CN103091606B - Grounding fault detecting method for direct current system with high anti-interference capacity - Google Patents
Grounding fault detecting method for direct current system with high anti-interference capacity Download PDFInfo
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Abstract
The invention discloses a grounding fault detecting method for a direct current system with high anti-interference capacity, and belongs to the field of electric power detection. The grounding fault detecting method aims to solve the problems that when an alternating current signal injection method is adopted to monitor a grounding fault of the direct current system and interference exists, measurement is not accurate and misjudgment is caused. The grounding fault detecting method comprises the following steps of injecting low-frequency alternating current signals between a direct current system bus and the ground at a set interval T, wherein the frequency of the signals is lower than that of the power frequency, and the T is 1 second-5 seconds; measuring and obtaining current signals in a determined fault branch circuit and obtaining signals of all frequency components of the current signals by the utilization of a harmonic wave extraction unit and by the adoption of the windowing interpolation method; comparing the low-frequency alternating current signals injected in step 1 with the signals of all the frequency components of the current signals obtained in step 2 to determine the positions where the signals of the frequency components, corresponding to the injected low-frequency alternating current signals, disappear. The positions are fault points.
Description
Technical field
The present invention relates to the Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity, belong to field of power detection.
Background technology
Direct supply is widely used in generating plant and transformer station.In normal state; it is powered to DC loads such as indicating relay, signal lamp, contactor coils; power to the breaking coil of isolating switch electromagnetic operating mechanism, closing coil; when AC mains failure; for the closing coil, breaking coil, carrier communication apparatus etc. of relay protection and aut.eq., isolating switch provide working dc power, its effect is irreplaceable especially.The safe and reliable operation of direct supply to electric system plays an important role.
One point earth is one of modal insulation breakdown fault of straight-flow system, if can not find in time and get rid of earth point, when multipoint earthing appears in system, easily causes the serious consequence such as DC load cisco unity malfunction, relay misoperation work.According to transformer station and power plant's straight-flow system design national standard, straight-flow system relay, control loop etc. can ensure that the grounding resistance of normal work should be not less than 20k Ω, and whether the standard therefore judging DC system grounding mainly grounding resistance is less than 20k Ω.
The main earth fault adopting bridge method and AC signal injection method monitoring straight-flow system at present.The ultimate principle of bridge method is that when system is normal, bridge balance, when certain one point earth appears in system, electric bridge out of trim, produces alerting signal by straight-flow system both positive and negative polarity ground connection equivalent resistance and artificial two the resistance composition electric bridges arranged.The method circuit is simple; with low cost; but still can not Normal Alarm to some situation, mainly, controls, the relay protection few at circuitry number of current the method, aut.eq. loop is simple, automatization level is lower and more to the use of power supply reliability less demanding small plant.AC signal injection method adopts following principle to realize usually: timing injects low-frequency ac electric current signal between straight-flow system bus and the earth, the fault branch determined is measured and obtains current signal, the place that the AC signal respective frequencies component signal of injection disappears is trouble spot.The method does not have the shortcoming of bridge method, is the main stream approach of the earth fault of monitoring straight-flow system at present.
The key point of AC signal injection method judges whether the AC signal respective frequencies component signal injected disappears, more owing to collecting signal disturbing, especially occur that non-integer harmonics causes non-integer-period sampled time routine Fourier algorithm result of calculation there is error, there is erroneous judgement situation, must study and be improved.
Summary of the invention
The present invention seeks to, in order to solve the earth fault adopting AC signal injection method monitoring straight-flow system, to measure when there is interference inaccurate, causing the problem of erroneous judgement, providing a kind of Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity.
The Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity of the present invention, the method comprises the following steps:
Step one, at set intervals T, between straight-flow system bus and the earth, injected frequency is lower than the low-frequency ac electric current signal of power frequency, T=1s ~ 5s,
Step 2, the fault branch determined measured obtain current signal, utilize harmonic extraction unit, and adopt windowed interpolation method to obtain the signal of each frequency component in current signal,
The signal of each frequency component of the low-frequency ac electric current signal that step 3, comparison step one are injected and the current signal that step 2 obtains, determine the place that the low-frequency ac signal respective frequencies component signal injected disappears, this place is trouble spot.
In step 2, windowed interpolation method adopts and adds Hanning window interpolation Fourier algorithm and realize, and Hanning window function is:
N is natural number;
The process adopting windowed interpolation method to obtain the signal of each frequency component in current signal is:
Step 1, the current signal DFT result of signal after adding Hanning window is:
In formula: the DFT result that X (n) is discrete current signals x (n);
The first-harmonic of step 2, current signal or harmonic frequency f press following formula and obtain:
f=(k+△k)△f（3）
In formula: △ f=1 △ T, △ T is current signal sample duration;
K is sampling number; K is integer; △ k is decimal, and presses following formula acquisition:
Harmonic amplitude B after step 3, the first-harmonic of current signal obtained according to step 2 or harmonic frequency f obtain and correct
k:
B
k=B'
k2π△k(1-△k
2)sin(△kπ)（5）
In formula: B'
kthe first-harmonic of current signal obtained for step 2 or harmonic frequency f carry out Fourier transform gained harmonic amplitude,
Phase angle theta after step 4, the first-harmonic of current signal obtained according to step 2 or harmonic frequency f obtain and correct
k:
θ
k=angle(X
w(k)exp(-j△k(1-1N)π))（6）
J is imaginary unit, and angle (z) is for obtaining the phase angle of plural z;
Step 5, according to step 3 obtain correction after harmonic amplitude B
kwith phase angle theta after the correction that step 4 obtains
kobtain the signal of each frequency component in current signal.
Advantage of the present invention:
1, accuracy is calculated high: based on the amplitude adding Hanning window interpolation Fourier algorithm and can accurately obtain Injection Signal.
2, antijamming capability is strong: effectively can reduce based on adding Hanning window interpolation Fourier algorithm the error that non-integer harmonics brings to localization of fault.Therefore, antijamming capability is strong.
Accompanying drawing explanation
Fig. 1 is the process flow diagram of the Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity of the present invention.
Embodiment
Embodiment one: present embodiment is described below in conjunction with Fig. 1, the Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity described in present embodiment, the method comprises the following steps:
Step one, at set intervals T, between straight-flow system bus and the earth, injected frequency is lower than the low-frequency ac electric current signal of power frequency, T=1s ~ 5s,
Step 2, the fault branch determined measured obtain current signal, utilize harmonic extraction unit, and adopt windowed interpolation method to obtain the signal of each frequency component in current signal,
The signal of each frequency component of the low-frequency ac electric current signal that step 3, comparison step one are injected and the current signal that step 2 obtains, determine the place that the low-frequency ac signal respective frequencies component signal injected disappears, this place is trouble spot.
During synchronized sampling, each harmonic component is each frequency discrimination point corresponding just, and gained frequency, amplitude, phase place are exact value.Owing to becoming when power system signal frequency is, and the restriction being subject to hardware is difficult to dynamic conditioning sample frequency realizes synchronized sampling completely.In non-synchronous sampling situation, signal frequency is between two spectral lines, and the frequency of discrete Fourier transformation (Discrete Fourier Transform, DFT) gained, amplitude and phase angle are all inaccurate, needs to correct.Can main lobe centre coordinate being asked for according to spectral line in main lobe thus obtain frequency, amplitude and phase place accurately, the accuracy of above calculating can be improved by adding suitable window function further.
Window function has a variety of, and present embodiment selects Hanning window to be because the method has taken into account good frequency analysis effect, calculated amount is little, speed is fast, realization is easy.
If adopt conventional discrete fourier algorithm, the non-integer harmonics existed in electric system can affect the judgement of Injection Signal amplitude, adopts the Fourier algorithm adding Haning window interpolation to avoid this point.Realize high anti-jamming capacity Design of DC System Grounding Fault Detection system comprise following function:
1) at set intervals between straight-flow system bus and the earth injected frequency lower than the low-frequency ac electric current signal of power frequency.
2) on the fault branch determined, acquisition current signal is measured.
3) adopt windowed interpolation Fourier algorithm to obtain the signal of each frequency component, obtain the amplitude of the corresponding harmonic wave of Injection Signal frequency.
4) place that the AC signal respective frequencies component signal injected disappears is trouble spot.
Embodiment two: present embodiment is described further embodiment one, the low-frequency ac electric current signal described in step one adopts Low Frequency Sine Signals generator to send.
Embodiment three: present embodiment is described further embodiment one or two, in step 2, windowed interpolation method adopts and adds Hanning window interpolation Fourier algorithm and realize, and Hanning window function is:
The process adopting windowed interpolation method to obtain the signal of each frequency component in current signal is:
Step 1, the current signal DFT result of signal after adding Hanning window is:
In formula: the DFT result that X (n) is discrete current signals x (n);
The first-harmonic of step 2, current signal or harmonic frequency f press following formula and obtain:
f=(k+△k)△f（3）
In formula: △ f=1 △ T, △ T is current signal sample duration;
K is sampling number; K is integer; △ k is decimal, and presses following formula acquisition:
Harmonic amplitude B after step 3, the first-harmonic of current signal obtained according to step 2 or harmonic frequency f obtain and correct
k:
B
k=B'
k2π△k(1-△k
2)sin(△kπ)（5）
In formula: B'
kthe first-harmonic of current signal obtained for step 2 or harmonic frequency f carry out Fourier transform gained harmonic amplitude,
Phase angle theta after step 4, the first-harmonic of current signal obtained according to step 2 or harmonic frequency f obtain and correct
k:
θ
k=angle(X
w(k)exp(-j△k(1-1N)π))（6）
J is imaginary unit, and angle (z) is for obtaining the phase angle of plural z;
Step 5, according to step 3 obtain correction after harmonic amplitude B
kwith phase angle theta after the correction that step 4 obtains
kobtain the signal of each frequency component in current signal.
Embodiment four: present embodiment provides a specific embodiment: the validity of this system is described as follows: Injection Signal frequency is 20Hz, amplitude is 1, and interfering frequency is 21.5Hz, and amplitude is 2.Gather at the 1.5km place of fault branch and obtain current signal, this place is earth fault, Injection Signal disappears at this place, due to the impact of interference frequency component when adopting conventional Fourier algorithm, the Injection Signal component of corresponding 20Hz is still 0.87, judge not to be earth point herein, now will there is error to the localization of fault of straight-flow system.The component of 20Hz and 21.5Hz obtained after using algorithm of the present invention is respectively 0 and 2, consistent with truth, judges to be earth point herein, result entirely accurate.
Claims (3)
1. the Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity, is characterized in that, the method comprises the following steps:
Step one, at set intervals T, between straight-flow system bus and the earth, injected frequency is lower than the low-frequency ac electric current signal of power frequency, T=1s ~ 5s,
Step 2, the fault branch determined measured obtain current signal, utilize harmonic extraction unit, and adopt windowed interpolation method to obtain the signal of each frequency component in current signal,
In step 2, windowed interpolation method adopts and adds Hanning window interpolation Fourier algorithm and realize, and Hanning window function is:
The process adopting windowed interpolation method to obtain the signal of each frequency component in current signal is:
Step 1, the current signal DFT result of signal after adding Hanning window is:
In formula: the DFT result that X (n) is discrete current signals x (n);
The first-harmonic of step 2, current signal or harmonic frequency f press following formula and obtain:
f＝(k+△k)△f (3)
In formula: △ f=1/ △ T, △ T is current signal sample duration;
K is sampling number; K is integer; △ k is decimal, and presses following formula acquisition:
Harmonic amplitude B after step 3, the first-harmonic of current signal obtained according to step 2 or harmonic frequency f obtain and correct
k:
B
k＝B'
k2π△k(1-△k
2)/sin(△kπ) (5)
In formula: B'
kthe first-harmonic of current signal obtained for step 2 or harmonic frequency f carry out Fourier transform gained harmonic amplitude,
Phase angle theta after step 4, the first-harmonic of current signal obtained according to step 2 or harmonic frequency f obtain and correct
k:
θ
k＝angle(X
w(k)exp(-j△k(1-1/N)π)) (6)
J is imaginary unit, and angle (z) is for obtaining the phase angle of plural z;
Step 5, according to step 3 obtain correction after harmonic amplitude B
kwith phase angle theta after the correction that step 4 obtains
kobtain the signal of each frequency component in current signal;
The signal of each frequency component of the low-frequency ac electric current signal that step 3, comparison step one are injected and the current signal that step 2 obtains, determine the place that the low-frequency ac signal respective frequencies component signal injected disappears, this place is trouble spot.
2. the Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity according to claim 1, is characterized in that, the low-frequency ac electric current signal described in step one adopts Low Frequency Sine Signals generator to send.
3. the Detection Method for Earthing Fault of HVDC System of high anti-jamming capacity according to claim 1, it is characterized in that, the frequency of low-frequency ac electric current signal is 10Hz ~ 30Hz.
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| CN103983890B (en) * | 2014-05-30 | 2017-04-12 | 广州供电局有限公司 | Search method for fault points generated due to the influence of alternating current crosstalk on relay and test circuit |
| CN104198893B (en) * | 2014-09-24 | 2017-03-15 | 中国科学院电工研究所 | Adaptive failure electric current detecting method |
| CN104297624A (en) * | 2014-11-06 | 2015-01-21 | 国家电网公司 | Direct current ground fault detecting and handling method |
| CN104914352B (en) * | 2015-05-07 | 2017-09-29 | 国家电网公司 | A kind of NUGS method for locating single-phase ground fault differentiated based on harmonic wave difference |
| CN105403808B (en) * | 2015-11-12 | 2019-06-11 | 张烨 | A kind of localization method and device of DC line earth fault |
| CN110161391B (en) * | 2019-05-07 | 2021-01-01 | 四川大学 | Method for monitoring cable insulation on line through low-frequency signal reverse injection |
| CN110514945A (en) * | 2019-07-12 | 2019-11-29 | 国网浙江省电力有限公司嘉兴供电公司 | A kind of multifunctional DC grounding test apparatus and Method for Measuring Insulating Resistance |
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