Breaker metering protection system based on single current transformer

Abstract

The invention discloses a circuit breaker metering protection system, belongs to the technical field of current transformers, and particularly relates to a circuit breaker metering protection system based on a single current transformer, which comprises a self-power-generation circuit, a current transformer signal conversion circuit, a protection current sampling circuit, a protection voltage sampling circuit and a metering circuit, only one set of protection mutual inductor is needed to meet the standard requirement of measurement precision, the protection function can be achieved, the structure can be simplified, the cost can be reduced, and meanwhile the characteristic that the MOS transistor is low in conductive internal resistance is used for controlling the mutual inductor to work in a self-power-supply protection mode or is only used for a sampling mode. The control circuit is simple, the operational amplifier is used for isolating voltage signals, an isolation mutual inductor which is large in size and high in cost is abandoned, a signal reference point and a measurement reference point are made to be the same point, interference on digital signals is eliminated, and electricity is greatly simplified.

Description

Technical Field

[0001] The invention discloses a circuit breaker metering protection system, belongs to the technical field of current transformers, and specifically relates to a circuit breaker metering protection system based on a single set of current transformers. Background Art

[0002] Short circuit and overload faults often occur in power systems. If not handled in time, they will cause serious damage to electrical equipment and power grids. In order to ensure the normal operation of the power system and protect the safety of equipment, a power protection system is installed in the power system. Among them, current protection is the most basic form of protection in the power protection system. It mainly monitors the current in the power grid and cuts off the power supply in time when the current exceeds a certain threshold, thereby preventing overload and short circuit faults.

[0003] The current transformer is an important component of current protection in the power system. It is mainly a device that converts high current into low current. In the current transformer, the current I1 in the power grid flows through the main coil as the primary current, and the current I2 passing through the core of the transformer is the secondary current, which is transmitted to the protection device through the secondary output terminal. The protection device determines whether there is an overload or short circuit fault based on the magnitude of the secondary current. The current value measured on the secondary side of the current transformer is in a certain proportional relationship with the primary current value in the power grid.

[0004] In the power system, the circuit breaker is usually the switch of the equipment, which plays the role of controlling the current and isolating the high-voltage power equipment from the low-voltage power equipment. As one of the most important components of the power protection system, the current transformer can monitor and protect the current, thereby ensuring the safe operation of the power equipment and the power system. Connecting the current transformer to the upper end of the circuit breaker can monitor the current above the circuit breaker. Once the monitored current exceeds the set value, the circuit breaker will be triggered quickly to achieve rapid separation of live parts, thereby preventing accidents in the power system, which plays a very critical role.

[0005] The current detection of the traditional current transformer is realized through the sampling circuit and the metering chip. Due to the working characteristics of the metering chip, the reference point of the sampling signal needs to be the same reference point as the reference point of the metering chip reference source. The voltage sampling signal is converted through strong electricity. If the signal reference point is to be consistent with the reference point of the metering chip, there are two traditional solutions. The first is to use a dedicated voltage transformer, and the second is to directly connect the N phase to the signal reference point GND. The first voltage transformer of the above two solutions is large in size and high in cost. It occupies a large space inside the circuit breaker and is not easy to implement. Although the sampling principle of the second solution is simple, since the signal ground is directly connected to the N phase, it will cause greater interference to the digital signal, so the digital signal needs to be isolated again. At the same time, the traditional current measurement and current protection circuits need to use two sets of transformers to provide current signals respectively, which also increases the cost and design difficulty. Summary of the invention

[0006] Purpose of the invention: To provide a circuit breaker metering protection system based on a single set of current transformers to solve the above-mentioned problems.

[0007] Technical solution: A circuit breaker metering protection system based on a single set of current transformers, the current transformer protection system comprising: a self-generating circuit, a current transformer signal conversion circuit, a protection current sampling circuit, a protection voltage sampling circuit and a metering circuit;

[0008] The input end of the self-generated power circuit inputs voltage and the output end outputs driving voltage to the current transformer signal conversion circuit, the current transformer signal conversion circuit is connected to the metering circuit, the input end of the protection current sampling circuit is connected to the output end of the current transformer signal conversion circuit, the output end is connected to the metering circuit, and the protection voltage sampling circuit is connected to the metering circuit.

[0009] In a further embodiment, the self-generated power circuit includes: interface J1, diode D6, diode D1, diode D2, diode D2, diode D4, diode D5, transient suppression diode D7, low voltage MOS tube Q1, diode D8, resistor R20, voltage detector U4, diode D10, voltage regulator tube D9, resistor R19, capacitor C28;

[0010] The positive electrode of the diode D10 inputs the power supply voltage, and the negative electrode is simultaneously connected to the negative electrode of the diode D8 and the negative electrode of the voltage regulator D9. The No. 3 pin of the voltage detector U4 is simultaneously connected to the positive electrode of the voltage regulator D9, one end of the resistor R19 and one end of the capacitor C28. The No. 2 pin of the voltage detector U4 is simultaneously connected to the other end of the resistor R19, the other end of the resistor R28, the source of the low-voltage MOS tube Q1 and the positive electrode of the transient suppression diode D7. The No. 1 pin of the voltage detector U4 is connected to one end of the resistor R20, and the gate of the low-voltage MOS tube Q1 is connected to the positive electrode of the transient suppression diode D7. The drain of the low-voltage MOS tube Q1 is connected to the anode of the diode D8, the cathode of the transient suppression diode D7, the cathode of the diode D1, the cathode of the diode D2, the cathode of the diode D3, the cathode of the diode D4, the cathode of the diode D5 and the cathode of the diode D6 at the same time, and the anode of the diode D1, the anode of the diode D2, the anode of the diode D3, the anode of the diode D4, the anode of the diode D5 and the anode of the diode D6 are connected to the current transformer signal conversion circuit through the interface J1.

[0011] In a further embodiment, the current transformer signal conversion circuit includes: MOS tube Q2, MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6, MOS tube Q7, resistor R21, resistor R22, resistor R23, resistor R24, resistor R25, resistor R26, resistor R27, resistor R28, voltage regulator tube D15, voltage regulator tube D14, capacitor C34;

[0012] One end of the resistor R28 inputs the power supply voltage, and the other end is simultaneously connected to the negative electrode of the voltage regulator tube D15, the negative electrode of the voltage regulator tube D14 and one end of the capacitor C34. The positive electrode of the voltage regulator tube D14 and the other end of the capacitor C34 are grounded. The positive electrode of the voltage regulator tube D15 is simultaneously connected to one end of the resistor R27 and the gate of the MOS tube Q7 and connected to the shutdown control terminal OFF_CONT. The drain of the MOS tube Q2, the drain of the MOS tube Q3, the drain of the MOS tube Q4, the drain of the MOS tube Q5, the drain of the MOS tube Q6, and the drain of the MOS tube Q7 are correspondingly connected to the positive electrode of the diode D6, the positive electrode of the diode D1, the positive electrode of the diode D2, the positive electrode of the diode D4, and the positive electrode of the diode D5 through the interface J1. The source of the MOS tube Q2 is connected to one end of the resistor R21 and outputs a protection current sampling signal. The other end of the resistor R21 is grounded. The gate of the MOS tube Q2 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q3 is connected to one end of the resistor R22 and outputs a protection current sampling signal, the other end of the resistor R22 is grounded, the gate of the MOS tube Q3 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q4 is connected to one end of the resistor R23 and outputs a protection current sampling signal, the other end of the resistor R23 is grounded, the gate of the MOS tube Q4 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q5 is connected to one end of the resistor R24 ​​and outputs a protection current sampling signal, the other end of the resistor R24 ​​is grounded, the gate of the MOS tube Q5 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q6 is connected to one end of the resistor R25 and outputs a protection current sampling signal, the other end of the resistor R25 is grounded, and the gate of the MOS tube Q6 is connected to the shutdown control terminal OFF_CONT.

[0013] In a further embodiment, when the self-generated power circuit has an auxiliary power source EXDC12V input, a 9.1V driving voltage is generated to drive MOS tubes Q2, Q3, Q4, Q5, Q6, and Q7 to be turned on.

[0014] In a further embodiment, when MOS tubes Q2, Q3, Q4, Q5, Q6, and Q7 are turned on, the transformer provides a current sampling signal for measurement, which is input into the metering chip of the metering circuit. At this time, the transformer self-power supply circuit fails.

[0015] In a further embodiment, when there is no auxiliary power supply or the driving power supply is lower than the threshold, MOS tube Q2, MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6, and MOS tube Q7 are turned off. At this time, the self-power supply circuit resumes working, provides working power to the system, and the transformer provides a protection current sampling signal.

[0016] In a further embodiment, the protection voltage sampling circuit is composed of a differential input circuit and a multi-channel conversion isolation circuit;

[0017] The differential input circuit is composed of a voltage reference and an operational amplifier; the conversion isolation circuit is composed of an operational amplifier and a resistor;

[0018] The operational amplifier differential input of the differential input circuit provides a reference voltage and stabilizes the output signal;

[0019] The conversion isolation circuit uses a series resistor step-down pair to convert a strong electric signal and input it into an operational amplifier, and utilizes the isolation function of the operational amplifier to isolate the input and output ends of the voltage sampling.

[0020] In a further embodiment, the operational amplifier outputs a signal, which is input into a metering chip sampling circuit of the metering circuit through a ceramic capacitor, and the ceramic capacitor is used to pass AC and block DC to remove the DC component in the sampling signal, and then input into the metering chip to complete sampling.

[0021] In a further embodiment, the protection current sampling circuit is composed of a multi-channel conversion isolation circuit, and the conversion isolation circuit is composed of an operational amplifier and a resistor.

[0022] Beneficial effects: The present invention only needs one set of protection transformers to meet the standard requirements of measurement accuracy and realize the protection function, which can simplify the structure and reduce the cost. At the same time, the low internal resistance of the MOS tube is used to control the transformer to work in the self-powered protection mode or only in the sampling mode. In addition, the control circuit is simple, and the operational amplifier is used to isolate the voltage signal, and the isolation transformer with large volume and high cost is discarded. The signal reference point and the measurement reference point are the same point, which eliminates the interference to the digital signal and greatly simplifies the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the self-generated electricity circuit of the present invention.

[0024] Figure 2 The present invention provides a schematic diagram of a current transformer signal conversion circuit.

[0025] Figure 3 It is a schematic diagram of the protection current sampling circuit of the present invention.

[0026] Figure 4It is a schematic diagram of the protection voltage sampling circuit of the present invention.

[0027] Figure 5 It is a schematic diagram of a metering circuit of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] A circuit breaker metering protection system based on a single set of current transformers, comprising: a self-generating circuit, a current transformer signal conversion circuit, a protection current sampling circuit, a protection voltage sampling circuit and a metering circuit;

[0030] The input end of the self-generated power circuit inputs voltage and the output end outputs driving voltage to the current transformer signal conversion circuit, the current transformer signal conversion circuit is connected to the metering circuit, the input end of the protection current sampling circuit is connected to the output end of the current transformer signal conversion circuit, the output end is connected to the metering circuit, and the protection voltage sampling circuit is connected to the metering circuit.

[0031] In one embodiment, Figure 1 As shown, the self-generated power circuit includes: interface J1, diode D6, diode D1, diode D2, diode D2, diode D4, diode D5, transient suppression diode D7, low voltage MOS tube Q1, diode D8, resistor R20, voltage detector U4, diode D10, voltage regulator tube D9, resistor R19, capacitor C28;

[0032] The positive electrode of the diode D10 inputs the power supply voltage, and the negative electrode is simultaneously connected to the negative electrode of the diode D8 and the negative electrode of the voltage regulator D9. The No. 3 pin of the voltage detector U4 is simultaneously connected to the positive electrode of the voltage regulator D9, one end of the resistor R19 and one end of the capacitor C28. The No. 2 pin of the voltage detector U4 is simultaneously connected to the other end of the resistor R19, the other end of the resistor R28, the source of the low-voltage MOS tube Q1 and the positive electrode of the transient suppression diode D7. The No. 1 pin of the voltage detector U4 is connected to one end of the resistor R20, and the gate of the low-voltage MOS tube Q1 is connected to the positive electrode of the transient suppression diode D7. The drain of the low-voltage MOS tube Q1 is connected to the anode of the diode D8, the cathode of the transient suppression diode D7, the cathode of the diode D1, the cathode of the diode D2, the cathode of the diode D3, the cathode of the diode D4, the cathode of the diode D5 and the cathode of the diode D6 at the same time, and the anode of the diode D1, the anode of the diode D2, the anode of the diode D3, the anode of the diode D4, the anode of the diode D5 and the anode of the diode D6 are connected to the current transformer signal conversion circuit through the interface J1.

[0033] In one embodiment, Figure 2 As shown, the current transformer signal conversion circuit includes: MOS tube Q2, MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6, MOS tube Q7, resistor R21, resistor R22, resistor R23, resistor R24, resistor R25, resistor R26, resistor R27, resistor R28, voltage regulator tube D15, voltage regulator tube D14, capacitor C34;

[0034] One end of the resistor R28 inputs the power supply voltage, and the other end is simultaneously connected to the negative electrode of the voltage regulator tube D15, the negative electrode of the voltage regulator tube D14 and one end of the capacitor C34. The positive electrode of the voltage regulator tube D14 and the other end of the capacitor C34 are grounded. The positive electrode of the voltage regulator tube D15 is simultaneously connected to one end of the resistor R27 and the gate of the MOS tube Q7 and connected to the shutdown control terminal OFF_CONT. The drain of the MOS tube Q2, the drain of the MOS tube Q3, the drain of the MOS tube Q4, the drain of the MOS tube Q5, the drain of the MOS tube Q6, and the drain of the MOS tube Q7 are correspondingly connected to the positive electrode of the diode D6, the positive electrode of the diode D1, the positive electrode of the diode D2, the positive electrode of the diode D4, and the positive electrode of the diode D5 through the interface J1. The source of the MOS tube Q2 is connected to one end of the resistor R21 and outputs a protection current sampling signal. The other end of the resistor R21 is grounded. The gate of the MOS tube Q2 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q3 is connected to one end of the resistor R22 and outputs a protection current sampling signal, the other end of the resistor R22 is grounded, the gate of the MOS tube Q3 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q4 is connected to one end of the resistor R23 and outputs a protection current sampling signal, the other end of the resistor R23 is grounded, the gate of the MOS tube Q4 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q5 is connected to one end of the resistor R24 ​​and outputs a protection current sampling signal, the other end of the resistor R24 ​​is grounded, the gate of the MOS tube Q5 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q6 is connected to one end of the resistor R25 and outputs a protection current sampling signal, the other end of the resistor R25 is grounded, and the gate of the MOS tube Q6 is connected to the shutdown control terminal OFF_CONT.

[0035] In one embodiment, Figure 1 and Figure 2 As shown, when the self-generated power circuit has an auxiliary power supply EXDC12V input, a 9.1V driving voltage is generated to drive MOS tubes Q2, MOS tubes Q3, MOS tubes Q4, MOS tubes Q5, MOS tubes Q6, and MOS tubes Q7 to be turned on.

[0036] In one embodiment, Figure 1 and Figure 2 As shown, when MOS tubes Q2, Q3, Q4, Q5, Q6, and Q7 are turned on, the transformer provides a current sampling signal for measurement, which is input into the metering chip of the metering circuit. At this time, the transformer self-power supply circuit fails.

[0037] In one embodiment, Figure 1 and Figure 2 As shown, when there is no auxiliary power supply or the driving power supply is lower than the threshold, MOS tubes Q2, Q3, Q4, Q5, Q6 and Q7 are turned off. At this time, the self-powered circuit resumes working and provides working power to the system, and the transformer provides a protection current sampling signal.

[0038] In one embodiment, Figure 4 As shown, the protection voltage sampling circuit is composed of a differential input circuit and a multi-channel conversion isolation circuit;

[0039] The differential input circuit is composed of a voltage reference and an operational amplifier; the conversion isolation circuit is composed of an operational amplifier and a resistor;

[0040] The operational amplifier differential input of the differential input circuit provides a reference voltage and stabilizes the output signal;

[0041] The conversion isolation circuit uses a series resistor step-down pair to convert a strong electric signal and input it into an operational amplifier, and utilizes the isolation function of the operational amplifier to isolate the input and output ends of the voltage sampling.

[0042] In one embodiment, Figure 4 and Figure 5 As shown, the operational amplifier outputs a signal, which is input into the metering chip sampling circuit of the metering circuit through the ceramic capacitor. The ceramic capacitor is used to pass AC to block DC to remove the DC component in the sampling signal, and then the signal is input into the metering chip to complete the sampling.

[0043] In one embodiment, Figure 3 As shown, the protection current sampling circuit is composed of a multi-channel conversion isolation circuit, and the conversion isolation circuit is composed of an operational amplifier and a resistor.

[0044] Working principle of current transformer signal conversion circuit:

[0045] 1. When the auxiliary power supply EXDC12V is input, a 9.1V driving voltage is generated to drive MOS tubes Q2, Q3, Q4, Q5, Q6, and Q7 to turn on;

[0046] 2. When the MOS tube is turned on, the transformer provides a current sampling signal and inputs it into the metering chip. At this time, the transformer self-power supply circuit fails;

[0047] 3. When there is no auxiliary power supply or the driving power supply is lower than 6.8V, the MOS tube is turned off. At this time, the self-powered circuit resumes working, providing working power to the system, and the transformer provides a protection current sampling signal.

[0048] Advantages of current transformer signal conversion circuit

[0049] 1. Traditional current measurement and current protection circuits require two sets of transformers to provide current signals respectively, while this circuit only requires one set of protection transformers to meet the standard requirements of measurement accuracy and realize the protection function, which can simplify the structure and reduce costs.

[0050] 2. Using the low internal resistance of the MOS tube, the transformer is controlled to work in the self-powered protection mode or only in the sampling mode. And the control circuit is simple.

[0051] Voltage signal conversion circuit principle:

[0052] 1. Use the series step-down principle to convert the strong electric signal into the operational amplifier, and use the isolation function of the operational amplifier to isolate the input and output ends of the voltage sampling;

[0053] 2. The operational amplifier has a differential input, provides a reference voltage, and stabilizes the output signal;

[0054] 3. The output signal of the operational amplifier is input into the sampling circuit of the metering chip through the ceramic capacitor. The DC component in the sampling signal is removed by using the principle that the ceramic capacitor passes AC and blocks DC, and then input into the metering chip to complete the sampling.

[0055] Advantages of this voltage signal conversion circuit:

[0056] 1. Due to the working characteristics of the metering chip, the reference point of the sampling signal needs to be the same reference point as the reference point of the metering chip reference source. The voltage sampling signal is converted through strong electricity. If the signal reference point is to be consistent with the reference point of the metering chip, there are two traditional solutions. The first is to use a dedicated voltage transformer, and the second is to connect the N phase directly to the signal reference point GND. The first voltage transformer of the above two solutions is large in size and high in cost. It occupies a large space inside the circuit breaker and is not easy to implement. Although the sampling principle of the second solution is simple, because the signal ground is directly connected to the N phase, it will cause greater interference to the digital signal, so the digital signal needs to be isolated again, which invisibly increases the cost and design difficulty.

[0057] 2. The advantage of using this design is that the operational amplifier is used to isolate the voltage signal, which discards the large and expensive isolation transformer, and makes the signal reference point and the measurement reference point the same point, eliminating interference with the digital signal and greatly simplifying the circuit.

[0058] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A circuit breaker metering protection system based on a single set of current transformers, characterized in that: The current transformer protection system comprises: a self-generating circuit, a current transformer signal conversion circuit, a protection current sampling circuit, a protection voltage sampling circuit and a metering circuit; The input end of the self-generated power circuit inputs voltage and the output end outputs driving voltage to the current transformer signal conversion circuit, the current transformer signal conversion circuit is connected to the metering circuit, the input end of the protection current sampling circuit is connected to the output end of the current transformer signal conversion circuit, the output end is connected to the metering circuit, and the protection voltage sampling circuit is connected to the metering circuit.

2. A circuit breaker metering protection system based on a single set of current transformers according to claim 1, characterized in that: The self-generated power circuit includes: an interface J1, a diode D6, a diode D1, a diode D2, a diode D2, a diode D4, a diode D5, a transient suppression diode D7, a low-voltage MOS tube Q1, a diode D8, a resistor R20, a voltage detector U4, a diode D10, a voltage regulator tube D9, a resistor R19, and a capacitor C28; The positive electrode of the diode D10 inputs the power supply voltage, and the negative electrode is simultaneously connected to the negative electrode of the diode D8 and the negative electrode of the voltage regulator D9. The No. 3 pin of the voltage detector U4 is simultaneously connected to the positive electrode of the voltage regulator D9, one end of the resistor R19 and one end of the capacitor C28. The No. 2 pin of the voltage detector U4 is simultaneously connected to the other end of the resistor R19, the other end of the resistor R28, the source of the low-voltage MOS tube Q1 and the positive electrode of the transient suppression diode D7. The No. 1 pin of the voltage detector U4 is connected to one end of the resistor R20, and the gate of the low-voltage MOS tube Q1 is connected to the positive electrode of the transient suppression diode D7. The drain of the low-voltage MOS tube Q1 is connected to the anode of the diode D8, the cathode of the transient suppression diode D7, the cathode of the diode D1, the cathode of the diode D2, the cathode of the diode D3, the cathode of the diode D4, the cathode of the diode D5 and the cathode of the diode D6 at the same time, and the anode of the diode D1, the anode of the diode D2, the anode of the diode D3, the anode of the diode D4, the anode of the diode D5 and the anode of the diode D6 are connected to the current transformer signal conversion circuit through the interface J1.

3. A circuit breaker metering protection system based on a single set of current transformers according to claim 2, characterized in that: The current transformer signal conversion circuit includes: MOS tube Q2, MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6, MOS tube Q7, resistor R21, resistor R22, resistor R23, resistor R24, resistor R25, resistor R26, resistor R27, resistor R28, voltage regulator tube D15, voltage regulator tube D14, capacitor C34; One end of the resistor R28 inputs the power supply voltage, and the other end is simultaneously connected to the negative electrode of the voltage regulator tube D15, the negative electrode of the voltage regulator tube D14 and one end of the capacitor C34. The positive electrode of the voltage regulator tube D14 and the other end of the capacitor C34 are grounded. The positive electrode of the voltage regulator tube D15 is simultaneously connected to one end of the resistor R27 and the gate of the MOS tube Q7 and connected to the shutdown control terminal OFF_CONT. The drain of the MOS tube Q2, the drain of the MOS tube Q3, the drain of the MOS tube Q4, the drain of the MOS tube Q5, the drain of the MOS tube Q6, and the drain of the MOS tube Q7 are correspondingly connected to the positive electrode of the diode D6, the positive electrode of the diode D1, the positive electrode of the diode D2, the positive electrode of the diode D4, and the positive electrode of the diode D5 through the interface J1. The source of the MOS tube Q2 is connected to one end of the resistor R21 and outputs a protection current sampling signal. The other end of the resistor R21 is grounded. The gate of the MOS tube Q2 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q3 is connected to one end of the resistor R22 and outputs a protection current sampling signal, the other end of the resistor R22 is grounded, the gate of the MOS tube Q3 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q4 is connected to one end of the resistor R23 and outputs a protection current sampling signal, the other end of the resistor R23 is grounded, the gate of the MOS tube Q4 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q5 is connected to one end of the resistor R24 ​​and outputs a protection current sampling signal, the other end of the resistor R24 ​​is grounded, the gate of the MOS tube Q5 is connected to the shutdown control terminal OFF_CONT, the source of the MOS tube Q6 is connected to one end of the resistor R25 and outputs a protection current sampling signal, the other end of the resistor R25 is grounded, and the gate of the MOS tube Q6 is connected to the shutdown control terminal OFF_CONT.

4. A circuit breaker metering protection system based on a single set of current transformers according to claim 3, characterized in that: When the self-generated power circuit has an auxiliary power supply EXDC12V input, a 9.1V driving voltage is generated to drive MOS tubes Q2, Q3, Q4, Q5, Q6, and Q7 to turn on.

5. A circuit breaker metering protection system based on a single set of current transformers according to claim 4, characterized in that: When MOS tubes Q2, Q3, Q4, Q5, Q6 and Q7 are turned on, the transformer provides a current sampling signal for measurement, which is input into the metering chip of the metering circuit. At this time, the transformer self-power supply circuit fails.

6. A circuit breaker metering protection system based on a single set of current transformers according to claim 4, characterized in that: When there is no auxiliary power supply or the driving power supply is lower than the threshold, MOS tubes Q2, Q3, Q4, Q5, Q6 and Q7 are turned off. At this time, the self-power supply circuit resumes working and provides working power to the system, and the transformer provides a protection current sampling signal.

7. A circuit breaker metering protection system based on a single set of current transformers according to claim 4, characterized in that: The protection voltage sampling circuit is composed of a differential input circuit and a multi-channel conversion isolation circuit; The differential input circuit is composed of a voltage reference and an operational amplifier; the conversion isolation circuit is composed of an operational amplifier and a resistor; The operational amplifier differential input of the differential input circuit provides a reference voltage and stabilizes the output signal; The conversion isolation circuit uses a series resistor step-down pair to convert a strong electric signal and input it into an operational amplifier, and utilizes the isolation function of the operational amplifier to isolate the input and output ends of the voltage sampling.

8. A circuit breaker metering protection system based on a single set of current transformers according to claim 7, characterized in that: The output signal of the operational amplifier is input into the metering chip sampling circuit of the metering circuit through the ceramic capacitor. The ceramic capacitor is used to pass AC and block DC to remove the DC component in the sampling signal, and then input into the metering chip to complete the sampling.

9. A circuit breaker metering protection system based on a single set of current transformers according to claim 4, characterized in that: The protection current sampling circuit is composed of a multi-channel conversion isolation circuit, and the conversion isolation circuit is composed of an operational amplifier and a resistor.

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