Zero-flux mutual inductor gear shifting protection circuit and electric energy standard meter

Abstract

The utility model discloses a zero magnetic flux mutual inductor shift protection circuit and electric energy standard meter, including zero magnetic flux mutual inductor and operational amplifier, said protection circuit also includes transient bidirectional protection TVS tube D5, D6 and thermistor R7, wherein: transient bidirectional protection TVS tube D5, D6 are connected between the second pin of sampling coil of mutual inductor and ground, and the thermistor R7 is connected with the operational amplifier. The high-voltage suppression module is used for suppressing high voltage within 12V in the gear shifting process; the thermistor R7 is a high-molecular PTC thermistor, is connected in series with an output loop of the mutual inductor, and is used for overcurrent protection. According to the zero-magnetic-flux mutual inductor gear shifting protection circuit, the transient bidirectional protection TVS tubes D5 and D6 and the thermistor R7 are introduced, so that high-voltage peaks in the gear shifting process are effectively restrained, and breakdown damage to the operational amplifier is prevented. The transient bidirectional protection TVS tubes D5 and D6 suppress the high voltage within 12V, and the thermistor R7 absorbs the peak current to protect the operational amplifier. The circuit improves the reliability of the electric energy standard meter, prolongs the service life of the electric energy standard meter, ensures the measurement precision of the mutual inductor under different current gears, and meets the requirements of high precision and high reliability.

Description

Technical Field

[0001] The utility model relates to a protection circuit, in particular to a zero-flux current transformer shift protection circuit and an electric energy standard meter. Background Art

[0002] A current transformer is an important measuring device in the power system and is an indispensable metering and control device for monitoring the operation status and parameters of the power grid and realizing relay protection.

[0003] In order to further improve the overall accuracy of the electric energy measurement system, it is also necessary to further improve the measurement accuracy of the current transformer.

[0004] The original technical solution of the adaptive zero-flux current transformer compensation circuit is as Figure 1 shown. In this adaptive zero-flux current transformer compensation circuit, a compensation winding N3 is added, and the detected current is I3. The voltage U0 is obtained through an amplifier power amplifier circuit, the amplification factor is K, and the sampling winding N2 is driven to generate a sampling current I2.

[0005] Then the current conversion relationship of the transformer is improved to:

[0006] (I p +I3)×N3×(1 + K) = I1N1.

[0007] It can be seen from the relationship that as long as very small I p and I3, the current conversion relationship can be made to hold. Due to the significant reduction of I p , the accuracy of the sampling winding I2 is improved.

[0008] However, when the original technical solution of the adaptive zero-flux current transformer compensation circuit is applied to an electric energy standard meter, the standard meter needs to shift gears, that is, the primary winding N1 needs to be switched under different current gears.

[0009] During the gear shifting process, a large current will flow into the small current windings of multiple windings, causing a very high magnetic flux in the magnetic core and generating a very high instantaneous voltage U′ on N2, which will break down the operational amplifier and thus damage the circuit.

[0010] The generated high voltage is captured by an oscilloscope, as Figure 2 shown. Summary of the Utility Model

[0011] To solve the above problems, the present utility model provides a zero - flux current transformer shift protection circuit and an electric energy standard meter, which significantly improve the reliability and service life of the electric energy standard meter during the shifting process, avoid circuit failures caused by high - voltage breakdown of operational amplifiers, ensure the measurement accuracy of the current transformer, enable it to operate stably under different current ranges, and meet the high requirements of the power system and other application fields for current measurement accuracy and reliability.

[0012] The present utility model is realized through the following technical solutions: A zero - flux current transformer shift protection circuit includes a zero - flux current transformer and an operational amplifier. It is characterized in that: The protection circuit further includes transient bidirectional protection TVS tubes D5, D6 and a thermistor R7, where:

[0013] The transient bidirectional protection TVS tubes D5, D6 are connected between the second pin of the sampling coil of the current transformer and the ground, and are used to suppress the high voltage within 12V during the shifting process;

[0014] The thermistor R7 is a polymer PTC thermistor, and the internal resistance of the thermistor R7 is between 30Ω and 60Ω. It is connected in series on the output loop of the current transformer for over - current protection.

[0015] As a preferred technical solution, the protection circuit further includes a plurality of LL4148 diodes. The LL4148 diodes and the thermistor R7 together form an RC filter circuit, which is used to delay the transmission time of the peak current during the shifting process, enable the LL4148 diodes to play a protective role, suppress the voltage of the 6th pin of the operational amplifier at 0.7V, thereby protecting the operational amplifier from being damaged by high - voltage breakdown.

[0016] As a preferred technical solution, the compensation winding of the current transformer is used to detect the current, and the amplifier power - amplification circuit is used to drive the sampling winding to generate a sampling current, so that the current conversion relationship of the current transformer is:

[0017] I3′N3 + I2N2 = I1N1, where N1 is the number of primary turns, I1 is the primary current, N2 is the number of secondary turns, I2 is the secondary current, N3 is the number of turns of the compensation winding, an exciting current I p and a compensation current I3 are generated on the winding N3, and the sum I3′ of I p and I3 = I p + I3.

[0018] As a preferred technical solution, the internal resistance of the thermistor R7 is between 30Ω and 60Ω.

[0019] As a preferred technical solution, the circuit further includes a current detection module for real-time monitoring of the current change of the mutual inductor. When the detected current exceeds a preset threshold, the transient bidirectional protection TVS tubes D5, D6 and the thermistor R7 are controlled to perform protection operations, thereby avoiding damage to the operational amplifier caused by high voltage.

[0020] As a preferred technical solution, the protection circuit further includes an overvoltage protection module. The overvoltage protection module includes a plurality of serially connected TVS diodes for further dispersing and suppressing high voltage during the gear shifting process, thereby enhancing the overvoltage protection ability of the entire circuit.

[0021] A watt-hour standard meter of the present utility model includes a flux mutual inductor gear shifting protection circuit for protecting the operational amplifier in the circuit from being damaged by high voltage breakdown when switching between different current gears.

[0022] The beneficial effects of the present utility model are as follows: The zero-flux mutual inductor gear shifting protection circuit provided by the present utility model effectively suppresses high voltage spikes during the mutual inductor gear shifting process by introducing transient bidirectional protection TVS tubes D5, D6 and the thermistor R7 into the circuit, preventing the operational amplifier from being damaged by high voltage breakdown;

[0023] The transient bidirectional protection TVS tubes D5, D6 can suppress the high voltage generated by the mutual inductor sampling coil within 12V during the gear shifting process, avoiding the influence of high voltage on other parts of the circuit; the thermistor R7 further improves the overcurrent protection ability of the circuit by absorbing the instantaneous peak current, and together with the LL4148 diode, forms an RC filter circuit to delay the transmission time of the peak current, enabling the protection diode to effectively play its role and protecting the operational amplifier from being damaged by high voltage;

[0024] The present utility model significantly improves the reliability and service life of the watt-hour standard meter during the gear shifting process, avoids circuit failures caused by high voltage breakdown of the operational amplifier, and at the same time ensures the measurement accuracy of the mutual inductor, enabling it to work stably under different current gears, meeting the high requirements of the power system and other application fields for current measurement accuracy and reliability. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 Schematic diagram of an adaptive zero-flux current mutual inductor compensation circuit for the prior art;

[0027] Figure 2 is the capture effect diagram of high voltage passing through an oscilloscope for the prior art;

[0028] Figure 3 is the improved circuit schematic diagram of the present utility model;

[0029] Figure 4 is the capture effect diagram of high voltage passing through an oscilloscope for the present utility model. Specific embodiments

[0030] All features disclosed in this specification, or all steps in the disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

[0031] Any feature disclosed in this specification (including any additional claims, abstract, and drawings), unless specifically recited, can be replaced by other equivalent or similar-purpose alternative features. That is, unless specifically recited, each feature is only an example of a series of equivalent or similar features.

[0032] As Figure 3 shown, a zero-flux current transformer shift protection circuit of the present utility model includes a zero-flux current transformer and an operational amplifier, and is characterized in that: the protection circuit further includes transient bidirectional protection TVS tubes D5, D6 and a thermistor R7, wherein:

[0033] The transient bidirectional protection TVS tubes D5, D6 are connected between the second pin of the sampling coil of the current transformer and the ground, and are used to suppress the high voltage within 12V during the shift process;

[0034] The thermistor R7 is a polymer PTC thermistor, which is connected in series on the output loop of the current transformer and is used for overcurrent protection.

[0035] The protection circuit further includes a plurality of LL4148 diodes. The LL4148 diodes and the thermistor R7 together form an RC filter circuit, which is used to delay the transmission time of the peak current during the shift process, so that the LL4148 diodes play a protection role, suppress the voltage of the 6th pin of the operational amplifier at 0.7V, thereby protecting the operational amplifier from being damaged by high voltage breakdown.

[0036] Among them, the compensation winding of the current transformer is used to detect the current, and the amplifier power amplifier circuit is used to drive the sampling winding to generate a sampling current, so that the current conversion relationship formula of the current transformer is:

[0037] I3′N3 + I2N2 = I1N1, where N1 is the number of primary turns, I1 is the primary current, N2 is the number of secondary turns, I2 is the secondary current, N3 is the number of turns of the compensation winding, and an exciting current I is generated on the winding N3 pand compensating currents I3, I p The sum I3′ = I with I3 p + I3.

[0038] The transient bidirectional protection TVS diodes D5 and D6 suppress the high voltage generated at the second pin of the sampling coil of the mutual inductor during the gear shifting process, preventing the high voltage from damaging the first pin of the operational amplifier.

[0039] The thermistor R7 is used to absorb the instantaneous peak current generated during the gear shifting process. The thermistor R7 in the RC filter circuit and the junction capacitance of the LL4148 diode work together. The high voltage generated during the mutual inductor gear shifting is filtered by the RC circuit, delaying the transmission time of the peak current and protecting the voltage of the sixth pin of the operational amplifier. The internal resistance of the thermistor R7 is between 30Ω and 60Ω;

[0040] The circuit further includes a current detection module for real-time monitoring of the current change of the mutual inductor. When the detected current exceeds the preset threshold, it controls the transient bidirectional protection TVS diodes D5 and D6 and the thermistor R7 to perform protection operations, thereby avoiding damage to the operational amplifier caused by high voltage.

[0041] The protection circuit further includes an overvoltage protection module. The overvoltage protection module includes a plurality of series-connected TVS diodes for further dispersing and suppressing the high voltage during the gear shifting process, thereby enhancing the overvoltage protection ability of the entire circuit.

[0042] The zero-flux mutual inductor gear shifting protection circuit of the present utility model is improved on the basis of the traditional adaptive zero-flux current mutual inductor compensation circuit, adding the transient bidirectional protection TVS diodes D5 and D6 and the thermistor R7, thereby providing more reliable protection during the gear shifting process of the electric energy meter.

[0043] During the gear shifting process, when the primary winding needs to be switched at different current levels, it may cause a large current to flow into the small current winding of the multi-winding, resulting in a high magnetic flux in the magnetic core and thus generating a high instantaneous voltage on the operational amplifier. To prevent this high voltage from breaking down the operational amplifier, the present utility model introduces the transient bidirectional protection TVS diodes D5 and D6 between the second pin of the mutual inductor sampling coil and the ground. The TVS3 diode can suppress the high voltage within 12V, protecting the first pin of the operational amplifier from being broken down by the high voltage.

[0044] In addition, a thermistor R7 is introduced into this circuit. RZ11 is a polymer PTC thermistor with an internal resistance between 30Ω and 60Ω. RZ11 is connected in series in the output loop of the current transformer. When an instantaneous peak current is generated during the gear shifting process, RZ11 can absorb the peak current and avoid being burned out through its special material. At the same time, the RC filter circuit composed of RZ11 and multiple LL4148 diodes can delay the transmission time of the peak current, enabling the LL4148 diodes to play a protective role when the peak current passes through, suppressing the voltage at the 6th pin of the operational amplifier within 0.7V, thereby avoiding the breakdown damage of the operational amplifier caused by high voltage.

[0045] As Figure 4 shown, through such an improved circuit protection method, when tested with an oscilloscope during the gear shifting process of the standard meter, the peak voltage is effectively eliminated, protecting the operational amplifier device from being damaged by high voltage breakdown.

[0046] The circuit of the present utility model can effectively suppress high voltage spikes during the gear shifting process, improving the reliability and service life of the electric energy standard meter. At the same time, it maintains a high-precision current measurement ability, ensuring the requirements for current measurement accuracy and reliability in the power system and other application fields.

[0047] The above is only the specific implementation manner of the present utility model, but the protection scope of the present utility model is not limited thereto. Any changes or substitutions that can be thought of without creative labor should be covered within the protection scope of the present utility model. Therefore, the protection scope of the present utility model should be subject to the protection scope defined by the claims.

Claims

1. A zero-flux current transformer shift protection circuit, comprising a zero-flux current transformer and an operational amplifier, characterized in that: The protection circuit further includes transient voltage suppression (TVS) diodes D5, D6 and a thermistor R7, where: The transient voltage suppression (TVS) diodes D5, D6 are connected between the second pin of the sampling coil of the mutual inductor and the ground, and are used to suppress the high voltage within 12V during the gear shifting process; The thermistor R7 is a polymer PTC thermistor, with its internal resistance between 30Ω and 60Ω, and is connected in series in the output loop of the mutual inductor for overcurrent protection.

2. The zero-flux current transformer shift protection circuit according to claim 1, characterized in that: The protection circuit further includes a plurality of LL4148 diodes. The LL4148 diodes and the thermistor R7 together form an RC filter circuit, which is used to delay the transmission time of the peak current during the gear shifting process, enabling the LL4148 diodes to play a protective role, suppressing the voltage at the 6th pin of the operational amplifier to 0.7V, thereby protecting the operational amplifier from being damaged by high voltage breakdown.

3. The zero-flux current transformer shift protection circuit according to claim 1, wherein: The compensation winding of the mutual inductor is used to detect current, and the amplifier power amplifier circuit is used to drive the sampling winding to generate a sampling current, so that the current conversion relationship of the mutual inductor is: I3′N3 + I2N2 = I1N1, where N1 is the number of turns of the primary side, I1 is the primary side current, N2 is the number of turns of the secondary side, I2 is the secondary side current, N3 is the number of turns of the compensation winding, and the exciting current I and the compensation current I3 are generated on the winding N3 p and the sum of I and I3, I3′ = I p + I3 p + I3.

4. The zero-flux current transformer shift protection circuit according to claim 1, wherein: The circuit further includes a current detection module, which is used to monitor the current change of the mutual inductor in real time. When the detected current exceeds the preset threshold, it controls the transient voltage suppression (TVS) diodes D5, D6 and the thermistor R7 to perform protection operations, thereby avoiding damage to the operational amplifier caused by high voltage.

5. The zero-flux current transformer shift protection circuit according to claim 1, characterized in that: The protection circuit further includes an overvoltage protection module, which includes a plurality of series-connected TVS diodes, and is used to further disperse and suppress high voltage during the gear shifting process, thereby enhancing the overvoltage protection ability of the entire circuit.

6. An electric energy standard meter, characterized in that: The electrical energy standard meter includes the zero-flux mutual inductor gear shifting protection circuit according to any one of claims 1 to 5, and is used to protect the operational amplifier in the protection circuit from being damaged by high voltage breakdown when switching between different current gears.

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