CN202794437U - On-line detection device for power capacitor - Google Patents
On-line detection device for power capacitor Download PDFInfo
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- CN202794437U CN202794437U CN 201220326818 CN201220326818U CN202794437U CN 202794437 U CN202794437 U CN 202794437U CN 201220326818 CN201220326818 CN 201220326818 CN 201220326818 U CN201220326818 U CN 201220326818U CN 202794437 U CN202794437 U CN 202794437U
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Abstract
The utility model discloses an on-line detection device for a power capacitor. A current sensor is used for collecting a noise-contained local electric discharge signal of a capacitor. After the signal is processed, a complex signal is decomposed into limited intrinsic mode function components by empirical mode decomposition. The intrinsic mode function components are subjected to mathematical morphology alternate mixing filter by a flat structure element. A threshold value and a hard thresholding rule are determined by a 3sigma gross error standard to carry out threshold value discrimination to a new intrinsic mode function component. The intrinsic mode function component processed by the threshold value is reconfigured to obtain a de-noised power capacitor local discharge signal. The signal is sent into the computer to obtain the on-line working condition of the capacitor. The on-line detection device has a clear physical meaning on processing non-linear and non-stable signals and has a good localized characteristic in a frequency domain and a time domain. Due to the adoption of the device, the original morphological characteristics of the signal can be kept to the maximum degree. Meanwhile, local signal dynamic behaviors and characteristics can be analyzed, and the on-line detection target of the power capacitor can be better realized.
Description
Technical field
The utility model belongs to field of power, is specifically related to a kind of power capacitor on-line measuring device.
Background technology
Along with socioeconomic development, social power consumption increases rapidly, and scale and the transmission capacity of electric system also increase rapidly, and be also more and more higher to the requirement of electric system reliability service.The effect of power capacitor in electric system mainly is the reactive power of compensates electric system inductive load, improves power factor, improves quality of voltage, reduces line loss, the safety and stability of its reliability of operation direct relation electric system.But owing in servicely be subject to the impacts such as superpotential, excess current, temperature, harmonic wave, so the intensity of insulating medium can descend gradually, and the starting potential that obviously shows as shelf depreciation reduces, and causes at last insulation breakdown.The statistical study of physical fault shows that insulation fault is the main cause that affects the normal operation of power capacitor, and shelf depreciation is to cause basic reason and the initial sign of insulation fault.Therefore, the power capacitor shelf depreciation is carried out effectively online the detection, significant to the safe and stable operation of power capacitor.
Be accompanied by the generation of power capacitor insulated local discharge, the transfer of discharge charge will form pulsed current signal in discharge loop, and generation broadband electromagnetical radiation signal, and the light and heat radiation, produced electrical measuring method and the non-electrometric method take ultrasonic Detection Method, light detection method etc. as representative take pulse current method, ultrahigh frequency detection method etc. as representative for these phenomenon correspondences.The method of the inner local discharge signal of detection high-voltage power capacitor commonly used mainly is supersonic testing method and pulse current method at present.Ultrasonic Detection Method is because power capacitor inside is the unitized construction of oil-paper, dipping film and impregnated paper and film very closely, the Acoustic Wave Propagation that shelf depreciation is produced is affected, and install and use and quantitatively on also have difficulties, therefore at present the online power capacitor local discharge signal that detects still take pulse current method as main.When the tradition pulse current method detected the power capacitor local discharge signal, because the electric capacity of test product is large, on-the-spot undesired signal was complicated and changeable, and sensitivity reduces greatly, so the key issue of pulse current method is the selection of sensor and the selection of noise-eliminating method.
At present traditional pulse current method basically adopts based on digital filtering or the hardware filtering method of Fourier transform when detecting local discharge signal and comes filtering.Although these methods can suppress undesired signal to a certain extent, the energy loss of original local discharge signal is larger, and when the centre frequency that new interference occurs or disturb changed, original parameter setting will be lost efficacy.Although wavelet transformation can extract local discharge signal preferably, the method can make the loss of signal portion of energy after the de-noising, can make to some extent distortion of signal.
The utility model content
Technical problem to be solved in the utility model provides a kind of easy for installation, power capacitor on-line measuring device that antijamming capability is strong, highly sensitive.
For addressing the above problem, the utility model is realized by following scheme:
A kind of power capacitor on-line measuring device, mainly be comprised of current transformer, signal condition unit, data acquisition process unit and computing machine, wherein the data acquisition process unit comprises that analog-to-digital conversion module, data sampling module, EMD decompose screening IMF component module, mathematical morphology replaces compound filter, threshold value quantizing processing module and reconstructed module.Current transformer is socketed on the power capacitor low-tension bushing ground wire, the output terminal of current transformer links to each other via the input end of signal condition unit with the analog-to-digital conversion module of data acquisition process unit, the output terminal of analog-to-digital conversion module links to each other with the input end that EMD decomposes screening IMF component module through data sampling module, EMD decomposes screening IMF component module output terminal and connects the input end that mathematical morphology replaces compound filter, and the output terminal passing threshold quantification treatment module that mathematical morphology replaces compound filter is connected to the input end of reconstructed module; The output terminal access computing machine of reconstructed module.
Current transformer gathers the power capacitor local discharge signal.The signal condition unit carries out pre-service to the local discharge signal that collects.Analog-to-digital conversion module carries out analog to digital conversion to the power capacitor local discharge signal after nursing one's health.The power capacitor local discharge signal of data sampling module after to analog to digital conversion sampled.EMD decomposition screening IMF component module will contain noisy power capacitor local discharge signal and carry out the EMD decomposition, screening IMF component.Mathematical morphology replaces compound filter to be adopted flat-structure element that each IMF component is carried out mathematical morphology to replace mixed filtering.The threshold value quantizing processing module determines that by 3 σ rough error criterions then each threshold value utilize the hard-threshold rule that new IMF component is carried out threshold value quantizing and process.Reconstructed module is reconstructed by the IMF component after processing, and obtains de-noising power capacitor local discharge signal afterwards.Computing machine carries out statistical study and processing to the power capacitor local discharge signal after the de-noising.
In the such scheme, described signal condition unit comprises pre-amplifier unit, bandpass filtering unit and rear class amplifying unit; The input end of pre-amplifier unit links to each other with the output terminal of current transformer, the input end of bandpass filtering unit connects the output terminal of pre-amplifier unit, the output terminal of bandpass filtering unit links to each other with the input end of rear class amplifying unit, the output terminal connection data acquisition process unit of rear class amplifying unit.
In the such scheme, described current transformer is the wideband high-frequency current transformer.
The utility model gathers by the wideband current sensor and delivers to the data acquisition process unit after power capacitor contains noisy local discharge signal and the processing of process signal conditioning circuit, utilization is resolved into limited intrinsic mode function (IMF) component based on the Hilbert-Huang transform (Hilbert-Huang Transform HHT) that empirical modal (EMD) decomposes with sophisticated signal, replace mixed filtering and obtain new intrinsic mode function component by selecting flat-structure element that the intrinsic mode function component under each decomposition scale is carried out mathematical morphology, adopt again 3 σ rough error criterion definite thresholds and with the hard-threshold rule new intrinsic mode function component is carried out the threshold value differentiation, obtain the intrinsic mode function component after the threshold process, and be reconstructed by the intrinsic mode function component after the threshold process, obtain the power capacitor local discharge signal after the de-noising; Thereby the power capacitor local discharge signal after the de-noising is sent into and is carried out digital signal in the computing machine and carry out statistical study and processing and obtain the power capacitor situation that works online.The utility model has clearly physical significance to processing the nonlinear and nonstationary signal, has good localization property at frequency-domain and time-domain, the original form feature of stick signal to greatest extent, the dynamic behaviour of analytic signal local signal and characteristic have realized the online target that detects of power capacitor preferably.
Compared with prior art, the utlity model has following features:
(1) the utility model utilizes the wideband high-frequency current transformer not change the original connected mode of equipment for sensor, and highly sensitive, antijamming capability is strong, can realize the online detection of power capacitor shelf depreciation;
(2) bandpass filter in the signal condition unit can be eliminated the most of noise in the local discharge signal, improves the sensitivity that detects;
(3) adopt and to replace compound filter based on the adaptive direct-threshold algorithm (ADT algorithm) of EMD and 3 σ rough error criterions and mathematical morphology and combine and carry out digital filtering, remedied the deficiency of analog filtering, soft-hard filter combines and can better eliminate noise, simultaneously can not change the original morphological feature of signal, better keep the parameter characteristic of original local discharge signal.
(4) can adopt the virtual instrument monitoring of software take LabWindows/CVI as development platform that the digital signal of data capture card transmission is carried out statistical study and processing, electronic equipment and deeper combining of computer technology are applied in the power capacitor partial discharge monitoring technology, graphical interfaces is more friendly, can reflect better more intuitively power capacitor shelf depreciation state.
Description of drawings
Fig. 1 is a kind of schematic block circuit diagram of power capacitor on-line measuring device.
Fig. 2 is a kind of power capacitor online test method process flow diagram.
Fig. 3 is empirical mode decomposition (EMD decomposition) algorithm flow chart
Fig. 4 is that mathematical morphology alternately mixes the algorithm filter process flow diagram.
Embodiment
A kind of power capacitor on-line measuring device as shown in Figure 1, mainly be comprised of current transformer, signal condition unit, data acquisition process unit and computing machine, wherein the data acquisition process unit comprises that analog-to-digital conversion module, EMD decompose screening IMF component module, mathematical morphology replaces compound filter, threshold value quantizing processing module and reconstructed module.Current transformer is socketed on the power capacitor low-tension bushing ground wire, the output terminal of current transformer links to each other via the input end of signal condition unit with the analog-to-digital conversion module of data acquisition process unit, the output terminal of analog-to-digital conversion module links to each other with the input end that EMD decomposes screening IMF component module, EMD decomposes screening IMF component module output terminal and connects the input end that mathematical morphology replaces compound filter, and the output terminal passing threshold quantification treatment module that mathematical morphology replaces compound filter is connected to the input end of reconstructed module; The output terminal access computing machine of reconstructed module.
Current transformer gathers the power capacitor local discharge signal.In the present embodiment, current transformer is selected the wideband high-frequency current transformer, this wideband high-frequency current transformer is with relativepermeabilityμr=2000, frequency of utilization is that the ferrite of 5KHz～13MHz is iron core, pull-up resistor R is 200～500 Ω, number of turn N is between 50～70, stray capacitance is little, its frequency band range is 100KHz～10MHz, gain is 20dB, the band characteristics that meets the power capacitor local discharge signal, be socketed on the power capacitor low-tension bushing ground wire with it and gather local discharge signal, this sensor also is equivalent to a bandpass filter and amplifier, not only need not to change the original connection status of power capacitor, and can gather safely and effectively local discharge signal.
The signal condition unit carries out pre-service to the local discharge signal that collects.In the present embodiment, the signal condition unit comprises pre-amplifier unit, bandpass filtering unit and rear class amplifying unit; The input end of pre-amplifier unit links to each other with the output terminal of current transformer, the input end of bandpass filtering unit connects the output terminal of pre-amplifier unit, the output terminal of bandpass filtering unit links to each other with the input end of rear class amplifying unit, the output terminal connection data acquisition process unit of rear class amplifying unit.Utilize pre-amplification circuit that original signal is fixed the amplification of multiple, make the amplitude of signal satisfy the requirement of A/D sampling.Utilize the frequency band of bandpass filter restricting signal to suppress high frequency interference and frequency aliasing.Utilize the rear class amplifying circuit that compensation is amplified in the decay of filter output signal and the decay of teletransmission, thereby strengthen the transmission driving force.It is 0～10MHz that amplifier is selected bandwidth, meets power capacitor shelf depreciation bandwidth, matches with the sensor bandwidth.Because the AD input voltage range of this device is between ± 10V, sensor gain is 20dB, and the power capacitor typical case partial discharge pulse scope of sensor output is between 5mV～10mV, so enlargement factor should be 100～200 times.The bandwidth of bandpass filter is 100KHz～10MHz, with frequency less than 100KHz and greater than the undesired signal filtering of 10MHz.
Further sample and core processing to pretreated local discharge signal in the data acquisition process unit.In the present embodiment, the data acquisition process unit comprises that analog-to-digital conversion module, data sampling module, EMD decompose screening IMF component module, mathematical morphology replaces compound filter, threshold value quantizing processing module and reconstructed module.Analog-to-digital conversion module carries out analog to digital conversion to the power capacitor local discharge signal after nursing one's health.The power capacitor local discharge signal of data sampling module after to analog to digital conversion sampled.EMD decomposition screening IMF component module will contain noisy power capacitor local discharge signal and carry out the EMD decomposition, screening IMF component.Mathematical morphology replaces compound filter to be adopted flat-structure element that each IMF component is carried out mathematical morphology to replace mixed filtering.The threshold value quantizing processing module determines that by 3 σ rough error criterions then each threshold value utilize the hard-threshold rule that new IMF component is carried out threshold value quantizing and process.Reconstructed module is reconstructed by the IMF component after processing, and obtains de-noising power capacitor local discharge signal afterwards.In the present embodiment, to adopt the highest sample frequency be that 40MHz, data precision are that 12 high-speed A/D converter AD9224 is as analog-to-digital conversion module in the data acquisition process unit.The EMD of data acquisition process unit decomposes screening IMF component module, mathematical morphology replaces compound filter, threshold value quantizing processing module and reconstructed module and can realize by the entity circuit, also can realize by integrated dsp chip, in the present embodiment, adopt TMS320F2812 as core DSP data processing chip.Employing replaces method that compound filter the combines signal after to the hardware conditioning based on the adaptive direct-threshold algorithm (ADT algorithm) of EMD and 3 σ rough error criterions and mathematical morphology and carries out digital filtering and process, and extracts pure local discharge signal.
Terminal adopts the virtual instrument monitoring of software take LabWindows/CVI as development platform that the power capacitor local discharge signal after the de-noising is carried out statistical study and processing, the various parameters that show the power capacitor local discharge signal, comprise maximum pd quantity, mean discharge magnitude, discharge time, the discharge amplitude, phase place and discharge development trend etc.
A kind of power capacitor online test method that said apparatus is realized comprises the steps: as shown in Figure 2
(1) gathers the power capacitor local discharge signal by the current sensor that is socketed on the power capacitor low-tension bushing ground wire.
(2) the power capacitor local discharge signal that collects is delivered to the data acquisition process unit through behind the signal condition.
(3) the data acquisition process unit carries out analog to digital conversion and data sampling to the power capacitor local discharge signal after nursing one's health.
(4) the data acquisition process unit will contain noisy local discharge signal x(t) carry out empirical mode decomposition (EMD), obtain n intrinsic mode function (IMF) component c
iWith a residual components r, i=1 wherein, 2 ..., n.
The process that above-mentioned EMD decomposes as shown in Figure 3, it is specially:
(4.1) determine original local discharge signal x(t) all maximum points and minimum point;
(4.2) adopt splines to obtain x(t) up and down envelope, and calculate up and down envelope average m(t);
(4.3) make poor h(t)=x(t)-m(t);
(4.4) judge h(t) whether satisfy and screen end condition: mean[h
I, k(t)]＜ε, wherein mean[h
I, k(t)] expression h
I, k(t) Mean curve, ε are a default enough little numerical value, then turn (4.5) if satisfy above-mentioned screening conditions, otherwise with h(t) go to (4.1) as new input signal;
(4.5) make c=h(t), c is an IMF component, makes poor r=x(t)-c;
(4.6) judge whether r satisfies end condition: r
iBe the function of a constant or a dullness, if satisfy the then EMD decomposable process end of above-mentioned end condition, what can not extract is residual quantity, then r is not gone to (4.1) as new input signal if do not satisfy;
Be the time series of n for total exponent number, the signal after decomposing can be expressed as:
Wherein: c
i(t) be the IMF component, r (t) is remaining function, is monotonic quantity.
(5) select flat-structure element g to each IMF component c
iCarry out mathematical morphology and replace mixed filtering, obtain new IMF component c
i '
Because the dilation and erosion computing of flat-structure element (referring to get in field of definition the structural element of constant 0) has the number of winning the confidence local maximum and local minimum function, thus present embodiment to select length be that the flat-structure element of signal length 1/100 carries out mathematical morphology to signal and replaces mixed filtering and process.
Referring to Fig. 4, the process that above-mentioned mathematical morphology replaces mixed filtering is:
(5.1) to IMF component c
iCarry out mathematical morphology expansion, corrosion and opening operation and closed operation.If c
i(n) for list entries is the IMF component, g (m) is the structural element sequence, c
i(n) field of definition is C={0,1 .... N-1}, the field of definition of g (m) be G=0,1 .... M-1}, N, M are sequence length, and N 〉=M, then:
( c
i⊕ g ) ( n ) = max [c
i(n-m) + g(m)] (n-m∈F,m∈G)
( c
iΘ g ) ( n ) = min [ c
i(n+m) - g(m)] (n+m∈F,m∈G)
( c
i ○ g ) ( n ) = ( c
i Θ g ⊕ g) ( n )
(c
i ● g ) ( n ) = ( c
i ⊕ g Θ g) ( n )
In the formula, ⊕ represents dilation operation, and Θ represents erosion operation, zero expression opening operation, ● the expression closed operation.
(5.2) utilize structural element to IMF component c
iCarry out opening and closing operation (closed operation behind the first opening operation) and make and break computing (opening operation after the first closed operation).
[(c
i)oc(g)](n)=(c
i○g●g)(n)
[(c
i)co(g)](n)=(c
i●g○g)(n)
(5.3) opening and closing operation and make and break computing are carried out average value processing, obtain the algorithmic formula that mathematical morphology replaces compound filter:
(6) signal after the morphology processing is carried out threshold process, further denoising.At first adopt 3 σ rough error criterions to detect new IMF component c
i ', calculate the mean square value σ of noise under each decomposition scale
i, further calculate the threshold value t of multiresolution
i, i=1 wherein, 2 ..., n.Then adopt the hard-threshold method to IMF component c new under each yardstick
i' carry out threshold value and differentiate, obtain the IMF component c after the threshold process
i' ';
The key issue of this step is determining of threshold value and choosing of threshold rule.
By 3 σ rough error criterion definite thresholds, during being defined as observing, rough error neither has the error that the clear and definite regularity of distribution does not have the stochastic distribution rule yet.Each IMF component that contained random noise obtains after EMD decomposition and morphology processing in the signal still satisfies the stochastic distribution rule, and signal does not have this regularity of distribution, so signal is considered as rough error, can realizes separating of noise and signal in conjunction with the threshold process method.The basic thought of 3 σ criterions is: because stochastic error is Normal Distribution, then the absolute value of error mainly concentrates near the average, has been formulated:
p{-3σ＜z-μ＜3σ}＝0.9974
In the formula, z～N (0, σ
2), namely getting average is 0, mean square deviation is σ
2White noise, therefore the anti-data of surveying then are considered as rough error greater than 3 σ.Use above-mentioned 3 σ rough error criterion detected signal components, obtain the mean square value σ of random noise
i, obtain σ
iRear desirable threshold value t
iBe 3 σ
i
Adopt the hard-threshold disposal route that signal is carried out threshold process, to keep the feature of local discharge signal as far as possible, formula is:
In the formula, c
i(k) ' be the IMF component after morphology is processed, c
i(k) " be IMF component after the threshold process, t
iBe threshold value.
(7) according to the IMF component c after the threshold process
i(k) " reconstruct obtains de-noising power capacitor local discharge signal afterwards.
(8) terminal adopts the virtual instrument monitoring of software take LabWindows/CVI as development platform that the digital signal of data capture card transmission is carried out statistical study and processing, the various parameters that show the power capacitor local discharge signal, comprise maximum pd quantity, mean discharge magnitude, discharge time, the discharge amplitude, phase place and discharge development trend etc. are obtained the power capacitor situation that works online.
Claims (3)
1. power capacitor on-line measuring device, it is characterized in that: mainly be comprised of current transformer, signal condition unit, data acquisition process unit and computing machine, wherein the data acquisition process unit comprises that analog-to-digital conversion module, data sampling module, empirical mode decomposition screening intrinsic mode function component module, mathematical morphology replace compound filter, threshold value quantizing processing module and reconstructed module; Current transformer is socketed on the power capacitor low-tension bushing ground wire, the output terminal of current transformer links to each other via the input end of signal condition unit with the analog-to-digital conversion module of data acquisition process unit, the output terminal of analog-to-digital conversion module links to each other with the input end of empirical mode decomposition screening intrinsic mode function component module, empirical mode decomposition screening intrinsic mode function component module output terminal connects the input end that mathematical morphology replaces compound filter, and the output terminal passing threshold quantification treatment module that mathematical morphology replaces compound filter is connected to the input end of reconstructed module; The output terminal access computing machine of reconstructed module.
2. power capacitor on-line measuring device according to claim 1, it is characterized in that: described signal condition unit comprises pre-amplifier unit, bandpass filtering unit and rear class amplifying unit; The input end of pre-amplifier unit links to each other with the output terminal of current transformer, the input end of bandpass filtering unit connects the output terminal of pre-amplifier unit, the output terminal of bandpass filtering unit links to each other with the input end of rear class amplifying unit, the output terminal connection data acquisition process unit of rear class amplifying unit.
3. power capacitor on-line measuring device according to claim 1, it is characterized in that: described current transformer is the wideband high-frequency current transformer.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104776941A (en) * | 2015-01-09 | 2015-07-15 | 济南智轩智能科技有限公司 | Adaptive amplification system for echo signal of ultrasonic heat meter |
| CN105242124A (en) * | 2015-11-04 | 2016-01-13 | 桂林电力电容器有限责任公司 | Testing circuit and testing method for audible noise of high-voltage direct current filter capacitor |
| CN110554270A (en) * | 2019-08-24 | 2019-12-10 | 上海佳特高电压电气设备有限公司 | Power capacitance test line measurement and control system |
| CN110646714A (en) * | 2019-09-26 | 2020-01-03 | 杭州电力设备制造有限公司 | Feature extraction method of ultrasonic partial discharge signal and related equipment |
| CN112269067A (en) * | 2020-10-22 | 2021-01-26 | 国网天津市电力公司 | Capacitor dielectric loss angle on-line monitoring method based on morphology and 3 sigma criterion |
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2012
- 2012-07-06 CN CN 201220326818 patent/CN202794437U/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104776941A (en) * | 2015-01-09 | 2015-07-15 | 济南智轩智能科技有限公司 | Adaptive amplification system for echo signal of ultrasonic heat meter |
| CN105242124A (en) * | 2015-11-04 | 2016-01-13 | 桂林电力电容器有限责任公司 | Testing circuit and testing method for audible noise of high-voltage direct current filter capacitor |
| CN110554270A (en) * | 2019-08-24 | 2019-12-10 | 上海佳特高电压电气设备有限公司 | Power capacitance test line measurement and control system |
| CN110646714A (en) * | 2019-09-26 | 2020-01-03 | 杭州电力设备制造有限公司 | Feature extraction method of ultrasonic partial discharge signal and related equipment |
| CN112269067A (en) * | 2020-10-22 | 2021-01-26 | 国网天津市电力公司 | Capacitor dielectric loss angle on-line monitoring method based on morphology and 3 sigma criterion |
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