CURRENT TRANSFORMER WITH ADDITIONAL VOLTAGE INDICATION FOR THE USE IN MEDIUM OR HIGH VOLTAGE EQUIPMENT

Abstract

 The invention relates to a Current transformer with an additional voltage indicating functionality or for the use in medium or high voltage equipment, with primary terminals and primary conductors and a secondary circuit, according to the preamble of claim 1. In order to reduce the number of needed parts, and to support standardization, in the manufacture of the current transformer, the invention is, that beside the secondary circuit a shielded output wire (4) is arranged in such, that the output wire (4) is electrically connected to the end of discrete primary capacitor (C1), where capacitor (C1) is connected between the primary conductor (2) and the output wire (4) and defines the capacitance between the primary conductor (2) and the output wire (4), shielding (4') of output wire (4) is connected to a ground terminal (6).

Description

[0001] The invention relates to a current transformer with additional voltage indication for the use in medium or high voltage equipment, with primary terminals and primary conductors and a current transformer core, according to the preamble of claim 1.

[0002] Current Transformers with a voltage indication are well known, in which the voltage indication is realized by brass nets, forming a capacitive electrode, which is measuring the capacitance between this brass net and the primary conductor of the current transformer. As current transformers has many options of primary conductor design as well as different capacitance requirement applies to different voltage levels, there are too many variants of the capacitance net electrodes to be used in the manufacture of such current transformers.

[0003] A high amount of variant are causing complexity in manufacture as well as purchasing many different but similar shapes.

[0004] So the object of the invention is, to reduce the number of needed parts, and to support standardization, in the manufacture of the current transformer.

[0005] This problem is solved by the features of claim.

[0006] Further embodiments are mentioned in the depending claims.

[0007] So the basic feature combination for the invention is, that beside the current transformer an output conductor is arranged in such, that the output conductor is electrically connected to a part of voltage divider used for voltage indication or voltage measurement, which consists of at least one discrete capacitor located within the current transformer body arranged in such, that it provides the primary capacitance from the primary conductor, needed for voltage indication systems. Secondary capacitance of the voltage divider is either fully or at least partly located outside the current transformer body.

[0008] In order to achieve required primary capacitance distribution, also two or more discrete capacitors can be used. Such capacitors can be connected in series or in parallel. Additional discrete capacitors connected between the primary capacitor and the ground can also be used, in order to adjust the secondary capacitance value, thus adjusting the voltage ratio of voltage divider. In order to achieve required secondary capacitance distribution, two or more discrete capacitors can be used as well, connected in series or in parallel.

[0009] In a further advantageous embodiment, the output conductor is shielded in order to reduce influence of stray capacitances or transformer design on the output of voltage divider and thus affects performance or parameters of voltage indicator. Conductive shielding of such output conductor is connected to the ground potential.

[0010] In a further important and advantageous embodiment, the conductive connection between the primary and the secondary capacitor or capacitors and/or between the primary conductor and the primary capacitor is provided with a thermal dilatation compensation element.

[0011] According to high electric current passing through the current transformer, varying temperature of the current transformer can occur, resulting in various dilatation of materials used within the current transformer. The effects of such dilatations on voltage indication and/or capacitors used is compensated with the aforesaid thermal dilatation compensation element.

[0012] Concerning to that, an advantageous embodiment is, that the thermal dilatation compensation element is embellished as a spiral or a cylindric spring shaped conductor.
By that, high dilatation rates can be compensated by a comparatively short and compact element.

[0013] In a further advantageous embodiment, the current transformer as well as the voltage indicator are mounted on a support element, which is provided with a grounding terminal.

[0014] In a final advantageous embodiment, the current transformer as well as the voltage indicator as well as the support element, as well as the grounding terminal, as well as further connecting terminal are moulded in a common housing.

[0015] In sum, a lot of advantages result from the invention.

[0016] The current transformer voltage indication is reduced in the number of variants. Dependencies on geometry of primary conductor and grounded parts are eliminated.

[0017] Furthermore standard parts can be used, and the moulding is simpler.
The values of capacity result with higher stability.
Less space is required for the current transformer.

[0018] Furthermore, checking of the assembly before casting is not needed, manual setting of geometry is not required.

[0019] An advantageous embodiment of the invention is displayd in the drawing.

Figure 1: perspective view on a current transformer

Figure 2: perspective view on a current transformer having only voltage indication functionality

Figure 3: electrical scheme of voltage indication feature located inside the current transformer

[0020] Figure 1 displays a perspective view on a current transformer 1. Primary terminals 2 are connected to primary conductor 2' which is passing through at least one secondary circuit 3'. The secondary circuit 3' is connected to secondary terminals 3.

[0021] The shielded output cable 4 is arranged close beside the secondary circuits 3' and/or close beside the wires connecting the secondary circuits with the secondary terminals 3, in such, that the shielding cable 4 is electrically connected to a voltage divider 5 as voltage indicator which consists of a first primary capacitance C1, and a secondary capacitance C2, which are serially arranged in such, that a first capacitor C1 creates the capacitance between the primary conductor 2 and the shielding cable 4, and the secondary capacitor C2, if used, creates the capacitance between the shielded cable 4 and the ground potential 6.

[0022] The voltage indicator 5, embellished as voltage divider consist of two capacitances C1 and C2 in line, that means connected in series.

[0023] The upper end of the voltage divider 5 is electrically connected via a HV connection 8 to the primary conductor, and at the bottom side to ground terminal 6. The voltage divider is connected to its middle point between the capacitances C1 and C2 with the output wire 4. Output wire 4 can be also shielded in order to reduce influence of stray capacitances or current transformer design on the performance or parameters of voltage indicator. Gorund terminal (6) can be located either close to the secondary capacitor (C2) or close to the secondary terminals (3).

[0024] The aforesaid upper-end connection of the voltage divider 5 to the primary conductor 2' (windings) is realized by a conductive element which can be structured as a dilatation compensating element 7. The dilatation compensating element 7 is formed in a spiral or cylindric spiral spring form.

[0025] The lower-end of the voltage divider is connected electrially to ground terminal 6.

[0026] Figure 2 displays another possible application or housing of the new voltage divider structure described above. This application/product provides voltage indication functionality and does not contain any current transformer, thus no secondary circuits of current transformer.

[0027] Figure 3 dispays the electrical scheme of voltage divider 5 considering the use of shielded output wire and secondary capacitor (C2). In the preferred embodiment and its simplest form, the construction of voltage indication functionality cosists of output wire (4) and primary capacitor (C1) only. In another preferred embodiment, also secondary capacitor (C2) is used to define secondary capacitance more precisely, and/or the shielding (4') of the output wire is used to avoid interferrences from surrounded parts of current transformer.

Numbering:

[0028] 

1

Current transformer

2

Primary terminals

2'

Primary windings

3

Secondary terminals

3'

Secondary circuits

4

Output conductor, output wire

4'

Shielding of output conductor

5

Voltage divider (Voltage indicator)

6

Ground terminal

7

Dilatation compensating element (electrically conductive element)

8

HV Connection to primary terminals

C1

first capacitor

C2

second capacitor

Claims

1. Current transformer with an additional voltage indicating functionality or for the use in medium or high voltage equipment, with primary terminals and primary conductors and a secondary circuit,
characterized in
that beside the secondary circuit a shielded output wire (4) is arranged in such, that the output wire (4) is electrically connected to the end of discrete primary capacitor (C1), where capacitor (C1) is connected between the primary conductor (2) and the output wire (4) and defines the capacitance between the primary conductor (2) and the output wire (4), shielding (4') of output wire (4) is connected to a ground terminal (6).

2. Current transformer according to claim 1,
characterized in
that the conductive connection between the primary conductor (2) and the first capacitor (C1) is provided with a thermal dilatation compensation element (7).

3. Current transformer according to claim 1,
characterized in
that the connection between the capacitor (C1) and ground terminal (6) is provided with at least partly non-conductive thermal dilatation compensation element (7).

4. Current transformer according to claim 1,
characterized in
that the discrete secondary capacitor (C2) is used as well and is connected between the output wire (4) and the ground terminal (6) in order to define or adjust the capacitance between the output wire (4) and the ground terminal (6).

5. Current transformer according to claim 4,
characterized in
that the conductive connection between the primary capacitor (C1) and the secondary capacitor (C2) is provided with a thermal dilatation compensation element (7).

6. Current transformer according to claim 2, 3 or 5,
characterized in
that the thermal dilatation compensation element (7) is embellished as a spiral or a cylindric spring shaped conductor.

7. Current transformer to one of the aforesaid claims,
characterized in
that the current transformer (1) as well as the voltage indicator (5) are mounted on an U-Shaped support element, which provided with a grounding terminal.

8. Current transformer to one of the aforesaid claims,
characterized in
that the current transformer as well as the voltage indicator as well as the grounding terminal, are moulded in a common housing.

9. Current transformer according to any of the aforesaid claims,
characterized in
that the output wire (4) does not need to have its shielding (4') in case of negligible influences from surrounding parts.

10. Current transformer according to claim 4,
characterized in
that the voltage divider can be used for voltage measurement.

11. Current transformer according to any of the aforesaid claims,
characterized in
that the secondary circuit or circuits (3') and secondary terminals (3) are not used, utilizing only voltage indication or voltage measurement functionalities.

Drawing