Transformer and a transformer arrangement

Abstract

A transformer comprising at least two phase windings, each phase winding having coil turns around a coil axis, wherein the at least two phase windings comprise at least a first type of phase winding and a second type of phase winding, each of the first type of phase winding and the second type of phase winding comprising a plurality of winding portions comprising at least a first winding portion and a second winding portion, the first type of phase winding comprising a first winding portion having a first winding portion stiffness and a second winding portion having a second winding portion stiffness, and characterized in that a stiffness difference between said first winding portion stiffness and said second winding portion stiffness of said first type of phase winding is such that the acoustic power is minimized at said main frequency.

Claims

1. A transformer comprising at least two phase windings, each phase winding having coil turns around a coil axis, said transformer being adapted to transform voltage at a predetermined frequency, when said transformer is operating, said transformer is excited by a mechanical load having a main frequency corresponding to said predetermined frequency multiplied by two and having vibration modes, wherein the combination of load and vibration modes results in a vibration of said transformer, said transformer having a set of vibration modes, each vibration mode having a vibration mode frequency, wherein at least one main contributing vibration mode of the set of vibration modes is the vibration mode resulting in a largest acoustic power, of said vibration modes, when the transformer is excited by said load, the at least two phase windings comprising at least a first type of phase winding and a second type of phase winding, each of the first type of phase winding and the second type of phase winding comprising a plurality of winding portions comprising at least a first winding portion and a second winding portion, the first type of phase winding comprising the first winding portion having a first winding portion stiffness and the second winding portion having a second winding portion stiffness, a stiffness difference between said first winding portion stiffness and said second winding portion stiffness of said first type of phase winding being such that acoustic power is minimized at said main frequency, said first winding portion of the first type of phase winding having the first winding portion stiffness, as seen along said coil axis, and said second winding portion of the first type of phase winding having the second winding portion stiffness, as seen along said coil axis, said first winding portion stiffness being different from said second winding portion stiffness, and the first winding portion of the second type of phase winding having the first winding portion stiffness, as seen along said coil axis, and said second winding portion of the second type of phase winding also having the first winding portion stiffness, as seen along said coil axis, and the transformer comprising three phase windings arranged along a second axis, such that one first type of phase winding is arranged centrally, between two second type of phase windings, or one second type of phase winding is arranged centrally, between two first type of phase windings.

2. The transformer according to claim 1, wherein the first type of phase winding is provided with a plurality of spacers between the coil turns, and wherein the first winding portion of the first type of phase winding is provided with a first type of spacers and the second winding portion of the first type of phase winding is provided with a second type of spacers, said first type of spacers being different from said second type of spacers.

3. The transformer according to claim 2, wherein the first type of spacers has a first modulus of elasticity and the second type of spacers has a second modulus of elasticity, said first modulus of elasticity being different from said second modulus of elasticity.

4. The transformer according to claim 1, wherein said first winding portion is located radially inwards of said second winding portion.

5. The transformer according to claim 1, wherein the predetermined frequency is in a range of 50 Hz to 60 Hz.

6. The transformer according to claim 5, wherein the main frequency is in a range of 100 Hz to 120 Hz.

7. The transformer according to claim 1, wherein the one first type of phase windings is arranged centrally, between two second type of phase windings.

8. The transformer according to claim 1, wherein one second type of phase winding is arranged centrally, between two first type of phase windings.

9. A transformer arrangement comprising a transformer enclosed in a transformer tank, the transformer comprising: at least two phase windings, each phase winding having coil turns around a coil axis, said transformer being adapted to transform voltage at a predetermined frequency, when said transformer is operating, said transformer is excited by a mechanical load having a main frequency corresponding to said predetermined frequency multiplied by two and having vibration modes, wherein the combination of load and vibration modes results in a vibration of said transformer, said transformer having a set of vibration modes, each vibration mode having a vibration mode frequency, wherein at least one main contributing vibration mode of the set of vibration modes is the vibration mode resulting in a largest acoustic power, of said vibration modes, when the transformer is excited by said load, the at least two phase windings comprising at least a first type of phase winding and a second type of phase winding, each of the first type of phase winding and the second type of phase winding comprising a plurality of winding portions comprising at least a first winding portion and a second winding portion, the first type of phase winding comprising the first winding portion having a first winding portion stiffness and the second winding portion having a second winding portion stiffness, a stiffness difference between said first winding portion stiffness and said second winding portion stiffness of said first type of phase winding being such that acoustic power is minimized at said main frequency, said first winding portion of the first type of phase winding having the first winding portion stiffness, as seen along said coil axis, and said second winding portion of the first type of phase winding having the second winding portion stiffness, as seen along said coil axis, said first winding portion stiffness being different from said second winding portion stiffness, and the first winding portion of the second type of phase winding having the first winding portion stiffness, as seen along said coil axis, and said second winding portion of the second type of phase winding also having the first winding portion stiffness, as seen along said coil axis, and the transformer comprising three phase windings arranged along a second axis, such that one first type of phase windings is arranged centrally, between two second type of phase windings, or one second type of phase winding is arranged centrally, between two first type of phase windings.

10. The transformer arrangement of claim 9, wherein said first winding portion is located radially inwards of said second winding portion.

11. The transformer arrangement of claim 9, wherein the first type of phase winding is provided with a plurality of spacers between the coil turns, and wherein the first winding portion of the first type of phase winding is provided with a first type of spacers and the second winding portion of the first type of phase winding is provided with a second type of spacers, said first type of spacers being different from said second type of spacers.

12. The transformer arrangement of claim 11, wherein the first type of spacers has a first modulus of elasticity and the second type of spacers has a second modulus of elasticity, said first modulus of elasticity being different from said second modulus of elasticity.

13. The transformer arrangement according to claim 9, wherein the predetermined frequency is in a range of 50 Hz to 60 Hz.

14. The transformer arrangement according to claim 13, wherein the main frequency is in a range of 100 Hz to 120 Hz.

15. The transformer arrangement according to claim 9, wherein the one first type of phase windings is arranged centrally, between two second type of phase windings.

16. The transformer arrangement according to claim 9, wherein one second type of phase winding is arranged centrally, between two first type of phase windings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further objects and advantages of, and features of the disclosure will be apparent from the following description of one or more embodiments, with reference to the appended drawings, where:

(2) FIG. 1 shows a side view cross-section of an exemplary prior art transformer in an asymmetric vibration mode;

(3) FIG. 2 shows a side view cross-section of the prior art transformer of FIG. 1 in a symmetric vibration mode;

(4) FIG. 3 shows the noise power generated by the prior art transformer of FIG. 1 and FIG. 2 at predetermined frequencies;

(5) FIG. 4 illustrates the concept of noise generation in a symmetric vibration mode;

(6) FIG. 5 illustrates the concept of noise generation in an asymmetric vibration mode;

(7) FIG. 6 shows a side view cross-section of an exemplary transformer according to the present disclosure;

(8) FIG. 7 is detailed view of coil turns and spacers of the transformer of FIG. 6; and

(9) FIG. 8 shows a top view cross-section of the exemplary transformer of FIG. 6.

DETAILED DESCRIPTION

(10) The present disclosure is developed in more detail below referring to the appended drawings which show examples of embodiments. The disclosure should not be viewed as limited to the described examples of embodiments; instead, it is defined by the appended patent claims. Like numbers refer to like elements throughout the description.

(11) FIG. 1 and FIG. 2 show side view cross-sections of an exemplary prior art transformer 100 under different vibration modes. The prior art transformer 100 has a first extension along a first axis z, a second extension along a second axis x and a third extension along a third axis y (not shown). The first, second and third axes are perpendicular to each other. The prior art transformer 100 is further exemplified with three phase windings 110 being located at a distance from each other as seen along said second axis (x).

(12) Each phase winding has first end and an opposite second end along the first axis (z). The first and second ends are respectively provided with a first pressplate 112 and a second pressplate 114, between which two pressplates the phase winding 110 is clamped. When the transformer 100 is in operation, electromagnetic forces and the clamping of the phase windings between the pressplates generate load noise, which is a significant part of the total noise of transformers, especially for large units.

(13) Symmetric movements (piston-like displacements) of a transformer tank 200, in which the transformer 100 may be enclosed, radiate significant noise to the far field as compared to asymmetric movement because symmetric vibrations displace more air and thereby radiate sound more efficiently than asymmetric movements. Phase windings 110 under load usually vibrate at 100 Hz or 120 Hz mechanical main frequency (i.e., 50 Hz or 60 Hz predetermined electrical operating (excitation) frequency multiplied by two).

(14) FIGS. 1 and 2 illustrate the movement of the pressplates 112, 114 by arrows M of the transformer 100. For the sake of clarity, the arrows are only shown for one phase winding 110. In practice, for the prior art transformer 100, all phase windings 110 exhibit the same vibration pattern, albeit at a 1200 phase shift in relation to each other, for e.g., a three-phase transformer 100 such as shown in FIG. 1 and FIG. 2.

(15) FIG. 3 shows how acoustic power of the transformer 100 varies with frequency. The horizontal axis displays the mechanical vibration frequency. The curve represents a superposition of vibration modes of the structure of the transformer 100. The modes of interest of the transformer 100 may be identified at the peak amplitudes, where the acoustic power is largest.

(16) FIG. 4 and FIG. 5 illustrate symmetric and asymmetric vibration modes, respectively and further explain the sound producing properties thereof. FIG. 4 conceptually shows a symmetric mode acting on the transformer tank 200. It can be seen that a certain volume of media, ?V (positive or negative), such as air, surrounding the transformer tank 200 is displaced. This displacement radiates noise to the audible far field, which may be perceived as disturbing noise. In contrast, the asymmetric vibration mode shown in FIG. 5 moves one part of the transformer tank 200 up as another part is moved down, theoretically resulting in a net volume displacement, ?V, equal to zero. Such an asymmetric vibration mode radiates noise to the near field, which is not audible at a distance. In other words, it is not perceived as disturbing noise. A center plane P is shown in FIG. 4 and FIG. 5. The arrows M in FIG. 4 illustrate how every portion of the transformer tank 200, located on opposite sides of the center plane P, is displaced in the same direction at the same time for displacements in directions parallel to the center plane P. In FIG. 5 the asymmetric vibration mode results in opposing directions on opposite sides of the center plane P.

(17) FIG. 6 shows a side view cross-section of an exemplary transformer 100 according to the present disclosure. The transformer 100 comprises at least two phase windings 110. The illustrated exemplary transformer comprises three phase windings 110. Each phase winding 110 has coil turns 120 (FIG. 7) around a coil axis. The transformer 100 is adapted to transform voltage at a predetermined frequency, when the transformer 100 is operating. The transformer 100 is excited by a mechanical load having a main frequency corresponding to the predetermined frequency multiplied by two and having vibration modes. The combination of load and vibration modes results in vibration of the transformer 100. The transformer 100 further has a set of vibration modes, each vibration mode having a vibration mode frequency, where at least one main contributing vibration mode of the set of vibration modes is the vibration mode which results in the largest acoustic power, of the vibration modes, when the transformer 100 is excited by the load.

(18) The at least two phase windings 110 comprise at least a first type of phase winding 110a and a second type of phase winding 110b, each of the first type of phase winding 110a and the second type of phase winding 110b comprises a plurality of winding portions 116 comprising at least a first winding portion 116a and a second winding portion 116b. The first type of phase winding (110a) comprises a first winding portion (116a) having a first winding portion stiffness and a second winding portion (116b) having a second winding portion stiffness. A stiffness difference between said first winding portion stiffness and said second winding portion stiffness of said first type of phase winding is such that the acoustic power is minimized at the main frequency.

(19) FIG. 7 shows a magnified detail of the coil turns 120 of a phase winding 110. The at least one phase winding 110 is provided with a plurality of spacers 130 between the coil turns 120. The spacers are conventionally distributed along the axial length of the phase winding 110, between the coil turns, so as to separate and electrically isolate the turns of the coil from each other.

(20) The transformer 100 further has a first extension along a first axis z. The coil axis is parallel to the first axis z. The transformer 100 has a second extension along a second axis x and a third extension along a third axis y (see FIG. 8). The first, second and third axes are perpendicular to each other and the center of the at least two phase windings 110 are located at a distance from each other as seen along said second axis x. The transformer 100 comprises a first center plane A which extends along the second axis x and third axis y and splits the transformer in half, as seen in along the first axis z. The transformer 100 comprises a second center plane B (see FIG. 8) which extends along the second axis x and first axis z and splits the transformer 100 in half, as seen in along the third axis y. The transformer 100 comprises a third center plane C which extends along the third axis y and first axis z and splits said transformer 100 in half, as seen in along the second axis x.

(21) Each phase winding 110 may have a first end and an opposite second end along the coil axis, i.e., parallel with the first axis z. The first and second ends are respectively provided with a first pressplate 112 and a second pressplate 114, between which two pressplates the phase winding 110 is clamped.

(22) A symmetric mode of mechanical vibration of said transformer 100 results in that every portion of said transformer 100, located on opposite sides of one of said center planes A, B, C, are displaced in the same direction at the same time for displacements in directions parallel to the center plane concerned. An asymmetric mode of mechanical vibration of said transformer 100 results in that every portion of said transformer 100, located on opposite sides of one of said center planes A, B, C, are displaced in the opposite direction at the same time for displacements in directions parallel to the center plane concerned.

(23) A mode spectrum may be used to study a structure's vibration amplitude in response to different frequencies. Devices and methods for creating a mode spectrum are known to a person skilled in the art. A transformer tank wall can for instance be caused to vibrate by means of a pulse hammer and the vibrations of the tank wall can be measured by acceleration sensors or by piezoelectric force transducers that are distributed over the surface of the tank wall, for example. These measured signals can be forwarded to a computer system which performs a modal analysis and numerically determines the dynamic characteristics of the tank wall therefrom.

(24) As discussed in conjunction with FIGS. 1-5, the noise generating mechanism of transformers, e.g., power transformers, is controlled by a nearly symmetric phase winding axial force distribution. The transformer 100 of the present disclosure seeks to break this match by introducing an asymmetric vibration mode shape in an assembly of phase windings which constitute the transformer 100 such that the dot products ?.sub.n.sup.TF tend towards zero. The force distribution for a transformer is a given due to the structure. The shape and design of the core, the coil turns and/or pressplates are presets to obtain the desired electrical performance of the transformer. Other properties on which transformer vibrations depend may, however, be modified without affecting performance. Such a property is mechanical stiffness. Another property is the mass of the phase windings 110. However, the degrees of freedom for modifying mass are limited due to design restrictions placed on transformers and windings.

(25) For this purpose, and as described above, the transformer 100 according to the present disclosure, has at least one of its phase windings 110 provided with a plurality of winding portions 116. The plurality of winding portions comprises at least a first winding portion 116a and a second winding portion 116b, wherein the first winding portion 116a has a first winding portion stiffness and said second winding portion 116b has a second winding portion stiffness.

(26) In the exemplary embodiment of FIG. 8, which is a top-side cross-sectional view of the exemplary transformer 100 of FIG. 6, each phase winding 110 is shown to have an inner winding and an outer winding. The inner winding may be a low-voltage winding and the outer winding may be a high-voltage winding, or vice versa. The first winding portion 116a may be located radially inwards of the second winding portion 116b. In the exemplary embodiment of FIG. 8, the first winding portion 116a may be a low-voltage winding and the second winding portion 116b may be a high-voltage winding.

(27) According to the present disclosure, a phase winding comprises at least two winding portions 116. Thus, any number of winding portions 116 greater than two is also within the scope of the disclosure.

(28) A winding portion 116 herein means a part of the coil turns of a phase winding 110. As exemplified in FIG. 8, a winding portion 116 may be the entire inner or outer winding. A winding portion may alternatively be a part of a winding, such as a section of a winding, limited in length along the first axis z (not shown). A winding portion may also/alternatively be a sector of a winding, limited by an angle ?, around the coil axis, to a circumferential sector of the winding.

(29) The introduction of a stiffness difference or a mass difference, or a stiffness difference AND a mass difference, between the winding portions 116 breaks the symmetric mode of mechanical vibration and instead introduces an asymmetric mode of vibration in the transformer comprising the at least one phase winding 110 having differing winding portions. As a result of the at least one differing phase winding, the symmetric mode of mechanical vibration of the transformer 100 as a whole is broken.

(30) In a transformer arrangement 300, such as shown in FIG. 6 or FIG. 8, comprising a transformer 100 according to the present disclosure, enclosed in a transformer tank 200, noise emitted to the surroundings is significantly reduced. This is a consequence of breaking the symmetric mode of mechanical vibration in the transformer 100. Thereby the symmetric mode of the transformer tank 200 is also broken, such that acoustic power, and noise radiated from the transformer tank 200, are reduced.

(31) In order to break the symmetric mode of mechanical vibration of the transformer 100, the first winding portion 116a of the first type of phase winding 110a may have a first winding portion stiffness, as seen along the coil axis z. The second winding portion 116b of the first type of phase winding 110a may have a second winding portion stiffness, as seen along the coil axis z. As before, the first winding portion stiffness is different from said second winding portion stiffness.

(32) The first winding portion 116a is provided with a first spacer distribution and the second winding portion 116b is provided with a second spacer distribution. The first spacer distribution is different from said second spacer distribution. Choice of materials for the spacers 130, and/or the density of the spacer distribution, are factors that may be used to break the symmetric mode of mechanical vibration. When the coil turns 120 vibrate, the elasticity provided by the spacers 130 affect the stiffness of the phase winding 110 and the transformer 100 as a whole, and thereby affect the modes of vibration of the transformer 100, the oil and the transformer tank 200.

(33) The first spacer distribution may comprise a first type of spacers and the second spacer distribution may comprise a second type of spacers. The first type of spacers is different from said second type of spacers. The first type of spacers may for instance have a first modulus of elasticity and the second type of spacers may have a second modulus of elasticity. The first modulus of elasticity is different from said second modulus of elasticity by at least 3 GPa, or more preferably by at least 5 GPa, such as at least 10 GPa.

(34) The main contributing mode, or the symmetric mode, of the transformer may thus be modified by providing spacers 130 of different modulus of elasticity. The modulus of elasticity may for instance be selected by selecting appropriate materials for the spacers 130. The modulus of elasticity of selectable/applicable materials range between 0.1 GPa-120 GPa, or higher.

(35) Alternatively, the first spacer distribution may comprise spacers arranged at a first distance between each other in a direction around the coil axis and the second spacer distribution may comprise spacers arranged at a second distance between each other in a direction around the coil axis. The first distance is different from said second distance. By decreasing the distance between the spacers in, for instance, the first winding portion as compared to the second winding portion, the stiffness of the first winding portion may be increased as compared to the second winding portion. This would mean a greater number of spacers per unit length of the coil turns 120 in the first winding portion as compared to the second winding portion.

(36) Optionally, the first type of spacers could be structurally shaped to have a first stiffness as seen along the coil axis and the second type of spacers are shaped to have a second stiffness as seen along the coil axis, said first stiffness being different from said second stiffness. The spacers 130 may have structural shapes to provide an increased, or a reduced, stiffness as compared to conventional spacers. Consequently, the first type and the second type of spacers may be of the same material but may be provided with different shapes in order to provide at least the first and the second winding portions with different stiffnesses. As an example, hollow spacers 130 may provide a reduced stiffness as compared to solid spacers 130.

(37) It is advantageous that at least one of the phase windings 110 of the transformer 100 is not provided with different winding portions 116 having different winding portion stiffnesses. Thereby, at least one phase winding may have single type of spacers, which simplifies manufacturing. Also, simulations have shown that better results are achieved when not all phase windings have differing winding portion stiffnesses.

(38) In other words, in an exemplary embodiment, the first winding portion 116a of the second type of phase winding 110b may have the first winding portion stiffness, as seen along said coil axis, and said second winding portion 116b of the second type of phase winding 110b may also have the first winding portion stiffness, as seen along said coil axis. As such, the second type of phase winding 110b has the same winding portion stiffness, in both the first winding portion 116a and in the second winding portion 116b. The winding portion stiffness of the second type of winding 110b is the same as the winding portion stiffness of the first winding portion 116b.

(39) Two exemplary embodiments result in particularly significant noise reduction. In a first exemplary embodiment, the transformer 100 comprises three phase windings 110 arranged along a second axis x. One second type of phase winding 110b is arranged centrally, between two first type of phase windings 110a.

(40) In a second exemplary embodiment, as shown in FIGS. 6 and 8, the transformer 100 comprises three phase windings 110 arranged along a second axis x, and wherein one first type of phase winding 110a is arranged centrally, between two second type of phase windings 110b.

(41) Table 1 below shows simulated results of a transformer 100 and transformer arrangement 300 of the second exemplary embodiment shown in FIGS. 6 and 8. The transformer operates at 100 Hz mechanical main frequency. In this example, only the stiffness/elasticity of the spacers 130 is adapted to affect the main contributing mode. As can be seen, the spacers 130 of all the low-voltage windings, e.g., the inner windings, have the same modulus of elasticity. The high-voltage windings of the phase windings 110 on the sides also have spacers of the same modulus of elasticity as the low-voltage windings. Only the high-voltage winding of the middle phase winding 110 is arranged with spacers 130 of a differing modulus of elasticity than the other windings.

(42) The fourth column shows simulated radiated acoustic power as a result of different modulus of elasticity. The acoustic power of a corresponding transformer 100 and transformer arrangement 300 of nominal design is 80.2 dB, which is 10.1 dB higher than the lowest simulated acoustic power of 70.1 dB. Thus, the simulation shows a significant improvement of the transformer 100 and transformer arrangement 300 according to the present disclosure over prior art.

(43) TABLE-US-00001 TABLE 1 LV All HV Side HV Middle Acoustic Windings Windings Winding Power (GPa) (GPa) (GPa) 100 Hz (dB) 72 72 38 70.7 52 52 38 71.2 52 52 30 71.4 40 40 3 74.4 110 110 3 74.1 110 110 40.8 70.1 110 110 40 70.13

(44) The first exemplary embodiment results in similar noise reduction but is not disclosed herein in detail.

(45) Modifications and other embodiments of the disclosed embodiments will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiment(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.