CN108551160B - Method and system for judging fault section of multi-terminal direct-current power transmission system based on polar wave energy - Google Patents
Method and system for judging fault section of multi-terminal direct-current power transmission system based on polar wave energy Download PDFInfo
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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
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- 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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a method for judging a fault section of a multi-terminal direct current transmission system based on polar wave energy, which comprises the following steps: recording the fault starting time, collecting the electrical quantity in a time section before and after the fault starting time, and calculating the line-mode components of the voltage and the current at the protective installation position by using the electrical quantity; calculating polar wave values of each sampling point in a time section at a protection installation position at a specified moment according to the linear-mode components of the voltage and the current; extracting the polar wave wavelet coefficient of each sampling point in the time section on any layer, and calculating the energy of the polar wave wavelet coefficient; acquiring a maximum value of the wavelet coefficient energy of the polar wave at a protection installation position in a time section, taking the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point; and judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, judging that the fault section is an intra-area fault.
Description
Technical Field
The invention relates to the technical field of power system protection, in particular to a method and a system for judging a fault section of a multi-terminal direct-current power transmission system based on polar wave energy.
Background
In a multi-terminal direct-current power grid, as the damping value of a direct-current line is very small and each converter station is directly interconnected with the direct-current line, once any position in a direct-current field fails, all the direct-current lines can rapidly overflow. Therefore, the fast and reliable actions of the dc grid protection are the inevitable requirements for the development of the dc grid. At present, traveling wave protection is widely applied in the existing high-voltage direct-current power transmission system, but the inherent defects of high sampling rate requirement, weak transition resistance tolerance and the like exist; the overcurrent protection has poor capability of resisting transition resistance and requires the ultra-fast action of a direct current breaker; distance protection requires time delay to meet protection selectivity, and cannot meet the requirement of fast action to protect a direct current line. In the prior art 0, in engineering practice, a converter station direct current outlet is often connected with a filter and a series direct current reactor in parallel to play roles of filtering and limiting current. For a direct current line, the primary devices form a natural boundary, so that the internal and external fault identification can be carried out through harmonic current of a specific frequency band by utilizing the inherent boundary such as a direct current system filter, a parallel large capacitor and the like. However, in the method, the pulse number in the power frequency period is used as a criterion, the action time is at least 20ms (power frequency 50Hz), and the requirement of the flexible direct current system on the action speed of protection cannot be met. The differential protection method formed by capacitance parameter identification overcomes the influence of line distributed capacitance on the traditional differential protection, however, in a multi-end flexible direct current system, the capacitance parameter cannot be accurately identified even in the case of an intra-area fault due to the existence of the capacitance of each end converter station, and the method cannot be applied any more. The method utilizes 3 electrical quantities of current, voltage wavelet coefficient and voltage differential to carry out multi-parameter judgment, improves the reliability of protection, but no obvious boundary exists between the tail end in a protection area and the head end of an adjacent line, and the reliability of protection action needs to be improved. In view of the current situation, it is necessary to provide a novel single-ended protection method suitable for a multi-ended dc power transmission system.
Therefore, a technology is needed to realize the technology for determining the fault section of the multi-terminal direct current transmission system based on the polar wave energy.
Disclosure of Invention
The invention provides a method for judging a fault section of a multi-terminal direct-current power transmission system based on polar wave energy, which aims to solve the problem of how to judge the fault section of the multi-terminal direct-current power transmission system based on polar wave energy.
In order to solve the above problem, the present invention provides a method for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy, the method comprising:
recording fault starting time, collecting electrical quantities in time sections before and after the fault starting time, and calculating line-mode components of voltage and current at a protective installation position by using the electrical quantities;
calculating polar wave values of all sampling points in the time section at the protection installation position at a specified moment according to the line-mode components of the voltage and the current;
extracting a polar wave wavelet coefficient of each sampling point in the time section on any layer, and calculating the energy of the polar wave wavelet coefficient according to the polar wave wavelet coefficient;
acquiring a maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in the time section, taking the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the at least one sampling point;
and judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, judging that the fault section is an intra-area fault.
Preferably, the electrical quantity comprises: positive dc voltage UpNegative electrode DC voltage UnPositive electrode direct current IpNegative electrode direct current In。
Preferably, said calculating with said electrical quantity a voltage U at the protective installation1And current I1Comprises:
preferably, the calculating polar wave values of the protection installation at specified time instants of the sampling points in the time section includes:
the polar wave value of each sampling point at the protective installation position at the time K is shown as the following formula.
P(K)＝I1(K)*Zc1-U1(K) (3)。
Preferably, the extracting polar wavelet coefficients of each sampling point in the time section at any layer includes:
and extracting the polar wave wavelet coefficients of each sampling point in the time section at any layer by using discrete wavelet transform.
Preferably, taking at least one sample backward by using the maximum value of the wavelet coefficient energy of the polar wave as a reference sample point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sample point and the wavelet coefficient energy of the at least one sample point, comprises:
and backward taking two sampling points, and calculating the polar wave wavelet coefficient energy sum of the reference sampling point and the two sampling points.
Preferably, the time sections before and after the fault starting time are as follows: and 1 second before the fault starting time to 2 seconds after the fault starting time.
According to another aspect of the present invention, there is provided a system for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy, the system including:
the first calculation unit is used for recording the fault starting time, collecting the electrical quantity in a time section before and after the fault starting time, and calculating the line-mode component of the voltage and the current at the protective installation position by using the electrical quantity;
the second calculation unit is used for calculating polar wave values of all sampling points in the time section at the protection installation position at a specified moment according to the line-mode components of the voltage and the current;
the third calculation unit is used for extracting a polar wave wavelet coefficient of each sampling point in the time section on any layer and calculating the energy of the polar wave wavelet coefficient according to the polar wave wavelet coefficient;
the fourth calculation unit is used for acquiring the maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in the time section, using the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point;
and the judging unit is used for judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, the fault section is judged to be an intra-area fault.
Preferably, the electrical quantity comprises: positive dc voltage UpNegative electrode DC voltage UnPositive electrode direct current IpNegative electrode direct current In。
Preferably, the first calculation unit is configured to: calculating electricity for protecting installation site by using the electric quantityPress U1And current I1Comprises:
preferably, the second computing unit is configured to: calculating the polar wave value of each sampling point in the time section at the protection installation at a specified moment, wherein the calculation comprises the following steps:
the polar wave value of each sampling point at the protective installation position at the time K is shown as the following formula.
P(K)＝I1(K)*Zc1-U1(K) (3)。
Preferably, the third computing unit is configured to: extracting the polar wave wavelet coefficients of each sampling point in the time section in any layer, wherein the extracting comprises the following steps:
and extracting the polar wave wavelet coefficients of each sampling point in the time section at any layer by using discrete wavelet transform.
Preferably, the fourth calculation unit is configured to: utilizing the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the at least one sampling point, wherein the method comprises the following steps:
and backward taking two sampling points, and calculating the polar wave wavelet coefficient energy sum of the reference sampling point and the two sampling points.
Preferably, the time sections before and after the fault starting time are as follows: and 1 second before the fault starting time to 2 seconds after the fault starting time.
The technical scheme of the invention provides a method and a system for judging a fault section of a multi-terminal direct-current power transmission system based on polar wave energy, wherein the method comprises the following steps: recording the fault starting time t, and acquiring the time t before the fault starting time0After t1And utilizing the electrical quantity in the time section ofCalculating line mode components of voltage and current at the protection installation; calculating polar wave values of each sampling point in a time section at a protection installation position at a specified moment according to the linear-mode components of the voltage and the current; extracting the polar wave wavelet coefficient of each sampling point in the time section on any layer, and calculating the energy of the polar wave wavelet coefficient; the method comprises the steps of obtaining the maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in a time section, utilizing the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backwards taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point. According to the method, the energy sum of the wavelet coefficients of the polar waves is judged, and if the energy sum of the wavelet coefficients of the polar waves is larger than a preset setting value, a fault section is judged to be an intra-area fault. The technical scheme of the invention provides a single-terminal quantity protection scheme for identifying a fault section by using polar wave transient energy, aiming at the problems that the fault identification in a multi-terminal flexible direct-current power grid is difficult and the existing protection scheme is not sufficient when being directly applied to the multi-terminal flexible direct-current power distribution grid, so that the fault can be quickly and reliably identified. The technical scheme of the invention can realize the rapid identification of the fault within a few ms, and the protection action speed is high. Meanwhile, the technical scheme of the invention only adopts the local electric quantity to judge and identify the fault without communicating with other convertor stations, thereby saving the cost. Finally, the method also has strong anti-transition resistance capability and strong protection applicability.
Drawings
A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
fig. 1 is a flowchart of a method for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of a multi-terminal DC grid topology according to a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of a traveling wave propagation process under normal conditions in accordance with a preferred embodiment of the present invention;
FIG. 4 is a schematic diagram of a traveling wave propagation process in the event of a fault according to a preferred embodiment of the present invention; and
fig. 5 is a structural diagram of a system for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy according to a preferred embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Fig. 1 is a flowchart of a method for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy according to a preferred embodiment of the present invention. The embodiment of the invention discloses a rapid single-end quantity protection method suitable for a multi-end direct-current power transmission system. The embodiment of the invention provides a method for judging a fault section of a multi-terminal direct-current power transmission system based on polar wave energy, which comprises the following steps: recording a fault starting time t, collecting electric quantities in time sections including the time section t0 before and the time section t1 after the fault starting time, and calculating line-mode components of voltage and current at a protective installation position by using the electric quantities; calculating polar wave values of each sampling point in a time section at a protection installation position at a specified moment according to the linear-mode components of the voltage and the current; extracting the polar wave wavelet coefficient of each sampling point in the time section on any layer, and calculating the energy of the polar wave wavelet coefficient; the method comprises the steps of obtaining the maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in a time section, utilizing the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backwards taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point. According to the method, the energy sum of the wavelet coefficients of the polar waves is judged, and if the energy sum of the wavelet coefficients of the polar waves is larger than a preset setting value, a fault section is judged to be an intra-area fault. As shown in fig. 1, a method for determining a fault section of a multi-terminal direct current transmission system based on polar wave energy includes:
preferably, in step 101: and recording the fault starting time, collecting the electrical quantity in a time section before and after the fault starting time, and calculating the line-mode components of the voltage and the current at the protective installation position by using the electrical quantity. Preferably, the electrical quantity comprises: positive dc voltage UpNegative electrode DC voltage UnPositive electrode direct current IpNegative electrode direct current In. Preferably, the time sections before and after the fault starting time are as follows: 1 second before the fault starting time to 2 seconds after the fault starting time. If the starting time of the fault is recorded as t, let t0＝t-1ms，t1T +2 ms. The time section is t0To t1。
Preferably, the voltage U at the protective installation is calculated using the electrical quantity1And current I1Comprises:
preferably, at step 102: and calculating the polar wave value of each sampling point in the time section at the protection installation position at the specified moment according to the line-mode components of the voltage and the current. Preferably, the step of calculating the polar wave value of each sampling point in the time section at the protection installation at the specified moment comprises the following steps:
the polar wave value of each sampling point at the protective installation position at the time K is shown as the following formula.
P(K)＝I1(K)*Zc1-U1(K) (3)。
Preferably, in step 103: and extracting the polar wave wavelet coefficient of each sampling point in the time section on any layer, and calculating the energy of the polar wave wavelet coefficient according to the polar wave wavelet coefficient. Preferably, extracting the polar wavelet coefficients of each sampling point in the time section at any layer comprises: and extracting the polar wave wavelet coefficients of each sampling point in the time section at any layer by using discrete wavelet transform. The application utilizes discrete wavelet transform to extract t0To t1Polar wave wavelet coefficient d of j-th layer of each sampling point in time periodj(K) And calculating the energy of the wavelet coefficient of the polar wave as shown in the formula (4), wherein the energy represents the high-frequency component of the energy of the polar wave.
Ej(K)＝|dj(K)|2 (4)
Preferably, at step 104: the method comprises the steps of obtaining the maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in a time section, using the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backwards taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point. Preferably, taking at least one sample backward by using the maximum value of the wavelet coefficient energy of the polar wave as a reference sample point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sample point and the wavelet coefficient energy of the at least one sample point, comprising: and backward taking two sampling points, and calculating the energy sum of the polar wave wavelet coefficients of the reference sampling point and the two sampling points. (4) Go through to obtain t0To t1The maximum value of the polar wave energy at the protective installation position in the time period is recorded as K at the sampling pointmax. And taking the sampling point corresponding to the maximum value of the polar wave energy as a reference, then backwards taking two sampling points, and calculating the sum of the three sampled polar wave energies. As shown in formula (5).
E＝|Ej(Kmax)|+|Ej(Kmax+1)|+|Ej(Kmax+2)| (5)
Preferably, at step 105: and judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, judging that the fault section is an intra-area fault. According to the method, as shown in formula (6), if the sum of the polar wave energy is greater than a setting value, an intra-area fault is judged, and otherwise, an extra-area fault is judged.
E＞Eset (6)
In the above formula, EsetThe method is a setting value of a high-frequency transient energy criterion, and the setting value setting principle is to avoid the most serious fault outside a zone and ensure the reliable action under the condition of weak fault inside the zone.
After the direct current power grid fails, the fault overcurrent can quickly relate to the whole system, so that the safe and reliable operation of the power grid is influenced. Therefore, the relay protection of the multi-terminal direct current transmission system should be able to operate quickly and reliably after a fault occurs.
According to the rapid single-end-quantity protection method suitable for the multi-end direct-current power transmission system, the polar wave transient energy is used as a protection criterion to identify faults, and therefore rapid and reliable protection actions are achieved. Since the polar wave is essentially a backward traveling wave, it can be represented by equation (1).
p＝I1*Zc1-U1 (1)
In the formula (1), Zc1Representing the line mode wave impedance of the direct current line; i isl、UlAre the dc line current and voltage line mode components.
Fig. 2 is a schematic diagram of a multi-terminal dc grid topology according to a preferred embodiment of the present invention. As an example of a multi-terminal dc transmission system as shown in fig. 2, the main types of dc faults are ac side faults, converter station outlet faults and adjacent dc line faults. Wherein a smoothing reactor arranged at the outlet of the converter is used as a high-frequency energy boundary of the protection scheme provided by the patent. Fig. 3 is a schematic diagram of a traveling wave propagation process under normal conditions according to a preferred embodiment of the present invention. As shown in fig. 3, under normal operation, the backward traveling wave measured at the protection M is mainly a reflected wave formed by the forward traveling wave emitted by the power supply being reflected by the end of the line, and the reflected wave has a small amplitude due to attenuation by the line, and when the line is very long with uniform loss, the reflected wave tends to zero near the beginning of the line. Therefore, the measured pole wave amplitude at the guard M under normal operation can be considered to be a small value close to zero.
Fig. 4 is a schematic view of a traveling wave propagation process in case of a fault according to a preferred embodiment of the present invention. When a fault occurs in the protection zone, the fault source will send out fault traveling waves to both ends, as shown in fig. 4. For protection M, fault traveling waves emitted by a fault point are reverse traveling waves, and the action effect of the fault traveling waves is far greater than that of the reverse traveling waves under the normal operation condition. Therefore, the fault section can be positioned in the direct current system by detecting and calculating the polar wave amplitude of the protection installation position. When the back side of the protection M has a fault, the fault traveling wave sent by the fault point is a forward traveling wave for the protection M, the reverse traveling wave measured by the protection M is a reflected wave from the fault traveling wave to the opposite end, and the amplitude of the reflected wave is small due to attenuation of the line and reflection of the tail end. Therefore, the measured pole wave amplitude at protection M is small at backside failure.
According to the principle, the method for protecting the single-end energy of the multi-end direct-current transmission system based on the polar wave energy comprises the following specific steps:
(1) recording the starting time of the fault as t, and making t0＝t-1ms，t1T +2 ms. Acquisition of t0To t1Positive DC voltage Up and negative DC voltage U at timenAnd a positive electrode direct current Ip and a negative electrode direct current In. The line mode components of the voltage and the current at the protective installation position are calculated according to the electric quantity and are shown in the formulas (2) and (3).
(2) Calculating t from the line mode components of the voltage and current0To t1And protecting the polar wave value at the installation position at the moment K of each sampling point in the time period as shown in the following formula.
P(K)＝I1(K)*Zc1-U1(K) (4)
(3) By usingDiscrete wavelet transform extraction t0To t1Polar wave wavelet coefficient d of j-th layer of each sampling point in time periodj(K) And calculating the energy of the wavelet coefficient of the polar wave as shown in the formula (5), wherein the energy represents the high-frequency component of the energy of the polar wave.
Ej(K)＝|dj(K)|2 (5)
(4) Go through to obtain t0To t1The maximum value of the polar wave energy at the protective installation position in the time period is recorded as K at the sampling pointmax. And taking the sampling point corresponding to the maximum value of the polar wave energy as a reference, then backwards taking two sampling points, and calculating the sum of the three sampled polar wave energies. As shown in equation (6).
E＝|Ej(Kmax)|+|Ej(Kmax+1)|+|Ej(Kmax+2)| (6)
(5) If the sum of the polar wave energies is greater than the setting value, the fault is judged to be an internal fault, otherwise, the fault is judged to be an external fault.
E＞Eset (7)
In the above formula, EsetThe method is a setting value of a high-frequency transient energy criterion, and the setting value setting principle is to avoid the most serious fault outside a zone and ensure the reliable action under the condition of weak fault inside the zone.
Fig. 5 is a structural diagram of a system for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy according to a preferred embodiment of the present invention. As shown in fig. 5, a system for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy includes:
the first calculating unit 501 is configured to record a fault starting time, collect electrical quantities in a time segment before and after the fault starting time, and calculate line-mode components of voltage and current at a protection installation by using the electrical quantities. Preferably, the electrical quantity comprises: positive dc voltage UpNegative electrode DC voltage UnPositive electrode direct current IpNegative electrode direct current In。
Preferably, the first calculation unit 501 is configured to: calculating the voltage U at the protective installation by means of an electrical quantity1And current I1OfA modulus component comprising:
preferably, the time sections before and after the fault starting time are as follows: 1 second before the fault starting time to 2 seconds after the fault starting time. Preferably, the time sections before and after the fault starting time are as follows: 1 second before the fault starting time to 2 seconds after the fault starting time. If the starting time of the fault is recorded as t, let t0＝t-1ms，t1T +2 ms. The time section is t0To t1。
And the second calculating unit 502 is used for calculating the polar wave value of each sampling point in the time section at the protection installation position at the specified moment according to the line-mode components of the voltage and the current. Preferably, the second calculation unit 502 is configured to: the polar wave value of each sampling point in the time section at the protection installation position at the appointed moment is calculated, and the method comprises the following steps:
the polar wave value of each sampling point at the protective installation position at the time K is shown as the following formula.
P(K)＝I1(K)*Zc1-U1(K) (3)。
And a third calculating unit 503, configured to extract a polar wavelet coefficient of each sampling point in the time segment at any layer, and calculate energy of the polar wavelet coefficient according to the polar wavelet coefficient. Preferably, the third calculation unit 503 is configured to: the method for extracting the polar wave wavelet coefficients of each sampling point in the time section in any layer comprises the following steps: and extracting the polar wave wavelet coefficients of each sampling point in the time section at any layer by using discrete wavelet transform. The application utilizes discrete wavelet transform to extract t0To t1Polar wave wavelet coefficient d of j-th layer of each sampling point in time periodj(K) And calculating the energy of the wavelet coefficient of the polar wave as shown in the formula (4), wherein the energy represents the high-frequency component of the energy of the polar wave.
Ej(K)＝|dj(K)|2 (4)
The fourth calculating unit 504 is configured to obtain a maximum value of wavelet coefficient energy of a polar wave at a protection installation location in a time zone, use the maximum value of wavelet coefficient energy of the polar wave as a reference sampling point, backward fetch at least one sampling point, and calculate a sum of wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point. Preferably, the fourth calculating unit 504 is configured to: the method comprises the following steps of utilizing the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backwards taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point, wherein the sum comprises the following steps: and backward taking two sampling points, and calculating the energy sum of the polar wave wavelet coefficients of the reference sampling point and the two sampling points. The application obtains t through traversal of formula (4)0To t1The maximum value of the polar wave energy at the protective installation position in the time period is recorded as K at the sampling pointmax. And taking the sampling point corresponding to the maximum value of the polar wave energy as a reference, then backwards taking two sampling points, and calculating the sum of the three sampled polar wave energies. As shown in formula (5).
E＝|Ej(Kmax)|+|Ej(Kmax+1)|+|Ej(Kmax+2)| (5)
And the judging unit is used for judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, judging the fault section as an intra-area fault.
The system 500 for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy in the preferred embodiment of the present invention corresponds to the method 100 for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy in the preferred embodiment of the present invention, and will not be described herein again.
The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
Claims (10)
1. A method for determining a fault section of a multi-terminal direct current transmission system based on polar wave energy, the method comprising:
recording fault starting time, collecting electrical quantities in time sections before and after the fault starting time, and calculating line-mode components of voltage and current at a protective installation position by using the electrical quantities;
calculating polar wave values of each sampling point in the time section at the protection installation at a specified moment according to the line-mode components of the voltage and the current, and the method comprises the following steps:
protecting the polar wave value of the installation position at the K moment of each sampling point:
P(K)＝I1(K)*Zc1-U1(K) (ii) a K is K time, and P (K) is a polar wave value at the K time; i is1(K) The direct current line current at the moment K; zC1Is the direct current line mode wave impedance; u shape1(K) Is the voltage line modulus component at time K;
extracting the polar wave wavelet coefficient of each sampling point in the time section in any layer, and calculating the energy of the polar wave wavelet coefficient according to the polar wave wavelet coefficient, wherein the method comprises the following steps:
extracting a polar wave wavelet coefficient of each sampling point in any layer in the time section by utilizing discrete wavelet transform;
extracting t using discrete wavelet transform0To t1Polar wave wavelet coefficient d of j-th layer of each sampling point in time periodj(K) And calculating the energy of the wavelet coefficient of the polar wave: ej(K)＝|dj(K)|2；
Acquiring a maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in the time section, taking the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the at least one sampling point;
and judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, judging that the fault section is an intra-area fault.
2. The method of claim 1, the electrical quantity comprising: positive dc voltage UpNegative electrode DC voltage UnPositive electrode direct current IpNegative electrode direct current In。
3. The method of claim 2, said calculating a voltage U at a protective installation using said electrical quantity1And current I1Comprises:
4. the method of claim 1, using the maximum value of the wavelet coefficient energy as a reference sample point, backward taking at least one sample point, and calculating the sum of the wavelet coefficient energies of the reference sample point and the at least one sample point, comprising:
and backward taking two sampling points, and calculating the polar wave wavelet coefficient energy sum of the reference sampling point and the two sampling points.
5. The method of claim 1, wherein the time segments before and after the fault start time are: and 1 second before the fault starting time to 2 seconds after the fault starting time.
6. A system for determining a fault section of a multi-terminal dc power transmission system based on polar wave energy, the system comprising:
the first calculation unit is used for recording the fault starting time, collecting the electrical quantity in a time section before and after the fault starting time, and calculating the line-mode component of the voltage and the current at the protective installation position by using the electrical quantity;
the second calculating unit is used for calculating polar wave values of each sampling point in the time section at the protection installation position at a specified moment according to the line-mode components of the voltage and the current, and comprises:
protecting the polar wave value of the installation position at the K moment of each sampling point:
P(K)＝I1(K)*Zc1-U1(K) (ii) a K is K time, and P (K) is a polar wave value at the K time; i is1(K) The direct current line current at the moment K; zC1Is the direct current line mode wave impedance; u shape1(K) Is the voltage line modulus component at time K;
the third calculating unit is used for extracting a polar wave wavelet coefficient of each sampling point in the time section in any layer and calculating the energy of the polar wave wavelet coefficient according to the polar wave wavelet coefficient; extracting the polar wave wavelet coefficient of each sampling point in the time section in any layer, wherein the extracting comprises the following steps:
extracting a polar wave wavelet coefficient of each sampling point in any layer in the time section by utilizing discrete wavelet transform;
extracting t using discrete wavelet transform0To t1Polar wave wavelet coefficient d of j-th layer of each sampling point in time periodj(K) And calculating the energy of the wavelet coefficient of the polar wave:
Ej(K)＝|dj(K)|2；
the fourth calculation unit is used for acquiring the maximum value of the wavelet coefficient energy of the polar wave at the protection installation position in the time section, using the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the wavelet coefficient energy of the polar wave of the at least one sampling point;
and the judging unit is used for judging the energy sum of the wavelet coefficients of the polar waves, and if the energy sum of the wavelet coefficients of the polar waves is greater than a preset setting value, the fault section is judged to be an intra-area fault.
7. The system of claim 6, the electrical quantity comprising: positive dc voltage UpNegative electrode DC voltage UnPositive electrode direct current IpNegative electrode direct current In。
8. The system of claim 7, the first computing unit to: calculating the voltage U at the protective installation by means of said electrical quantity1And current I1Comprises:
9. the system of claim 6, the fourth computing unit to: utilizing the maximum value of the wavelet coefficient energy of the polar wave as a reference sampling point, backward taking at least one sampling point, and calculating the sum of the wavelet coefficient energy of the polar wave of the reference sampling point and the at least one sampling point, wherein the method comprises the following steps:
and backward taking two sampling points, and calculating the polar wave wavelet coefficient energy sum of the reference sampling point and the two sampling points.
10. The system of claim 6, wherein the time segments before and after the fault start time are: and 1 second before the fault starting time to 2 seconds after the fault starting time.
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