CN1243254A - Isofrequency measuring method for earth resistance and apparatus thereof - Google Patents
Isofrequency measuring method for earth resistance and apparatus thereof Download PDFInfo
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Abstract
The present invention relates to an abnormal frequency measurement method of grounding resistance and its equipment. It is characterized by injecting the measuring current signal which is produced by difference frequency power source and different from working frequency into the measured grounded counterpoise to measure grounding resistance, making the abnormal frequency current and measured voltage undergo the process of filtering treatment and data analysis to obtain real part and imaginary part of its fundamental component, adopting hardware and software and utilizing formula to calculate the grounding resistance of the measured grounded counterpoise, and displaying its measured result. Said abnormal frequency measuring signal uses two frequencies of 40Hz and 60Hz,so it can effectively suppress the interference on working frequency and other signal, therefore its measurement accuracy is high, and its measured data is real and reliable.
Description
The present invention relates to the High-Voltage Technology field, especially for grounded screen power frequency earthing resistance different-frequency measuring method and devices such as transformer station, power house and operating offices.
At present, according to the knowledge of the applicant, the measuring technique of the stake resistance of grounded screen is mainly contained big current method and different-frequency measure method.Wherein, big current method must be raised the current potential of earth mat for the interference of elimination power frequency to measuring of the transformer station that is in operation, and promptly realizes by the measurement electric current that strengthens the electric current utmost point, maximum measurement electric current can reach 100A, make the bulky of equipment needed thereby, and need heavy in section electric current utmost point lead-in wire, when field survey, unwrapping wire even drag line with tractor, field conduct is difficulty quite, and the equipment manufacturing cost height of use carries the transportation inconvenience.The method of existing different-frequency measure stake resistance generally adopts the less measuring-signal that differs from power frequency, can avoid power frequency and disturb, and is convenient for measuring, and uses equipment manufacturing cost cheap.Chinese patent literature CN92208327,4 disclose a kind of ground meter, this instrument adopts frequency-selective filtering to produce 70-250HZ, the sinusoidal wave measuring-signal of 50-500mA, realize using the different-frequency measuring method measurement of Grounding Resistance, because the different-frequency measure signal gets too small that this instrument adopts, maximum also has only 500mA, grounding resistance of transformer substation grounding net is mostly between 0.1 Ω-0.5 Ω, if inject measurement electric current 500mA to grounded screen by the electric current utmost point, then the voltage drop that obtains on extremely at boosting voltage then has only 0.05V-0.25V, and the power frequency interference current of grounded screen can reach about 10V in the pressure drop that boosting voltage produces on extremely, it adopts passive double T, potential double T and active double-t circuit constitute frequency-selecting filter and eliminate interference units, the equifrequent undesired signal of filtering direct current and 50HZ, actual value in the hope of the stake resistance that obtains tested earthing device, but because the filtering mode that this instrument adopts can not be eliminated power frequency and other high fdrequency component fully, the precision of its measurement data still is affected, this instrument can only be measured the impedance ground value of earth mat simultaneously, and can't record grounding resistance R, and the different-frequency measure signal of this instrument employing is in the scope of 70-250HZ, 50HZ is far away from power frequency, has also increased the inaccuracy that the power frequency earthing resistance actual value is measured.This instrument can only replace the ground connection megger, is used for the stake resistance of measuring staff tower, is unsuitable for surveying the stake resistance of large-scale earth mat.At present, in the world stake resistance being adopted the representational of different-frequency measuring method is the test that Ontario, Canada hydroelectric board once did, see IEEE91 meeting paper in winter concentrate record by P.R, " substation grounding system test and calculating " literary composition of work such as Pitlai Member, the measurement source that is different from power frequency (the power frequency standard of Canadian state is 60HZ) frequency is adopted in test, promptly provide the sine ac power supply of 65HZ-70HZ to inject the measurement electric current of 5-20A (240V voltage) again to the electric current utmost point by a transformer by this set generator group, adopt the binary channels spectrum analyzer, the measuring-signal of 65-70HZ is separated from power frequency and other high-frequency signals, this method is relatively bigger near power frequency and signal to noise ratio (S/N ratio) because of its alien frequencies that adopts, thereby reaches and remove the influence to its measurement of power frequency and other high-frequency interferencing signal.But, the measuring-signal source that the test method of this measurement adopts is provided by transformer by this set generator, make the equipment heaviness, inconvenience is on-the-spot to be used, and be growing on and on required the comparing with equipment of big current method, and measure portion is only finished by spectrum analyzer, except that complicated operation, show that measurement data is not too directly perceived, and only deficiency is also arranged, be not easy to the correcting measuring error with the sine wave source that is higher than power frequency.Chinese patent literature 91219435.9 disclosed " ultralow frequency microcomputer type ground resistance measuring instrument ", by microcomputer, the ultralow frequency power generator, signal selecting circuit, the voltage signal passage, the signal of current return calculates and correction error, demonstrate measured value intuitively by display, although it has easy to use, simple in structure, and jamproof characteristic is arranged, but still exist not enough on its circuit design, measuring-signal is less, only use passive low ventilating filter and active low-pass filter to get rid of power frequency and the undesired signal that is higher than power frequency, by the measuring-signal of calculating testing instruments self-correcting and the ratio between the actual measured signal, determine the actual value of stake resistance by means of sample resistance, and come the corrected Calculation error through the phase differential of the square-wave signal exported after the shaping by the electrical measurement electric signal that sends, obviously be not enough, the final stake resistance that shows on display is not got rid of the influence of capacitive reactance and induction reactance component, more effectively this influence is not dropped to minimumly, fundamentally improve the measuring accuracy of device.
The objective of the invention is, different-frequency measuring method imperfection at above-mentioned prior art existence, it is excessive that the different-frequency measure signal frequency departs from power frequency, the power of different-frequency measure signal is too small, be difficult to really realize the signal to noise ratio (S/N ratio) height, can not suppress the influence of power frequency and other undesired signal effectively to measuring, be difficult for guaranteeing measuring accuracy, the measuring equipment that uses is excessive or cross the defective of complicated or metering circuit self design adopted and be difficult to adapt to the needs of in-site measurement and be far from being and guarantee the deficiency of accuracy of measurement, improve, a kind of new stake resistance different-frequency measuring method and device are proposed, for realizing to operating transformer station, on-the-spot stake resistance such as power house and communication station convenient, measure accurately condition and guarantee are provided.
The technical scheme of the stake resistance different-frequency measuring method that the present invention proposes is, adopt the alien frequencies power source to produce the measurement current signal that is different from power frequency, inject the auxiliary current utmost point of tested earth mat, obtain the alien frequencies voltage signal that this measurement electric current produces from tested earth mat boosting voltage, non-power-frequency current, voltage measurement signal obtains the real part and the imaginary part of non-power-frequency current signal and voltage signal fundametal compoment through Filtering Processing and data analysis, it is characterized in that, stake resistance and the reactance of adopting hardware and software equipment to calculate tested earth mat by formula, show the end product of measuring calculating by display device, the alien frequencies power source that adopts is a Sine Wave Pulse Width Modulation formula adjustable frequency power source, the electric current amount of exports that injects the tested earth mat auxiliary current utmost point is 3-5A, and the alien frequencies frequency of employing is 40HZ and two frequencies of 60HZ.
It is characterized in that the alien frequencies power source that is adopted is a 500W Sine Wave Pulse Width Modulation formula adjustable frequency power source.
It is characterized in that, to non-power-frequency current, voltage signal carries out Filtering Processing and carries out respectively, at first they are taken a sample respectively, make their timesharing carry out filtering by notch filter and bandpass filter, obtain the alien frequencies signal that can detect, it is to become digital quantity and send into intelligent processing system handling by the A/D change-over circuit by the measurement voltage signal after the Filtering Processing and current signal that this alien frequencies signal is carried out data analysis, filtered alien frequencies signal is being carried out in the processing procedure, measuring system is to the Frequency Synchronization of voltage and current signals sampling and alien frequencies power source, to current signal, voltage signal is done to widen the window spectrum analysis and is finished by the intelligent processing system that single-chip microcomputer constitutes, fundametal compoment is wherein separated, further removed interference components.
It is characterized in that, adopt following computing formula,
U＝Ur+jUi
I=Ir+jIiUr, Ui, Ir, Ii are respectively the fundamental voltage of alien frequencies signal, the real part and the imaginary part of electric current
Z is impedance, and R is the equivalent stake resistance of grounded screen, and X is a grounded screen equivalence earthing reactance, and f is the alien frequencies frequency, 40HZ or 60HZ
Because reactance value and frequency dependence should be adapted to the value f=50HZ under the power frequency
Should deduct the mutual inductance anti-(this value can obtain according to the distance calculation between wire length and lead-in wire) between the lead-in wire simultaneously.
The device that the stake resistance different-frequency measuring method that the present invention proposes adopts, comprise the alien frequencies power source, current sensor, voltage sensor, two operational amplifiers, programmable amplifying circuit, the A/D change-over circuit, Single Chip Microcomputer (SCM) system, liquid crystal display and control panel, it is characterized in that, trap and bandwidth-limited circuit have been adopted, the Synchronous Sampling Pulse loop, sampling hold circuit, the current output terminal mouth of alien frequencies power source connects current output terminal respectively, current sensor, operational amplifier connects trap and bandwidth-limited circuit, the output of trap and bandwidth-limited circuit connects programmable amplifying circuit, programmable amplifying circuit connects sampling hold circuit, the synchronous signal output end S2 of alien frequencies power source and the input end in Synchronous Sampling Pulse loop join, the output in Synchronous Sampling Pulse loop connects the control end of sampling hold circuit, the output termination A/D change-over circuit of sampling hold circuit, become the A/D change-over circuit of digital signal to connect with Single Chip Microcomputer (SCM) system analog signal conversion, Single Chip Microcomputer (SCM) system links to each other with liquid crystal display and control panel by control line and address/data bus again.
It is characterized in that the alien frequencies power source adopts sinusoidal pulse width modulation formula (SPWM) the adjustable frequency power source that has (IGBT) module to constitute.
It is characterized in that; the alien frequencies power source has adopted two filtering circuits; modulation circuit; totalizer; triangular-wave generator; comparer; isolation drive and holding circuit; the start-up control circuit; bridge rectifier circuit; the DC-AC inverter bridge of forming by (IGBT) module; the LC filtering circuit; feedback circuit and isolation transformation electrical equipment are formed; wherein; the input end of the output termination filtering circuit of Single Chip Microcomputer (SCM) system sinusoidal modulation signal; the output terminal of filtering circuit has one the tunnel as synchronous signal output end and connect the input end of modulation circuit; the output of modulation circuit and the output of feedback circuit are joined with an input end of totalizer respectively; the output terminal of totalizer is connected to the reverse input end of comparer; the positive input of the output termination comparer of triangular-wave generator; the output of comparer links to each other through the gate pole of the DC-AC inverter bridge that isolation drive and holding circuit and IGBT module are formed; the start-up control circuit meets 220V and exchanges input; the output terminal of start-up control circuit connects bridge rectifier circuit; bridge rectifier circuit connects filtering circuit; the output of filtering circuit is connected to the input end of inverter bridge; the output of inverter bridge connects the LC filtering circuit; the LC filtering circuit connects the input end of feedback circuit and the input end of output isolation transformer more respectively; the output of output isolation transformer is the output port of non-power-frequency current; in addition, start-up control circuit; isolation drive links to each other with Single Chip Microcomputer (SCM) system by control bus with the control end of holding circuit and inverter bridge.
It is characterized in that, trap and bandwidth-limited circuit are by two multi-way switchs, 50HZ quadravalence trap filter, 4 0HZ quadravalence biquadratic bandpass filter and 60HZ quadravalence biquadratic bandpass filter are formed, two input ends of multi-way switch are respectively voltage signal input end and current signal input end, the output of multi-way switch links to each other with the input end of 50HZ quadravalence notch filter, the output of 50HZ quadravalence trap filter links to each other with two input ends of multi-way switch respectively with the output of 40HZ quadravalence biquadratic bandpass filter and 60HZ quadravalence biquadratic bandpass filter, and the output of multi-way switch is the output of trap and bandwidth-limited circuit.
Advantage of the present invention is, overcome the deficiency that prior art exists, be operating power house (factory), the measurement of grounded screen such as transformer station and operating office industrial frequency electric resistance provides convenient practicality, measuring method that accuracy is high and device, this different-frequency measuring method is simple and easy to do, accurately and reliably, it has adopted power is the alien frequencies power source of 500W, can send 3-5A different-frequency measure current signal, and high performance trap and bandwidth-limited circuit, can overcome the influence of power frequency and other undesired signals effectively to measurement result, can reflect the power frequency earthing resistance value of tested grounded screen truly, precision is better than 1.0%, and the device that is adopted is integrated in one alien frequencies signal source and measurement component, accomplished that volume is little, in light weight, be suitable for on-the-spot the use, be convenient for carrying.
Fig. 1, stake resistance different-frequency measure measurement device circuit electricity functional-block diagram
Fig. 2, the present invention adopt the circuit block diagram of different-frequency measure device
Fig. 3, the present invention adopt the circuit block diagram of the alien frequencies power source of device
Fig. 4, the present invention adopt the trap of device and the block scheme of bandwidth-limited circuit
Embodiments of the invention at length are described in detail in detail below with reference to the accompanying drawings.
As shown in Figure 1, tested earth mat auxiliary current utmost point lead-in wire is connected to current output terminal (red end) C2 of the measurement mechanism of the present invention's employing, the lead-in wire of the tested earth mat boosting voltage utmost point is linked voltage input end (red end) P2 of measurement mechanism, voltage input end (black terminal) P1 and current output terminal (black terminal) C1 receive tested earth mat center respectively, by the utmost point of the stake resistance of amount earth mat, line is arranged and distance is confirmed by " the measurement guide rule of earthing device power frequency characterisitic parameter " requirement (DL475-92), if adopt " three electrode method ", auxiliary current utmost point wire length is 4-5 a times of tested earth mat diagonal distance, boosting voltage utmost point wire length is about 62% of auxiliary current utmost point lead-in wire, after ready, turn on the power switch, select the frequency (40HZ or 60HZ) of the non-power-frequency current of output by button on the measurement mechanism panel that adopts, there is power frequency interference signals if find on the voltage pole, can trap and bandwidth-limited circuit 6 be dropped into by the button on the panel, the alien frequencies power source 1 that adopts is that 500W Sine Wave Pulse Width Modulation formula (SWPM) adjustable frequency power source produces the different-frequency measure current signal, by the sub-C1 of current output terminal, C2 injects the 60HZ measurement electric current I 1 of 3-5A a little more than power frequency to tested earth mat, perhaps a little less than the measurement electric current I 2 of the 40HZ of power frequency.Obtain voltage signal U at boosting voltage on extremely by the sub-P1 of voltage input end, P2, according to selecting for use the alien frequencies frequency to determine that voltage signal U is U1 (the alien frequencies frequency is that the measurement electric current I 1 of 60HZ flows through the voltage drop that the boosting voltage utmost point is produced) or U2 (voltage drop of boosting voltage utmost point generation is crossed in the drainage of 40HZ alien frequencies frequency measurement electric current).By current sensor 2 and voltage sensor 3, to different-frequency measure signal I1 (non-power-frequency current of 60HZ), U1 or I2 (non-power-frequency current of 40HZ), U2 (the alien frequencies voltage of 40HZ) takes a sample, make it pass through the pre-process circuit of forming by operational amplifier, and by 60HZ or 40HZ quadravalence biquadratic band filter 28 all, 29, obtain purer 60HZ or 40HZ alien frequencies signal, the alien frequencies signal is passed through programmable amplifying circuit 7, amplification is sent into A/D converter 10 and is handled, and signal amplitude adjusted to full scale near A/D converter 10, to guarantee the precision of data-switching, then the digital signal after A/D converter 10 conversions is sent into Single Chip Microcomputer (SCM) system 11 based on 80196KC, measurement data is handled and measurement result is shown, measurement data is stored.Single Chip Microcomputer (SCM) system 11 regulating and controlling sinusoidal signal S1 frequency and amplitudes; thereby change the frequency and the amplitude of alien frequencies power source 1; single-chip microcomputer 11 has a control bus S3; the startup of S3 control alien frequencies power source 1; the start and stop of IGBT inverter bridge in the control alien frequencies power source 1; and thereby the fault that detection alien frequencies power source 1 may occur is taked safeguard measure; measure electric current and assist out terminal C1 through excess current; C2 is added to tested earth mat by auxiliary current utmost point lead-in wire; on the current return that the auxiliary current utmost point and the earth constitute; current signal I (being I1 or I2) and voltage signal U (being U1 or U2); I1 is corresponding to U1; I2 is corresponding to U2) be quick timesharing by trap and bandwidth-limited circuit 6; the output of trap and bandpass filter 6 is through programmable amplifying circuit 7; to send into sampling hold circuit 9 after the signal amplitude amplification; the homogenous frequency signal S2 of alien frequencies power 1 source generation is through Synchronous Sampling Pulse loop 8 simultaneously; its frequency becomes 256 times of S2; deliver to the synchronizing signal of the control end do measurement of sampling hold circuit 9 through signal; the measurement current signal that A/D converter 10 is sent sampling hold circuit 9 here and the analog signal conversion of voltage signal are digital signal; the electric current that 11 pairs of A/D converters 10 of 80196KC Single Chip Microcomputer (SCM) system are sent here; voltage signal carries out spectrum analysis; promptly carry out filtering once more by software; further remove various interference components; with the real part of the fundametal compoment that accurately obtains different-frequency measure electric current and voltage and imaginary part (with voltage signal positive going zeror crossing point as the vector reference point); Ir; Ii; Ur; the then tested earth mat equivalence of Ui stake resistance R, reactance X is calculated by following formula by software and shows on LCD.
F is alien frequencies frequency 60HZ or 40HZ
Since the relevant reactance value of reactance value need with frequency the value under the power frequency:
F is alien frequencies frequency 60HZ or 40HZ
Reactance value should be adapted to the value f=50HZ under the power frequency, should deduct the mutual inductance between the lead-in wire simultaneously, and this value can obtain according to the physical length of lead-in wire and the distance calculation between the lead-in wire.
As Fig. 2, Fig. 3, shown in Figure 4, the measurement mechanism that the stake resistance different-frequency measuring method that proposes according to the present invention adopts, comprise alien frequencies power 1, current sensor 2, voltage sensor 3, two operational amplifiers 4 and 5, trap and bandwidth-limited circuits 6, programmable amplifying circuit 7, Synchronous Sampling Pulse loop 8, sampling hold circuit 9, A/D converter 10, Single Chip Microcomputer (SCM) system 11, liquid crystal display and control panel 12.The sub-C1 of current output terminal, C2 on the panel that the current output terminal mouth S4 of alien frequencies power source 1, S5 connect measurement mechanism respectively, the size of its electric current are by current sensor 2 sampling decisions.Current sensor 2, the output of voltage sensor 3 is concatenation operation amplifier 4 and 5 respectively, connect trap and bandwidth-limited circuit 6, the output of trap and bandwidth-limited circuit 6 connects programmable amplifying circuit 7, programmable amplifier 7 connects sampling hold circuit 9, the synchronous signal output end S2 of alien frequencies power source 1 links to each other with the input in Synchronous Sampling Pulse loop 8, the output in Synchronous Sampling Pulse loop 8 connects sampling hold circuit 9, the output termination A/D change-over circuit 10 of sampling hold circuit 9, become the A/D converter 10 of digital signal to connect with Single Chip Microcomputer (SCM) system 11 again analog signal conversion, Single Chip Microcomputer (SCM) system 11 links to each other with liquid crystal display and control panel 12 by control line and address/data bus, and control bus S3 of Single Chip Microcomputer (SCM) system 11 and control end S1 and alien frequencies power source 1 connect.The alien frequencies power source 1 that adopts is for having adopted Sine Wave Pulse Width Modulation formula (SDWM) power amplifier of IGBT module, power 〉=500W, non-power-frequency current output valve 3-5A.Alien frequencies power source 1 has adopted filtering circuit 13 and filtering circuit 21, and modulation circuit 14, totalizer 15, triangular-wave generator 16, comparer 17, isolation drive and holding circuit 18, start-up control circuit 19, bridge rectifier circuit 20, IGBT form DC-AC inverter bridge 22, LC filtering circuit 23, feedback circuit 24 and output and isolate transformation electrical equipment 25 compositions.Wave-wave circuit 13 is an active filter, and filtering circuit 21 is a passive filter.The sine wave of the frequency adjustable constant amplitude that is provided by Single Chip Microcomputer (SCM) system 11 is through filtering circuit 13 inputs, as synchronous signal output end S2 output, and the frequency adjustable constant amplitude of synchronizing signal.Filtering circuit 13 with and modulation circuit 14 connect; the output of the output of modulation circuit 14 and feedback circuit 24 is joined with an input end of totalizer 15 respectively; the output of totalizer 15 is connected to the reverse input end of comparer 17; the positive input of the output termination comparer of triangular-wave generator 16; the output of comparer 17 is through the input end of isolation drive with the DC-AC inverter bridge 22 of holding circuit 18 and IGBT composition; the output of inverter bridge 22 connects LC filtering circuit 23; LC filtering circuit 23 connects the input end of feedback circuit 24 and the input end of output isolation transformer 25 respectively; the start-up control circuit 19 in addition; the control end of isolation drive and holding circuit 18 and inverter bridge 22 connects by control bus S3 and Single Chip Microcomputer (SCM) system 11; the output S4 of output isolation transformer; S5 is the output port of alien frequencies power source.The frequency output signal VS that the output of filtering circuit 13 is carried out the amplitude adjusting and come through totalizer 15 and feedback through modulation circuit 14; produce the high frequency triangle wave of a fixed frequency as carrier signal Ut by triangular-wave generator 16; from the rect.p. of comparer 17 outputs one pulsewidth with sinusoidal rule variation; the moving gate pole that is applied to the DC-AC inverter bridge 22 of IGBT composition by isolation drive and holding circuit 18 simultaneously of taut pulse; power frequency 220V exchanges through start-up control circuit 19 again through the DC voltage of bridge rectifier circuit 22 rectifications becoming pulsation; the rect.p. electric current that the pulsewidth that the output terminal that is loaded into the DC-AC inverter bridge 22 that IGBT forms again after filtration behind wave circuit 21 wave-waves has obtained amplifying changes with sinusoidal rule; through delivering to output isolation transformer 25 behind the LC filtering circuit 23 filtering carrier signal Ut; export the pure alien frequencies sine wave signal of 3-5A at the output terminal of output isolation transformer 25; most preferred embodiment of the present invention provides 40HZ and two Frequency points of 60HZ; alien frequencies power source 1 can be selected to export 40HZ non-power-frequency current measuring-signal or select output 60HZ non-power-frequency current measuring-signal as required; the output of LC filtering circuit 23 enters the input end of totalizer 15 through backfeed loop 24, is the stability in order to ensure 1 output of alien frequencies power source.It is in order to control the startup in industrial frequency rectifying loop that control bus S3 links to each other with the control end of start-up control circuit 19; the control end of control bus S3 and isolation drive and holding circuit 18 connects; it is the temperature that detects each element in the alien frequencies power source 1; too high as temperature; promptly send alerting signal, taking safeguard measure, and on control panel, show corresponding prompt; simultaneously control bus S3 links to each other with the control end of inverter bridge 22, is for the startup of controlling inverter bridge and stops.Trap that the present invention adopts and bandwidth-limited circuit 6 are by two multi-way switchs 26,30,50HZ quadravalence resistance-trap filter 27,40HZ quadravalence biquadratic bandpass filter 28 and 60HZ quadravalence biquadratic bandpass filter 29 are formed, voltage signal U wherein, current signal I, connect two input ends of multi-way switch 26, the output of multi-way switch 26 links to each other with the input end of 50HZ quadravalence biquadratic bandpass filter 27, the output of 50HZ quadravalence trap filter 27 connects the input of 40HZ quadravalence biquadratic bandpass filter 28 and 60HZ quadravalence biquadratic bandpass filter 29, and the output of 40HZ quadravalence biquadratic bandpass filter 28 and 60HZ quadravalence biquadratic bandpass filter 29 links to each other with two input ends of multi-way switch 30 respectively.The output of multi-way switch 30 is every the output that involves bandwidth-limited circuit 6.Trap and bandwidth-limited circuit 6 have reasonably been selected 50HZ quadravalence notch filter 27 and bandpass filter 28,29 exponent number, i.e. filtering power frequency to greatest extent and other audio disturbances signal, can allow the timesharing of alien frequencies voltage and current respectively by same group of 50HZ quadravalence notch filter 27 and bandpass filter 28 or 29 again, its amplitude and U, phase place between the I does not produce skew, multi-way switch 26 is adjusted timesharing cut-in voltage signal U and current signal I, handoff delay was less than 1 second, the output of multi-way switch 26 at first enters 50HZ notch filter 27, through the centre frequency f of notch filter 27
o=50HZ, bandwidth B=0.26f
o, stopband SB=0.024f
o, the minimal attenuation of stopband is not less than 40dB, promptly disturbs for the 50HZ power frequency and still can decay more than 100 times.The output of 50HZ quadravalence trap filter 27 connects 40HZ quadravalence biquadratic bandpass filter 28 and 60HZ quadravalence biquadratic bandpass filter 29 simultaneously, only allow the measuring-signal of 40HZ and 60HZ to pass through respectively, the time power frequency and frequency thereof various undesired signals can decay more than the 40dB, after multi-way switch 30 switched, the different-frequency measure signal that obtains purer 40HZ or 60HZ was made a gift to someone and is handled in the programmable amplifying circuit 7 by the output signal of 40HZ quadravalence secondary bandpass filter 28 and 60HZ biquadratic bandpass filter 29.
Claims (8)
1, the stake resistance different-frequency measuring method, adopt the alien frequencies power source to produce the measurement current signal that is different from power frequency, inject the tested earth mat auxiliary current utmost point, from the tested earth mat boosting voltage utmost point obtain this measurement electric current by the time alien frequencies voltage signal that produces, non-power-frequency current, voltage measurement signal obtains the real part and the imaginary part of the fundametal compoment of non-power-frequency current signal and voltage measurement signal through Filtering Processing and data analysis, it is characterized in that, stake resistance and the reactance of adopting hardware and software equipment to calculate tested earth mat by formula, show the end product of measuring calculating by display device, the alien frequencies power source that adopts is a Sine Wave Pulse Width Modulation formula adjustable frequency power source, the electric current amount of exports that injects the tested earth mat auxiliary current utmost point is 3-5A, and the alien frequencies frequency of employing is 40HZ and two frequencies of 60HZ.
2, stake resistance different-frequency measuring method according to claim 1 is characterized in that, the alien frequencies power source that is adopted is a 500W Sine Wave Pulse Width Modulation formula adjustable frequency power source.
3, stake resistance different-frequency measuring method according to claim 1, it is characterized in that, to non-power-frequency current, voltage signal carries out Filtering Processing and carries out respectively, at first they are taken a sample respectively, make their timesharing carry out filtering by notch filter and bandpass filter, obtain the alien frequencies signal that can detect, it is to become digital quantity and send into intelligent processing system handling by the A/D change-over circuit by the measurement voltage signal after the Filtering Processing and current signal that this alien frequencies signal is carried out data analysis, filtered alien frequencies signal is being carried out in the processing procedure, measuring system is to the Frequency Synchronization of voltage and current signals sampling and alien frequencies power source, to current signal, voltage signal is done to widen the window spectrum analysis and is finished by the intelligent processing system that single-chip microcomputer constitutes, fundametal compoment is wherein separated, further removed interference components.
4, stake resistance different-frequency measuring method according to claim 1 is characterized in that, adopts following computing formula,
U＝Ur+jUi
I＝Ir+jIi
Ur, Ui, Ir, Ii are respectively the fundamental voltage of alien frequencies signal, the real part and the imaginary part of electric current
Z is impedance, and R is the equivalent stake resistance of grounded screen, and X is a grounded screen equivalence earthing reactance, and f is the alien frequencies frequency, and 40HZ or 60HZ are because reactance and frequency dependence
It is anti-that reactance value should be adapted to the mutual inductance that value f=50HZ under the power frequency should deduct between the lead-in wire simultaneously, and this value can obtain according to the distance calculation between wire length and lead-in wire.
5, the device that stake resistance different-frequency measuring method according to claim 1 adopts, comprise the alien frequencies power source, current sensor, voltage sensor, two operational amplifiers, programmable amplifying circuit, the A/D change-over circuit, Single Chip Microcomputer (SCM) system, liquid crystal display and control panel, it is characterized in that, trap and bandwidth-limited circuit (6) have been adopted, Synchronous Sampling Pulse loop (8), sampling hold circuit (9), wherein, the current output terminal mouth S4 of alien frequencies power source (1), S5 connects the sub-C1 of current output terminal respectively, C2, current sensor (2), operational amplifier (4), (5) connect trap and bandwidth-limited circuit (6), the output of trap and bandwidth-limited circuit (6) connects programmable amplifying circuit (7), programmable amplifying circuit (7) connects sampling hold circuit (9), the input end of the synchronous signal output end S2 of alien frequencies power source (1) and Synchronous Sampling Pulse loop (8) joins, the output in Synchronous Sampling Pulse loop (8) connects the control end of sampling hold circuit (9), the output termination A/D change-over circuit (10) of sampling hold circuit (9), become the A/D change-over circuit (10) of digital signal to connect with Single Chip Microcomputer (SCM) system (11) analog signal conversion, Single Chip Microcomputer (SCM) system (11) links to each other with liquid crystal display and control panel (12) by control line and address/data bus again.
6, the device of stake resistance different-frequency measuring method employing according to claim 5 is characterized in that, the Sine Wave Pulse Width Modulation formula SPWM adjustable frequency power source that alien frequencies power source (1) adopts the IGBT module to constitute.
7; the device that stake resistance different-frequency measuring method according to claim 5 adopts; it is characterized in that; alien frequencies power source (1) has adopted two filtering circuits (13) and (21); modulation circuit (14); totalizer (15); triangular-wave generator (16); comparer (17); isolation drive and holding circuit (18); start-up control circuit (19); bridge rectifier circuit (20); the DC-AC inverter bridge (22) that the IGBT module is formed; LC filtering circuit (23); feedback circuit (24) and isolation transformation electrical equipment (25) are formed; wherein; the output terminal S1 of Single Chip Microcomputer (SCM) system (11) sinusoidal modulation signal connects the input end of filtering circuit (13); the output terminal of filtering circuit (13) has one the tunnel as synchronous signal output end S2 and connect the input end of modulation circuit (14); an input end of the same respectively totalizer of the output of the output of modulation circuit (14) and feedback circuit (24) (15) joins; the output terminal of totalizer (15) is connected to the reverse input end of comparer (17); the positive input of the output termination comparer (17) of triangular-wave generator (16); the output of comparer (17) links to each other through the gate pole of the DC-AC inverter bridge (22) that isolation drive and holding circuit (18) and IGBT module are formed; start-up control circuit (19) meets 220V and exchanges input; the output terminal of start-up control circuit (19) connects bridge rectifier circuit (20); bridge rectifier circuit (20) connects filtering circuit (21); the output of filtering circuit (2 1) is connected to the input end of inverter bridge (22); the output of inverter bridge (22) connects LC filtering circuit (23); LC filtering circuit (23) connects the input end of feedback circuit (24) and the input end of output isolation transformer (25) more respectively; the output of output isolation transformer (25) is the output port S4 of non-power-frequency current; S5; in addition, start-up control circuit (19); isolation drive links to each other with Single Chip Microcomputer (SCM) system (11) by control bus S3 with the control end of holding circuit (18) and inverter bridge (22).
8, the device that stake resistance different-frequency measuring method according to claim 5 adopts, it is characterized in that, trap and bandwidth-limited circuit (6) are by two multi-way switchs (26), (30), 50HZ quadravalence trap filter (27), 40HZ quadravalence biquadratic bandpass filter (28) and 60HZ quadravalence biquadratic bandpass filter (29) are formed, two input ends of multi-way switch (26) are respectively voltage signal input end and current signal input end, the output of multi-way switch (26) links to each other with the input end of 50HZ quadravalence notch filter (27), the output of 50HZ quadravalence trap filter (27) links to each other with two input ends of multi-way switch (30) respectively with the output of 40HZ quadravalence biquadratic bandpass filter (28) and 60HZ quadravalence biquadratic bandpass filter (29), and the output of multi-way switch (30) is the output of trap and bandwidth-limited circuit (6).
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| CNB991166019A CN1133878C (en) | 1999-08-16 | 1999-08-16 | Isofrequency measuring method for earth resistance and apparatus thereof |
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| CNB991166019A CN1133878C (en) | 1999-08-16 | 1999-08-16 | Isofrequency measuring method for earth resistance and apparatus thereof |
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