Method for controlling the machine sets in a hydroelectric power plant

Abstract

Method for controlling the machine sets (1, 2, 3) in a hydroelectric power station with at least two machine sets (1, 2, 3), wherein each machine set (1, 2, 3) comprises an electrical and a hydraulic machine, and wherein the hydroelectric power station comprises a control device (4) which is designed such that it has a mechanical phase φ x of the hydraulic machines, and wherein the hydroelectric power plant comprises at least one sensor (5) for generating a signal and the method comprises the following steps: - generating a signal with the at least one sensor (5); - Calculation of a vibration index from the generated signal; - Adjusting the mechanical phases φ x of the hydraulic machines by the control device (4) in order to minimize the vibration index.

Description

[0001] The invention relates to a method for controlling the machine units in a hydroelectric power plant, wherein the hydroelectric power plant comprises several machine units, and the method aims to positively influence the vibration behavior of the machine units in the hydroelectric power plant. The invention further relates to a control device for a hydroelectric power plant, which is designed to implement the method according to the invention.

[0002] The vibration behavior of the machine units in a hydropower plant can negatively impact material stress and thus the maintenance requirements of the machine units. Furthermore, suboptimal vibration behavior of the machine units leads to high noise levels, which can pose health risks or impair the quality of life for the hydropower plant's personnel or residents. Therefore, a variety of measures have been developed to positively influence the vibration behavior of machine units in hydropower plants. Examples of known measures include the design of the guide vane, turbine design, power plant motor design, penstock design, and the reduction of manufacturing tolerances.A very good list of measures to reduce vibrations and noise in hydropower plants can be found in the journal article by MOHANTA, Rati Kanta [et al.] “Sources of vibration and their treatment in hydro power stations – A review” (in: Engineering Science and Technology, An International Journal (JESTECH), Vol. 20, 2017, No. 2, pp. 637-648. - ISSN 2215-0986 (E)).

[0003] Furthermore, JP 2001-323867 A discloses a hydroelectric power plant with multiple machine sets and a method for reducing vibrations in such a hydroelectric power plant. Using the example of a hydroelectric power plant with two machine sets, the cited document proposes operating the two machine sets such that the vibrations generated by each machine have opposite phases. To this end, the impellers of the two machine sets are installed so that they have a fixed phase difference. The phase difference between the impellers is selected such that the vibrations generated by each machine set have opposite phases, so that these two vibrations destructively overlap to reduce the overall vibration.

[0004] The inventors have recognized that the concept disclosed in JP 2001-323 867 A presents various problems during implementation, making it virtually impossible or producing suboptimal results. One of the causes is that the vibrations caused by a machine set comprise a complex spectrum with a multitude of excitation and resonance frequencies, so that no clear phase can be assigned to the vibration caused. Furthermore, the vibration spectrum depends on many time-varying factors. In modern hydropower plants, the machine sets must be able to operate efficiently over the widest possible operating range. The respective vibration spectrum depends on the corresponding operating point.It can happen that vibrations in certain operating areas become so severe that they must be avoided due to the vibrations they cause, while other operating areas pose no such problems. A hydroelectric power plant is a complex dynamic system whose individual components are interconnected by dynamic couplings. These couplings are particularly significant when the individual machine units are connected to the downstream area by shared penstocks and / or water drainage devices, as hydrodynamic couplings are then added to the mechanical coupling mechanisms.

[0005] The object of the invention is to provide a method for controlling the machine sets of a hydroelectric power plant with several machine sets, by means of which the vibrations and noise generation in the hydroelectric power plant can be significantly reduced.

[0006] The object is achieved according to the invention by an embodiment according to the independent claim. 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: Hydroelectric power plant with several machine sets Fig. 2: Machine set in a first embodiment Fig. 3: Machine set in another embodiment Fig. 4: Machine set in another embodiment Fig. 5: Machine set in another embodiment

[0008] Fig. Figure 1 shows a highly schematic representation of a hydroelectric power plant with several machine sets. The hydroelectric power plant comprises at least two machine sets. Fig. The hydroelectric power plant shown in Figure 1 comprises, by way of example, three machine sets. Each machine set comprises an electrical machine and a hydraulic machine, with each electrical machine comprising a rotor and each hydraulic machine comprising a runner. Each rotor is connected to the associated runner via a shaft. The electrical machines are marked "Ex," where "x" is the serial number of the respective machine set. The hydraulic machines are marked "Hx." The electrical machines are electrically connected to a transmission grid. The transmission grid is operated with an alternating electrical voltage. The electrical frequency of the transmission grid is designated "f N ” and the electrical phase of the transmission network with “φ NThese quantities are also referred to as electrical parameters of the transmission grid. The dashed lines indicate the electrical connection of the electrical machines to the transmission grid.

[0009] Below each machine set, the mechanical parameters “mechanical rotation frequency” and “mechanical phase” are represented by “f x ' and 'φ x '. In most machine sets, the mechanical parameters refer to both the electrical and hydraulic machine, since the rotor and impeller are firmly connected to each other by means of the shaft. In the embodiment according to Fig. 5, however, this connection is not fixed, but adjustable via a hydrodynamic converter, so that the mechanical parameters of the electric and hydraulic machines do not have to match, but are independent of each other. Therefore, the terms "mechanical parameters," "mechanical rotational frequency," and "mechanical phase" in this document generally refer only to the respective hydraulic machines.

[0010] Each electrical machine (possibly together with an inverter) can be assigned electrical parameters (frequency and phase). Fig. 1, these electrical parameters are not shown for the sake of clarity. The relationship between electrical and mechanical parameters depends on the design of the respective machine set. These relationships are explained below using the Fig. 2 to 5 are explained in more detail.

[0011] A hydroelectric power plant also includes a control device that can control the machine sets of the hydroelectric power plant. Fig. 1, such a control device is indicated by the rectangle labeled 4. The control device 4 is designed such that it can adjust the mechanical parameters, in particular the mechanical phase of the hydraulic machines. The control device 4 regulates the mechanical parameters of the hydraulic machines such that the electrical parameters of the electrical machines (if necessary in conjunction with a converter) match the electrical parameters of the transmission network. This form of control is known from the prior art. According to the invention, this form of control is supplemented in order to improve the vibration behavior of the power plant by adjusting the mechanical phases of the hydraulic machines. The specific design of these inventive supplements to the control depends, in turn, on the design of the machine sets and is also described below with reference to the Fig. 2 to 5 are explained in more detail.

[0012] The Fig. 1 further comprises at least one sensor for generating a signal, which is designed so that a vibration characteristic can be calculated from the signal generated by the sensor. In Fig. In Figure 1, the sensor is indicated by the rectangle labeled 5. The signal from sensor 5 is fed into the control device 4, which calculates the vibration index. The vibration index can also be calculated in a separate device, which then makes the vibration index available to the control device 4. If the hydroelectric power plant comprises more than one such sensor 5 (which is advantageous), the vibration index is calculated from the signals of the individual sensors 5, with a specific weighting factor being used for each sensor if necessary. Any sensors whose signal can be used to calculate a vibration index can be used as sensors 5. Examples include acoustic sensors (microphones), piezoelectric acceleration sensors, laser sensors, and radar sensors. It is advantageous if the sensors are mounted at sensitive locations in the hydroelectric power plant.Sensitive locations are those where vibrations and the resulting noise have a particularly damaging effect. Therefore, it is advantageous to install acoustic sensors in areas where hydropower plant personnel typically spend time. It is also advantageous to locate sensors on parts subject to wear (such as bearings).

[0013] According to the invention, the control device 4 is designed such that it can adjust the mechanical parameters of the hydraulic machines in such a way that the vibration index is minimized. In doing so, the control device 4 utilizes the respective degrees of freedom of the machine sets that exist when adjusting the mechanical phase of the machine sets. The available degrees of freedom depend on the design of the machine sets. The inventors have recognized that the vibration index can be varied by varying the mechanical phases φ xof the machine sets can be influenced. The term “minimization of the vibration coefficient” means that the mechanical phases φ x of the machine sets must be adjusted so that the vibration characteristic V(φ1, φ2, φ3, ...) reaches at least a local minimum.

[0014] The method according to the invention comprises the following steps: - Generating a signal with the at least one sensor 5 - Calculation of a vibration index from the generated signal - Adjusting the mechanical phases φ x of the machine sets by the control device 4 in order to minimize the vibration index

[0015] The aforementioned steps are iterated until the vibration index has reached at least a local minimum. After that, the mechanical phases of the machine sets can be kept constant as long as the vibration index shows no significant change. The control loop characterized by the above-mentioned steps can equally well be kept continuously active. The vibration index will usually change significantly when the operating point of a machine set changes. It is therefore advantageous to activate the control loop after such a change.

[0016] Based on the Fig. Figures 2 to 5 describe the special features of the method according to the invention, which depend on the design of the hydropower plant's machine units. A hydropower plant generally comprises machine units of the same design. However, this does not preclude the possibility that a hydropower plant operated according to the invention may also comprise machine units of different designs.

[0017] Fig. Figure 2 shows a machine set in a first embodiment, in which the electrical machine is designed as a synchronous machine, and whose stator is connected to the transmission grid via a frequency converter. Such an arrangement is also referred to as a synchronous machine with a full converter. Due to the power electronic topology of the converter, the mechanical characteristics of the machine set are completely decoupled from the electrical characteristics of the transmission grid. In principle, the machine set can therefore operate at any mechanical rotational frequency f x and any mechanical phase φ x In practice, the rotational frequency f x However, it is adjusted so that the efficiency of the machine set is as high as possible. The respective mechanical phase φ xHowever, this does not play a role and can therefore be freely selected. The mechanical phase of such a machine set can be changed simply by operating the machine set at a different rotational frequency for a certain period of time. Once the desired phase position has been established, the machine set is operated again at the optimum rotational frequency. For this purpose, the machine includes a device for determining the angular-related impeller alignment. Such devices are known from the prior art and are also used for other purposes. For example, pulse encoders or absolute encoders can be used to determine the impeller alignment. The angle of rotation can be measured, for example, on the shaft.

[0018] Fig. Figure 3 shows a machine set in a further embodiment, in which the electric machine is designed as a doubly fed asynchronous machine. The rotor of the electric machine is connected to the transmission grid via a frequency converter. This embodiment also allows a certain degree of speed variability of the machine set. Since a small adjustment of the rotational frequency is sufficient for freely adjusting the mechanical phase, this embodiment also offers full freedom in adjusting the mechanical phase of such a machine set.

[0019] Fig. Figure 4 shows a machine set in a further embodiment, in which the electrical machine is designed as a synchronous machine. Synchronous machines run synchronously with the frequency and phase of the transmission network. However, synchronicity refers to the electrical characteristics of the electrical machine. Only in a synchronous machine with two poles, i.e., one pole pair, do the electrical characteristics match the mechanical characteristics, since the mechanical rotational frequency is then equal to the frequency of the electrical alternating voltage at the stator of the electrical machine. If the electrical machine has more than one pole pair, the relationship f applies. N = p * f x , where p is the number of pole pairs. The poles are in Fig. 4 in the rotor. The number of pole pairs is 9. At a mains frequency of 50 Hz, such a machine would have to rotate at a mechanical rotational frequency of approximately 5.55 revolutions per second to be synchronized. For synchronization, the electrical phase of the electrical machine must also match the electrical phase of the transmission network. The electrical machine has a magnetic periodicity of 360° / p. This means that from an electrical point of view, it makes no difference if the rotor (and thus the impeller) is rotated by an angle of 360° / p. In terms of the mechanical phase, such a machine therefore has a stepped degree of freedom, with the step size being 360° / p. In order to vary the mechanical phase, the control device must be able to synchronize the machine with the desired impeller alignment.Thus, with each change in the mechanical phase initiated by the control device, the machine is resynchronized. A variation of the mechanical phase according to the invention is possible in machine sets with at least two pole pairs. The electrical machines used in the machine sets of hydroelectric power plants typically have a large number of pole pairs.

[0020] Fig. 5 shows a machine set in a further embodiment, in which the electrical machine as in the embodiment according to Fig. 4 is designed as a synchronous machine. In addition, the machine set includes a hydrodynamic converter, ie a hydrodynamic gear, which is arranged between the impeller of the hydraulic machine and the rotor of the electrical machine. In Fig. 5, the converter is designated 6. Converter 6 enables decoupling of the rotary motions of the impeller and rotor, i.e., by temporarily changing the impeller speed, the mechanical phase of the impeller can be continuously adjusted. Due to the hydraulic losses in converter 6, continuous operation of converter 6 is associated with efficiency losses. Therefore, it is advantageous if converter 6 is only activated when the mechanical phase of the impeller of the machine set is to be varied. After such a control intervention, the two shaft sections of the machine set are firmly connected by means of a gear coupling, and converter 6 is emptied. In this way, the mechanical phase of the impeller can be adjusted in steps, with the step size being proportional to the inverse of the number of teeth of the gear coupling. Fig. 5 the gear coupling is indicated by the jagged line. List of reference symbols 1 machine set 2 machine sets 3 machine sets 4 Control device 5 Sensor 6 converters

Claims

[1] Method for controlling the machine sets (1, 2, 3) in a hydroelectric power station with at least two machine sets (1, 2, 3), each machine set (1, 2, 3) comprising an electrical and a hydraulic machine, and the hydroelectric power station comprising a control device (4) which is designed such that it has a mechanical phase φ x of the hydraulic machines, and wherein the hydroelectric power plant comprises at least one sensor (5) for generating a signal, characterized by that the procedure includes the following steps: - generating a signal with the at least one sensor (5); - Calculation of a vibration index from the generated signal; - Adjusting the mechanical phases φ x of the hydraulic machines by the control device (4) in order to minimize the vibration index. [2] Method according to claim 1, wherein the method is carried out after a change in an operating point of the at least two machine sets (1, 2, 3). [3] Method according to claim 1 or 2, wherein the electrical machine of at least one machine set (1, 2, 3) is designed as a synchronous machine with a full converter, and the setting of the mechanical phase φ x of the associated hydraulic machine by a temporary change in the mechanical rotation frequency of this machine set. [4] Method according to one of the preceding claims, wherein the electrical machine of at least one machine set (1, 2, 3) is designed as a double-fed asynchronous machine, and the setting of the mechanical phase φ x of the associated hydraulic machine by a temporary change in the mechanical rotation frequency of this machine set. [5] Method according to one of the preceding claims, wherein the electrical machine of at least one machine set (1, 2, 3) is designed as a synchronous machine with at least two pole pairs, and the setting of the mechanical phase φ x of the associated hydraulic machine by synchronization in the mechanical phase φ to be set x takes place. [6] Method according to one of the preceding claims, wherein the electrical machine of at least one machine set (1, 2, 3) is designed as a synchronous machine, and wherein a hydrodynamic converter (6) is arranged between the associated hydraulic machine and the synchronous machine, and wherein the setting of the mechanical phase φ x of the associated hydraulic machine by a time-limited change in the mechanical rotational frequency of the associated hydraulic machine by decoupling it from the synchronous machine by the hydraulic converter. [7] Method according to one of the preceding claims, wherein at least one sensor (5) is designed as a microphone and is arranged in an area of ​​the hydroelectric power plant in which operating personnel are present. [8] Method according to one of the preceding claims, wherein at least one sensor (5) is designed and arranged such that the sensor (5) can detect vibrations of a component of the hydroelectric power plant that is susceptible to wear. [9] Control device (4) for a hydroelectric power plant with at least two machine sets (1, 2, 3), and wherein the control device (4) is designed such that it can carry out a method according to one of the preceding claims.

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