TRANSFORMER ARRANGEMENT AND METHOD FOR ELECTRICALLY CONNECTING AND DISCONNECTING A TRANSFORMER

Abstract

A transformer arrangement includes a transformer having a winding and a surge arrester arrangement connected thereto. The SAA includes a surge arrester (SA) connected across at least a section of the winding and a switch operable between a closed and open state. In the closed state, SA is electrically connected across at least the section, and in the open state, the SA electrically disconnected from at least the section. The SAA includes at least one further SA .sub.arranged to be connected across at least one further section and at least one further switch, operable between a closed and open state, wherein in the closed state the further SA is electrically connected across the at least one further section, and in the open state, the at least one further SA is electrically disconnected from the further section. A method for electrically connecting/disconnecting the transformer to/from the SAA—is also described.

Claims

1. A transformer arrangement comprising: a transformer having a winding; a surge arrester arrangement configured to be connected to the winding of the transformer, and wherein the surge arrester arrangement comprises a surge arrester arranged to be connected across at least a section of the winding of the transformer and a switch, and wherein the switch is operable between a closed state and an open state, such that in the closed state, the surge arrester is electrically connected across at least the section of the winding of the transformer, and in the open state, the surge arrester is electrically disconnected from at least the section of the winding of the transformer, wherein the surge arrester arrangement further comprises: at least one further surge arrester arranged to be connected across at least one further section of the winding of the transformer; at least one further switch; and wherein the at least one further switch, is operable between a closed state and an open state, such that in the closed state the at least one further surge arrester is electrically connected across the at least one further section of the winding of the transformer, and in the open state, the at least one further surge arrester is electrically disconnected from the at least one further section of the winding of the transformer.

2. The transformer arrangement of claim 1, wherein the surge arrester arrangement comprises an intermediate connection that is arranged between two surge arresters and configured to connect to the winding of the transformer such that the two surge arresters are connected across respective sections of the winding.

3. The transformer arrangement of claim 1, wherein the entire surge arrester arrangement is configured to be electrically connected to the transformer when the switch, or each switch, of the surge arrester arrangement is in the closed state and the entire surge arrester arrangement is configured to be electrically disconnected from the transformer when the switch, or each switch, of the surge arrester arrangement is in the open state.

4. The transformer arrangement of claim 1, further comprising a transformer tank containing insulation fluid, wherein the transformer and the surge arrester arrangement is configured to be at least partly immersed in the insulation fluid in the transformer tank.

5. The transformer arrangement of claim 4, wherein the insulation fluid is an insulation liquid.

6. The transformer arrangement of claim 1, wherein the switch, or each switch, is a rotary switch or a tap changer.

7. The transformer arrangement of claim 1, wherein the surge arrester is a zinc oxide varistor.

8. The transformer arrangement of claim 1, wherein the transformer is a single-phase transformer.

9. The transformer arrangement according to any one of the claim 1, wherein the transformer comprises phase leg windings of a plurality of phase legs.

10. The transformer arrangement of claim 9, wherein the phase leg windings are connected in delta configuration.

11. The transformer arrangement of claim 10, wherein the phase leg windings are connected in wye configuration.

12. The transformer arrangement of claim 11, wherein the phase leg windings are connected in zigzag configuration.

13. The transformer arrangement of claim 1, wherein the transformer arrangement further comprises an auxiliary surge arrester arrangement electrically connected between the transformer and ground.

14. A method for electrically connecting or disconnecting a transformer to or from a surge arrester arrangement comprising at least one surge arrester and at least one switch, the method comprising the step of: electrically connecting or disconnecting the at least one surge arrester to or from one or more sections of a winding of the transformer by means of the at least one switch, wherein the at least one switch is operable between a closed state and an open state, such that in the closed state, the at least one surge arrester is electrically connected across one or more sections of a winding of the transformer, and in the open state, the at least one surge arrester is electrically disconnected from one or more windings of the transformer, wherein the surge arrester arrangement further comprises: at least one further surge arrester arranged to be connected across at least one further section of the winding of the transformer; at least one further switch; and wherein the step of electrically connecting or disconnecting the at least one surge arrester to or from one or more sections of a winding of the transformer by means of the at least one switch further includes connecting or disconnecting the at least one further surge arrester to or from the at least one further sections of a winding of the transformer by means of the at least one further switch.

15. The method of claim 14, wherein the surge arrestor arrangement further comprises an intermediate connection, the method further comprising: arranging the intermediate connection between two surge arresters and connecting the intermediate connection to the winding of the transformer such that the two surge arresters are connected across respective sections of the winding.

16. The method of claim 15, wherein the surge arrester arrangement comprises at least one further intermediate connection, the method further comprising connecting the at least one further intermediate connection to a further surge arrester across a further section of the winding of the transformer.

17. The method of claim 14, further comprising partly immersing the transformer and the surge arrestor arrangement in insulation fluid of a transformer tank containing the insulation fluid.

18. The method of claim 14 wherein the switch, or each switch, is a rotary switch or a tap changer.

19. The method of claim 14 wherein connecting or disconnecting the at least one surge arrester to or from the one or more sections of the winding of the transformer by means of the at least one switch comprises connecting or disconnecting the entire surge arrester arrangement when the switch, or each switch, of the surge arrester arrangement is in the closed state and disconnecting the entire surge arrester arrangement from the transformer when the switch, or each switch, of the surge arrester arrangement is in the open state.

20. The transformer arrangement of claim 2, wherein the surge arrester arrangement further comprises at least one further intermediate connection, wherein each further intermediate connection connects a further surge arrester across a further section of the winding of the transformer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Further objects and advantages of, and features of the present disclosure will be apparent from the following description of one or more embodiments, with reference to the appended drawings, where:

[0038] FIG. 1 shows a single-phase transformer configuration according to an embodiment of the present disclosure.

[0039] FIG. 2-3 show variations of a single-phase transformer configuration installed in a transformer tank according to an embodiment of the present disclosure.

[0040] FIG. 4 shows a sectioned single-phase transformer configuration according to an embodiment of the present disclosure.

[0041] FIG. 5 shows a multi-phase delta transformer configuration according to an embodiment of the present disclosure.

[0042] FIG. 6 shows a multi-phase wye transformer configuration according to an embodiment of the present disclosure.

[0043] FIG. 7 shows a multi-phase wye transformer configuration according to an embodiment of the present disclosure.

[0044] FIG. 8 shows a multi-phase z transformer configuration according to an embodiment of the present disclosure.

[0045] It should be noted that the drawings have not necessarily been drawn to scale and that the dimensions of certain features may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION

[0046] The present disclosure is described in more detail below, with references to the appended drawings showing examples of embodiments. The present 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.

[0047] Embodiments of the transformer arrangement comprising the surge arrester arrangement of the present disclosure will now be discussed with reference to FIGS. 1-7.

[0048] FIG. 1 illustrates a first embodiment of a transformer arrangement 1. A transformer 2 has a winding 3. The transformer 2 illustrated in FIG. 1 is configured as a single-phase transformer, being connected to an AC voltage at terminal A. A surge arrester arrangement 4 is configured to be connected to the winding 3 of the transformer 2. The surge arrester arrangement 4 comprises a surge arrester 5 arranged to be connected across at least a section 3a of the winding 3 of the transformer 2. The term “section” of a winding is a section 3a of a wire length of the winding 3 of the transformer 2 and may extend either the full wire length of the winding 3 or a part of the wire length of the winding 3 of the transformer 2. The surge arrester arrangement 4 also comprises a switch 6. The switch 6 is operable between a closed state and an open state, such that in the closed state, the surge arrester 5 is electrically connected across at least the section 3a of the winding 3 of the transformer 2, and in the open state, the surge arrester 5 is electrically disconnected from at least the section 3a of the winding 3 of the transformer 2.

[0049] The switch needs to have a certain required voltage withstand capability in the open state so that the transformer may be subjected to a factory acceptance test. Further, it needs to have sufficient current-leading capacity to conduct current through the arresters in the closed state when the surge arrester arrangement is configured as a transient voltage protection for the transformer. The switch 6 may thus be a rotary switch or a tap changer.

[0050] The surge arrester 5 may be a zinc oxide (ZnO) varistor. The ZnO varistor comprises blocks of ZnO stacked together, which allows installation in insulation fluid, such as insulating oil. The surge arrester/ZnO varistor may further comprise a tap configured to connect to the winding. Such taps allow simple installation and connection to the transformer.

[0051] The transformer 2 is further connected to ground 9.

[0052] FIG. 2 and FIG. 3 show the single-phase transformer 2 of FIG. 1 installed in a transformer tank 10 containing insulation fluid. The transformer 2 and the surge arrester arrangement 4 are configured to be at least partly immersed in the insulation fluid in the transformer tank 10. The insulation fluid may be a liquid, such as an oil, e.g. a hydrocarbon oil or an ester-based liquid/oil.

[0053] The transformer may be externally connected via the terminal A to the AC voltage through a bushing 11 in the transformer tank wall.

[0054] Because of the switched arrangement of the surge arrester 5 to the transformer 2, the switch 6 and the surge arrester 5 may be arranged together with the transformer inside the transformer tank, reducing the number of necessary bushings through the transformer tank wall for connecting the surge arrester arrangement 4 with the transformer 2. In addition, by accommodating the surge arrester arrangement inside the transformer tank 10, space is saved on the outside of the tank, making installation of the transformer tank 10 easier in limited spaces, such as in high-voltage cabinets, etc.

[0055] FIG. 2 shows connection of the transformer arrangement 1 to ground 9 outside the transformer tank 10. However, as shown in FIG. 3, it is also possible to connect the transformer arrangement 1 to ground 9 inside the transformer tank 10, eliminating one bushing 11 as compared to the embodiment of FIG. 2.

[0056] The surge arrester arrangement 4 of the transformer arrangement 1 may further comprise at least one further surge arrester 5, as shown in FIG. 4, arranged to be connected across at least one further section 3a of the winding 3 of the transformer 2. The winding 3 of the transformer 2 is divided into a number of sections 3a, wherein a surge arrester 5 is connected across each section 3a. The surge arrester arrangement may further comprise at least one further switch 6. The at least one further switch 6, is operable between a closed state and an open state, such that in the closed state the at least one further surge arrester 5 is electrically connected across the at least one further section 3a of the winding 3 of the transformer 2, and in the open state, the at least one further surge arrester 5 is electrically disconnected from the at least one further section 3a of the winding 3 of the transformer 2.

[0057] The surge arrester arrangement 4 may comprise an intermediate connection 7 that is arranged between two surge arresters 5 and configured to connect to the winding 3 of the transformer such that the two surge arresters 5 are connected across respective sections 3a of the winding. Optionally wherein the surge arrester arrangement 4 comprises at least one further intermediate connection 7, each further intermediate connection 7 connects a further surge arrester 5 across a further section 3a of the winding 3 of the transformer 2.

[0058] The intermediate connections 7 are arranged between pairs of switches 6 and surge arresters 5. The intermediate connection 7 within the winding 3 may be at the middle of the winding 3, to form two equally large sections 3a, i.e. first and second sections 3a, of the winding 3. Alternatively, the connection within the winding 3 may be such that the first and second winding sections 3a are of different sizes. By means of the intermediate connection 7, a first surge arrester 5 is connected across (to and in parallel with) the first section 3a of the winding 3, and a second surge arrester 5 is connected across (to and in parallel with) the second section 3a of the winding 3. In the embodiment of FIG. 4, the winding 3 is divided into two sections 3a, each with a corresponding surge arrester 5 and switch 6 connected across it. However, a winding 3 may be divided into any number of sections 3a by means of additional intermediate connections 7 (not shown), where each section 3a has a corresponding surge arrester 5 and switch 6 of the series of surge arresters and switches 6 connected across the winding 3. In the closed state, the surge arresters 5 are electrically connected in series with each other and each surge arrester 5 is further electrically connected in parallel with a respective section 3a of the winding 3 of the transformer 2.

[0059] The benefit of one or more intermediate connections 7 between at least two surge arresters 5 connected in series with each other in the closed state across (i.e. connected to and in parallel with) the transformer winding 3 and the other connection point(s) within the winding 3, e.g. at the midpoint of the winding 3, is that it limits the internal resonance of the winding 3.

[0060] The switches 6 are arranged so that the entire surge arrester arrangement 4 is configured to be electrically connected to the transformer 2 when the switch 6, or each switch 6, of the surge arrester arrangement 4 is in the closed state and the entire surge arrester arrangement 4 is configured to be electrically disconnected from the transformer 2 when the switch 6, or each switch 6, of the surge arrester arrangement (4) is in the open state. When the entire surge arrester arrangement 4 is electrically disconnected from the transformer 2, the transformer 2 may be subjected to the factory acceptance test. The switches allow simple connection and disconnection of the entire surge arrester arrangement 4 to and from the winding 3 of the transformer 2. The switched arrangement is especially beneficial when the transformer arrangement 1 is installed in a transformer tank 10 since the transformer 2 has to be tested without the transient voltage protection after installation in the transformer tank 10.

[0061] The transformer 2 may alternatively be a multi-phase transformer, such as a three-phase transformer. The transformer 2 then comprises multiple windings 3 comprising at least one section 3a in the form of phase leg windings of a plurality of phase legs. In terms of the present disclosure regarding the surge arrester arrangement 4 connectable and disconnectable to a transformer 2, each phase leg winding corresponds to a winding 3 of the transformer arrangement 1 described hereinbefore. Accordingly, a phase leg winding is herein equivalent to a winding 3, which comprises at least one section 3a, across which a surge arrester 5 is connectable via a switch 6.

[0062] FIG. 5 shows a three-phase transformer 2. The three phases are connected to a respective phase leg winding via terminals A, B and C through bushings 11 in the wall of the transformer tank 10. The purpose of FIG. 5 is to illustrate the configuration of the surge arrester arrangement 4 applied to a common three-phase transformer. Each winding 3 (phase leg) of the transformer 2 is thus configured with a surge arrester arrangement 4 comprising a surge arrester 5 arranged to be connected across at least a section 3a of the winding 3 (phase leg) of the transformer 2 and a switch 6, and wherein the switch 6 is operable between a closed state and an open state, such that in the closed state, the surge arrester 5 is electrically connected across at least the section 3a of the winding 3 of the transformer 2, and in the open state, the surge arrester 5 is electrically disconnected from at least the section 3a of the winding 3 of the transformer 2.

[0063] Similarly, FIG. 6, FIG. 7 and FIG. 8 show further embodiments of a three-phase transformer 2.

[0064] The transformer arrangement 1 of any of the previously described embodiments may comprise an auxiliary surge arrester arrangement 8 electrically connected between the transformer 2 and ground 9. The auxiliary surge arrester arrangement 8 comprises a surge arrester 5, such as a ZnO varistor. Each phase may comprise one surge arrester connected between the respective phase terminal A, B, C of the transformer 2 and ground 9. The auxiliary surge arrester 8 may alternatively be connected either inside or outside a transformer tank 10.

[0065] As compared to prior art, the presently disclosed surge arrester arrangement 4 is easily connectable and disconnectable and allows a reduced number of bushings 11 and a more compact size of the transformer arrangement 1. The single-phase transformer 2 of FIGS. 1-4 requires one or two bushings 11 if installed in a transformer tank 10, depending on whether the transformer 2 is connected to ground outside or inside the transformer tank 10. The three-phase transformers 2 of FIGS. 5-7 require three or four bushings 11, depending on whether the transformer 2 is connected to ground outside or inside the transformer tank 10.

[0066] Due to the connections of the surge arrester arrangement 4 to the winding 3, a transformer arrangement 1 having a surge arrester arrangement outside the transformer tank, as described in prior art, might require one bushing per connection. In other words, a winding 3 divided into two sections 3a would require three connections to the surge arrester arrangement, i.e. one bushing for a connection at each end of the winding and one bushing for the intermediate connection.

[0067] For a prior art three-phase delta-configuration, six bushings may be needed, one for each intermediate connection and one for each terminal wherein a bushing for a connection of one phase leg winding is also for a another connection of an adjacent phase leg winding of the three-phase transformer, as discernible in FIG. 5.

[0068] In the case of a prior art three-phase wye configuration, a connection of each phase leg winding is interconnected with the others, forming a neutral point of the transformer. Typically, the neutral point in the wye configuration may be accommodated in the same bushing. Thus, a total of seven bushings may be needed for a three-phase wye configuration; one for the neutral point, three for the terminals, and one second bushing for the intermediate connection of each phase leg winding.

[0069] It can thus be seen that the present disclosure achieves a significant advantage over prior art.