A transformer device with a loop patrol function

Abstract

The application belongs to the technical field of electric power measurement, and discloses a transformer device with loop inspection function, which comprises a power frequency inductor, a first high-frequency inductor, a second high-frequency inductor and a peripheral circuit, wherein the peripheral circuit comprises a single-chip microcomputer, a power supply circuit, a square wave injection circuit, an inductance detection circuit and a power frequency measurement signal conditioning circuit; the two ends of the first high-frequency inductor are connected with the secondary side of a primary transformer; the second high-frequency inductor and the first high-frequency inductor form a transformer; the output end of the square wave injection circuit is connected with the first high-frequency inductor; the input end of the inductance detection circuit is connected with the second high-frequency inductor, and the output end is connected with the single-chip microcomputer; the input end of the power frequency measurement signal conditioning circuit is connected with the power frequency inductor, and the output end is connected with the single-chip microcomputer; and the application can realize the detection of open circuit, short circuit and rectification state of the secondary side of the primary transformer through the single-chip microcomputer.

Description

Technical Field

[0001] This invention belongs to the field of power metering technology, and specifically relates to a current transformer device with circuit inspection function. Background Technology

[0002] Currently, electricity metering mainly consists of current transformers, secondary circuits, and electricity meters. A problem with any of these three components will severely affect the accuracy of electricity metering. Some sophisticated and covert methods of electricity theft targeting the secondary circuit of current transformers (CTs) lack direct inspection tools, thus requiring circuit inspection equipment to monitor the circuit status of current transformers. Power terminal equipment often transmits sampling signals to the metering chip through two stages of current transformers. Generally, the external current transformer that converts currents from hundreds to thousands of amperes to a few A is called the primary current transformer, while the internal current transformer that converts currents from a few A to mA is called the secondary current transformer. The secondary side of the primary transformer is usually connected to the primary side of the secondary transformer through terminals to form a circuit.

[0003] Circuit condition monitoring equipment primarily detects the circuit status of current transformers, such as detecting open circuits, short circuits, and current shunting on the secondary side of the primary current transformer. Existing circuit condition monitoring mainly involves detecting the insulation resistance to ground of the secondary circuit, determining whether there are multiple grounding points in the secondary circuit, or making judgments based on set voltage and current inputs to the secondary circuit. Therefore, some existing circuit condition monitoring and testing equipment suffers from inaccurate fault diagnosis or inability to properly detect circuit faults in practical applications. Improvements to existing circuit condition monitoring equipment are needed to enhance the accuracy of circuit condition detection. Summary of the Invention

[0004] To meet the actual needs of the field of power metering technology, this invention overcomes the shortcomings of the existing technology and the technical problem to be solved is: to provide a current transformer device with circuit inspection function.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a current transformer device with loop inspection function, including a power frequency inductor, and further including: a first high frequency inductor, a second high frequency inductor and peripheral circuits, wherein the peripheral circuits include: a microcontroller, a power supply circuit, a square wave injection circuit, an inductance detection circuit and a power frequency metering signal conditioning circuit;

[0006] The two ends of the first high-frequency inductor are connected to the secondary side of the primary current transformer; the second high-frequency inductor and the first high-frequency inductor form a current transformer;

[0007] The square wave injection circuit is used to generate a square wave AC signal under the drive of the PWM signal of the microcontroller, and the output terminal of the square wave injection circuit is connected to the first high-frequency inductor.

[0008] The input terminal of the inductance detection circuit is connected to the second high-frequency inductor. The inductance detection circuit includes capacitor C29, capacitor C31 and Schmitt inverter. The capacitor C29, capacitor C31 and Schmitt inverter form a resonant circuit with the second high-frequency inductor. The resonant circuit is used to output a resonant signal to the microcontroller.

[0009] The power frequency metering signal conditioning circuit includes a non-inverting amplifier D1A, a DC blocking capacitor C2, and a voltage comparator D1B. The input terminal of the non-inverting amplifier D1A is connected to the power frequency inductor, and the two ends of the power frequency inductor are connected to the secondary side of the primary transformer. The output terminal of the non-inverting amplifier D1A is connected to the non-inverting input terminal of the voltage comparator D1B through the DC blocking capacitor C2. The input terminal of the voltage comparator D1B is also connected to a boost voltage, and the output terminal of the voltage comparator D1B is connected to the microcontroller.

[0010] The microcontroller is used to determine whether the secondary side of the primary transformer is open or short-circuited based on the frequency of the resonant signal output by the resonant circuit, and is also used to determine whether a rectifier circuit is connected in series on the secondary side of the primary transformer based on the output signal of the power frequency metering signal conditioning circuit.

[0011] The current transformer device with loop inspection function further includes an inductance detection circuit and a filtering circuit, which includes a high-pass filter and a low-pass filter.

[0012] The microcontroller is also used to control the frequency of the PWM signal so that it equals the signal amplitude of the resonant circuit to reach its maximum. The resonant signal output by the resonant circuit passes through the high-pass filter and the low-pass filter in sequence to obtain a high-frequency AC signal, which is then input into the microcontroller to detect its frequency.

[0013] The cutoff frequency of the high-pass filter circuit is 4.78K, and the cutoff frequency of the low-pass filter is 17.6K.

[0014] The high-pass filter includes an operational amplifier D2A, resistors R23, R27, R30, and R31, and capacitors C22 and C23. One end of capacitor C22 is connected to the output of the resonant circuit, and the other end is connected to the non-inverting input of the operational amplifier D2A via capacitor C23. The inverting input of the operational amplifier D2A is grounded through resistor R27, and the non-inverting input is grounded through resistor R30. The output is connected to the inverting input through resistor R23, and the output is connected to the non-inverting input through resistor R31 and capacitor C23.

[0015] The low-pass filter includes resistors R28, R29, R25, and R22, an operational amplifier D2B, and capacitors C27 and C28. One end of resistor R28 is connected to the output terminal of operational amplifier D2A, and the other end is connected to the non-inverting input terminal of operational amplifier D2B via resistor R29. The non-inverting input terminal of operational amplifier D2B is grounded via capacitor C27, and the inverting input terminal is grounded via resistor R25. The output terminal is connected to the inverting input terminal of operational amplifier D2A via resistor R22, and the output terminal is also connected to the non-inverting input terminal of operational amplifier D2A via capacitor C23 and resistor R29.

[0016] The inductance detection circuit also includes an AC signal boosting circuit. The input terminal of the AC signal boosting circuit is connected to the output terminal of the filter circuit, and is used to input the filtered high-frequency AC signal after DC blocking and boosting into the microcontroller to detect its frequency.

[0017] The AC signal boosting circuit includes a proportional amplifier D2C and a voltage follower D2D. The output of the filter circuit is connected to the non-inverting input of the proportional amplifier D2C and the voltage follower D2D. The non-inverting input of the proportional amplifier D2C and the voltage follower D2D is also connected to a boosting voltage. The output of the proportional amplifier D2C and the voltage follower D2D is connected to the microcontroller.

[0018] The square wave injection circuit includes: resistor R41, resistor R42, field-effect transistor V7, resistor R37, field-effect transistor V4, field-effect transistor V6, resistor R38, capacitor C36, bidirectional transient suppression diode V5, capacitor C37, capacitor C40, resistor R39, and resistor R40. One end of resistor R41 is connected to the PWM signal output by the microcontroller, and the other end is connected to the gate of field-effect transistor V7. The source of field-effect transistor V7 is grounded, the gate is grounded through resistor R42, and the drain is connected to the positive terminal of the power supply through resistor R37. The gates of field-effect transistors V4 and V6 are connected to the drain of field-effect transistor V7. The source of field-effect transistor V4 is connected to the positive power supply, and its drain is connected to the drain of field-effect transistor V6 via resistor R38. The source of field-effect transistor V6 is grounded, and its drain is connected to one end of bidirectional transient suppression diode V5 via capacitor C36. The other end of bidirectional transient suppression diode V5 is connected to the positive power supply via resistor R39 and to ground via resistor R40. Capacitor C37 is connected in parallel with resistor R39, and capacitor C40 is connected in parallel with resistor R40.

[0019] The power supply circuit includes a power chip and peripheral circuitry, used to convert external power supply into 3.3V to power devices such as the MCU and Schmitt inverter.

[0020] In the power frequency metering signal conditioning circuit, the input terminal of voltage comparator D1B is connected to a boost voltage of 1.65V.

[0021] The aforementioned current transformer device with loop inspection function further includes a housing. The power frequency inductor, the first high-frequency inductor, the second high-frequency inductor, and the peripheral circuit are disposed inside the housing. The housing is provided with a first interface and a second interface. The first interface is used to connect to the secondary side of the primary current transformer, and the second interface is used to connect the microcontroller to the host computer.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention provides a current transformer device with loop inspection function, which can formulate fault judgment criteria according to the characteristics of different power lines. It can detect the open circuit, short circuit and rectification status of the secondary side of the primary current transformer, and its judgment results are more accurate and reliable.

[0024] 2. This invention adopts a modular design, with the inductor and peripheral circuits all housed inside the casing. The casing has only two interfaces, which can be embedded inside different power inspection terminals. It is simple to connect, easy to use, and provides accurate diagnosis. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a current transformer device with loop inspection function provided in Embodiment 1 of the present invention;

[0026] Figure 2 This is a circuit diagram of the square wave injection circuit in Embodiment 1 of the present invention;

[0027] Figure 3 This is a circuit diagram of the resonant circuit in Embodiment 1 of the present invention;

[0028] Figure 4 This is a circuit diagram of the filter circuit in Embodiment 1 of the present invention;

[0029] Figure 5 This is a circuit diagram of the AC signal boosting circuit in Embodiment 1 of the present invention;

[0030] Figure 6 This is a circuit diagram of the power frequency metering signal conditioning circuit in Embodiment 1 of the present invention;

[0031] Figure 7 This is a circuit diagram of the microcontroller in Embodiment 1 of the present invention.

[0032] Specific implementation methods

[0033] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments; based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1 As shown, this embodiment of the invention provides a current transformer device with loop inspection function, including a power frequency inductor, and further including: a first high-frequency inductor, a second high-frequency inductor, and peripheral circuitry. The peripheral circuitry includes: a microcontroller, a power supply circuit, a square wave injection circuit, an inductance detection circuit, and a power frequency metering signal conditioning circuit. The two ends of the first high-frequency inductor are connected to the secondary side of the primary current transformer to form a loop. The second high-frequency inductor and the first high-frequency inductor form a current transformer. The square wave injection circuit is used to generate a square wave AC signal under the drive of the PWM signal of the microcontroller, and the output terminal of the square wave injection circuit is connected to the first high-frequency inductor. The input terminal of the inductance detection circuit is connected to the second high-frequency inductor and includes a resonant circuit, which is used to output a resonant signal to the microcontroller.

[0036] like Figure 6 As shown, the power frequency metering signal conditioning circuit includes a non-inverting amplifier D1A, a DC blocking capacitor C2, and a voltage comparator D1B. The input terminal of the non-inverting amplifier D1A is connected to the power frequency inductor. The two ends of the power frequency inductor are connected to the secondary side of the primary transformer to form a loop. The output terminal of the non-inverting amplifier D1A is connected to the non-inverting input terminal of the voltage comparator D1B through the DC blocking capacitor C2. The input terminal of the voltage comparator D1B is also connected to a boost voltage. The output terminal of the voltage comparator D1B is connected to the microcontroller. The microcontroller is used to determine whether the secondary side of the primary transformer is open-circuited or short-circuited based on the frequency of the resonant signal output by the resonant circuit. It is also used to determine whether a rectifier circuit is connected in series on the secondary side of the primary transformer based on the output signal of the power frequency metering signal conditioning circuit.

[0037] The power frequency metering signal conditioning circuit uses an operational amplifier TL084 to amplify the power frequency AC signal by 11 times using a non-inverting proportional amplifier D1A. After passing through a DC blocking capacitor C2, the signal is boosted to 1.65V. A square wave signal is then obtained through a voltage comparator D1B and sent to the microcontroller's I / O port for pulse capture to obtain the zero-crossing point of the power frequency current. A Schottky diode TS1 serves as the clamping protection I / O port for the MCU. The circuit also detects whether a rectifier circuit is connected in series on the secondary side of the primary transformer. The difference is as follows: without series connection, the output is a sine wave boosted to 1.65V. With series connection, the output is a non-sine wave signal containing even harmonics.

[0038] like Figure 2 The diagram shown is a schematic of the square wave injection circuit in this embodiment. The square wave injection circuit includes: resistor R41, resistor R42, MOSFET V7, resistor R37, MOSFET V4, MOSFET V6, resistor R38, capacitor C36, bidirectional transient suppression diode V5, capacitor C37, capacitor C40, resistor R39, and resistor R40. One end of resistor R41 is connected to the PWM signal output by the microcontroller, and the other end is connected to the gate of MOSFET V7. The source of MOSFET V7 is grounded, the gate is grounded through resistor R42, and the drain is grounded through resistor R48. R37 is connected to the positive terminal of the power supply; the gates of MOSFET V4 and MOSFET V6 are connected to the drain of MOSFET V7; the source of MOSFET V4 is connected to the positive terminal of the power supply; the drain of MOSFET V4 is connected to the drain of MOSFET V6 via resistor R38; the source of MOSFET V6 is grounded; the drain of MOSFET V6 is connected to one end of bidirectional transient suppression diode V5 via capacitor C36; the other end of bidirectional transient suppression diode V5 is connected to the positive terminal of the power supply via resistor R39, and also connected to ground via resistor R40; capacitor C37 is connected in parallel with resistor R39, and capacitor C40 is connected in parallel with resistor R40.

[0039] In the square wave injection circuit, a push-pull structure is formed using a WPM1483 PMOS (V4) and a WNM3008 NMOS (V5). The WNM3008 NMOS is controlled by a PWM wave to drive the push-pull structure and generate an AC square wave signal. Capacitors C37 and C40 are connected in series to obtain a midpoint voltage of 2.5V. Resistors R39 and R40 balance the capacitor voltages. Capacitor C36 is a DC blocking capacitor. A 2.5V peak square wave AC voltage is obtained between O1 and O2 of the bidirectional transient suppression diode V5, driven by the preceding PWM driver of the NMOS, to drive the injection inductor (the first high-frequency inductor). To prevent shoot-through between the upper and lower bridge arms, a 10R current-limiting resistor R38 is added between the MOSFETs V3 and V4.

[0040] like Figure 3The diagram shown is a circuit schematic of the resonant circuit in an embodiment of the present invention. It includes a Schmitt inverter U2 (model SN74LV14). Terminals 1A and 1Y of the Schmitt inverter U2 are connected to the two ends of the second high-frequency inductor, respectively. Furthermore, terminals 1A and 1Y are grounded via capacitors C29 and C31, respectively. A resistor R34 and a bidirectional transient suppression diode V1 are connected in parallel across capacitor C29, and a resistor R35 and a bidirectional transient suppression diode V3 are connected in parallel across capacitor C31. The Schmitt inverter SN74LV14, the secondary coil inductance of the secondary current transformer, and the capacitors form a resonant circuit. Terminals 1 and 2 of terminal XS1 are connected to the second high-frequency inductor, with the center passing through the secondary side of the primary current transformer. If the secondary side of the primary current transformer is short-circuited, its internal resistance is approximately 0, and the inductance of the secondary side of the secondary current transformer decreases, approaching 0. The inductor, along with C29, C31, and the Schmitt trigger inverter, forms a resonant circuit. Changes in the inductance cause a change in the resonant frequency. The resonant signal is further shaped and output as a square wave signal, which is then input to the MCU. The MCU captures the input and calculates the square wave frequency. By detecting changes in the frequency, the change in the inductance of the inductor connected to XS1 can be determined, further indicating whether there is a short circuit on the secondary side of the primary transformer.

[0041] Furthermore, such as Figure 1 As shown, in this embodiment, the inductance detection circuit further includes a filtering circuit, which comprises a high-pass filter and a low-pass filter. The microcontroller is also used to control the frequency of the PWM signal so that it equals the signal amplitude of the resonant circuit to reach its maximum. The resonant signal output by the resonant circuit passes through the high-pass filter and the low-pass filter in sequence to obtain a high-frequency AC signal, which is then input to the microcontroller to detect its frequency. In this embodiment, by controlling the frequency of the injected signal to equal the resonant frequency of the circuit, the induced signal with the largest amplitude is obtained. At this time, the signal is input to the high-pass filter and the low-pass filter. The cutoff frequency of the low-pass filter is 17.6K, and the cutoff frequency of the high-pass filter is 4.78K. After filtering out low-frequency signals such as power frequency and high-frequency interference, the signal is further amplified to obtain a high-frequency AC signal with a suitable amplitude.

[0042] like Figure 4As shown in the embodiment of the present invention, the high-pass filter includes an operational amplifier D2A, resistors R23, R27, R30, and R31, and capacitors C22 and C23. One end of capacitor C22 is connected to the output terminal of the resonant circuit, and the other end is connected to the non-inverting input terminal of the operational amplifier D2A via capacitor C23. The inverting input terminal of the operational amplifier D2A is grounded through resistor R27, the non-inverting input terminal is grounded through resistor R30, the output terminal is connected to the inverting input terminal through resistor R23, and the output terminal is connected to the non-inverting input terminal through resistor R31 and capacitor C23; the low-pass filter... The amplifier includes resistors R28, R29, R25, and R22, operational amplifier D2B, capacitors C27 and C28. One end of resistor R28 is connected to the output terminal of operational amplifier D2A, and the other end is connected to the non-inverting input terminal of operational amplifier D2B via resistor R29. The non-inverting input terminal of operational amplifier D2B is grounded via capacitor C27, and the inverting input terminal is grounded via resistor R25. The output terminal is connected to the inverting input terminal of operational amplifier D2A via resistor R22, and the output terminal is also connected to the non-inverting input terminal of operational amplifier D2A via capacitor C23 and resistor R29.

[0043] Furthermore, such as Figure 1 As shown in this embodiment, the inductance detection circuit further includes an AC signal boosting circuit. The input terminal of the AC signal boosting circuit is connected to the output terminal of the filter circuit, and is used to input the filtered high-frequency AC signal into the microcontroller for frequency detection after DC blocking and boosting.

[0044] Specifically, such as Figure 5 As shown, the AC signal boosting circuit includes a proportional amplifier D2C and a voltage follower D2D. The output of the filter circuit is connected to the non-inverting inputs of the proportional amplifier D2C and the voltage follower D2D. A boosting voltage is also connected to the non-inverting inputs of the proportional amplifier D2C and the voltage follower D2D. The outputs of the proportional amplifier D2C and the voltage follower D2D are connected to the microcontroller. The AC signal boosting circuit uses an operational amplifier TL084 to boost the filtered and amplified high-frequency AC signal by 1.65V. Then, it outputs in two paths: one path is connected to the microcontroller's ADC port via the voltage follower D2D, and the other path is amplified 2.96 times by the non-inverting proportional amplifier D2C before being sent to another ADC port of the microcontroller. By processing the two paths separately and then inputting them to the microcontroller's ADC port, the microcontroller can switch to the input port of the voltage follower D2D when signal distortion occurs due to the 2.96x amplification by the non-inverting proportional amplifier D2C.

[0045] The power supply circuit includes a power chip WL2861K33 and peripheral circuitry, which converts external power supply into 3.3V to power devices such as the MCU and Schmitt inverter.

[0046] Furthermore, in this embodiment, in the power frequency metering signal conditioning circuit, the input terminal of the voltage comparator D1B is connected to a boosted voltage of 1.65V. This is obtained by dividing the 3.3V DC voltage output from the power supply circuit through resistors R11 and D12. The resulting 1.65V voltage is then input to the non-inverting input terminal of the voltage follower D1C. The signal output from the output terminal of the voltage follower D1C is the 1.65V DC boosted voltage, which can be used simultaneously by the power frequency metering signal conditioning circuit and the AC signal boosting circuit.

[0047] like Figure 7 The diagram shown is the circuit schematic of the microcontroller in this embodiment. The microcontroller is an STM32F103C8T6 with an ARM Cortex-M3 core, responsible for data acquisition, analysis, and processing. Its oscillation circuit has a normal resonant frequency of 15kHz, and the program checks for short circuit, open circuit, and rectification status every 1 second.

[0048] Short-circuit detection and judgment: The resonant circuit composed of Schmitt inverters is sensitive to changes in inductance. When a short circuit occurs on the secondary side of the primary current transformer, the internal resistance is approximately zero, and the inductance on the secondary side of the secondary transformer decreases, approaching zero. This change in inductance causes a change in the resonant frequency. The resonant signal is rectified into a square wave signal and captured by the MCU input to calculate the square wave frequency. Testing shows that if the frequency is significantly increased compared to the normal state (test data varies depending on the environment), a short circuit is considered to have occurred on the secondary side of the transformer.

[0049] Open-circuit detection: With the resonant circuit closed and the square wave injection circuit open, the injected signal is the circuit's resonant frequency. If an open circuit occurs on the secondary side of the current transformer, no sine wave signal will be generated, and the sine wave frequency detected by the MCU will decrease significantly.

[0050] Detection and judgment based on series rectifier connection: If a rectifier is connected in series to the secondary side of the primary current transformer, the signal detected by the microcontroller is a non-sinusoidal signal containing even harmonics. Without a rectifier connected in series, the signal detected by the MCU is a 50Hz sinusoidal signal boosted to 1.65V.

[0051] Furthermore, the current transformer device with loop inspection function in this embodiment also includes a housing. The power frequency inductor, the first high-frequency inductor, the second high-frequency inductor, and the peripheral circuitry are disposed within the housing. The housing is provided with a first interface and a second interface. The first interface is used to connect to the secondary side of the primary current transformer, and the second interface is used to connect the microcontroller to a host computer or terminal device. The microcontroller can connect to the host computer or terminal device via SPI communication. Simultaneously, the terminal provides ±5V power to the peripheral circuitry of the current transformer device of this invention.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A transformer device with a loop patrol function, comprising a power frequency inductor, characterized in that, Also include: The first high-frequency inductor, the second high-frequency inductor and the peripheral circuit, the peripheral circuit includes: single-chip microcomputer, power supply circuit, square wave injection circuit, inductance detection circuit and power frequency measurement signal conditioning circuit; The two ends of the first high-frequency inductor are connected to the secondary side of the primary transformer;The second high-frequency inductor forms a mutual inductor with the first high-frequency inductor; The square wave injection circuit is used to generate square wave alternating current signal under the driving of the PWM signal of the single-chip microcomputer, and the output end of the square wave injection circuit is connected with the first high-frequency inductor; The input end of the inductance detection circuit is connected with the second high-frequency inductor, and the inductance detection circuit includes capacitor C29, capacitor C31 and Schmitt trigger, the capacitor C29, capacitor C31 and Schmitt trigger form a resonance circuit with the second high-frequency inductor, and the resonance circuit is used to output resonance signal to the single-chip microcomputer; The power frequency measurement signal conditioning circuit includes non-inverting amplifier D1A, DC blocking capacitor C2 and voltage comparator D1B, the input end of the non-inverting amplifier D1A is connected with the power frequency inductor, the two ends of the power frequency inductor are connected to the secondary side of the primary transformer, the output end of the non-inverting amplifier D1A is connected with the non-inverting input end of the voltage comparator D1B through the DC blocking capacitor C2, the input end of the voltage comparator D1B is also connected with a lifting voltage, and the output end of the voltage comparator D1B is connected with the single-chip microcomputer; The single-chip microcomputer is used to judge whether the secondary side of the primary transformer is open circuit or short circuit according to the frequency of the resonance signal output by the resonance circuit;The single-chip microcomputer is also used to judge whether the secondary side of the primary transformer is connected with rectifier circuit according to the output signal of the power frequency measurement signal conditioning circuit, and the judgment method is that if the output voltage is a sinusoidal wave after lifting, it is determined that the rectifier circuit is not connected, and if the output is a non-sinusoidal signal containing even harmonic, it is determined that the rectifier circuit is connected; The square wave injection circuit includes resistor R41, resistor R42, field effect tube V7, resistor R37, field effect tube V4, field effect tube V6, resistor R38, capacitor C36, bidirectional transient suppression diode V5, capacitor C37, capacitor C40, resistor R39 and resistor R40, one end of the resistor R41 is connected with the PWM signal output by the single-chip microcomputer, the other end is connected with the gate of the field effect tube V7, the source of the field effect tube V7 is grounded, the gate is grounded through the resistor R42, and the drain is connected with the positive electrode of the power supply through the resistor R37;The gate of the field effect tube V4 and the gate of the field effect tube V6 are connected with the drain of the field effect tube V7, the source of the field effect tube V4 is connected with the positive electrode of the power supply, and the drain is connected with the drain of the field effect tube V6 through the resistor R38;The source of the field effect tube V6 is grounded, the drain is connected with one end of the bidirectional transient suppression diode V5 through the capacitor C36, the other end of the bidirectional transient suppression diode V5 is connected with the positive electrode of the power supply through the resistor R39, and is also connected with the ground through the resistor R40, the capacitor C37 is connected with the resistor R39 in parallel, and the capacitor C40 is connected with the resistor R40 in parallel.

2. The transformer device with a loop patrol function according to claim 1, characterized in that, The inductance detection circuit further comprises a filter circuit, and the filter circuit comprises a high-pass filter and a low-pass filter; The single-chip microcomputer is further configured to control the frequency of the PWM signal, so that the signal amplitude of the resonance circuit reaches the maximum, and the resonance signal output by the resonance circuit is sequentially filtered by the high-pass filter and the low-pass filter, and then a high-frequency alternating-current signal is obtained and input into the single-chip microcomputer to detect the frequency.

3. The transformer device with a loop patrol function according to claim 2, characterized in that, The cut-off frequency of the high-pass filter is 4.78K, and the cut-off frequency of the low-pass filter is 17.6K.

4. The transformer device with a loop patrol function according to claim 2, characterized in that, The high-pass filter comprises an operational amplifier D2A, resistors R23, R27, R30, R31, a capacitor C22 and a capacitor C23, one end of the capacitor C22 is connected to the output end of the resonance circuit, the other end is connected to the non-inverting input end of the operational amplifier D2A through the capacitor C23, the inverting input end of the operational amplifier D2A is grounded through the resistor R27, the non-inverting input end is grounded through the resistor R30, the output end is connected to the inverting input end through the resistor R23, and the output end is connected to the non-inverting input end through the resistor R31 and the capacitor C23. The low-pass filter comprises a resistor R28, a resistor R29, a resistor R25, a resistor R22, an operational amplifier D2B, a capacitor C27 and a capacitor C28, one end of the resistor R28 is connected to the output end of the operational amplifier D2A, the other end is connected to the non-inverting input end of the operational amplifier D2B through the resistor R29, the non-inverting input end of the operational amplifier D2B is grounded through the capacitor C27, the inverting input end is grounded through the resistor R25, the output end is connected to the non-inverting input end of the operational amplifier D2A through the resistor R22, and the output end is further connected to the non-inverting input end of the operational amplifier D2A through the capacitor C23 and the resistor R29.

5. The transformer device with a loop patrol function according to claim 2, characterized in that, The inductance detection circuit further comprises an alternating-current signal lifting circuit, an input end of the alternating-current signal lifting circuit is connected to an output end of the filter circuit, and the alternating-current signal lifting circuit is configured to input the filtered high-frequency alternating-current signal after direct-current isolation and voltage lifting into the single-chip microcomputer to detect the frequency.

6. The transformer device with a loop patrol function according to claim 5, characterized in that, The alternating-current signal lifting circuit comprises a proportional amplifier D2C and a voltage follower D2D, the output end of the filter circuit is connected to the non-inverting input end of the proportional amplifier D2C and the voltage follower D2D, the non-inverting input end of the proportional amplifier D2C and the voltage follower D2D is further connected to a lifting voltage, and the output end of the proportional amplifier D2C and the voltage follower D2D is connected to the single-chip microcomputer.

7. The transformer device with a loop patrol function according to claim 1, characterized in that, The power supply circuit comprises a power supply chip and a peripheral circuit, and is configured to convert external power supply into 3.3V to supply power to the MCU and the Schmitt inverter device.

8. The transformer device with a loop patrol function according to claim 1, characterized in that, In the power frequency measurement signal conditioning circuit, the input end of the voltage comparator D1B is connected to a lifting voltage of 1.65V.

9. The transformer device with a loop patrol function according to claim 1, characterized in that, Further, a shell is provided, the power frequency inductor, the first high-frequency inductor, the second high-frequency inductor and the peripheral circuit are arranged in the shell, the shell is provided with a first interface and a second interface, the first interface is configured to be connected to the secondary side of the primary mutual inductor, and the second interface is configured to realize the connection between the single-chip microcomputer and the upper computer.

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