Low-frequency current transformer open-circuit protection circuit with temperature compensation function

Abstract

The utility model relates to low frequency current transformer technical field, the utility model discloses to solve the problem that the existing technology is that the voltage stabilizing tube, triode, diode are all semiconductor devices, and its parameter is influenced obviously by temperature change, and the limiting voltage of protection circuit can be lower than the design value when temperature is higher, leads to the problem of malfunction, provides a kind of low frequency current transformer open-circuit protection circuit with temperature compensation function. Including the interactor of access to line net, the interactor has first output and second output, and first output and second output are all connected with load;Protection circuit is further connected between first output and second output, and protection circuit includes multiple series connection voltage stabilizing devices, and each voltage stabilizing device is connected with NTC thermistor in parallel, when temperature rises, the resistance of NTC thermistor reduces, and the current of shunt increases, offsets the influence of breakdown voltage drop of voltage stabilizing device.

Description

Technical Field

[0001] This utility model relates to the field of low-frequency current transformer technology, and in particular to an open-circuit protection circuit for a low-frequency current transformer with temperature compensation function. Background Technology

[0002] Chinese patent (title: "A Current Transformer Circuit with Open-Circuit Protection", publication number: CN208174260U, publication date: 20181130) discloses a current transformer circuit with open-circuit protection. The core design of its protection circuit is as follows: Scheme 1 uses multiple forward-connected first diodes and reverse-connected second diodes to form a voltage regulator circuit, limiting the voltage when the transformer's secondary circuit is open. Scheme 2 uses a combination circuit of "current-limiting resistor + Zener diode + transistor + diode," using the transistor to conduct and short-circuit the secondary circuit.

[0003] The common feature of both solutions is that they do not require an external power supply and achieve voltage regulation using passive components. However, they have the following potential drawbacks: Zener diodes, transistors, and diodes are all semiconductor devices, and their parameters are significantly affected by temperature changes. When the temperature is high, the limiting voltage of the protection circuit may be lower than the design value, leading to malfunction. Utility Model Content

[0004] This invention addresses the problem that in existing technologies, Zener diodes, transistors, and diodes are all semiconductor devices whose parameters are significantly affected by temperature changes. When the temperature is high, the limiting voltage of the protection circuit may be lower than the design value, leading to malfunction. This invention provides a low-frequency current transformer open-circuit protection circuit with temperature compensation function.

[0005] The technical solution adopted in this utility model is:

[0006] A low-frequency current transformer open-circuit protection circuit with temperature compensation function includes:

[0007] The current transformer connected to the power grid has a first output terminal and a second output terminal, both of which are connected to the load. A protection circuit is also connected between the first output terminal and the second output terminal. The protection circuit includes multiple voltage regulators connected in series. Each voltage regulator includes multiple first diodes connected in forward series and multiple second diodes connected in reverse series. The multiple first diodes connected in forward series form a forward voltage regulator circuit, and the multiple second diodes connected in reverse series form a reverse voltage regulator circuit. Both ends of the forward voltage regulator circuit and the reverse voltage regulator circuit are connected to the first output terminal and the second output terminal, respectively.

[0008] Each voltage regulator is connected in parallel with an NTC thermistor. When the temperature rises, the resistance of the NTC thermistor decreases, the shunt current increases, and the effect of the voltage regulator's breakdown voltage drop is offset.

[0009] Furthermore, the voltage regulator is connected in parallel with an indicator light circuit and an optocoupler-isolated alarm circuit.

[0010] Furthermore, the indicator light circuit includes a current-limiting resistor R11 and a light-emitting diode LED1, wherein the current-limiting resistor R11 and the light-emitting diode LED1 are connected in series; the optocoupler isolated alarm circuit includes a phototransistor PT1, a current-limiting resistor R12 and a controller A, wherein the phototransistor PT1 is connected in series with the current-limiting resistor R12, and the connection point of the phototransistor PT1 and the current-limiting resistor R12 is connected to the controller A, and the controller A can send the alarm signal to the remote monitoring terminal A.

[0011] A low-frequency current transformer open-circuit protection circuit with temperature compensation function includes a current transformer connected to a power grid. The current transformer has a first output terminal and a second output terminal, both of which are connected to a load. A protection circuit is also connected between the first output terminal and the second output terminal. The protection circuit includes multiple voltage regulators connected in series. The voltage regulators include multiple first unidirectional TVS diodes connected in forward series and multiple second unidirectional TVS diodes connected in reverse series. The multiple first unidirectional TVS diodes connected in forward series form a forward voltage regulator circuit, and the multiple second unidirectional TVS diodes connected in reverse series form a reverse voltage regulator circuit. The two ends of the forward voltage regulator circuit and the reverse voltage regulator circuit are respectively connected to the first output terminal and the second output terminal.

[0012] Each voltage regulator is connected in parallel with an NTC thermistor. When the temperature rises, the resistance of the NTC thermistor decreases, the shunt current increases, and the effect of the voltage regulator's breakdown voltage drop is offset.

[0013] Furthermore, the voltage regulator is connected in parallel with an indicator light circuit and an optocoupler-isolated alarm circuit.

[0014] Furthermore, the indicator light circuit includes a current-limiting resistor R21 and a light-emitting diode LED2, wherein the current-limiting resistor R21 and the light-emitting diode LED2 are connected in series; the optocoupler isolation alarm circuit includes a phototransistor PT2, a current-limiting resistor R22 and a controller B, wherein the phototransistor PT2 is connected in series with the current-limiting resistor R22, and the connection point of the phototransistor PT2 and the current-limiting resistor R22 is connected to the controller B, and the controller B can send the alarm signal to the remote monitoring terminal B.

[0015] The beneficial effects of this utility model are:

[0016] The open-circuit protection circuit for low-frequency current transformers with temperature compensation disclosed in this utility model has significant advantages due to the use of NTC thermistors. When the temperature rises, the breakdown voltage of semiconductor voltage regulators tends to decrease, while the resistance of the NTC thermistor decreases accordingly, rapidly increasing the shunt current. In this way, the NTC thermistor effectively compensates for performance fluctuations in the voltage regulator caused by temperature changes, ensuring voltage stability under different temperature conditions and preventing malfunctions due to temperature increases. This greatly improves the reliability and stability of the open-circuit protection circuit for low-frequency current transformers. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of an open-circuit protection circuit for a low-frequency current transformer with temperature compensation function.

[0019] Figure 2 This is a schematic diagram of the protection circuit for a diode-based solution.

[0020] Figure 3 This is a schematic diagram of the protection circuit for a unidirectional TVS diode scheme. Detailed Implementation

[0021] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0022] The following disclosure provides many different embodiments or examples for implementing various structures of this invention. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this invention.

[0023] The embodiments of the utility model will now be described in detail with reference to the accompanying drawings.

[0024] Example 1

[0025] The low-frequency current transformer open-circuit protection circuit with temperature compensation function disclosed in this embodiment includes a current transformer 2 connected to the network 1. The current transformer 2 has a first output terminal and a second output terminal, both of which are connected to the load 3. A protection circuit 5 is also connected between the first output terminal and the second output terminal. The protection circuit 5 includes eight series-connected voltage regulators, including four forward-connected first diodes 51 and four reverse-connected second diodes 52. The four forward-connected first diodes 51 form a forward voltage regulator circuit, and the four reverse-connected second diodes 52 form a reverse voltage regulator circuit. The two ends of the forward voltage regulator circuit and the reverse voltage regulator circuit are respectively connected to the first output terminal and the second output terminal; as shown in the attached figure. Figure 1 , Figure 2 As shown.

[0026] Under normal operating conditions, the port voltage of current transformer 2 should be the limiting voltage set by protection circuit 5. The current flowing through protection circuit 5 is very small and almost negligible. Therefore, protection circuit 5 does not consume current and does not affect the accuracy or other specifications of current transformer 2. It has no impact on protection circuit 5 or normal metering. If a secondary open circuit occurs in current transformer 2, the port voltage of current transformer 2 will rise, but it will be limited by the four series-connected diodes. The secondary voltage will thus be kept within the limiting voltage and will not cause any damage to subsequent circuits, thereby providing protection.

[0027] However, since diodes are semiconductor devices, their parameters are significantly affected by temperature changes. At higher temperatures, the limiting voltage of protection circuit 5 may fall below the design value, leading to malfunction. Therefore, an NTC thermistor RNTC_A is connected in parallel with each voltage regulator. When the temperature rises, the resistance of the NTC thermistor RNTC_A decreases, increasing the shunt current and offsetting the decrease in the breakdown voltage of the voltage regulator, thus preventing malfunction. (See attached diagram) Figure 2 As shown.

[0028] Furthermore, the voltage regulator is connected in parallel with an indicator light circuit and an optocoupler-isolated alarm circuit. The indicator light circuit includes a current-limiting resistor R11 and a light-emitting diode LED1, wherein the current-limiting resistor R11 and the light-emitting diode LED1 are connected in series. The optocoupler-isolated alarm circuit includes a phototransistor PT1, a current-limiting resistor R12, and a controller A. The phototransistor PT1 is connected in series with the current-limiting resistor R12, and the other end of the current-limiting resistor R12 is connected to VCC. The connection point between the phototransistor PT1 and the current-limiting resistor R12 is connected to the controller A, which can send an alarm signal to the remote monitoring terminal. This allows for timely alarm signal generation and transmission to the remote monitoring terminal after a secondary open circuit occurs in the current transformer 2, achieving both local and remote alarm functionality. (See attached diagram) Figure 2 As shown.

[0029] Under normal operating conditions, the current through LED1 is very small, LED1 does not light up and is almost negligible. The phototransistor PT1 is cut off, and the controller receives a high level (voltage is almost equal to VCC). If the secondary open circuit of transformer 2 occurs, LED1 lights up, the phototransistor PT1 conducts, and the controller receives a low level.

[0030] Example 2

[0031] As attached Figure 1 , Figure 3 As shown, the low-frequency current transformer open-circuit protection circuit with temperature compensation function disclosed in this embodiment includes a current transformer connected to the network. The current transformer has a first output terminal and a second output terminal, both of which are connected to the load. A protection circuit is also connected between the first output terminal and the second output terminal. The protection circuit includes eight voltage regulators connected in series. The voltage regulators include four first unidirectional TVS diodes 53 connected in forward direction and four second unidirectional TVS diodes 54 connected in reverse direction. The four first unidirectional TVS diodes 53 connected in forward direction form a forward voltage regulator circuit, and the four second unidirectional TVS diodes 54 connected in reverse direction form a reverse voltage regulator circuit. The two ends of the forward voltage regulator circuit and the reverse voltage regulator circuit are respectively connected to the first output terminal and the second output terminal.

[0032] Compared to diodes, unidirectional TVS diodes have a faster response speed, which can significantly improve the reliability and practicality of secondary open-circuit protection for current transformers.

[0033] Each voltage regulator is connected in parallel with an NTC thermistor. When the temperature rises, the resistance of the NTC thermistor decreases, the shunt current increases, and the effect of the voltage regulator's breakdown voltage drop is offset.

[0034] The indicator light circuit includes a current-limiting resistor R21 and a light-emitting diode LED2, wherein the current-limiting resistor R21 and the light-emitting diode LED2 are connected in series; the optocoupler-isolated alarm circuit includes a phototransistor PT2, a current-limiting resistor R22, and a controller B, wherein the phototransistor PT2 is connected in series with the current-limiting resistor R22, and the connection point between the phototransistor PT2 and the current-limiting resistor R22 is connected to the controller B, which can send alarm signals to the remote monitoring terminal B. The working principle is the same as in Example 1.

Claims

1. A low-frequency current transformer open-circuit protection circuit with temperature compensation function, characterized in that, The device includes a current transformer connected to the power grid. The current transformer has a first output terminal and a second output terminal, both of which are connected to the load. A protection circuit is also connected between the first output terminal and the second output terminal. The protection circuit includes multiple voltage regulators connected in series. The voltage regulators include multiple first diodes connected in forward series and multiple second diodes connected in reverse series. The multiple first diodes connected in forward series form a forward voltage regulator circuit, and the multiple second diodes connected in reverse series form a reverse voltage regulator circuit. The two ends of the forward voltage regulator circuit and the reverse voltage regulator circuit are respectively connected to the first output terminal and the second output terminal. Each voltage regulator is connected in parallel with an NTC thermistor. When the temperature rises, the resistance of the NTC thermistor decreases, the shunt current increases, and the effect of the voltage regulator's breakdown voltage drop is offset.

2. The low-frequency current transformer open-circuit protection circuit with temperature compensation function according to claim 1, characterized in that, The voltage regulator is connected in parallel with an indicator light circuit and an optocoupler-isolated alarm circuit.

3. The low-frequency current transformer open-circuit protection circuit with temperature compensation function according to claim 2, characterized in that, The indicator light circuit includes a current-limiting resistor R11 and a light-emitting diode LED1, wherein the current-limiting resistor R11 and the light-emitting diode LED1 are connected in series; the optocoupler isolated alarm circuit includes a phototransistor PT1, a current-limiting resistor R12 and a controller A, wherein the phototransistor PT1 is connected in series with the current-limiting resistor R12, and the connection point of the phototransistor PT1 and the current-limiting resistor R12 is connected to the controller A, and the controller A can send the alarm signal to the remote monitoring terminal A.

4. A low-frequency current transformer open-circuit protection circuit with temperature compensation function, characterized in that, The device includes a current transformer connected to the power grid. The current transformer has a first output terminal and a second output terminal, both of which are connected to the load. A protection circuit is also connected between the first output terminal and the second output terminal. The protection circuit includes multiple voltage regulators connected in series. The voltage regulators include multiple first unidirectional TVS diodes connected in forward series and multiple second unidirectional TVS diodes connected in reverse series. The multiple first unidirectional TVS diodes connected in forward series form a forward voltage regulator circuit, and the multiple second unidirectional TVS diodes connected in reverse series form a reverse voltage regulator circuit. The two ends of the forward voltage regulator circuit and the reverse voltage regulator circuit are respectively connected to the first output terminal and the second output terminal. Each voltage regulator is connected in parallel with an NTC thermistor. When the temperature rises, the resistance of the NTC thermistor decreases, the shunt current increases, and the effect of the voltage regulator's breakdown voltage drop is offset.

5. The low-frequency current transformer open-circuit protection circuit with temperature compensation function according to claim 4, characterized in that, The voltage regulator is connected in parallel with an indicator light circuit and an optocoupler-isolated alarm circuit.

6. The low-frequency current transformer open-circuit protection circuit with temperature compensation function according to claim 5, characterized in that, The indicator light circuit includes a current-limiting resistor R21 and a light-emitting diode LED2, wherein the current-limiting resistor R21 and the light-emitting diode LED2 are connected in series; the optocoupler isolated alarm circuit includes a phototransistor PT2, a current-limiting resistor R22 and a controller B, wherein the phototransistor PT2 is connected in series with the current-limiting resistor R22, and the connection point of the phototransistor PT2 and the current-limiting resistor R22 is connected to the controller B, and the controller B can send the alarm signal to the remote monitoring terminal B.

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