematically part of a speed governing system in accordance with one form of the present invention; and

FIGURE 2 shows somewhat schematically a part of a speed governing system in accordance with an alternative form of the invention using a fire-resistant fluid circuit.

In the speed governing system for a steam turbine as illustrated in FIGURE 1, the system comprises a speed governor 1 of a well known type mounted on shaft 2 which is driven directly or indirectly by the turbine. In a hydraulic system operable by the governor, pilot oil is fed through a pre-set regulating valve i from inlet line c and then to the governor through ports 3, the oil also being fed through line b to relays operating the governor valves (not shown), which valves control the amount of steam admitted to the turbine. If the turbine speed changes, the position of the plunger 4 in sleeve 5 changes to alter the pilot oil pressure. Thus in the governor shown, an increase in turbine speed would move plunger 4 to the left of the drawing to uncover a part or the whole of ports 5a in the sleeve 5, thus connecting the pilot oil system to drain through line a and reducing the pressure in the system. Reduction of the pilot oil pressure operates the valve relays so as to reduce the opening of the governor valves and hence reduce the steam admitted to the turbine. Conversely if the turbine speed falls the plunger 4 moves to the right of the drawing to reduce the opening of ports 5a and increase the pilot oil pressure in the system. This operates the valve relays to open further the governor valves to increase the steam admitted to the turbine. The pilot oil pressure can also be changed by moving the sleeve 5 for setting purposes under normal operating conditions.

Incorporated in the governing system is a turbine unloading arrangement which in the form shown incorporates a vacuum unloading device 6 and a main steam stop valve pressure unloading device 7. In the form illustrated the vacuum unloading device comprises a casing housing a bellows 8 closed at its lower end by a baseplate 9a forming a bellows piston. The baseplate is formed integral with a hollow plunger 9 which has ports 10 formed therein and moves in a ported bush 11. The bush 11 is surrounded by a chamber 12 to which pilot oil is admitted. The bellows 8 is subjected to condenser pressure internally through connection 11, the bellows being subjected to atmospheric pressure externally. Under conditions of normal condenser vacuum the difference of pressure across the bellows piston holds it against a top stop (not shown), and the ports 10 in the plunger 9 have no communication with the ports in the bush 11.

If the condenser vacuum falls the pressure inside the bellows 8 increases and moves the plunger 9 downwardly assisted by the action of spring 13, and at a predetermined pressure in the condenser the plunger ports 10 are put into communication with the ports in bush 11. Pilot oil can then flow from chamber 12 to drain through the ports 10 and 11 and connection d, thus reducing the pilot oil pressure in the unloader section of the hydraulic system, and in turn reducing the opening of the governor valve to reduce the steam admitted to the turbine in a manner subsequently to be described.

The stop valve unloading device 7 comprises a casing housing a plunger 14 operated through lever 15 by the rod 16 of a spring loaded bellows piston 17. The chamber 18 containing the bellows piston is connected to the steam circuit adjacent the main stop valve through connection f, valves k and l, strainer m and inlet 19. The pressure of the steam is reduced before it reaches the device 7 by being tapped from the connection 1 between orifice 20 and orifice n. The plunger 14 operates in a ported bush 21 which is surrounded by chamber 22 into which pilot oil is admitted.

Under normal conditions the pressure acting on the bellows piston 17 holds the rod 16 against a stop (not shown). The plunger 14 is then in its lowermost position and completely covers the ports in the bush 21, thus preventing escape of oil in the pilot oil system to drain through connection e. If the stop valve pressure falls by a predetermined amount below normal, the pressure acting on bellows piston 17 is reduced, and the rod 16 begins to move downwardly under the action of the spring loaded bellows piston 17. The lever 15 raises plunger 14 to uncover the ports in the bush 21 and allow pilot oil to fiow to drain through connection e, thus reducing the pilot oil pressure in the unloader section of the hydraulic system, and in turn reducing the opening of the governor valve thus reducing the steam admitted to the turbine, in a manner to be described subsequently.

Either of the devices 6 and 7 can unload the turb ne completely if the pressures to which they are sensit ve change by a sufficient degree from their normal operating values. In many instances, however, it is not desirable to unload the turbine completely, and toward this end the device 6 may incorporate a spring loaded piston 23 and plunger 24, the plunger 24 operating in a ported bush 25. During normal operating conditions the pilot oil pressure holds the iston 23 against a top stop, and the ports in the bush 25 allow free access of oil to the chamber 12 in device 6 and chamber 22 in device 7. Should either device 6 or 7 operate and reduce the pilot oil pressure to a predetermined value, for instance a value equivalent to 10% load on the turbine, the piston 23 and plunger 24 move down to cover the ports in the bush 25 to prevent further escape to drain, and thus the pilot oil pressure is maintained at a predetermined minimum pressure.

The unloader hydraulic system, that is, the pilot oil system or circuit operated by the devices 6 and 7, incorporates a separate pilot oil regulating valve j, and is normally isolated from the governor hydraulic system, that is, the pilot oil system or circuit operated by the speed governor 1, by means of a non-return valve 29 which forms part of the turbine unloading arrangement. The valve 29 normally remains closed and maintains the governor hydraulic system isolated from the unloader hydraulic system, although the valve may open under certain conditions to permit fiow from the governor hydraulic system to the unloader hydraulic system as will be described subsequently. To enable the governor setting to be adjusted to a new operating load on the turbine, resulting from the operation of devices 6 and 7, the pilot oil system of the governor 1 and that of the devices 6 and 7 are connected to a differential pressure gauge 26 which incorporates electrical contacts 27 and forms part of the turbine unloading arrangement. Reduction of pilot oil pressure in the pilot oil system of the devices 6 and 7 to a value equal to that of the governor pilot oil system as a result of the action of device 6 or device 7 closes 27 and operates through electrical connections g a governor motor which adjusts the setting of the governor accordingly, for example, by adjusting the position of sleeve 5. Upon adjustment of the governor setting the governor pilot oil pressure then falls in step with the pilot oil pressure operated by device 6 or device 7, and the load on the machine is reduced. If the pilot oil pressure in the system associated with devices 6 and 7 ceases to fall, the contacts 27 will remain open and the governor motor will come to rest with the governor remaining at the adjusted setting. On restoration of vacuum or stop valve pressure the device 6 or 7 will return to its normal position and restore the pilot oil pressure associated with it, but the contacts 27 will remain open so that the governor setting remains at a setting corresponding to the reduced load, the governor oil pressure being prevented from rising by the non-return valve 29. The load on the machine can then be restored in the normal manner by alteration of the governor setting under the control of the operator.

The non-return valve 2 makes provision for the un likely condition that in certain circumstances the governor pilot oil pressure may not fall as rapidly as that of the devices 6 or 7. Depending upon the possibility of this happening, the valve 29 may be arranged to open when the pressure in the pilot oil system of the devices 6 and 7 falls below that in the governor pilot oil system so as to equalize the pressure in both systems through pipe 28. Normally, however, when the pressure in the unloader hydraulic system falls to or substantially to the level of the pressure in the governor hydraulic system the governor setting is adjusted so as to reduce the hydraulic pressure therein before any substantial flow could take place through valve 29.

Referring now to FIGURE 2, the system illustrated therein comprises a main governor 31 associated with turbine-driven shaft 32. An auxiliary governor 31a is also shown, but this is not essential to the invention. Pilot oil is fed via connection 1 and pilot oil regulating valve w to the governor through :ports 33 and also passes to a pressure converter 34. The governor is connected to drain through line 0. The fluid for the governor valve relays and for the turbine unloading means is a fire-resistant flui-d and is kept separate from the pilot oil system. The fluid system includes pumps (not shown) driven independently of the turbine, and pilot fluid passes through line 1.! and a preset regulating valve x to the pressure converter 34 before passing to a relay operating the governor valve. In parallel with the converter in the pilot fluid system are vacuum unloading device 35 and stop valve pressure unloading device 35a, which are part of the turbine unloading arrangement. These are constructed as described in connection with FIGURE 1. Connections q, r, y and z correspond to connections d, e, h and f of FIGURE 1. The pilot fluid passing to the converter is taken from the pilot fluid system of the devices 35 and 35a. Normally the pressure in this system is constant as the ports of these devices are closed.

The pressure converter comprises a casing in which are located two bellows 36 and 37 mounted back to back with a common floating baseplate 38. Connected to baseplate 38 is a plunger 39. Pilot oil is admitted to the inside of bellows 36, and pilot fluid passing from the converter to the governor valve relays is admitted to the inside of bellows 37. The plunger 39 moves in a ported bush E0, arid when the pressure in the bellows 36 equals the pressure in bellows 37 the plunger is in a neutral position in which the ports in bush 40 are closed, and no flow of pilot fluid takes place through the converter. If the pilot oil pressure increases, the plunger 39 moves downwardly to allow pilot fluid to flow through the ported bush 40 and thence through chamber 41 into the pilot fluid system through line v feeding the governor valve relays. This increases the pressure in the pilot fluid system, thus increasing the opening of the governor valve until equilibrium is again reached in the converter with the plunger in the neutral position. If the pilot oil pressure falls, the plunger moves upwardly in the ported bush 44 to allow the pilot fluid to flow to drain through line s, thus reducing the pressure in the pilot fluid system at the relays, and consequently reducing the opening of the governor valve. To reduce the response time of the converter to a rapid fall in pilot oil pressure a second pair of bellows 42 and 43 may be included in back to back relationship as shown. They have a common baseplate 44 to which is attached plunger 45. A fall in the pilot oil pressure moves the plunger 45 upwardly to provide a further connection between the pilot fluid system at the governor valve relays and the drain.

If the turbine is running at, for instance, full load, and the vacuum unloading device 35 or the stop valve pressure unloading device 35a operates to lower the pilot fluid pressure supplied to the converter, the pressure after the converter at the valve relays also falls by virtue of the bypass incorporating non-return valve 29a, and as it falls below the pilot oil pressure the plunger 39 moves downwardly, and the turbine unloading means overrides the governor. The pressures before and after the converter become equal, and as they fall instep the load on the turbine is reduced. The pilot oil pressure remains constant during the initial stage of the fall in pilot fluid pressure since the governor setting is not altered.

When a predetermined fall in pilot fluid pressure has taken place, the plunger 39 has moved by a distance sufficient to close electrical contacts of an electrical switch device 46, which in turn operates the governor motor to adjust the governor setting. The governor setting is then adjusted to correspond with the new load on the turbine as determined by devices 35 or 35a. The pilot oil pressure will then be approximately equal to the pilot fluid pressure. If the pressure in the pilot fluid system associated with devices 35 and 35a ceases to fall the electrical contacts of switch device 46 open and the governor motor comes to rest. When the devices 35 and 35a return to normal the electrical circuit remains open, and the governor will remain at the low load setting and override the turbine unloading means. The load on the turbine will therefore remain at its reduced value until the governor setting is adjusted by the operator.

From the foregoing description of the structure and operation of the two exemplary embodiments, it will be seen that each embodiment provides an unloader arrangement operable in response to changes in at least one predetermined operating condition of the turbine other than speed to vary the pressure in the hydraulic system in the sense to at least partially unload the turbine by partially closing the governor valve, the unloader arrangement providing for automatically adjusting the governor setting to correspond to the reduction in turbine load so as to prevent restoration of turbine load when thepredetermined operating condition returns to its normal value.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible, and my invention, therefore, is not to be restricted to the precise details of construction shown and described, but is intended to cover all modifications coming within the scope of the appended claims.

Having thus fully described my invention in the manner required by the patent statutes, I claim:

1. A speed governing system for a steam turbine, comprising a governor valve for controlling the flow of steam to a turbine; a hydraulic control system for variably controlling said governor valve in accordance with the pressure in said hydraulic system; a governor for varying the pressure of said hydraulic control system in response to changes in turbine speed so as in turn to control said governor valve; turbine unloading means operable in response to changes in at least one predetermined operating condition of the turbine other than speed to vary the pressure in said hydraulic system in the sense to at least partially close said governor valve, said unloading means including means for automatically adjusting the governor setting to correspond to reduction in turbine load produced by operation of said unloading means and for leaving the governor setting at its adjusted value upon removal of said predetermined operating condition so as not to restore the load on the turbine when the unloading means ceases to operate.

2. In a steam turbine plant, a turbine speed governing system comprising a governor valve for controlling the flow of steam to a turbine; a hydraulic system for variably controlling said governor valve in accordance with the pressure of the hydraulic system; a governor for varying the pressure of said hydraulic system in response to changes in turbine speed; an unloader means operable in response to changes in at least one predetermined operating condition of the turbine other than speed to vary the pressure in said hydraulic system in the sense to at least partially unload the turbine by partially closing said governor valve, said unloader means including means for automatically adjusting the governor setting to correspond to the reduction in turbine load so as to prevent automatic restoration of turbine load when said unloader means ceases to vary said pressure in said sense.

3. Apparatus as set forth in claim 2 wherein said unloader means is adapted to operate in response to changes in condenser vacuum of a steam condenser associated with the turbine.

4. Apparatus as set forth in claim 2 wherein said unloader means is adapted to operate in response to changes in steam pressure supplied to the turbine.

5. Apparatus as set forth in claim 2 in which the hydraulic system comprises two separate circuits, a first circuit using a fire-resistant fluid and incorporating the said governor valve and the unloader means, and a second circuit incorporating the governor; a pressure converter connected with each circuit whereby changes in pressure in the second circuit produced by the governor effect changes of pressure in the fluid in the first circuit to operate the governor valves therein; electrical contacts associated with said pressure converter for closing when the pressure in the part of the second circuit in said converter exceeds the pressure in the part of the first circuit in said converter by a predetermined amount, and a motor connected to said governor and operable on closure of said electrical contacts to adjust the governor setting until the pressure difference in the converter between the first and second circuits is restored to its original value.

6. In a steam turbine plant, a turbine speed governing system comprising a governor valve for controlling the flow of steam to a turbine; a governor hydraulic system for variably controlling said governor valve in accordance with the pressure of .the governor hydraulic system; a governor for varying the pressure of said governor hydraulic system in response to changes in turbine speed; an unloader hydraulic system; means for varying the pressure in said unloader hydraulic system in response to changes in at least one predetermined operating condition of the turbine other than speed; and differential pressure means operable in response to a predetermined differential pressure between said governor hydraulic system and said unloader hydraulic system to adjust the governor setting so as to vary the pressure in said governor hydraulic system in the sense to reduce the opening of said governor valve until the differential pressure between the two systems is changed from said predetermined value, whereby when the pressure in said unloader hydraulic system is varied in response to changes in said predetermined condition to the extent that the predetermined pressure differential is reached, the turbine will be at least partially unloaded and the governor setting will be adjusted in accordance with the unloaded condition to remain at the adjusted setting should the pressure in said unloader hydraulic system return to its original level.

7. Apparatus as set forth in claim 6 wherein said governor operates to reduce the pressure in said governor hydraulic system in response to increases in turbine speed, wherein said means for varying the pressure in said unloader hydraulic system operates to reduce the pressure therein in response to changes in said predetermined operating condition, and wherein said predetermined pressure differential is reached when the pressure in said unloader hydraulic system falls to substantially the pressure in said governor hydraulic system.

8. Apparatus as set forth in claim 7 further comprising a non-return valve for permitting flow from said governor hydraulic system to said unloader hydraulic system.

9. Apparatus as set forth in claim 7 wherein said pressure differential means includes a pair of electrical contacts which are closed when the differential pressure reaches said predetermined value and which are open when the pressure differential is above said predetermined value, and a motor controlled by the closing of said contacts for adjusting the governor setting in the sense to reduce the governor hydraulic system pressure to reduce the opening of the governor v alve when said contacts are closed.

No references cited.

MARTIN P. SCHWADRON, Primary Examiner.

R. R. BUNEVICH, Assistant Examiner.

Claims (1)

1. A SPEED GOVERNING SYSTEM FOR A STEAM TURBINE, COMPRISING A GOVERNOR VALVE FOR CONTROLLING THE FLOW OF STEAM TO A TURBINE; A HYDRAULIC CONTROL SYSTEM FOR VARIABLY CONTROLLING SAID GOVERNOR VALVE IN ACCORDANCE WITH THE PRESSURE IN SAID HYDRAULIC SYSTEM; A GOVERNOR FOR VARYING THE PRESSURE OF SAID HYDRAULIC CONTROL SYSTEM IN RESPONSE TO CHANGES IN TURBINE SPEED SO AS IN TURN TO CONTROL SAID GOVERNOR VALVE; TURBINE UNLOADING MEANS OPERABLE IN RESPONSE TO CHANGES IN AT LEAST ONE PREDETERMINED OPERATING CONDITION OF THE TURBINE OTHER THAN SPEED TO VARY THE PRESSURE IN SAID HYDRAULIC SYSTEM IN THE SENSE TO AT LEAST PARTIALLY CLOSE SAID GOVERNOR VALVE, SAID UNLOADING MEANS INCLUDING MEANS FOR AUTOMATICALLY ADJUSTING THE GOVERNOR SETTING TO CORRESPOND TO REDUCTION IN TURBINE LOAD PRO-

Images