WO2013044510A1

WO2013044510A1 - Method of assembling electric transformer

Info

Publication number: WO2013044510A1
Application number: PCT/CN2011/080473
Authority: WO
Inventors: Chengguang CHEN; Clemens Joachim Rudolf; Christian Schmied
Original assignee: Siemens Aktiengesellschaft
Priority date: 2011-09-30
Filing date: 2011-09-30
Publication date: 2013-04-04
Also published as: KR20140054361A; CN103843085B; EP2745299A4; BR112014007475A2; CN103843085A; EP2745299B1; BR112014007475B8; EP2745299A1; BR112014007475B1

Abstract

A method of assembling an electric transformer (100) comprises the steps of : combining an electric coil (20) and a transformer core (10) to form an electromagnetic component (50); providing the coil (20) with a press (60); drying the electromagnetic component (50) in a drying oven (70) while the press (60) simultaneously applies mechanical pressure to the coil (20); during or after completing the drying step, providing the coil (20) with at least one mechanical element (80) adapted to prevent the coil (20) from increasing its size; and removing the press (60) from the coil (20) after the at least one mechanical element (80) ensures that the mechanical pressure previously provided by the press (60) is steadily maintained.

Description

METHOD OF ASSEMBLING ELECTRIC TRANSFORMER The invention relates to a method of assembling an electric transformer. More particularly, the invention relates to a method where coils of the transformer are compressed during the assembly . Background of the invention

Electric transformers usually comprise at least two coils, namely at least one primary coil for inputting electrical energy and at least one secondary coil for outputting electrical energy. The relation between the number of windings of the primary coil and the number of windings of the secondary coil determines the electric characteristics of the transformer.

In high power applications, transformers may be immersed in transformer oi1 that both cools and insulates the windings of the coils. In order to prevent electrical breakdown under load, such oil-filled transformers undergo prolonged drying processes to ensure that the transformer is completely free of water vapor before the cooling oil is introduced. A method for drying the active part of a transformer is described in German Patent Application DE 195 01 323 Al . The transformer is coupled to a vacuum pump, and the windings are supplied with a low frequency heating current that causes the solid insulation within the transformer to have gas or water content removed.

During the assembly of high power transformers, the coils are usually compressed in order to avoid that the coils might change their size and position under the exposure of high electrical currents .

Objective of the present invention It is an objective of the invention to provide a method of assembling electric transformers, which is more efficient than prior art methods . Brief summary of the invention

An embodiment of the invention relates to a method of assembling an electric transformer, comprising the steps of:

- combining an electric coil and a transformer core to form an electromagnetic component;

- providing the coil with a press;

- drying the electromagnetic component in a drying oven while the press simultaneously applies mechanical pressure to the coil ;

- during or after completing the drying step, providing the coil with at least one mechanical element adapted to prevent the coil from increasing its size; and

- removing the press from the coil after said at least one mechanical element ensures that the mechanical pressure previously provided by the press, is steadily maintained.

An advantage of this embodiment is that both drying and compressing may be carried out simultaneously. Therefore the assembling may be carried out very time efficient and

cost-saving .

Furthermore, the exposure of the dried and compressed coil to the ambient atmosphere may be substantially shortened compared to prior art assembly. After removing the electromagnetic component from the drying oven, the electromagnetic component may immediately be inserted into a transformer vessel which may be filled with oil or evacuated after the insertion of the electromagnetic component. There is no need to compress the coils outside the oven under ambient atmosphere because the coils have already been compressed during the drying and are ready for final assembly in the transformer vessel.

The step of combining the electric coil and the transformer core to form the electromagnetic component may comprise the step of mounting the coil on the transformer core or the step of mounting the transformer core on the coil.

The at least one mechanical element is preferably installed in the drying oven .

During the drying step the coil may slightly change its size. This effect may be addressed by using a tunable press. The tunable press allows generating a defined mechanical pressure over time even if the coil changes its size over time during the drying process .

Preferably, a hydrolic press is used to apply the mechanical pressure. The hydraulic press may comprise a pressure cylinder and a control unit that controls the pressure applied to the coil whilst the coil is dried.

According to a preferred embodiment, the press is controlled to apply a constant mechanical pressure over time during the step of drying the coil.

According to another preferred embodiment, the press is controlled to modify the mechanical pressure over time during the step of drying the coil. For instance, a predefined pressure profile may be applied during the drying step. The predefined pressure profile may address an anticipated change of size of the coil during the drying step.

The pressure that is applied by the press is preferably monitored . This allows controlling the press to maintain the pressure on a predefined level or to provide a given pressure profile over time .

Moreover, the size of the coil may be measured whilst the mechanical pressure is applied by the press and the coil is dried. This allows adapting the pressure on the coil to achieve a predefined coil size after completing the drying step. The step of drying the electromagnetic component may be - at least temporarily - carried out in a kerosene containing gas or in vacuum. In this case, at least those parts of the press, which are in contact with the coil, are preferably kerosene-resistant and/or vacuum-resistant.

The mechanical elements for ensuring that the mechanical pressure previously provided by the press is steadily maintained may comprise pull rods and/or wedges.

The step of forming the electromagnetic component preferably includes providing a closed magnetic circuit in the

electromagnetic component before the drying in the drying oven is started.

Brief description of the drawings

In order that the manner in which the above-recited and other advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings . Understanding that these drawings depict only typical embodiments of the invention and are therefore not to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail by the use of the accompanying drawings in which

Figures 1-7 show a first exemplary embodiment of a method according to the present invention;

Figure 8 illustrates a first modification of the method as shown in Figures 1-7 in an exemplary fashion;

Figure 9 illustrates a second modification of the method as shown in Figures 1-7 in an exemplary fashion; and

Figures 10-11 illustrate a third modification of the method as shown in Figures 1-7 in an exemplary fashion. Detailed description of the preferred embodiment

The preferred embodiment of the present invention will be best understood by reference to the drawings, wherein identical or comparable parts are designated by the same reference signs throughout .

It will be readily understood that the present invention, as generally described and illustrated in the figures herein, could vary in a wide range. Thus, the following more detailed description of the exemplary embodiments of the present invention, as represented in Figures 1-11, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.

Figure 1 shows in an exemplary fashion an E-shaped transformer core 10. The shape of the transformer core may vary in a wide range . As such, the shape shown in Figure 1 has been chosen for illustrating purposes , only, and may be replaced by any other core shape. For instance, in case of a multiple phase transformer the core shape might be chosen differently to accommodate the required number of coils.

In the following, the assembling of the transformer will be explained and illustrated with reference to a single coil which represents all coils of the respective transformer.

On the middle section 11 of the transformer core 10, a coil 20 is mounted such that the middle section 11 of the transformer core penetrates the coil 20 (see Figure 2) . The coil 20 may comprise primary and secondary windings which are not shown in further detail .

In order to provide a closed magnetic circuit, the E-shaped transformer core 10 is provided with an I-shaped core element 30 which is placed on top of the E-shaped transformer core 10 (see Figure 3) . If electric current flows through the windings of coil 20, a magnetic flux will be generated as schematically indicated by reference sign 40.

The original size of the coil 20 before the compressing is indicated by reference sign H.

The resulting electromagnetic component 50 which comprises the E-shaped transformer core 10, the I-shaped transformer element 30, and the coil 20, is then subjected to a drying step. The drying step is preferably combined with a step of compressing the coil 20 such that both steps are carried out simultaneously.

To this end, a tunable press 60 is attached to the coil 20. The press 60 is preferably a hydraulic press which comprises a pressure cylinder 61 and a control unit 62. The control unit 62 controls the pressure applied by the pressure cylinder 61 and therefore regulates the extent to which the coil 20 is compressed. The size of the compressed coil 20 is designated by reference sign h (h < H) in Figure 4.

Then, the electromagnetic component 50 is moved into a drying oven 70 as shown in Figure 5. In order to allow the hydraulic press 60 to compress the coil 20, the entire press 60 may be moved into the drying oven 70 as shown in Figure 5.

Alternatively, only those parts of the press 60 may be moved into the drying oven 70 which have direct physical contact with the coil 20. Figure 8 and 9 show alternative embodiments. In Figure 8, the pressure cylinder 61 and pressure rods 63 are placed inside the drying oven 70 whereas the control unit 62 is placed outside.

In Figure 9, the pressure rods 63 are placed inside the drying oven, only, whereas the pressure cylinder 61 and the control unit 62 are placed outside. It is apparent, that the sequence of the above discussed steps of attaching the hydraulic press 60 and moving the

electromagnetic component 50 into the drying oven 70 may be opposite. For instance, the electromagnetic component 50 may be moved into the drying oven 70 before the hydraulic press 60 in its entirety or parts thereof (for instance the pressure rods 63 and/or the pressure cylinder 61), are mounted on the coil 20.

During or after completing the drying step, mechanical elements 80 are attached to the coil 20. These mechanical elements 80 prevent the coil 20 from increasing its size if and when the hydraulic press 20 is detached from the coil 20. In other words, the mechanical elements 80 ensure that the mechanical pressure previously provided by the hydraulic press 60 is maintained without interruption.

The mechanical elements 80 may be attached in the drying oven 70 or outside thereof, depending on where the press 60 or its parts are removed. Figures 6 and 7 illustrate the removal of the press 60 or its parts outside the drying oven 70. The assembled transformer is designated by reference numeral 100.

Figures 10 and 11 illustrate the removal of the press 60 or its parts inside the drying oven 70. In this case the mechanical elements 80 are attached to the electromagnetic component 50 before the press is detached.

Claims

1. Method of assembling an electric transformer (100) , comprising the steps of:

- combining an electric coil (20) and a transformer core (10) to form an electromagnetic component (50);

- providing the coil (20) with a press (60);

- drying the electromagnetic component (50) in a drying oven (70) while the press (60) simultaneously applies mechanical pressure to the coil (20);

- during or after completing the drying step, providing the coil (20) with at least one mechanical element (80) adapted to prevent the coil (20) from increasing its size; and

- removing the press (60) from the coil (20) after said at least one mechanical element (80) ensures that the mechanical pressure previously provided by the press (60), is steadily maintained .

2. Method according to claim 1, wherein said at least one mechanical element (80) is installed in the drying oven (70) .

3. Method according to claim 1, wherein

- a tunable press (60) is used and

- the tunable press (60) is tuned to generate a defined

mechanical pressure over time.

4. Method according to any of the preceding claims,

- wherein a hydraulic press (60) is used to apply said mechanical pressure, said hydraulic press (60) comprising a pressure cylinder (61) and a control unit (62), and

- wherein said control unit (62) controls the pressure applied to said coil (20) whilst the coil (20) is dried.

5. Method according to any of the preceding claims, wherein the press (60) is controlled to apply a constant mechanical pressure over time during the step of drying the coil (20) .

6. Method according to any of the preceding claims, wherein the press (60) is controlled to modify the mechanical pressure over time during the step of drying the coil (20) .

7. Method according to any of the preceding claims, wherein the pressure applied by the press (60) is monitored and the press (60) is controlled to maintain the pressure on a predefined level.

8. Method according to any of the preceding claims, wherein the size of the coil (20) is measured whilst the mechanical pressure is applied by the press (60) and the coil (20) is dried.

9. Method according to any of the preceding claims,

- wherein said step of drying the electromagnetic component (50) is at least temporarily carried out in a kerosene containing gas , and

- wherein at least those parts of the press (60), which are in contact with the coil (20), are kerosene-resistant.

10. Method according to any of the preceding claims, wherein at least one pull rod (63) and/or at least one wedge is installed to maintain the mechanical pressure previously provided by the press ( 60 ) .

11. Method according to any of the preceding claims, wherein said step of forming the electromagnetic component (50) includes providing a closed magnetic circuit (40) in the electromagnetic component (50) before the drying in the drying oven (70) is started .