CN113484706A - Double-sensor detection method and system for partial discharge of cable under series resonance - Google Patents
Double-sensor detection method and system for partial discharge of cable under series resonance Download PDFInfo
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Abstract
The invention discloses a double-sensor detection method and a system for cable partial discharge under series resonance, which comprises the steps of detecting a pulse signal flowing through a cable grounding wire as a main signal by using a high-frequency current sensor based on the propagation characteristic of a cable partial discharge signal, and detecting a pulse interference signal generated by a variable frequency power supply by using an ultrahigh frequency sensor as a reference signal; and pulse extraction is carried out on the two paths of signals by adopting a time domain sliding energy search method based on a threshold window, and separation and identification of partial discharge signals in the HFCT signals are realized by adopting an intersection discrimination algorithm according to the characteristic that interference signals and UHF signals in the HFCT overlap on a time domain. And finally, constructing a local discharge phase distribution spectrogram to determine the type of a local discharge source. The method can realize the voltage resistance and PD test and has certain guiding significance on the actual engineering.
Description
Technical Field
The invention relates to the technical field of cable discharge detection, in particular to a double-sensor detection method and system for cable partial discharge under series resonance.
Background
Cross-linked polyethylene (XLPE) cables are widely used in power distribution networks because of their reliable electrical and mechanical properties, however, partial discharge (hereinafter referred to as "partial discharge") is one of the manifestations of power cable insulation aging and one of the main causes of cable insulation failure due to further insulation degradation, so that performing partial discharge detection on power cables is beneficial to safe and reliable operation of power cables.
Both IEC and national standards indicate: the insulation performance of the newly completed power cable must be checked through a withstand voltage test. The frequency conversion series resonance voltage-withstanding method is the most effective voltage-withstanding test method at present because of small equipment power, good equivalence with power frequency and high feasibility of field implementation. However, latent defects of the cable, such as bubbles in the cable body, air gaps in joint accessories, protrusions of the semiconductive layer, and the like, are likely to cause a breakdown accident by further development under a long-term voltage after the withstand voltage test. Therefore, the industry recommends synchronous testing of cable voltage resistance and partial discharge.
At present, the voltage resistance and partial discharge synchronous test under frequency conversion resonance is mostly adopted in the industry. However, in the conventional variable frequency series resonant system, strong electromagnetic interference generated by the action of the switching element of the variable frequency power supply is distributed on the whole phase period. Therefore, the key to the difficulty in implementing such a synchronization test technique is the separation of the partial discharge signal from the interference signal. At present, a plurality of relevant practitioners and scholars at home and abroad research the problem from algorithm and hardware. According to waveform characteristics and time-frequency parameters, the literature utilizes a clustering algorithm to realize separation and identification of partial discharge signals and interference signals, but a clustering center needs to be set artificially, and the self-adaptability is poor. The literature utilizes a least square method to fit a waveform profile based on pulse waveform characteristics so as to realize the separation of PD signals and interference signals, the effect is better, but the dependence on the selection of initial values is large, and the convergence speed is slower. Both of the above methods start from the aspect of algorithm, and both of the latter methods start from the aspect of hardware, and the improvement of the conventional variable frequency series system is required. For example: the method comprises the steps of utilizing equal pulse width modulation to replace Sinusoidal Pulse Width Modulation (SPWM) technology and utilizing time domain windowing technology to process partial discharge signals. The method has good effect, but the resonance frequency of the method is less than 300Hz, so that the partial discharge test result is not influenced. 2 high-speed bidirectional switches (IGBT) are added on a traditional resonance system, the test system is divided into two parts of resonance withstand voltage and oscillation wave partial discharge test, but the duration of oscillation wave is short, and the obtained partial discharge information is less. Compared with the signals measured by IEC60270 method and HFCT by SDMF algorithm, the PD signal is effectively extracted, but the method is only used for power frequency voltage partial discharge test at present, and the signals measured by IEC60270 method and HFCT under resonance voltage are interfered by stronger variable frequency power supply, and the signal-to-noise ratio of both is lower, so that the interference is difficult to filter.
Disclosure of Invention
The invention aims to provide a double-sensor detection method for partial discharge of a cable under series resonance.
In order to achieve the above object, the present invention provides the following technical solution, a method for detecting partial discharge of a cable under series resonance by using a dual sensor, comprising the steps of:
acquiring an original partial discharge signal with interference and a high-frequency pulse interference signal in a variable-frequency series resonant circuit;
eliminating the interference signals by using an intersection discrimination method for the obtained original partial discharge signals and high-frequency pulse interference signals, and extracting PD pulses;
and drawing a PRPD spectrogram according to the extracted PD pulse peak value and the corresponding phase, and judging the type of the partial discharge signal.
Preferably: the intersection discrimination method comprises the following steps: extracting effective pulses in the HFCT signal and high-frequency interference pulses in the UHF signal based on a sliding threshold window searching method; performing time domain overlapping judgment on a certain pulse extracted by the HFCT and all pulses extracted by the UHF, and if the HFCT pulse and the UHF pulse are overlapped, considering the HFCT pulse as an interference pulse; if the two are not overlapped, the HFCT pulse is judged as a PD pulse.
Further in any of the above embodiments, the sliding threshold window searching method includes scanning the denoised signal with a sliding time window, when the first data in the window is greater than the threshold, recording the position of the point as the pulse position, moving the threshold window backwards, and repeatedly positioning the pulse until the threshold window moves to the end of the denoised signal.
In any of the above embodiments, further, when extracting the effective pulse in the HFCT signal and the high frequency interference pulse in the UHF signal, the method further includes: initializing a preset threshold of a sliding threshold window, a window length of a preset threshold sliding time window and a preset sliding step length; searching the two paths of de-noising signals by using a threshold window respectively to obtain pulse rough position sequences of the two paths of de-noising signals: lceUHF＝[C1,C2,…,Cm,]，LceHFCT＝[C1,C2,…,Cn,]，CiIndexing the coarse position of the corresponding pulse in the raw data;
setting an energy threshold EthThe number of data windows is M, in LceUHFAnd LceUHFSearching the pulse edge leftwards and rightwards for the center to obtain transient pulses and index sequences of two paths of signals: pUHF＝[P1；P2；…；Pm]；PHFCT＝[P1；P2；…；Pn]；LocUHF＝[L1,L2,…,Lm,]，LocHFCT＝[L1,L2,…,Ln](ii) a Wherein P isiRepresents a pulse sequence, LiThe index of the corresponding pulse in the original data is m, the number of pulses detected by the UHF sensor is m, the number of pulses detected by the HFCT is n, and n is more than or equal to m.
The invention also provides a double-sensor detection system for partial discharge of the cable under series resonance, which is used for implementing the method and comprises a variable-frequency series resonance circuit and a sampling unit; the sampling unit comprises a UHF sensor arranged at a variable frequency power supply end, an HFCT sensor arranged at a tested cable, an oscilloscope and a PC (personal computer); the HFCT sensor is used for acquiring an original partial discharge signal with interference in the variable-frequency series resonant circuit. The UHF sensor is used for acquiring a high-frequency pulse interference signal in the variable-frequency series resonant circuit. The PC utilizes an oscilloscope to obtain an original partial discharge signal and a high-frequency pulse interference signal, eliminates the interference signal by an intersection discrimination method, and extracts PD pulses; and drawing a PRPD spectrogram according to the extracted PD pulse peak value and the corresponding phase, and judging the type of the partial discharge signal.
Further, preferably, the signal input end of the oscilloscope is connected to the HFCT sensor and the UHF sensor at the same time, and the trigger end of the oscilloscope is connected to the capacitive voltage divider in the variable frequency series resonant circuit, and is configured to use the resonant voltage signal as the oscilloscope trigger signal.
Preferably, the oscilloscope stores data in a screen mode, and saves signal data peak value information in a burr capturing mode to realize data storage in a frequency reduction mode; and the PC runs an LABVIEW program control oscilloscope to realize the storage of data in a plurality of resonance periods.
Further preferably, the variable frequency series resonant circuit comprises a rectification module, an inversion module, a boost module and a resonant circuit which are connected in sequence.
Further preferably, when the type of the placement point is judged, the resonance PRPD spectrogram and the power frequency PRPD spectrogram are used for comparison. The judgment of the type of the discharge signal at least comprises a cutter mark defect, a protrusion of a semi-conducting layer, metal particles and dislocation of a prefabricated part. The power frequency PRPD spectrogram is a power frequency partial discharge PRPD spectrogram constructed according to different defect types.
Compared with the prior art, the double-sensor detection method and the system for the partial discharge of the cable under the series resonance have the beneficial effects that:
1. the invention provides a double-sensor detection method for cable partial discharge under series resonance, which is used for extracting pulses of laboratory measured signals, eliminating interference signals by using an intersection discrimination method, extracting PD signals and judging the type of partial discharge signals according to a PRPD spectrogram drawn by the PD signals.
2. According to the double-sensor detection method for cable partial discharge under series resonance, the time domain sliding energy search method based on the threshold window can effectively extract pulse waveforms, and the method is simple and small in calculation amount.
3. The double-sensor detection method for cable partial discharge under series resonance provided by the invention provides an intersection discrimination algorithm to compare signals of two sensors, and can effectively separate and identify partial discharge signals in HFCT. The partial discharge judgment is further realized by utilizing the PRPD spectrogram.
4. The invention provides a double-sensor detection method and a double-sensor detection system for partial discharge of a cable under series resonance, and provides a double-sensor detection technology for partial discharge of the cable under variable frequency series resonance under the combination of hardware and an algorithm. Experiments prove that the method can effectively separate and identify partial discharge signals and realize the cooperative test of voltage resistance and partial discharge under variable frequency resonance.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 is a schematic diagram of a conventional variable frequency series resonant system;
FIG. 2 is a schematic diagram of a dual sensor variable frequency series resonant system of the present invention;
FIG. 3 is a flow chart of a pulse extraction method of the dual sensor detection method of partial discharge of a cable under series resonance of the present invention;
FIG. 4 illustrates a partial discharge pulse separation strategy under resonance conditions in accordance with the present invention;
FIG. 5 is a schematic diagram of a dual sensor variable frequency series resonance partial discharge test platform according to the present invention;
FIG. 6(a) is a waveform diagram of two paths of HFCT and UHF original signals;
FIG. 6(b) is a partial discharge signal waveform of the HFCT signal containing PD pulses and interference pulses;
FIG. 6(c) a waveform of an interference pulse signal extracted from the HFCT signal;
FIG. 6(d) a waveform of a PD pulse signal extracted from the HFCT signal;
FIG. 7(a) is a signal waveform diagram of a UHF high frequency interference signal (without partial discharge signal);
FIG. 7(b) is a waveform diagram of a certain high frequency interference pulse signal extracted from the UHF signal;
FIG. 8(a) is a signal waveform of an HFCT signal at one resonance period;
FIG. 8(b) is a signal waveform diagram of PD pulses isolated and extracted from the HFCT signal;
FIG. 9(a) a spectrum of the PD signal domain prior to processing;
FIG. 9(b) PD signal domain spectrum after processing.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
As shown in fig. 1, a conventional variable frequency series resonant system mainly includes four parts, i.e., rectification, inversion, boosting, and resonance. Because the traditional frequency conversion series resonance system changes the frequency and the duty ratio of output voltage by controlling the inverter bridge, the external reactor and the tested cable generate series resonance, thereby generating high voltage. The inverter circuit adopts an SPWM modulation mode, and the switch control device adopts a fully-controlled device Insulated Gate Bipolar Transistor (IGBT). The working principle is as follows: the alternating voltage is rectified and filtered to be changed into corresponding direct voltage; the direct current voltage is converted into a sinusoidal voltage reaching the resonant frequency through an H-bridge inverter module; the sinusoidal voltage is boosted to a preset value through an excitation transformer, and the cable is tested in the resonant circuit. The inversion module controls the on-off of the switching device to control the duty ratio and frequency of the inversion output voltage by collecting the output voltage and current of the resonant circuit, so that the inversion output voltage reaches the resonant frequency.
When the voltage is inverted, the switching device frequently acts in the whole voltage period to generate high-frequency pulses which are transmitted to the resonant circuit and the detection unit through the ground wire or the excitation transformer. If the partial discharge detection is carried out on the test article, the high-frequency pulse signals can be collected by the sensor, and the detected signals comprise partial discharge signals and high-frequency interference signals, so that the partial discharge judgment is seriously influenced.
The direct application of the series resonance system based on the SPWM modulation technology to PD detection brings about large interference. In order to realize the synchronous test of cable voltage resistance and local discharge, the problem of high-frequency pulse interference in the conventional variable-frequency series resonance system needs to be solved urgently, and a series resonance system based on double sensors is provided in consideration of engineering applicability and equipment cost, and the specific principle is shown in fig. 2.
Referring to fig. 2 and 5, the present invention provides a technical solution: a double-sensor detection system for partial discharge of a cable under series resonance comprises a variable-frequency series resonance circuit and a sampling unit; the frequency conversion series resonance circuit comprises a rectification module, an inversion module, a boosting module and a resonance loop which are connected in sequence.
The sampling unit comprises a UHF sensor arranged at a variable frequency power supply end, an HFCT sensor arranged at a tested cable, an oscilloscope and a PC (personal computer); the HFCT sensor is used for acquiring an original partial discharge signal with interference in the variable-frequency series resonant circuit.
The UHF sensor is used for acquiring a high-frequency pulse interference signal in the variable-frequency series resonant circuit; as shown in fig. 2, the UHF sensor is placed at the variable frequency power supply end and is as far away from the sample as possible to ensure that the partial discharge signal generated by the sample cannot be detected by UHF due to long-distance attenuation. Therefore, UHF only measures variable frequency power supply interference. The HFCT sensor is buckled on a ground wire at the position of a test article, so that not only can a partial discharge signal be measured, but also a variable frequency power supply interference signal transmitted through an exciting transformer and the ground wire can be measured. The signals measured by the two are subjected to pulse extraction and comparison in a time domain, so that the separation of the partial discharge signal and the frequency conversion interference signal in the HFCT signal is realized.
The PC utilizes an oscilloscope to obtain an original partial discharge signal and a high-frequency pulse interference signal, eliminates the interference signal by an intersection discrimination method, and extracts PD pulses; and drawing a PRPD spectrogram according to the extracted PD pulse peak value and the corresponding phase, and judging the type of the partial discharge signal.
The signal input end of the oscilloscope is simultaneously connected with the HFCT sensor and the UHF sensor, and the trigger end of the oscilloscope is connected with the capacitive voltage divider in the variable-frequency series resonance circuit and used for utilizing the resonance voltage signal as the trigger signal of the oscilloscope.
In one embodiment of the invention, the partial discharge test was performed on a 35kV XPLE cable of 4m length. The model of the frequency conversion power supply used in the experiment is SAMCO-vm5, the input voltage is 380V, and the capacity is 40 kW; the capacity of the excitation transformer is 40kVA, the output voltage is 2kV/6kV/20kV, and the output frequency is 30-300 Hz; the reactor is formed by connecting four cables in series, and the total inductance of the reactor is 400H; the withstand voltage of the capacitive voltage divider is 150kV, and the capacitance of the high-voltage arm is 1000 pF; the cable model is YJV22-26/35-1 × 95mm2And artificially manufacturing a tool mark defect with the length of 100mm, the width of 1mm and the height of 1mm at the joint. The bandwidth of HFCT-6dB adopted in the experiment is 2.5-216 MHz, the maximum sensitivity is 5.83mV/mA, and the partial discharge signal of the cable is measured by measuring a pulse signal on a grounding wire of the cable. The UHF type is TK-93024, the bandwidth is 80-2000 MHz, and the UHF type is mainly used for collecting electromagnetic interference generated by a switching element in a variable frequency power supply. The oscilloscope used in the experiment is of a RIGOL DS6104 model, the maximum sampling rate is 5GSa/s, and the bandwidth is up to 1 GHz. Particularly, according to the attenuation characteristic of electromagnetic waves and multiple experimental analysis, the UHF sensor is placed at a distance d from the variable frequency power supply1No more than 0.5m and a distance d from the cable sample2At least 3 m. The measured resonant frequency was about 186.8Hz and the resonant voltage was 27.4 kV.
The oscilloscope stores data in a screen mode, and protects signal data peak value information in a burr capturing mode to realize frequency reduction data storage; and the PC runs an LABVIEW program control oscilloscope to realize the storage of data in a plurality of resonance periods.
In the experiment, an oscilloscope is used for simultaneously acquiring signals of two sensors, a voltage divider signal (resonance voltage) is taken as an oscilloscope trigger signal, the sampling frequency of the oscilloscope is 2.5GHz, and the sampling length of the oscilloscope is 7ms which is greater than the resonance voltage period of 5.35 ms. However, under the sampling rate, the number of points acquired by the oscilloscope is large, and if data is stored in a memory mode, the time consumption is long, and the memory occupation is large. In order to improve the storage speed, the oscilloscope stores data in a screen mode, namely the oscilloscope protects signal data peak value information in a 'glitch capture' mode, and the data is stored in a frequency reduction mode. And controlling the oscilloscope by utilizing an LABVIEW program written on a PC (personal computer), and realizing the storage of data under a plurality of resonance periods, wherein the data under 1 resonance period are recorded as 1 group.
As shown in fig. 3 to 9, the following describes a method for detecting partial discharge of a cable under series resonance by using two sensors, which is implemented based on the above system, and comprises the following steps:
s1, acquiring an original partial discharge signal and a high-frequency pulse interference signal with interference in the variable-frequency series resonance circuit;
the variable frequency power supply interference and the local discharge signal are propagated in the form of electromagnetic waves in space, and the spatial attenuation characteristic of the variable frequency power supply interference and the local discharge signal in the line of sight meets the formula (1):
Ploss＝32.4+20lgF+20lgD (1)
wherein: plossRepresents spatial loss; f represents a frequency; d represents a distance.
As can be seen from the above equation, the loss of the electromagnetic wave increases with the distance at a certain frequency. If the variable frequency power supply is taken as the center, the attenuation is smaller as the distance between the high frequency interference and the center is closer. If the partial discharge source is taken as the center, the partial discharge signal is greatly attenuated along with the increase of the distance. Therefore, based on the attenuation characteristic of electromagnetic waves, the UHF sensor is close to the variable frequency power supply as far as possible and is far away from the partial discharge test article, and UHF can be realized by only acquiring the interference of the variable frequency power supply.
S2, eliminating interference signals by using an intersection discrimination method for the acquired original partial discharge signals and high-frequency pulse interference signals, and extracting PD pulses;
further, the intersection discrimination method includes the steps of:
s201, extracting effective pulses in an HFCT signal and high-frequency interference pulses in a UHF signal based on a sliding threshold window searching method;
the sliding threshold window searching method comprises the steps of scanning a denoising signal by using a sliding time window, recording the position of a point as a pulse position when the first data in the window is larger than a threshold value, moving the threshold window backwards, and repeatedly positioning pulses until the threshold window moves to the tail end of the denoising signal.
Setting a threshold value Vth1、Vth2And a threshold window length N, the sliding step length is N, wherein the threshold comprises Vth1Is 2-3 times of the white noise amplitude of the signal measured by the UHF sensor, Vth2Is 2 to 3 times of the white noise amplitude of the signal measured by HFCT, the time corresponding to the threshold window N is 1.5 to 2 μ s,
when extracting the effective pulse in the HFCT signal and the high-frequency interference pulse in the UHF signal, the method also comprises the following steps:
initializing a preset threshold of a sliding threshold window, a window length of a preset threshold sliding time window and a preset sliding step length;
searching the two paths of de-noising signals by using a threshold window respectively to obtain pulse rough position sequences of the two paths of de-noising signals: lceUHF＝[C1,C2,…,Cm,]，LceHFCT＝[C1,C2,…,Cn,]，CiIndexing the coarse position of the corresponding pulse in the raw data;
setting an energy threshold EthThe number of data windows is M, in LceUHFAnd LceUHFSearching the pulse edge leftwards and rightwards for the center to obtain transient pulses and index sequences of two paths of signals: pUHF＝[P1；P2；…；Pm]；PHFCT＝[P1；P2；…；Pn]；LocUHF＝[L1,L2,…,Lm,]，LocHFCT＝[L1,L2,…,Ln](ii) a Wherein P isiRepresents a pulse sequence, LiThe index of the corresponding pulse in the original data is m, the number of pulses detected by the UHF sensor is m, the number of pulses detected by the HFCT is n, and n is more than or equal to m. It is worth mentioning that the threshold value Vth1And Vth2Can not be set too high, otherwise part of HFCT effective pulse and UHF high frequency pulse can be mistaken for white noise interference and automatically filtered, and the threshold value Vth1And Vth2And cannot be set too low, otherwise part of the white noise interference is mistaken for a valid pulse and extracted, thereby affecting the separation and identification of the PD in the following. The specific pulse extraction flow is shown in fig. 3.
S202, performing time domain overlapping judgment on a certain pulse extracted by the HFCT and all pulses extracted by the UHF, and if the HFCT pulse is overlapped with the UHF pulse, considering the HFCT pulse as an interference pulse; if the two are not overlapped, the HFCT pulse is judged as a PD pulse.
Immediately judge the LocHFCTi∩LocUHF(i∈[1,2,…,n]) Determining whether the HFCT pulse is a PD pulse or an interference pulse according to whether the HFCT pulse is an empty set, and recording P if the HFCT pulse is an empty setHFCTiFor PD pulsing, Loc is reservedHFCTi(ii) a If it is not an empty set, then note PHFCTiFor disturbing pulses, deleting PHFCTi、LocHFCTi. The separation strategy flow is shown in fig. 4.
And S3, drawing a PRPD spectrogram according to the extracted PD pulse peak value and the corresponding phase, and judging the type of the partial discharge signal.
As shown in fig. 6(a) -6 (d), in a specific test embodiment of the present invention, the two sensor signals of one resonance period (5.35ms) are simultaneously collected by the dual-sensor resonance testing platform, as shown in fig. 6(a), and the HFCT signal and the UHF signal are respectively processed by the pulse extraction method, and the extraction results are respectively shown in fig. 6 and 7. Wherein, for HFCT signals, the threshold window N is 10, the step size is 10, and the amplitude isValue threshold VTh1Take 6.7 mV. For UHF signals, the threshold window N is 10, the step length is 10, and the amplitude threshold V isTh2Take 3.25 mV. The time domain sliding energy window M of both is 10, and the energy threshold E can be known by looking up the tableThIs 26.
The partial discharge signal shown in fig. 8(b) can be obtained by processing the HFCT signal at one resonance period (5.35 ms).
First, 500 sets of HFCT signals and 500UHF sets of signals were acquired simultaneously using a dual sensor series resonant platform, each set having a time length of 5.35ms for a total of 500 resonant voltage cycles. Then, the partial discharge pulse in the HFCT signal is separated using the method in section 2. Finally, the amplitude and phase of the PD pulse are extracted, and a PRPD spectrum as shown in fig. 9 is plotted.
As can be seen from fig. 9, the partial discharge signal is submerged in the high-frequency interference before processing, and the discharge characteristic is not obvious and the discharge type cannot be determined; the processed partial discharge signals are symmetrically distributed in a three-quadrant manner in a sine period and are consistent with the characteristics of an internal discharge partial discharge spectrogram, so that the signals are judged to be knife mark discharge. The results show that: the method can effectively extract and judge the PD signal under the series resonance, and realizes the cooperative test of voltage resistance and partial discharge.
In order to study the influence of interference signals only coupled by HFCT on PD determination, the experiment platform in 3.1.1 was used to detect interference without partial discharge source, i.e. using the voltage divider capacitor as the resonant capacitor, where the resonant voltage is 27.4kV and the resonant frequency is 204.9 Hz. Then, 500 sets of HFCT signals and 500 sets of UHF signals acquired simultaneously were compared using the method described above, where each set was 4.88ms in length for a total of 500 resonance periods. Finally, it was found that only 2 pulses of the 500 sets of signals were coupled only by the HFCT. This indicates that there are very few interfering signals to which HFCT only couples. Therefore, the interference coupled only by the HFCT has a very low occurrence probability, and does not affect the partial discharge judgment.
The partial discharge signal is random and therefore the PD pulse and the interference pulse can have an overlap problem. In order to study the influence of the overlapping of the two on the partial discharge judgment, the partial discharge detection number of the method under different data volumes is counted, and the result is shown in table 1.
TABLE 1 statistics of PD detection numbers for different data volumes
As can be seen from the above table, the method can detect a large number of partial discharge signals with different data amounts, and the PD detection number increases linearly as the data amount increases. This indicates that a few partial discharge pulses overlap with the interference pulses at resonance, while most partial discharge pulses do not overlap with the interference pulses. Therefore, the influence of the overlapping of the two on the partial discharge judgment is within an acceptable range, and the partial discharge can be effectively detected and judged by the method. And when the point placing type is judged, comparing the resonance PRPD spectrogram with the power frequency PRPD spectrogram. The judgment of the type of the discharge signal at least comprises a cutter mark defect, a protrusion of a semi-conducting layer, metal particles and dislocation of a prefabricated part. The power frequency PRPD spectrogram is a power frequency partial discharge PRPD spectrogram constructed according to different defect types.
In the description of the present invention, it is to be understood that the indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings and are only for convenience in describing the present invention and simplifying the description, but are not intended to indicate or imply that the indicated devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the present invention.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (9)
1. A double-sensor detection method for partial discharge of a cable under series resonance is characterized in that:
acquiring an original partial discharge signal with interference and a high-frequency pulse interference signal in a variable-frequency series resonant circuit;
eliminating the interference signals by using an intersection discrimination method for the obtained original partial discharge signals and high-frequency pulse interference signals, and extracting PD pulses;
and drawing a PRPD spectrogram according to the extracted PD pulse peak value and the corresponding phase, and judging the type of the discharge signal.
2. The method for detecting partial discharge of a cable under series resonance as claimed in claim 1, wherein: the intersection discrimination method comprises the following steps:
extracting effective pulses in the HFCT signal and high-frequency interference pulses in the UHF signal based on a sliding threshold window searching method;
performing time domain overlapping judgment on a certain pulse extracted by the HFCT and all pulses extracted by the UHF, and if the HFCT pulse and the UHF pulse are overlapped, considering the HFCT pulse as an interference pulse; if the two are not overlapped, the HFCT pulse is judged as a PD pulse.
3. The method for detecting partial discharge of a cable under series resonance as claimed in claim 2, wherein:
the sliding threshold window searching method comprises the steps of scanning a denoising signal by using a sliding time window, recording the position of a point as a pulse position when the first data in the window is larger than a threshold value, moving the threshold window backwards, and repeatedly positioning pulses until the threshold window moves to the tail end of the denoising signal.
4. The method of claim 3, wherein the method comprises the steps of: when extracting the effective pulse in the HFCT signal and the high-frequency interference pulse in the UHF signal, the method also comprises the following steps:
initializing a preset threshold of a sliding threshold window, a window length of a preset threshold sliding time window and a preset sliding step length;
searching the two paths of de-noising signals by using a threshold window respectively to obtain pulse rough position sequences of the two paths of de-noising signals: lceUHF＝[C1,C2,…,Cm,]，LceHFCT＝[C1,C2,…,Cn,]，CiIndexing the coarse position of the corresponding pulse in the raw data;
setting an energy threshold EthThe number of data windows is M, in LceUHFAnd LceUHFSearching the pulse edge leftwards and rightwards for the center to obtain transient pulses and index sequences of two paths of signals: pUHF＝[P1；P2；…；Pm]；PHFCT＝[P1；P2；…；Pn]；LocUHF＝[L1,L2,…,Lm,]，LocHFCT＝[L1,L2,…,Ln](ii) a Wherein P isiRepresents a pulse sequence, LiThe index of the corresponding pulse in the original data is m, the number of pulses detected by the UHF sensor is m, the number of pulses detected by the HFCT is n, and n is more than or equal to m.
5. A dual sensor detection system for partial discharge of a cable at series resonance for implementing the method of any one of claims 1 to 4, comprising a variable frequency series resonant circuit and a sampling unit; the sampling unit comprises a UHF sensor arranged at a variable frequency power supply end, an HFCT sensor arranged at a tested cable, an oscilloscope and a PC (personal computer);
HFCT sensor for acquiring original partial discharge signal with interference in variable frequency series resonant circuit
The UHF sensor is used for acquiring a high-frequency pulse interference signal in the variable-frequency series resonant circuit;
the PC utilizes an oscilloscope to obtain an original partial discharge signal and a high-frequency pulse interference signal, eliminates the interference signal by an intersection discrimination method, and extracts PD pulses; and drawing a PRPD spectrogram according to the extracted PD pulse peak value and the corresponding phase, and judging the type of the partial discharge signal.
6. The dual sensor detection system for partial discharge of a cable at series resonance as recited in claim 5,
the signal input end of the oscilloscope is simultaneously connected with the HFCT sensor and the UHF sensor, and the trigger end of the oscilloscope is connected with the capacitive voltage divider in the variable-frequency series resonance circuit and used for utilizing the resonance voltage signal as the trigger signal of the oscilloscope.
7. The dual-sensor system for detecting partial discharge of a cable under series resonance as claimed in claim 5, wherein said oscilloscope stores data in a screen manner, and saves peak information of signal data in a glitch capture manner to realize data storage in a frequency reduction manner; and the PC runs an LABVIEW program control oscilloscope to realize the storage of data in a plurality of resonance periods.
8. The system as claimed in claim 5, wherein the variable frequency series resonant circuit comprises a rectifying module, an inverting module, a boosting module and a resonant tank connected in sequence.
9. The dual-sensor system for detecting partial discharge of cable under series resonance as claimed in claim 5, wherein the resonance PRPD spectrum is compared with the power frequency PRPD spectrum when the discharge point type is determined.
The judgment of the type of the discharge signal at least comprises a cutter mark defect, a protrusion of a semi-conducting layer, metal particles and dislocation of a prefabricated part. The power frequency PRPD spectrogram is a power frequency partial discharge PRPD spectrogram constructed according to different defect types.
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| CN115047302A (en) * | 2022-08-15 | 2022-09-13 | 国网江西省电力有限公司电力科学研究院 | Cable series resonance partial discharge detection system and method based on double transformers |
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| CN115144705A (en) * | 2022-06-28 | 2022-10-04 | 广东电网有限责任公司 | Partial discharge detection method, device, equipment and medium based on propagation distortion compensation |
| CN117892067A (en) * | 2024-03-15 | 2024-04-16 | 国网上海市电力公司 | Low-frequency current partial discharge monitoring anti-interference method, device, equipment and medium |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115116308A (en) * | 2022-06-15 | 2022-09-27 | 华南理工大学 | Partial discharge detection teaching system and method suitable for laboratory |
| CN115144705A (en) * | 2022-06-28 | 2022-10-04 | 广东电网有限责任公司 | Partial discharge detection method, device, equipment and medium based on propagation distortion compensation |
| CN115144705B (en) * | 2022-06-28 | 2024-05-03 | 广东电网有限责任公司 | Partial discharge detection method, device, equipment and medium based on propagation distortion compensation |
| CN115047302A (en) * | 2022-08-15 | 2022-09-13 | 国网江西省电力有限公司电力科学研究院 | Cable series resonance partial discharge detection system and method based on double transformers |
| CN117892067A (en) * | 2024-03-15 | 2024-04-16 | 国网上海市电力公司 | Low-frequency current partial discharge monitoring anti-interference method, device, equipment and medium |
| CN117892067B (en) * | 2024-03-15 | 2024-05-28 | 国网上海市电力公司 | Low-frequency current partial discharge monitoring anti-interference method, device, equipment and medium |
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