PELTON TYPE HYDRAULIC MACHINE AND OPERATING METHODS

Description

[0001] The invention relates to a hydraulic machine of the Pelton type and an operating method for such a hydraulic machine. In the following, a hydraulic machine of the Pelton type is usually referred to as a Pelton turbine.

[0002] Pelton turbines are generally used for larger heads. Therefore, the penstocks leading to the turbine are correspondingly long and must be designed for high water pressures. A Pelton turbine is controlled by one or more nozzles that can be continuously opened and closed. Rapid closure of the nozzles is known to result in a so-called water surge, which in extreme cases can lead to the penstock bursting. This problem is avoided by limiting the closing speed of the nozzles. In principle, this could be ensured in modern turbines by an electronic implementation in the controller's control unit. Since electronic failure is a scenario that can certainly occur, this is not sufficient to guarantee the required safety. For example, the turbine must be able to be brought to a safe standstill even in the event of a power failure.Therefore, mechanical limitations of the closing speed are still in use.

[0003] WO 2005 / 103486 A1 discloses a method for operating a Pelton turbine comprising a runner, at least one nozzle, a water path and a control device for controlling an opening degree of the nozzle, wherein the runner comprises a plurality of buckets, and wherein the Pelton turbine comprises mechanical means for implementing a single-stage control law, whereby the control speed of the nozzle is limited to a maximum permissible control speed.

[0004] Furthermore, it has been found that in most Pelton turbines, a quick shutdown from 100% nozzle opening to 0% does not even represent the worst case scenario in terms of pressure surge. This is, however, the so-called reflection pressure surge. This type of reflection pressure surge occurs when a rapid closing process is followed by a brief rapid opening process, which in turn is followed by a rapid closing process. In conventional turbines, a damaging reflection pressure surge is avoided by implementing multi-stage closing speed limitation. This means that different maximum permissible closing speeds are specified depending on the degree of opening of the nozzles. The maximum permissible closing speeds decrease as the degree of opening of the nozzles decreases. This means that with small nozzle opening degrees, closing must be slower than with larger nozzle opening degrees.These multi-stage nozzle closing laws also have to be implemented mechanically, which, on the one hand, leads to very complicated, expensive, and error-prone mechanical designs, and, on the other hand, severely limits the actuating speed at low power levels (i.e., with small nozzle openings). This applies to both closing and opening, since the mechanical limitation of the nozzle actuating speed always applies to both opening and closing. Therefore, the aforementioned multi-stage closing speed limitation is better referred to as a multi-stage actuating speed limitation or a multi-stage actuating law.

[0005] The object of the invention is to provide a hydraulic machine of the Pelton type and an operating method for the same, which provides the necessary safety against a reflection pressure surge without a multi-stage mechanically implemented control law.

[0006] The object is achieved according to the invention by embodiments according to the independent claims. Further advantageous embodiments of the present invention can be found in the subclaims.

[0007] The invention is explained below with reference to the figures. The figures show in detail: Fig. 1 Hydraulic machine according to the invention Fig. 2 Operating method according to the invention Fig. 3 Diagrams for illustrating the operating method according to the invention Fig. 4 Diagram for illustrating an embodiment of step S6 Fig. 5 Diagram for illustrating an embodiment of step S6 Fig. 6 Diagram for illustrating an embodiment of step S6 Fig. 7 Diagram for illustrating an embodiment of step S6

[0008] Figure 1shows a hydraulic machine of the Pelton type (Pelton turbine for short) according to the invention in a schematic representation. The Pelton turbine comprises a rotor, which is designated by 1. The rotor 1 comprises a plurality of buckets, one of which is designated by 2. The Pelton turbine comprises at least one nozzle, which is designated by 3. The Figure 1 The Pelton turbine shown comprises 6 nozzles 3. The Pelton turbine comprises a control device for controlling the degree of opening of the nozzles 3, which is designated by 4.

[0009] To enable the control device 4 to control the degree of opening of the nozzles 3, the Pelton turbine comprises suitable means to do so. Typically, the degree of opening of the nozzles 3 is adjusted using hydraulic cylinders. The Pelton turbine then comprises a suitable hydraulic unit, and the control device 4 actuates one or more valves, which cause the supply or discharge of hydraulic fluid into the chambers of one or more hydraulic cylinders. However, it is also conceivable for the nozzles 3 to be actuated using electric drives. In this case, the control device 4 controls the movement of the electric drives.

[0010] The Pelton turbine according to the invention further comprises means with which a single-stage control law can be mechanically implemented. Figure 1These means are indicated by the rectangle labeled 5. A mechanically implemented single-stage actuating law means that the actuating speed of the nozzles 3 is mechanically limited to a maximum permissible actuating speed, regardless of the respective degree of opening of the nozzles 3. This means that the maximum permissible actuating speed of the nozzles 3 is constant over the entire adjustable opening range of the nozzles 3. In the case of hydraulically actuated nozzles, the conventional mechanical implementation of such a single-stage actuating law consists of a throttle located in the associated hydraulic circuit, which thus limits the flow rate of hydraulic fluid. In the case of electrically actuated nozzles, a mechanical brake can be used to limit the actuating speed in this way.

[0011] The maximum permissible actuating speed is set so that, during a closing process from 100% to 0%, this actuating speed just barely prevents a damaging pressure surge from occurring. The necessary calculation is carried out in a conventional manner, including appropriate safety margins.

[0012] The inventors were guided by the idea that the combination of consecutive closing and opening processes leading to a reflection pressure surge can be avoided by limiting the opening speed of the nozzles by the control device 4, in addition to the mechanical limitation by the single-stage control law, if a closing process has occurred in a preceding time interval of a predefined length. In this case, the control device ensures that the opening speed is lower than the maximum opening speed specified by the mechanical control law.

[0013] The predefined length of the upstream time interval is determined by at least twice the wave travel time in the water path of the Pelton turbine. The inventors recognized that a reflection surge can only occur if closing and subsequent opening occur within the specified time period. For many Pelton turbines, the double wave travel time in the water path is 5-10 seconds. This means that the length of the upstream time interval must be at least twice the wave travel time to avoid a reflection surge. In a Pelton turbine, the water path extends between an upstream water basin and the nozzles. Figure 1The water path is indicated by the dashed arrow, labeled 8, which extends between a stylized headwater basin and a nozzle. In Pelton turbines with more than one nozzle, the water path also includes a distributor located between the nozzles and the penstock. However, the vast majority of the water path is formed by the penstock. Figure 1 The distribution list is not shown for reasons of clarity.

[0014] In addition to the reflection pressure surge described in the previous section, there are also reflection pressure surges caused by the disturbance traveling up and down the waterway not just once, but multiple times. Such reflection pressure surges can be referred to as higher-order reflection pressure surges. However, these are generally less severe than the first-order reflection pressure surge. Depending on the design of the hydraulic machine in question, higher-order reflection pressure surges must also be avoided. This can be achieved according to the invention by ensuring that the length of the upstream time interval is at least four times, at least six times... the wave travel time in the waterway.

[0015] According to the invention, the control device 4 is designed such that it can limit the speed of an opening process if a closing process has taken place in the preceding time interval. To this end, the control device 4 must be able to store the completed opening and closing processes for at least a period of time corresponding to the length of the preceding time interval. Furthermore, an algorithm must be installed in the control device 4 that checks whether a closing process has taken place within the preceding time interval and then, if necessary, further limits the speed of an upcoming opening process as described, in addition to the mechanical limitation.

[0016] Figure 2shows the flowchart of an operating method according to the invention. The rectangle labeled S1 represents a process in which the control device 4 determines an upcoming change in the opening degree of the nozzles 3. The reason for such a change in the opening degree can be varied.

[0017] For example, there may be a changed demand from the grid. This means that more or less energy output may be required from the Pelton turbine. Furthermore, malfunctions may also require a change in the opening degree of nozzles 3. For example, in the event of load shedding, nozzles 3 must be closed as quickly as possible ("quick closure"). The diamond labeled S2 represents a case distinction. The criterion for the case distinction in S2 is whether the change in the opening degree of nozzles 3 determined in S1 represents an opening or a closing of the same. If it represents a closing, then the process symbolized by rectangle S3 is carried out. The closing in S3 occurs at a speed that is only limited by the mechanical control law. If the distinction in S2 represents an opening, then the case distinction symbolized by diamond S4 is carried out.The criterion for distinguishing between cases in S4 is whether a closing process took place in the preceding time interval of predefined length. If no closing process took place in the preceding time interval, the process symbolized by rectangle S5 is carried out. Process S5 is an opening at a speed that is only limited by the mechanical control law. If a closing process took place in the preceding time interval, the process symbolized by rectangle S6 is carried out. Process S6 is an opening at a speed that is lower than the maximum control speed specified by the mechanical control law. This means that the opening speed of the nozzles in S6 is limited by control device 4 in addition to the mechanical limitation via the single-stage control law.

[0018] It is clear that steps S1, S2, S3, and S5 correspond to the corresponding steps in the conventional operating method of a Pelton turbine with a single-stage control system. The method according to the invention differs from this conventional operating method by the additional case distinction S4 and by the process S6. Steps S4 and S6 ensure that reflection recoil can be reliably avoided even in a Pelton turbine with only a single-stage mechanically implemented control system.

[0019] Figure 3contains three diagrams that illustrate the different cases leading to processes S3, S5 and S6. The diagrams are representations in which the time axis runs horizontally and is labeled t, and in which the opening degree of nozzles 3 is plotted vertically. This axis is labeled O. In all diagrams, the current time is labeled t 0. This means that all times to the left of t 0 belong to the past. The predefined length of the preceding time interval is T, i.e. the preceding time interval extends between the times t 0 -T and t 0 .

[0020] The upper diagram of Figure 3represents a possible situation leading to step S3. In step S1, a closing process was determined as the pending change in the degree of opening. This is indicated by the dashed descending line extending to the right of the time. Since there is no additional restriction on the actuating speed beyond the mechanically limited maximum permissible actuating speed for case S3, the closing process can occur at this speed. The history in the preceding time interval is irrelevant. In the case shown, a closing process took place in this time interval at the mechanically limited maximum permissible actuating speed.

[0021] The middle diagram of Figure 3represents a possible situation leading to step S5. In step S1, an opening process was determined as the pending change in the degree of opening. This is indicated by the dashed rising line extending to the right of time t0. If an opening process was determined in step S1, then step S4 must check whether a closing process took place in the preceding time interval. This is evidently not the case (there was only one opening process). Therefore, the opening process determined in step S1 after t0 can take place at the mechanically limited maximum permissible actuating speed.

[0022] The lower diagram of Figure 3represents a possible situation leading to step S6. In step S1, an opening process was determined as the upcoming change in the degree of opening. This is indicated by the dashed rising line extending to the right of time t0. If an opening process was determined in step S1, then step S4 must check whether a closing process took place in the previous time interval. This is obviously the case (there was a closing process). Therefore, the opening process determined in step S1 after t0 must not take place at the mechanically limited maximum permissible actuating speed, but the opening must take place at a lower speed, which is indicated by the lower gradient of the rising line to the right of t0 compared to the corresponding line in the middle diagram.It should be noted at this point that it is sufficient to proceed to step S6 if, during the check in step S4, the temporal end point of a closing process falls within the preceding time interval. The entire closing process does not have to fall within the preceding time interval.

[0023] There are various options for the additional restriction of the opening speed in step S6. Figure 4 illustrates an embodiment of step S6 in which the opening is completely suppressed as long as a closing process has taken place in the preceding time interval. This corresponds, so to speak, to an opening at a vanishing speed. Therefore, the dashed line to the right of t 0 runs horizontally.

[0024] Figure 5illustrates an embodiment of step S6 in which the opening is not completely suppressed as long as a closing process has taken place in the preceding time interval. Rather, the stroke of the closing process that took place in the preceding time interval is used to determine the additional limitation of the opening speed. Figure 5 This stroke is designated H. If several separate closing operations have taken place in the preceding time interval, the total stroke of these closing operations is used. If a closing operation only partially falls within the preceding time interval, either the stroke of the entire closing operation or only the stroke of the part of the closing operation that falls within the preceding time interval can be used. The larger H is, the more the opening speed is limited, i.e., the pending opening operation is carried out at a lower speed.

[0025] Figure 6 illustrates an embodiment of step S6 in which the opening is not completely suppressed as long as a closing process has taken place in the preceding time interval. Rather, the speed of the closing process that took place in the preceding time interval is used to determine the additional limitation of the opening speed. Figure 6This speed is indicated by the dashed line with a gradient of m. Here, m is the magnitude of the gradient, since in this document, nozzle opening speeds are generally considered positive values. The sign is contained in the terms "closing" or "opening" cited. If several separate closing processes have taken place in the preceding time interval, the maximum value or the average of the associated speeds, or the speed of the most recent closing process, is used as m. Weights can also be used when calculating the average, e.g., the length of each closing process. The larger m, the more the opening speed is limited, i.e., the upcoming opening process is carried out at a lower speed.

[0026] Figure 7illustrates an embodiment of step S6 in which opening is not completely suppressed as long as a closing operation has taken place in the preceding time interval. Rather, the parameter t SE is used to specify the additional limitation of the opening speed. The parameter t SE results from determining the time at which the last closing operation was completed. The closer t SE is to t 0, the more the opening speed is limited, i.e., the upcoming opening operation is carried out at a lower speed.

[0027] Apparently, t SE can also be used to formulate the condition tested in S4: If t SE lies in the preceding interval (t SE ∈ [t 0 -T, t 0 ]), then S6 is executed, otherwise S5.

[0028] The use of the parameter t SE is particularly advantageous when higher-order reflection pressure surges are to be suppressed, as this parameter allows for differentiation between pressure surges of different orders. For example, if t SE is more than twice the wave travel time in the waterway, then it is a reflection pressure surge of at least second order, which must be suppressed. Accordingly, as already described in the previous section, the opening limitation can be eliminated. The Figures 5-7 The parameters H, m and t SE defined can also be used in any combination to determine the limitation of the opening speed in step S6.

[0029] Further possibilities for designing the method according to the invention arise from the fact that there are several possibilities for the time period during which the additional limitation of the opening speed defined in S6 remains effective. One possibility is that at least t SE -t 0 +T is selected for this time period. After this time has elapsed, t SE is no longer in the preceding time interval. In particular, with the embodiment according to Figure 4 This means you are always on the safe side, as opening is completely suppressed as long as the limitation set in S6 remains effective. After the time period t SE -t 0 +T has elapsed, the Figure 2The process described above can be executed from the beginning. Another possibility is for the additional limitation of the opening speed specified in S6 to remain effective for a predetermined period of time Δt. For Δt, the shortest period of time after which a change can be expected in the relevant Pelton turbine, which could cause the control unit to initiate a change process regarding the nozzle opening, can advantageously be selected. Δt can be, for example, 1 second.

[0030] After Δt has elapsed, the process is then repeated according to Figure 2 run through again.

[0031] In particular in connection with the embodiments according to the Figures 5-7 This results in a dynamic behavior with regard to the additional limitation of the opening speed, so that the reaction of the turbine with regard to opening requirements is affected as little as possible.

[0032] The parameter T is determined using known calculation methods for the respective Pelton turbine. The relationship between the parameters H, m, t SE and the additional limitation of the opening speed determined in step S6 is derived from known simulation calculations. All possible scenarios are run through, and the relationship is determined such that a reflection pressure surge cannot occur in any possible scenario. Safety margins can advantageously be taken into account. In other words, the simulation must ensure that in every conceivable state that the Pelton turbine can assume when executing the method according to the invention, a quick closure of the Pelton turbine cannot lead to a reflection pressure surge. For the embodiment according to Figure 4Such additional simulation calculations are apparently not necessary (the calculation required for the design of the single-stage control system is sufficient). This embodiment can therefore be implemented without additional simulation effort.

[0033] If the control system reliably executes the inventive method described so far, this already provides security against power outages if it is ensured that the turbine is automatically shut down in the event of a power failure. This is the standard practice in conventional Pelton turbines. This means that the inventive method requires no additional safety measures beyond the usual standard regarding power outages.

[0034] In order to meet the usual safety standards, it only remains to ensure that a malfunction of the control device when carrying out the method according to the invention is either avoided or reliably intercepted. To this end, the control device can, for example, be designed to be safe, i.e. the control device is designed with regard to the implementation of the method according to the invention so that a malfunction can be ruled out in accordance with the usual safety standards. Another possibility is to provide a control device which monitors the implementation of the method according to the invention by the control device. At least steps S4 and S6 must be monitored. When a malfunction is detected, the control device immediately initiates a quick shutdown of the turbine (i.e. before the erroneous control commands take effect).This is possible without risk because the control device has functioned correctly up to this point according to the method according to the invention, and the simulation calculations ensure that a quick shutdown is possible at any time in this case. It is clear that safety can be further increased by implementing the control device multiple times (redundancy). Figure 1 shows a control device, which is designated 6.

[0035] Furthermore, the present application is directed to a computer program configured such that the control device can execute the method according to the invention by means of the program, i.e., the computer program comprises instructions that cause the control device to execute the method according to the invention. Furthermore, the present application is directed to a computer-readable medium on which the computer program is stored. Figure 1 shows such a computer-readable medium, which is designated 7. List of reference symbols

[0036] 1Impeller 2Cup 3Nozzle 4Control device 5Means for the mechanical implementation of a single-stage control law 6Control device 7Computer-readable medium 8Waterway

Claims

1. A method of operating a Pelton turbine comprising a runner (1), at least one nozzle (3), a water way (8) and a control device (4) for controlling a degree of opening of the nozzle (3), wherein the runner (1) comprises a plurality of buckets (2), and wherein the Pelton turbine comprises mechanical means for realising a single-stage actuating set, whereby the actuating speed of the nozzle (3) is limited to a maximum permissible actuating speed, characterised in that the method comprises the following steps: S1: Determining a pending change in the degree of opening of the nozzle (3) by the control device (4); S4: If the change determined in step S1 is an opening, checking whether a closing operation has taken place in a time interval of predefined length T preceding the current time t0 ; S6: If the check in step S4 has shown that a closing operation has taken place in the upstream time interval, the opening determined in step S1 is carried out at a velocity which is limited to a value which is smaller than the mechanically realised maximum permissible actuating velocity in order to avoid a reflection pressure shock; and wherein the length T is at least twice the wave travel time in the water way (8).

2. The method according to claim 2, wherein T is at least four times the wave travel time in the water way (8).

3. The method according to claim 1 or 2, wherein in step S6 the opening determined in step S1 is completely suppressed.

4. The method according to claim 1 or 2, wherein in step S6 a parameter H is used for the determination of the velocity at which the opening determined in step S1 is performed, wherein the parameter H is the stroke of the closing operation which took place in the preceding time interval.

5. The method according to any one of claims 1, 2 or 4, wherein in step S6 a parameter m is used for the determination of the velocity at which the opening determined in step S1 is performed, wherein the parameter m is the velocity of the closing operation which took place in the preceding time interval.

6. The method according to any one of claims 1, 2, 4 or 5, wherein in step S6 a parameter tSE is used to determine the velocity at which the opening determined in step S1 is performed, wherein the parameter tSE is the time which is at the end of the closing operation which took place in the preceding time interval.

7. Method according to one of the previous claims, wherein in step S6 the time tSE is determined which is at the end of the closing operation which took place in the preceding time interval, and wherein the opening speed limitation is maintained in step S6 for at least a time duration which is given by t -tSE0 +T.

8. The method according to any one of claims 1 to 6, wherein the opening velocity in step S6 is maintained for a predetermined time duration Δt, and wherein after the time duration Δt has elapsed, the steps of the method are run through again.

9. The method according to any one of the previous claims, wherein in the event of a power failure, a fast shutdown of the Pelton turbine is automatically performed.

10. A Pelton turbine comprising a runner (1), at least one nozzle (3), a water way (8) and a control device (4) for controlling an opening degree of the nozzle (3), wherein the runner (1) comprises a plurality of buckets (2), and wherein the Pelton turbine comprises mechanical means for realising a single-stage actuating set, whereby the actuating speed of the nozzle (3) can be limited to a maximum permissible actuating speed, and wherein the Pelton turbine comprises means adapted to carry out the steps of the method according to any one of claims 1 to 9.

11. Pelton turbine according to claim 10, wherein the Pelton turbine comprises a control device (6) for monitoring the control device (4).

12. A computer program comprising instructions that cause the apparatus of claim 10 or 11 to perform the method steps of any one of claims 1 to 9.

13. A computer-readable medium on which the computer program according to claim 12 is stored.