CN103954843A - Method for determining injection current frequency range in tower ground resistance measurement process without disconnecting ground lead - Google Patents

Abstract

The invention relates to a method for determining an injection current frequency range in a tower ground resistance measurement process without disconnecting a ground lead. The method aims to solve the problems that when tower ground resistance measurement is conducted without disconnecting the ground lead through a high-frequency parallel connection method, if the injection current signal frequency is relatively high, the grounding body inductance effect will be remarkable, and measuring errors will be increased; besides, a measured tower ground resistance value obtained through the high-frequency parallel connection method is greatly related to the ground measurement current frequency and the relative permeability of soil surrounding a tower, practical surrounding situations are not taken into account in the high-frequency parallel connection method, and therefore the high-frequency parallel connection method is poor in adaptability. According to the method for determining the injection current frequency range in the tower ground resistance measurement process without disconnecting the ground lead, a model for measuring the tower ground resistance without disconnecting the ground lead is built, all influence factors are given comprehensive consideration under the circumstance that the ground lead is not disconnected, and the method is combined with a mathematical analysis method to determine the injection signal frequency range in the accurate tower ground resistance measurement process; a measurement device is constructed according to the theoretical analysis, and efficient and accurate measurement of the tower ground resistance is completed.

Description

A kind of definite method that does not disconnect ground lead pole tower ground resistance measurement Injection Current frequency range

Technical field

The present invention relates to pole tower ground resistance field of measuring technique, particularly a kind of definite method of measuring pole tower ground resistance Injection Current frequency range under ground lead condition that do not disconnect.

Background technology

Pole tower ground resistance is the main parameter of measurement of tower grounding system, directly affects the tripping operation number of times of transmission line of electricity, and operation of power networks is had to vital effect, and therefore measuring accurately and efficiently shaft tower grounding resistance has important engineering significance.

In the method for at present conventional measurement pole tower ground resistance, during fall-of-potential method measurement of Grounding Resistance, need repeated measurement, workload is large, and is difficult for drawing potential drop curve, execute-in-place difficulty; Pincers meter method for measuring adopts electromagnetic induction principle, simple to operate, measures fast, but is easily disturbed, and measuring error is larger, can not meet precision measure requirement; Three electrode method is measured pole tower ground resistance, and accuracy is higher, stable performance, but need take all ground leads apart while measuring, workload is large, inefficiency.

On the basis of three electrode method Measurement accuracy, proposed again high frequency multiple process, the method, by inject single constant high frequency electric current in tested tower grounding body, increases lightning conducter induction reactance, make lightning conducter induction reactance very large and approximate think open circuit, realize the measurement that does not disconnect ground lead.But the method when Injection Current frequency be constant high frequency 10kHz, now, the relatively resistive part of small-sized grounded screen perception can not be ignored, and impedance ground value is with entering to measure power frequency and soil relative permeability increases.Therefore, high frequency multiple process is not considered the impact of grounding body inductive effect on measurement result can not adapt to well field condition according to combined factors such as on-site soil character, measurement power frequencies.

The defect existing for high frequency multiple process, set up relatively complete pole tower ground resistance Measuring System Models, do not disconnect the pole tower ground resistance Measuring System Models that under ground lead condition, theoretical analysis is complete, drawing the Simplified equivalent model of Measurement accuracy pole tower ground resistance when not disconnecting ground lead and considering grounding body inductive effect.Based on this Simplified equivalent model, rational optimized algorithm (reducing as much as possible the impact of grounding body inductive effect on measurement accuracy) is proposed, finally draw in the reasonable measurement current signal frequency range of considering on grounding body perception effect basis, inject the measuring-signal in this frequency range, can facilitate, measure accurately pole tower ground resistance, be different from the single constant high frequency of high frequency multiple process.So just, under the condition that does not disconnect ground lead, take into full account grounding body inductive effect, make up the defect that high frequency multiple process measuring error is large and application is limited.

Summary of the invention

The definite method that the object of this invention is to provide shaft tower grounding resistance measurement Injection Current frequency range under a kind of condition not disconnecting ground lead, measurement defect based on high frequency multiple process when inputting single constant high frequency measuring-signal, the present invention does not disconnect ground lead pole tower ground resistance measurement model by setting up, take into full account grounding body inductance, shaft tower self-resistance, lightning conducter resistance, the factor that the impact such as inductance is measured, through theoretical analysis, draw the equivalent simplified model of Measurement accuracy pole tower ground resistance, and further analyze on this basis Injection Signal frequency range while considering grounding body inductance, reach the object of Measurement accuracy pole tower ground resistance.

For achieving the above object, the technical scheme of employing is that a kind of definite method that ground lead pole tower ground resistance is measured Injection Current frequency range that do not disconnect provided by the invention, comprises the steps:

1) set up measurement model

Being embedded in time-limited tower grounding body equiva lent impedance in soil is Z=R+jX=R+j ω L, raising along with survey frequency f, in impedance ground, inductive effect can be more and more obvious, and when injecting high-frequency current, the pole tower ground resistance value of measurement shows as tower-footing impedance value; If Injection Current signal size reaches kHz when above, thinks that tested shaft tower and other shaft tower around do not form loop, just ignore the stake resistance R of other shaft tower around _nand the inductance L of other shaft tower around _n, lightning conducter resistance R _lnwith tested shaft tower self-resistance R _tnbe all to be made by the very little rigid material of resistivity, the relatively tested pole tower ground resistance value of its resistance can be ignored, thereby obtains measuring the equivalent simplified model of pole tower ground resistance, i.e. measurement model.When Injection Current signal is kHz when above, tower grounding body perception effect can not be left in the basket completely, so do not disconnect under ground lead high-frequency signal measurement, measures gained pole tower ground resistance value and shows as a resistance value.The present invention is according to the grounding design standard GBJ65-83 > > of power industry standard DL/T596-1996 < < power equipment preventive experiment rules > > and < < industry and civilian electric device, within the scope of selection rules, grounding resistance and impact do not disconnect each factor of ground lead measurement pole tower ground resistance (lightning conducter resistance, inductance, shaft tower self-resistances etc.) parameter builds circuit analysis model, through strict theoretical analysis and calculation, thereby determine, do not disconnect the equivalent-circuit model that ground lead is measured pole tower ground resistance, simplify equivalent measurement model.According to this model, to analyze and draw rational measurement pole tower ground resistance frequency range, the impedance ground value while making not disconnect ground lead measurement approaches grounding resistance as far as possible.

2) determine Injection Current frequency

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

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

In formula, f represents Injection Current frequency, L _xrepresent tested tower grounding body inductance, R _xrepresent tested tower grounding bulk resistor, L _eqthe lightning conducter equivalent inductive reactance value that represents two shaft towers contiguous with tested shaft tower;

The inequality that formula (4) is converted to Injection Current 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. Injection Current lower-frequency limit value determines

For meeting (4) formula, need to make

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

Make Injection Current lower-frequency limit function △ (f) be:

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

When △ (f) → 0, can meet to the full extent two formula conditions in (6) formula simultaneously, describe △ (f) with the change curve of frequency f, determine the lower limit of Injection Current frequency;

2. Injection Current upper frequency limit value determines

According to step 1) measurement model built, measured result is R _x+ 2 π fL _xwith 2 π fL _eqparallel connection value, make result more accurate, need to meet

R _x+2πfL _x<<2πfL _eq (8)

Make Injection Current upper frequency limit function δ (f) be:

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

When δ (f) → 0, can meet to the full extent the condition of (8) formula, draw out the curve map that δ (f) changes with frequency f, according to curved line relation, determine the higher limit of Injection Current frequency;

3) according to the lower limit of Injection Current frequency and higher limit, determine Injection Current frequency range, in this frequency range, regulate adjustable excitation current source to measure.

Particularly, above-mentioned adjustable excitation current source comprises power circuit module, central control unit module, signal generator module and power amplifier module, power circuit module is given respectively central control unit module, signal generator module and power amplifier module power supply, central control unit module control signal generator module produces measures required current waveform signal, and the current waveform signal that signal generator module produces carries out power amplification by power amplifier module.

The pole tower ground resistance measurement model of setting up in the present invention affects pole tower ground resistance and measures on each factor basis and set up taking into full account, there is higher reliability and accuracy, frequency range when analyzing and determining measurement pole tower ground resistance based on this model, the grounding resistance measuring like this can accurately be reflected in the exact value of pole tower ground resistance under high-frequency signal measurement.In the determined Injection Current frequency range of the inventive method, can accurately measure pole tower ground resistance, and can not ignore emotional resistance part.

Accompanying drawing explanation

Fig. 1 is tower grounding body equivalent electrical circuit;

Fig. 2 is the equivalent measurement circuit while not disconnecting ground lead measurement pole tower ground resistance;

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

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

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

Fig. 6 is △ (f) and Injection Current frequency f relation curve;

Fig. 7 is δ (f) and Injection Current frequency f relation curve;

Fig. 8 is that adjustable signal encourages former theory diagram.

Embodiment

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

The present invention discloses a kind of ground lead that do not disconnect and measures pole tower ground resistance and inject letter current rate method of determining range, and therefore, the concrete embodiment of the present invention does not disconnect under ground lead condition on shaft tower grounding resistance measurement basis.Method of the present invention is carried out to labor and description below.

1, measurement model is set up and is analyzed

Be embedded in limited stock tower grounding body in soil and can be equivalent to a LR lumped circuit (capacity effect is not obvious in the ordinary course of things), be rendered as impedance Z=R+jX=R+j ω L, circuit model as shown in Figure 1.When injecting direct current or power current, grounding body is approximately equal to resistance R.But along with the raising of survey frequency, in impedance ground, inductive effect can be more and more obvious.In the present invention, by strict theoretical analysis, will make tested shaft tower not disconnect at high frequency the grounding resistance that impedance ground value under ground lead condition is approximately equal to tested shaft tower.

Based on a complete pole tower ground resistance measuring system, set out, the present invention has set up an Equivalent Physical measurement model, as shown in Figure 2.R wherein _lnlightning conducter resistance, R _tnbe shaft tower self-resistance, L is lightning conducter inductance (supposing that the inductance value between adjacent two shaft towers equates) L _ntested shaft tower is other tower grounding body inductance around, R _xtested tower grounding bulk resistor, L _xtested tower grounding body inductance, R _ntested shaft tower other pole tower ground resistances around.

Known according to < < GB50169 erection works of electrical installations code for construction and asseptance of earthed devices > > and < < DL/T621 > >, at soil resistivity, not higher than 500 Ω/m in the situation that, pole tower ground resistance value need be between 4 Ω to 10 Ω.In addition, grounding design standard GBJ65-83 > > according to < < industry with civilian electric device, in transmission system, the normal lightning conducter model adopting is LGJ-185 steel strand wires, its inductance value is 1.28 μ H/m, when span is hundreds of rice, its lightning conducter equivalent inductance is mH level, when injecting measuring-signal, be that kHz is when above, lightning conducter induction reactance value will reach tens hundreds of ohms even, when measuring-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, because it is all to consist of the very little material of resistivity, therefore its value is all less than 0.1 Ω, grounding body inductance value L _nsize in μ H level.

In Fig. 2, Injection Current (following all compute signs are scalar value), wherein via tower grounding body and soil flow, wire back and flow the utmost point, and by ground lead, flow to shaft tower, lightning conducter and the loop stream of the adjacent stems tower formation around telegram in reply stream utmost point.Now, if inject direct current or power current, according to describing, and compare R with tested pole tower ground resistance value size above _tn, R _ln, L _n, L can be left in the basket, the pole tower ground resistance value R trying to achieve _loopfor:

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

From formula (1), while not disconnecting ground lead, what three electrode method measured while injecting power current or direct current is all pole tower ground resistances values in parallel, much smaller than pole tower ground resistance value R to be measured _x.

According to Fig. 2, do not disconnect ground lead measurement model, when while being high-frequency signal measurement, lightning conducter induction reactance value will increase.Now, based on describing, compare R with tested pole tower ground resistance value size above _tn, R _lcan be left in the basket.Yet, L, L _nbut can not be left in the basket, Fig. 2 circuit can be evolved into circuit shown in Fig. 3.

Based on circuit analysis, grounding design standard GBJ65-83 > > according to < < industry with civilian electric device, get each parameter representative value in Fig. 3 circuit: the distance between two shaft towers is elected 350m as, R _x, R _nall be set as 5 Ω, L _n, L _xbe set as 20 μ H, according to circuit shown in Fig. 3, I ₁, I ₂can be by approximate treatment:

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

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, when I is high-frequency signal, (gets f=3kHz),

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

According to above-mentioned calculating rule, I ₂₁, I ₂₂, I ₂₁₁, I ₂₁₂, can be by approximate treatment, work as Injection Current while not being very large, around the electric current of shaft tower can be more and more less to flow into tested shaft tower, almost nil.So, fully think that not disconnecting ground lead measures pole tower ground resistance only two base shaft towers contiguous with tested shaft tower are relevant, Fig. 3 circuit can be converted into circuit shown in Fig. 4.

Work as Injection Current frequency when higher, j ω L _eqwith R _x+1+ j ω L _x+1compare, it is larger that numerical values recited differs, so the metering circuit shown in Fig. 4 can be evolved into the simple equivalent circuit shown in Fig. 5.L in Fig. 5 _eqlightning conducter equivalent inductive reactance value for two shaft towers with tested shaft tower vicinity.

So far, do not disconnect ground lead and measure pole tower ground resistance simple equivalent circuit as shown in Figure 5, based on this model, carry out circuit analysis, determine that not disconnecting ground lead pole tower ground resistance measures Injection Current frequency range.

2, Injection Current frequency range determines

The pole tower ground resistance measurement method cloth utmost point principle proposing in the present invention adopts the measurement guide rule > > and the DL887-2004 < < electric power line pole tower power frequency earthing resistance that are subject to power industry standard DL475-92 < < earthing device power frequency characterisitic parameter to measure three utmost point cloth utmost point principles that > > recommends, under the condition that does not disconnect ground lead, inject the high-frequency signal measurement within the scope of certain frequency, by measuring voltage pole, the voltage that electric current is extremely gone up, the current signal tested pole tower ground resistance value that converts.In the present invention, propose the method for location survey amount pole tower ground resistance frequency range really and can reasonably determine measuring-signal frequency range, reduce the impact of tower grounding body perception on measurement result.Shown in Fig. 5, when not disconnecting ground lead, make the condition that measuring error is as far as possible little be:

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

The inequality that formula (4) is converted to the power frequency f that needs injection 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), Injection Current lower-frequency limit value determines

The pole tower ground resistance measurement model of setting up according to Fig. 5, carries out when pole tower ground resistance is measured meeting the definite inequality group of (4) formula not disconnecting ground lead, for meeting (4) formula condition, needs to make

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

But in actual measurement, power frequency f can not make simultaneously level off to 0, establish Injection Current lower-frequency limit function △ (f) and be:

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

When △ (f) → 0, can meet to the full extent two formula conditions in (6) formula simultaneously, calculate the value that △ (f) meets the Frequency point as much as possible of formula (6) requirement, and describe △ (f) with the change curve of frequency f, just can determine the lower limit of Injection Current frequency.

2), Injection Current upper frequency limit value determines

According to Fig. 5, build and measure pole tower ground resistance model, do not disconnect ground lead carry out pole tower ground resistance while measuring the stake resistance model of tested shaft tower actual be a resistance value, and measured result is R _x+ 2 π fL _xwith 2 π fL _eqparallel connection value, make result more accurate, need to meet

R _x+2πfL _x<<2πfL _eq (8)

If Injection Current upper frequency limit function δ (f) 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, can meet to the full extent the condition of (8) formula, calculate the value that δ (f) meets the Frequency point as much as possible of (8) formula requirement, and draw out the curve map that δ (f) changes with frequency f, according to curved line relation, just can determine the higher limit of Injection Current frequency.

3), the accurate scope of Injection Current frequency determines

By the R in Fig. 5 _x, L _x, L _eqaccording to < < GB50169 erection works of electrical installations code for construction and asseptance of earthed devices > > and < < GB50057-94 lightning Protection Design standard > >, compose respectively with the reference value within the scope of rules: R _x=10 Ω, L _x=10uH, L _eq=10mH, brings in formula (4), (5) and obtains:

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

By formula (10), roughly drawn in theory the frequency range of measuring electric current place.But in conjunction with practical measurement requirement, should improve and measure power frequency increase lightning conducter induction reactance, avoid itself and peripheral rod tower to form measuring circuit, increase error, simultaneously avoid again measuring power frequency when higher, grounding body inductive effect is obvious, increases measuring error, comprehensive above factor, determines a frequency measurement scope more accurately.

According to definite method of the Injection Current frequency upper limit value and lower limit value of mentioning in the present invention, calculate pole tower ground resistance measurement model each several part resistance value (R _x=10 Ω, L _x=10uH, L _eq=10mH), then calculate △ (f) (%), δ (f) value (%).Make △ (f) and Injection Current frequency f relation curve and δ (f) and Injection Current frequency f relation curve 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) levels off to 0, and variable quantity is very little, almost levels off to zero, and according to practical measurement requirement, the lower frequency limit of measuring electric current is set as 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 of measuring power frequency is set as to 12kHz.

In sum, can determine the current signal of pole tower ground resistance measurement more accurately frequency measurement scope a: 3kHz<f<12kHz.

After determining survey frequency scope, just can within the scope of this, select many class frequencys value to measure, then the data that measure are carried out to data pre-service and fitting of a polynomial, obtain a measured value the most accurately.

The pole tower ground resistance measurement method that multifrequency electric current injects and device can be realized the Measurement accuracy of pole tower ground resistance resistance in the situation that not disconnecting ground lead.By adjustable signal driving source, produce the measuring-signal within the scope of certain frequency, the current signal that signal source is 1kHz every 15 seconds output 3-12kHz stepping, measure the measuring-signal of voltage pole and the electric current utmost point under each frequency, then by measuring the grounding resistance obtaining that converts, carry out certain optimization process, so just can on the basis of considering grounding body inductive effect, accurately reflect the grounding resistance of tested shaft tower.The structural drawing of adjustable excitation current source is as Fig. 8.

Adjustable excitation current source mainly consists of power circuit module 1, central control unit module 2, signal generator module 3 and power amplifier module 4.Wherein central control unit module 2 control signal generator modules 3 produce and measure required current waveform signal (being mainly sine wave signal), and the current waveform signal that signal generator module 3 produces carries out power amplification by power amplifier module 4.

Power circuit module 1 is the effectively basis of operation of whole system, and because system function module is more, the supply voltage of each module is not identical, therefore need to carry out conversion process to ensure the normal effectively operation of constructing system to the voltage of power supply source lithium battery.PA05 chip power supply voltage range in power amplifier module 4 is 15V to 45V, therefore can adopt longer draw ± 20V of 20V lithium battery group series connection voltage in serviceable life.And signal generator module 3 be take AD9833 as core, its required voltage scope is+2.3V is to+5.2V, so can adopt high performance LM2576-5.0 chip to realize voltage transitions and to its power supply.Another central control unit module 2 required voltages are 5V, and we still can adopt LM2576-5.0 chip conversion output to its power supply.

The high-performance microprocessor PIC18F5420 that central control unit module 2 adopts U.S. Microchip company to produce, this chip has 44 ports, programmed environment easy operating, cost performance is higher.By programming control signal generator module 3, produce and measure required waveform signal.

Signal generator module 3 adopts DDS (Direct Digital Synthesis, Direct Digital frequency synthesis) technology to realize the output of variable ratio frequency changer sinusoidal signal.This technology is a kind ofly to take sampling thheorem as basic totally digitilized Waveform generating method, is the third generation frequency synthesis technique after Direct Digital Frequency Synthesizer Technology and PLL pll frequency synthesizer.The Direct Digital frequency synthesis chip AD9833 of Ta Yi ADI company is that core forms, and AD9833 is a low-power consumption, programmable waveform generator, has the serial line interface line with SPI interface standard compatibility.Central control unit module 2 is connected with AD9833 by spi bus, and realize central control unit module 2 control signal generators and produce sine wave signal, and conditioning signal source frequency.

The signal that power amplifier module 4 is mainly used in signal generator module 3 to produce carries out power amplification, because common power amplifier module cannot meet the requirement of measuring signal power, power amplifier module 4 of the present invention adopts military project articles for use PA05 power amplifier chips, this chip operation is stable, temperature accommodation is wide, have higher signal to noise ratio (S/N ratio) etc., the signal that can well signal generator module 3 be produced carries out power amplification, signal power requirement while measuring to meet.

Electricity voltage-controlled current source VCCS adopts Howland current pump to realize signal power amplification, produce and measure electric current, the defects such as power-efficient is low, change in voltage scope is little have been overcome, in circuit, introduce two current feedback, the output current of amplifying circuit is highly stable, be subject to load effect very little, and realized current source one end ground connection.

The adjustable driving source of realizing according to AD9833 and Howland current pump can be exported the measuring-signal of the frequency range that meets the demands, under the condition that does not disconnect ground lead, complete fast and accurately the measurement of pole tower ground resistance value, to improving power system power supply reliability and saving human and material resources, have great importance.

Claims (5)

1. do not disconnect ground lead pole tower ground resistance and measure a definite method for Injection Current frequency range, it is characterized in that, comprise the steps:

1) set up measurement model

Being embedded in time-limited tower grounding body equiva lent impedance in soil is Z=R+jX=R+j ω L, raising along with survey frequency f, in impedance ground, inductive effect can be more and more obvious, and when injecting high-frequency current, the pole tower ground resistance value of measurement shows as tower-footing impedance value; If Injection Current signal size reaches kHz when above, thinks that tested shaft tower and other shaft tower around do not form loop, just ignore the stake resistance R of other shaft tower around _nand the inductance L of other shaft tower around _n, lightning conducter resistance R _lnwith tested shaft tower self-resistance R _tnbe all to be made by the very little rigid material of resistivity, the relatively tested pole tower ground resistance value of its resistance can be ignored, thereby obtains measuring the equivalent simplified model of pole tower ground resistance, i.e. measurement model;

2) determine Injection Current frequency

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

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

In formula, f represents Injection Current frequency, L _xrepresent tested tower grounding body inductance, R _xrepresent tested tower grounding bulk resistor, L _eqthe lightning conducter equivalent inductive reactance value that represents two shaft towers contiguous with tested shaft tower;

The inequality that formula (4) is converted to Injection Current 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. Injection Current lower-frequency limit value determines

For meeting (4) formula, need to make

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

Make Injection Current lower-frequency limit function △ (f) be:

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

When △ (f) → 0, can meet to the full extent two formula conditions in (6) formula simultaneously, describe △ (f) with the change curve of frequency f, determine the lower limit of Injection Current frequency;

2. Injection Current upper frequency limit value determines

According to step 1) measurement model built, measured result is R _x+ 2 π fL _xwith 2 π fL _eqparallel connection value, make result more accurate, need to meet

R _x+2πfL _x<<2πfL _eq (8)

Make Injection Current upper frequency limit function δ (f) be:

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

When δ (f) → 0, can meet to the full extent the condition of (8) formula, draw out the curve map that δ (f) changes with frequency f, according to curved line relation, determine the higher limit of Injection Current frequency;

3) according to the lower limit of Injection Current frequency and higher limit, determine Injection Current frequency range, in this frequency range, regulate adjustable excitation current source to measure.

2. a kind ofly according to claim 1 do not disconnect definite method that ground lead pole tower ground resistance is measured Injection Current frequency range, it is characterized in that: described adjustable excitation current source comprises power circuit module (1), central control unit module (2), signal generator module (3) and power amplifier module (4), power circuit module (1) is given respectively central control unit module (2), signal generator module (3) and power amplifier module (4) power supply, central control unit module (2) control signal generator module (3) produces measures required current waveform signal, the current waveform signal that signal generator module (3) produces carries out power amplification by power amplifier module (4).

3. a kind ofly according to claim 2 do not disconnect definite method that ground lead pole tower ground resistance is measured Injection Current frequency range, it is characterized in that: the microprocessor PIC18F5420 that described central control unit module (2) adopts U.S. Microchip company to produce.

4. a kind ofly according to claim 2 do not disconnect definite method that ground lead pole tower ground resistance is measured Injection Current frequency range, it is characterized in that: described signal generator module (3) adopts the AD9833 of ADI company.

5. a kind ofly according to claim 2 do not disconnect definite method that ground lead pole tower ground resistance is measured Injection Current frequency range, it is characterized in that: described power amplifier module (4) adopts PA05 power amplifier chips.