Method for detecting a topological structure of a grounding grid under extremely cold condition
A method for detecting a topological structure of a grounding grid under extremely cold condition, includes the following steps: in a substation in an extremely cold area, determining a measuring area S on a ground surface of a grounding grid according to the positions of branches and nodes of the grounding grid in a selected area, acquiring dynamic current values of the branches and nodes through a current sensor based on TMR tunnel magnetoresistance, and then indirectly acquiring the magnetic induction intensity of the measuring area S through conversion; calculating moduli of first to third derivatives of magnetic induction intensities; and determining specific positions and laying depths of the branches of the grounding grid according to peak distances between main lobe peaks and side peaks between strong peaks of the moduli. According to the method, the calculation amount is greatly reduced, and the detection method has strong anti-interference.
1 . 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 B z (x, y) in a direction perpendicular to the ground surface and a magnetic induction intensity B y (x, y) in a direction parallel to the ground surface;
Step 2, calculating a modulus
❘
"\[LeftBracketingBar]"
B
z
(
1
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of a first derivative and a modulus
❘
"\[LeftBracketingBar]"
B
z
(
3
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of a third derivative of the magnetic induction intensity B z (x, y) in the direction perpendicular to the ground surface and a modulus
❘
"\[LeftBracketingBar]"
B
y
(
2
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of a second derivative of the magnetic induction intensity B y (x, y) in the direction parallel to the ground surface by a software processing terminal; and
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.
2 . The method according to claim 1 , wherein Step 1 comprises:
A, selecting any of upper grounding conductors to inject a current, and leading out the current from another upper grounding conductor except the upper grounding conductor into which the current is injected, which process utilizes upper grounding conductors of the grounding grid;
B, determining a rectangular measuring area(S) on the ground surface of the grounding grid according to the positions of the branches of the selected grounding grid, wherein the measuring area(S) is located between the two upper grounding conductors respectively injected with the current and leading out the current in Step A; arranging the current sensor based on TMR tunnel magnetoresistance in the measuring area, calibrating a measuring distance between a TMR chip and a current conductor and a position in a sensitive direction of the chip accurately before a device is installed, obtaining a numerical conversion relationship between a magnitude of a magnetic field at the TMR chip and a current in the current conductor, obtaining a relationship among an output voltage of the TMR chip, a power supply voltage of the TMR chip, and a magnitude of a magnetic field in a sensitive direction of the TMR chip according to output characteristics of the chip, determining the power supply voltage of the chip by above calculation and analysis, and obtaining a relationship between the output voltage of the chip and a magnitude of the current in the current conductor; establishing a right-hand cartesian coordinate system xyz with a midpoint of the branches of the selected grounding grid as an coordinate origin, and an upward direction perpendicular to the measuring area(S) as a positive direction of z axis, wherein the branches of the selected grounding grid is on x axis, a current direction of the branches of the selected grounding grid is the same as a positive direction of x axis, x axis and y axis are parallel or perpendicular to sides of the measuring area S;
C, dividing the measuring area(S) into M×N grids, wherein boundaries of the grids are parallel or perpendicular to x axis, selecting a node P ij of the grids as a measuring point, a position coordinate corresponding to the measuring point being (x ij , y ij ), and measuring the magnetic induction intensity B z (x, y) perpendicular to the ground surface and the magnetic induction intensity B y (x, y) along a positive direction of y axis at the measuring point P ij , wherein M is a number of rows of the grids, and N is a number of columns of the grids, in which 1≤i≤M+1, and 1≤j≤N+1.
3 . The method according to claim 2 , wherein in Step B, the obtaining a numerical conversion relationship between a magnitude of a magnetic field at the TMR chip and a current in the current conductor, obtaining a relationship among an output voltage of the TMR chip, a power supply voltage of the TMR chip, and a magnitude of the magnetic field in a sensitive direction of the TMR chip according to output characteristics of the chips, determining the power supply voltage of the chip by above calculation and analysis, and obtaining a relationship between the output voltage of the chip and a magnitude of the current in the current conductor, comprise:
(1) establishing a relationship between the magnetic field and the current, in which the magnetic field generated by current-carrying conductors in space according to Biot-Savart Law is expressed as:
B
→
=
∫
d
B
→
=
∫
μ
0
I
4
π
d
l
→
×
r
→
r
3
(2) assuming that a current flows inside a long straight wire, a distance between a point P and a wire CD in space is r 0 , included angles between connecting lines between the point P and both ends of the long straight wire and the wire are θ 1 and θ 2 , respectively, and a magnetic field at the point P is expressed as:
B
=
μ
0
I
4
π
r
0
∫
θ
1
θ
2
sin
θdθ
=
μ
0
I
4
π
r
0
(
cos
θ
1
-
cos
θ
2
)
wherein, according to characteristics of the TMR sensor, an output voltage of the TMR sensor has a linear relationship with a magnitude of a surrounding magnetic field in a certain range of magnetic field intensity; when a current/flows inside the current conductor, according to a right-hand screw rule, a spiral linear magnetic field is generated around the wire, and a magnitude of the magnetic field is proportional to a magnitude of the current inside the current conductor;
(3) wherein since an output voltage of a bridge structure inside the TMR sensor has a linear relationship with a resistance of a tunnel magnetoresistance element, a change of resistance of the tunnel magnetoresistance element caused by a change of an external magnetic field caused by a change of the current of the current conductor linearly affects the output voltage of the bridge structure, so that the TMR tunnel magnetoresistance sensor is capable of measuring the current of the current conductor.
4 . The method according to claim 1 , wherein the TMR chip measuring module comprises a TMR chip and a mechanical support structure, the TMR chip measuring module is fixed at a designated position, and an included angle between the mechanical support structure and an axis of the current conductor is arbitrary; the TMR chip uses a line sensitive direction or a surface sensitive direction; the TMR chip is a tunnel magnetoresistance element, which is capable of converting a magnetic signal into an electrical signal based on magnetoresistance effect and positioning magnets with different magnetic field intensities and located in a moving p rt at differ detection distances from the TMR chip; an included angle between a sensitive direction of the TMR chip and a direction perpendicular to the axis of current conductor is arbitrary; the sensitive direction of the TMR chip is perpendicular to a direction of environmental noise magnetic field, or has an arbitrary angle with the direction of environmental noise magnetic field.
5 . The method according to claim 4 , wherein the TMR chip is a chip made of TMR tunnel magnetoresistance material, which is used to accurately measure a magnitude of a magnetic field and generate a voltage output signal in extremely cold environment; for the microcontroller is selected a low-temperature resistant military-level master control chip, which is capable of working in an extremely cold temperature range and being directly cold started.
6 . The method according to claim 1 , wherein an inner layer of the device housing of the current sensor of the TMR tunnel magnetoresistance is an insulation layer made of insulation materials, a plurality of groups of protrusions are arranged between the inner insulation layer and an outer electromagnetic shielding layer that prevents the two layers from contacting and transferring heat, and air between the inner insulation layer and the outer electromagnetic shielding layer is evacuated to form a vacuum cavity; the heating unit is in heat conduction connection with a heat conduction layer covered on an inner surface of the device housing, so that the heat conduction layer conducts heat generated by the heating unit to all parts in the device; and for the display unit is adopted a cold-proof liquid crystal display or a digital tube.
7 . The method according to claim 2 , wherein the current injected with the upper grounding conductor in Step A is a stable sinusoidal signal with a frequency of 20 to 2000 Hz and an amplitude of 0 to 10 A;
the M×N grids have an equal interval Δx in x axis direction and an equal interval Δy in y axis direction.
8 . The method according to claim 1 , wherein the side peaks of the strong peaks of the moduli of all-order derivatives in Step 3 refer to first side peaks next to main peaks; the peak distances between the main peaks and the side peaks refer to distances between peak values of the main peaks and peak values of the side peaks in a direction parallel to y axis;
the buried depths and positions of the branches of the grounding grid in the measuring area(S) in Step 3 are 0.577 times of the peak distance between the main peak and the side peak of the modulus
❘
"\[LeftBracketingBar]"
B
z
(
1
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of the first derivative of the magnetic induction intensity B z (x, y) in the direction perpendicular to the ground surface, 1.376 times of the peak distance between the main peak and the side peak of the modulus
❘
"\[LeftBracketingBar]"
B
z
(
3
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of the third derivative, and/or 1 time of the peak distance between the main peak and the side peak of the modulus
❘
"\[LeftBracketingBar]"
B
y
(
2
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of the second derivative of the magnetic induction intensity B y (x, y) in the direction parallel to the ground surface.
9 . A method for detecting a topological structure of a grounding grid, comprising:
Step 1, in a substation, 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 B z (x, y) in a direction perpendicular to the ground surface and a magnetic induction intensity B y (x, y) in a direction parallel to the ground surface;
Step 2, calculating a modulus
❘
"\[LeftBracketingBar]"
B
z
(
1
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of a first derivative and a modulus
❘
"\[LeftBracketingBar]"
B
z
(
3
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of a third derivative of the magnetic induction intensity B z (x, y) in the direction perpendicular to the ground surface and a modulus
❘
"\[LeftBracketingBar]"
B
y
(
2
)
(
x
,
y
)
❘
"\[RightBracketingBar]"
of a second derivative of the magnetic induction intensity B y (x, y) in the direction parallel to the ground surface by a software processing terminal; and
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 program 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; 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 unit processes data according to a current measuring method based on TMR tunnel magnetoresistance, and writing a corresponding microcontroller program algorithm by using a voltage signal gain 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 a magnetic induction intensity according to a magnitude of the output voltage, (4) calculating a magnitude of the current by means of Biot-Savart Law based on an 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.