US3657552A - Method for employment of fast turbine valving - Google Patents

Abstract

In a process of fast steam turbine valving employed as a way to avoid loss of synchronism within a power system in the event of a transmission line fault, automatic modification of post fault sustained turbine driving power is programmed in response to operation of generating station protective relay means employed to initiate opening of transmission voltage level back-up circuit breakers, when the opening of such breakers would cause the opening of two transmission lines.

Description

United States Patent [151 3,657,552 Park Apr. 18,1972

[54] METHOD'FOR EMPLOYMENT OF FAST TURBINE VALVING Primary Examiner-Remard A. Gilheany Assistant ExaminerW. E. Duncanson, Jr.

[72] Inventor: Robert H. Park, Main Street, Brewster, 57 ABSTRACT Mass. 02631 In a process of fast steam turbine valving employed as a way to Flled! June 1, 1970 avoid loss of synchronism within a power system in the event [21] APP] Na; 42 281 of a transmission line fault, automatic modification of post fault sustained turbine driving power is programmed in response to operation of generating station protective relay [52] US. Cl ..290/40 B, 290/52 means employed to initiate opening of transmission voltage [51] Int. Cl ..F01k 13/02 level back-up circuit breakers, when the opening of such [58] Field of Search ..290/2, 40, 43, 51, 52, 54 breakers would cause the opening of two transmission lines. [56] References Cited UNITED STATES PATENTS 2 Claims, 2 Drawing Figures 3,421,014 l/l969 Moorganov ..290/40 lP LP GENERATOR STEAM H Q IV SOURCE 200 205 TO BREAKER "A" I P Ol SERVO HAM RAM 207 TR C L n VALVE TIMER .2o4

STATION PROTECTIVE RELAY SYSTEM GOVERNING SYSTEM (PORTIONS NOT SQS F Z 209v SEPARATELY SHOWN) BREAKER "A" DELAYED FAULT CLEARANCE RELAY PATENTEDAPR 18 I972 m OE mom

00 nix-r m T N E V m TwE ROBERT H. PARK CROSS-REFERENCE TO RELATED INVENTIONS My invention relates in its principal aspect to means for rapidly controlling power flow within power transmission elements of interconnected power systems with a view to favorably affecting the stability of such systems when jeopardized by suddenly occuring adverse events. This patent application is a continuation-in-part of my issued US. Pat. Nos. 3,051,842 and Re. 26,571, and of a copending application, Ser. No. 525,615 filed Feb. 7, 1966.

BACKGROUND OF THE INVENTION 1. Field of Invention The area of utility of the invention comprises prevention of development of system instability within power systems when threatened by transmission line faults.

The area of method comprises employment of means of automatic full or partial closure of valves controlling input of steam to steam turbine type generator prime movers of power systems, effected within one-fourth second following a fault, followed by full or partial valve reopening, effected within a matter of seconds.

2. Prior Art Early patents that are of interest as in the nature of prior art comprise U.S. Pat. Nos. 1,705,688 and 1,935,292 which issued respectively to S. A. Staege on Mar. 19, 1929, and to S. B. Griscom et al. on Nov. 14, 1933.

Tests reported in reference (6), and carried out in 1930, on a 50,000 k.w. reheat type turbine generator, showed that useful results could be obtained if sufficiently fast valve closure was achieved with the aid of valve operating oil dumping.

In 1966 a technical paper was presented before The American Power Conference which reviewed potentialities of rapidly executed valve closing as a system stability improving measure. (2)* (*Numbers in parentheses refer to a table of references located at the end of the specification) Following this paper, computer implemented studies were carried out which indicated that what was termed either early valving, or fast valving could significantly improve stability (c.f. references lb, 2, 3, 4, 5), and these and other studies, in turn, led to the placement of orders for the furnishing of steam-electric generating units that would be suitably equipped to allow employment of rapid valving as a stability benefiting means.

In the matter of controls, ability of manufacturers to respond to customer interest was aided by the development of electro-hydraulic turbine control systems (10, 1d) which included provision to rapidly discharge steam valve actuator oil, in response to operation of dump valves, as a way to avoid development of excessive turbine speed on loss of electrical load with fast response achieved by use of a fast acting powerload unbalance type relay responsive to the difference between turbine driving power and generator load, employed to control the operation of solenoid controlled trip valves that act to collapse dump valve pilot oil pressure, (c.f. refs. la-p 43, lc-pp l36-l38,and ldpp 195-200).

To adapt this equipment to stability improvement, the procedure has been to provide so that a line fault would cause a turbines intercepting valves la, lb, 2, 4, 5), or both the intercepting and control valves (3( to close and after a period of the order of one second, reopen in response to the timed reclosure of dump valves.

My issued patents describe employment of rapidly executed changes in position of servo valves of turbine governing systems, executed independently of speed change as a way to achieve fast turbine full or partial closure and reopening.

Whereas this approach is workable if large enough servo valves are used, as already noted, it is also possible to employ dumping of oil from rams of steam valve actuators as a way to rapidly close such valves and since this has been the approach to fast valving that has been principally employed commercially to date the election was made to employ it in the embodiment described in the present disclosure.

Both my issued patents and my copending application deal with applications of fast valving that require sustained reduction of generator output following a line fault, and with this need in mind provide for sustained partial closure of turbine control valves following faults, in response to prefault system conditions.

My copending application introduces the concept of elTecting sustained partial valve closure when two of a group of three or more lines open in response to a fault.

The present application describes a control system which selectively rapidly initiates valve closing in advance of the opening of two lines when a fault occurs that would cause the opening of two lines if delay in fault clearance occured.

It was an aspect of my issued patents that they described procedures for modification of fast valving programs in response to the occurence of a refault on automatic faulted line circuit breaker reclosure. The present application responds to the post fault event of delay in fault clearance by modifying the fast valving program that would otherwise apply.

I SUMMARY THE INVENTION Briefly stated the invention has application in situations in which a generating station is united to a transmission network by at least three lines, and consists in a. initiating fast steam turbine valving in response to any line fault which if delayed in clearance could cause the opening of two lines b. responding to delay in fault clearance by initiating a change in the load reference signal of the governor of the turbine of such nature that the sustained value of turbine driving power following the fault will be lower than the prefault value.

It is an object of the invention to employ sustained partial control valve closure type fast valving as a way of solving problems of transient and/or steady state stability such as arise when a line fault causes the opening of two out of a total of three or more lines that provide parallel paths of power flow from a power station to a power transmission network.

Another object of the invention is to employ sustained partial control valve closure type fast valving as a way to preserve system stability when endangered by delay in clearance of a transmission line fault.

Another object is to avoid such employment in cases that would not cause the opening of two lines.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of a power station high voltage bus.

FIG. 2 is a view of a steam turbine and turbine control system that is adapted to effect rapid turbine driving power changes as a way to improve system stability.

DETAILED DESCRIPTION OF THE INVENTION results will be as in table I below.

protective relay system will operate TABLE I.B REAKER OPENINGS Fast valve closing with employment of sustained partial control valve closure could be needed when due to delay in the opening of breaker A lines L1 and L3 are lost, but might not be needed when due to delay in the opening of breaker B lines L1 and L2 are lost, or vice versa, or might be required in both of these cases.

Again fast valve closing not employing sustained partial control valve closure might suffice in one case but might not suffice in another.

The invention is concerned with cases where fast valving plus sustained partial control valve closure is needed in the case of delay in fault clearance and not needed, or needed in less degree, if there is no delay.

Power system planners are able to predict what will take place in any specific case through employment of computer implemented calculations, and thereby identify which conditions are critical.

To illustrate the invention it will be assumed that a fault on either line L1 or line L3 requires fast valving including use of sustained partial control valve closure when, but only when, delay in fault clearance causes the opening of both lines.

Whether or not fast valving would be needed if only the faulted line opened it will be desirable to immediately apply it for a fault on either line in order to avoid delay in application, which if not provided against would impair ability to handle the stability problem that develops if two lines open.

On the other hand it will usually be advantageous to avoid unnecessary use of sustained partial control valve closure.

Achievement of selective application of partial control valve closure can be accomplished by providing so as to rapidly apply a suitable bias to the load reference setting of the turbines governing system when there is evidence of delay in the opening of breaker A.

Referring now to Fig. 2, wherein figures below 200 correspond to those of a U.S. Pat. No. 3,097,488 which describes an electro-hydraulic turbine control system, steam from steam source 1 can flow to control valves 4 through stop valve 2 and thence through high pressure turbine 8 and reheater 10,intercepting valve 11, intermediate pressure turbine 13, and low pressure turbine 15, to end up as water in condenser 16.

Oil operated ram actuator 200, which is spring loaded, controls the position of a disc or plug of control valve 4 subject to the operation of servo valve 201 and oil dump valve installation 202 which is subject to the control of relay 204 and timer 203, which could comprise a normally closed time delay opening relay. A similar type of ram actuator 205 determines the position of the disc of intercepting valve 11 subject to the control of oil dump valve 206 which is controlled by relay 204 and by timer 207 which also could comprise a normally closed time delay opening relay.

Governing system 208 controls servo valve 201 subject to a speed signal received from permanent magnet generator 35, and a feed back from ram 200, and is also influenced by load signal modifier 43 which activates on closure of relay 209.

Details as to how load signal modifier 43 could be constructed can be had by reference to U.S. Pat. No. 3,198,954.

Taking up now the case of a fault on lines 1 or 3, when such a fault occurs the station protective relay system 210 energizes relay 204 which energizes both breaker A trip coil and causes operation of solenoid valves within dump valve installations 202 and 206 which when activated initiate oil dumping and rapid closure of valves 4 and 11.

Timers 203 and 207 are energized and when timed out cause the dump valves to close whereupon oil reenters the rams and brings about a process of valve lifting which typically procedes at a rate such that the control valve opens in a period of 5 seconds and the intercepting valves in a period of 5 to 10 seconds.

The rams will move full stroke downward in a small fraction of a second and thereby fully close the steam valves within say one-fourth second following a line fault that initiates control action. Readmission of oil may be advantageously started in say one-fourth to one-half second.

At a certain stage of control valve plug lift the oil supply to the control valve ram will begin to decrease due to the fact that the servo valve is approaching its closed position.

The control valve plug lift at which the servo valve acts to I shut off oil flow is determined by the turbine control systems load and speed reference settings as obtaining prior to the fault and the influence of load signal modifier 43, and as well as by the further influence of tie line and economic control systems which however typically do not act rapidly.

When a fault occurs on lines L1 or L3 the station protective relay system 210 will cause relay 204 to close, which in turn will initiate fast valving.

If now breaker A clears normally breaker A delayed fault clearance relay 209 remains open and as the rams refill with oil the servo valve will cause the control valve to be restored to its prefault position.

If however breaker A should fail to open when a fault occurs on either line L1 or line L3 relay 209 will close, typically after one-eighth to one-fourth second delay, and when this occurs load signal modifier 43 will modify the governors load reference signal to an extent determined by whatever load modification signal has been established in advance, and thereby cause the servo valve to shutoff oil flow to ram 200 at a new value of ram stroke which in turn will cause the turbine to develop reduced driving power relative to prefault conditions, subject only to the action of tie line and economic controls, which if desired, can be rendered inactive.

It is thus possible to set into the turbine control system provision for reduced post fault turbine driving power relative to prefault value.

It is not necessary to employ an electro-hydraulic governing system and in this connection U.S. Pat. No. 3,198,954 and also my U.S. Pat. No. Re. 26,571 shows how a mechanical hydraulic governor can be subject to fast modification of load reference whereby to effect a shift in a turbines speed-load characteristic.

With use of two load signal modifiers one could be arranged to respond to a breaker A delayed fault clearance relay, and the other to a relay that would respond to delay in fault clearance operation of breaker B.

Provision could also be made to apply one value of load modification signal if breaker A opened normally and another if delay in fault clearance occurred.

Reference to Fig. 2 of U.S. Pat. No. 3,198,954 will reveal that in the case of electro-hydraulic-governors load signal modification can be accomplished merely by altering one of the voltage inputs to a control system. This implies that it is easy to make provision to vary the magnitude of the load modification signal as by a potentiometer that would be turned manually, or manually controlled as to setting from a remote control station, or by one or another automatic means.

With manual control a station operator could vary the magnitude of the load modification signal so as to take account of the influence of system load and factors such as lines or generators out of service and loadings of generators, arm in doing so could be guided by information arrived at through system stability studies, and when conditions warranted could provide for a zero magnitude signal that would be without effect, and it should be regarded as an aspect of this invention that an operator could elect to employ manual control of load modification signal.

Extension to include response to a signal generator such as described in my copending application would represent a step that might not be accepted as merely involving the skill of any qualified control system engineer or technician, but can be.

dealt with in a further continuation-in-part of my copending application.

Convenient means of effecting load reference modification of mechanical-hydraulic governors can be had by minor modification of what is shown in my U.S. Pat. No. Re. 26,571 or by providing worm gear and motor means for rotating abutment member 34 of U.S. Pat. No. 3,198,954, or in other ways providing to vary the stroke of rod 31 of that patent.

Whereas Fig. 1 of the present application shows only three lines, a single generator, and a ring bus in which lines are separated by only one breaker, the invention has application regardless of the number of generators and line terminations, provided only that the bus arrangement is such that delay in fault clearance will cause the opening of two lines of a group of three or more that serve to tie the station to a transmission network of a system or power system interconnection, and in such event operate to weaken the connection of the station to the system or interconnection to a greater extent than would the loss of only one line.

If two breakers are used at each line termination, and all lines are separated by two breakers, as in what is termed a complete double bus, delay in fault clearance will not cause loss of two lines, but as this type of bus is expensive, various other arrangements are widely used and numerous important installations utilize bus arrangements for which faults on some lines will cause the opening of two lines if delay in fault clearance occurs.

In any case, where delay in fault clearance causes the open ing of two lines, the present invention has a useful field of application when the opening of two lines will, or in at least some situations can cause system instability.

Whereas in Fig. 2 load signal modification was made responsive to breaker A delayed fault clearance relay 209, which has for its main function the tripping of the appropriate back-up breaker, i.e., either breaker B or breaker D, the purpose of the invention could also be served by alternate use of a circuit that, with employment of circuit breaker A and B auxiliary switches in series connection, and also breaker A and breaker D auxiliary switches in series connection, would respond to whether or not both breakers A and B, or A and D, had opened, and hence to whether both lines L1 and L3 had opened, rather than to whether a second breaker had been energized to open.

References cited in the text are listed below.

TABLE OF REFERENCES 1. IEEE Tutorial Course Text 70 M29 PWR The Role of Prime Movers in System Stability a. D. J. Aanstad, Westinghouse DYNAMIC RESPONSE AND DATA CONSTANTS FOR LARGE STEAM TUR- BINES pp. 40-49 h. R. T. Byerly, Westinghouse POWER SYSTEM STA- BILITY EFFECTS OF CONTROL SYSTEM PER- FORMANCE pp. 57-65 C. M. A. Eggenberger, General Electric Co. A SIM- PLIFIED ANALYSIS OF THE NO-LOAD STABILITY OF MECHANICAL-HYDRAULIC SPEED CONTROL SYSTEMS FOR STEAM TURBINES" pp. 101-118 INTRODUCTION TO THE BASIC ELEMENTS OF CONTROL SYSTEMS FOR LARGE STEAM TUR- BINE-GENERATORS pp. 1 19-141 d. M. Birnbaum, and E. G. Noyes, Westinghouse ELEC- TRO-l-IYDRAULIC CONTROL FOR IMPROVED AVAILABILITY AND OPERATION OF LARGE STEAM TURBINES pp. 193-200 2. F. P. DeMello, D. N. Ewart, M. Temoshok and M. A. Eggenberger, TURBINE ENERGY CONTROLS AID IN POWER SYSTEM PERFORMANCE Proc. American Power Conference 1966, Vol 28, pp. 438-445 3. R. G. Farmer, R. H. Hartley, M. II. Kent, L. M. Wheeler,

FOUR CORNERS PROJECT STABILITY STUDIES IEEE Conference Paper 68 CP 708 PWR 4. P. G. Brown, F. P. deMello, E. H. Lenfest, R. J. Mills, EF- FECTS OF EXCITATION, TURBINE ENERGY CONTROL AND TRANSMISSION ON TRANSIENT STABILITY" IEEE Transactions Paper 70 TP 203 PWR 5. W. A. Morgan, H. B. Peck, D. R. Holland, F. A. Cullen, MODERN STABILITY AIDS FOR CALVERT CLIFF UNITS," IEEE Transactions Paper 70 TP 147 PWR 6. R. C. Buell, R. J. Caughey, E. M. Hunter, and V. M. Marquis GOVERNOR PERFORMANCE DURING SYSTEM DISTURBANCES," Trans. AIEE March 1931, vol. 50am e 354 et seq.

hi e the present invention has been described in con unction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.

For example in some situations employment of fast turbine valving with simultaneous fast closure of control and intercepting valves can cause lifting of high pressure safety valves and where this will occur, and remedies are not easily at hand, it can be desirable to execute fast valving by rapidly closing only intercepting valves. (cf. references 1a, 2, 4, 5)

This involves no need to change what has been shown other than to provide so that relay 204 is not arranged to activate dump valve installation 202.

As another example, it would be possible to effect a modification of load signal at the instant of initiation of fast valving and cancel this signal if normal fault clearance occurs within a predetermined time following fault occurrence.

In the matter of claim terminology,- the term fast valving is to be interpreted as valving in which as a minimum a turbines intercepting valve is closed at highest available speed, which in present practice means one-fourth second or less, and next, with or without benefit of delay, lifted at a speed that can be controlled within certain limits but that in present practice has been kept at a value of full stroke in 5 seconds or more, as a way to avoid hazard of overspeed when a generator is tripped off under heavy load.

Equally fast simultaneous control valve closing represents an option.

The term fast turbine governor load signal modification" is to be interpreted as a change in turbine load reference accomplished in a small fraction of a second, as is feasible using what is shown in U.S. Pat. No. 3,198,954, and in practice, with an electro-hydraulic governor, is feasible in say one-sixtieth second.

The term system conditions" is to mean station and line loadings, power output of generators, direction of power flow over lines, and lines and generators out of service.

The term responding to delay in fault clearance" is to mean responding to operation of a relay, such as relay 209, that has been provided as part of a back-up protection scheme, or responding to some other effect of delay in fault clearance such as the fact that two lines opened.

What I claim is:

1. The method of avoiding development of instability within a power system as a consequence of a transmission line fault which comprises the steps of,

a. automatically initiating fast steam turbine valving in response to the occurrence of faults that would cause the opening of two lines if delay in fault clearance caused operation of a delayed fault clearance relay,

b. responding to delay in fault clearance by initiating a turbine governor load signal modification of a nature adapted to reduce sustained post fault turbine driving power below values that would otherwise apply.

2. The method of claim 1 supplemented by prefault manual adjustment of the magnitude of the load modification signal, whereby to take account of the influence of system conditions on the amount of signal needed to avoid loss of system stability.

Claims (2)

1. The method of avoiding development of instability within a power system as a consequence of a transmission line fault which comprises the steps of, a. automatically initiating fast steam turbine valving in response to the occurrence of faults that would cause the opening of two lines if delay in fault clearance caused operation of a delayed fault clearance relay, b. responding to delay in fault clearance by initiating a turbine governor load signal modification of a nature adapted to reduce sustained post fault turbine driving power below values that would otherwise apply.

2. The method of claim 1 supplemented by prefault manual adjustmenT of the magnitude of the load modification signal, whereby to take account of the influence of system conditions on the amount of signal needed to avoid loss of system stability.

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