CN114578122B - Non-contact alternating voltage measuring method and electrode probe - Google Patents

Non-contact alternating voltage measuring method and electrode probe Download PDF

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CN114578122B
CN114578122B CN202210484608.0A CN202210484608A CN114578122B CN 114578122 B CN114578122 B CN 114578122B CN 202210484608 A CN202210484608 A CN 202210484608A CN 114578122 B CN114578122 B CN 114578122B
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CN114578122A (en
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罗耀强
陈俊长
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Nanjing Estable Electric Power Technology Co ltd
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Nanjing Estable Electric Power Technology Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0084—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring voltage only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/04—Measuring peak values or amplitude or envelope of ac or of pulses
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G01R23/16—Spectrum analysis; Fourier analysis
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/14—Fourier, Walsh or analogous domain transformations, e.g. Laplace, Hilbert, Karhunen-Loeve, transforms
    • G06F17/141—Discrete Fourier transforms
    • G06F17/142—Fast Fourier transforms, e.g. using a Cooley-Tukey type algorithm

Abstract

The invention discloses a non-contact alternating voltage measuring method and an electrode probe, wherein the electrode probe comprises 2N cylindrical tubes made of insulating non-metallic materials, copper foils are wound outside the cylindrical tubes to form inner-layer rings, the inner-layer rings with odd and even numbers are respectively and electrically connected together, the outer-layer rings wound by the copper foils are arranged outside the inner-layer rings, and the inner-layer rings and the outer-layer rings are electrically isolated; a non-contact ac voltage measurement method, comprising: (1) acquiring a voltage signal through an electrode probe; (2) conditioning the acquired voltage signal through a signal conditioning circuit; (3) carrying out digital processing; the double-layer multi-section copper foil cylindrical structure probe, the double-signal heterogeneous conditioning, the two-path signal synchronous sampling and the digital feature processing technology, which are constructed by the invention, realize non-contact alternating voltage measurement, have the advantages of strong anti-interference capability, high precision and capability of measuring the characteristics of voltage amplitude, harmonic wave, frequency and the like, and better meet the engineering application requirements.

Description

Non-contact alternating voltage measuring method and electrode probe
Technical Field
The invention relates to a non-contact alternating voltage measuring method which is used for alternating voltage measurement in a non-contact mode and belongs to the technical field of power measurement. The invention also relates to an electrode probe for the non-contact alternating voltage measurement.
Background
The traditional alternating voltage measurement needs direct metal contact between a measuring instrument and a conductor to be measured, and signals are introduced into the measuring instrument through a wiring terminal and a wire to be measured. For the power distribution system, the invasive contact type measurement mode increases the complexity of engineering construction on one hand, and increases the probability of system abnormity and fault on the other hand.
Therefore, the non-contact measurement can avoid the problems and bring great convenience to engineering implementation. However, the current non-contact voltage measuring method adopting the electric field induction principle has the problems of easy interference of electric fields near other lines, complex measuring circuit, low precision, improper phase shift and conditioning, incapability of measuring voltage harmonics and the like, and is difficult to put into practical use.
Disclosure of Invention
The invention aims to provide a non-contact alternating voltage measuring method, which realizes the high-precision measurement of non-contact alternating voltage. The invention also provides an electrode probe for the non-contact alternating voltage measurement.
In order to achieve the above object, the non-contact ac voltage measuring method of the present invention includes:
(1) acquiring voltage signals through an electrode probe:
the electrode probe comprises 2N cylindrical tubes made of insulating non-metallic materials, wherein N is a positive integer. The cylindrical pipe is made of insulating non-metallic materials such as PVC and the like into a cylindrical tubular structure or two semi-tubular clamps. The inner diameter is determined according to the thickness range of the wire to be measured, and the diameter is usually 1-6 cm.
The cylindrical tube is sequentially penetrated on a wire to be tested, and a copper foil is wound outside the cylindrical tube to form an inner layer ring (a copper foil circular ring), namely a first inner layer ring and a second inner layer ring … …. On a wire to be tested, two adjacent inner-layer rings are electrically insulated, the inner-layer rings with odd serial numbers are electrically connected together, and the inner-layer rings with even serial numbers are electrically connected together; an outer ring is arranged outside the 2N inner rings, namely a shielding layer is wound outside the inner rings, the outer ring is wound by copper foil, the outer ring is wound by the copper foil with the same thickness as the inner rings, and the outer ring is electrically isolated from the inner rings. Specifically, the radial length of the outer ring is at least ten times or more of the cumulative radial length of the plurality of inner rings, so as to achieve the shielding effect. And the outer ring and the inner ring are electrically isolated by an insulating film.
The inner ring and the lead to be tested form a capacitor, the copper foil ring is one polar plate of the capacitor, and the lead to be tested is the other polar plate of the capacitor. The capacitance calculation formula formed by the inner ring and the wire to be tested is as follows:
Figure 824111DEST_PATH_IMAGE001
Figure 749342DEST_PATH_IMAGE002
is the dielectric constant, S is the electrode plate area, d is the diameter of the electrode plate, and k is a constant. It can be seen that the capacitance is determined by the diameter, material and insulating material of the wire to be measured, and the diameter and area of the inner ring. Therefore, for the same section of conducting wire, if the first inner ring and the second inner ring are arranged, the capacitance values of the first inner ring and the second inner ring are equal.
The winding scheme can adopt a method of winding two inner-layer rings, namely a first inner-layer ring and a second inner-layer ring, and in order to prevent a lead section which is just opposite to the first inner-layer ring and the second inner-layer ring from influencing two capacitance values due to manufacturing process differences, a multi-section inner-layer ring winding mode is adopted for eliminating the influence. Namely, the fourth inner ring is wound in turn around the third inner ring with the same size and the same size by the same method with the edge interval of the second inner ring being less than 1 mm. The steel wire can be wound to a plurality of inner rings according to the requirement, and the number of the inner rings is even, namely 2N. And then electrically connecting the inner-layer rings with the odd serial numbers into a group, and electrically connecting the inner-layer rings with the even serial numbers into a group. The inner rings with odd serial numbers and the inner rings with even serial numbers are respectively connected with different signal wires in the shielding cable, the outer rings are connected with the shielding layer of the shielding cable, and the signals led out from the inner rings are wrapped by the shielding layer.
(2) And conditioning the acquired voltage signal through a signal conditioning circuit:
output signals of the odd-number group (odd-number) inner-layer ring and the even-number group (even-number) inner-layer ring adopt different conditioning modes to form two groups of different signal equations so as to obtain the coupling capacitor and the voltage value to be measured through simultaneous equation solution. The coupling capacitance of the odd-number inner ring and the wire to be tested is marked as C 1x And the coupling capacitance of the even number group of inner-layer rings and the wire to be tested is marked as C 2x . The first group of signal conditioning circuits consists of odd-number inner-layer rings and coupling capacitors C of the wires to be tested 1x A feedback resistor R f A high impedance operational amplifier (i.e., a first operational amplifier) OA1 and an instrumentation amplifier INA 1. The second group of signal conditioning circuits consists of even number of inner rings and coupling capacitors C of the wires to be tested 2x And a voltage-dividing capacitor C a A high impedance operational amplifier (i.e., a second operational amplifier) OA2 and an instrumentation amplifier INA 2. The circuit is shown in fig. 1, and specifically:
the signal conditioning circuit comprises a first group of signal conditioning circuits and a second group of signal conditioning circuits, the first group of signal conditioning circuits comprises a first operational amplifier, an inner ring with odd serial numbers is connected with the inverting input end of the first operational amplifier, an outer ring is connected with the non-inverting input end of the first operational amplifier, the inverting input end of the first operational amplifier and the output end of the first operational amplifier are connected with a feedback resistor, the non-inverting input end of the first operational amplifier is connected with a grounding end, the output end of the first operational amplifier is connected with the input end of an instrument amplifier, and the output end of the instrument amplifier outputs a first group of output signals; the second group of signal conditioning circuits comprise a second operational amplifier, an even-numbered inner ring is connected with a non-inverting input end of the second operational amplifier, the non-inverting input end of the second operational amplifier is connected with a grounding end through a voltage-dividing capacitor, an outer ring is connected on a circuit between the voltage-dividing capacitor and the grounding end, an inverting input end of the second operational amplifier is connected with an output end of the second operational amplifier, and the output end of the second operational amplifier outputs a second group of output signals;
according to a signal conditioning circuit, a first set of output signals V 01 Comprises the following steps:
Figure 973650DEST_PATH_IMAGE003
（Ⅰ）
wherein V inx For the AC voltage amplitude of the wire signal to be tested,
Figure 97464DEST_PATH_IMAGE004
For the angular frequency of the voltage to be measured, G 1 Is the amplification factor, R, of the first operational amplifier f As a feedback resistance value, C 1x Is the coupling electricity of the odd-number (i.e. odd-number) inner ring and the wire to be testedA capacitance value;
second set of output signals V 02 Comprises the following steps:
Figure 381815DEST_PATH_IMAGE005
（Ⅱ）
wherein V inx For the AC voltage amplitude of the signal of the conductor to be tested, C a Is a partial pressure capacitance value, C 2x The capacitance value of the coupling capacitor of the even group (even serial number) inner ring and the wire to be tested;
since the inner rings in the odd-numbered groups have the same form as the inner rings in the even-numbered groups, C is considered to be 1x And C 2x And (3) equally, simultaneously solving by the above formulas (I) and (II) to obtain a voltage value to be measured:
Figure 794341DEST_PATH_IMAGE006
（Ⅲ）
from formulas (I) and (II), the first group of output signals V 01 Phase-lagging second set of output signals V 02 Phase 90 degrees, hence V inx The amplitude of (d) is:
Figure 822340DEST_PATH_IMAGE007
（Ⅳ）
wherein:
Figure 3923DEST_PATH_IMAGE008
(3) digital processing:
first set of output signals V 01 And a second set of output signals V 02 Respectively sent to an ADC analog-to-digital conversion circuit after passing through a low-pass anti-aliasing filter, and the ADC analog-to-digital conversion circuit outputs a first group of signals V 01 And a second set of output signals V 02 Carrying out synchronous sampling; the synchronous sampling frequency is determined according to the number of the harmonic waves to be measured, and is usually between 1 kps and 100kps to meet the requirement of higher harmonic wave measurement. Anti-aliasing filter cut-off frequency according to nyquistThe law is set to 1/2 times the sampling frequency.
The digital sampling data output by the ADC analog-to-digital conversion circuit is sent to a microprocessor to finish:
1) first of all according to a first set of output signals V 01 The sampling sequence calculates the frequency of the voltage signal to be measured, and V is adopted because the RC loop in the first group of signal conditioning circuits can form better filtering and anti-disturbance characteristics 01 The digital sampling sequence is calculated by adopting a discrete Fourier transform method, a Mini-Norm power grid frequency estimation method and the like to obtain the frequency of the voltage signal to be measured
Figure 193596DEST_PATH_IMAGE009
Then the angular frequency is calculated
Figure 890156DEST_PATH_IMAGE010
；
2) Respectively calculating a first set of output signals V 01 And a second set of output signals V 02 An effective value of amplitude of; calculating a first set of output signals V based on the previously obtained frequencies 01 And a second set of output signals V 02 The time of each cycle of the analog-to-digital converter is T =1/f, the number of sampling points of each cycle of the signal obtained according to the sampling frequency of the ADC analog-to-digital converter circuit is N, then:
Figure 456267DEST_PATH_IMAGE011
wherein, V 01 ' is V 01 Effective value, V 02 ' is V 02 Effective value, v 1i 、v 2i Respectively, a first set of output signals V 01 And a second set of output signals V 02 The ith sample point value within the cycle.
3) Calculating according to the formulas (III) and (IV) to obtain a voltage value V to be measured inx ；
4) Calculating the harmonic wave of the voltage to be measured: the second group of output signals V can be seen according to the formula (II) 02 And the voltage value V to be measured inx Without phase deviation and with the characteristic of no difference attenuation of each frequency band, selectingTaking a second set of output signals V 02 Calculating the harmonic wave of the signal to be measured by the digital sampling sequence; and according to the effective value and the frequency obtained by calculation, sampling and calculating by using a fast Fourier algorithm to obtain each subharmonic component.
The double-layer multi-section copper foil cylindrical structure probe, the double-signal heterogeneous conditioning, the two-path signal synchronous sampling and the digital feature processing technology, which are constructed by the invention, realize non-contact alternating voltage measurement, have the advantages of strong anti-interference capability, high precision and capability of measuring the characteristics of voltage amplitude, harmonic wave, frequency and the like, and better meet the engineering application requirements.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is a schematic diagram of a signal conditioning circuit.
Fig. 2 is a schematic view of an electrode probe.
Fig. 3 is a circuit diagram of signal conditioning.
FIG. 4 is a diagram of the connection between the electrode probe and the signal conditioning circuit.
Detailed Description
Electrode probe:
as shown in fig. 2, a double-layer multi-section copper foil cylinder structure is adopted, specifically, a PVC material with a diameter of 2 cm and a thickness of 0.5 mm is adopted as a base material, a copper foil with a thickness of 0.02 mm and a width of 1 cm is wound around a circle along the outer side of a tube to form a circular ring (called as a first inner ring), the circular ring and a lead to be tested form a capacitor, the copper foil circular ring is one polar plate of the capacitor, and the lead to be tested is the other polar plate of the capacitor. The second inner ring 2 is wound by the same size in the same way when the interval with the edge of the first inner ring 1 along the pipe diameter direction is less than 1 mm, and the first inner ring 1 and the second inner ring 2 are kept electrically insulated. And a third inner layer ring 3 and a fourth inner layer ring 4 are wound in sequence. Then, the first inner ring 1 and the third inner ring 3 are electrically connected into one group, and the second inner ring 2 and the fourth inner ring 4 are electrically connected into the other group.
A shielding layer, called outer ring 5, is wrapped around the inner ring. The outer ring 5 is wound by copper foil with the same thickness as the inner ring, and the radial length of the outer ring is 20 cm, so that the shielding effect is achieved. The outer ring 5 and the inner ring are electrically isolated by an insulating film.
And finally, respectively leading out odd-number group inner ring signals, even-number group inner ring signals and outer ring signals by adopting a shielding signal cable, respectively connecting the odd-number inner ring and the even-number inner ring with different signal lines in the shielding cable, connecting the outer ring 5 with the shielding layer of the shielding cable, and wrapping the inner ring leading-out signals by the shielding layer.
The signal conditioning circuit:
output signals of the inner-layer rings of the odd-even group adopt different conditioning modes to form two groups of different signal equations so as to obtain coupling capacitance and a voltage value to be measured finally through simultaneous equation solution. The coupling capacitance of the odd-number inner ring and the wire to be tested is marked as C 1x And the coupling capacitance of the even number of inner rings and the wire to be tested is marked as C 2x . The first group of signal conditioning circuits consists of odd-number inner-layer rings and coupling capacitors C of the wires to be tested 1x A feedback resistor R f The operational amplifier comprises a high-resistance operational amplifier U1A (namely a first operational amplifier) and an instrumentation amplifier U5, wherein the operational amplifier U is 1M ohm. The second group of signal conditioning circuits consists of even number of inner rings and coupling capacitors C of the wires to be tested 2x And a voltage-dividing capacitor C a A circuit of =1nf nanofarad and a high impedance operational amplifier U7 (i.e., a second operational amplifier) is shown in fig. 3, and the specific connection manner is shown in fig. 4.
According to the circuit, the first group of output signals V 01 Comprises the following steps:
Figure 757935DEST_PATH_IMAGE012
（1）
wherein V inx Is the AC voltage amplitude of the signal to be measured,
Figure 118509DEST_PATH_IMAGE004
For the angular frequency of the voltage to be measured, G 1 Is the amplification factor of the amplifier INA1, R f As a feedback resistance value, C 1x The capacitance value of the coupling capacitor of the odd groups of inner rings and the lead to be tested.
Second set of output signals V 02 Comprises the following steps:
Figure 505628DEST_PATH_IMAGE013
（2）
wherein V inx For the AC voltage amplitude of the signal to be measured, C a Is a partial pressure capacitance value, C 2x The capacitance value of the coupling capacitor of the even number of groups of inner rings and the lead to be tested.
Since the inner rings in the odd-numbered groups have the same form as the inner rings in the even-numbered groups, C is considered to be 1x And C 2x And (3) equally solving to obtain a voltage value to be measured through the simultaneous solution of the following formulas (1) and (2):
Figure 875430DEST_PATH_IMAGE014
（3）
the first group of output signals V is shown in the formulas (1) and (2) 01 Phase-lagging second set of output signals V 02 Phase 90 degrees, hence V inx Has an amplitude of
Figure 595386DEST_PATH_IMAGE015
（4）
Wherein:
Figure 392441DEST_PATH_IMAGE016
digital processing:
first set of output signals V 01 And a second set of output signals V 02 And the signals are respectively sent to an ADC (analog-to-digital converter) circuit after passing through a low-pass anti-aliasing filter circuit, and the ADC circuit synchronously samples the two paths of signals. The synchronous sampling frequency was set to 12.8kps to meet the 50 th order inter-harmonic measurement requirement. The anti-aliasing filter cutoff frequency is set to 1/2 times the sampling frequency according to nyquist's law.
The digital sampling data output by the ADC analog-to-digital conversion circuit is sent to a microprocessor, and the following steps are completed in the microprocessor:
first according to the first groupOutput signal V 01 And calculating the frequency of the voltage signal to be measured by the sampling sequence. Because the RC loop in the first group of signal conditioning circuits can form better filtering and anti-disturbance characteristics, the first group of output signals V is adopted 01 The digital sampling sequence is calculated by adopting a discrete Fourier transform method, a Mini-Norm power grid frequency estimation method and the like to obtain the frequency of the voltage signal to be measured
Figure 1277DEST_PATH_IMAGE018
Then the angular frequency is calculated
Figure 174769DEST_PATH_IMAGE020
。
Respectively calculating a first set of output signals V 01 And a second set of output signals V 02 Is a significant value of the amplitude of (a). Calculating an AC output signal V from the previously obtained frequency 01 And V 02 The time of each cycle of the analog-to-digital converter is T =1/f, the number of sampling points of each cycle of the signal obtained according to the sampling frequency of the ADC analog-to-digital converter circuit is N, then:
Figure 185451DEST_PATH_IMAGE011
wherein, V 01 ' is V 01 Effective value, V 02 ' is V 02 Effective value, v 1i 、v 2i Respectively, a first set of output signals V 01 And a second set of output signals V 02 The ith sample point value within the cycle.
Calculating according to the formulas (3) and (4) to obtain a voltage value V to be measured inx 。
And calculating the harmonic wave of the voltage to be measured. The second group of output signals V can be seen according to the formula (2) 02 And the voltage value V to be measured inx The phase deviation is avoided, and the characteristic of no difference attenuation of each frequency band is achieved. Thus selecting the second set of output signals V 02 To calculate the harmonics of the signal under test. And according to the effective value and the frequency obtained by the previous calculation, sampling and calculating by using a fast Fourier algorithm to obtain each subharmonic component.
The above embodiments do not limit the present invention in any way, and all technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims (10)

1. A non-contact alternating voltage measuring method is characterized by comprising the following steps:
(1) acquiring voltage signals through an electrode probe:
the electrode probe comprises 2N cylindrical tubes made of insulating non-metallic materials, N is a positive integer, the cylindrical tubes sequentially penetrate through a lead to be tested, and copper foils are wound outside the cylindrical tubes to form an inner-layer ring; on a wire to be tested, two adjacent inner-layer rings are electrically insulated, when N is larger than 1, the inner-layer rings with odd serial numbers are electrically connected together, and the inner-layer rings with even serial numbers are electrically connected together; an outer ring is arranged outside the 2N inner rings, the outer ring is wound by copper foil, and the outer ring and the inner rings are electrically isolated; the inner rings with odd serial numbers and the inner rings with even serial numbers are respectively connected with different signal wires in the shielded cable, and the outer rings are connected with the shielded layer of the shielded cable;
(2) and conditioning the acquired voltage signal through a signal conditioning circuit:
the signal conditioning circuit comprises a first group of signal conditioning circuits and a second group of signal conditioning circuits, the first group of signal conditioning circuits comprises a first operational amplifier, an inner ring with odd serial numbers is connected with the inverting input end of the first operational amplifier, an outer ring is connected with the non-inverting input end of the first operational amplifier, the inverting input end of the first operational amplifier and the output end of the first operational amplifier are connected with a feedback resistor, the non-inverting input end of the first operational amplifier is connected with a grounding end, the output end of the first operational amplifier is connected with the input end of an instrument amplifier, and the output end of the instrument amplifier outputs a first group of output signals; the second group of signal conditioning circuits comprise a second operational amplifier, an even-numbered inner ring is connected with a non-inverting input end of the second operational amplifier, the non-inverting input end of the second operational amplifier is connected with a grounding end through a voltage-dividing capacitor, an outer ring is connected on a circuit between the voltage-dividing capacitor and the grounding end, an inverting input end of the second operational amplifier is connected with an output end of the second operational amplifier, and the output end of the second operational amplifier outputs a second group of output signals;
according to a signal conditioning circuit, a first set of output signals V 01 Comprises the following steps:
Figure 166973DEST_PATH_IMAGE001
（Ⅰ）
wherein V inx For the AC voltage amplitude of the wire signal to be tested,
Figure 84114DEST_PATH_IMAGE002
For the angular frequency of the voltage to be measured, G 1 Is the amplification factor, R, of the first operational amplifier f As a feedback resistance value, C 1x The capacitance value of the coupling capacitors of the odd groups of inner rings and the wires to be tested;
second set of output signals V 02 Comprises the following steps:
Figure 863851DEST_PATH_IMAGE003
（Ⅱ）
wherein V inx For the AC voltage amplitude of the signal of the conductor to be tested, C a Is a partial pressure capacitance value, C 2x The capacitance value of the coupling capacitors of the even groups of inner rings and the wires to be tested;
since the inner rings in the odd-numbered groups have the same form as the inner rings in the even-numbered groups, C is considered to be 1x And C 2x And (3) equally, simultaneously solving through the formulas (I) and (II) to obtain a voltage value to be measured:
Figure 55798DEST_PATH_IMAGE004
（Ⅲ）
from formulas (I) and (II), the first group of output signals V 01 Phase-lagging second set of output signals V 02 Phase 90 degrees, hence V inx Has an amplitude of
Figure 870170DEST_PATH_IMAGE005
（Ⅳ）
Wherein:
Figure 692633DEST_PATH_IMAGE006
(3) digital processing:
first set of output signals V 01 And a second set of output signals V 02 Respectively sent to an ADC analog-to-digital conversion circuit after passing through a low-pass anti-aliasing filter, and the ADC analog-to-digital conversion circuit outputs a first group of signals V 01 And a second set of output signals V 02 Carrying out synchronous sampling;
the digital sampling data output by the ADC analog-to-digital conversion circuit is sent to a microprocessor to finish:
1) first of all according to a first set of output signals V 01 The sampling sequence calculates the frequency of the voltage signal to be measured, and V is adopted because the RC loop in the first group of signal conditioning circuits can form better filtering and anti-disturbance characteristics 01 The digital sampling sequence is calculated by adopting a discrete Fourier transform method and a Mini-Norm power grid frequency estimation method to obtain the frequency of the voltage signal to be measured
Figure 959666DEST_PATH_IMAGE007
Then the angular frequency is calculated
Figure 158566DEST_PATH_IMAGE008
；
2) Respectively calculating a first set of output signals V 01 And a second set of output signals V 02 An effective value of amplitude of; calculating a first set of output signals V based on the previously obtained frequencies 01 And a second set of output signals V 02 The time of each cycle of the analog-to-digital conversion circuit is T =1/f, and the number of sampling points of each cycle of the signal obtained according to the sampling frequency of the ADC analog-to-digital conversion circuit is N, then:
Figure 827445DEST_PATH_IMAGE009
wherein, V 01 ' is V 01 Effective value, V 02 ' is V 02 Effective value, v 1i 、v 2i Respectively, a first set of output signals V 01 And a second set of output signals V 02 The ith sampling point value in the first cycle;
3) calculating according to the formulas (III) and (IV) to obtain a voltage value V to be measured inx ；
4) Calculating the harmonic wave of the voltage to be measured: selecting a second set of output signals V 02 Calculating the harmonic wave of the signal to be measured by the digital sampling sequence; and according to the effective value and the frequency obtained by calculation, sampling and calculating by using a fast Fourier algorithm to obtain each subharmonic component.
2. The noncontact ac voltage measuring method according to claim 1, characterized in that: the distance between two adjacent inner-layer rings is less than 1 mm.
3. The noncontact ac voltage measuring method according to claim 1, characterized in that: and the outer ring and the inner ring are electrically isolated by an insulating film.
4. The noncontact ac voltage measuring method according to claim 1, characterized in that: the cylindrical tube is made of two halves.
5. The noncontact ac voltage measuring method according to claim 1, characterized in that: the radial length of the outer ring is at least more than ten times of the sum of the radial lengths of the 2N inner rings.
6. The noncontact ac voltage measuring method according to claim 1, characterized in that: in the step (3) digital processing, the synchronous sampling frequency is 1-100 kps.
7. The noncontact ac voltage measuring method according to claim 1 or 6, characterized in that: the anti-aliasing filter cutoff frequency is 1/2 times the sampling frequency.
8. The electrode probe for non-contact alternating voltage measurement is characterized by comprising 2N cylindrical tubes made of insulating non-metallic materials, wherein N is a positive integer, the cylindrical tubes are sequentially penetrated on a wire to be measured, and copper foils are wound outside the cylindrical tubes to form an inner-layer ring; on a wire to be tested, the distance between two adjacent inner-layer rings is less than 1 mm, the two adjacent inner-layer rings are electrically insulated, when N is greater than 1, the inner-layer rings with odd serial numbers are electrically connected together, and the inner-layer rings with even serial numbers are electrically connected together; an outer ring is arranged outside the 2N inner rings, the outer ring is wound by copper foil, and the outer ring and the inner rings are electrically isolated; the inner rings with odd serial numbers and the inner rings with even serial numbers are respectively connected with different signal wires in the shielded cable, and the outer rings are connected with the shielding layer of the shielded cable.
9. The electrode probe for noncontact ac voltage measurement according to claim 8, characterized in that: the radial length of the outer layer ring is at least more than ten times of the sum of the radial lengths of the 2N inner layer rings.
10. The electrode probe for noncontact ac voltage measurement according to claim 8, characterized in that: the inner ring with odd serial numbers is connected with the inverting input end of a first operational amplifier, the outer ring is connected with the non-inverting input end of the first operational amplifier, the inverting input end of the first operational amplifier and the output end of the first operational amplifier are connected with a feedback resistor, the non-inverting input end of the first operational amplifier is connected with a grounding end, the output end of the first operational amplifier is connected with the input end of an instrument amplifier, and the output end of the instrument amplifier outputs a first group of output signals; the inner ring with even serial numbers is connected with the in-phase input end of the second operational amplifier, the in-phase input end of the second operational amplifier is connected with the grounding end through the voltage-dividing capacitor, the outer ring is connected on a circuit between the voltage-dividing capacitor and the grounding end, the reverse phase input end of the second operational amplifier is connected with the output end of the second operational amplifier, and the output end of the second operational amplifier outputs a second group of output signals.
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