Secondary open circuit protection device for current transformer

Abstract

The current transformer secondary open circuit protection device is composed of a shell, a bimetallic strip, a thermal element resistance wire, a first lead, a movable contact, a static contact, a conductive metal sheet and a second lead, and has the advantages that inert gas is filled in a closed glass tube, glow discharge is generated through ionization, the bimetallic strip is heated to deform through heat of the glow discharge, and the current transformer secondary open circuit protection device is safe and reliable. The movable contact on the bimetallic strip is in contact with the static contact on the conductive metal sheet, so that the lead wire I and the lead wire II are conducted, and the K1 terminal and the K2 terminal on the secondary side of the current transformer are short-circuited, the short circuit of the open-circuit winding of the electromagnetic current transformer is achieved, high voltage generated by secondary open circuit is eliminated, and the electromagnetic current transformer has the advantages of long service life and low cost. The size is small, the mechanism is simple, and the device can be repeatedly used after faults disappear.

Description

Technical Field

[0001] This application belongs to the field of power protection technology, and relates to the scope of open circuit protection for current transformers, specifically to a secondary open circuit protection device for current transformers. Background Technology

[0002] Currently, the vast majority of current transformers used in power systems are electromagnetic. Structurally, electromagnetic current transformers have only one or two turns in the primary winding, while the secondary winding has hundreds or even thousands of turns wound around the same closed silicon steel sheet assembly. According to the principle of electromagnetic induction, when an AC voltage is applied to the primary side, an electromotive force is induced in the secondary side. From N1 / N2 = U1 / U2, it can be seen that the side with fewer turns has a lower voltage, and the side with more turns has a higher voltage; the number of turns is directly proportional to the voltage. In practical operation, when the secondary winding of an electromagnetic current transformer is open-circuited, it will generate overvoltages of thousands of volts, causing insulation breakdown between conductors, burning out instruments, and even personal injury. To eliminate this high voltage, the open-circuited winding of the current transformer's secondary winding must be short-circuited, thus eliminating the hazards caused by the high voltage.

[0003] Chinese patent CN119448167A discloses a secondary open-circuit protector for a current transformer. The protector includes: a first current transformer, a second current transformer, a central processing unit (CPU), a nonlinear resistor, and a switch. The switch is connected to the circuit under test via the primary winding of the first current transformer. The CPU senses whether an open circuit has occurred on the primary side of the second current transformer and outputs an action signal based on the signal sensed from the second current transformer. This action signal controls the switch to close. The nonlinear resistor is connected in parallel between the primary winding of the first current transformer and ground, and it limits the overvoltage generated when the primary side of the current transformer is open. While this method achieves the desired effect, it has high manufacturing costs and a complex structure.

[0004] Chinese patent CN222354862U discloses a current transformer with a built-in open-circuit protection device, including a coil body, a housing, a built-in open-circuit protection device, a base, a secondary terminal block, and an insulating layer. The housing is a ring-shaped structure with a busbar hole, vertically mounted on the base. The built-in open-circuit protection device and the coil body are housed within the housing, which is filled with epoxy resin to form an insulating layer. The built-in open-circuit protection device and the coil body are sealed within this insulating layer. The secondary terminal block is embedded in the insulating layer at the bottom of the coil body. The secondary terminals of the coil body are located on the secondary terminal block. Two wires of the built-in open-circuit protection device are connected to the secondary terminals. The built-in open-circuit protection device is used to prevent secondary open circuits. This application can fundamentally and effectively prevent and eliminate the hazards caused by secondary open circuits, avoiding product explosions caused by secondary open circuits, ensuring safety and reliability, and guaranteeing personal and equipment safety. However, resin is brittle, has poor crack resistance, is prone to cracking, and has poor thermal stability, unable to withstand strong temperature shocks. Summary of the Invention

[0005] To address the aforementioned issues in the prior art, this application aims to provide a secondary open-circuit protection device for current transformers. When the secondary winding of a current transformer is open-circuited, it can directly and promptly short-circuit the open-circuited secondary winding, preventing damage caused by the high voltage generated by the open circuit. This application provides a secondary open-circuit protection device for current transformers, comprising a housing, a bimetallic strip, a heating element resistance wire, a first lead, a moving contact, a stationary contact, a conductive metal strip, and a second lead. Its key feature is that one end of the bimetallic strip is fixed inside the housing, while the other end of the bimetallic strip is suspended in the middle of the housing. A moving contact is located at this suspended position, connected to the heating element resistance wire. The heating element resistance wire is wound along the bimetallic strip, and its end is led out of the housing via the first lead. A stationary contact is located at the position corresponding to the moving contact, situated at the suspended end of the conductive metal strip. The other end of the conductive metal strip is fixed to the housing and led out of the housing via the second lead.

[0006] The housing is made of glass or ceramic, and its main structure is a closed hollow slender ellipse filled with inert gas. Lead wire 1 and lead wire 2 are led out from both ends respectively. The ends of lead wire 1 and lead wire 2 are provided with wiring lugs, which are respectively connected to the K1 and K2 terminals of the current transformer.

[0007] The moving and stationary contacts are made of materials with a melting point greater than 500 degrees Celsius and a resistivity of less than 100 nΩ·m at 20 degrees Celsius, including graphene and molybdenum-aluminum alloy.

[0008] The heating element resistance wire and the wound bimetallic sheet are insulated from each other, as are the turns of the heating element resistance wire. Attached Figure Description

[0009] Figure 1This is a schematic diagram of the structure of a secondary open-circuit protection device for a current transformer according to this application.

[0010] In the diagram: 1. Housing, 2. Bimetallic strip, 3. Heating element resistance wire, 4. Lead 1, 5. Moving contact, 6. Stationary contact, 7. Conductive metal strip, 8. Lead 2. Detailed Implementation

[0011] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0012] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0013] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0014] It should also be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this application specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0015] It should also be further understood that the term “and / or” as used in this specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0016] The accompanying drawings illustrate various structural schematics according to embodiments disclosed in this application. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0017] A secondary open-circuit protection device for a current transformer comprises a housing 1, a bimetallic strip 2, a heating element resistance wire 3, a lead wire 4, a moving contact 5, a stationary contact 6, a conductive metal strip 7, and a lead wire 8. Its features include: one end of the bimetallic strip 2 is fixed inside the housing 1, and the other end of the bimetallic strip 2 is suspended in the middle of the housing 1. A moving contact 6 is provided at the suspended position, connected to the heating element resistance wire 3. The heating element resistance wire 3 is wound along the bimetallic strip 2, and its end is led out of the housing 1 via the lead wire 4. A stationary contact 6 is provided at the position corresponding to the moving contact 5, located at the suspended end of the conductive metal strip 7. The other end of the conductive metal strip 7 is fixed to the housing 1 and led out of the housing 1 via the lead wire 8.

[0018] The housing 1 is made of either glass or ceramic. Its main structure is a closed, hollow, slender elliptical body filled with inert gas. Lead wire 4 and lead wire 8 are led out from both ends respectively. The ends of lead wire 4 and lead wire 8 are provided with wiring lugs, which are respectively connected to the K1 and K2 terminals of the current transformer.

[0019] The moving contact 5 and the stationary contact 6 are made of materials with a melting point greater than 500 degrees Celsius and a resistivity of less than 100 nΩ·m at 20 degrees Celsius, including graphene and molybdenum-aluminum alloy.

[0020] The heating element resistance wire 3 is insulated from the bimetallic strip 2 and from the turns of the heating element resistance wire 3.

[0021] When the open-circuit voltage on the secondary side of the current transformer is high, the inert gas inside the casing 1 ionizes, generating a glow discharge. The heat from the glow discharge deforms the bimetallic strip 2, causing the moving contact 5 to displace and contact the stationary contact 6, short-circuiting the K1 and K2 terminals of the current transformer. The secondary current of the transformer flows through the heating element resistance wire 3, which generates heat under the action of the current. This causes the bimetallic strip 2 to remain deformed after the heat from the glow discharge dissipates, closing the moving contact 5 and the stationary contact 6, thus eliminating the high voltage generated on the secondary side of the current transformer. Once the open-circuit fault on the secondary side of the current transformer is resolved, the current flowing through the heating element resistance wire 3 disappears, the bimetallic strip 2 is no longer heated and deformed, and the separation device between the moving contact 5 and the stationary contact 6 returns to its normal standby state.

[0022] The beneficial effects of this application are:

[0023] A sealed glass tube filled with inert gas is used. After ionization, a glow discharge is generated. The heat from the glow discharge causes the bimetallic strip to deform. This deformation, through the moving contact on the bimetallic strip, contacts the stationary contact on the conductive metal strip, short-circuiting leads one and two and short-circuiting the K1 and K2 terminals on the secondary side of the current transformer. This achieves short-circuiting of the open winding of the electromagnetic current transformer. The process is inexpensive and reusable. The metal components are sealed in an inert gas environment, preventing contact with the external environment. This significantly reduces contact oxidation and carbonization caused by sparks during opening and closing, and prevents corrosion from external vapors and dust. It boasts a long service life and advantages such as small size, simple structure, and reusability after a fault.

Claims

1. A secondary open-circuit protection device for a current transformer, comprising a housing (1), a bimetallic strip (2), a heating element resistance wire (3), a first lead (4), a moving contact (5), a stationary contact (6), a conductive metal strip (7), and a second lead (8), characterized in that: One end of a bimetallic strip (2) is fixed inside the housing (1), and the other end of the bimetallic strip (2) is suspended in the middle of the housing (1). A moving contact (5) is provided at the suspended position. The moving contact (5) is connected to the heating element resistance wire (3). The heating element resistance wire (3) is wound along the bimetallic strip (2) and its end is led out of the housing (1) through lead wire one (4). A stationary contact (6) is provided at the position corresponding to the moving contact (5). The stationary contact (6) is set at the suspended end of the conductive metal strip (7). The other end of the conductive metal strip (7) is fixed on the housing (1) and led out of the housing (1) through lead wire two (8).

2. A secondary open circuit protection device for a current transformer according to claim 1, characterized in that: The housing (1) is made of either glass or ceramic. Its main structure is a closed, hollow, slender elliptical body filled with inert gas. Lead wire 1 (4) and lead wire 2 (8) are led out from both ends respectively. The ends of lead wire 1 (4) and lead wire 2 (8) are provided with wiring lugs, which are respectively connected to the K1 and K2 terminals of the current transformer.

3. The secondary open circuit protection device for a current transformer according to claim 1, characterized by: The moving contact (5) and the stationary contact (6) are made of a material with a melting point greater than 500 degrees Celsius and a resistivity of less than 100 nΩ·m at 20 degrees Celsius.

4. The secondary open circuit protection device for a current transformer according to claim 1, characterized by: The heating element resistance wire (3) is insulated from the bimetallic strip (2) and from each other as well as from the turns of the heating element resistance wire (3).

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