Method for detecting a topological structure of a grounding grid under extremely cold condition

A method capable of detecting a topological structure of a grounding grid in extremely cold conditions below minus 40 degrees Celsius, comprising following steps:

• Step 1, which comprises in a substation in an extremely cold area, determining a measuring area(S) on a ground surface of a grounding grid according to positions of branches and nodes of the grounding grid in a selected area, acquiring dynamic current values of the branches and the nodes through a current sensor based on tunnel magnetoresistance (TMR), and indirectly acquiring, through conversion, a magnetic induction intensity of the measuring area(S), which comprises a magnetic induction intensity Bz(x, y) in a direction perpendicular to the ground surface and a magnetic induction intensity By(x, y) in a direction parallel to the ground surface;
• Step 2, calculating a modulus
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• of a first derivative and a modulus
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• of a third derivative of the magnetic induction intensity Bz (x, y) in the direction perpendicular to the ground surface and a modulus
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• of a second derivative of the magnetic induction intensity By(x, y) in the direction parallel to the ground surface by a software processing terminal;
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• Step 3, determining specific positions and laying depths of the branches of the grounding grid in the measuring area(S) according to peak distances between main lobe peaks and side peaks between strong peaks of the moduli of all-order derivatives in Step 2;
• wherein the current sensor based on TMR tunnel magnetoresistance comprises a TMR chip measuring module, a data processing unit, a display unit, a temperature detecting unit, a control unit, a heating unit and a device housing, wherein the TMR chip measuring module generates a voltage output signal under an action of the magnetic field of the current conductor and transmits the voltage output signal to the data processing unit inside the device through a signal transmission line;
• the data processing unit processes data according to a current measuring method based on TMR tunnel magnetoresistance, and writing a corresponding microcontroller tram algorithm by using a voltage signal gain of a signal amplification module in the data processing unit, and performing denoising process by using an Fast Fourier Transform (FFT) algorithm in the program algorithm to obtain an accurate current value of the current conductor, and display the accurate current value on the display unit;
• the control unit consists of an integrated microcontroller, and is capable of working in an extremely cold temperature range below minus 40 degrees Celsius by selecting a military-level master control chip with strong low-temperature resistance, and is capable of being directly cold started, so that a main program of a core unit of the current sensor based on TMR tunnel magnetoresistance is capable of being started under the extremely cold conditions;
• during measurement, the temperature detection unit detects an internal temperature of the device and transmits a detection result to the control unit, which starts the heating unit if a value of the acquired temperature is less than a preset temperature threshold, and thereafter turns off the heating unit if the value of the temperature acquired by the temperature detection unit is greater than a preset upper temperature threshold, thus repeatedly heating to ensure that the internal temperature of the device is within a suitable range;
• wherein, the data processing ta according to a current measuring method based on TMR tunnel magnetoresistance, and writing a corresponding microcontroller program algorithm by using a voltage signal of a signal amplification module in the data processing unit, and performing denoising process by using an FFT algorithm in the program algorithm to obtain an accurate current value of the current conductor, comprises:
• the current measuring method based on TMR tunnel magnetoresistance, comprising:
• (1) measuring the output voltage of the TMR sensor, (2) filtering collected signals, (3) calculating a magnitude of retic induction Intensity according magnitude of the output voltage, (4) calculating of the current as of Biot-Savart Law based on-site size and material parameters, and writing corresponding microcontroller program algorithm based on the voltage signal gain of the signal amplification module in the data processing unit, and performing a denoising process by using the FFT algorithm in the program algorithm, specifically comprising:
• (1) reading a magnitude of the voltage output by the TMR sensor with an Analog-to-Digital Converter (ADC);
• (2) performing FFT transformation on a collected discrete signal sequence in time domain;
• (3) processing frequency spectrums resulted from the transformation, and performing zero setting on unnecessary signals to eliminate noises of a specific frequency component:
• (4) performing Inverse Fast Fourier Transform (IFFT) transformation on signals of the processed frequency spectrum to obtain filtered signals.