CN112230100B - Slow-development permanent fault early warning method and system - Google Patents
Slow-development permanent fault early warning method and system Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
Abstract
The invention discloses a slowly developing permanent fault early warning method and a system, comprising the following steps: acquiring a recording waveform of each instantaneous fault before a permanent fault occurs on a line; judging a fault section through a recording waveform, and extracting key characteristic quantity; calculating an insulation degradation value during each transient fault according to the key characteristic quantity; accumulating the insulation degradation values obtained for multiple times in the same fault section to obtain an accumulated insulation degradation value; and when the accumulated insulation degradation value exceeds an insulation degradation threshold value, giving an early warning. Acquiring each instantaneous fault recording waveform before a permanent fault occurs, extracting fault key characteristic quantity, judging the insulation degradation degree of the circuit according to the extracted key characteristic quantity, and then sending out early warning according to the insulation degradation degree.
Description
Technical Field
The disclosure relates to a slowly developing permanent fault early warning method and system.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
Distribution lines are directly connected with users, the aspects of life and production are directly influenced, the distribution network has an extremely important role in an electric power system, the distribution network has a large coverage area due to the responsibility of distributing electric energy, has the characteristics of multiple feeders, multiple branches, changeable topology, multiple points, wide range and the like, has a relatively severe operating environment and is very easy to break down, and statistical data shows that most line faults belong to instantaneous faults.
For a distribution line, when a single-phase instantaneous earth fault occurs at the same position for many times, each fault releases energy at the earth point, and the line insulation at the earth point is damaged. Although the fault is temporary and the fault duration is mostly from several milliseconds to several minutes, the insulation of the line is degraded to different degrees after each fault occurs, so that the insulation degradation of the line reaches the limit due to the accumulation of multiple faults, and finally permanent faults are formed by concentrated explosion after a certain grounding.
How to early warn about a slowly developing permanent fault so as to avoid the permanent fault is extremely important.
Disclosure of Invention
In order to solve the above problems, the present disclosure provides a slowly developing permanent fault early warning method and system, which acquire each instantaneous fault recording waveform before a permanent fault occurs, extract a fault key feature quantity, determine an insulation degradation degree of a line according to the extracted key feature quantity, and then send out an early warning according to the insulation degradation degree.
The first purpose of the present disclosure is to provide a slow-developing permanent fault early warning method, which includes:
acquiring a recording waveform of each instantaneous fault before a permanent fault occurs on a line;
judging a fault section through a recording waveform, and extracting key characteristic quantity;
calculating an insulation degradation value during each transient fault according to the key characteristic quantity;
accumulating the insulation degradation values obtained for multiple times in the same fault section to obtain an accumulated insulation degradation value;
and when the accumulated insulation degradation value exceeds an insulation degradation threshold value, giving an early warning.
Further, the key characteristic quantities comprise the number of times of transient faults occurring in a period of time, the interval between two transient faults, the amplitude of the transient zero-mode current, the fault duration and the low-frequency-band energy factor of the zero-sequence current.
Furthermore, the occurrence frequency of transient faults in a period of time is positively correlated with the insulation degradation degree; the interval between two transient faults is in negative correlation with the insulation degradation degree; the transient zero-mode current amplitude is in positive correlation with the insulation degradation degree; the fault duration is positively correlated with the degree of insulation degradation; the zero sequence current low-frequency band energy factor is in negative correlation with the insulation degradation degree.
Furthermore, the occurrence frequency of transient faults, the interval between two transient faults, the transient zero-mode current amplitude and the fault duration in a period of time are directly obtained from the obtained recording waveform.
Furthermore, the obtained wave recording waveform is subjected to frequency band decomposition to obtain energy of each sub-frequency band, and a zero-sequence current low-frequency band energy factor is obtained according to the ratio of the energy of the first sub-frequency band to the sum of the energy of each sub-frequency band.
Further, when calculating the insulation degradation value of each transient fault, the correlation between the key characteristic quantity and the insulation degradation degree is considered.
Further, a larger insulation degradation value indicates a larger degree of insulation degradation.
Further, the insulation degradation threshold is determined according to actual operation experience of a specific power distribution network.
The second purpose of the disclosure is to provide a slowly developing permanent fault early warning system, which includes a detection module, a controller and an alarm model, wherein a wave recording waveform of a transient fault is acquired through the detection module, the controller extracts a key characteristic quantity of the wave recording waveform after receiving the wave recording waveform acquired by the detection module, calculates an insulation degradation value during each transient fault according to the key characteristic quantity, accumulates insulation degradation values acquired for multiple times, acquires an accumulated insulation degradation value, and sends alarm information to the alarm module to give an alarm when the accumulated insulation degradation value exceeds an insulation degradation threshold value.
Further, the controller extracts key characteristic quantities from the recording waveform, including the number of times of transient faults occurring in a period of time, the interval between two transient faults, the transient zero-mode current amplitude, the fault duration and the zero-sequence current low-frequency band energy factor.
Compared with the prior art, the beneficial effect of this disclosure is:
1. the method and the device utilize each instantaneous fault recording waveform before the permanent fault occurs to obtain the key characteristic quantity of the fault, calculate the accumulated insulation degradation value of the line through the extracted key characteristic quantity, judge the insulation degradation degree according to the accumulated insulation degradation value, and send out early warning, thereby realizing the early warning of the slowly-developing permanent fault.
2. According to the method, only the transient fault recording waveform is obtained, early warning of the slowly-developing permanent fault can be completed, other fault characteristics do not need to be additionally detected, a large number of additional other fault characteristic detection and processing devices do not need to be installed, the operation cost is reduced, and the requirement of practical application is met.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
Fig. 1 is a fault early warning process of a slowly evolving permanent fault early warning method of the present disclosure;
FIG. 2 is a graph illustrating cumulative insulation degradation value variation according to the present disclosure;
FIG. 3(a) is a spectrum energy distribution diagram of a slow-developing permanent fault transient fault 1 in example 1;
FIG. 3(b) is a spectrum energy distribution diagram of a slow developing permanent fault transient fault 2 in example 1;
FIG. 3(c) is a spectrum energy distribution diagram of a slow developing permanent fault transient fault 3 in example 1;
FIG. 4 is a single phase ground fault component mode network diagram;
FIG. 5 is a transient single-phase earth fault equivalent circuit;
fig. 6 is a graph showing the variation of the line parameters at different times of insulation degradation.
The specific implementation mode is as follows:
the present disclosure is further described with reference to the following drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example 1
For an overhead line, a large number of devices are arranged on the overhead line, instantaneous ground faults occur with a high probability, for example, lightning strikes, flashover of insulating parts, instantaneous discharge, short-time contact of foreign matters such as branches and the like can cause the instantaneous ground faults of a distribution line, according to actual fault statistics, in a power distribution network with a certain overhead line as a main part, 7 instantaneous faults occur before the faults in different degrees in 20 times of permanent ground faults, wherein 2 instantaneous grounds occur up to 15 times and 16 times respectively in three days before the permanent faults, 1 instantaneous ground occurs 7 times in one hour before the permanent faults, like a transformer substation, an instantaneous ground phenomenon occurs in 72 hours before the 6 permanent ground faults, and the maximum 16 instantaneous faults occur. For a cable line, an insulating layer of a modern cable is mainly crosslinked polyethylene, the insulating layer is generally considered to be high in insulating level and irreversible in insulation breakdown, once the insulating layer is broken down, the insulating layer cannot be recovered, in the practical statistics of cable faults, a considerable part of transient faults are also found, such as faults of a cable middle joint and a terminal and transient breakdown phenomena of a cable body, and in a certain cable fault case, before a permanent ground fault which lasts for 100 minutes internally occurs, 8 transient ground faults are detected.
It can be seen that for a distribution line, when a single-phase instantaneous ground fault occurs at the same location multiple times, each fault will discharge energy at the ground point, destroying the line insulation at the ground point. Although such a fault is temporary, the fault duration is mostly from several milliseconds to several minutes, and mostly less than 1s, the insulation of the line is degraded to different degrees after each fault occurs, so that the insulation degradation of the line is limited by the accumulation of multiple times, and finally permanent faults are formed by concentrated explosion after a certain grounding, and the fault mode can be summarized as a slowly-developing permanent grounding fault, and the fault mode also conforms to many fault scenarios in practice.
With the development of a power grid synchronous measurement system and a dispatching automation system based on modern information technology, high-precision synchronous measurement devices such as a fault recording device and a distribution network side PMU further cover all important nodes of a power distribution network, more and more accurate information with unified synchronous time scales can be acquired by a dispatching center, and the actual change waveforms of all electric quantities of early insulation discharge can be recorded in a time sequence form, wherein rich information reflecting the running state of the system is contained.
Therefore, the method is extremely important for analyzing the transient fault recording data of each time before the permanent fault occurs, finding out the early-stage fault characteristics, obtaining the fault characteristics-space-time distribution response characteristics, further analyzing and judging the insulation level of the line, giving out the alarm signal in due time and providing the early warning method for the slowly-developing permanent ground fault so as to avoid the permanent fault.
The overall development law of the permanent fault is analyzed, so that the formation of the permanent fault is a slowly-developed process, before the permanent fault occurs, transient fault grounding often occurs, and at the moment, the element has a physical evolution process of intermittent discharge-breakdown. The overall development rule of the permanent faults of the distribution line is obtained by analyzing the insulation aging and fault formation of main equipment such as cables, overhead lines, insulators and the like.
Under the long-term action of operating voltage, thermal stress, external mechanical force, moisture and other environmental conditions, the insulation of the power distribution network power equipment presents a slow degradation process. For solid insulation inside cables, insulators and the like, the insulation generally cannot be broken down under the operation voltage, and the insulation can be broken down under the action of transient overvoltage, but the transient overvoltage is not long in duration and disappears after a few seconds, and then the power grid returns to normal operation. For the external insulation, oil insulation and gas insulation of power equipment, as the medium-low voltage distribution network is a low-current grounding system, the fault current is small, the arc suppression coil can suppress instantaneous arcs, even if instantaneous breakdown is likely to occur under the operating voltage, the arcs can be extinguished at the high-frequency zero crossing point of the fault current, and then considering that impurities and moisture at the fault point are heated by the arcs to be burnt and dried, the arcs can be naturally extinguished and cannot be reignited. In the initial stage of degradation, single-phase earth faults have a distinct arc grounding characteristic, when overvoltage and various severe operating conditions occur again, insulation weak points can be continuously punctured and further damage insulation, unstable arc grounding also gradually develops to metallic grounding, and finally permanent single-phase grounding occurs. In the process, the instantaneous insulation breakdown times are in an ascending state on the whole, and the time interval between two instantaneous faults is also in a shortening trend.
It is also found in the related work of studying the change rule of the insulation resistance and the distributed capacitance caused by the electrical branch formed by the insulation deterioration that the distributed capacitance fluctuates and increases continuously in the early period of the deterioration and the equivalent resistance gradually decreases in the middle and later periods of the deterioration, the decrease of the resistance and the increase of the capacitance are consistent with the degree of the electrical branch formed by the insulation deterioration, and the relative dielectric constant and the insulation resistance of the insulation both show nonlinear changes, as shown in fig. 6. It can be seen that the degradation of the line insulation is generally accompanied by an increase in the equivalent distributed capacitance and a decrease in the insulation resistance, i.e., the transition resistance tends to decrease during the transient fault development phase of the slowly developing permanent ground fault.
Other various faults in the power distribution network are mostly developed by single-phase earth faults, after the single-phase earth faults occur, firstly, the non-fault phase voltage is increased to the line voltage, the single-phase faults are likely to be developed into two-phase or even three-phase faults at the insulation weak points, particularly, the intermittent arc earthing enables the non-fault phase to have arc earthing overvoltage as high as 3.5p.u. to cause tripping, and secondly, for switch equipment such as circuit breakers, two-phase or three-phase short circuits are caused by the fact that the earthing arc is in contact with the non-fault, and the line tripping is caused to enlarge the fault range.
The principle of analyzing the transient earth fault can be known that most of the running modes of the power distribution network in China are that a neutral point is grounded through an arc suppression coil, when the transient single-phase earth fault occurs, the transition process of the system can be equivalent by adding a zero-sequence voltage source at the fault point, actual data shows that the damping rate of the line network in the resonant earth power distribution network is low, namely the ratio of the active current of the fault earth point to the capacitive current is small, and the active current of the earth point is ignoredThe analysis result is not influenced, and the instantaneous single-phase earth fault equivalent circuit is obtained on the basis of the single-phase earth fault component mode network diagram of fig. 4 as a simplified condition of the next analysis as shown in fig. 5, wherein L is the sum of two-wire mode loop inductances and is approximately equal to twice of the line positive sequence inductance, R is the sum of two-wire mode loop resistances and is approximately twice of the line positive sequence resistance, and R is a simplified condition of the next analysistrRepresenting zero sequence equivalent resistance, equivalent transition resistance in the arc path formed by the fault ground point, C0Is zero mode capacitance, 3LLIndicating arc-suppression coil inductance value, ukIndicating an additional zero sequence supply voltage at the fault point, the closing of the switch S corresponds to an instantaneous earth fault occurrence. According to the dynamic circuit analysis theory, the capacitance and the inductive current of the equivalent circuit are deduced by means of Laplace transformation and inverse transformation, and the equations (1) and (2) are shown.
In the formula ICmAmplitude of capacitive current flowing through a single-phase earth fault, ICm＝UmωC0；ωf-transient current free oscillation angular frequency; delta-transient capacitance current decay factor; omega-supply voltage angular frequency; i isLm-the magnitude of the inductor current in the loop;
-a fault phase voltage initial phase angle; tau isL-an inductive loop time constant.
Wherein iCFor the capacitance loop current, the first term in the equation (1) is a transient capacitance current component, which has a high-frequency free oscillation property, and is generated due to the inductance and capacitance contained in the loop, because the loop also has a resistor, the first term will gradually decay, and finally only a steady-state capacitance current component is contained in the loop, that is, the second term in the equation (1). i.e. iLSince the loop does not have a capacitor and only includes an inductor and a resistor, the transient inductor current in the first term in equation (2) is a decaying dc component, and the steady inductor current component in the second term.
The two components are superposed to obtain the total current of the grounding point fault, as shown in formula (3):
the first term in the formula (3) is a steady-state component of the total current, and the first term is observed to show that the steady-state current is the difference between the steady-state components of the capacitance and the inductance current, the angular frequencies of the capacitance and the inductance current are the same and are power supply voltage angular frequencies, so that the steady-state component of the total current is single in component, the property of the steady-state component is related to the compensation degree of the arc suppression coil, and when the compensation degree is greater than 1, a small inductive fundamental current flows through the head end and the grounding point of the fault line; when the compensation degree is less than 1, the fault line and the grounding point flow smaller capacitive fundamental current; when the compensation degree is equal to 1, the fundamental wave current of the fault line and the grounding point is zero. The compensation of the crowbar coil therefore makes the steady-state component very weak, from which no further information about the momentary fault can be derived.
The second term is total current transient component, which is formed by overlapping transient components of capacitance current and inductance current, the two components have different frequencies and even have larger difference, so that the two components can not be mutually counteracted but are more likely to become larger.
Then, the transient zero-mode current is specifically analyzed, and the expression of the transient zero-mode current is
1) Initial phase angle of fault
In most cases, a transient ground fault caused by insulation breakdown at a certain position of a line in a power distribution network often occurs at the moment when a phase voltage is close to a maximum value, that is, at the moment when a fault initial phase angle phi is pi/2, a transient zero-mode current component can be expressed as follows:
that is, when the transient earth fault occurs, the transient zero-mode current component does not contain an inductive component, but only a capacitive component of oscillation attenuation.
2) Transition resistance and transient current oscillation frequency
Transient current free oscillation angular frequency omegafThe oscillation frequency of the capacitive component is determined, and after the actual power distribution network parameters are considered, the calculation formula is as follows:
distribution line parameter R, L, C for a resonant grounded distribution network0The transient current free oscillation angular frequency is mainly determined by the transition impedance, and the change of the transition resistance can cause the change of the transient current oscillation frequency. Considering the actual parameters of power distribution, the increase of the transition resistance can shift the spectral energy distribution of the fault signal to the low frequency band direction, i.e. the transition resistance becomes large, and the content of the high frequency band of the transient zero-mode current becomes small.
3) Transition resistance and transient zero-mode current amplitude
When single phase ground fault occurs in actual power distribution network, fault transient state zero mode current oscillation frequency omega of overhead linefIn the range of about 300Hz to 1500Hz, the cable lines are divided by their inductance being much smaller than the overhead linesThe distributed capacitance is larger than that of an overhead line, and the fault transient zero-mode current oscillation frequency omegafThe range is 1500 Hz-3000 Hz, so the fault transient zero-mode current oscillation frequency omegafIs much larger than the power frequency omega. The amplitude of the fault transient zero-mode current mainly consists of omegafThe ratio of/ω is determined and the amplitude is proportional to the oscillation frequency, the oscillation frequency ωfThe transient zero-mode current is related to the transition resistance, so that the amplitude of the transient zero-mode current is changed while the oscillation characteristic of the transition resistance is changed, and the larger the transition resistance is, the smaller the amplitude of the transient zero-mode current is.
Based on the analysis of the permanent earth fault rule and the transient earth fault principle, the characteristics of the slowly-developing permanent earth fault are summarized:
1) transient earth faults are typically single-phase earth faults
In an actual power distribution network, the insulation degradation degree of a three-phase line is not completely consistent, so that transient faults always occur at the weakest point of insulation to form single-phase grounding, and therefore the transient faults are generally single-phase grounding faults.
2) When the permanent faults are close to occurring, the frequency and the duration time of the transient faults are in an increasing trend
When the deterioration of the insulation of the line is aggravated, the insulation strength becomes less easily restored, the duration of arc burning becomes longer in the event of a transient fault, and the line becomes more likely to establish an arc, which in turn further aggravates the insulation deterioration, which progresses to the end of complete insulation failure. The frequency and duration of transient faults are on the rise near the occurrence of permanent faults.
3) Abundant instantaneous grounding related information is contained in fault transient zero-mode current
Transient earth faults caused by insulation degradation often occur at the initial phase angle
Nearby, the transient component in the zero-mode current mainly contains oscillation attenuation capacitive component and is much larger than the steady-state component, and the zero-mode current is suitable for being used for researching the insulation state of the lineThe source of the data.
4) Transient zero-mode current frequency spectrum change and amplitude change caused by transition resistance
The transient zero-mode current amplitude value is changed while the oscillation characteristic of the transition resistor is changed, so that the transient zero-mode current amplitude value is increased.
Based on the above research, in this embodiment, a slow-developing permanent fault early warning method is provided, including:
acquiring a recording waveform of each instantaneous fault before a permanent fault;
secondly, positioning a fault section from the obtained wave recording waveform, and extracting key characteristic quantities, wherein the key characteristic quantities comprise the number of times of transient faults in a period of time, the interval between two transient faults, the transient zero-mode current amplitude, the fault duration and the zero-sequence current low-frequency band energy factor;
a. number of transient faults occurring N within a period of timek
Setting a window with a fixed time length, and observing the occurrence frequency of transient faults in the time window in the process that the window slides along a time track, wherein the more frequent the transient faults occur, the more serious the damage to the line insulation is, the closer the permanent ground fault occurs, and the positive correlation is formed between the damage degree and the insulation degradation degree.
b. Interval between two faults Tkit
The time interval between the current transient fault and the last transient fault of the kth line is considered to be negatively related to the insulation degradation degree, and the time interval is shorter and shorter in the process that the frequency of the insulation ground fault rises and the insulation damage of the line is aggravated.
c. Transient zero-mode current amplitude Ik
The transient zero-mode current amplitude reflects the size of the grounding impedance of a fault point to a certain extent, and also indirectly reflects the degree of insulation degradation, and is positively correlated with the degree of insulation degradation, and the larger the transient zero-mode current amplitude is, the higher the degree of insulation degradation is, and the more serious the transient fault is.
d. Duration of failure Tkdt
The longer the fault duration, the greater the intensity of this transient earth fault, the more severe the dielectric breakdown, and the greater the degree of reduction in the line insulation level, which positively correlates with the degree of insulation degradation.
e. Zero sequence current low frequency band energy factor ELk
The proportion of low-frequency-band energy in the total energy is defined as a low-frequency-band energy factor of zero-sequence current, and the low-frequency-band energy factor of the zero-sequence current is associated with the reduction of insulation resistance and the increase of equivalent distributed capacitance in the process of line insulation deterioration, wherein the energy distribution of the zero-sequence current in each frequency band is related to the intensity of instantaneous fault, and the smaller the low-frequency-band energy factor of the zero-sequence current is, the smaller the transition resistance is, the more serious the insulation deterioration is, and the insulation deterioration degree is in negative correlation.
Except the zero sequence current low-frequency band energy factor, other four characteristics can be directly calculated according to instantaneous fault recording data, and the zero sequence current low-frequency band energy factor needs to be calculated after the wave recording waveform is subjected to frequency band decomposition. The zero sequence current is decomposed in an equal-bandwidth frequency band by utilizing wavelet packet transformation, namely, the signals pass through a conjugate orthogonal filter bank formed by high-low pass combination, the signals of the previous layer are continuously subdivided into different frequency bands, the sampling interval is doubled after the filter acts on the signals once, and the data points are halved. If the sampling frequency of the signal is fsThen by the sampling theorem, the Nyquist frequency is f s2, the bandwidth of the frequency band after n layers of decomposition is fs/2/2n＝fs/2n+1The frequency range of the jth sub-band may be expressed as:
recording signal xkThe coefficient of the j sub-band after n-layer decomposition is
m is the number of coefficients under each sub-band, and the energy of each sub-band is:
by reasonably setting the number n of decomposition layers, the power frequency 50Hz appears in the frequency band j equal to 1, and the third harmonic, the fifth harmonic and the power frequency aliasing are avoided, so that the low-frequency band energy factor E of the zero-sequence current can be obtainedLkComprises the following steps:
calculating an insulation degradation value during each transient fault according to the key characteristic quantity, and accumulating insulation degradation values obtained for multiple times in the same fault section to obtain an accumulated insulation degradation value;
each key characteristic quantity is constructed as an insulation degradation value function D according to the correlation between the key characteristic quantity and the insulation degradation degree, and the larger D is, the more serious the insulation degradation degree is. Cumulative degradation value of line k
Defined as historical degradation value
And a degradation value D 'caused by the current transient fault'kAnd (3) the sum is represented by formula (10):
the insulation degradation value function is updated after each characteristic quantity is calculated by using the waveform of the transient fault, and the obtained cumulative insulation degradation value change curve is shown in fig. 2.
According to the method, besides constructing the function through the correlation relationship between the key characteristic quantity and the insulation degradation degree, the mapping relationship between the key characteristic quantity and the insulation degradation degree can be obtained based on a neural network method trained by a sample, and the contribution of different key characteristic quantities to the insulation degradation degree can be distinguished through introducing weights.
And fourthly, when the accumulated insulation degradation value exceeds an insulation degradation threshold value, giving out an early warning, wherein the insulation degradation threshold value is determined according to actual operation experience of the specific power distribution network.
The spectral energy distribution of each transient fault in a slowly evolving permanent fault case is shown in fig. 3(a) -3(c), and three transient faults occurred before the permanent fault.
On the basis of analyzing the development rule of the permanent fault and the transient earth fault principle and summarizing the characteristics of the slowly-developing permanent earth fault, the key characteristic set of the early transient fault discharge waveform is extracted from the two aspects of the occurrence frequency of the transient fault and the transient fault intensity, and the insulation degradation process in the slowly-developing permanent earth fault is well reflected by the extracted key characteristic set, so that the slowly-developing permanent fault is predicted.
The early warning method is designed based on a signal processing mechanism of the power distribution network fault recording device, the problem that the operation cost is excessively increased due to the fact that a large number of additional fault characteristic detection and processing devices need to be installed is solved, and the requirements of practical application are met.
Example 2
In the embodiment, a slowly-developing permanent fault early warning system is provided, and the system comprises a detection module, a controller and an alarm model, wherein the detection module acquires a wave recording waveform of a transient fault, the controller extracts a key characteristic quantity of the wave recording waveform after receiving the wave recording waveform acquired by the detection module, calculates an insulation degradation value during each transient fault according to the key characteristic quantity, accumulates insulation degradation values acquired for multiple times to acquire an accumulated insulation degradation value, and sends alarm information to the alarm module to give an alarm when the accumulated insulation degradation value exceeds an insulation degradation threshold value.
The controller extracts key characteristic quantities from the recording waveform, wherein the key characteristic quantities comprise the occurrence frequency of transient faults in a period of time, the interval between two transient faults, the amplitude of transient zero-mode current, the fault duration and the low-frequency-band energy factor of zero-sequence current.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.
Claims (6)
1. A slow-developing permanent fault early warning method is characterized by comprising the following steps:
acquiring a recording waveform of each instantaneous fault before a permanent fault occurs on a line;
judging a fault section through a recording waveform, and extracting key characteristic quantity;
calculating an insulation degradation value during each transient fault according to the key characteristic quantity;
accumulating the insulation degradation values obtained for multiple times in the same fault section to obtain an accumulated insulation degradation value;
when the accumulated insulation degradation value exceeds an insulation degradation threshold value, sending out an early warning;
constructing an insulation degradation value function according to the correlation between each key characteristic quantity and the insulation degradation degree, and obtaining an accumulated insulation degradation value according to the insulation degradation value function;
the insulation degradation value function is:
wherein the content of the first and second substances,
as an accumulated degradation value of the line k,
is a historical deterioration value, D'kFor the degradation value, T, caused by the present transient faultkdtFor the duration of the fault, IkIs the transient zero-mode current amplitude, NkThe number of transient faults occurring over a period of time, ELkIs a low-frequency band energy factor E of zero-sequence currentLk，TkitThe interval between two faults.
2. The method of claim 1, wherein the number of transient faults occurring within a period of time, the interval between two transient faults, the transient zero mode current amplitude and the fault duration are directly obtained from the obtained recording waveform.
3. The slow-developing permanent fault pre-warning method as claimed in claim 1, wherein the obtained recording waveform is subjected to band decomposition to obtain energy of each sub-band, and a zero-sequence current low-band energy factor is obtained according to a ratio of the energy of the first sub-band to the sum of the energy of each sub-band.
4. The slow-developing permanent fault warning method as claimed in claim 1, wherein a larger insulation degradation value indicates a more serious insulation degradation.
5. The slow-developing permanent fault pre-warning method as claimed in claim 1, wherein the insulation degradation threshold is determined according to actual operation experience of a specific distribution network.
6. A slowly-developing permanent fault early warning system is characterized by comprising a detection module, a controller and an alarm model, wherein a wave recording waveform of a transient fault is obtained through the detection module, the controller extracts key characteristic quantities of the wave recording waveform after receiving the wave recording waveform obtained by the detection module, an insulation degradation value during each transient fault is calculated according to the key characteristic quantities, the insulation degradation values obtained for multiple times are accumulated to obtain an accumulated insulation degradation value, and when the accumulated insulation degradation value exceeds an insulation degradation threshold value, alarm information is sent to the alarm module to give an alarm;
constructing an insulation degradation value function according to the correlation between each key characteristic quantity and the insulation degradation degree, and obtaining an accumulated insulation degradation value according to the insulation degradation value function;
the insulation degradation value function is:
wherein the content of the first and second substances,
as an accumulated degradation value of the line k,
is a historical deterioration value, D'kFor the degradation value, T, caused by the present transient faultkdtFor the duration of the fault, IkIs the transient zero-mode current amplitude, NkThe number of transient faults occurring over a period of time, ELkIs a low-frequency band energy factor E of zero-sequence currentLk，TkitThe interval between two faults.
Priority Applications (2)
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| CN113741387A (en) * | 2021-08-16 | 2021-12-03 | 北京工业大学 | Threshold value judgment method for instantaneous fault occurrence intensity |
| CN114779016B (en) * | 2022-05-07 | 2023-04-07 | 四川大学 | Repetitive instantaneous fault identification method based on improved DTW |
| CN115130595B (en) * | 2022-07-05 | 2023-06-27 | 重庆电子工程职业学院 | Prediction-based aircraft data analysis and maintenance system |
| CN117269694B (en) * | 2023-10-24 | 2024-02-20 | 安徽斯凯奇电气科技有限公司 | Partial discharge fault monitoring system |
| CN117216485B (en) * | 2023-11-09 | 2024-01-30 | 国网山东省电力公司电力科学研究院 | Objective weighting-based power transmission wave-recording bird damage fault judging method and system |
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