CN114520500B - Flexible direct current power grid power transmission line protection and lightning stroke recognition method and system - Google Patents
Flexible direct current power grid power transmission line protection and lightning stroke recognition method and system Download PDFInfo
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- CN114520500B CN114520500B CN202210139013.1A CN202210139013A CN114520500B CN 114520500 B CN114520500 B CN 114520500B CN 202210139013 A CN202210139013 A CN 202210139013A CN 114520500 B CN114520500 B CN 114520500B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/08—Measuring electromagnetic field characteristics
- G01R29/0807—Measuring electromagnetic field characteristics characterised by the application
- G01R29/0814—Field measurements related to measuring influence on or from apparatus, components or humans, e.g. in ESD, EMI, EMC, EMP testing, measuring radiation leakage; detecting presence of micro- or radiowave emitters; dosimetry; testing shielding; measurements related to lightning
- G01R29/0842—Measurements related to lightning, e.g. measuring electric disturbances, warning systems
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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
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
Abstract
The invention discloses a method and a system for protecting a power transmission line of a flexible direct-current power grid and identifying lightning stroke, wherein the method comprises the following steps: acquiring current and voltage data of two ends of a tested power transmission line; respectively calculating the fault reverse traveling wave slopes of the positive and negative lines when the power transmission line has a fault, and judging whether the power transmission line has a single-pole fault or a double-pole fault based on a set value; calculating polar mode fault traveling waves at two ends of the power transmission line by phase-mode conversion, and calculating the difference between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window; and comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line. According to the invention, the upper envelope line and the lower envelope line of the polar mode voltage traveling wave are adopted to form the lightning stroke identification criterion, so that the difficulty in determining a setting value is reduced, and the identification accuracy is improved; the unipolar fault and the bipolar fault can be accurately distinguished, and the fault type judgment efficiency is higher; the identification method is simple in principle and easy to implement in engineering.
Description
Technical Field
The invention relates to the technical field of relay protection of flexible direct-current power transmission lines, in particular to a method and a system for protecting the power transmission lines of a flexible direct-current power grid and identifying lightning stroke.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
With the rapid development of the power industry, high voltage transmission plays an important role under the current energy structure. And dc transmission has been greatly developed because of its advantages in long-distance transmission. With the reduction of fossil energy and the increasing severity of environmental problems, clean energy such as wind energy and light energy will occupy a greater proportion. However, clean energy is difficult to be accommodated by conventional dc transmission systems due to its random geographical location, day-night intermittency and power uncertainty. The flexible direct current transmission system is a new generation direct current transmission technology, is a voltage source converter formed on the basis of a turn-off power electronic device IGBT, and can flexibly adjust the voltage amplitude and the phase angle. Based on the advantages that these traditional dc transmission networks do not have, the flexible dc transmission system has great advantages in receiving and consuming clean energy.
According to the level number of the voltage source converter adopted by the flexible direct current power grid converter station, the voltage source converter can be divided into a two-level converter, a three-level converter and a multi-level converter. Compared with a two-level converter which is commonly used, the Modular Multilevel Converter (MMC) has more remarkable advantages, such as easier expansion of power capacity and voltage level, reduction of loss due to switching frequency reduction, more economical modular production and higher output waveform quality without a filter. However, similar to the two-level voltage source converter, when a fault occurs on the direct current side of the line, the sub-module capacitor of the converter discharges, and because the system damping is small, the fault current has a high rising speed and a large amplitude. And the semiconductor elements of the converter station are fragile, and after the fault current rises to a certain degree, the converter station is locked, so that the normal operation of the whole system is greatly influenced.
In the actual operation process, the transmission line is susceptible to natural disasters such as flood, debris flow, snow disaster, earthquake, typhoon, lightning stroke and the like. Among them, lightning stroke causes trip accidents of transmission lines most easily, lightning current invades a converter station along the transmission line, possibly causes converter devices to be damaged, seriously affects safe and stable operation of a power system, and causes great influence on production and life of residents. According to the operation statistical data, the tripping accidents of the power transmission line caused by lightning strike account for 40% -70% of the total tripping accidents. And the flexible direct current transmission line is more easily affected by lightning stroke because the transmission distance is long and the span of the overhead line is long. And non-fault lightning strike can cause sudden change of voltage and current, possibly cause protection maloperation based on transient quantity, and influence the normal operation of a relay protection system.
Therefore, the flexible direct-current line fault transient characteristic is researched, a reliable and effective direct-current line protection method and a lightning stroke recognition method are provided, and the flexible direct-current line fault transient characteristic protection method has great theoretical significance and engineering value for the transmission reliability, safe and stable operation, follow-up fault removal and lightning protection improvement of a flexible direct-current power grid.
In order to better adapt to the protection requirement of the flexible direct current system, on one hand, students actively improve the traditional direct current power grid protection method and apply the method to the flexible direct current power grid; on the other hand, a protection scheme aiming at the flexible direct-current power grid is provided based on the fault characteristics of the flexible direct-current power grid.
The prior art provides a single-ended protection method for a direct current line based on transient voltage traveling waves. By analyzing the fault transient characteristics at the boundary of the flexible direct-current transmission line, the difference of voltage traveling wave change rates under the conditions of an intra-area fault, an out-area forward fault and an out-area reverse fault is found, and a fault identification criterion based on the transient voltage change rate is constructed; and identifying a fault pole based on the positive and negative pole current traveling wave rate of change. This protection principle is simple and easy to implement, but is susceptible to the effects of transition resistance.
The prior art proposes a pilot protection method based on the voltage polarity of a current-limiting inductor. When an intra-area fault occurs, the polarities of the voltages on the current-limiting inductors at the two ends of the line are the same; when an out-of-range fault occurs, the polarities of the voltages on the current-limiting inductors at the two ends of the line are opposite, and a pilot protection method based on the polarities of the current-limiting inductors at the two ends of the line is provided based on the difference of the polarities of the voltages of the current-limiting inductors at different fault positions. The protection method is simple in principle and has absolute selectivity, but the protection speed is slightly insufficient due to the fact that communication is needed to be carried out at two ends of a line.
The prior art proposes a single-ended magnitude protection method based on intra-and inter-zone high-frequency components. In order to inhibit the rising rate and amplitude of fault current, the flexible direct current system is provided with current-limiting inductors at two ends of a power transmission line. The current-limiting inductor has a higher blocking effect on high-frequency components in the traveling wave, and a protection method is provided based on the difference of the high-frequency components inside and outside the area. The protection method has high quick-action performance, but needs high sampling frequency and has high requirements on hardware.
The prior art proposes a method for protecting high frequency component difference based on wavelet transform. The method extracts high-frequency components in fault transient voltage through wavelet transformation, and judges faults inside and outside the area by utilizing a square value and an energy value of the high-frequency transient voltage respectively by means of the boundary action of a current-limiting inductor at a port of a power transmission line. The protection method relies on the transient component to form a protection criterion, and has the problem of insufficient resistance to transition resistance.
The prior art provides a lightning stroke identification method based on current waveforms. The method utilizes the difference of current traveling waves under lightning stroke faults and lightning stroke non-faults. The presence of the earth component in the event of a lightning stroke fault causes its general trend of traveling waves to increase monotonically, while the lightning stroke non-fault traveling waves remain fluctuating around the time axis. Therefore, the ratio of the up-and-down integrals of the traveling waves on the time axis is utilized to construct the identification criterion. The protection method is simple in principle, but the threshold value is difficult to set.
The prior art provides a lightning stroke identification method based on wavelet transformation. The characteristic that a traveling wave of a line is more in high-frequency components after lightning stroke is utilized, wavelet transformation is utilized to carry out frequency domain decomposition on the traveling wave, and identification criteria are constructed by comparing frequency components on various frequency domains. The protection method has high identification accuracy, but the lightning stroke component is in a higher frequency domain, so that higher sampling frequency is required, and higher requirements on hardware are met.
Therefore, the existing flexible direct current transmission line does not have a protection scheme for matching line protection with lightning stroke interference identification, and the lightning stroke identification method has the problems that the setting value is difficult to determine, the sampling rate is required to be high, and the like.
Disclosure of Invention
In order to solve the problems, the invention provides a method and a system for protecting a transmission line of a flexible direct-current power grid and identifying lightning stroke, wherein a protection criterion is formed by utilizing the slope of fault reverse waves on a positive electrode line and a negative electrode line, and a single-pole grounding fault or a double-pole short-circuit fault is judged through different setting values; converting the current voltage on the positive and negative pole lines into zero mode and polar mode current voltage by utilizing phase-mode conversion, solving a maximum value and a minimum value of the polar mode voltage traveling wave, fitting the maximum value and the minimum value into upper and lower envelope lines of the polar mode voltage traveling wave respectively, integrating the upper and lower envelope lines respectively, and comparing the value obtained by comparing the integral with a setting value to judge whether a lightning stroke fault section exists.
In some embodiments, the following technical scheme is adopted:
a method for protecting a power transmission line of a flexible direct-current power grid and identifying lightning stroke comprises the following steps:
acquiring current and voltage data of two ends of a tested power transmission line;
respectively calculating the slope of the fault reverse traveling wave of the positive pole line and the negative pole line when the power transmission line has a fault, and judging whether the power transmission line has a single-pole fault or a double-pole fault based on a set setting value;
calculating polar mode fault traveling waves at two ends of the power transmission line through phase-mode transformation, and calculating the difference between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window;
and comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line.
As an optional scheme, the comparing the difference values with different setting values respectively to determine a specific fault type of the power transmission line, specifically including:
if the power transmission line is judged to be in the single-pole fault state, comparing the difference value with a set first setting value, and judging whether the power transmission line is in the lightning pole tower or the lightning conductor non-fault state; if not, comparing the difference value with a set second setting value, and judging whether the single-phase earth fault exists; if not, judging the fault type to be a lightning stroke fault or a non-fault of a lightning stroke line based on the integral of upper and lower envelope lines of the polar mode fault voltage traveling wave;
if the power transmission line is judged to be the bipolar fault, comparing the difference value with a set first setting value, and judging whether the power transmission line is a lightning stroke non-fault; if not, comparing the difference value with a set third setting value, and judging the fault type to be a bipolar short-circuit fault or a lightning stroke fault.
As an optional scheme, based on the integral of the upper envelope and the lower envelope of the polar mode fault voltage traveling wave, the fault type is judged to be a lightning stroke fault or a non-fault of a lightning stroke line, and the method specifically comprises the following steps:
order:
if J is larger than a set threshold value, the lightning stroke fault is detected, otherwise, the lightning stroke line is not in fault;
wherein l up And l down The upper envelope line and the lower envelope line of the pole mode fault voltage traveling wave are respectively, and N and M are respectively the number of data points of the fitted envelope lines.
As an optional scheme, comparing the difference with a set third setting value, and determining that the fault type is a bipolar short-circuit fault or a lightning fault, specifically:
if the difference value is larger than a set third setting value, the lightning stroke fault is detected; otherwise, it is a double short circuit fault.
As an optional scheme, the calculation of the slope of the reverse fault wave of the positive and negative lines when the power transmission line fails is specifically:
respectively calculating fault reverse waves of the positive and negative lines when the power transmission line has a fault, and calculating the slope of the fault reverse waves of the positive and negative lines based on the fault reverse waves;
the fault reverse wave of the positive line of the power transmission line is determined based on the difference value of the product of the component voltage of the positive fault of the power transmission line and the product of the line wave impedance and the component current of the positive fault of the power transmission line;
and the fault reverse wave of the negative pole line of the power transmission line is determined based on the difference value of the product of the component voltage of the negative pole fault of the power transmission line and the product of the line wave impedance and the negative pole fault component current of the power transmission line.
As an optional scheme, based on a set setting value, it is determined whether the power transmission line is a unipolar fault or a bipolar fault, specifically:
criterion one is as follows: the ratio of the slope of the fault reverse wave of the positive line of the power transmission line to the slope of the fault reverse wave of the negative line is larger than a set value;
criterion two: the ratio of the slope of the fault reverse wave of the negative line of the power transmission line to the slope of the fault reverse wave of the positive line is greater than a set value;
if the two criteria are met, the fault or disturbance is a bipolar fault or disturbance, otherwise, the fault or disturbance is a unipolar fault or disturbance.
As an optional scheme, calculating the polar mode fault traveling waves at two ends of the power transmission line by phase-mode transformation specifically includes:
wherein u is - Is a polar mode fault traveling wave, Δ u l And Δ i l Respectively a polar mode voltage and a polar mode current, z c Is the line wave impedance.
In other embodiments, the following technical solutions are adopted:
a flexible direct current power grid transmission line protection and lightning stroke recognition system comprises:
the data acquisition module is used for acquiring current and voltage data of two ends of the tested power transmission line;
the fault determination module is used for respectively calculating the fault reverse wave slopes of the positive and negative lines when the power transmission line fails and determining whether the power transmission line is in a single-pole fault or a double-pole fault based on a set value; calculating polar mode fault traveling waves at two ends of the power transmission line through phase-mode transformation, and calculating the difference between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window; and comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line.
In other embodiments, the following technical solutions are adopted:
a terminal device comprising a processor and a memory, the processor being arranged to implement instructions; the memory is used for storing a plurality of instructions, and the instructions are suitable for being loaded by the processor and executing the flexible direct current power grid transmission line protection and lightning stroke identification method.
In other embodiments, the following technical solutions are adopted:
a computer readable storage medium, wherein a plurality of instructions are stored, and the instructions are adapted to be loaded by a processor of a terminal device and to execute the flexible direct current power grid transmission line protection and lightning stroke identification method.
Compared with the prior art, the invention has the beneficial effects that:
(1) The method only needs to collect the electric quantity at one end, does not need to communicate at two ends of a line, and has higher speed.
(2) The invention adopts phase-mode conversion to convert the voltage and current of the positive pole and the negative pole into the voltage and current of the zero line mode, thereby avoiding the influence of the induced voltage and current of the other pole when one pole is struck by lightning; the upper envelope line and the lower envelope line of the polar mode voltage traveling wave are adopted to form a lightning stroke identification criterion, so that the difficulty in determining a setting value is reduced, and the identification accuracy is improved; the unipolar fault and the bipolar fault can be accurately distinguished, and the fault type judgment efficiency is higher; the identification method is simple in principle and easy to implement in engineering.
(3) According to the simulation result of PSCAD, the invention can accurately judge about 5ms under different faults and lightning strokes, and can still ensure the correct judgment of the protection scheme under the condition of larger transition resistance. In addition, the invention converts the current and voltage of the positive electrode and the negative electrode into the current and voltage of the polar mode, thereby eliminating the influence of induced current and voltage. In addition, the invention uses the envelope curve of the polar-mode fault traveling wave to form a protection criterion, thereby increasing the sensitivity of identification and being easier to set a setting value.
Additional features 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 fault traveling wave propagation in an embodiment of the present invention;
FIG. 2 is a schematic diagram of an additional network for lightning fault in an embodiment of the invention;
FIG. 3 is a schematic diagram of a non-fault lightning strike attachment network in an embodiment of the invention;
FIG. 4 is a model of a four-terminal flexible DC transmission system according to an embodiment of the invention;
5 (a) - (b) are traveling wave curves of the point f1 under different transition resistances when a single-pole ground fault occurs;
6 (a) - (b) are traveling wave curves of point f2 where a single-pole ground fault occurs;
FIGS. 7 (a) - (b) are traveling wave curves of point f1 under different transition resistances, where a bipolar short-circuit fault occurs;
FIGS. 8 (a) - (b) are traveling wave curves for bipolar short fault at point f 2;
9 (a) - (b) are traveling wave curves of different faults occurring at point f 3;
FIGS. 10 (a) - (b) are traveling wave curves for a 15kA lightning strike fault at point f 1;
FIGS. 11 (a) - (b) are traveling wave curves for a 15kA lightning strike fault at point f 2;
FIGS. 12 (a) - (b) are traveling wave curves for a 25kA lightning strike fault at point f 1;
FIGS. 13 (a) - (b) are traveling wave curves for a 25kA lightning strike fault at point f 2;
FIGS. 14 (a) - (b) are traveling wave curves for 10kA non-fault lightning strikes at point f 1;
15 (a) - (b) are traveling wave curves for 10kA non-fault lightning strikes at point f 2;
FIGS. 16 (a) - (b) are traveling wave curves of a lightning conductor generating 50kA lightning at point f1 and a tower generating 50kA lightning at point f 4;
fig. 17 is a flowchart of a method for protecting a power transmission line of a flexible direct-current power grid and identifying lightning stroke in the embodiment of the invention.
Detailed Description
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 exemplary 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 one
In one or more embodiments, a method for protecting a flexible direct current transmission line based on traveling wave waveform characteristics and a method for identifying lightning stroke are disclosed, which, in combination with fig. 17, include the following steps:
(1) Acquiring current and voltage data of two ends of a tested power transmission line;
(2) Respectively calculating the slope of the fault reverse traveling wave of the positive pole line and the negative pole line when the power transmission line has a fault, and judging whether the power transmission line has a single-pole fault or a double-pole fault based on a set setting value;
in this embodiment, the calculation of the fault traveling wave and the pole mode fault traveling wave according to the positive and negative line voltage circuit information collected at the protection installation location specifically includes:
P p ＝Δu p -Z c ·Δi p ，P n ＝Δu n -Z c ·Δi n ，
wherein P is p And P n Backward travelling waves, Δ u, on the positive and negative lines, respectively l And Δ i l Are respectively the polar mode voltage current u - Is a polar mode fault travelling wave, Δ u p And Δ i p And Δ u n And Δ i n Respectively positive pole fault component voltage, current and negative pole fault component voltage, current, z c Is the line wave impedance.
Taking the average slope of the second, the sixth and the eleventh self-voltage abrupt change points of the fault reversal wave as the slope of the fault reversal wave of the positive and negative lines:
ΔG i ＝[P i (k+1)+P i (k+5)+P i (k+10)-3P(k)]/3Δt，(i＝1,2)
comparing the positive and negative slopes of the fault reverse traveling wave, and constructing the criterion as follows:
wherein, Δ G 1 、ΔG 2 Positive and negative slopes of fault reverse wave, G set Setting value is set;
and when the two criterion conditions are simultaneously met, judging that the fault or disturbance is a bipolar fault or disturbance, otherwise, judging that the fault or disturbance is a unipolar fault or disturbance.
(3) Calculating polar mode fault traveling waves at two ends of the power transmission line through phase-mode transformation, and calculating the difference between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window;
in this embodiment, the pole mode fault traveling wave specifically includes:
under the condition of normal operation, no fault traveling wave exists on the transmission line, and when a fault occurs on the line, the fault traveling wave can be transmitted from a fault point to two ends of the line. When a single-pole fault occurs, the fault pole traveling wave has high amplitude and high rising speed, but the non-fault pole traveling wave is formed by line coupling, and the fault pole traveling wave has small amplitude and low rising speed; when bipolar fault occurs, the upward traveling waves of the positive electrode line and the negative electrode line are symmetrical, and the amplitude value is consistent with the rising speed. And the protection setting value is reasonably selected, so that unipolar faults and bipolar faults can be distinguished.
Because each fault has great difference with the travelling wave amplitude that the thunderbolt disturbed and caused, can construct the criterion according to this principle, distinguish the thunderbolt circuit, the lightning rod tower and the lightning conductor and ordinary trouble:
in this embodiment, the maximum value and the minimum value of the polar mode fault traveling wave in a specified time window are calculated, and a criterion is constructed by subtracting the maximum value and the minimum value:
S＝|u max -u min |；
wherein u is max 、u min Maximum of fault travelling wave of polar modeAnd a minimum value.
(4) And comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line. The specific process is as follows:
(1) if the power transmission line is judged to be in the single-pole fault state, comparing the difference value with a set first setting value, and if the difference value is smaller than the first setting value, judging that the lightning pole tower or the lightning conductor is not in the fault state;
otherwise, comparing the difference with a set second setting value, and if the difference is smaller than the second setting value, judging that the single-phase earth fault occurs;
if not, judging the fault type to be a lightning stroke fault or a non-fault of a lightning stroke line based on the integral of the upper envelope line and the lower envelope line of the pole mode fault voltage traveling wave;
specifically, the polar-mode fault traveling wave of a lightning strike fault monotonically decreases due to the presence of the ground component, while the polar-mode fault traveling wave of a non-faulty lightning strike fluctuates up and down around the time axis. Therefore, according to the waveform characteristics of the traveling waves under different conditions, the upper envelope line and the lower envelope line of the polar mode fault traveling wave are obtained, and compared with the upper envelope line and the lower envelope line after a few minutes, the upper envelope line and the lower envelope line have a larger value under the non-fault lightning stroke condition and a smaller value under the lightning stroke fault condition:
in this embodiment, a maximum value and a minimum value of a polar mode fault traveling wave within a specified time window are calculated, an upper envelope and a lower envelope are calculated, an integral value of the upper envelope and the lower envelope is compared, and a subtraction is performed to construct a criterion:
wherein l up And l down The upper and lower envelope lines of the polar mode traveling wave are respectively, and N and M are the number of data points fitted with the envelope lines respectively.
If J is larger than a set threshold value, the lightning stroke fault is detected, otherwise, the lightning stroke line is not in fault;
(2) if the power transmission line is judged to be a bipolar fault, comparing the difference value with a set first setting value, and if the difference value is smaller than the first setting value, judging that the lightning pole tower or the lightning conductor is not in fault; otherwise, comparing the difference with a set third setting value, if the difference is smaller than the third setting value, judging the bipolar short-circuit fault, and if the difference is larger than the third setting value, judging the lightning stroke fault.
It should be noted that the first setting value, the second setting value, and the third setting value in this embodiment are all obtained based on simulation, and generally speaking, lightning strikes the tower or the lightning conductor, and non-fault disturbance < unipolar grounding < bipolar grounding < lightning strike fault, therefore, generally speaking, the first setting value < the second setting value < the third setting value.
In this embodiment, a four-terminal flexible direct-current power transmission system simulation model is constructed by using a PSCAD, and a protection method and a lightning stroke recognition method are subjected to simulation verification:
(1) modeling
The theoretical models are respectively shown in fig. 1-fig. 3, fig. 1 is a schematic diagram of a common ground fault, fig. 2 is a schematic diagram of a lightning stroke fault, and fig. 3 is a schematic diagram of a lightning stroke fault. The simulation model is set up as shown in FIG. 4. The positive and negative voltages of the system are respectively +/-500 kV, the system adopts a symmetrical bipolar structure, and each converter station is respectively provided with an MMC converter connected with a positive and negative wire. The power ratings of the converter stations 1 and 2 are 1500MVA and the power ratings of the converter stations 3 and 4 are 3000MVA. The length of line 1 is 205.9km, the length of line 2 is 188.1km, the length of line 3 is 208.4km and the length of line 4 is 49.6km. The line wave impedance is 237.68 omega. The fault points f1, f2, f3, f4 are located at line 1 at 102km from the converter station 1, line 1 at 2.5km from the converter station 1, line 2 at 94.5km from the converter station 1 and at towers on line 1, respectively.
(2) Fault simulation
Setting positive pole ground faults and bipolar short-circuit faults with transition resistances of 0 omega, 50 omega and 200 omega at a point f1, setting unipolar ground faults and bipolar short-circuit faults without transition resistances at a point f2, setting positive pole ground faults and bipolar short-circuit faults without transition resistances at a point f3, setting lightning stroke amplitudes of lightning stroke positive poles at 15kA and 25kA at the point f1, setting lightning stroke amplitudes of the lightning stroke positive poles at 15kA and 25kA at the point f2, setting non-fault lightning strokes of the lightning stroke positive poles at 10kA at the points f1 and f2, setting 50kA non-fault lightning strokes of lightning stroke lines at the point f1, and setting 50kA non-fault lightning strokes of tower lightning strokes at the point f 4. The specific waveforms of the forward curves of the failure are shown in fig. 5 (a) to 16 (b).
As can be seen from the analysis of fig. 5 (a) to 16 (b), no matter what kind of failure occurs, the calculated amount rapidly exceeds the set value in the failure section in a very short time after the occurrence of the failure. The lightning stroke detection circuit can rapidly and reliably act under various conditions, accurately identify non-fault lightning stroke and has strong transition resistance tolerance capability.
The window for calculating the maximum value and the minimum value of polar mode traveling waves is 0.5ms, and the window for calculating envelope lines and integration is 5ms. The simulation results are shown in tables 1 to 4. J. the design is a square set Set to-0.5, G set Is set to be 1.5,P set Set to 0.5 kV/. Mu.s., S set1 Set to 50,S set2 Set to 400,and S set3 Set to 1000.
Table 1 simulation results for common faults in the area
| Type of failure | Transition resistance/omega | Distance/km | ΔG 1 /kV/μs | ΔG 2 /kV/μs | γ | L up /kV | L down /kV | | S |
| PGF | |||||||||
| 0 | 102 | 14.14 | 5.79 | 2.44 | / | / | / | 281.70 | |
| PGF | 50 | 102 | 11.52 | 6.66 | 1.73 | / | / | / | 205.09 |
| |
200 | 102 | 6.73 | 3.90 | 1.73 | / | / | / | 123.23 |
| |
0 | 2.5 | 36.32 | 7.05 | 5.15 | / | / | / | 259.50 |
| |
0 | 102 | 25.25 | 25.24 | 1.00 | / | / | / | 723.43 |
| PPF | 50 | 102 | 27.40 | 27.40 | 1.00 | / | / | / | 607.98 |
| |
200 | 102 | 17.86 | 17.86 | 1.00 | / | / | / | 405.96 |
| |
0 | 2.5 | 44.59 | 44.60 | 1.00 | / | / | / | 801.89 |
TABLE 2 simulation results in case of common faults outside the zone
TABLE 3 simulation results in case of lightning stroke failure in the zone
TABLE 4 simulation results in non-fault lightning strikes
| Type of failure | Transition resistance/omega | Distance/km | ΔG 1 /kV/μs | ΔG 2 /kV/μs | γ | L up /kV | L down /kV | J | |
| Conducting wire | |||||||||
| 10 | 102 | 25.75 | 10.41 | 2.47 | 314.78 | -63.03 | -4.99 | 538.38 | |
| |
10 | 2.5 | 88.49 | 18.16 | 4.87 | 406.95 | -112.19 | -3.63 | 681.32 |
| Lightning conductor | 50 | 102 | 5.73 | 5.74 | 1.00 | / | / | / | 2.74 |
| Tower tower | 50 | 102 | 5.65 | 5.64 | 1.00 | / | / | / | 5.16 |
As can be seen from the simulation results in tables 1, 2, 3, and 4, when different faults occur, no matter the occurrence location and the fault type of the fault, the simulated values in the fault section satisfy the criteria, and the fault is determined, while the simulated values in the non-fault section do not satisfy the criteria. And under the conditions of different amplitudes, different positions and different types of lightning stroke faults and lightning stroke interference, although simulation values are slightly different, the lightning stroke faults and non-fault lightning strokes can be always correctly identified. Therefore, for different types of common faults and lightning stroke faults, the flexible direct current power transmission system protection scheme and the lightning stroke recognition method based on the traveling wave waveform characteristics can correctly judge the faults and the lightning stroke interference.
According to the simulation results, the flexible direct-current power transmission system protection scheme and the lightning stroke recognition method based on the traveling wave waveform characteristics are suitable for a multi-terminal flexible direct-current power transmission network, can reflect faults of different positions and different types and lightning strokes of different amplitudes and different positions, ensure correct judgment of the faults and the lightning strokes, and have high sensitivity.
According to the simulation result of PSCAD, the invention can accurately judge about 5ms under different faults and lightning strokes, and can still ensure the correct judgment of the protection scheme under the condition of larger transition resistance. In addition, the invention converts the current and voltage of the positive electrode and the negative electrode into the current and voltage of the polar mode, thereby eliminating the influence of induced current and voltage. In addition, the invention uses the envelope curve of the polar-mode fault traveling wave to form a protection criterion, thereby increasing the sensitivity of identification and being easier to set a setting value.
Example two
In one or more embodiments, a flexible dc power grid transmission line protection and lightning stroke recognition system is disclosed, comprising:
the data acquisition module is used for acquiring current and voltage data of two ends of the tested power transmission line;
the fault judgment module is used for respectively calculating the fault reverse wave slopes of the positive pole line and the negative pole line when the power transmission line has a fault, and judging whether the power transmission line has a single-pole fault or a double-pole fault based on a set value; calculating polar mode fault traveling waves at two ends of the power transmission line by phase-mode conversion, and calculating the difference between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window; and comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line.
It should be noted that, the specific implementation of each module described above has been described in the first embodiment, and is not described in detail here.
EXAMPLE III
In one or more embodiments, a terminal device is disclosed, which includes a server, where the server includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor executes the computer program to implement the method for protecting a transmission line of a flexible direct current power grid and identifying a lightning stroke in the first embodiment. For brevity, no further description is provided herein.
It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general purpose processor, a digital signal processor DSP, an application specific integrated circuit ASIC, an off-the-shelf programmable gate array FPGA or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The memory may include both read-only memory and random access memory, and may provide instructions and data to the processor, and a portion of the memory may also include non-volatile random access memory. For example, the memory may also store device type information.
In implementation, the steps of the above method may be performed by integrated logic circuits of hardware in a processor or by instructions in the form of software.
Example four
In one or more embodiments, a computer-readable storage medium is disclosed, wherein a plurality of instructions are stored, and the instructions are adapted to be loaded by a processor of a terminal device and to perform the flexible direct current power grid transmission line protection and lightning stroke identification method in the first embodiment.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (6)
1. A method for protecting a power transmission line of a flexible direct-current power grid and identifying lightning stroke is characterized by comprising the following steps:
acquiring current and voltage data of two ends of a tested power transmission line;
respectively calculating the slope of the fault reverse traveling wave of the positive pole line and the negative pole line when the power transmission line is in fault, specifically:
respectively calculating fault reverse traveling waves of the positive pole line and the negative pole line when the power transmission line is in fault, and calculating the slope of the fault reverse traveling waves of the positive pole line and the negative pole line based on the fault reverse traveling waves; the fault reverse wave of the positive line of the power transmission line is determined based on the difference value of the product of the component voltage of the positive fault of the power transmission line and the product of the line wave impedance and the component current of the positive fault of the power transmission line; the fault reverse wave of the negative pole line of the power transmission line is determined based on the difference value of the product of the component voltage of the negative pole fault of the power transmission line and the product of the line wave impedance and the negative pole fault component current of the power transmission line;
judging whether the power transmission line has a single-pole fault or a double-pole fault based on the set setting value;
calculating polar mode fault traveling waves at two ends of the power transmission line through phase-mode transformation, and calculating the difference value between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window;
comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line; the method specifically comprises the following steps:
if the power transmission line is judged to have the single-pole fault, comparing the difference value with a set first setting value, and judging whether the power transmission line is a lightning pole tower or a lightning conductor is not in fault; if not, comparing the difference value with a set second setting value, and judging whether the single-phase earth fault exists; if not, judging the fault type to be a lightning stroke fault or a non-fault of a lightning stroke line based on the integral of the upper envelope line and the lower envelope line of the polar mode fault voltage traveling wave;
if the power transmission line is judged to be a bipolar fault, comparing the difference value with a set first setting value, and judging whether the power transmission line is a lightning stroke line non-fault; if not, comparing the difference value with a set third setting value, and judging the fault type to be a bipolar short-circuit fault or a lightning stroke fault;
wherein, based on the integral of the upper envelope and the lower envelope of the pole mode fault voltage traveling wave, the fault type is judged to be a lightning stroke fault or a non-fault of a lightning stroke line, and the method specifically comprises the following steps:
order:
if J is larger than a set threshold value, the lightning stroke fault is detected, otherwise, the lightning stroke line is not in fault;
wherein l up And l down Respectively an upper envelope line and a lower envelope line of the pole mode fault voltage traveling wave, wherein N and M are respectively the number of data points of the fitted envelope lines;
comparing the difference with a set third setting value, and judging whether the fault type is a bipolar short-circuit fault or a lightning stroke fault, wherein the specific steps are as follows:
if the difference value is larger than a set third setting value, a lightning stroke fault is detected; otherwise, it is a bipolar short circuit fault.
2. The method for protecting the transmission line of the flexible direct-current power grid and identifying the lightning stroke according to claim 1, wherein the transmission line is judged to be a single-pole fault or a double-pole fault based on a set value, and specifically comprises the following steps:
criterion one is as follows: the ratio of the slope of the fault reverse wave of the positive line of the power transmission line to the slope of the fault reverse wave of the negative line is greater than a set value;
and criterion two: the ratio of the slope of the fault reverse wave of the negative line of the power transmission line to the slope of the fault reverse wave of the positive line is larger than a set value;
if the two criteria are met simultaneously, bipolar faults or disturbances are found, and if the two criteria are not met, unipolar faults or disturbances are found.
3. The method for power transmission line protection and lightning stroke identification of the flexible direct current power grid according to claim 1, wherein the calculation of the polar mode fault traveling waves at the two ends of the power transmission line by phase-mode transformation specifically comprises:
wherein u is - Is a polar mode fault traveling wave,. DELTA.u l And Δ i l Respectively, the polar mode voltage and the polar mode current, z c Is the line wave impedance.
4. The utility model provides a flexible direct current electric wire netting transmission line protection and thunderbolt identification system which characterized in that includes:
the data acquisition module is used for acquiring current and voltage data of two ends of the tested power transmission line;
the fault judgment module is used for respectively calculating the fault reverse wave slopes of the positive pole line and the negative pole line when the power transmission line has a fault, and judging whether the power transmission line has a single-pole fault or a double-pole fault based on a set value; calculating polar mode fault traveling waves at two ends of the power transmission line through phase-mode transformation, and calculating the difference value between the maximum value and the minimum value of the polar mode fault traveling waves in a set time window; and comparing the difference values with different setting values respectively, and judging the specific fault type of the power transmission line.
5. A terminal device comprising a processor and a memory, the processor being arranged to implement instructions; the memory is used for storing a plurality of instructions, wherein the instructions are suitable for being loaded by the processor and executing the flexible direct current power grid transmission line protection and lightning stroke identification method according to any one of claims 1-3.
6. A computer readable storage medium having stored thereon a plurality of instructions, wherein the instructions are adapted to be loaded by a processor of a terminal device and to perform the flexible direct current grid power transmission line protection and lightning stroke identification method according to any one of claims 1 to 3.
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