CN105116230A - Method using multi-frequency combination to measure impulse grounding resistance of grounding device - Google Patents

Abstract

The invention discloses a method using multi-frequency combination to measure the impulse grounding resistance of a grounding device. According to the invention, experimental measurement and numerical calculation are used; Fourier decomposition is carried out on lightning current waveform to form sinusoidal waveform; the sinusoidal waveform is used as an incentive and is loaded on a grounding device to convert transient lightning impulse response into steady response; voltage and current response laws of the grounding device can be easily studied; and a result acquired by carrying out inverse Fourier transform on an acquired response is basically consistent with a result under lightning impulse. According to the measurement method provided by the invention, the impulse grounding resistance of the grounding device can be accurately assessed; grounding reforming can be guided; and the safety of personnel and equipment can be ensured.

Description

A kind of method adopting multi-frequency multiple measurement earthing device impulse earthed resistance

Technical field

The present invention relates to a kind of method adopting multi-frequency multiple measurement earthing device impulse earthed resistance, the method is applicable to the measurement of the earthing device such as transformer station, electric power line pole tower, belongs to Hyper-Voltage of Power Systems field.

Background technology

Lightning surge causes the one of the main reasons of transmission line of electricity tripping fault at present, and transformer station and electric power line pole tower earthing device are the important measures of personal security near protection power system security reliability service, protection.The impulse earthed resistance of accurate evaluation earthing device is for appropriate design transformer station and overhead line structures grounding body pattern and reduce impulse earthed resistance and have important directive significance.Existing research mainly concentrates on the size of simulated experiment and the impulse earthed resistance by simulation study earthing device.Due to the finite capacity of current surge-power generator, cannot accomplish the test condition that true type is tested, and when calculating with simulation software soil resistivity gets substantially is uniform soil, result of calculation and actual conditions are certain to there is error.Existing experiment and simulation calculation are difficult to the impulse earthed resistance accurately calculating earthing device.

The present invention measures and numerical evaluation by experiment, find by carrying out the sinusoidal waveform after Fourier decomposition to lightning current waveform as excitation, be carried in the response that the response of the lightning impulse of transient state can be converted into by earthing device stable state, more easily study the voltage of earthing device, current-responsive rule, by basically identical for the result under the result that obtains after the response inversefouriertransform obtained and lightning impulse.

The measuring method that the present invention proposes can achieve a butt joint ground the assessing more accurately of device impulse earthed resistance, and guides and carries out grounding reconstruction, guarantee the safety of personnel and equipment.

Summary of the invention

The object of the present invention is to provide the test method of the impulse earthed resistance of accurate evaluation thunderbolt earthing device, use the method to may be used for the impulse earthed resistance of accurate evaluation earthing device, and guide and carry out grounding reconstruction, guarantee the safety of personnel and equipment.

The technical solution adopted for the present invention to solve the technical problems comprises the following steps:

The first step, carries out Fourier transform to lightning current waveform expression formula, obtains the spectrum expression formula of lightning current waveform; The lightning current waveform expression formula that the present invention adopts is double-exponential function:

i(t)＝I _m(e ^-αt-e ^-βt)

Wherein I _mfor the amplitude of lightning current, its value is any positive integer, gets 10kA in the present invention.Due to domestic many documents (with reference to the article transient state Potential distribution of transmission tower and earthing device thereof " when being struck by lightning " and " the shaft tower impulse grounding characteristic computing method of consideration spark discharge "), standard lightning current waveform all adopts 2.6/50 μ s to calculate, therefore the present invention also adopts standard lightning current waveform 2.6/50 μ s to calculate.When adopting lightning current reference waveform 2.6/50 μ s, α=14790.2 in formula, β=1877833 (computing method are with reference to article " spectrum analysis of standard thunder and lightning waveform and application thereof ").After this function is carried out Fourier transform, its spectrum expression formula is:

$i\left(\mathrm{\ω}\right)=I_m(\frac{\mathrm{\α}}{{\mathrm{\α}}^2+{\mathrm{\ω}}^2}-\frac{\mathrm{\β}}{{\mathrm{\β}}^2+{\mathrm{\ω}}^2}-\frac{j\mathrm{\ω}}{{\mathrm{\α}}^2+{\mathrm{\ω}}^2}+\frac{j\mathrm{\ω}}{{\mathrm{\β}}^2+{\mathrm{\ω}}^2})$

Second step, determine measuring fundamental frequency f:

$f=\frac{1}{T}$

And integer multiple frequency harmonic wave f _i=i*f; Wherein T is the wavelength of lightning current, i=0,1 ..., n; When lightning current waveform adopts 2.6/50 μ s, T=50 μ s, n=120.

3rd step, decomposes the frequency that lightning current provides by second step, and the time-domain function expression formula obtaining each frequency current corresponding is:

Wherein $A_i=\sqrt{P{\left({\mathrm{\ω}}_i\right)}^2+Q{\left({\mathrm{\ω}}_i\right)}^2}$

ω _i＝2πf _i

$P\left({\mathrm{\ω}}_i\right)=I_m(\frac{\mathrm{\α}}{{\mathrm{\α}}^2+{{\mathrm{\ω}}_i}^2}-\frac{\mathrm{\β}}{{\mathrm{\β}}^2+{{\mathrm{\ω}}_i}^2})$

$Q\left({\mathrm{\ω}}_i\right)=I_m(\frac{{\mathrm{\ω}}_i}{{\mathrm{\β}}^2+{{\mathrm{\ω}}_i}^2}-\frac{{\mathrm{\ω}}_i}{{\mathrm{\α}}^2+{{\mathrm{\ω}}_i}^2})$

4th step, to earthing device to be measured, measures the three electrode method wire laying mode adopting and advise in DL475-1992 code, measures power supply variable frequency alternating current power source, its frequency is adjusted to one by one the frequency that second step provides, measure and obtain at f ₀to f ₁₂₀the current amplitude A ' that power supply under each frequency exports _i, and the Stable State of Sine response voltage amplitude B of correspondence _i, voltage and input current phase differential ψ _i, under obtaining this frequency, time domain response voltage expression is:

5th step, the response voltage expression formula the 4th step being obtained each frequency carries out cumulative summation, and the lightning impulse response voltage approximate expression obtaining earthing device is:

6th step, draws the oscillogram of the 5th step lightning impulse response voltage expression formula, reads shock response voltage magnitude u from figure _max, and calculate earthing device impulse earthed resistance R by following formula _ch:

$R_{ch}=\frac{u_{max}}{I_m}$

In above-mentioned steps, in the 4th step, measured wiring method adopts the angle-off set of advising in DL475-1992 code.

In above-mentioned steps, EXCEL or MATHEMATICK when the 6th step is drawn, is adopted to possess the software simulating of drawing function.

Accompanying drawing explanation

The present invention is further illustrated below in conjunction with drawings and Examples.

Accompanying drawing 1 is 2.6/50 μ s standard lightning current waveform.

Accompanying drawing 2 is the test philosophy figure of three electrode method measurement grounding body voltage responsive, and in figure, u place is sinusoidal excitation, d ₁₂distance should be d ₁₃0.618 times.

The shock response voltage waveform that accompanying drawing 3 obtains according to the 6th step formulae discovery for utilizing MATLAB.

Embodiment

Below by case study on implementation, by reference to the accompanying drawings 1, accompanying drawing 2, accompanying drawing 3, embodiment in introduction scene.

The first step, to lightning current reference waveform 2.6/50 μ s, is shown in accompanying drawing 1, carries out Fourier transform, obtain the spectrum expression formula of lightning current waveform;

$i\left(\mathrm{\ω}\right)=I_m(\frac{\mathrm{\α}}{{\mathrm{\α}}^2+{\mathrm{\ω}}^2}-\frac{\mathrm{\β}}{{\mathrm{\β}}^2+{\mathrm{\ω}}^2}-\frac{j\mathrm{\ω}}{{\mathrm{\α}}^2+{\mathrm{\ω}}^2}+\frac{j\mathrm{\ω}}{{\mathrm{\β}}^2+{\mathrm{\ω}}^2})$

I _mget 10kA, α=14790.2 in formula, β=1877833.

Second step, determine measuring fundamental frequency f:

$f=\frac{1}{T}$

And integer multiple frequency harmonic wave f _i=i*f;

Wherein T=50 μ s, f ₁=20000Hz, f _i=i*20000Hz, i=0,1 ..., n; N=120.

3rd step, decomposes the frequency that lightning current provides by second step, and the time-domain function expression formula obtaining each frequency current corresponding is:

Wherein $A_i=\sqrt{P{\left({\mathrm{\ω}}_i\right)}^2+Q{\left({\mathrm{\ω}}_i\right)}^2}$

ω _i＝2πf _if ₁＝20000Hz，f _i＝i*20000Hz，i＝0,1,…，n；n＝120。

$P\left({\mathrm{\ω}}_i\right)=I_m(\frac{\mathrm{\α}}{{\mathrm{\α}}^2+{{\mathrm{\ω}}_i}^2}-\frac{\mathrm{\β}}{{\mathrm{\β}}^2+{{\mathrm{\ω}}_i}^2})$

$Q\left({\mathrm{\ω}}_i\right)=I_m(\frac{{\mathrm{\ω}}_i}{{\mathrm{\β}}^2+{{\mathrm{\ω}}_i}^2}-\frac{{\mathrm{\ω}}_i}{{\mathrm{\α}}^2+{{\mathrm{\ω}}_i}^2})$

4th step, electric power line pole tower to be measured is measured, measure the three electrode method wire laying mode adopting and advise in DL475-1992 code, see accompanying drawing 2, measure power supply variable frequency alternating current power source, its frequency is adjusted to one by one the frequency that second step provides, the current amplitude that power supply exports is 10A, measures and obtains at f ₀to f ₁₂₀stable State of Sine response voltage amplitude B corresponding under each frequency _i, voltage and input current phase differential ψ _i, under obtaining this frequency, time domain response voltage expression is:

I=0 in formula, 1 ..., 120;

5th step, the response voltage expression formula the 4th step being obtained each frequency carries out cumulative summation, and the lightning impulse response voltage approximate expression obtaining electric power line pole tower grounding body is:

6th step, adopts MATLAB software to draw the oscillogram of the 5th step lightning impulse response voltage expression formula, sees accompanying drawing 3, read shock response voltage magnitude u from figure _max, be 342.44kV by the lightning current shock response voltage magnitude calculated in this kind of situation;

And the impulse earthed resistance R of electric power line pole tower grounding body is calculated by following formula _ch:

$R_{ch}=\frac{u_{max}}{I_m}$

Then in this kind of situation, the impulse earthed resistance of grounding body is:

$R_{ch}=\frac{342.44kVv}{10kA}=34.244\mathrm{\Ω}.$

Claims (4)

1. adopt a method for multi-frequency multiple measurement earthing device impulse earthed resistance, it is characterized in that, comprise the following steps:

The first step carries out Fourier transform to lightning current waveform expression formula, obtains the spectrum expression formula of lightning current waveform; The lightning current waveform expression formula adopted is double-exponential function:

i(t)＝I _m(e ^-αt-e ^-βt)

Wherein I _mfor the amplitude of lightning current, its value is any positive integer; When lightning current waveform adopts 2.6/50 μ s, α=14790.2 in formula, β=1877833; After this function is carried out Fourier transform, its spectrum expression formula is:

$i\left(\mathrm{\ω}\right)=I_m(\frac{\mathrm{\α}}{{\mathrm{\α}}^2+{\mathrm{\ω}}^2}-\frac{\mathrm{\β}}{{\mathrm{\β}}^2+{\mathrm{\ω}}^2}-\frac{j\mathrm{\ω}}{{\mathrm{\α}}^2+{\mathrm{\ω}}^2}+\frac{j\mathrm{\ω}}{{\mathrm{\β}}^2+{\mathrm{\ω}}^2})$

Second step, determine measuring fundamental frequency f:

$f=\frac{1}{T}$

And integer multiple frequency harmonic wave f _i=i*f; Wherein T is the wavelength of lightning current, i=0,1 ..., n; When lightning current waveform adopts 2.6/50 μ s, T=50 μ s, n=120;

3rd step, decomposes the frequency that lightning current provides by second step, and the time-domain function expression formula obtaining each frequency current corresponding is:

Wherein $A_i=\sqrt{P{\left({\mathrm{\ω}}_i\right)}^2+Q{\left({\mathrm{\ω}}_i\right)}^2}$

ω _i＝2πf _i

$P\left({\mathrm{\ω}}_i\right)=I_m(\frac{\mathrm{\α}}{{\mathrm{\α}}^2+{{\mathrm{\ω}}_i}^2}-\frac{\mathrm{\β}}{{\mathrm{\β}}^2+{{\mathrm{\ω}}_i}^2})$

$Q\left({\mathrm{\ω}}_i\right)=I_m(\frac{{\mathrm{\ω}}_i}{{\mathrm{\β}}^2+{{\mathrm{\ω}}_i}^2}-\frac{{\mathrm{\ω}}_i}{{\mathrm{\α}}^2+{{\mathrm{\ω}}_i}^2})$

4th step, to earthing device to be measured, measures the three electrode method wire laying mode adopting and advise in DL475-1992 code, measures power supply variable frequency alternating current power source, its frequency is adjusted to one by one the frequency that second step provides, and records the current amplitude A that power supply under each frequency exports _i', and the Stable State of Sine response voltage amplitude B of correspondence _iand voltage and input current phase differential ψ _i, under obtaining this frequency, time domain response voltage expression is:

5th step, the response voltage expression formula the 4th step being obtained each frequency carries out cumulative summation, and the lightning impulse response voltage approximate expression obtaining earthing device is:

6th step, draws the oscillogram of the 5th step lightning impulse response voltage expression formula, reads shock response voltage magnitude u from figure _max, and the impulse earthed resistance R of earthing device is calculated by following formula _ch:

$R_{ch}=\frac{u_{max}}{I_m}.$

2. a kind of method adopting multi-frequency multiple measurement earthing device impulse earthed resistance according to claim 1, is characterized in that, in the 4th step, measured wiring method adopts the angle-off set of advising in DL475-1992 code.

3. a kind of method adopting multi-frequency multiple measurement earthing device impulse earthed resistance according to claim 1, is characterized in that, EXCEL or MATHEMATICK can be adopted to possess the software simulating of drawing function when the 6th step is drawn.

4. a kind of method adopting multi-frequency multiple measurement earthing device impulse earthed resistance according to claim 1, it is characterized in that, earthing device comprises the earthing device of electric power line pole tower and the earthing device of transmission transformer station.