EP2457240B1 - Method for reducing the noise emission of a transformer - Google Patents

Description

Technical area

The invention relates to a method for reducing the noise emission of a transformer whose transformer tank is filled with a liquid and the boiler wall executes vibrations during operation.

State of the art

During operation of a transformer caused by magnetostriction shape change of the soft magnetic core and / or acting on the windings electrodynamic forces leads to pressure waves in the cooling liquid of the transformer, which excite the wall of the transformer tank to vibrate. These boiler vibrations have a sound radiation in the audible range, which is particularly disturbing when the transformer is installed, for example, in the vicinity of a residential area.

In order to reduce operating noise of a transformer, various active devices are known. From the DE 699 01 596 T2 For example, a low-noise transformer is known in which a vibration cell is arranged in the transformer tank, which generates a vibration in phase opposition to the pressure waves and thereby attenuates the vibrations of the boiler wall. A similar Procedure is in the US 5,394,376 proposed where also a liquid displacement device counteracts pressure waves inside the transformer tank. However, these known devices have in common that a connection between an actuator and the liquid inside the boiler is required. In addition, the actuator consumes a considerable amount of energy. Out US 5,617,479 a device is known in which actuators are positioned in areas of maximum transverse deflection of the boiler wall.

Illustrations of the invention

It is an object of the present invention to provide a method which effectively reduces the noise emission of a transformer in the simplest and most reliable way, while consuming as little energy as possible. This object is achieved by a method having the features of claim 1. Advantageous embodiments are defined in the subclaims.
According to a basic idea of the invention, on the outside of the wall of the transformer tank, a vibration applying device for vibration in antiphase is arranged so that it lies as close as possible to maximum curvature or maximum transverse deflection of an eigenform of the vessel wall. As a result, an efficient action on the disturbing vibration of the boiler wall is possible. An eigenform, or fashion, describes the appearance of a waveform at a natural frequency. At each natural frequency, there is a certain geometric shape of the boiler wall vibration, that is, a particular mode. In a first approximation, a boiler wall can be used as a plate with a fixed edge. The plate modes occurring there are named with an ordinal number (mn). When the vibration applying means, hereinafter also referred to as actuator for short, is placed in a large deflection range of the eigenform, comparatively little energy is required for the vibration damping.
A particularly favorable embodiment of the method according to the invention is characterized in that a piezoelectric element is used as the vibration-applying device. A particular advantage of this piezoelectric element is that it can be used both as an actuator and as a transmitter. According to the invention, it is provided that the piezoelectric element or another measuring transducer supplies a measurement signal proportional to the oscillation of the boiler wall and this is passed back to the control device. The control device analyzes this measurement signal and determines therefrom amplitude and phase for a control signal with which the piezoactuator is driven to cancel out the oscillation. In this way, an adaptation of the vibration damping to changing operating conditions is possible. This maintains the effect of noise reduction over a long period of operation.

Brief description of the drawings

Figur 1

Kesselschwingung bei einer Anregung von 100 Hz und deren Zerlegung in Eigenformen;

Figur 2

eine Darstellung von Simulationsbildern, welche die Zerlegung einer Plattenschwingung in ihre Eigenformen zeigen;

Figur 3

eine Darstellung von Simulationsbildern, welche eine Überlagerung eines 2-3-Modes mit einem 1-5-Mode zeigen;

Figur 4

eine Darstellung von Simulationsbildern, welche eine Überlagerung eines 2-3-Modes mit einem 2-6-Mode und eine Überlagerung eines 1-5-Modes mit einem 1-7-Mode zeigen.

To further explain the invention, reference is made in the following part of the description to the drawings in which further advantageous embodiments, details and further developments of the invention can be found.
It shows:

FIG. 1

Boiler vibration at excitation of 100 Hz and its decomposition into eigenmodes;

FIG. 2

a representation of simulation images showing the decomposition of a plate vibration in its eigen forms;

FIG. 3

a representation of simulation images showing a superposition of a 2-3 mode with a 1-5 mode;

FIG. 4

a representation of simulation images showing a superposition of a 2-3 mode with a 2-6 mode and a superimposition of a 1-5 mode with a 1-7 mode.

Embodiment of the invention

The FIG. 1a shows in a spatial representation of a transformer tank. As already mentioned, the boiler wall of the transformer is excited to oscillate during operation by the transformer core and / or the transformer winding. Especially with a transformer of high power, this noise emission is disturbing. In a distribution or power transformer, the excitation frequency is usually 50 Hz or 60 Hz.

In FIG. 1b is shown forming on the wall of the transformer tank waveform. Such a pictorial representation of a boiler vibration form can be obtained experimentally by analyzing the vibration during operation. In FIG. 1b, FIG. 1c and FIG. 1d in each case the speed of the boiler surface is drawn. That is, the speed of change of the wall around its rest position. From the illustration, the areas with maximum deflection (belly) and the areas with the minimum deflection (node) can be seen. In Figure 1e the fashion spectrum is shown. For this purpose, the person skilled in the art knows devices and methods with which a mode spectrum can be created. For example, with an impulse hammer, a container wall can be excited to oscillate and the vibrations of the vessel wall can be measured, for example, with acceleration sensors or piezoelectric force transducers distributed on the boiler wall surface. These measurement signals can be fed to a computer system, which performs a modal analysis and numerically determines the dynamic behavior of the boiler wall.
As already stated above, a waveform is composed of the interference of its natural modes and can thus be decomposed into their modes. This can be done for example by a simulation. The FIG. 1 shows an analysis of a 100 Hz boiler vibration as a result of a simulation on a computer system. In the simulation pictures Figure 1c and Figure 1d the eigenmodes are shown. How out Figure 1c and 1d can be seen, the boiler vibration is essentially composed of two modes of natural vibration: a 2-3 mode (see FIG. 2b ) and a 1-5 mode (see Figure 2c ). This composition of the boiler vibration also illustrates the diagram of FIG. 1 e; it shows the proportion of the amplitude of the modes in the boiler vibration as a function of frequency.

• Die Figur 3 zeigt im Schwingungsbild 40 einen 2-3-Mode. Gebiete, in denen sich dieser 2-3 Mode besonders gut anregen und somit dämpfen lässt, sind mit dem Bezugszeichen 401 gekennzeichnet und zeichnerisch grau schraffiert dargestellt. Rechts daneben ist der 1-5-Mode 50 dargestellt, der sich in den Bereichen 501 besonders gut anregen lässt.

Die weißen Bereiche in den beiden Bildern 40, 50 kennzeichnen Gebiete, in denen sich der jeweilige Mode nur schlecht anregen lässt. Um nun mit möglichst wenigen Aktuatoren eine effiziente Reduktion der Geräusche herbeizuführen, werden von den grau schraffiert dargestellten Flächen des 2-3-Mode (Figur 3a) die grau schraffiert gezeichneten Flächen des 1-5-Mode (Figur 3b) subtrahiert. Das Ergebnis ist in Figur 3c (Bild 100) dargestellt. Die Differenzflächen 101 stellen Gebiete auf der Kesselwand dar, welche besonders günstig sind, um einen der beiden Moden wirkungsvoll zu dämpfen, ohne dass der andere Mode unbeabsichtigter Weise angeregt wird. Figur 3c zeigt sichel- und tropfenförmigen Restflächen, in denen ein Aktuator angeordnet werden kann, der durch gegenphasige Schwingungseinleitung wirkungsvoll den 2-3-Mode dämpft, ohne den 1-5-Mode zu verstärken. Subtrahiert man hingegen die grauen Flächen 401 von den grauen Flächen 501, - siehe Figur 3d Bild 200 -, so erhält man jene Gebiete 201, in denen sich der Mode 1-5 gut anregen lässt, der Mode 2-3 hingegen schlecht.The vertical dotted line indicates the excitation frequency 100 Hz. The peak to the left thereof shows the more pronounced extreme of the 2-3 mode at its associated natural frequency of 99 Hz. The peak to the right thereof shows the extreme value of the 1-5 mode at its inherent natural frequency of 101 Hz.
FIG. 2 shows in the upper simulation image, the waveform 30; the two underlying simulation images 40 and 50 represent the 2-3 mode ( FIG. 2b ) or the 1-5-mode ( Figure 2c ). In diagram 60 in the middle of FIG. 2 again the amplitude is drawn as a function of the frequency.
In the noise reduction, one strives to achieve the greatest possible effect of noise reduction with as few actuators. For the reduction of the boiler vibration per attachment at least one actuator is required. In order to find out on the boiler surface those areas which are particularly suitable for a damping of the oscillation, oscillation patterns are superimposed. It must be ensured that the one mode is damped, the other is not inadvertently stimulated. In order to find out these areas on the boiler surface, a subtraction of the mode images is carried out according to the invention, which is explained in more detail below:

• The FIG. 3 shows a 2-3 mode in the vibration image 40. Areas in which this 2-3 mode excite particularly well and thus can be dampened, are identified by the reference numeral 401 and shown graphically gray hatched. To the right is the 1-5 mode 50, which can be particularly well stimulated in the areas 501.

The white areas in the two pictures 40, 50 indicate Areas in which the respective fashion can only be stimulated poorly. In order to bring about an efficient reduction of the noise with as few actuators as possible, the areas of the 2-3-mode (shaded in gray) FIG. 3a ) the gray hatched areas of the 1-5-Mode ( FIG. 3b subtracted. The result is in Figure 3c (Figure 100). The differential surfaces 101 represent areas on the boiler wall which are particularly favorable to effectively damp one of the two modes without inadvertently exciting the other mode. Figure 3c shows sickle-shaped and teardrop-shaped residual surfaces in which an actuator can be arranged, which effectively attenuates the 2-3 mode by antiphase oscillation initiation without amplifying the 1-5 mode. On the other hand, one subtracts the gray areas 401 from the gray areas 501, - see 3d figure Picture 200 -, you get those areas 201, in which the mode 1-5 can be well stimulated, the mode 2-3, however bad.

In this way, those areas have been identified on the boiler wall in which vibrations can be attenuated particularly efficiently.

In principle, efforts are made to dampen as many frequencies and modes as possible with as few actuators as possible. Not only the basic excitation, but also the higher harmonics of the basic excitation are disturbing.

FIG. 4 shows a representation of simulation images for the case of an excitation frequency of 100 Hz (f ₁ ) and the first harmonic at 200 Hz (f ₂ ). The boiler vibration at 200 Hz is composed of a 1-7 mode (oscillation image 41) and a 2-6 mode (oscillation image 51).

In the overlay image 400, the gray areas of the eigen-shape 40 and 51 were merged and the gray areas of the eigen-shape 50 were subtracted. The areas 401 identify those areas in which the eigenvagant 40 and 51 can be damped separately, ideally by means of an actuator.

In the overlay image 500, the gray areas of the eigenform 50 and 41 were merged and the gray areas of the eigenform 51 were subtracted. The gray hatched areas 501 identify those areas in which the eigenvagant 50 and 41, in the ideal case by means of an actuator, can be damped separately.

By controlling an actuator with a frequency mix of 100 Hz and 200 Hz, it can be used both to reduce the 100 Hz component and to reduce the 200 Hz component. This allows you to dampen two frequencies and four modes with two actuators. In other words, in order to reduce the number of actuators, one does not consider each stimulating frequency 100 Hz, 200 Hz, 300 Hz, 400 Hz, etc. alone, but overlays all considered eigenmodes of all frequencies and determines by superposition those areas that correspond to the optimization strategy presented above. In this case, the number of actuators is increased stepwise until all modes are separately ausregelbar.

Although the boiler is energized at the frequency of 100 Hz, the amplitude and phase vary depending on the operating condition and operating time, the contribution of the natural vibration modes that make up the boiler vibration. Over the entire operating period an effective suppression of the To achieve sound radiation, the noise suppression system must be adapted to the actual state. This is achieved by the piezo elements are temporarily used as a vibration absorber, at times as a transducer for receiving a vibration. In this measuring phase, the measurement signal generated by the piezoelectric element is fed back into the control unit. In the control unit, the magnitude and phase of the measured oscillation are determined from the measurement signal. The boiler vibration is broken down into its own forms. If the piezoelectric element is used again as a vibration absorber, this information is used for the control of the piezoelectric element, possibly also other actuators. Each actuator is assigned its own control loop. In this way, the suppression of sound radiation is adjusted. Each actuator is thereby adjusted to the temporal changes in the boiler oscillation within its operating range. Thus, the overall effect of noise reduction over a long period of operation is maintained.

Compilation of the reference numbers used

1

transformer tank

2

waveform

3

Fashion 2-3

4

Fashion 1-5

5

mode spectrum

30

Simulation image, waveform

40

Simulation picture Mode 2-3

41

Simulation screen Mode 1-7

50

Simulation screen Mode 1-5

51

Simulation picture Mode 2-6

60

diagram

100

Difference image (40 without 50)

101

Areas of favorable stimulation of the 2-3-Mode

200

Difference image (50 without 40)

201

Areas of favorable excitation of the 1-5-Mode

400

Difference image ((40 combined with 51) without 50)

500

Difference picture ((50 united with 41) without 51)

401

Regions effective excitation of the 2-3 mode at f ₁ and f ₂ 2-6 mode at

501

Areas of favorable excitation of the 1-5-mode at f ₁ and 1-7-mode at f ₂

Claims (7)

1. Method for reducing the noise emission of a transformer, the transformer tank (1) of which is filled with a liquid and the tank wall of which vibrates during operation, characterised by the following sequence of method steps:

   a.) detecting natural vibration values of the tank wall for at least one excitation frequency;

   b.) determining at least two eigenforms (3,4,30,40,41,50,51), from which the vibration of the tank wall is composed at an excitation frequency, by means of computer-aided processing of the natural vibration values, wherein a subtraction of the at least two eigenforms is performed and difference areas (100,200,400,500) of the tank wall are determined on the tank wall by means of computer-aided superimposition;

   c.) arranging at least one vibration loading device in at least one of these difference areas;

   d.) activating the at least one vibration loading device by means of a control device in order to counteract the vibration of the tank wall.
2. Method according to claim 1, characterised in that the activation is performed such that each eigenform is counteracted separately.
3. Method according to claim 2, characterised in that the activation is effected by a control signal which is composed of a frequency mixture in order to damp a plurality of eigenforms using different excitation frequencies.
4. Method according to one of the preceding claims, characterised in that the vibration loading device takes the form of a piezoelectric element.
5. Method according to claim 4, characterised in that use is made of a measuring transducer which converts the vibrations of the tank wall into a measured signal that is supplied to the control device.
6. Method according to claim 5, characterised in that the control device determines magnitude and phase of an eigenform from the supplied measured signal and, on the basis of these, calculates a control variable for the piezoelectric actuator, said control variable being used for the activation of the piezoelectric element in a time interval following the measurement interval.
7. Method according to one of the claims 4 to 6, characterised in that the at least one piezoelectric element is fastened to the tank wall by means of adhesive.

Images