Hydropower plant with a cylinder gate and method for retrofitting such a hydropower plant

Abstract

Retrofitting a hydroelectric power plant (4) with a waterway (2), an electric machine (6), an impeller (5) arranged in the waterway (2) and a cylinder gate, wherein the impeller (5) has an axis of rotation by which an axial (z) and a radial (r) direction are defined, and wherein the cylinder gate comprises a ring (1) and a gate chamber (3) with a housing, and wherein the ring (1) can be moved in an axial direction, and wherein the ring (1) has a projection which is designed to modify a secondary flow in such a way as to suppress unstable states of the cylinder gate at opening degrees below 30%.

Description

The invention relates to a hydropower plant with a ring gate. Ring gates are used in hydropower plants to stop the flow of water through a hydraulic machine of the plant. The invention relates to the retrofitting of such a hydropower plant. A cylinder contactor is used in hydraulic machines that include a guide vane assembly (i.e., the hydraulic machine is usually of the Francis type) and is located within the guide vane assembly. A cylinder contactor comprises a cylindrical ring that moves axially to open and close. In the open position, the cylindrical ring is located in a so-called contactor chamber. The diameter of the ring can be very large, as it usually encircles the movable guide vanes of the hydraulic machine when closed. Hydraulic cylinders are used to move the ring. A cylinder contactor is generally a safety device that must be able to stop the hydraulic machine, even under full load, in the event of a fault. Hydropower plants with a cylinder gate are known from the prior art. For example, the publication "Alstom Francis Turbine Ring Gates: From Retrofitting to Commissioning" (Nguyen PA et al 2014 IOP Conf. Ser.: Earth Environ. Sci. 22 012008) discloses such a hydropower plant. Document US 3,489,391 A also reveals a water power plant with a cylinder gate. The inventors have discovered that during an emergency shutdown under full load using a cylinder contactor, strong vibrations of the contactor often occur, accompanied by high pressure fluctuations in the contactor chamber and the hydraulic cylinders. The object of the invention is to provide a retrofit method for a hydroelectric power plant with a cylinder gate, in which the described problems do not occur after the retrofit or only to a much lesser extent. The problem is solved according to the invention by an embodiment according to the independent claim. Further advantageous embodiments of the present invention are found in the dependent claims. The inventors thoroughly analyzed the described problems and, based on this analysis, proposed a solution. Surprisingly, it turned out that the problem could be solved by minor geometric adjustments to the cylindrical ring and the firing chamber. The invention is explained below with reference to the figures. The figures show in detail: Fig. 1: Water power plant with a cylinder gate according to the prior art; Fig. 2: Water power plant with a cylinder gate according to the present invention; Fig. 3: Details of the embodiment according to Fig. 2; Fig. 4: Further embodiment according to the invention; Fig. 5: Further embodiment according to the invention; Fig. 6: Water power plant according to the invention. Fig. 1 shows a hydroelectric power plant with a cylinder gate according to the prior art. The three sub-figures (a), (b), and (c) of Fig. 1 show the cylinder gate in three different positions. Sub-figure (a) shows the cylinder gate in the fully open position. Sub-figure (b) shows the cylinder gate in a position where it is only 30% open. Sub-figure (c) shows the cylinder gate in the fully closed position. In general, a hydroelectric power plant with a cylindrical gate comprises a watercourse, designated 2 in Fig. 1(a), a cylindrical ring, designated 1 in Fig. 1(a), and a gate chamber, designated 3 in Fig. 1(b). The phrase "cylindrical" refers to the general shape of the ring 1; that is, in detail, the ring 1 may deviate from a strictly cylindrical shape (e.g., at the projection forming the seal). The gate chamber 3 is surrounded by a pressure-tight housing. Fig. 1 shows an axial section through the aforementioned elements of the hydroelectric power plant, with each sub-figure depicting only the portion of these elements located to the right of the axis of rotation. In part (a), i.e., in the fully open state, the cylindrical ring 1 is completely enclosed within the guard chamber 3, allowing the water to flow unimpeded through the water path 2, as indicated by the horizontal arrows. In the representation of Fig. 1 (a), the water flows radially from the outside to the inside, whereas in reality, the water also exhibits a tangentially oriented flow component, which cannot be shown in the representation of Fig. 1. To close the cylinder gate, the cylindrical ring 1 is moved axially into the water channel 2, thus reducing the free cross-section of the water channel 2 accordingly. Figure (b) shows the situation where the cylindrical ring 1 has already been moved 70% of its full stroke into the water channel 2. The degree of opening is therefore only 30%. The mechanics, actuators, and control technology required for the movement of the cylindrical ring 1 are not shown in Fig. 1, as they are not relevant to the present invention. Therefore, for the implementation of the present invention, a person skilled in the art can use any known embodiment for these elements. In the situation depicted in partial figure (b), the water flow through waterway 2 is already significantly impeded by ring 1. At an opening degree of less than 100%, a secondary water flow increasingly develops, indicated by the small curved arrows. Due to the damming effect caused by the partially closed ring 1, water flows from waterway 2 through various gaps in the gate chamber 3, past the upper edge of the cylindrical ring 1, and back into waterway 2. These gaps are located in the gate chamber 3 and occur when the opening degree is not equal to 0%, with the gaps situated between ring 1 and the housing of the gate chamber 3. The inventors analyzed the flow conditions sketched in part (b) using CFD calculations and determined that the vibrations and pressure fluctuations that can occur during the emergency closure in the last 30% of the closing process are caused by the self-excitation of horizontal vibration modes of the cylindrical ring 1 as a result of strong flow through the gaps which change due to the vibrations. Figure (c) shows the cylinder gate in its fully closed position. The projection located on the inside of the cylindrical ring at the top forms a seal, which interacts with part of the inner wall of the gate chamber 3. This allows the ring 1, in the position shown, to prevent both the primary and secondary water flow. Simultaneously, the pressure of the upstream water is present in the gate chamber 3, thus securely holding the cylindrical ring 1 in the closed position. This gives the cylinder gate a tendency to close. During the last few percent of the closing process, the described vibrations and pressure fluctuations subside as the water flows that cause them become increasingly weak and eventually disappear. It seems logical to make the relevant gaps so narrow that the secondary water flows become so small that vibrations and pressure fluctuations can no longer occur. While this would theoretically work, it is not feasible in practice for several reasons, which will be explained below. When the cylindrical ring closes, a sufficient amount of water must be able to flow into the gate chamber to ensure the required closing time. During the closing process, the gate chamber must be connected to the upstream water to guarantee a closing tendency. The manufacturing tolerances inherent in the large diameter of ring 1 prevent the necessary narrow gap design. Furthermore, the risk of ring 1 tilting during closing increases with the narrowness of the gap. It must also be considered that the hydrostatic pressure can cause deformation of the ring.This effect can only be compensated for if the gaps are wide enough. Furthermore, gaps that are too narrow could be damaged by the normal vibrations of the hydroelectric plant, i.e., widened and thus rendered ineffective. The inventors were able to demonstrate, using CFD calculations, that narrowing the gap to a practically feasible width would not improve the described situation to the desired extent. Since preventing the secondary flow would not achieve the desired result, the inventors focused on designing the secondary flow in such a way that it would dampen vibrations rather than excite them. Fig. 2 shows the inventive design of the cylinder gate after retrofitting in a first particularly preferred embodiment. The cylinder gate shown is in the same position as the cylinder gate in Fig. 1(c), i.e., at an opening degree of 30%. The cylindrical ring 1 has a projection on its upper edge at the outer circumference, which is designated 1.1. The housing of the gate chamber 3 has a wall which can interact with the projection 1.1 to form a gap. The term "wall" is understood to mean a part of the housing of the gate chamber 3 oriented towards the ring. The projection 1.1 and the wall 3.1 are designed and arranged such that the gap-forming interaction can occur over a specific opening degree range.The gap-forming interaction occurs when the ring assumes positions corresponding to opening degrees within the specified opening degree interval. Further details of the invention are described in connection with Fig. 3. Fig. 3 shows an enlarged section of Fig. 2 with the designations for various gap dimensions. In the upper part of Fig. 3, the axial direction, i.e., the direction of the axis of rotation of the hydroelectric power plant and the direction of movement of the cylindrical ring of the gate, is designated by z. The direction designated by r indicates the radial direction, which points from the inside out. All gap dimensions are measured in the radial direction. The width of the gap between the projection 1.1 and the wall 3.1 is designated w1. The width of the gap between the ring 1 in the region of the projection forming the seal and the housing of the guard chamber 3 is designated w2. The gap on the inside between the ring 1 and the lower end of the housing is designated w3. The gap on the outside between the ring 1 and the lower end of the housing is designated w4. According to the invention, the width w1 of the gap between the projection 1.1 and the wall 3.1 is less than or equal to 4 / 5 or 80% of the width of all other gaps that are present between the ring 1 and the housing of the guard chamber 3, i.e., w1 ≤ 80% * w2, w1 ≤ 80% * w3, and w1 ≤ 80% * w4. It is clear that to fulfill this condition, only the smallest of the values ​​w2, w3 and w4 should be used, since then the condition is also fulfilled for the other values. The aforementioned condition naturally only applies if the projection 1.1 and the wall 3.1 interact to form a gap. This is the case when the ring 1 assumes an axial position in which the projection 1.1, viewed radially, is opposite the wall 3.1. Fig. 3 shows the ring 1 in a position in which the projection 1.1 is opposite the wall 3.1 along its entire axial length. The position shown corresponds to an opening degree of 30%. If the ring 1 is moved upwards, the projection 1.1 is no longer opposite the wall 3.1 along its entire axial length, and with further upward movement, it is no longer opposite the wall 3.1 at all. Conversely, when the ring 1 is moved downwards, the projection 1.1 is always opposite the wall 3.1 along its entire axial length.The axial displacement, denoted as s1, indicates the maximum downward movement of ring 1 before its lower edge contacts the seal. This displacement s1 corresponds to an opening degree interval length of 30%, i.e., the length of the opening degree interval from 30% to 0%. The inventors have recognized that, for solving the problem at hand, it is particularly advantageous if the aforementioned condition for the gap width w1 applies to an opening degree range that encompasses at least the range from 30% to 1%. To a somewhat lesser, but still satisfactory, extent, the inventive advantages arise if the aforementioned condition for the gap width w1 applies to an opening degree range that encompasses at least the range from 3% to 15%. Since, as the inventors have recognized, the strongest vibrations generally occur in an opening degree range of 3% to 10%, the advantages of the invention arise at least when the condition for the gap width w1 applies to this opening degree range. The inventors further recognized that it is advantageous if the aforementioned condition for the gap width w1 does not apply when the opening degree is greater than 40%. The aforementioned condition does not apply when the projection 1.1 is no longer opposite the wall 3.1, since the gap width w1 is then no longer defined, or, if one still wishes to speak of a gap with width w1, this would have to be measured radially between the projection 1.1 and the housing wall located much further to the right. In the latter case, it is clear that w1 is then greater than each of the gap widths w2, w3, and w4. However, it is sufficient if w1 is greater than the width of at least one other gap. The effect of the larger gap width w1 at opening degrees greater than 40% is that the risk of the ring tilting is reduced, and a reliable closing tendency is ensured despite reduced flow forces.Furthermore, at such high degrees of opening, the difficulties mentioned at the outset do not occur, so that the measures according to the invention for vibration reduction are not required. The inventors have recognized that it is not necessary for the projection 1.1 to be positioned at the very top edge of the ring 1, as shown in Figures 2, 3, and 5. For the advantages of the invention to be satisfactorily realized after retrofitting, it suffices if the axially measured distance of the projection 1.1 is no greater than the axial displacement corresponding to an opening degree interval length of 15%. Such an arrangement is shown in Figure 4. The projection is located from the top edge of the ring 1 by the axially measured displacement, which is denoted by a. In the illustrated embodiment, the displacement a corresponds to an opening degree interval length of approximately 13%. The displacement s1, as in Figure 3, has a length corresponding to an opening degree interval length of 30%. The gap width w1 is thus adjusted over an opening degree interval with a length greater than 30% and less than 40%.The dashed boundary lines that separate the rectangle designated 3.2 refer to the retrofit procedure described below. Fig. 5 shows another embodiment of the invention. The embodiment according to Fig. 5 differs from the embodiment according to Fig. 2 only in that the wall 3.1 in Fig. 5 is arranged on a wall of the housing of the guard chamber 3 that projects into the guard chamber 3, whereas the wall 3.1 in Fig. 2 is arranged on the inner wall of the housing of the guard chamber 3. The dashed boundary line, which separates the rectangle designated 3.2, refers to the retrofit method described below. The embodiment according to Fig. 5 is particularly advantageous for equipping existing systems with the features of the invention, in which the guard chamber 3 is very voluminous. In this embodiment, cylindrical ring segments are connected to the housing of the existing guard chamber 3 to form the wall projecting into the housing, with the wall 3.1 being formed at least partially by the radially inner wall of the cylindrical ring segments. In systems with a less voluminous guard chamber 3, cylindrical ring segments can also be connected to the housing of the existing guard chamber 3 to ensure a sufficient axial length of the wall 3.1. In this case, the radially outer side of the cylindrical ring segments contacts the existing inner wall of the housing of the guard chamber 3. Here, too, the wall 3.1 is formed at least partially by the radially inner wall of the cylindrical ring segments. In Figures 4 and 5, dashed lines indicate the contact surfaces of retrofitted cylindrical ring segments, each labeled 3.2. The cylindrical ring segments can be connected to the housing of the existing guard chamber 3 by bolting or welding. In any case, the ring 1 must have a projection 1.1 according to the invention. The projection 1.1 can be welded or screwed onto the existing ring 1. Alternatively, the existing ring 1 can be replaced by a new ring 1 with a projection 1.1 according to the invention. It is advantageous if, after the insertion of the cylindrical ring segments 3.2, the inner surface of the segments, which at least partially forms the wall 3.1, is reworked to adjust the desired gap width w1 as precisely as possible on all sides. In addition to the measures mentioned above, further modifications to the existing system may be necessary so that the retrofitted system has the features according to the invention. Such further measures may, for example, concern the gap widths of the other gaps (w2, w3, w4), if necessary. The axial length of the projection 1.1 does not need to be very large. It is advantageous if the axial length is no greater than a distance corresponding to an opening degree interval of 10%. The projection 1.1 can extend completely around the entire ring 1 in the circumferential direction. In reality, however, this may not be possible, for example, because guide rails are provided to guide the axial movement of the ring. In this case, the projection 1.1 can have interruptions, at least in the area of ​​the guide rails. Interruptions in the projection 1.1 can also be used to increase the closing speed of the cylinder gate, or the gap width w1 can be selected to be smaller without excessively reducing the closing speed. Such interruptions impair the effectiveness of the projection 1 according to the invention.1 not or only insignificantly, as long as the total length of the interruptions does not exceed 25% of the total length of the projection 1.1 measured in the circumferential direction. The features characterizing the invention can be summarized as follows: The ring 1 comprises a projection 1.1, which is arranged on the radially outer circumference of the ring 1, and the housing of the guard chamber 3 comprises a wall 3.1, wherein the projection 1.1 and the wall 3.1 are arranged and designed such that over an opening degree interval, which includes at least the opening degree interval [3%, 10%], a gap is formed between the projection 1.1 and the wall 3.1 with a width w1, and wherein the width w1 is less than or equal to 80% of the width of other gaps between the housing of the guard chamber 3 and the ring 1. The inventors have verified the effectiveness of the measures according to the invention using CFD calculations. The instabilities described in connection with Fig. 1 were effectively prevented. Fig. 6 shows a section through a water power plant according to the invention, designated by 4. The water power plant comprises a cylindrical gate according to the invention, which surrounds an impeller designated by 5. The impeller 5 is connected to an electric machine designated by 6. The dashed line indicates the axis of rotation of the impeller 5 and the electric machine 6. Typically, a water power plant 4 with a cylindrical gate includes a guide vane assembly, which is not shown in Fig. 6. Reference symbol list 1 Ring 1.1 Projection 2 Waterway 3 Gate chamber 3.1 Wall 3.2 Cylindrical ring segment for retrofitting an existing system 4 Hydroelectric power plant 5 Impeller 6 Electric machine r Radial direction s1 Axial path length w1 Gap width in radial direction w2 Gap width in radial direction w3 Gap width in radial direction w4 Gap width in radial direction z Axial direction

Claims

Method for retrofitting an existing hydropower plant (4), wherein the existing hydropower plant (4) comprises a waterway (2), an electric machine (6), an impeller (5) arranged in the waterway (2), and a cylinder gate, wherein the impeller (5) has an axis of rotation by which an axial (z) and a radial (r) direction are defined, and wherein the cylinder gate comprises a ring (1) and a gate chamber (3) with a housing, and wherein the ring (1) can be moved in the axial direction to set an opening degree, and wherein the ring (1) is arranged in the gate chamber (3) at an opening degree of 100% and in the waterway (2) at an opening degree of 0%, and wherein gaps are formed at an opening degree other than 0%, which are arranged in the radial direction between the ring (1) and the housing of the gate chamber (3), and which can be penetrated by a secondary water flow at opening degrees of less than 100%.wherein the method comprises the step of connecting cylindrical ring segments (3.2) to the housing of the existing gate chamber (3), and wherein, after retrofitting, the ring (1) of the hydroelectric power plant (4) comprises a projection (1.1) which is arranged on a radially outer edge of the ring (1), and wherein the housing of the gate chamber (3) comprises a wall (3.1), and wherein the projection (1.1) and the wall (3.1) are arranged and designed such that, over an opening degree interval which includes at least the opening degree interval 3% to 10%, a gap is formed between the projection (1.1) and the wall (3.1) with a radially measured width w1, and wherein the width w1 is less than or equal to 80% of the radially measured width of other gaps between the housing of the gate chamber (3) and the ring (1) through which the secondary water flow passes.and wherein the wall (3.1) is formed at least partially by a radially inner wall of the cylindrical ring segments (3.2). Hydroelectric power plant (4) which has been retrofitted according to claim 1, wherein the projection (1.1) and the wall (3.1) are arranged and designed such that over an opening degree interval, which comprises at least the opening degree interval 3% to 15%, preferably 1% to 30%, a gap is formed between the projection (1.1) and the wall (3.1) with a width w1 measured in the radial direction, and wherein the width w1 is less than or equal to 80% of the width measured in the radial direction of other gaps between the housing of the gate chamber (3) and the ring (1). Hydroelectric power plant (4) which has been retrofitted according to claim 1 or 2, wherein the projection (1.1) and the wall (3.1) are arranged and designed such that, at opening degrees greater than 40%, the radially measured width w1 of the gap between the projection (1.1) and the wall (3.1) is greater than the radially measured width of at least one other gap between the housing of the gate chamber (3) and the ring (1). Hydroelectric power plant (4) which has been retrofitted according to one of the preceding claims, wherein an axially measured distance of the projection (1.1) from an axially upwardly located edge of the ring (1) is not greater than an axial path length of the ring (1) which corresponds to an opening degree interval length of 15%. Hydroelectric power plant (4) which has been retrofitted according to one of the preceding claims, wherein an axially measured length of the projection (1.1) is not greater than an axial path length of the ring (1) which corresponds to an opening degree interval length of 10%. Hydroelectric power plant (4) which has been retrofitted according to one of the preceding claims, wherein the projection (1.1) has interruptions in a circumferential direction around the ring (1), and wherein the total length of the interruptions does not exceed 25% of the total length of the projection (1.1), the lengths being measured in the circumferential direction.

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