A TAP CHANGER ASSEMBLY AND A TRANSFORMER TANK ASSEMBLY

Abstract

A tap changer assembly includes a tap changer assembly housing completely enclosing a tap changer volume and an overflow volume. The tap changer assembly includes at least a part of a tap changer located in the tap changer volume. The tap changer volume and the overflow volume are connectable to each other via an overflow assembly. When a pressure in the tap changer volume is equal to or higher than the predetermined overflow pressure threshold, fluid communication between the tap changer volume and the overflow volume via the overflow assembly is enabled, and is prevented when the pressure is lower that the threshold. when fluid communication is enabled, an area at least 10% of a largest internal cross-sectional area between the tap changer volume and the overflow volume is enabled for fluid communication via said overflow assembly.

Claims

1-11. (canceled)

12. A tap changer assembly comprising a tap changer assembly housing completely enclosing a tap changer volume and an overflow volume, respectively, said tap changer assembly further comprising at least a part of a tap changer located in said tap changer volume, said tap changer volume and said overflow volume being connectable to each other via an overflow assembly, such that said overflow assembly is such that: when a pressure in said tap changer volume is lower than a predetermined overflow pressure threshold, fluid communication between said tap changer volume and said overflow volume via said overflow assembly is prevented and when said pressure in said tap changer volume is equal to or higher than said predetermined overflow pressure threshold, fluid communication between said tap changer volume and said overflow volume via said overflow assembly is enabled, wherein the tap changer volume and the overflow volume are aligned along an axis, wherein the tap changer assembly housing has a largest internal cross-sectional area, enclosing said tap changer volume, orthogonal to the axis, and wherein, when fluid communication between said tap changer volume and said overflow volume via said overflow assembly is enabled, an area at least 10% of said largest internal cross-sectional area between the tap changer volume and the overflow volume is enabled for fluid communication via said overflow assembly, and wherein the overflow assembly comprises a fluid passage which is closed by a biased cover when fluid communication between said tap changer volume and said overflow volume is prevented, and which fluid passage is open when fluid communication between said tap changer volume and said overflow volume is enabled.

13. The tap changer assembly according to claim 12, wherein said a tap changer assembly housing is such that: fluid communication between said tap changer volume and the environment ambient of said tap changer volume is prevented when said pressure in said tap changer volume is lower than a predetermined precaution pressure threshold, said predetermined precaution pressure threshold being greater than said predetermined overflow pressure threshold, and fluid communication between said tap changer volume and the environment ambient of said tap changer volume is enabled when said pressure in said tap changer volume is equal to or exceeds said predetermined precaution pressure threshold.

14. The tap changer assembly according to claim 13, wherein fluid communication between said tap changer volume and the environment ambient of said tap changer volume is enabled by allowing a rupture in said tap changer assembly housing completely enclosing said tap changer volume when said pressure in said tap changer volume is equal to or exceeds said predetermined precaution pressure threshold.

15. The tap changer assembly according to claim 12, wherein the tap changer assembly further comprises a pressure relief assembly connected to said overflow volume, said pressure relief assembly being such that: fluid communication between said overflow volume and the environment ambient of said overflow volume via said pressure relief assembly is prevented when said pressure in said overflow volume is lower than a predetermined relief pressure threshold, said predetermined relief pressure threshold being greater than said predetermined overflow pressure threshold, and fluid communication between said overflow volume and the environment ambient of said overflow volume via said pressure relief assembly is enabled when said pressure in said overflow volume is equal to or exceeds said predetermined relief pressure threshold.

16. The tap changer assembly according to claim 15, wherein said a tap changer assembly housing is such that: fluid communication between said tap changer volume and the environment ambient of said tap changer volume is prevented when said pressure in said tap changer volume is lower than a predetermined precaution pressure threshold, said predetermined precaution pressure threshold being greater than said predetermined overflow pressure threshold, and fluid communication between said tap changer volume and the environment ambient of said tap changer volume is enabled when said pressure in said tap changer volume is equal to or exceeds said predetermined precaution pressure threshold, said predetermined relief pressure threshold being greater than said predetermined precaution pressure threshold.

17. The tap changer assembly according to claim 12, wherein the overflow assembly comprises a fluid passage which is closed by a rupture disc when fluid communication between said tap changer volume and said overflow volume is prevented, said rupture disc being adapted to rupture when said pressure in said tap changer volume is equal to or higher than said predetermined overflow pressure threshold.

18. A transformer tank assembly comprising a transformer tank and the tap changer assembly according to claim 12, the tap changer assembly housing being assembled with the transformer tank such that at least part of the tap changer volume is arranged inside the transformer tank.

19. The transformer tank assembly according to claim 18, wherein said a tap changer assembly housing is such that: fluid communication between said tap changer volume and the environment ambient of said tap changer volume is prevented when said pressure in said tap changer volume is lower than a predetermined precaution pressure threshold, said predetermined precaution pressure threshold being greater than said predetermined overflow pressure threshold, and fluid communication between said tap changer volume and the environment ambient of said tap changer volume is enabled when said pressure in said tap changer volume is equal to or exceeds said predetermined precaution pressure threshold, wherein fluid communication between said tap changer volume and the environment ambient of said tap changer volume is enabled by allowing a rupture in said tap changer assembly housing completely enclosing said tap changer volume when said pressure in said tap changer volume is equal to or exceeds said predetermined precaution pressure threshold, and wherein the environment ambient of said tap changer volume is at least partially inside the transformer tank such that said rupture in said tap changer assembly housing completely enclosing said tap changer volume results in a fluid communication between said tap changer volume and an inside of said transformer tank.

20. A transformer tank assembly comprising a transformer tank and the tap changer assembly according to claim 1, the tap changer assembly housing being assembled with the transformer tank such that at least part of the overflow volume is arranged outside the tank.

21. The transformer tank assembly according to claim 20, wherein the tap changer assembly further comprises a pressure relief assembly connected to said overflow volume, said pressure relief assembly being such that: fluid communication between said overflow volume and the environment ambient of said overflow volume via said pressure relief assembly is prevented when said pressure in said overflow volume is lower than a predetermined relief pressure threshold, said predetermined relief pressure threshold being greater than said predetermined overflow pressure threshold, and fluid communication between said overflow volume and the environment ambient of said overflow volume via said pressure relief assembly is enabled when said pressure in said overflow volume is equal to or exceeds said predetermined relief pressure threshold, and wherein the environment ambient of said overflow volume is an environment outside the transformer tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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:

[0029] FIG. 1 shows a schematic side view of a prior art tap changer assembly.

[0030] FIG. 2 shows a pressure release sequence of the prior art tap changer assembly of FIG. 1.

[0031] FIG. 3 shows a schematic side view of a tap changer assembly according to the present disclosure.

[0032] FIG. 4 shows a pressure release sequence of the tap changer assembly of FIG. 3.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

[0033] 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. Like numbers refer to like elements throughout the description.

[0034] FIG. 1 shows a schematic side view of a prior art tap changer assembly 100, which comprises a tap changer volume 10 in which at least a part of a tap changer 13 is enclosed. The tap changer assembly 100 may be assembled with a transformer tank 30, which does not form part of the tap changer assembly 100. The transformer tank 30 is in the figures only indicated by a part of a wall, which encloses a transformer tank volume. In practice, the transformer tank 30 houses a transformer (not shown), which may be immersed in an insulating oil inside the transformer tank 30. The tap changer assembly 100 is conventionally mounted on the wall of the transformer tank 30 such that part of the tap changer assembly 100 is accessible from an outside 32 of the transformer tank 30.

[0035] The at least part of the tap changer 13 is further electrically connected to the transformer on an inside 34 of the transformer tank 30, i.e. inside the transformer tank volume. A tap changer allows the effective number of turns of a winding of the transformer to be increased or decreased, thereby regulating an output voltage of the transformer.

[0036] On the outside of the transformer tank 30, the tap changer volume 10 may be sealed by a reinforced top cover 11 comprising a pressure release device (PRD) e.g. spring-biased pressure release device and/or a burst disc or an explosion valve. In case of a flash-over between contacts inside the tap changer volume 10, a short-circuit arc discharge of several hundred kiloamperes may be generated. This would immediately vaporize the surrounding insulating oil and send a dynamic pressure shockwave along the tap changer volume 10 followed by a significant over-pressure inside the tap changer volume 10. If too much energy is released, the top cover 11possibly followed by the bottom of the housingwill be blown and oil will be pushed through the opening, risking a dangerous transformer fire. The prior art tap changer assembly 100 shown in FIG. 1, having the pressure release device is configured for a low-pressure trip level slightly above an expected normal operating pressure. It is not able to fully depressurize the tap changer volume 10 at larger energy faults.

[0037] As shown in FIG. 2, in the event of a short-circuit and generation of an over-pressure, a first pressure release 1 occurs through the pressure release device to the outside 32 of the transformer tank 30, possibly followed by a second pressure release 2 into the transformer tank.

[0038] FIG. 3 shows a schematic side view of a tap changer assembly 100 according to the present disclosure. The tap changer assembly 100 comprises a tap changer assembly housing 110 completely enclosing a tap changer volume 10 and an overflow volume 12, respectively. The tap changer assembly 100 further comprises at least a part of a tap changer 13 located in said tap changer volume 10. The tap changer volume 10 and the overflow volume 12 are connectable to each other via an overflow assembly 14. The overflow assembly 14 is configured such that when a pressure in the tap changer volume 10 is lower than a predetermined overflow pressure threshold, fluid communication between the tap changer volume 10 and the overflow volume 12 via the overflow assembly 14 is prevented. When the pressure in the tap changer volume 10 is equal to or higher than the predetermined overflow pressure threshold, fluid communication between the tap changer volume 10 and the overflow volume 12 via the overflow assembly 14 is enabled.

[0039] The overflow assembly 14 may comprise a fluid passage 16 which may be closed by a biased cover 140 when fluid communication between the tap changer volume 10 and the overflow volume 12 is prevented. The fluid passage 16 is open when fluid communication between the tap changer volume 10 and said overflow volume 12 is enabled.

[0040] The fluid passage 16 may alternatively be closed by a rupture disc (not shown) when fluid communication between the tap changer volume 10 and the overflow volume is prevented. The rupture disc may be adapted to rupture when the pressure in the tap changer volume 10 is equal to or higher than the predetermined overflow pressure threshold. The rupture disc is designed to quickly relieve pressure when the pressure exceeds a predetermined threshold but needs to be replaced after it has been triggered.

[0041] The tap changer volume 10 and the overflow volume 12 may be aligned along an axis Z. The tap changer assembly housing 110 may have a largest internal cross-sectional area, enclosing the tap changer volume 10, orthogonal to the axis Z. In the FIG. 3 embodiment, the tap changer volume 10 exemplified as a prismatic volume along the axis Z. However, it is also envisaged that the tap changer volume 10 may be non-prismatic such that the cross-section of the of the tap changer volume 10, orthogonal to the axis Z, may vary. In any event, the largest internal cross-sectional area of the tap changer assembly housing 110 is the largest internal cross-sectional area thereof which encloses the tap changer volume 10.

[0042] When fluid communication between the tap changer volume 10 and the overflow volume 12 via the overflow assembly 14 is enabled, an area at least 10% of the cross-sectional area between the tap changer volume 10 and the overflow volume 12 is enabled for fluid communication via the overflow assembly 14. By providing a relatively large area for the fluid communication via the overflow assembly 14, it is ensured that pressure in the tap changer volume 10 may quickly be relieved into the overflow volume 12.

[0043] The biased cover 140 may cover an area equal to or greater than 50%, such as greater than 90%, of the largest internal cross-sectional area of the tap changer assembly housing 10. Spring bolts 142, may be arranged around a perimeter of the biased cover 140 to force it against the fluid passage 16. The springs bolts 142 are adapted to allow the biased cover 140 to open the fluid passage 16 and enable fluid communication via the fluid passage 16 when the pressure in the tap changer volume 10 is equal to or greater than the predetermined overflow pressure threshold. Using spring-bolts arranged around the perimeter of the biased cover, instead of a hinged cover, allows the relatively large area of the fluid passage to be opened quickly to enable fluid communication between the tap changer volume 10 and the overflow volume 12. Instead of, or in addition to the above-mentioned spring bolts 142, other biasing means (not shown) may be used to force the cover 140 to seal the fluid passage 16 when the pressure in the tap changer volume 10 is lower than the predetermined overflow pressure threshold. Purely by way of example, such biasing means may be obtained by magnetic elements (not shown) or sealing members biasing the cover 140 to seal the fluid passage 16 by means of gravity.

[0044] The tap changer assembly housing 110 may further be adapted such that fluid communication between the tap changer volume 10 and the environment ambient of the tap changer volume 10 is prevented when said pressure in said tap changer volume 10 is lower than a predetermined precaution pressure threshold, where the predetermined precaution pressure threshold is greater than the predetermined overflow pressure threshold. Fluid communication between the tap changer volume 10 and the environment ambient of the tap changer volume 10 is enabled when the pressure in the tap changer volume 10 is equal to or exceeds the predetermined precaution pressure threshold.

[0045] The tap changer volume 10 may comprise a reinforced surface 18, such as an end surface, e.g. a reinforced bottom, of the tap changer volume 10. The reinforced surface 18 may be arranged perpendicular to the axis Z.

[0046] A part of the tap changer assembly housing 110 enclosing the tap changer volume 10 may be provided with a flexible wall. The flexible wall may for instance be made of glass fibre. The flexible wall of the tap changer volume 10 may have a cylindrical shape and may be joined with the reinforced surface 18 at an interface between the flexible wall and the reinforced surface 18. As compared to a rigid wall, the flexible wall may delay the point in time at which a certain pressure is reached, such as the predetermined overflow pressure threshold or the predetermined precaution pressure threshold. More time may allow circuit breakers to break the current and extinguish the arc which creates the over-pressure. Further pressure release from the tap changer volume 10 may thereby not be required.

[0047] Fluid communication between the tap changer volume 10 and the environment ambient of the tap changer volume 10 may be enabled by allowing a rupture in the tap changer assembly housing 110 completely enclosing the tap changer volume 10, such as the flexible wall enclosing the tap changer volume 10, when the pressure in the tap changer volume 10 is equal to or exceeds the predetermined precaution pressure threshold. The connection between the flexible wall and the reinforced surface 18 may be adapted to rupture when the pressure in the tap changer volume 10 is equal to or exceeds the predetermined precaution pressure threshold. As such, though purely by way of example, the environment ambient of the tap changer volume may be at least partially inside the transformer tank 30. The flexible wall and the reinforced surface 18 may be adapted such that the rupture in the tap changer assembly housing 110 completely enclosing the tap changer volume 10 results in a fluid communication between the tap changer volume 10 and the interior of the transformer tank 30.

[0048] The tap changer assembly 100 may further comprise a pressure relief assembly 19 connected to said overflow volume 12. The pressure relief assembly 19 is such that fluid communication between the overflow volume and the environment ambient of the overflow volume 12 via the pressure relief assembly 19 is prevented when the pressure in the overflow volume 12 is lower than a predetermined relief pressure threshold. The predetermined relief pressure threshold is greater than the predetermined overflow pressure threshold. Fluid communication between the overflow volume 12 and the environment ambient of the overflow volume 12 via the pressure relief assembly 19 is enabled when the pressure in the overflow volume 12 is equal to or exceeds the predetermined relief pressure threshold.

[0049] Since the predetermined relief pressure threshold is greater than the predetermined overflow pressure threshold, the overflow volume will contain the overpressure until the pressure in the overflow volume reaches the predetermined relief pressure threshold, whereupon the pressure will be relieved into the environment ambient of the overflow volume. The predetermined overflow pressure threshold, set by the pressure relief assembly 19, is higher than the conventional pressure release device comprised in the top cover 11 in FIGS. 1 and 2. The purpose of the predetermined relief pressure threshold is to provide a further delay to relieve the overpressure in the tap changer volume 10, and especially in the overflow volume 10, to prevent an explosion of the overflow volume 12, which could lead to oil being leaked to the environment ambient of the overflow volume 12.

[0050] The predetermined relief pressure threshold may be greater than the predetermined precaution pressure threshold. Thereby, the fluid communication between the overflow volume 12 and the environment ambient of the overflow volume 12, via the pressure relief assembly 19, will only be enabled after the fluid communication between the tap changer volume 10 and the environment ambient of said tap changer volume 10 has been enabled.

[0051] FIG. 3 also shows a second embodiment of the present disclosure. There is provided a transformer tank assembly 300 comprising a transformer tank 30 (only partly shown) and the tap changer assembly 100 as described hereinabove. The tap changer assembly housing 110 is assembled with the transformer tank 30 such that at least part of the tap changer volume 10 is arranged inside the tank, i.e. on the inside 34 of the transformer tank 30. When fluid communication between the tap changer volume 10 and the environment ambient of the tap changer volume 10 is enabled it may be defined as a fluid communication between the tap changer volume 10 and the inside 34 of the transformer tank 30,

[0052] The tap changer assembly housing 110 may be assembled with the transformer tank 30 such that at least part of the overflow volume 12 is arranged outside the tank, i.e. on the outside 32 of the transformer tank 30. The environment ambient of the overflow volume 12 may thus be defined as an environment outside the transformer tank 30.

[0053] FIG. 4 shows a pressure release sequence of the tap changer assembly 100 of FIG. 3. In the event of a short-circuit and generation of an over-pressure, a first pressure release 1 occurs by enabling fluid communication via the overflow assembly 14, which may be a biased cover 140, from the tap changer volume 10 into the overflow volume 12 when the pressure in the tap changer volume 10 is equal to or higher than the predetermined overflow pressure threshold.

[0054] A second pressure release 2 may occur by enabling fluid communication between the tap changer volume 10 and the environment ambient of the tap changer volume 10 when the pressure in the tap changer volume 10 is equal to or exceeds the predetermined precaution pressure threshold. Such fluid communication may be enabled by a rupture in the tap changer assembly housing 110 as described hereinabove.

[0055] In case of a very high over-pressure, a third pressure release 3 may occur by enabling fluid communication between the overflow volume 12 and the environment ambient of the overflow volume 12 via the pressure relief assembly 19 when the pressure in the overflow volume 12 is equal to or exceeds the predetermined relief pressure threshold. In order to avoid damage and personal injuries, such fluid communication may be guided by tubing to control expulsion of e.g. transformer oil away from areas which may be occupied by people in the vicinity of the overflow volume 12.

[0056] By providing the sequence of pressure relief events, dangerous leakage of oil outside the transformer tank 30 may be avoided and a transformer fire may be prevented. By delaying/extending the development of the over-pressure time may also be provided to allow the circuit breakers of the at least part of a tap changer 13 to break the current and extinguish the arc to stop the increase of the over-pressure. Moreover, the above procedure implies an appropriately low risk of having fluid leaking from the transformer tank assembly 300 since at least each one of the first pressure release 1 and the second pressure release 2 may be carried out without any leakage outside the transformer tank assembly 300.

[0057] The sequence may be established by ensuring that the predetermined relief pressure threshold is greater than both the predetermined overflow pressure threshold and the predetermined precaution pressure threshold. Further, the predetermined precaution pressure threshold is greater than the overflow pressure threshold.

[0058] The transformer tank assembly 300 and/or the tap changer assembly 100 may further comprise an oil conservator (not shown) fluidly connectable to the transformer tank 30 and/or to the overflow volume 12 via conduits (not shown). The conduits may comprise a shutter valve, a sensor and a control unit such that when the sensor detects a predetermined over-pressure in the tap changer assembly 100, the control unit disables fluid communication between the oil conservator and the transformer tank 30 and or to the overflow volume 12. Thereby, it can be ensured that oil is prevented from leaking to the outside 32 of the transformer tank 30 in the unlikely event that the overflow volume 12 breaks due to the over-pressure.