Method for controlling the machine sets in a hydroelectric power plant

Abstract

The invention relates to a method for controlling the machine sets (1, 2, 3) in a hydroelectric power plant having at least two machine sets (1, 2, 3), each machine set (1, 2, 3) comprising an electrical machine and a hydraulic machine, the hydroelectric power plant comprising a control device (4) which is designed in such a way that it can adjust a mechanical phase φx of the hydraulic machines, and the hydroelectric power plant comprising at least one sensor (5) for generating a signal; the method comprising the following steps: - generating a signal by means of the at least one sensor (5); - calculating a vibration characteristic from the generated signal; and - adjusting the mechanical phases φx of the hydraulic machines by means of the control device (4) in order to minimize the vibration characteristic.

Description

[0001] Method for controlling the turbine sets in a hydroelectric power plant

[0002] The invention relates to a method for controlling the turbine-generator sets in a hydroelectric power plant, wherein the hydroelectric power plant comprises several turbine-generator sets and the method aims to positively influence the vibration behavior of the turbine-generator sets in the hydroelectric power plant. The invention further relates to a control device for a hydroelectric power plant, which is configured to execute the method according to the invention.

[0003] The vibration behavior of turbine-generator sets in a hydroelectric power plant can negatively impact material stress and thus the maintenance requirements of these sets. Furthermore, suboptimal vibration behavior leads to high noise levels, which can cause health problems or impair the quality of life for power plant personnel or residents. Therefore, numerous measures have been identified in the art to positively influence the vibration behavior of turbine-generator sets in hydroelectric power plants. Examples of such measures include: design of the brazing apparatus, turbine design, design of the motors in the power plant, design of the penstock(s), and 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 “Sources of vibration and their treatment in hydropower stations - A review” (Engineering Science and Technology, an International Journal 20 (2017) 637-648).

[0004] Furthermore, JP 2001 323867 A2 discloses a hydroelectric power plant with multiple generating sets and a method for reducing vibrations in such a power plant. Using the example of a hydroelectric power plant with two generating sets, the document proposes operating the two sets in such a way that the vibrations caused by each set have opposite phases. To achieve this, the impellers of the two 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 set have opposite phases, allowing these two vibrations to superimpose destructively and thus reduce the overall vibration.

[0005] The inventors recognized that the concept disclosed in JP 2001 323867 A2 presents several problems in its implementation, making it virtually impossible or yielding suboptimal results. One reason for this is that the vibrations caused by a turbine set represent a complex spectrum with a multitude of excitation and resonance frequencies, meaning that a single, unambiguous phase cannot be assigned to the vibration itself. Furthermore, the vibration spectrum depends on many time-varying influencing factors. In modern hydropower plants, the turbine sets are expected to operate efficiently across the widest possible operating range. The specific vibration spectrum depends on the corresponding operating point.It can happen that in certain operating areas, vibrations become so intense that these areas must be avoided due to the vibrations they cause, while other operating areas do not present such problems. A hydroelectric power plant represents a complex dynamic system whose individual components are interconnected by dynamic couplings. These couplings are particularly strong when the individual generating units are connected to the tailrace via common penstocks and / or water discharge devices, as hydrodynamic couplings are then added to the mechanical coupling mechanisms.

[0006] The object of the invention is to provide a method for controlling the machine sets of a hydroelectric power plant with multiple machine sets, by which the vibrations and noise generation in the hydroelectric power plant can be significantly reduced.

[0007] 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 invention is explained below with reference to figures. The figures show in detail:

[0008] Fig. 1: Hydroelectric power plant with multiple generating sets

[0009] Fig. 2: Machine set in a first embodiment

[0010] Fig. 3: Machine set in a further embodiment

[0011] Fig. 4: Machine set in a further embodiment

[0012] Fig. 5: Machine set in a further embodiment

[0013] Figure 1 shows a highly schematic representation of a hydroelectric power plant with several generating sets. The hydroelectric power plant comprises at least two generating sets. The hydroelectric power plant shown in Figure 1 includes, by way of example, three generating sets. Each generating set comprises an electric machine and a hydraulic machine, with each electric machine comprising a rotor and each hydraulic machine comprising an impeller. Each rotor is connected to its associated impeller via a shaft. The electric machines are labeled "Ex", where "x" is the sequential number of the respective generating set. The hydraulic machines are labeled "Hx". The electric machines are electrically connected to a transmission network. The transmission network operates with an alternating current. The electrical frequency of the transmission network is labeled "N" and the electrical phase of the transmission network is labeled "(PN)".These quantities are also referred to as electrical parameters of the transmission network. The dashed lines indicate the electrical connection of the electrical machines to the transmission network.

[0014] Below each machine set, the mechanical parameters "mechanical rotational frequency" and "mechanical phase" are denoted by "f". x “ and “cp x“marked.” In most machine sets, the mechanical parameters refer to both the electric and the hydraulic machine, since the rotor and impeller are rigidly connected by the shaft. In the embodiment shown in Figure 5, however, this connection is not rigid but adjustable via a hydrodynamic converter, so that the mechanical parameters of the electric and hydraulic machines do not have to be the same, but are independent of each other. Therefore, in this document, the terms “mechanical parameters,” “mechanical rotational speed,” and “mechanical phase” generally refer only to the respective hydraulic machines.

[0015] Each electrical machine (possibly together with a converter) can be assigned electrical parameters (frequency and phase). For clarity, these electrical parameters are not shown in Figure 1. The relationship between electrical and mechanical parameters depends on the specific design of the respective machine set. These relationships are explained in more detail below with reference to Figures 2 to 5.

[0016] A hydroelectric power plant further comprises a control unit that can control the turbine sets of the power plant. In Figure 1, such a control unit is indicated by the rectangle labeled 4. The control unit 4 is designed to adjust the mechanical parameters, in particular the mechanical phase of the hydraulic machines. The control unit 4 regulates the mechanical parameters of the hydraulic machines so that the electrical parameters of the electric machines (possibly in conjunction with a converter) match the electrical parameters of the transmission network. This type of control is known from the prior art. According to the invention, this control method is extended to improve the vibration behavior of the power plant by adjusting the mechanical phases of the hydraulic machines.How these inventive additions to the control system are designed in detail depends in turn on the embodiment of the machine sets and is also explained in more detail below with reference to Figures 2 to 5.

[0017] The hydroelectric power plant shown in Figure 1 further comprises at least one sensor for generating a signal, which is configured such that a vibration index can be calculated from the signal generated by the sensor. In Figure 1, the sensor is indicated by the rectangle labeled 5. The signal from sensor 5 is fed into the control unit 4, which calculates the vibration index from it. The calculation of the vibration index can also be performed in a separate unit, which then provides the vibration index to the control unit 4. If the hydroelectric power plant comprises more than one such sensor 5 (which is advantageous), then the vibration index is calculated from the signals of the individual sensors 5, optionally using a specific weighting factor for each sensor. Any sensor from whose signal a vibration index can be calculated can be used as sensor 5.Examples of suitable sensors include acoustic sensors (microphones), piezoelectric accelerometers, laser sensors, and radar sensors. It is advantageous to position these sensors at sensitive points within the hydroelectric power plant. Sensitive points are those where vibrations and the resulting noise have a particularly damaging effect. For instance, acoustic sensors are best placed in areas where power plant personnel typically work. It is also beneficial to position sensors on components prone to wear and tear (such as bearings).

[0018] 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 as to minimize the vibration coefficient. 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 embodiment of the machine sets. The inventors have recognized that the vibration coefficient can be reduced by varying the mechanical phases (p x The machine sets can be influenced. The term "minimizing the vibration coefficient" means that the mechanical phases cp x The machine sets are adjusted so that the vibration coefficient V(cpi, q>2, q>3, ... ) is at least a local minimum.

[0019] The method according to the invention comprises the following steps: - Generating a signal with the at least one sensor 5

[0020] - Calculation of a vibration parameter from the generated signal

[0021] - Setting the mechanical phases <p x The machine sets are controlled by the control unit 4 to minimize the vibration coefficient.

[0022] The aforementioned steps are iterated until the vibration parameter reaches at least a local minimum. Afterward, the mechanical phases of the machine sets can be kept constant as long as the vibration parameter does not change significantly. Alternatively, the control loop characterized by the steps mentioned above can be kept continuously active. The vibration parameter will typically change significantly when the operating point of a machine set changes. It is therefore advantageous to activate the control loop after such a change.

[0023] The appendix to Figures 2 to 5 describes the special features of the method according to the invention, which depend on the embodiment of the turbine sets of the hydroelectric power plant. A hydroelectric power plant generally comprises turbine sets of the same embodiment. However, this does not preclude the possibility that a hydroelectric power plant operated according to the invention may also comprise turbine sets of different embodiments.

[0024] Figure 2 shows a machine set in a first embodiment, in which the electric machine is designed as a synchronous machine and its stator is connected to the transmission network 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 network. In principle, the machine set can therefore be operated at any mechanical rotational frequency f. x and any mechanical phase <p x to be operated. In practice, the rotational frequency f x However, it is set up to maximize the efficiency of the machine set. The respective mechanical phase plays a role in this. <p xHowever, the phase is irrelevant and can therefore be freely chosen. The mechanical phase of such a machine set can be easily changed by operating the machine set at a different rotational frequency for a certain period of time. Once the desired phase is established, the machine set is operated again at the optimal rotational frequency. For this purpose, the machine includes a device for determining the angular impeller alignment. Such devices are known from the prior art and are also used for other purposes. For example, pulse generators or absolute encoders can be used to determine the impeller alignment. The rotational angle measurement can, for example, be performed at the shaft.

[0025] Figure 3 shows a further embodiment of a machine set in which the electric machine is designed as a doubly fed asynchronous machine. The rotor of the electric machine is connected to the transmission network via a frequency converter. This embodiment also allows for a certain degree of speed variability of the machine set. Since only a small adjustment of the rotational frequency is sufficient for freely setting the mechanical phase, this embodiment also offers full freedom in setting the mechanical phase of such a machine set.

[0026] Figure 4 shows a machine set in a further embodiment, in which the electric 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 electric machine. Only in the case of a synchronous machine with two poles, i.e., one pole pair, do the electrical characteristics coincide with the mechanical characteristics, since then the mechanical rotational frequency is the same as the frequency of the alternating voltage applied to the stator of the electric machine. If the electric machine has more than one pole pair, then the relationship fN = p * f applies. x, where p is the number of pole pairs. The poles are indicated in Figure 4 in the rotor. The number of pole pairs is 9. At a grid frequency of 50 Hz, such a machine would have to rotate at a mechanical rotational speed of approximately 5.55 revolutions per second to be synchronized. For synchronization, the electrical phase of the electric machine must also match the electrical phase of the transmission grid. The electric machine has a magnetic periodicity of 3607p. This means that, electrically, it makes no difference if the rotor (and thus the impeller) is rotated by an angle of 3607p. With respect to the mechanical phase, such a machine therefore has a stepped degree of freedom, with a step size of 3607p. The control device must be able to synchronize the machine at the desired impeller orientation by varying the mechanical phase.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 for machine sets with at least two pole pairs. The electric machines used in the machine sets of hydroelectric power plants generally have a large number of pole pairs.

[0027] Figure 5 shows a machine set in a further embodiment, in which the electric machine is designed as a synchronous machine, as in the embodiment according to Figure 4. The machine set additionally includes a hydrodynamic converter, i.e., a hydrodynamic transmission, which is arranged between the impeller of the hydraulic machine and the rotor of the electric machine. In Figure 5, the converter is designated 6. The converter 6 enables the decoupling of the rotary motions of the impeller and rotor; that is, by temporarily changing the impeller speed, the mechanical phase of the impeller can be continuously adjusted. Due to the hydraulic losses in the converter 6, continuous operation of the converter is associated with efficiency losses. Therefore, it is advantageous if the converter 6 is only activated when the mechanical phase of the impeller of the machine set needs to be varied.Following such a control intervention, the two shaft sections of the machine set are rigidly connected by means of a gear coupling, and the 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. In Figure 5, the gear coupling is indicated by the serrated line. Reference numeral list.

[0028] 1 machine set

[0029] 2 machine sets

[0030] 3 machine set

[0031] 4 Control unit

[0032] 5 Sensor

[0033] 6 converters

Claims

Patent claims 1. Method for controlling the machine sets (1, 2, 3) in a hydroelectric power plant with at least two machine sets (1, 2, 3), wherein each machine set (1, 2, 3) comprises an electric and a hydraulic machine, and wherein the hydroelectric power plant comprises a control device (4) which is designed such that it controls a mechanical phase <p x the hydraulic machines can be adjusted, and wherein the hydroelectric power plant comprises at least one sensor (5) for generating a signal, characterized in that the method comprises the following steps: - Generating a signal using at least one sensor (5); - Calculation of a vibration parameter from the generated signal; - Setting the mechanical phases <p x the hydraulic machines by the control device (4) in order to minimize the vibration coefficient.

2. Method according to claim 1, wherein the method is carried out after a change of an operating point of the at least two sets of machines (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 adjustment of the mechanical phase <p x the associated hydraulic machine is changed by a time-limited change in the mechanical rotational 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 doubly fed asynchronous machine, and the adjustment of the mechanical phase <p x the associated hydraulic machine is changed by a time-limited change in the mechanical rotational 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 adjustment of the mechanical phase <p x the associated hydraulic machine by synchronization in the mechanical phase to be set <p x This has been done.

6. A method according to one of the preceding claims, wherein the electric 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 adjustment of the mechanical phase <p x the associated hydraulic machine is changed 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 located.

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 wear-prone component of the hydroelectric power plant.

9. Control device (4) for a hydroelectric power plant with at least two generating sets (1 , 2, 3), wherein the control device (4) is designed such that it can perform a method according to one of the preceding claims.

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