Converter

Abstract

To provide a converter which is small as well even when the load of being connected to a secondary side is small in an eddy current test.SOLUTION: A converter (1) includes: an iron core (10); a primary coil (21) wound around the iron core; a secondary coil (22) with more turns than the primary coil, wound around the iron core; and a container (30) for storing the iron core, the primary coil, and the secondary coil. The converter further includes a resistor (50) stored in the container and serially connected to the secondary coil.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to current transformers. [Background technology]

[0002] An example of a current transformer that converts a large current into a smaller current is disclosed in Patent Document 1. The current transformer includes an annular core, a secondary conductor wound around the annular core, and a primary conductor that passes through a central hole in the annular core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-037465 A Summary of the Invention [Problem to be solved by the invention]

[0004] Overcurrent testing is one type of testing for current transformers. In overcurrent testing, a large current (e.g., 300 times the rated current) is passed through the current transformer under test for a certain period of time (e.g., 1 second), and then the transformer is checked to see if it has any faults or fluctuations in characteristics.

[0005] In an overcurrent test, the load on a current transformer increases as the load connected to the secondary side of the current transformer decreases. For example, the load on a current transformer is greater when the secondary side is short-circuited, i.e., when no load is applied, than when a load of 25% of the rated load is connected to the secondary side. In order to make a current transformer suitable for testing with a large load, design changes are required to reduce the load, such as increasing the cross-sectional area of ​​the wire forming the secondary coil and changing the core structure to one that is less affected by the electromagnetic force of the wire. This results in a problem of the current transformer becoming larger.

[0006] One aspect of the present disclosure aims to realize a small current transformer even when the secondary side is short-circuited in an overcurrent test.

Means for Solving the Problems

[0007] In order to solve the above problems, a current transformer according to one aspect of the present disclosure includes a core, a primary coil wound around the core, a secondary coil wound around the core and having a larger number of turns than the primary coil, and a container that houses the core, the primary coil, and the secondary coil, and further includes a resistance increasing element connected in series to the secondary coil and housed inside the container.

Advantages of the Invention

[0008] According to one aspect of the present disclosure, a small current transformer can be realized even when the secondary side is short-circuited in an overcurrent test.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, one embodiment of the present disclosure will be described in detail.

[0011] FIG. 1 is a partial cross-sectional view showing the configuration of a current transformer 1 according to an embodiment. As shown in FIG. 1, the current transformer 1 includes a core 10, a primary coil 21, a secondary coil 22, and a container 30. The current transformer 1 has a shape that is substantially symmetric with respect to the center line C in FIG. 1. In FIG. 1, the internal structure of the current transformer 1 can be visually recognized by showing only one side with respect to the center line C as a cross-sectional view.

[0012] The iron core 10 is an iron core around which the primary coil 21 and the secondary coil 22 are wound. The iron core 10 has a so-called laminated iron core structure in which a plurality of steel plates are laminated. However, the structure of the iron core 10 is not necessarily limited to the laminated iron core structure. Also, the iron core 10 may have an annular shape. The central axis of the iron core 10 is parallel to the left-right direction of the paper surface in FIG. 1.

[0013] The primary coil 21 is a coil to which a primary current is input. The secondary coil 22 is a coil that outputs a secondary current as a primary current is input to the primary coil 21. The number of turns of the secondary coil 22 is larger than the number of turns of the primary coil 21. For this reason, in the current transformer 1, the secondary current becomes smaller than the primary current.

[0014] In the example shown in FIG. 1, the primary coil 21 has a so-called U-shaped form. Specifically, the primary coil 21 is wound around the iron core 10 a plurality of times in the vicinity of the secondary coil 22, and both ends thereof extend toward the primary terminal 33a described later. When assembling the current transformer 1, the annular iron core 10 is divided and joined in a state of being inserted into the primary coil 21.

[0015] The container 30 houses the iron core 10, the primary coil 21, and the secondary coil 22. The container 30 is filled with insulating oil. The container 30 includes a lower container 31, a bushing 32, and an upper container 33. The lower container 31, the bushing 32, and the upper container 33 communicate with each other.

[0016] The lower container 31 is located at the lower part of the current transformer 1. The lower container 31 houses the iron core 10, the primary coil 21, and the secondary coil 22. The lower container 31 is provided with a secondary terminal (not shown) that is electrically connected to the secondary coil 22. The upper container 33 is located at the upper part of the current transformer 1. A primary terminal 33a that is electrically connected to the primary coil 21 is provided on the wall surface of the upper container 33.

[0017] The barrier tube 32 is located between the lower container 31 and the upper container 33. The barrier tube 32 houses an electric wire that connects the portion of the primary coil 21 wound around the iron core 10 and the primary terminal 33a. The barrier tube 32 has a tapered shape that becomes thinner as it approaches the upper container 33 side from the lower container 31 side. However, the shape of the barrier tube 32 is not limited to this, and for example, it may be a cylindrical shape.

[0018] The current transformer 1 further includes an oil quantity adjusting device 40. The oil quantity adjusting device 40 adjusts the pressure of the insulating oil in the container 30. Specifically, the oil quantity adjusting device 40 includes a storage tank (not shown) that stores the insulating oil and expands or contracts according to the increase or decrease in volume due to the temperature change of the insulating oil, and a flow path (not shown) for the insulating oil from the container 30 to the storage tank. The oil quantity adjusting device 40 is located above the container 30.

[0019] The current transformer 1 further includes a resistor 50. The resistor 50 is a resistance increasing element connected in series to the secondary coil 22. The resistor 50 increases the electrical resistance on the secondary side of the current transformer 1. As the resistor 50, a known resistance element can be used without particular limitation. The resistor 50 is housed inside the container 30, specifically, inside the lower container 31. The resistance value of the resistor 50 is appropriately set by the manufacturer of the current transformer 1. For example, the resistance value of the resistor 50 may be a value corresponding to 25% of the rated burden of the current transformer 1.

[0020] In the overcurrent test for the conventional current transformer described above, when a burden is connected to the secondary terminal, the magnetic flux passing through the iron core saturates, thereby limiting the secondary current. However, in the overcurrent test of the conventional current transformer, when the secondary terminal is short-circuited, the magnetic flux passing through the iron core does not saturate, so the secondary current density becomes excessive. For this reason, in order to make the conventional current transformer compatible with the overcurrent test in the state where the secondary terminal is short-circuited, it was necessary to change the electric wire constituting the secondary coil to one with a large cross-sectional area.

[0021] In addition, in the overcurrent test for a conventional current transformer, when the secondary terminal is short-circuited, the secondary current becomes excessive, resulting in an increase in electromagnetic force. Therefore, in a conventional current transformer, there may be a case where it is necessary to change the structure of the iron core to withstand the electromagnetic force. An example of such a change in the iron core structure is changing from a stacked iron core structure to a wound iron core structure.

[0022] As described above, the change in the cross-sectional area of the electric wire and the change in the iron core structure lead to an increase in the size of the current transformer. Therefore, in a conventional current transformer, even for the same rated burden, in order to cope with the overcurrent test with the secondary terminal short-circuited, it may be necessary to increase the size compared to a current transformer that does not need to cope with such a test.

[0023] On the other hand, as described above, the current transformer 1 includes a resistor 50 connected in series with the secondary coil 22 in the container 30. In the current transformer 1, the electrical resistance on the secondary side is increased by the resistor 50. Therefore, even when the secondary terminal is short-circuited in the overcurrent test, the secondary current is limited by the resistance value of the resistor 50. Therefore, according to the current transformer 1, it is possible to cope with the overcurrent test with the secondary terminal short-circuited without increasing the size of the device. Therefore, a small current transformer can be realized even when the secondary side is short-circuited in the overcurrent test.

[0024] (Modification example) FIG. 2 is an exploded perspective view showing a modification example of the secondary coil 22 shown in FIG. 1. FIG. 2 shows only the configuration related to the modification example of the secondary coil 22. As shown in FIG. 2, the modification example of the secondary coil 22 is different from the configuration shown in FIG. 1 in that it includes an electric resistance wire 60 and press boards 71, 72, 73, 74, 75 instead of the resistor 50.

[0025] The press boards 71 to 75 are members that fix the secondary coil 22 around the iron core 10. Each of the press boards 71 to 75 has a shape in which a plate material is curved. The press boards 71 to 75 are arranged along the side surface of the iron core 10. The press boards 71 to 75 fix the secondary coil 22 around the iron core 10 by pressing the secondary coil 22 toward the iron core 10. The shape and number of the press boards 71 to 75 in the present embodiment are examples.

[0026] The electric resistance wire 60 is a wire formed of a material having a higher resistivity than the wire forming the secondary coil 22. The electric resistance wire 60 functions as a resistance increasing element that increases the electric resistance on the secondary side of the current transformer 1. Examples of the material of the electric resistance wire 60 include manganin (registered trademark). The length of the electric resistance wire 60 is appropriately determined by the manufacturer of the current transformer 1 so that the resistance on the secondary side of the current transformer 1 becomes a desired value. The length of the electric resistance wire 60 may be, for example, a length such that the resistance value of the electric resistance wire 60 corresponds to 25% of the rated burden of the current transformer 1.

[0027] The electric resistance wire 60 is wound along the circumference of the annular iron core 10. Specifically, the electric resistance wire 60 is wound around the press board 72. Therefore, the winding direction of the electric resistance wire 60 is different from the winding direction of the secondary coil 22. Thereby, the electric resistance wire 60 can be made to function only as a resistance increasing element without functioning as a part of the secondary coil 22.

[0028] In the modification shown in FIG. 2, the resistance value on the secondary side is increased by the electric resistance wire 60. Therefore, also by this modification, it is possible to cope with the overcurrent test in a state where the secondary terminals are short-circuited without increasing the size of the device. Therefore, even when the secondary side is short-circuited in the overcurrent test, a small-sized current transformer can be realized.

[0029] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

Description of Symbols

[0030] 1 Converter 10 Core 21 Primary Coil 22 Secondary Coil 30 Container 50 Resistor (Resistance-Increasing Element) 60 Electric Resistance Wire (Resistance-Increasing Element)

Claims

1. An iron core, a primary coil wound around the iron core, a secondary coil wound around the iron core and having a larger number of turns than the primary coil, a current transformer comprising the iron core, the primary coil, and a container housing the iron core, the primary coil, and the secondary coil, The current transformer further comprising a resistance increasing element connected in series to the secondary coil and housed inside the container.

2. The current transformer according to claim 1, wherein the resistance increasing element is a resistor.

3. The current transformer according to claim 1, wherein the resistance increasing element is an electric resistance wire formed of a material having a higher resistivity than the material of the electric wire forming the secondary coil.

4. The current transformer according to claim 3, wherein the iron core is annular and the electric resistance wire is wound along the circumference of the iron core.

Images