CN116565813A - Active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance - Google Patents
Active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
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- 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 an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance, which utilizes voltage and current positive sequence fault components on two sides of a line section to calculate line estimated impedance on each side, subtracts the line estimated impedance to obtain novel comprehensive impedance, divides the line impedance to obtain impedance coefficient, and constructs an intra-area short circuit fault protection criterion to identify intra-area short circuit faults; and reconstructing a broken line impedance coefficient, and establishing a broken line fault protection criterion in the area so as to identify broken line faults in the area. The invention can accurately identify the short circuit and disconnection faults inside and outside the circuit area by utilizing the comprehensive impedance and the coefficient thereof, is not influenced by fault types, fault positions, distributed power supply types and distributed power supply permeability, and has stronger transitional resistance.
Description
Technical Field
The invention relates to the technical field of power distribution network line protection, in particular to an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance.
Background
The active power distribution network fully utilizing clean energy has low energy consumption, and along with the access of large-scale distributed power supplies (Distributed Generation, DG), a single-power radiation type network is changed into a multi-terminal power supply system, the fault characteristics are changed, the conventional current protection loses selectivity, and the operation of the power distribution network is disadvantageous. The distribution network is easily affected by various natural disasters, the occurrence of small-probability high-loss events is realized, the occurrence probability of broken line faults except short circuit faults is increased, and the voltage and the current at the power supply and the load side are asymmetric. The characteristics of different DGs when a power distribution network breaks down are different, the improvement of DG permeability brings certain challenges to the fault discrimination of the power distribution network, and more power distribution network protection algorithms are proposed.
Xu Meng, guibin, high epitaxy (positive sequence impedance pilot protection [ J ] of power distribution network with inversion type distributed power supply, power system automation, 2017, 41 (12): 93-99.) provides a new pilot protection principle based on positive sequence component comprehensive impedance. The ratio of the difference between the positive sequence voltage phasors at the two ends of the line and the sum of the positive sequence current phasors at the two ends of the line is used to form the positive sequence component comprehensive impedance. When faults occur in the area and outside the area, the amplitude change of the comprehensive impedance of the positive sequence component is obvious, and accordingly internal faults and external faults on the line can be distinguished.
Liang Yingyu, lu Zhengjie (active distribution network adaptive current differential protection based on compensation coefficient [ J ]. Grid technology, 2022, 46 (6): 2268-2275.) proposes a new type of current differential protection. According to the scheme, the compensation coefficient is constructed by adopting the reconstructed sigmoid function, and the compensation degree can be determined according to the amplitude ratio of the currents at two sides, so that the amplitude and the phase of the measured current can be adjusted in a self-adaptive mode.
Wang Zhiyuan, high-strength army Zhang Jianlei (active distribution network protection considering short-circuit and broken-line faults [ J ]. Automation of power system, 2021, 45 (12): 133-141 ]) based on analyzing characteristic differences of voltage fault components in different fault types of internal and external faults, a new protection method based on voltage fault component comparison is proposed. The method utilizes a voltage fault component calculation formula, a voltage fault component and a current fault component at one end of a measured line to calculate a voltage fault component at the other end of the line, compares the calculated voltage fault component with the measured voltage fault component to obtain a voltage fault component ratio, and then utilizes the voltage fault component ratio to identify internal and external faults of the line.
The invention patent publication No. CN101295874A discloses a pilot protection judging method of a power transmission line based on positive sequence comprehensive impedance of a fault component, and provides a comprehensive impedance calculating method based on the positive sequence fault component, and whether faults exist in a line section or not is judged according to the magnitude relation between a positive sequence fault component comprehensive impedance module value and a fixed value, so that a fault line is detected.
The methods proposed in the above documents have respective disadvantages in that the method of calculating the integrated impedance using three-phase currents is affected by load currents. In order to solve the problem, the invention provides an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance.
Disclosure of Invention
The invention aims to provide an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance so as to solve the problems in the background technology.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance comprises the following steps:
collecting current and voltage of a bus M side of a line MN, starting protection when the current abrupt quantity exceeds a starting threshold value, and calculating to obtain positive sequence fault component current of the M sidePositive sequence fault component voltage->Similarly, collecting current and voltage of the busbar N side of the line MN, and calculating to obtain positive sequence fault component current of the N side>Positive sequence fault component voltage->
Step two, calculating the estimated impedance Z of the line M by using the positive sequence fault component current and voltage on the two sides of the line MN obtained in the step one M ' line estimated impedance Z on N side N ′：
Step three, using the estimated impedance Z of the two sides of the line calculated in the step two M ′、Z N ' the overall impedance Z of the line is constructed:
Z＝Z M ′-Z N ′ (2)
fourth, based on the comprehensive impedance of the circuit obtained in the third step, constructing an impedance coefficient k:
wherein Z is L Representing the line impedance;
step five, establishing a line fault protection criterion aiming at the impedance coefficient k, wherein the line fault protection criterion comprises the following specific contents:
(1) protection criterion of line short-circuit fault:
wherein θ mn Representing current on both sides of the lineThe unit is angle; k (K) set Representing a protection threshold;
(2) auxiliary criterion of line short-circuit fault:
wherein k is θ The phase difference compensation coefficient is the phase difference compensation coefficient of the positive sequence current fault component;
(3) protection criterion of line breakage fault:
wherein k' is a broken line impedance coefficient;
and step six, completing fault detection and judgment work of the power distribution network line containing the distributed power supply according to the line short-circuit fault protection criterion and the broken line fault protection criterion obtained in the step five, and realizing protection of the active power distribution network line.
Preferably, the formulas of the estimated impedance of the line and the integrated impedance of the line described in the second and third steps are derived and defined as follows:
when the line MN fails out of the area, the impedance Z is estimated at two sides of the line M ′＝Z N ′＝Z L Thus the impedance coefficient k=0;
in the occurrence area of the line MN, assuming that alpha is the ratio of the distance between the fault point and the bus on the M side to the length of the line MN, the estimated impedance Z of the line on the M side is respectively calculated by the positive sequence fault component current and voltage on the two sides of the line M, N M ' line estimated impedance Z on N side N ′：
Constructing an impedance coefficient k by utilizing the line comprehensive impedance Z obtained in the step three:
wherein F is the positive sequence current fault component at two sides of the lineAmplitude ratio, θ mn Is->Is a phase difference of (a) and (b).
Preferably, the characteristic analysis of the integrated impedance coefficient k in the fourth step includes the following:
when the line MN has an intra-area short-circuit fault, the impedance coefficient k has the following characteristics:
1) When the downstream inverter interface-containing distributed power source IIDG, the internal impedance Z of IIDG dg Is externally shown as infinity, and the impedance Z of the back side of the N end is equivalent by continuously changing impedance n I.e.
When a short circuit fault occurs in a power distribution network line, the external output current of IIDG is less than or equal to 1.2-2 pu, and the positive sequence current fault component of the power supply sideIs the load side->3 to 12 times of the phase difference theta mn From 0 to 160 °; as the fault point gradually gets away from the system power supply side, the amplitude ratio F gradually decreases;
when the downstream contains an internal short-circuit fault under IIDG, the impedance coefficient k gradually increases along with the increase of the fault position alpha, namely gradually away from the system power supply side;
in the case of short-circuit fault at 5% of the line head end, the amplitude ratio f=12, θ mn Impedance coefficient k has a minimum value of 0.379 when=0°;
2) When short circuit fault occurs in a power distribution network generating area containing a motor type distributed power supply MTDG at the downstream, the MTDG and the synchronous power supply are equivalent to a linear system; MTDG is equivalent to internal impedance Z dg Its size is inversely proportional to MTDG capacity, internal impedance Z dg Much smaller than the load impedance and therefore neglectA slight load impedance, in this case an N-terminal backside impedance Z n ＝Z dg ；
When a short circuit fault occurs in a power distribution network line generation area, fault currents at two ends of the line are respectively provided by a system power supply and MTDG, and the short circuit current provided by the MTDG is 4-6 pu, theta mn Epsilon (0,18 DEG), the amplitude ratio F of the positive sequence current fault components at the two sides is between 0.5 and 2;
when short circuit faults occur in a region under the condition that MTDG is contained in the downstream, different fault positions correspond to certain amplitude ratio regions, as the fault position alpha increases, the amplitude ratio F gradually decreases, the impedance coefficient k decreases firstly and then increases, the k values of the head end and the tail end of the line are larger, and the k value near the middle section of the line is smaller;
for the extreme case that k at the middle section of the line approaches 0 with extremely small probability, the phase difference of the positive sequence current fault components needs to be introduced to compensate for the auxiliary fault detection.
Preferably, according to the line short-circuit fault protection criterion and the auxiliary criterion thereof and the line disconnection fault protection criterion in the fifth step, the specific protection judging method for the line short-circuit fault and the disconnection fault is as follows:
1) If the impedance coefficient K of a line is greater than K set Judging that the short circuit fault exists in the area; otherwise, calculating k' and judging the next step;
2) If k'>1, judging that the line breakage fault exists in the area, otherwise, calculating k again θ Making a next judgment;
3) If k is θ >And 1, judging that the short circuit fault exists in the area, and otherwise, judging that the operation is normal.
Compared with the prior art, the invention provides an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance, which has the following beneficial effects:
the invention provides a novel protection method based on novel positive sequence fault component comprehensive impedance, which utilizes voltage and current positive sequence fault components at two ends of a line to calculate line impedance at each side, obtains novel comprehensive impedance by subtraction, compares the obtained novel comprehensive impedance with the line impedance to obtain the comprehensive impedance coefficient of the line impedance, and utilizes the impedance coefficient to identify short circuit faults in a region, broken line faults in a region and faults outside the region, so that protection work of a power distribution network line can be completed.
Drawings
FIG. 1 is a flow chart of an active distribution network pilot protection method based on positive sequence fault component comprehensive impedance;
fig. 2 is a schematic diagram of a fault additional network of the DG-containing power distribution network according to the present invention;
FIG. 3 is a schematic diagram of a fault-added network of the present invention with a short-circuit fault in the downstream IIDG-containing zone;
FIG. 4 is a schematic diagram of a fault-added network of the present invention with a short-circuit fault in the downstream MTDG-containing zone;
FIG. 5 is a graph showing the variation of the impedance coefficient k and the fault location α of the downstream IIDG-containing system according to the present invention;
FIG. 6 is a graph showing the variation of the impedance coefficient k and the fault location α of the MTDG downstream in the present invention;
fig. 7 is a schematic diagram of a fault additional network for an out-of-line disconnection fault in embodiment 1 of the present invention;
fig. 8 is a schematic diagram of a fault additional network for a broken line fault in a line area in embodiment 1 of the present invention;
fig. 9 is a diagram of an active power distribution network according to embodiment 1 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.
Referring to fig. 1, an active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance includes the steps:
collecting current and voltage of a bus M side of a line MN, starting protection when the current abrupt quantity exceeds a threshold value, and calculating to obtain positive sequence fault component current of the M sidePositive sequence fault component voltage->Similarly, collecting current and voltage of the busbar N side of the line MN, and calculating to obtain positive sequence fault component current of the N side>Positive sequence fault component voltage->A schematic diagram of a fault additional network of the distribution network containing DGs is shown in fig. 2;
step two, calculating the estimated impedance Z of the line M by using the positive sequence fault component current and voltage on the two sides of the line MN obtained in the step one M ' line estimated impedance Z on N side N ′：
Step three, using the estimated impedance Z of the two sides of the line calculated in the step two M ′、Z N ' the overall impedance Z of the line is constructed:
Z＝Z M ′-Z N ′ (2)
the formula of the estimated impedance of the circuit and the comprehensive impedance of the circuit is deduced and defined as follows:
when the line MN fails out of the area, the impedance Z is estimated at two sides of the line M ′＝Z N ′＝Z L Thus the impedance coefficient k=0;
in the occurrence area of the line MN, alpha is the ratio of the distance between the fault point and the bus on the M side to the length of the line MN, and the estimated impedance Z of the line on the M side is respectively calculated by the positive sequence fault component current and voltage on the two sides of the line M, N M ' line estimated impedance Z on N side N ′：
Constructing an impedance coefficient k by utilizing the line comprehensive impedance Z obtained in the step three:
wherein F is the positive sequence current fault component at two sides of the lineAmplitude ratio, θ mn Is->Is a phase difference of (2);
fourth, based on the comprehensive impedance of the circuit obtained in the third step, constructing an impedance coefficient k:
wherein Z is L Representing the line impedance;
the characteristic analysis of the integrated impedance coefficient k includes the following:
when the line MN has an intra-area short-circuit fault, the impedance coefficient k has the following characteristics:
1) When the downstream inverter interface-containing distributed power source IIDG, the internal impedance Z of IIDG dg Is externally shown as infinity, and the impedance Z of the back side of the N end is equivalent by continuously changing impedance n I.e.A schematic diagram of a fault additional network of the short-circuit fault in the downstream IIDG-containing generation area is shown in fig. 3;
when a short circuit fault occurs in a power distribution network line, the external output current of IIDG is less than or equal to 1.2-2 pu, and the positive sequence current fault component of the power supply sideIs the load side->3 to 12 times of the phase difference theta mn From 0 to 160 °; as the fault point gradually gets away from the system power supply side, the amplitude ratio F gradually decreases;
when the downstream contains IIDG and internal short circuit fault occurs, as the fault position alpha increases, namely, the impedance coefficient k gradually increases along with the increase of the fault position alpha, namely, the fault position alpha gradually gets away from the system power supply side, and a change curve graph of the impedance coefficient k and the fault position alpha under the downstream contains IIDG is shown in fig. 5;
in the case of short-circuit fault at 5% of the line head end, the amplitude ratio f=12, θ mn Impedance coefficient k has a minimum value of 0.379 when=0°;
2) When short circuit fault occurs in a power distribution network generating area containing a motor type distributed power supply MTDG at the downstream, the MTDG and the synchronous power supply are equivalent to a linear system; MTDG is equivalent to internal impedance Z dg Its size is inversely proportional to MTDG capacity, internal impedance Z dg Much smaller than the load impedance and therefore neglecting the load impedance, in this case the N-terminal backside impedance Z n ＝Z dg A schematic diagram of a fault additional network including a short-circuit fault in an MTDG generating region at the downstream is shown in fig. 4;
when a short circuit fault occurs in a power distribution network line generation area, fault currents at two ends of the line are respectively provided by a system power supply and MTDG, and the short circuit current provided by the MTDG is 4-6 pu, theta mn Epsilon (0,18 DEG), the amplitude ratio F of the positive sequence current fault components at the two sides is between 0.5 and 2;
when short-circuit faults occur in a region under the condition that MTDG is contained in the downstream, different fault positions correspond to certain amplitude ratio intervals, as the fault position alpha increases, the amplitude ratio F gradually decreases, the impedance coefficient k decreases firstly and then increases, the k value of the head end and the tail end of the line is larger, the k value near the middle section of the line is smaller, and a change curve graph of the impedance coefficient k and the fault position alpha under the condition that MTDG is contained in the downstream is shown in figure 6;
for the extreme case that k at the middle section of the line approaches 0 with extremely small probability, the phase difference of the positive sequence current fault components needs to be introduced to compensate for auxiliary fault detection;
step five, establishing a line fault protection criterion aiming at the impedance coefficient k, wherein the line fault protection criterion comprises the following specific contents:
(1) protection criterion of line short-circuit fault:
wherein θ mn Representing current on both sides of the lineThe unit is angle; k (K) set Representing a protection threshold;
(2) auxiliary criterion of line short-circuit fault:
wherein k is θ The phase difference compensation coefficient is the phase difference compensation coefficient of the positive sequence current fault component;
(3) protection criterion of line breakage fault:
wherein k' is a broken line impedance coefficient;
the schematic diagram of the additional network for the line break fault outside the line area is shown in fig. 7, and the schematic diagram of the additional network for the line break fault inside the line area is shown in fig. 8;
according to the circuit short-circuit fault protection criterion, the auxiliary criterion and the circuit disconnection fault protection criterion in the fifth step, the specific protection judging method of the circuit short-circuit fault and the disconnection fault is as follows:
1) If the impedance coefficient K is greater than K set Judging that the short circuit fault exists in the area; otherwise, calculating k' and judging the next step;
2) If k'>1, judging that the line breakage fault exists in the area, otherwise, calculating k again θ Making a next judgment;
3) If k is θ >1, judging that the short circuit fault exists in the area, otherwise, judging that the operation is normal;
and step six, completing fault detection and judgment work of the power distribution network line containing the distributed power supply according to the line short-circuit fault protection criterion and the broken line fault protection criterion obtained in the step five, and realizing protection of the active power distribution network line.
Based on the above operations, specific examples are as follows:
example 1:
to verify the effectiveness of the protection herein, a 10kV active distribution network model as shown in fig. 9 was built using PSCAD/EMTDC simulation software. The reference voltage is 10.5kV, the transformer capacity is 50MVA, the line parameters are (0.17+j0.34) Ω/km, the length is 4km, the IIDG capacity is 2.5MW, the MTDG capacity is 5MW, and the load active power and the load reactive power are 0.8MW and 0.4MVA respectively.
1) Short circuit fault test
As can be seen from Table 1, f 2 When the short circuit fault in the IIDG generation area is connected to the downstream, k minimum is 0.94 when the short circuit fault occurs at the head end of the B1C1 section, the impedance coefficient k increases along with the increase of the position parameter alpha, the k is consistent with theoretical analysis, and k is reliably greater than a threshold value to protect the action.
As can be seen from Table 2, f 3 When the downstream is connected with an MTDG occurrence area internal short circuit fault, the impedance coefficient K is firstly reduced and then increased along with the increase of the position parameter alpha, and K has a very small value of 0.032 when 54% of the sections are in fault, and corresponds to K set = 0.00079, still with K > K set The effectiveness of the protection algorithm is verified.
TABLE 1f 2 Short circuit fault simulation result (IIDG) under 0.01Ω transition resistance
TABLE 2f 3 Short circuit fault simulation result (MTDG) under 0.01 transition resistance
2) Broken line fault test
Different types of disconnection faults are arranged at different positions of B1-C1 and B1-C2 for simulation, and simulation results are shown in tables 3 and 4.
As can be seen from tables 3 and 4, f 2 When the broken line fault occurs, the impedance coefficient k is 0, but the broken line impedance coefficient k' is far greater than 1, so that the broken line fault can be correctly identified, and the effectiveness of the protection algorithm is shown.
TABLE 3f 2 Simulation result of line breakage fault
TABLE 4f 3 Simulation result of line breakage fault
3) DG permeability adaptation test
To test the behavior of the present protection method at different DG permeabilities, line AB 1f 1 Faults were set for different DG permeability at different positions, and simulation results are shown in Table 5. It can be seen that the present protection is still able to act accurately at different DG permeabilities.
TABLE 5f 1 Simulation result of short circuit fault under different DG permeabilities
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4) Transition resistance capability test
At a different position f on the line AB1 1 Setting various short-circuit faults at the position f 1 The simulation results of short-circuit faults under different transition resistances are shown in table 6, and it can be seen that the method is less affected by the transition resistance and can still accurately act under higher transition resistance.
TABLE 6f 1 Simulation result of short circuit fault under different transition resistances
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (4)
1. An active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance comprises the following steps:
collecting current and voltage of a bus M side of a line MN, starting protection when the current abrupt quantity exceeds a starting threshold value, and calculating to obtain positive sequence fault component current of the M sidePositive sequence fault component voltage->Similarly, collecting current and voltage of the busbar N side of the line MN, and calculating to obtain positive sequence fault component current of the N side>Positive sequence fault component voltage->
Step two, calculating the estimated impedance Z of the line M by using the positive sequence fault component current and voltage on the two sides of the line MN obtained in the step one M ' N side line estimated impedance Z N ′：
Step three, using the estimated impedance Z of the two sides of the line calculated in the step two M ′、Z N ' the overall impedance Z of the line is constructed:
Z＝Z M ′-Z N ′ (2)
fourth, based on the comprehensive impedance of the circuit obtained in the third step, constructing an impedance coefficient k:
wherein Z is L Representing the line impedance;
step five, establishing a line fault protection criterion aiming at the impedance coefficient k, wherein the line fault protection criterion comprises the following specific contents:
(1) protection criterion of line short-circuit fault:
wherein θ mn Representing current on both sides of the lineThe unit is angle; k (K) set Representing a protection threshold;
(2) auxiliary criterion of line short-circuit fault:
wherein k is θ The phase difference compensation coefficient is the phase difference compensation coefficient of the positive sequence current fault component;
(3) protection criterion of line breakage fault:
wherein k' is a broken line impedance coefficient;
and step six, completing fault detection and judgment work of the power distribution network line containing the distributed power supply according to the line short-circuit fault protection criterion and the broken line fault protection criterion obtained in the step five, and realizing protection of the active power distribution network line.
2. The active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance according to claim 1, wherein the method comprises the following steps: the formulas of the estimated impedance of the line and the comprehensive impedance of the line are deduced and defined as follows:
when the line MN fails out of the area, the impedance Z is estimated at two sides of the line M ′＝Z N ′＝Z L Thus the impedance coefficient k=0;
in the occurrence area of the line MN, assuming that alpha is the ratio of the distance between the fault point and the bus on the M side to the length of the line MN, the estimated impedance Z of the line on the M side is respectively calculated by the positive sequence fault component current and voltage on the two sides of the line M, N M ' line estimated impedance Z on N side N ′：
Constructing an impedance coefficient k by utilizing the line comprehensive impedance Z obtained in the step three:
wherein F is the positive sequence current fault component at two sides of the lineAmplitude ratio, θ mn Is->Is a phase difference of (a) and (b).
3. The active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance according to claim 1, wherein the method comprises the following steps: the characteristic analysis of the comprehensive impedance coefficient k in the fourth step comprises the following contents:
when the line MN has an intra-area short-circuit fault, the impedance coefficient k has the following characteristics:
1) When the downstream inverter interface-containing distributed power source IIDG, the internal impedance Z of IIDG dg Is externally shown as infinity, and the impedance Z of the back side of the N end is equivalent by continuously changing impedance n I.e.
When a short circuit fault occurs in a power distribution network line, the external output current of IIDG is less than or equal to 1.2-2 pu, and the positive sequence current fault component of the power supply sideIs the load side->3 to 12 times of the phase difference theta mn From 0 to 160 °; as the fault point gradually gets away from the system power supply side, the amplitude ratio F gradually decreases;
when the downstream contains an internal short-circuit fault under IIDG, the impedance coefficient k gradually increases along with the increase of the fault position alpha, namely gradually away from the system power supply side;
in the case of short-circuit fault at 5% of the line head end, the amplitude ratio f=12, θ mn Impedance coefficient k has a minimum value of 0.379 when=0°;
2) When short circuit fault occurs in a power distribution network generating area containing a motor type distributed power supply MTDG at the downstream, the MTDG and the synchronous power supply are equivalent to a linear system; MTDG is equivalent to internal impedance Z dg Its size is inversely proportional to MTDG capacity, internal impedance Z dg Much smaller than the load impedance and therefore neglecting the load impedance, in this case the N-terminal backside impedance Z n ＝Z dg ；
When a short circuit fault occurs in a power distribution network line generation area, fault currents at two ends of the line are respectively provided by a system power supply and MTDG, and the short circuit current provided by the MTDG is 4-6 pu, theta mn Epsilon (0,18 DEG), the amplitude ratio F of the positive sequence current fault components at the two sides is between 0.5 and 2;
when short circuit faults occur in a region under the condition that MTDG is contained in the downstream, different fault positions correspond to a certain amplitude ratio region, and as the fault position alpha increases, the amplitude ratio F gradually decreases, and the impedance coefficient k decreases and then increases;
and for the extreme condition that k at the middle section of the line approaches 0 with extremely small probability, introducing a positive sequence current fault component phase difference to compensate for the phase difference, and performing auxiliary fault detection.
4. The active power distribution network pilot protection method based on positive sequence fault component comprehensive impedance according to claim 1, wherein the method comprises the following steps: according to the circuit short-circuit fault protection criterion, the auxiliary criterion and the circuit disconnection fault protection criterion in the fifth step, the specific protection judging method of the circuit short-circuit fault and the disconnection fault is as follows:
1) If the impedance coefficient K of a line is greater than K set Judging that the short circuit fault exists in the area; otherwise, calculating k' and judging the next step;
2) If k'>1, judging that the line breakage fault exists in the area, otherwise, calculating k again θ Making a next judgment;
3) If k is θ >And 1, judging that the short circuit fault exists in the area, and otherwise, judging that the operation is normal.
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