CN114072891B

CN114072891B - Tap changer barrier in a power transformer

Info

Publication number: CN114072891B
Application number: CN202080048598.5A
Authority: CN
Inventors: H·海德斯滕; J·马塔伊; M·斯文伯格; A·C·约翰逊; K·奥尔夫奎斯特; K·科塔比
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2019-07-01
Filing date: 2020-06-30
Publication date: 2024-02-27
Anticipated expiration: 2040-06-30
Also published as: EP3761334B1; CN114072891A; EP3761334A1; WO2021001379A1; KR20220016202A

Abstract

The present disclosure relates to an on-load tap changer (OLTC) (1) for a fluid filled power transformer. The OLTC comprises a barrier (2) sealingly arranged to separate an electrically insulating tap changer fluid (3) of the OLTC from an electrically insulating transformer fluid (13) in a transformer tank of the power transformer. The OLTC further comprises a diverter switch unit (4) arranged in the tap-changer fluid and fixed to an inner side surface (9 a) of a back plate (16) of the barrier. The OLTC further comprises a tap selector unit (5) arranged in the transformer fluid and fixed to an outer side surface (9 b) of the back plate. The shunt switch unit and the tap selector unit are electrically connected to each other via a phase hole in the back plate, and the back plate is arched such that the back plate is shaped like a longitudinal envelope section of a circular, elliptical or parabolic cylinder, preferably a circular cylinder.

Description

Tap changer barrier in a power transformer

Technical Field

The present disclosure relates to an On-Load Tap Changer (OLTC) for a fluid filled power transformer.

Background

Tap changer barrier systems are used to separate tap changer insulation fluid, which is prone to contamination by particles formed by the diverter switch, from insulation fluid of the transformer. Typically, the back plate of the barrier system is flat and relatively thick to be able to withstand pressure differences and structural deformations in the interface between the transformer liquid and the OLTC. Problems with these thick barriers include that they occupy a lot of space, they are difficult to stress release from strong electric fields, and they are difficult to manufacture with homogeneous materials, and shrinkage cracks and internal bubbles are easily obtained. Thus, a thicker barrier also reduces the number of manufacturing methods that may be used (especially if a good structural material (such as an epoxy glass system) is used), which may be preferable if the material should pass through a transformer drying process.

JP discloses a gas OLTC with an insulating isolation barrier for separating a gas with a higher pressure in a transformer from a gas with a lower pressure in the OLTC.

Disclosure of Invention

It is an object of the present invention to provide an improved barrier for separating an insulating fluid of a tap-changer from an insulating fluid of a transformer to avoid contamination of the transformer fluid and for protecting the tap-changer from pressure variations in the transformer fluid during operation of the power transformer. The tap-changer is typically an OLTC, as illustrated herein.

According to an aspect of the present invention, an on-load tap changer (OLTC) for a fluid filled power transformer is provided. The OLTC comprises a barrier sealingly arranged to separate electrically insulating tap changer fluid of the OLTC from electrically insulating transformer fluid in a transformer tank of the power transformer. The OLTC further includes a shunt switch unit disposed in the tap-changer fluid and secured to an inside surface of the back plate of the barrier. The OLTC further includes a tap selector unit disposed in the transformer fluid and secured to an outside surface of the back plate. The shunt switch unit and the tap selector unit are electrically connected to each other via a phase hole in the back plate, and the back plate is arched such that the back plate is shaped like a longitudinal envelope section of a circular cylinder, an elliptical cylinder or a parabolic cylinder, preferably a circular cylinder.

According to another aspect of the invention, a dome-shaped back plate of a barrier is provided, or a barrier comprising said back plate, for fluidly separating an electrically insulating tap changer fluid of an OLTC from an electrically insulating transformer in a transformer tank of an electrical transformer. The back plate includes a phase hole for allowing a shunt switch unit disposed in the tap-changer fluid and secured to an inside surface of the back plate to communicate (e.g., electrically (e.g., galvanically) and/or mechanically) with a tap selector unit disposed in the transformer fluid and secured to an outside surface of the back plate. The back plate further comprises a keyway in the inner or outer surface (preferably in the outer surface) along the longitudinal end surface of the back plate for allowing the barrier to be sealingly arranged in the OLTC. The back plate is arched such that the back plate is shaped like a longitudinal envelope section of a circular cylinder, an elliptical cylinder or a parabolic cylinder, preferably a circular cylinder.

According to another aspect of the present invention, there is provided a fluid-filled power transformer comprising an embodiment of the OLTC of the present disclosure.

By designing the barrier in an arched shape, or more specifically its back plate, the barrier can better withstand pressure changes without deformation (e.g. flexing inwards or outwards as a flat barrier would be easy to do), and can thus be made thinner. Thinner barriers have the advantage of involving less space, less material usage and reduced electric field problems. The arched form also allows the back plate to be integrated in the tap-changer in a more space-saving manner, making the tap-changer more compact and less bulky.

The barrier back-plate may be made of a suitable material for allowing the barrier to pass through the drying process of the transformer, for example of an epoxy glass material (e.g. wound filaments),

this may also be suitable for withstanding the pressure difference between the tap-changer and the transformer liquid (e.g. transformer oil, ester liquid or other electrically insulating fluid) and any structural deformations associated therewith.

It should be noted that any feature of any of the aspects may be applicable to any other aspect as appropriate. As such, any advantage of any of these aspects may be applied to any of the other aspects. Other objects, features and advantages of the appended embodiments will become apparent from the following detailed disclosure, from the appended dependent claims and from the drawings.

In general, all terms used in the claims should be interpreted according to their ordinary meaning in the technical field, unless explicitly defined herein. All references to "a/an/the element, device, component, means, step, etc" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of "first," "second," etc. for different features/components of the present disclosure is merely intended to distinguish the features/components from other similar features/components, and does not impart any order or hierarchy to the features/components.

Drawings

Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 is a schematic cross-sectional side view of a liquid filled power transformer including an OLTC according to an embodiment of the invention.

Fig. 2 is a schematic cross-sectional side view of an OLTC according to an embodiment of the present invention.

FIG. 3 is a schematic perspective view of an embodiment of an arched backplate of an OLTC according to an embodiment of the invention.

Detailed Description

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown.

However, many different forms of other embodiments are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout. Fig. 1 shows an electrical transformer 10 comprising a tap changer 1, typically an OLTC, here a fluid filled transformer 10 filled with an electrically insulating fluid 13, such as a gas or a liquid, typically a liquid, e.g. an oil or an ester liquid, which is arranged for insulating a transformer winding 14 of the transformer.

The transformer 10 comprises a transformer tank 11 enclosing transformer windings 14 and containing an insulating fluid 13, a wall 12 (typically a side wall, e.g. a vertical side wall 12) with a tap changer may be arranged therein.

The tap changer 1 is arranged to connect different Alternating Currents (AC) to different taps along respective phase windings of the transformer windings 14, thereby controlling the power output of the transformer 10.

Fig. 2 shows a tap changer 1 arranged in a wall 12 of a power transformer 10, e.g. as in fig. 1. The tap-changer 1 may comprise a tap-changer tank 15 forming together with the barrier 2 a housing containing an electrically insulating tap-changer fluid 3, such as a gas or a liquid, typically a liquid, e.g. an oil or an ester liquid. The barrier 2 is sealingly fixed to the tap-changer tank 15, for example by means of a metal (such as aluminium) profile 8 of the barrier, so that the tap-changer fluid 3 remains separated from the transformer fluid 13 on the other side of the barrier 2. Thus, the barrier is impermeable to tap-changer fluid and transformer fluid.

In some embodiments, the barrier 2 may be fixed directly to the transformer tank 11, e.g. to the side 12 thereof, whereby a tap-changer tank 15 for separating tap-changer fluid from transformer fluid may not be required.

The tap changer 1 comprises a shunt switch unit 4 arranged in a tap changer tank 15 and at the inside of the barrier 2, and a selector switch unit 5 arranged in a transformer tank 11 at the outside of the barrier 2. The shunt switch of the shunt switch unit 4 is in electrical communication with the tap selector(s) (typically one for each phase) of the tap selector unit 5 via a phase hole 33 (see fig. 3) in the back plate 16 of the barrier 2. In order to separate the transformer fluid 13 from the tap-changer fluid 3, for example to avoid contamination of the transformer fluid 13 by contaminants formed by the diverter switch unit 4, the diverter switch and/or the tap-selector units 4 and 5 are sealingly arranged around the phase holes 33 on the respective sides 9 of the back plate 16. Thus, the shunt switch unit 4 is fixed to the inner side surface 9a of the back plate 16 and the tap selector unit 5 is fixed to the outer side surface 9b of the back plate, for example via some sealing means at the phase holes. The tap changer 1 may conventionally also comprise a motor 6 and a drive shaft 7 for driving the diverter switch of the diverter switch unit 4. The back plate 16 is typically arched outwardly in the direction of the windings 14 and the interior of the transformer 10, according to an embodiment of the invention, but may instead be arched inwardly in some embodiments. Thus, the inner or outer surface 9a or 9b (preferably the outer surface 9 b) has a convex shape, and the other surface 9b or 9a (preferably the inner surface 9 a) has a concave shape. The arching may be in two dimensions, but is typically only in one dimension (perpendicular to the plane of the backplate 16 and along the longitudinal axis 36 of the barrier 2 (see fig. 3)) such that the backplate is shaped like a longitudinal envelope section of a cylinder (e.g. a circular, elliptical or parabolic cylinder, preferably a circular cylinder).

By designing the barrier 2 in an arched shape, the barrier can better withstand pressure changes without deformation and can thus be made thinner. If instead a flat barrier is used as according to the prior art, the pressure applied to either side of the barrier will cause the barrier to flex inwards or outwards, respectively, which will also increase the risk of leakage of insulating fluid at the interface of the barrier with e.g. a tap-changer tank or a transformer tank, unless a thicker and thus less flexible back plate is used. The thinner barrier of the present invention has the advantage of including taking up less space, using less material, and reducing the problems of electric fields (stress relief of the insulating material and the insulating material surface of the back plate 16). The arched form may also allow the back plate to be integrated in the tap-changer 1 in a more space-saving manner, making the tap-changer more compact and less bulky.

Traditionally, with a flat barrier, the thickness of the back plate is about 5% of the width of the back plate. However, when equal loads are compared, less than 5% (e.g., 1 to 4%, such as about 2%) of the width of the back plate may be sufficient according to some embodiments of the invention. This is mainly due to the arch shape, but also to the improved materials that may be used when using the arch shape. By way of example, the back plate 16 may be made by well-controlled processes, such as filament winding with an epoxy glass material 39. By using such a material, the back plate may also be included in the drying process of the transformer 10 without being damaged.

Fig. 3 illustrates an embodiment of an arched backplate 16, such as described with respect to fig. 2. The back plate may have a longitudinal axis 36, which in some embodiments may also be the axis of symmetry of the back plate. The back plate comprises phase holes 33, here three phase holes 33a, 33b and 33c, one for each phase of the three-phase AC system.

Because the back plate is arched along the longitudinal axis 36, it may include two substantially straight and generally parallel longitudinal side surfaces 34a and 34b, and two curved and generally parallel lateral side surfaces 35a and 35b. The arched form of the back plate means that the pressure applied to the outer side surface 9b of the barrier is typically taken up by the longitudinal side surfaces 34 at their interface/fixing with the tap-changer tank 15. Respective longitudinal keyways 38a and 38b may be arranged along respective longitudinal side surfaces 34a and 34b of the outer side surfaces 9b, which longitudinal keyways are arranged to cooperate with (or engage with) corresponding keys of a fixation system, for example comprising a profile 8, for sealingly fastening the barrier 2 to the tap-changer tank 15 or the transformer tank 11, for example. Thus, the pressure applied to the inside surface 9a of the back plate may be borne by the keyways 38 at their interface with the fixation system. If the back plate 16 is instead inwardly arched, the key ways 38 may alternatively be arranged in the inner side surface 9 a.

The back plate 16 may be made of a suitable material 39 that is impermeable to the tap-changer and transformer fluids 3 and 13 and is adapted to withstand any pressure differences between the tap-changer and the transformer fluids and any structural deformations associated therewith during operation of the transformer. Material 39 may also be suitable to allow back plate 16 to pass through the drying process of transformer 10. The material 39 may, for example, comprise or consist of an epoxy glass material (e.g., wound filaments).

To help prevent slippage of the barrier 2 in the longitudinal direction and to minimize thermal and structural movement of the barrier, the longitudinal side surfaces 34 of the back plate 16 may be provided with protrusions 37 extending outwardly from said longitudinal side surfaces. The protrusions 37 may for example engage with corresponding recesses or holes in a fixation system, such as the profile 8, and thus fix the barrier in the longitudinal direction with or without engagement with the key and keyway, if present. In the example of fig. 3, one respective protrusion 37a or 37b is provided in each of the longitudinal side surfaces 34a and 34b (e.g., in the middle thereof).

In some embodiments of the invention, the back plate is arched such that the outside surface has a concave shape and the inside surface has a concave shape. However, in other embodiments, the inside surface has a convex shape and the outside surface has a concave shape. As discussed above, the back plate may be arched in one or two dimensions, but is typically arched in only one dimension.

In some embodiments of the invention, the barrier 2 is sealingly arranged by being sealingly fixed to the tap-changer tank 15 of OLTC 1.

However, in other embodiments, the barrier 2 may additionally or alternatively be directly sealingly fixed to the transformer tank 11, possibly exiting the tap-changer tank 15.

In some embodiments of the invention, the barrier 2 is sealingly arranged by means of a keyway 38 along the longitudinal end surface 34 of the back plate, the keyway 38 being in the inner side surface 9a or the outer side surface 9b of the back plate 16, preferably in the outer side surface 9 b. In some embodiments, the barrier 2 is sealingly arranged by a metallic profile 8 of the barrier arranged along the longitudinal end surface 34 of the back plate 16, and is typically engaged with the key slot 38 by protruding keys in the profile 8, which protruding keys are configured to fit in recesses of the key slot(s) 38.

In some embodiments of the invention, OLTC is sealingly arranged in the opening of the side wall 12 of the transformer tank 11. This may facilitate easy installation and access to OLTC 1 from outside the transformer tank 11.

In some embodiments of the present invention, back plate 16 is made of an epoxy glass material 39. In some embodiments, back plate 16 is made from filament windings of epoxy glass material 39. The resulting material 39 may thus be electrically insulating and strong and able to withstand the drying process of the transformer, whereby the back plate may be installed in the transformer 10 prior to drying.

The present disclosure has been described above mainly with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the disclosure, as defined by the appended claims.

Claims

1. An on-load tap changer (1) for a fluid-filled power transformer (10), the on-load tap changer comprising:

-a barrier (2) sealingly arranged to separate an electrically insulating tap-changer fluid (3) of the on-load tap-changer from an electrically insulating transformer fluid (13) in a transformer tank (11) of the power transformer;

-a diverter switch unit (4) arranged in the tap-changer fluid (3) and fixed to an inner side surface (9 a) of a back plate (16) of the barrier; and

a tap selector unit (5) arranged in the transformer fluid (13) and fixed to an outer side surface (9 b) of the back plate;

wherein the shunt switch unit and the tap selector unit are electrically connected to each other via a phase hole (33) in the back plate;

characterized in that the back plate (16) is arched such that the back plate is shaped like a longitudinal envelope section of a circular cylinder, an elliptical cylinder or a parabolic cylinder.

2. The on-load tap changer according to claim 1, wherein the back plate (16) is arched such that the outer side surface (9 b) has a convex shape and the inner side surface (9 a) has a concave shape.

3. An on-load tap changer according to claim 1, wherein the barrier (2) is sealingly arranged by a tap changer tank (15) sealingly fixed to the on-load tap changer (1).

4. A load tap changer according to any one of claims 1-3, wherein the barrier (2) is sealingly arranged by means of a keyway (38) along a longitudinal end surface (34) of the back plate, the keyway (38) being in the inner or outer side surface (9 a;9 b) of the back plate (16).

5. The on-load tap changer according to claim 4, wherein the barrier (2) is sealingly arranged by means of a metal profile (8) arranged along a longitudinal end surface (34) of the back plate and engaging with the key groove (38).

6. A load tap changer according to any one of claims 1-3, wherein the load tap changer (1) is sealingly arranged in an opening of a side wall (12) of the transformer tank (11).

7. A load tap changer according to any of claims 1-3, wherein the back plate (16) is made of an epoxy glass material (39).

8. The on-load tap changer of claim 7, wherein the back plate (16) is made of filament windings of the epoxy glass material (39).

9. A fluid-filled power transformer (10) comprising an on-load tap changer (1) according to any one of claims 1 to 8.