CN103954843B - One does not disconnect ground lead pole tower ground resistance and measures injection power frequency method of determining range - Google Patents

Abstract

The present invention relates to one and do not disconnect ground lead pole tower ground resistance measurement injection power frequency method of determining range, when measuring pole tower ground resistance for high frequency multiple process when not disconnecting ground lead, when injecting electric current signal frequency and be bigger, ground connector perception effect is relatively obvious, increases measuring error. And the method measures gained tower grounding impedance value and measure power frequency with entering and shaft tower surrounding soil relative magnetic permeability has much relations, high frequency multiple process does not consider practical situation around, and adaptability is poor. The present invention establishes and does not disconnect ground lead pole tower ground resistance measurement model, consider each influence factor when measuring when not disconnecting ground lead, inject the method for power frequency scope when proposing not disconnect ground lead Measurement accuracy pole tower ground resistance, when determining Measurement accuracy pole tower ground resistance in conjunction with Mathematical Method, inject signal frequency scope. Build measuring apparatus for above-mentioned theory analysis, complete pole tower ground resistance efficiently, measure accurately.

Description

One does not disconnect ground lead pole tower ground resistance and measures injection power frequency method of determining range

Technical field

The present invention relates to pole tower ground resistance field of measuring technique, measure pole tower ground resistance when not disconnecting ground lead in particular to one and inject power frequency method of determining range.

Background technology

Pole tower ground resistance is the principal measure parameter of tower grounding system, directly affects the tripping operation number of times of transmitting line, and operation of power networks has most important effect, therefore measures shaft tower grounding resistance accurately and efficiently and has important engineering significance.

In the method for measurement pole tower ground resistance conventional at present, need to repeatedly measuring during fall-of-potential method measurement of Grounding Resistance, workload is big, and not easily draws potential drop curve, execute-in-place difficulty; Pincers meter method for measuring adopts electromagnetic induction principle, simple to operate, measures quick, but is easily disturbed, and measuring error is bigger, can not meet precision measure requirement; Three pole methods measure pole tower ground resistance, and accuracy is higher, stable performance, but need to take all ground leads apart when measuring, and workload is big, inefficiency.

On the basis of three pole method Measurement accuracies, also been proposed high frequency multiple process, the method, by injecting single constant high frequency electric current in tested tower grounding body, increases lightning conducter induction reactance, make lightning conducter induction reactance very big and approximate think open circuit, it is achieved do not disconnect the measurement of ground lead. But the method is constant high frequency 10kHz when injecting power frequency, now, small-sized ground net perception relatively resistive portion can not ignore, and impedance ground value increases with measuring power frequency and the increase of soil relative magnetic permeability with entering.Therefore, according to combined factors such as on-site soil character, measurement power frequencies, high frequency multiple process does not consider that ground connector inductance effect is on the impact of measuring result, can not adapt to field condition well.

For the defect that high frequency multiple process exists, set up relatively complete pole tower ground resistance Measuring System Models, the pole tower ground resistance Measuring System Models that theoretical analysis is complete when not disconnecting ground lead, draws the Simplified equivalent model of the Measurement accuracy pole tower ground resistance when not disconnecting ground lead and consider ground connector inductance effect. Propose based on this Simplified equivalent model reasonably to optimize algorithm (reducing ground connector inductance effect as much as possible to the impact of measurement accuracy), finally draw in the reasonable measurement electric current signal frequency scope considered on ground connector perception effect basis, inject the measurement signal in this range of frequency, can facilitate, measure pole tower ground resistance accurately, be different from the single constant high frequency of high frequency multiple process. So just, fully consider ground connector inductance effect when not disconnecting ground lead, make up the defect that high frequency multiple process measuring error is big and application is limited.

Summary of the invention

It is an object of the invention to provide a kind of when not disconnecting ground lead pole tower ground resistance measure inject power frequency method of determining range, based on high frequency multiple process input single constant high frequency measurement signal time measurement defect, the present invention does not disconnect ground lead pole tower ground resistance measurement model by setting up, fully consider ground connector inductance, shaft tower self-resistance, lightning conducter resistance, the factor that the impact such as inductance is measured, the equivalent simplified model of Measurement accuracy pole tower ground resistance is drawn through theoretical analysis, and analyze signal frequency scope of injecting when considering ground connector inductance on this basis further, reach the object of Measurement accuracy pole tower ground resistance.

For achieving the above object, the technical scheme of employing is, one provided by the invention does not disconnect ground lead pole tower ground resistance and measures injection power frequency method of determining range, comprises the steps:

1) measurement model is set up

The tower grounding body equivalent impedance being embedded in soil to have limit for length is Z=R+jX=R+j ω L, along with the raising of survey frequency f, in impedance ground, inductance effect can be more and more obvious, and when injecting high-frequency current, the pole tower ground resistance value of measurement shows as tower grounding impedance value; If injecting electric current signalWhen size reaches more than kHz, then think that tested shaft tower and other shaft tower of surrounding do not form loop, just ignore the stake resistance R of other shaft tower around_nAnd the inductance L of other shaft tower of surrounding_n, lightning conducter resistance R_LnWith tested shaft tower self-resistance R_TnBeing all be made up of the rigid material that resistivity is very little, the relatively tested pole tower ground resistance value of its resistance can be ignored, thus obtains measuring the equivalent simplified model of pole tower ground resistance, i.e. measurement model. When injection electric current signal is more than kHz, tower grounding body perception effect can not be ignored completely, so not disconnecting under ground lead high-frequency signal measurement, measuring gained pole tower ground resistance value and showing as an impedance value. The present invention is according to power industry standard DL/T596-1996 " power equipment preventive experiment code " and " the ground connection design specifications GBJ65-83 of industry and civilian electric device ", select grounding resistance and impact within the scope of code not to disconnect ground lead and measure pole tower ground resistance each factor (lightning conducter resistance, inductance, shaft tower self-resistance etc.) parameter structure circuit analysis model, through strict theoretical analysis and calculation, so that it is determined that go out not disconnect the equivalent-circuit model that pole tower ground resistance measured by ground lead, namely simplify equivalent measurement model.According to this model, analyze and draw reasonably measurement pole tower ground resistance range of frequency, make impedance ground value when not disconnecting ground lead measurement as far as possible close to grounding resistance.

2) determine to inject power frequency

Very according to step 1) measurement model set up, adopt three cloth pole, pole principles to measure pole tower ground resistances, when not disconnecting ground lead so that the condition that measuring error is little as far as possible is:

$\left\{\begin{array}{c}2\mathrm{\&pi;F}{l}_X<<R_x\\ R_x<<2\mathrm{\&pi;f}{L}_{\mathrm{eq}}\end{array}\right.---\left(4\right)$

In formula, f represents injection power frequency, L_xRepresent tested tower grounding body inductance, R_xRepresent tested tower grounding body resistance, L_eqRepresent the lightning conducter equivalent inductive reactance value of two shaft towers contiguous with tested shaft tower;

Formula (4) is converted to the inequality injecting power frequency f is:

$\left\{\begin{array}{c}\frac{R_x}{2\mathrm{\&pi;}{L}_{\mathrm{eq}}}<<f\\ f<<\frac{R_x}{2\mathrm{\&pi;}{L}_x}\end{array}\right.---\left(5\right)$

1. the determination of power frequency lower value is injected

For meeting (4) formula, then need to make

$\left\{\begin{array}{c}\frac{2\mathrm{\&pi;}{\mathrm{fL}}_x}{R_x}\&RightArrow;0\\ \frac{R_x}{2\mathrm{\&pi;}{\mathrm{fL}}_{\mathrm{eq}}}\&RightArrow;0\end{array}\right.---\left(6\right)$

Power frequency lower limit function △ (f) is injected in order:

$\mathrm{\&Delta;}\left(f\right)=\frac{2\mathrm{\&pi;}{\mathrm{fL}}_x}{R_x}-\frac{R_x}{2\mathrm{\&pi;}{\mathrm{fL}}_{\mathrm{eq}}}---\left(7\right)$

When △ (f) → 0, two formula conditions in (6) formula can be met to the full extent simultaneously, describe the change curve of △ (f) with frequency f, it is determined that inject the lower value of power frequency;

2. the determination of power frequency higher limit is injected

According to step 1) measurement model built, measured result is R_x+2πfL_xWith 2 π fL_eqParallel value, result to be made more accurate, need to meet

R_x+2πfL_x<<2πfL_eq(8)

Power frequency upper limit function δ (f) is injected in order:

$\mathrm{\&delta;}\left(f\right)=\frac{R_x+2\mathrm{\&pi;}{\mathrm{fL}}_x}{2\mathrm{\&pi;}{\mathrm{fL}0}_{\mathrm{eq}}}---\left(9\right)$

When δ (f) → 0, then can meet the condition of (8) formula to the full extent, draw out the graphic representation that δ (f) changes with frequency f, determine to inject the higher limit of power frequency according to curved line relation;

3) determine to inject power frequency scope according to the lower value and higher limit of injecting power frequency, regulate adjustable excitation current source to measure in this range of frequency.

Specifically, above-mentioned adjustable excitation current source comprises power source circuit module, center-control unit module, signal generator module and power amplifier module, power source circuit module powers to respectively center-control unit module, signal generator module and power amplifier module, center-control unit module control signal generator module produces the current waveform signal needed for measurement, and the current waveform signal that signal generator module produces carries out power magnification by power amplifier module.

The pole tower ground resistance measurement model set up in the present invention is fully considering that affecting pole tower ground resistance measures foundation on each factor basis, there is higher reliability and accuracy, carry out analyzing based on this model and determine range of frequency when measuring pole tower ground resistance, measure the exact value that the grounding resistance obtained can accurately reflect pole tower ground resistance under high-frequency signal measurement like this. Within the scope of the determined injection power frequency of the inventive method, it is possible to accurately measure pole tower ground resistance, and emotional resistance part can not be ignored.

Accompanying drawing explanation

Fig. 1 is tower grounding body equivalent electrical circuit;

Fig. 2 does not disconnect equivalent measurement circuit when pole tower ground resistance measured by ground lead;

Fig. 3 does not disconnect the simple equivalent circuit 1 that pole tower ground resistance measured by ground lead;

Fig. 4 does not disconnect the simple equivalent circuit 2 that pole tower ground resistance measured by ground lead;

Fig. 5 does not disconnect the simple equivalent circuit 3 that pole tower ground resistance measured by ground lead;

Fig. 6 is △ (f) and injection power frequency f relation curve;

Fig. 7 is δ (f) and injection power frequency f relation curve;

Fig. 8 is that adjustable signal encourages former functional block diagram.

Embodiment

Below in conjunction with accompanying drawing, the technical scheme of the present invention is described further:

The open one of the present invention does not disconnect ground lead and measures pole tower ground resistance and inject letter current rate method of determining range, and therefore, the concrete enforcement mode of the present invention is not all when disconnecting ground lead in pole tower ground resistance Fundamentals of Measurement.The method of the present invention is carried out detailed analysis and description below.

1, measurement model is set up and is analyzed

Be embedded in soil limited stock tower ground connector can equivalence in a LR lumped parameter circuit (capacity effect is generally not obvious), be rendered as an impedance Z=R+jX=R+j ω L, circuit model is as shown in Figure 1. When injecting direct current or power current, ground connector is approximate equals resistance R. But the raising along with survey frequency, in impedance ground, inductance effect can be more and more obvious. In the present invention, by strict theoretical analysis, the impedance ground value making tested shaft tower when high frequency does not disconnect ground lead is similar to the grounding resistance equaling tested shaft tower.

Setting out based on a complete pole tower ground resistance measuring system, the present invention establishes an equivalent physics measurement model, as shown in Figure 2. Wherein R_LnIt is lightning conducter resistance, R_TnBeing shaft tower self-resistance, L is lightning conducter inductance (assuming that the inductance value between adjacent two shaft towers is equal) L_nOther tower grounding body inductance around tested shaft tower, R_xIt is tested tower grounding body resistance, L_xIt is tested tower grounding body inductance, R_nIt is other pole tower ground resistances around tested shaft tower.

According to " construction of GB50169 electrical means installation work grounding device and acceptance specification " and " DL/T621 " it will be seen that when soil resistivity is not higher than 500 Ω/m, pole tower ground resistance value need between 4 Ω to 10 Ω. In addition, according to " the ground connection design specifications GBJ65-83 of industry and civilian electric device ", in transmission of electricity system, the normal lightning conducter model adopted is LGJ 185 steel strand, its inductance value is 1.28 μ H/m, and shelves are apart from, when being several hundred meters, its lightning conducter equivalent inductance is mH level, when injection measurement signal is more than kHz, lightning conducter induction reactance value will reach tens even several hundred ohm, and when measurement signal is power frequency component, lightning conducter induction reactance value will be less than 0.01 Ω. Meanwhile, lightning conducter resistance R_LnWith shaft tower self-resistance R_Tn, it is all be made up of the material that resistivity is very little because of it, therefore its value is all less than 0.1 Ω, ground connector inductance value L_nSize in μ H level.

In fig. 2, electric current is injected(following all calculating symbols are scalar value), whereinElectric current pole is flowed back to via tower grounding body and soil, andFlow to shaft tower, lightning conducter and surrounding adjacent stems tower by ground lead and form loop stream telegram in reply stream pole. Now, if injecting direct current or power current, according to describing above, and compare with tested pole tower ground resistance value size, R_Tn、R_Ln、L_n, L can be ignored, then the pole tower ground resistance value R tried to achieve_loopFor:

$R_{\mathrm{loop}}=\frac{1}{\frac{1}{R_1}+\frac{1}{R_2}...+\frac{1}{R_x}+...+\frac{1}{R_{n-1}}+\frac{1}{R_n}}---\left(1\right)$

By formula (1) it will be seen that when not disconnecting ground lead, what when three pole methods inject power current or direct current, measurement obtained is all pole tower ground resistance parallel value, much smaller than pole tower ground resistance value R to be measured_x。

Ground lead measurement model is not disconnected according to Fig. 2, whenWhen being high-frequency signal measurement, lightning conducter induction reactance value will increase. Now, based on describing above, compared with tested pole tower ground resistance value size, R_Tn、R_LCan be ignored. But, L, L_nBut can not being ignored, Fig. 2 circuit can be evolved into circuit shown in Fig. 3.

Based on circuit analysis, according to " the ground connection design specifications GBJ65-83 of industry and civilian electric device ", get each parameter typical case value in Fig. 3 circuit: the distance between two shaft towers elects 350m as, R_x、R_nAll it is set as 5 Ω, L_n、L_xIt is set as 20 μ H, according to circuit shown in Fig. 3, I₁、I₂Can be by proximate calculation:

$\left\{\begin{array}{c}{I}_1\&ap;\frac{\sqrt{{R_{x+1}}^2{(\mathrm{\&omega;L}+\mathrm{\&omega;}{L}_{x+1})}^2}/2}{\sqrt{{R_x}^2+{\left(\mathrm{\&omega;}{L}_x\right)}^2}+\sqrt{{R_{x+1}}^2+{(\mathrm{\&omega;L}+\mathrm{\&omega;}{L}_{x+1})}^2}/2}I\\ I_2\&ap;\frac{\sqrt{{R_x}^2+{\left(\mathrm{\&omega;}{L}_x\right)}^2}}{\sqrt{{R_x}^2+{\left(\mathrm{\&omega;}{L}_x\right)}^2}+\sqrt{{R_{x+1}}^2+{(\mathrm{\&omega;L}+\mathrm{\&omega;}{L}_{x+1})}^2}/2}I\end{array}\right.---\left(2\right)$

By R_x=5 Ω, R_x+1=5 Ω, L_x=20 μ H, L_x+1=20 μ H, L=12.8 μ H/m*350m=4.48mH brings equation (2) into, (gets f=3kHz) when I is high-frequency signal,

$\left\{\begin{array}{c}{I}_1\&ap;\frac{\sqrt{{R_{x+1}}^2{(\mathrm{\&omega;L}+\mathrm{\&omega;}{L}_{x+1})}^2}/2}{\sqrt{{R_x}^2+{\left(\mathrm{\&omega;}{L}_x\right)}^2}+\sqrt{{R_{x+1}}^2+{(\mathrm{\&omega;L}+\mathrm{\&omega;}{L}_{x+1})}^2}/2}I\&ap;\frac{9}{10}I\\ I_2\&ap;\frac{\sqrt{{R_x}^2+{\left(\mathrm{\&omega;}{L}_x\right)}^2}}{\sqrt{{R_x}^2+{\left(\mathrm{\&omega;}{L}_x\right)}^2}+\sqrt{{R_{x+1}}^2+{(\mathrm{\&omega;L}+\mathrm{\&omega;}{L}_{x+1})}^2}/2}I\&ap;\frac{1}{10}I\end{array}\right.---\left(3\right)$

According to above-mentioned calculating rule, I₂₁,I₂₂,I₂₁₁,I₂₁₂, it is possible to by proximate calculation,When injection electric currentWhen not being very big, the electric current flowing into shaft tower around tested shaft tower can be more and more less, almost nil.So, fully not think that the two base shaft towers disconnecting ground lead measurement pole tower ground resistance only contiguous with tested shaft tower are relevant, Fig. 3 circuit can be converted into circuit shown in Fig. 4.

When injection electric currentFrequency higher time, j ω L_eqWith R_x+1+jωL_x+1Comparing, numerical values recited difference is relatively big, so, the metering circuit shown in Fig. 4 can be evolved into the simple equivalent circuit shown in Fig. 5. L in Fig. 5_eqFor the lightning conducter equivalent inductive reactance value of two shaft towers contiguous with tested shaft tower.

So far, do not disconnect ground lead and measure pole tower ground resistance simple equivalent circuit as shown in Figure 5, carry out circuit analysis based on this model, it is determined that do not disconnect ground lead pole tower ground resistance and measure injection power frequency scope.

2, the determination of power frequency scope is injected

The pole tower ground resistance measurement method cloth pole principle proposed in the present invention adopts three cloth pole, the pole principles being subject to power industry standard DL475-92 " measurement of grounding device power frequency characteristic parameter is led, " and DL887-2004 " measurement of electric power line pole tower power frequency earthing resistance " and recommending, inject the high-frequency signal measurement within the scope of certain frequency when not disconnecting ground lead, by measuring voltage pole, voltage that electric current is extremely gone up, electric current signal convert tested pole tower ground resistance value. The method of the determination thief rod tower stake resistance range of frequency proposed in the present invention can reasonably determine measurement signal range of frequency, reduces tower grounding body perception to the impact of measuring result. According to Fig. 5, when not disconnecting ground lead so that the condition that measuring error is little as far as possible is:

$\left\{\begin{array}{c}2\mathrm{\&pi;F}{l}_X<<R_x\\ R_x<<2\mathrm{\&pi;f}{L}_{\mathrm{eq}}\end{array}\right.---\left(4\right)$

By the inequality that formula (4) is converted to the power frequency f that need to inject it is:

$\left\{\begin{array}{c}\frac{R_x}{2\mathrm{\&pi;}{L}_{\mathrm{eq}}}<<f\\ f<<\frac{R_x}{2\mathrm{\&pi;}{L}_x}\end{array}\right.---\left(5\right)$

1) determination of power frequency lower value, is injected

The pole tower ground resistance measurement model set up according to Fig. 5, need to meet the inequality group that (4) formula is determined, be meet (4) formula condition, then need to make when not disconnecting ground lead and carry out pole tower ground resistance measurement

$\left\{\begin{array}{c}\frac{2\mathrm{\&pi;}{\mathrm{fL}}_x}{R_x}\&RightArrow;0\\ \frac{R_x}{2\mathrm{\&pi;}{\mathrm{fL}}_{\mathrm{eq}}}\&RightArrow;0\end{array}\right.---\left(6\right)$

But power frequency f can not make in actual measurement simultaneouslyLeveling off to 0, if injecting power frequency lower limit function △ (f) being:

$\mathrm{\&Delta;}\left(f\right)=\frac{2\mathrm{\&pi;}{\mathrm{fL}}_x}{R_x}-\frac{R_x}{2\mathrm{\&pi;}{\mathrm{fL}}_{\mathrm{eq}}}---\left(7\right)$

When △ (f) → 0, two formula conditions in (6) formula can be met to the full extent simultaneously, calculate the value that △ (f) meets the Frequency point as much as possible that formula (6) requires, and describe the change curve of △ (f) with frequency f, just can determine to inject the lower value of power frequency.

2) determination of power frequency higher limit, is injected

Being built according to Fig. 5 and measure pole tower ground resistance model, when not disconnecting ground lead and carry out pole tower ground resistance measurement, the stake resistance model of tested shaft tower is actual is an impedance value, and measured result is R_x+2πfL_xWith 2 π fL_eqParallel value, result to be made more accurate, need to meet

R_x+2πfL_x<<2πfL_eq(8)

If injecting power frequency upper limit function δ (f) it is:

$\mathrm{\&delta;}\left(f\right)=\frac{R_x+2\mathrm{\&pi;}{\mathrm{fL}}_x}{2\mathrm{\&pi;}{\mathrm{fL}0}_{\mathrm{eq}}}---\left(9\right)$

When δ (f) → 0, the condition of (8) formula can be met to the full extent, calculate the value that δ (f) meets the Frequency point as much as possible that (8) formula requires, and draw out the graphic representation that δ (f) changes with frequency f, just can determine to inject the higher limit of power frequency according to curved line relation.

3) determination of the accurate scope of power frequency, is injected

By the R in Fig. 5_x、L_x、L_eqCompose with the reference value within the scope of code according to " construction of GB50169 electrical means installation work grounding device and acceptance specification " respectively with " GB50057-94 design code for lightning-proof ": R_x=10 Ω, L_x=10uH, L_eq=10mH, brings in formula (4), (5) and obtains:

159.2Hz<<f<<159.2kHz(10)

The range of frequency measuring electric current place is roughly drawn in theory by formula (10). But in conjunction with practical measurement requirement, should improve and measure power frequency increase lightning conducter induction reactance, itself and surrounding shaft tower is avoided to form measuring circuit, increase error, when avoiding measurement power frequency higher again, ground connector inductance effect is obvious, increases measuring error simultaneously, comprehensive above factor, it is determined that a frequency measurement scope more accurately.

According to the defining method of the injection power frequency upper limit value and lower limit value mentioned in the present invention, calculate pole tower ground resistance measurement model each several part impedance value (R_x=10 Ω, L_x=10uH, L_eq=10mH), then calculate △ (f) (%), the value of δ (f) (%).Make △ (f) and with injecting power frequency f relation curve and δ (f) and inject power frequency f relation curve such as Fig. 6 and Fig. 7.

As can be seen from Figure 6, along with the increase of frequency, when f is after 3kHz during value, the value of △ (f) then levels off to 0, and variable quantity is very little, almost levels off to zero, and according to practical measurement requirement, the lower limit frequency setting measuring electric current is for being 3kHz.

As can be seen from Figure 7, along with the increase of frequency, when f is after 8kHz during value, the variable quantity of the value of δ (f) is very little, almost close to zero. For making the value of δ (f) closer to 0, and meet the requirement of high frequency measurement, in conjunction with actual measurement situation (can have Frequency point as much as possible during measurement), the higher limit measuring power frequency is set as 12kHz.

In sum, it may be determined that an electric current signal frequency measurement range of pole tower ground resistance measurement more accurately: 3kHz < f < 12kHz.

After determining survey frequency scope, so that it may to select many class frequencys value to measure within the scope of this, then carry out data prediction and polynomial fitting by measuring the data obtained, obtain an observed value the most accurately.

The pole tower ground resistance measurement method of multifrequency pulse current injectingt and device can realize the Measurement accuracy of pole tower ground resistance resistance when not disconnecting ground lead. Source is encouraged to produce the measurement signal within the scope of certain frequency by adjustable signal, signal source exported the electric current signal that 3-12kHz stepping is 1kHz every 15 seconds, measure the measurement signal of voltage pole and electric current pole under each frequency, then carry out certain optimization process by measuring the grounding resistance obtained that converts, so just can accurately reflect the grounding resistance of tested shaft tower on the basis considering ground connector inductance effect. The structure iron of adjustable excitation current source is such as Fig. 8.

Adjustable excitation current source is formed primarily of power source circuit module 1, center-control unit module 2, signal generator module 3 and power amplifier module 4. Wherein center-control unit module 2 control signal generator module 3 produces the current waveform signal needed for measurement (mainly sinusoidal wave signal), and the current waveform signal that signal generator module 3 produces carries out power magnification by power amplifier module 4.

Power source circuit module 1 is the basis that whole system is effectively run, and due to system function module more, the service voltage of each module is not identical, it is thus desirable to the voltage of power supply source lithium cell is carried out conversion process, to ensure, constructing system normally effectively runs. PA05 chip power supply voltage range in power amplifier module 4 is 15V to 45V, the 20V lithium cell group series connection extraction ± 20V voltage that work-ing life therefore can be adopted longer. And signal generator module 3 take AD9833 as core, its required voltage scope is+2.3V to+5.2V, thus can adopt high performance LM2576-5.0 chip realize voltage transitions and to its power supply. Another center-control unit module 2 required voltage is 5V, and we still can adopt the conversion of LM2576-5.0 chip to export its power supply.

Center-control unit module 2 adopts the high-performance microprocessor PIC18F5420 that Microchip company of the U.S. produces, and this chip has 44 ports, and programming environment is easy to operation, and cost performance is higher. The waveform signal needed for measuring is produced by programming control signal generator module 3.

Signal generator module 3 adopts DDS (DirectDigitalSynthesis, direct digital synthesis technique) technology to realize exporting by the sinusoidal signal of frequency conversion.This technology is a kind of totally digitilized Waveform generating method based on sampling theorem, is the third generation frequency synthesis technique after Direct frequency synthesizer technology and PLL pll frequency synthesizer. It is formed by core of the direct digital synthesis technique chip AD9833 of ADI company, and AD9833 is a low-power consumption, waveform generator able to programme, has and the serial line interface line of SPI interface standard compatibility. Center-control unit module 2 is connected with AD9833 by spi bus, it is achieved center-control unit module 2 control signal producer produces sinusoidal wave signal, and conditioning signal source frequency.

The signal that power amplifier module 4 is mainly used in producing signal generator module 3 carries out power magnification, the requirement to signal power is measured owing to common power amplifier module cannot meet, power amplifier module 4 of the present invention adopts military project articles for use PA05 power amplifier chips, this chip operation is stablized, thermal adaptation wide ranges, there is higher signal to noise ratio etc., well the signal that signal generator module 3 produces can be carried out power magnification, with signal power requirement during satisfied measurement.

Electricity voltage-controlled current source VCCS adopts Howland electric current pump to realize signal power amplification, produce to measure electric current, overcome the defects such as power-efficient is low, voltage change range is little, introduce two current feedback in circuit, the outward current amplifying circuit is highly stable, very little by load effect, and achieve current source one end ground connection.

The adjustable excitation source realized according to AD9833 and Howland electric current pump can export the measurement signal meeting and requiring range of frequency, complete the measurement of pole tower ground resistance value when not disconnecting ground lead fast and accurately, raising power system power supply reliability and saving human and material resources are had important meaning.

Claims (5)

1. one kind does not disconnect ground lead pole tower ground resistance measurement injection power frequency method of determining range, it is characterised in that, comprise the steps:

1) measurement model is set up

The tower grounding body equivalent impedance being embedded in soil to have limit for length is Z=R+jX=R+j ω L, along with the raising of survey frequency f, in impedance ground, inductance effect can be more and more obvious, and when injecting high-frequency current, the pole tower ground resistance value of measurement shows as tower grounding impedance value; If injecting electric current signalWhen size reaches more than kHz, then think that tested shaft tower and other shaft tower of surrounding do not form loop, just ignore the stake resistance R of other shaft tower around_nAnd the inductance L of other shaft tower of surrounding_n, lightning conducter and tested shaft tower are all be made up of the rigid material that resistivity is very little, and the relatively tested pole tower ground resistance value of its resistance can be ignored, thus obtain measuring the equivalent simplified model of pole tower ground resistance, i.e. measurement model;

2) determine to inject power frequency

According to step 1) measurement model set up, adopt three cloth pole, pole principles to measure pole tower ground resistances, when not disconnecting ground lead so that the condition that measuring error is little as far as possible is:

$\left\{\begin{array}{c}2{\mathrm{\&pi;fL}}_x<<R_x\\ R_x<<2{\mathrm{\&pi;fL}}_{eq}\end{array}\right.---\left(4\right)$

In formula, f represents injection power frequency, L_xRepresent tested tower grounding body inductance, R_xRepresent tested tower grounding body resistance, L_eqRepresent the lightning conducter equivalent inductive reactance value of two shaft towers contiguous with tested shaft tower;

Formula (4) is converted to the inequality injecting power frequency f is:

$\left\{\begin{array}{c}\frac{R_x}{2{\mathrm{\&pi;L}}_{eq}}<<f\\ f<<\frac{R_x}{2{\mathrm{\&pi;L}}_x}\end{array}\right.---\left(5\right)$

1. the determination of power frequency lower value is injected

For meeting (4) formula, then need to make

$\left\{\begin{array}{c}\frac{2{\mathrm{\&pi;fL}}_x}{R_x}\&RightArrow;0\\ \frac{R_x}{2{\mathrm{\&pi;fL}}_{eq}}\&RightArrow;0\end{array}\right.---\left(6\right)$

Power frequency lower limit function Δ (f) is injected in order:

$\mathrm{\&Delta;}\left(f\right)=\frac{2{\mathrm{\&pi;fL}}_x}{R_x}-\frac{R_x}{2{\mathrm{\&pi;fL}}_{eq}}---\left(7\right)$

When Δ (f) → 0, two formula conditions in (6) formula can be met to the full extent simultaneously, describe the change curve of Δ (f) with frequency f, it is determined that inject the lower value of power frequency;

2. the determination of power frequency higher limit is injected

According to step 1) measurement model built, measured result is R_x+2πfL_xWith 2 π fL_eqParallel value, result to be made more accurate, need to meet

R_x+2πfL_x<<2πfL_eq(8)

Power frequency upper limit function δ (f) is injected in order:

$\mathrm{\&delta;}\left(f\right)=\frac{R_x+2{\mathrm{\&pi;fL}}_x}{2{\mathrm{\&pi;fL}}_{eq}}---\left(9\right)$

When δ (f) → 0, then can meet the condition of (8) formula to the full extent, draw out the graphic representation that δ (f) changes with frequency f, determine to inject the higher limit of power frequency according to curved line relation;

3) determine to inject power frequency scope according to the lower value and higher limit of injecting power frequency, regulate adjustable excitation current source to measure in this range of frequency.

2. one does not disconnect the measurement of ground lead pole tower ground resistance and injects power frequency method of determining range according to claim 1, it is characterized in that: described adjustable excitation current source comprises power source circuit module (1), center-control unit module (2), signal generator module (3) and power amplifier module (4), power source circuit module (1) gives center-control unit module (2) respectively, signal generator module (3) and power amplifier module (4) power supply, center-control unit module (2) control signal generator module (3) produces the current waveform signal needed for measurement, the current waveform signal that signal generator module (3) produces carries out power magnification by power amplifier module (4).

3. one does not disconnect the measurement of ground lead pole tower ground resistance and injects power frequency method of determining range according to claim 2, it is characterised in that: described center-control unit module (2) adopts the microprocessor PIC18F5420 of Microchip company of U.S. production.

4. one does not disconnect the measurement of ground lead pole tower ground resistance and injects power frequency method of determining range according to claim 2, it is characterised in that: described signal generator module (3) adopts the AD9833 of ADI company.

5. one does not disconnect the measurement of ground lead pole tower ground resistance and injects power frequency method of determining range according to claim 2, it is characterised in that: described power amplifier module (4) adopts PA05 power amplifier chips.