Insulator leakage current digitizing sampling transformer

Abstract

The application relates to an insulator leakage current digitized sampling mutual inductor, belonging to the technical field of current mutual inductors. The sampled insulator leakage current is converted into a digital signal in the mutual inductor and is output. Active Hall devices are used to make the mutual inductor work in a zero magnetic flux state, and the sampling of the insulator leakage current is realized. A TIA transimpedance amplifier is used to realize accurate sampling of the insulator leakage current. A programmable TIA transimpedance amplifier is used to realize adjustment of the amplification ratio of the TIA transimpedance amplifier, and then accurate analog-digital conversion of a single ADC is realized, and the conversion of the analog signal into the digital signal is completed. The application solves the problem that the traditional analog voltage signal transmission is easy to be disturbed, and according to the state control of the amplification ratio of the programmable TIA transimpedance amplifier according to the size of the insulator leakage current, accurate sampling sampling from tens of microamperes to tens of milliamperes is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of current transformers, and particularly relates to an insulator leakage current digitized sampling transformer. BACKGROUND

[0002] Pollution flashover refers to a discharge phenomenon that when a solid, liquid or gaseous conductive substance is attached to the surface of an insulator string, the insulator surface is wetted by fog, dew, drizzle or ice (snow) and the like, the pollution layer on the surface of the insulator is wetted, the electric conductance is increased, the leakage current is increased, and a local arc is generated under the operating voltage to develop into a surface flashover. The surface leakage current of the insulator is one of important characteristic quantities for evaluating the pollution flashover of the insulator.

[0003] For insulators in coastal areas, the surface leakage current of the insulator is a main technical means for monitoring the change in pollution accumulation. At present, the insulator leakage current sampling technology usually adopts methods such as resistance sampling, metal sampling ring and current transformer. The existing sampling technology adopts a weak analog signal quantity transmission method to transmit the sampled signal to an online monitoring device for collection, analysis and processing. However, in a high-voltage power transmission environment, the analog signal is often disturbed by a high-voltage electric field, which reduces the accuracy of measurement, and the disturbance quantity is greatly affected by the humidity of the environment and is difficult to shield.

[0004] In addition, most of the existing Hall current transformers adopt resistance sampling, and a high-impedance sampling resistor is required when measuring a microampere-level small current. The high-impedance resistor brings more resistance noise, and it is difficult to achieve accurate sampling of a small current.

[0005] In addition, the size of the insulator leakage current is greatly affected by the state of the insulator and the working environment, and the insulator leakage current is distributed in the range of tens of microamperes to tens of milliamperes. At present, it is difficult to accurately perform analog-to-digital conversion using a single ADC for a signal with such a high dynamic range, and therefore most of the existing disclosed digital current transformers are designed to adopt a scheme of selecting a signal through digital judgment after sampling by multiple amplifiers and multiple ADCs, which is difficult to achieve low-power operation. SUMMARY

[0006] The application aims to solve the problem of reliable anti-interference sampling of the insulator leakage current, and provides an insulator leakage current digitized sampling transformer.

[0007] To achieve the above-mentioned purpose, the technical scheme of the application is as follows: an insulator leakage current digitized sampling transformer, which converts and outputs an analog signal to a digital signal for the sampled insulator leakage current in the transformer.

[0008] In an embodiment of the application, the transformer works in a zero-flux state based on an active Hall device to achieve sampling of the insulator leakage current.

[0009] In an embodiment of the present application, a TIA trans-impedance amplifier is used to accurately sample the leakage current of the insulator.

[0010] In an embodiment of the present application, a programmable TIA trans-impedance amplifier is used to adjust the amplification ratio of the TIA trans-impedance amplifier, so as to accurately perform analog-digital conversion by a single ADC and complete the conversion of the analog signal into the digital signal.

[0011] In an embodiment of the present application, the transformer comprises a Hall device H1, a differential input stage amplifier, an amplifier, a voltage follower, and a TL1 compensation coil wound on a magnetic core. The active Hall device is used to make the transformer work in a zero-flux state, and the specific implementation of sampling the leakage current of the insulator is as follows: the differential voltage signal output by the Hall device H1 is amplified by the input stage amplifier to output a single-ended voltage signal, and then the single-ended voltage signal is amplified by the amplifier and then driven by the voltage follower to drive the TL1 compensation coil. A current signal with the same amplitude and opposite phase to the leakage current Ip of the insulator is generated in the TL1 compensation coil, so that the transformer works in a zero-flux state. The size of the leakage current Ip of the insulator can be obtained by detecting the current in the TL1 compensation coil.

[0012] In an embodiment of the present application, a TIA trans-impedance amplifier is used to accurately sample the leakage current of the insulator, i.e., a zero-offset voltage TIA trans-impedance amplifier composed of a TIA trans-impedance amplifier and a TIA trans-impedance amplifier offset voltage feedback compensation circuit is used to detect the current in the TL1 compensation coil.

[0013] In an embodiment of the present application, the specific implementation of detecting the current in the TL1 compensation coil by using the TIA trans-impedance amplifier is as follows: according to the principle of virtual short of the input of the operational amplifier, the voltage at the reverse input end and the in-phase input end of the TIA trans-impedance amplifier is zero, i.e., the impedance at the reverse input end and the in-phase input end is zero. The current in the TL1 compensation coil is input through the reverse input end of the TIA trans-impedance amplifier and output through the in-phase input end of the TIA trans-impedance amplifier, and then the closed current loop is realized by grounding through the first resistor, so as to sample the current in the TL1 compensation coil in a state close to zero impedance. The output voltage of the TIA trans-impedance amplifier is input into the TIA trans-impedance amplifier offset voltage feedback compensation circuit through the second resistor, amplified by the TIA trans-impedance amplifier offset voltage feedback compensation circuit, and then fed back to the in-phase input end of the TIA trans-impedance amplifier through the third resistor and the first resistor, so as to compensate for the offset voltage of the TIA trans-impedance amplifier, thereby realizing the design of the zero-offset voltage TIA trans-impedance amplifier. The output voltage Vo of the TIA trans-impedance amplifier is I TL1 *Rf, I TL1 TL1 compensation coil, and Rf is the feedback resistance of the TIA trans-impedance amplifier.

[0014] In an embodiment of the present application, the amplification ratio of the TIA trans-impedance amplifier is adjusted by adjusting the value of the feedback resistance of the TIA trans-impedance amplifier.

[0015] In an embodiment of the present application, the TIA trans-impedance amplifier feedback resistance comprises a fourth resistance, a fifth resistance, a sixth resistance, a seventh resistance, an eighth resistance, a ninth resistance, and an analog switch; and the specific implementation of adjusting the value of the TIA trans-impedance amplifier feedback resistance is: controlling the fourth resistance, the fifth resistance, the sixth resistance, the seventh resistance, the eighth resistance, and the ninth resistance to be connected in series / parallel in different combinations by the analog switch to form different values of the TIA trans-impedance amplifier feedback resistance.

[0016] In an embodiment of the present application, the TIA trans-impedance amplifier output is driven by a tenth resistance and a second voltage follower to an ADC analog-to-digital converter for analog-to-digital conversion output.

[0017] Compared with the prior art, the present application has the following beneficial effects: the present application can solve the problem that the traditional analog voltage signal transmission is susceptible to interference, proposes to realize zero-flux Hall current detection based on an active Hall device, and adopts a TIA trans-impedance amplifier to realize the pickup of the TL1 compensation coil current, which can realize accurate sampling of weak current, and at the same time, according to the state of the insulator leakage current size, the amplification of the programmable TIA trans-impedance amplifier is controlled to obtain accurate sampling in the range of tens of microamperes to tens of milliamperes, and since the programmable TIA trans-impedance amplifier is adopted, only a single ADC is needed to realize analog-to-digital conversion, and low power consumption of the transformer is realized. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The present application is an insulator leakage current digitizing sampling transformer and an online monitoring logic diagram.

[0019] Figure 2 The present application is a digitizing sampling transformer schematic diagram. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be specifically described below with reference to the accompanying drawings.

[0021] The present application provides an insulator leakage current digitizing sampling transformer, which converts and outputs analog signals to digital signals in the transformer for the sampled insulator leakage current. Specifically, the transformer works in a zero-flux state based on an active Hall device, and a TIA trans-impedance amplifier is adopted to realize accurate sampling of the insulator leakage current. At the same time, a programmable TIA trans-impedance amplifier is adopted to adjust the amplification of the TIA trans-impedance amplifier, and then a single ADC is realized for accurate analog-to-digital conversion, and the conversion and output of analog signals to digital signals are completed.

[0022] The following is a specific implementation example of the present application.

[0023] As Figure 1As shown, the digital sampling transformer for insulator leakage current samples the insulator leakage current and converts it into a digital signal, which is then connected to an online monitoring device for insulator leakage current via a digital bus. The analog-to-digital signal conversion is completed within the transformer, while the external connection cable performs digital data transmission and exchange according to a predetermined protocol. It exhibits strong resistance to high-voltage electric field interference, is unaffected by high-voltage electric field interference, and is stable and reliable.

[0024] like Figure 2 The schematic diagram of a digital sampling current transformer is shown. The leakage current Ip from the insulator passes through the conductor in the magnetic core, generating a magnetic field on the conductor. This magnetic field is concentrated by the magnetic core and induced in an active Hall element H1. The Hall element H1 outputs a differential voltage signal proportional to the magnitude of the magnetic field. The magnitude of the magnetic field in the core is determined by the current Ip; that is, the amplitude of the differential voltage output by the Hall element H1 is proportional to the amplitude of the current Ip. Current transformers are based on the principle of electromagnetic induction; therefore, the presence of magnetic flux in the core is a prerequisite for the operation of the current transformer. To establish magnetic flux in the core, an excitation current is required. The excitation current is the main source of transformer error and a prerequisite for the minimum sampleable current. In practical engineering, the leakage current of insulators can be as low as tens of microamperes, making it difficult to accurately sample such small and weak currents using conventional methods. This invention proposes a zero-magnetic-flux operating state in the core. In this zero-flux state, no excitation current is needed, thereby eliminating the influence of the excitation current on measurement errors and solving the feasibility of sampling microampere currents from insulators. The differential voltage signal output by Hall element H1 is amplified into a single-ended voltage signal by differential input amplifier U2A, then amplified by amplifier U2B, and finally driven by voltage follower U3A to drive compensation coil TL1. This generates a current signal in TL1 with the same amplitude but opposite phase to Ip. TL1 is wound on a magnetic core. According to the principle of electromagnetic induction, the current in TL1 generates a magnetic field that concentrates in the core, and this magnetic field has the same amplitude but opposite phase as the magnetic field generated by the Ip current, thus keeping the transformer operating in a zero-flux state. Even a slight increase or decrease in the insulator leakage current Ip will cause an increase or decrease in the magnetic flux in the core, thus disrupting the zero-flux state. Simultaneously, Hall element H1 synchronously increases or decreases its differential output voltage, outputting more or less zero-flux compensation current through U2A, U2B, and U3A to maintain the zero-flux state in the core. Therefore, the magnitude of the insulator leakage current Ip can be obtained simply by detecting the current in TL1 compensation coil.

[0025] The existing design all adopts the sampling resistance in series in the TL1 compensation coil loop to realize the current pick-up. The high impedance sampling resistance is needed when measuring the microampere small current, the high impedance resistance brings more resistance noise and the driving ability requirement of U3A is higher, which is more difficult to realize the accurate sampling work of small current. The TIA trans-impedance amplifier is adopted to realize the pick-up work of TL1 compensation coil current in the application, U4 and U5 constitute the zero offset voltage TIA trans-impedance amplifier. U5 is designed as the TIA trans-impedance amplifier, according to the input virtual short principle of the operational amplifier, the voltage of the reverse input end and the in-phase input end of U5 is zero, that is, the impedance of the reverse input end and the in-phase input end is zero, the TL1 compensation coil current is input through the reverse input end of U5 and output through the in-phase input end of U5, then the closed current loop is grounded through R17, so that the TL1 compensation coil current is sampled in the state close to zero impedance. U4 is the TIA trans-impedance amplifier offset voltage feedback compensation, the offset voltage in the output voltage of U5 will affect the sampling circuit in the later stage, the output voltage of U5 is input to U4 through R16 to amplify the offset voltage, and the offset voltage is fed back to the in-phase input end of U5 through R15 and R17 to compensate the offset voltage of U5, so as to realize the zero offset voltage trans-impedance amplifier design. The feedback resistance of the TIA trans-impedance amplifier is Rf, the output voltage Vo of the TIA trans-impedance amplifier is I TL1 *Rf.

[0026] The size of the insulator leakage current is greatly influenced by the insulator state and working environment, and the distribution thereof is in the range of tens of microamperes to tens of milliamperes. At present, it is difficult to accurately perform analog-digital conversion work on the signal with such a high dynamic ratio range by using a single ADC, and most of the existing designs adopt a scheme of selecting the signal by digital judgment after sampling by multiple sets of amplifiers and multiple sets of ADCs. In actual engineering applications, the current transformer needs to work with low power consumption, and the existing scheme is difficult to realize low power consumption work. The programmable TIA transimpedance amplifier is designed to realize low power consumption and high dynamic single ADC accurate analog-digital conversion work. The TIA transimpedance amplifier Rf is realized by resistors R22, R23, R24, R25, R26 and R27, and an analog switch U8. The analog switch U8A, U8B and U8C are controlled by IN1, IN2 and IN3 input signals respectively. When the input signal is a logic low signal, the SxA end and the Dx end of the analog switch are disconnected, and the SxB end and the Dx end are turned on. When the input signal is a logic high signal, the SxA end and the Dx end of the analog switch are connected, and the SxB end and the Dx end are disconnected. The control port of the U8 analog switch is controlled by the controller, and U8A, U8B and U8C are in different states according to the control signal, so that resistors R22, R23, R24, R25, R26 and R27 are connected in series to form feedback resistors Rf with different values. In the example, the feedback resistors Rf have four values, and the amplification ratio of the TIA transimpedance amplifier can be realized. In particular, the number of resistors and the number of analog switches can be reduced or increased in the protection of the application, and the U8A analog switch can also be controlled by a bus (such as SPI, IIC, etc.) to control the state of the analog switch.

[0027] The output voltage signal of the TIA transimpedance amplifier is driven by the R18 and U3B voltage follower to drive the U6 ADC analog-digital converter to perform analog-digital conversion work. Thus, the insulator leakage current digitizing sampling transformer completes the sampling and numerical sampling conversion work of the insulator leakage current, and is connected to the online monitoring system through the digital communication bus, thereby solving the problem that the traditional analog voltage signal transmission is easily disturbed. The insulator leakage current monitoring device controls the sampling and numerical sampling of the transformer to obtain the size of the insulator leakage current, and controls the amplification ratio of the programmable TIA transimpedance amplifier according to the state of the current size to obtain accurate sampling in the range of tens of microamperes to tens of milliamperes.

[0028] The above is the preferred embodiment of the application, and any changes made according to the technical solutions of the application, as long as the generated function does not exceed the scope of the technical solutions of the application, belong to the protection scope of the application.

Claims

1. A digital sampling current transformer for insulator leakage current, characterized in that, The sampled insulator leakage current is converted from an analog signal to a digital signal within the current transformer. The current transformer includes a Hall device H1, a differential input stage amplifier, an amplifier, a voltage follower, and a TL1 compensation coil wound on a magnetic core. Based on the active Hall device, the current transformer operates in a zero-flux state. The specific implementation method for sampling the insulator leakage current is as follows: the differential voltage signal output by the Hall device H1 is amplified by the input stage amplifier into a single-ended voltage signal, and then amplified again by the amplifier before driving the TL1 compensation coil through the voltage follower. A current signal with the same amplitude but opposite phase to the insulator leakage current Ip is generated in the TL1 compensation coil, so that the current transformer operates in a zero-flux state. The magnitude of the insulator leakage current Ip can be obtained by detecting the current in the TL1 compensation coil.

2. The digital sampling transformer for insulator leakage current according to claim 1, characterized in that, A TIA transimpedance amplifier is used to achieve accurate sampling of insulator leakage current.

3. The digital sampling transformer for insulator leakage current according to claim 1, characterized in that, A programmable TIA transimpedance amplifier is used to adjust the amplification factor of the TIA transimpedance amplifier.

4. The digital sampling transformer for insulator leakage current according to claim 1, characterized in that, A TIA transimpedance amplifier is used to accurately sample the leakage current of the insulator. Specifically, a zero offset voltage TIA transimpedance amplifier, consisting of a TIA transimpedance amplifier and a TIA transimpedance amplifier offset voltage feedback compensation circuit, is used to detect the current in the TL1 compensation coil.

5. A digital sampling transformer for insulator leakage current according to claim 4, characterized in that, The specific implementation of using a TIA transimpedance amplifier to detect the current in the TL1 compensation coil is as follows: Based on the principle of virtual short at the operational amplifier input, the voltage between the inverting and non-inverting input terminals of the TIA transimpedance amplifier is zero, meaning the impedance between the inverting and non-inverting input terminals is zero. The current in the TL1 compensation coil is input through the inverting input terminal of the TIA transimpedance amplifier, output through the non-inverting input terminal, and then grounded through the first resistor to close the current loop. The output voltage of the TIA transimpedance amplifier is input through the second resistor to the TIA transimpedance amplifier offset voltage feedback compensation circuit for offset voltage amplification. The voltage is then fed back to the non-inverting input terminal of the TIA transimpedance amplifier via a voltage divider formed by the third and first resistors to compensate for the offset voltage of the TIA transimpedance amplifier, thus achieving the design of a zero-offset voltage TIA transimpedance amplifier. The output voltage Vo of the TIA transimpedance amplifier is I... TL1 *Rf,I TL1 Rf is the current in the TL1 compensation coil, and Rf is the feedback resistor of the TIA transimpedance amplifier.

6. A digital sampling transformer for insulator leakage current according to claim 5, characterized in that, The amplification factor of the TIA transimpedance amplifier can be adjusted by changing the value of the feedback resistor.

7. A digital sampling transformer for insulator leakage current according to claim 6, characterized in that, The TIA transimpedance amplifier feedback resistor includes a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, and an analog switch. The specific implementation method for adjusting the value of the TIA transimpedance amplifier feedback resistor is as follows: the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor, the eighth resistor, and the ninth resistor are controlled by the analog switch to be connected in series / parallel in different combinations to form different values ​​of the TIA transimpedance amplifier feedback resistor.

8. A digital sampling transformer for insulator leakage current according to claim 5, characterized in that, The TIA transimpedance amplifier output drives the ADC analog-to-digital converter via the tenth resistor and the second voltage follower to convert the analog signal to a digital signal.

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