CN114062761B - Transformer grounding wire AC and DC component detection device - Google Patents

Abstract

The present invention relates to a transformer grounding line AC and DC component detection device, including a current sensor, a collector, and a display terminal. The current sensor includes a plurality of TMR magnetic sensitive current sensors, and the TMR magnetic sensitive current sensor array is installed in a protective housing; the collector includes a sampling circuit, a main control unit, and an edge computing terminal. The TMR magnetic sensitive current sensor is electrically connected to the input end of the sampling circuit, and the output end of the sampling circuit is electrically connected to the input end of the main control unit, and the main control unit is respectively connected to the edge computing terminal and the display terminal. A plurality of TMR magnetic sensitive current sensors realize the measurement of AC and DC components, high-order harmonics, and bias magnetic signals. The TMR magnetic sensitive current sensor solves the problem of low parameter monitoring accuracy of conventional current sensors.

Description

Transformer grounding wire AC and DC component detection device

Technical Field

The invention relates to the technical field of measuring AC and DC components of transformer grounding wires, and in particular to a device for detecting AC and DC components of transformer grounding wires.

Background Art

At present, electromagnetic induction coils and Hall sensors are used to monitor the AC and DC conditions at the transformer grounding wire. For example, patent document CN 205015382U discloses a transformer neutral point DC component detection device. However, they have complex structures, high power consumption, and high field failure rates. On the one hand, engineering applications are complex and the operation and maintenance workload is large. On the other hand, Hall sensors have low accuracy and poor interchangeability in applications. Signals change with temperature, nonlinear output, and other reasons result in low accuracy in monitoring parameters such as AC, DC, and harmonics. The above problems are not conducive to the lean management requirements of equipment.

Summary of the invention

The object of the present invention is to provide a device for detecting AC and DC components of a transformer grounding line, so as to detect the AC and DC components of the transformer grounding line.

The technical solution of the present invention is:

A transformer grounding line AC and DC component detection device comprises a current sensor, a collector, and a display terminal, wherein the current sensor comprises a plurality of TMR magnetic-sensitive current sensors, and the TMR magnetic-sensitive current sensors are array-mounted in a protective housing; the collector comprises a sampling circuit, a main control unit, and an edge computing terminal, wherein the TMR magnetic-sensitive current sensor is electrically connected to an input end of the sampling circuit, and an output end of the sampling circuit is electrically connected to an input end of the main control unit, and the main control unit is respectively connected to the edge computing terminal and the display terminal.

Preferably, the collector also includes a power module and an on-site display screen, the sampling circuit is arranged in the analog data receiving module, the edge computing terminal has a built-in database, the main control unit is electrically connected to the on-site display screen, and the power module supplies power to the current sensor, the main control unit, the analog data receiving module, the edge computing terminal, and the on-site display screen.

Preferably, the display terminal includes at least one of a mobile phone, an IPAD and a computer.

Preferably, the protective shell is made of insulating flame-retardant material, and is composed of two half shells. A through hole is provided at the connection between the two half shells to facilitate open-type installation on the transformer grounding wire. Two magnetic shielding half rings, an insulating half ring, a magnetic sensor chip and a double-layer magnetic tunnel junction MTJ are provided in the protective shell.

Preferably, the main control unit is electrically connected to the computer via an RJ45 interface bus.

Preferably, the edge computing terminal has built-in Kalman filtering algorithm, Fourier transform and wavelet analysis algorithm, uses the Kalman filtering algorithm to filter the magnetic induction current, uses the wavelet packet transform to decompose the filtered magnetic induction current into a low-frequency approximate part and a high-frequency detail part, uses the wavelet packet transform to analyze the high-frequency detail part to obtain the characteristic information of the transient component; uses the Blackman window interpolation algorithm to analyze the low-frequency approximate part to obtain the frequency and amplitude of the steady-state component.

The beneficial effects of the present invention are:

1.TMR magnetic current sensor can be used to measure AC/DC components, high-order harmonics, and bias magnetic signals. When in use, one TMR magnetic current sensor is used to measure AC/DC components, high-order harmonics or bias magnetic signals, and multiple TMR magnetic current sensors can measure AC/DC components, high-order harmonics and bias magnetic signals. TMR magnetic current sensor solves the problems of low accuracy, poor interchangeability, signal changes with temperature, nonlinear output, etc. in conventional current sensor applications, which cause low accuracy in monitoring parameters such as AC/DC and harmonics.

2. The small current detection method using open-type installation can better meet the needs of field occasions, but it also loses the sampling resolution and accuracy, and inevitably increases the error and temperature drift and other adverse changes; the general structure of the magnetic tunnel junction MTJ is a sandwich structure of ferromagnetic layer/non-magnetic insulating layer/ferromagnetic layer. In order to solve the adverse effects of open-type installation, a double-layer magnetic tunnel junction is used to increase the magnetoresistance change rate.

3. Kalman filter algorithm can avoid the tedious solution of nonlinear equations and has relatively reliable measurement accuracy. In the harmonic detection of the transformer grounding copper bar, Fourier transform can obtain the harmonic order and amplitude of the measured current. This method improves the efficiency of calculation and has the advantages of high accuracy and simple operation, but it cannot be applied to the analysis of harmonic signals in the time domain and is mostly used for the detection of steady-state signals; wavelet analysis can project high-order harmonics in the power system to different scales, and can collect the time domain signal and frequency domain signal of the current at the same time, which makes up for the shortcomings of Fourier transform. The combination of the two can comprehensively and effectively analyze harmonic signals and improve the real-time and accuracy of current acquisition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a structural block diagram of a device for detecting AC and DC components of a transformer grounding line.

FIG2 is a schematic diagram of the structure of a TMR magnetic sensitive current sensor.

Explanation of the reference numerals: 1 - current sensor, 2 - collector, 3 - display terminal, 4 - protective housing, 5 - through hole, 6 - screw through hole, 7 - wiring terminal.

DETAILED DESCRIPTION

The present invention is described in the form of embodiments in conjunction with the accompanying drawings to assist those skilled in the art in understanding and implementing the present invention. Unless otherwise specified, the following embodiments and the technical terms therein should not be understood without departing from the technical knowledge background of the technical field.

Embodiment 1: A transformer grounding wire AC and DC component detection device, see Figure 1, includes a current sensor 1, a collector 2 and a display terminal 3, the current sensor 1 adopts a TMR magnetic sensitive current sensor; the collector 2 includes a main control unit, a power module, an analog data receiving module, an edge computing terminal, a database, and an on-site display screen; the display terminal 3 includes a mobile phone, an IPAD, and a computer.

Referring to FIG. 2 , the protective shell 4 of the current sensor 1 is a flame-retardant insulating material, such as epoxy resin, which has insulating and high temperature resistant properties to protect the internal components. The protective shell 4 is composed of two halves of the shell, and a through hole 5 is provided at the connection between the two halves of the shell to facilitate open installation on the transformer grounding wire. Such a current sensor is suitable for measuring various styles of transformer grounding wires, solving the problem that the transformer grounding wire cannot be disassembled. Two magnetic shielding half rings, an insulating half ring, a magnetic sensor chip and a double-layer magnetic tunnel junction MTJ are arranged inside the protective shell 4.

The current sensor 1 uses a TMR magnetic current sensor. Multiple current sensors 1 are arranged in an array and fixed on the transformer ground wire. Different current sensors are used to collect AC and DC components, high-order harmonics, and bias magnetic signals. The current sensor 1 is powered by a collector power module.

The analog data receiving module of the collector 2 receives the AC and DC components, high-order harmonics, and bias magnetic signals of the current sensor 1; the edge computing terminal has built-in Kalman filtering algorithm, Fourier transform algorithm, and wavelet analysis algorithm to process current data; the database includes historical current data, real-time current sampling data, basic information data, and expert database; the measured current data and database information are displayed on the local display screen; the terminal 7 is used to power the TMR magnetic sensitive current sensor and transmit real-time data to the display terminal 3. At the same time, the algorithm can be selected on the computer to match the collected measurement signal, so that the current data at multiple locations can be monitored, which is convenient for the staff to monitor the transformer wiring in real time and eliminate faults in time.

The method of Tmr to detect AC and DC is: Tmr current sensor can detect AC and DC signals, is powered by 5V, has an output range of 0.5V-4.5V, and a zero-point bias voltage of 2.5V, that is, an output of 2.5V is 0A, 0.5-2.5V represents reverse current, and 2.5V-4.5 represents forward current. If the output signal is between 0.5-4.5v, it is AC, and if it only appears at 0.5-2.5v or 2.5-4.5v, it is DC.

The Kalman filter algorithm is a recursive filtering algorithm. The specific method is to establish a known system model and statistically analyze the noise characteristics. By estimating and correcting the signal of the current acquisition module, the optimal linear estimation is solved under the condition of minimum mean square error. Recursive filtering is to estimate the current value in real time based on the previous estimated value and the last observed variable value, in conjunction with the state equation and variance matrix. The Kalman filter algorithm can avoid the tedious solution of nonlinear equations and has a more reliable measurement accuracy.

The Kalman filter algorithm is an algorithm that uses a recursive method to reduce the impact of noise. The magnetic induction current is the current output by the TMR magnetic sensitive current sensor. The Kalman filter algorithm is used to filter the magnetic induction current. First, the system state equation and measurement equation formula are established:

_xn ＝ _{Φnxn -1} + _wn

z _n =H _n x _n +v _n

In the formula, Φ _n and H _n represent the coefficients of the equation, x _n is the state of the scalar system, and z _n is the observed variable value of the state x _n including the noise v _n . The estimation formulas for the state value and covariance, as well as the Kalman filter gain are as follows:

x _n|n-1 =Φ _n x _n|n

Where w _n is a Gaussian white noise with a mean of 0 and a variance of Q _n-1 ; v _n is a Gaussian white noise with a mean of 0 and a variance of R _n ; K _n is the Kalman filter gain; and P _n|n-1 is the error covariance.

The filtered magnetic induction signal is decomposed into a low-frequency approximate part and a high-frequency detail part by wavelet packet transform. The transient component is contained in the high-frequency detail part, and each sub-steady-state component is in the low-frequency approximate part. The high-frequency detail part is analyzed by wavelet packet transform to obtain the characteristic information of the transient component. The decomposed steady-state component is analyzed by adding Blackman window interpolation algorithm to obtain the frequency and amplitude of the steady-state component.

Fourier transform can obtain the harmonic order and amplitude of the measured current in the harmonic detection of the transformer grounding copper bar. This method improves the efficiency of calculation and has the advantages of high precision and simple operation, but it cannot be applied to the analysis of harmonic signals in the time domain and is mostly used for the detection of steady-state signals. Wavelet analysis can project high-order harmonics in the power system to different scales and can collect the time domain signal and frequency domain signal of the current at the same time, which makes up for the shortcomings of Fourier transform. The combination of the two can comprehensively and effectively analyze harmonic signals and improve the real-time and accuracy of current acquisition.

When in use, the TMR magnetic current sensor uses the tunnel magnetoresistance effect to obtain the primary current data. Different from the Hall sensor and other products widely used on the market, the TMR magnetic current sensor has significant advantages in sensitivity, resolution, power consumption, and temperature characteristics. To ensure the accuracy of the measured current data, its shell is made of flame-retardant material such as epoxy resin, one side is placed on the inside of the transformer grounding wire, and the other side is placed on the outside, and the screws are tightened to fix it on the transformer grounding wire through the hole. In this way, multiple sensors are placed according to the operation rules to realize the array layout. The power module and analog receiving module of the collector 2 are connected through the wiring terminal, and the sensors at different positions are sequenced and named on the display terminal 3, and the corresponding algorithms are selected to collect different current data. The obtained current data is improved by the Kalman filter algorithm, Fourier and wavelet analysis algorithm built into the edge computing terminal to improve the accuracy and more accurate data analysis, and the current data and related data analysis are displayed on the local display screen, and will also be stored in the historical database. The analysis data can be generated through the display terminal 3, which is convenient for judging the possibility of future faults, further improving the protection capability, and also conducive to real-time monitoring by the staff, timely detection and troubleshooting.

The present invention is described in detail above with reference to the accompanying drawings and embodiments. It should be understood that it is impossible to describe all possible implementation methods in practice, and the inventive concept of the present invention is described as much as possible by way of example. Without departing from the inventive concept of the present invention and without creative work, the technical personnel in this technical field make selections and combinations of the technical features in the above embodiments, make experimental changes to the specific parameters, or use the prior art in this technical field to conventionally replace the disclosed technical means of the present invention to form specific embodiments, which should all belong to the implicit disclosure of the present invention.

Claims (5)

1. A transformer grounding line AC and DC component detection device, characterized in that it includes a current sensor, a collector and a display terminal, the current sensor includes a plurality of TMR magnetic sensitive current sensors, the TMR magnetic sensitive current sensors are array-mounted in a protective housing, and AC and DC components, high-order harmonics, and bias magnetic signals are respectively collected by different current sensors; the collector includes a sampling circuit, a main control unit and an edge computing terminal, the TMR magnetic sensitive current sensor is electrically connected to the input end of the sampling circuit, the output end of the sampling circuit is electrically connected to the input end of the main control unit, and the main control unit is respectively connected to the edge computing terminal and the display terminal; The edge computing terminal has built-in Kalman filtering algorithm, Fourier transform and wavelet analysis algorithm. The Kalman filtering algorithm is used to filter the magnetic induction current, and the filtered magnetic induction current is decomposed into a low-frequency approximate part and a high-frequency detail part using wavelet packet transform. The high-frequency detail part is analyzed using wavelet packet transform to obtain characteristic information of the transient component; the low-frequency approximate part is analyzed using the Blackman window interpolation algorithm to obtain the frequency and amplitude of the steady-state component. 2. The transformer grounding wire AC and DC component detection device as described in claim 1 is characterized in that the collector also includes a power supply module and an on-site display screen, the sampling circuit is arranged in the analog data receiving module, the edge computing terminal has a built-in database, the main control unit is electrically connected to the on-site display screen, and the power supply module supplies power to the current sensor, the main control unit, the analog data receiving module, the edge computing terminal, and the on-site display screen. 3. The transformer grounding line AC and DC component detection device according to claim 1, characterized in that the display terminal comprises at least one of a mobile phone, an IPAD and a computer. 4. The transformer grounding line AC and DC component detection device according to claim 3, characterized in that the main control unit is electrically connected to the computer via an RJ45 interface bus. 5. The transformer grounding wire AC and DC component detection device as described in claim 1 is characterized in that the protective shell is made of insulating flame-retardant material, the protective shell is composed of two half shells, a through hole is provided at the connection between the two half shells to facilitate open-type installation on the transformer grounding wire, and two magnetic shielding half rings, an insulating half ring, a magnetic sensor chip and a double-layer magnetic tunnel junction MTJ are arranged in the protective shell.