Method of operation of a pump-turbine between part-load operation and reverse pumping operation

The invention relates to a method of operation of a pump-turbine between part-load and reverse pumping operation in which the various operating conditions are produced by changing the position of the wicket gates in that some of the wicket gates are removed from the synchronous operation as provided by the mechanical gate ring operator and inserting a servo-motor between the wicket gate and the gate ring which functions to alter the connection between the selected wicket gates and the gate ring operator.

BACKGROUND OF THE INVENTION 
It is known that in the operation of pump-turbines, in a turbine mode, the 
pump-turbines are started, in the manner of any reaction turbine, by 
simultaneously opening the wicket gates. This causes the pump-turbine 
runner to accelerate from a stationary position to rated revolutions per 
minute. When the wicket gates are positioned at an idle running position 
for obtaining an idle running operation of the pump-turbine, the 
motor-generator can be synchronized and connected to the associated 
electric grid system. Upon further movement of the wicket gates toward an 
open position, the pump-turbine will operate as a turbine and will furnish 
power. The characteristic curve of pump-turbines become steeper and 
steeper with an increasing n.sub.1 in the n.sub.1 -Q.sub.1 diagram (unit 
number of revolutions over unit flow). The characteristic curves may even 
become vertical or have a negative direction. This means that the 
characteristic performance of the pump-turbine in this range may be 
erratic. 
A cutout of the four quadrant characteristic curve diagram of a given 
pump-turbine is shown in FIG. 1. As there shown, the curves for various 
wicket gate openings are identified as a.sub.1 through a.sub.5 where the 
largest wicket gate opening a.sub.5 is used for synchronization. The 
L-curve in FIG. 1 is the idle running operation curve for turbine 
operation with a movement of M=O. Below idle running curve L in area B, 
FIG. 1 depicts the so-called braking operation of a pump-turbine and 
indicates that the runner keeps absorbing power and that the flow is in 
turbine operation direction and is operating as a brake-up to the point 
when the flow of the turbine becomes zero. Further, below the abscissa the 
pump-turbine enters into a pumping operation in turbine rotation 
direction, i.e., it enters in what is called a reverse pumping operation. 
The water will be delivered in the pump flow direction in spite of the 
fact that the pump-turbine is running in a turbine rotational direction. 
In braking and in reverse turbine operation the curves, as shown in FIG. 1, 
depict an S-shape configuration; this condition causes undesirable effects 
such as the instability of operation of the pump-turbine. The result of 
this type of instability of operation is that synchronization in turbine 
mode operation is extremely difficult. Also, running idle for an extended 
period of time is impossible. The reason for this is that the smallest 
unavoidable pressure variations may cause sudden irregularities at a point 
when a load is taken on. In the transition period from synchronous 
operation in the direction of rotation in turbine mode, the following 
takes place: (a) the runner operates in air in preparation to operation in 
the turbine mode; (b) when the turbine is filled with water and the valve 
is opened, the temporary increase in power becomes undesirably large when 
the wicket gates are opened; (c) upon a further increase in the openings 
between the wicket gates a suddenly large power surge will be experienced 
when the pump-turbine starts to operate as a turbine. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improvement in a 
pump-turbine and a method for its operation in which the operational 
characteristic curves are improved and indicate that starting shows stable 
characteristics in that for each value of a curve in the n.sub.1 -Q.sub.1 
diagram only one single Q.sub.1 value exists. 
The novel method which this invention presents solves the erratic 
performance problem by having at least one wicket gate temporarily 
separate from the operating mechanism and opened prior to the opening of 
the remaining wicket gates. The wicket gates are either mechanically 
connected through the gate ring to the gate operating mechanism or are 
operated individually by means of servo-motors which are designed to move 
the gates in synchronism. The invention provides a method wherein one or 
more of the wicket gates are separate from the gate operating mechanism 
which causes them to open in advance of the opening of the remaining 
gates. This results in altering the configuration of the characteristic 
curves. When a few gates have a larger opening than the remaining gates 
which are mechanically connected to each other for synchronized operation, 
a small opening between the synchronized gates will be adequate to produce 
the same flow and the same rotational speed as that which would be 
produced by the synchronous opening movement of all the wicket gates. This 
is true because small gate openings always produce stable performance 
curves. To achieve the improved performance curves, mechanism is provided 
which opens individual gates prior to the majority of the gates being 
opened in synchronism by the mechanical operator. 
A further object of the present invention is to provide means wherein if 
more than one gate is to be removed from the synchronous operation by the 
mechanical operator, the gates removed from synchronous operation will be 
opposite with respect to each other. 
The method herein disclosed makes it possible to synchronize and connect 
the pump-turbine to an associated electrical grid with the pump-turbine 
being in a completely stable condition for idle running and for part-load 
operation. The danger of the pump-turbine operating as a reverse pump is 
reduced to a minimum or eliminated. 
A further advantage of the present invention is that the transition of 
operation from a pump-turbine mode to a turbine mode of operation can be 
accomplished with a minimized power intake surge which would normally 
occur. 
Still another object of this invention is to provide a pump-turbine having 
wicket gates that are adjusted by a gate ring with a means for removing 
some of the gates from the synchronous connection between the gate ring 
and gates and inserting a servo-motor between gates that have been 
disconnected and the gate ring. 
An advantageous relationship as taught by the present invention for a 
pump-turbine is in extending the gate lever of the gates which have been 
disconnected from the mechanically rigid connection between gate and gate 
ring and also having the length of the lever adjustable. 
A still further advantage of the present invention is in having the gate 
ring operate a lever which is constructed and arranged to rotate freely 
about the gate stem or post. This lever is connected to a separately 
controlled hydraulic servo-motor which also operates a gate lever that is 
rigidly connected to the gate stem or post. 
A pump-turbine having individual gate operating servo-motors has an 
advantage of being equipped for including an extra pre-opening gate 
movement arrangement in conjunction to the regular gate opening function, 
which extra gate pre-opening function can be utilized for the purpose of 
producing an additional amount of gate opening to the normal synchronous 
gate opening function.

DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates characteristic curves of a pump-turbine when all of the 
wicket gates are controlled in a synchronous operation. In contrast FIG. 2 
illustrates model tests characteristic curves of a pump-turbine in which 
several of the wicket gates are opened in advance of the majority of the 
wicket gates. 
As depicted by the curves A.sub.11 through A.sub.14, FIG. 2, it is evident 
that these curves show a completely stable operating condition of a 
pump-turbine. For each value of A.sub.11, along the abscissa of the 
characteristic curve in FIG. 2, there is only one Q.sub.1 value that 
exists. This is in contrast to characteristic curves of known 
pump-turbines which are illustrated by the curves in FIG. 1. 
In FIG. 3 there is shown two wicket gates, 6 and 12, which are operated by 
a gate ring 7. Gate 6 is representative of all gates to be operated in 
sychronism by gate ring 7. On the otherhand, gate 12 is representative of 
all gates to be removed from sychronous operation. The wicket gate 6 is 
connected to the gate ring 7 through a pivotal connected link 8 which, in 
turn, is pivotally connected to the end of gate lever 9 which, in turn, is 
operatively secured to the shaft or stub of the wicket gate 6. Rotational 
movement of the gate ring 7 in the direction indicated by the directional 
arrow 10 will effect movement of the wicket gate 6 to an open position. On 
the other hand, rotation of the gate ring 7 in a rotational direction as 
indicated by the directional arrow 11 will serve to move the wicket gate 6 
from an open position to a closed position. 
Wicket gate 12 is connected to be operated in synchronism with gate 6. To 
this end a link 13 has one end thereof pivotally connected to the gate 
ring 7 and has its opposite end pivotally connected to one extending arm 
15A of a double arm lever 15. The lever 15 is mounted on the stem 14 of 
the wicket gate 12 in a manner so as to be freely rotatable on the stem 
14. The opposite arm 15B of the lever 15 is operatively connected to the 
extending end of a piston rod 36 of a servo-motor 16, which includes a 
piston 37 to which the rod 36 is secured. The piston 37 operates within a 
cylinder 38 which is connected to the extending end 17A of a wicket gate 
lever 17 that is associated with the wicket gate 12. 
Gate lever 17 is rigidly connected to the stem 14 of gate 12 so as to 
effect its movement whenever the end 17A of the lever is moved. Assuming 
that the piston 37 of the servo-motor 16 is maintained in the position 
shown relative to the cylinder, the end 17A of link 17 will be connected 
to move with the arm 15 through the servo-motor 16. Thus, the angular 
position of gate 12 will only correspond to that of lever 15 when the 
servo-motor piston assembly 36-37 is in its shortest position (i.e., 
pressure in chamber 38A). However, gate 12 can be opened an additional 
amount corresponding to the change in angle between lever 17 and lever 15 
when the servo-motor piston assembly 36-37 moves from the shortest 
position, depicted in FIG. 3, to the longest position, that is, with the 
piston 37 moved to full bottom position in the cylinder. The movement of 
the piston 37 to its lowest position will cause the gate 12 to be opened 
an additional amount, for example, an additional 23.degree. from the 
4.degree. position of gate 6 as effected by the initial movement of the 
ring 7. This opening gives a required change in machine characteristics as 
indicated by FIGS. 1 and 2. Thus, gate 6 will be at 4.degree. open and 
gate 12 will be at 27.degree. open and the remaining gates (not shown) 
connected to the ring 7, as exemplified by the gate 6 arrangement, will 
also be at 4.degree. open positions. In this particular arrangement, the 
particular gate openings gave the necessary flow to spin the turbine at 
synchronous speed. 
After synchronization of the turbine to output the correct line frequency 
has been achieved, the wicket gates can move to a further open position 
which will be assumed to be a maximum of 33.degree. open to output more 
power. In this respect, the majority of the gates represented by gate 6 
will open an additional 6.degree., that is be moved to 10.degree. open 
position, which is their full open position. With gate 6 moved the 
additional 6.degree., gates 12 will also be moved the additional 6.degree. 
to a full open position of 33.degree.. This is true because gates 12 have 
been moved initially 4.degree. open, then an additional 23.degree. to 
27.degree. open (4.degree.+23.degree.). Thus, the additional 6.degree. of 
movement moves gates 12, to 33.degree. full open position, while gates 6 
are at 10.degree. full open. 
Since 33.degree. full open is the selected maximum gate opening, none of 
the gates are allowed to open more than the selected maximum. To this end, 
a positive stop 41 will be engaged by a stop lug 42 on the arm 17. The 
positive stop 41 permits a 1.degree. over opening, that is gates 12 could 
open to 34.degree.. Gates 6 also have a mechanical stop 43 which will be 
engaged by a stop lug 44. Thus, should failure in the hydraulic or 
electrical system occur, the mechanical positive stops 41-43 take over to 
protect the system. 
Another protection arrangement is provided in the form of a positive stop 
51 which can be located on the head cover (not shown). The stop 51 is set 
at maximum gate opening. Since a control valve 20 is carried by the lever 
17, the extending end 52 of the spool will contact the stop 51 at a point 
before lever 17, and thus gates 12, reach their maximum opening of 
33.degree.. This action causes the spool to be pushed downwardly at 
maximum gate some point before lever 17 reaches the opening of 33.degree.. 
Then as lever 17 continues to move toward maximum gate open position the 
spool will be positioned to bleed hydraulic fluid from chamber 38B of the 
servo-motor 16 and pressurize chamber 38A. This will effect the closing 
movement of the preopened gates to the same opening as all other gates. 
The normal control of gate opening is controlled by a limit switch 54 which 
is tripped when the relative angle between levers 15 and 17 reach 
23.degree.. Another limit switch 57 is provided and will be actuated 
whenever the lever arm 17 has moved the associated gate 12 to 33.degree. 
open position. The effect of switch 57 will cause a slow bleed from the 
pressurized side of the piston assembly 20. The provision of limit switch 
57 duplicates the operation of stop 51 and provides additional protection 
should such be necessary. 
Gate ring 7 is provided with an abutment 61 which operates to trip switches 
62 and 63. Switch 62 will be tripped when the gate ring 7 is shifted to a 
position which would give a gate opening on gates 6 of 40% of maximum 
(about 12.degree.). Switch 63 when tripped by the shift of the gate ring 
7, will give a gate opening of 50% of maximum which is about (15.degree.). 
Switch 63 when actuated by the engagement of abutment 61 is arranged to put 
out a signal which causes gate 12 to resynchronize with gate 6 above 
15.degree. opening. This is done by a signal which deenergizes solenoid 71 
of valve 72 causing the valve spool to be repositioned so as to vent 
chamber 73 of valve 20. This allows the valve spool 52 to move back to 
it's original position that it occupies as depicted in FIG. 3. 
Repositioning of the valve spool 52 will effect the pressurizing of 
chamber 38A and will vent chamber 38B of the servo-motor 16. This will 
shorten the piston assembly moving gate 12 back in synchronization with 
gate 6. 
Switch 62 does the reverse of switch 63. When the gate ring 7 is moved in a 
closing direction and reaches a position of 12.degree. gate open switch 62 
will be activated moving gate 12 back out of synchronization with gate 6. 
This allows gate 12 to be as much as 23.degree. further open than gate 6 
but not further than 33.degree.. 
A modification is shown in FIG. 4, wherein the gate 12A, which corresponds 
to gate 12 in FIG. 3, is depicted. Gate 12A is operated by lever arm 81 
which, in turn, is secured to a lug on the one end of cylinder 82. The 
extending end of the piston rod 83 is operatively connected to a gate 
operating ring 7A. Thus, movement of the operating ring 7A in either 
direction will move gate 12A. Gate 6A is connected to lever 84 which, in 
turn, is pivotally connected to operating lever 86. The free-end of lever 
84 is operatively connected to ring 7A operating ring. Lever 84 is 
substantially the same length as the extended rod 83 and associated 
cylinder 82. Thus initial movement of ring 7A in a gate opening direction, 
indicated by directional arrow 10A, will move gates 6A and 12A to a 
4.degree. open position. By shortening the connection between the end of 
lever 81 and the operating ring 7A, the gate 12A can be moved an 
additional 23.degree. or to a 27.degree. open position while gate 6A is 
maintained at 4.degree. open position. Further movement of ring 7A in an 
opening direction will cause gates 6A and 12A to be moved an additional 
amount of 6.degree., so that gate 6A will be at 10.degree. open position 
and gate 12A will be at 33.degree. open maximum position. 
The hydraulic control system shown in FIG. 3, is operable to provide the 
preopening movement of gate 12 and other gates, if so described. To this 
end in the initial opening movement of gate ring 7 in the direction of 
arrow 10 moving all the gates to 4.degree. open position. An abutment 91 
attached to ring 7 moves out of engagement with the actuating plunger of a 
control valve 92. The internal valve spool of valve 92 will be biased into 
a position to permit the flow of fluid under pressure from the pressurized 
line 93 through a connecting line 94 into a line 96. Line 96 communicates 
between valve 92 and valve 72. Thus, at a time that it is desired that 
gate 12 (or other like gates) preopen a signal will be received to 
energize solenoid 71 of valve 72. Valve 72 will then be conditioned to 
connect line 96 to a line 98 via a line 99. Line 99 may also be connected 
to one or more other valves similar to valve 20. Fluid under pressure will 
enter chamber 73 biasing the valve spool 52 upwardly uncovering ports 101 
and 102. In uncovering port 101 the chamber 38A will be vented through the 
valve via port 101 and a tank port 103. At the same time chamber 38B will 
be supplied with fluid under pressure via pressure line 93, port 102 and a 
port 106. This will cause the servo-motor to extend causing movement of 
gate 12 the additional 23.degree. from that of gate 6. This will cause 
synchronization of the machine to output to the correct line frequency. 
After this all of the gates will continue to open by operation of ring 7 
to a maximum of 33.degree. open to output more power, as previously 
described.