CN106841916B - Distribution automation system earth fault positioning method based on traveling wave measure and transient zero-mode reactive power direction - Google Patents

Distribution automation system earth fault positioning method based on traveling wave measure and transient zero-mode reactive power direction Download PDF

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CN106841916B
CN106841916B CN201710028169.1A CN201710028169A CN106841916B CN 106841916 B CN106841916 B CN 106841916B CN 201710028169 A CN201710028169 A CN 201710028169A CN 106841916 B CN106841916 B CN 106841916B
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feeder
traveling wave
zero
mode
fault
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CN106841916A (en
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闫光太
李祯
史吏
刘德才
王和先
蔡军
黄国强
闫昊
张庆海
李豹
张斌
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State Grid Corp of China SGCC
Liaocheng Power Supply Co of State Grid Shandong Electric Power Co Ltd
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State Grid Corp of China SGCC
Liaocheng Power Supply Co of State Grid Shandong Electric Power Co Ltd
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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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • 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 relates to a method for positioning a ground fault of a power distribution automation system based on traveling wave measurement and a transient zero-mode reactive power direction, which comprises the following steps: (1) determining a feeder line in which the ground fault is positioned by using a small current line selection method of traveling wave measurement; (2) based on the transient zero-mode reactive power flow direction, positioning a grounding fault point on a fault feeder line: on a feeder line where the ground fault is located, monitoring the flow direction of transient zero-mode reactive power of any two adjacent feeder terminal FTUs, if the product of the flow directions of the transient zero-mode reactive power of some two adjacent feeder terminal FTUs is negative, indicating that the ground fault occurs between the two adjacent feeder terminal FTUs, and if the product of the flow directions of the transient zero-mode reactive power of some two adjacent feeder terminal FTUs is positive, indicating that the ground fault does not occur between the two adjacent feeder terminal FTUs. The invention accurately positions the ground fault, and determines which two feeder terminal FTUs the ground fault is positioned between, and has good sensitivity to high-resistance ground faults.

Description

Distribution automation system earth fault positioning method based on traveling wave measure and transient zero-mode reactive power direction
Technical Field
The invention relates to a power distribution automation system ground fault positioning method based on traveling wave measurement and a transient zero-modulus reactive power direction, and belongs to the technical field of power distribution automation system ground fault positioning.
Background
The fault measure is a positive real number which can represent the similarity degree of the characteristics of the feeder line and the fault feeder line under the reference of a certain criterion. In a plurality of feeders of the power grid with the same voltage class, if the fault measure of a certain feeder is the maximum, the possibility that the feeder is a fault feeder can be shown to be the maximum. The traveling wave measure is a positive real number which can represent the similarity degree of the characteristics of the respective feeder line and the fault feeder line under the zero-mode initial current traveling wave polarity characteristic reference. In a plurality of feeders of the power grid with the same voltage class, if the traveling wave measure of a certain feeder is the largest, the possibility that the feeder is a fault feeder can be shown to be the largest.
Because the neutral point non-effectively grounded power grid has the advantage of high power supply reliability, the power distribution network in China is widely applied to a non-effectively grounded neutral point mode. In recent years, the development of power distribution automation systems is rapid, but the current power distribution automation systems do not have a protection function of integrating single-phase earth fault positioning, and have great limitation on processing of power distribution network cable earthing.
At present, the ground fault line selection method has different principle technologies, and each has practical applicability. The monitoring technology based on the fault power frequency steady-state component is difficult to extract fault steady-state current, and the method cannot be applied to a resonance grounding power grid and has certain limitation. The S signal injection method is accurate in monitoring, but does not have good economical efficiency, and new equipment is additionally arranged. The monitoring technology based on the transient high-frequency component is convenient in signal extraction and has good sensitivity, but the method is easy to interfere and cannot monitor high-resistance ground faults.
Chinese patent document CN103217622A discloses a power distribution network fault line selection method based on multi-terminal voltage traveling waves, and belongs to the technical field of power system relay protection. The method comprises the following steps: installing traveling wave acquisition devices at the tail ends of the transformer substations and the branch of each main feeder line in the power distribution network; utilizing a substation bus coupler switch to generate traveling wave signals, and calculating the time difference between the initial arrival time of the fault traveling wave at the tail end of each branch on the main feeder line and the initial arrival time of the fault traveling wave at the bus of the substation to obtain a reference time array; calculating the time difference between the initial arrival time of the fault traveling wave at the tail end of each branch on the main feeder line and the initial arrival time of the fault traveling wave at the bus of the transformer substation during fault, and establishing a fault time array; and performing least square fitting on the reference time array and the fault time array, realizing information fusion processing of the traveling wave arrival time recorded by each acquisition point, and finding out a fault feeder line. However, the patent does not consider the situations of over-high ground resistance and fault initial phase angle, and the fault simulation is too single to be well applied to the actual situation.
Chinese patent document CN102279346A discloses a fault line selection method for a low-current grounding system, which comprises the following steps: dividing sample data acquired by the protection device into a fault class and a non-fault class according to the spatial distance, and calculating various centers; when zero sequence voltage at the outlet of the feeder line is out of limit, recording sample data to be detected; and calculating the distance between the sample to be detected and the fault center and the non-fault center, and judging whether the feeder line has a fault according to the distance. The patent provides a fault line selection method by using sample data, and the traditional method of comparing fault characteristic quantity with a setting value as a protection criterion is broken by using a space relative distance as a criterion. However, this patent requires a large amount of sample data as a basis, and is limited by the accuracy of the sample data, which is too restrictive.
In summary, the power grid with a non-effectively grounded neutral point is affected by various factors, so that it is very difficult to accurately monitor the ground fault. Therefore, the method for positioning the ground fault by utilizing the traveling wave measurement and the reactive power direction is further researched, and the method has a good application prospect.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for positioning the ground fault of a power distribution automation system based on traveling wave measurement and a transient zero-mode reactive power direction;
summary of The Invention
Aiming at the problem that the accurate monitoring of the grounding fault is very difficult due to the influence of various factors on a neutral point non-effective grounding power grid, the invention creatively combines the initial traveling wave, the fault measurement and the transient zero-modulus reactive power direction, and when a fault feeder is judged, the principle can give the possibility that each feeder is a fault feeder and clearly determines which two Feeder Terminals (FTUs) the grounding fault is positioned between, and the method comprises the following steps: (1) firstly, a small current line selection method utilizing traveling wave measurement indicates the possibility of ground fault of each feeder line, and determines the feeder line where the ground fault is located. (2) Then, on the earth fault feeder, the directions of transient zero-mode reactive power of the front section and the rear section of the fault point are different, and the earth fault interval is determined by comparing the directions of the transient zero-mode reactive power of the two section switches, so that the earth fault feeder has good sensitivity to high-resistance earth faults.
Interpretation of terms:
1. FTU, feeder terminal unit, feeder terminal;
the technical scheme of the invention is as follows:
a power distribution automation system earth fault positioning method based on traveling wave measurement and transient zero-mode reactive power direction includes the following steps:
(1) the possibility of ground fault of each feeder line is indicated by a small current line selection method of traveling wave measure, and the feeder line in which the ground fault is positioned is determined;
(2) based on the transient zero-mode reactive power flow direction, positioning a grounding fault point on a fault feeder line: monitoring the zero-mode reactive power flow direction of any two adjacent feeder terminal FTUs on a feeder line where the ground fault is located: the method comprises the steps that three-phase transient voltage and current are obtained by utilizing PT and zero sequence CT, transient zero-mode reactive power is obtained by utilizing phase-mode transformation, if the product of the flow directions of the zero-mode reactive power of certain two adjacent feeder terminal FTUs is negative, namely the flow directions of the zero-mode reactive power of the two adjacent feeder terminal FTUs are opposite, the fact that the ground fault occurs between the two adjacent feeder terminal FTUs is indicated, and if the product of the flow directions of the zero-mode reactive power of certain two adjacent feeder terminal FTUs is positive, namely the flow directions of the zero-mode reactive power of the two adjacent feeder terminal FTUs are opposite, the fact that the ground fault does not occur between the two adjacent feeder terminal FTUs is indicated.
The method not only can accurately select the feeder line with the fault, but also can position the fault between two feeder line terminals, provides an accurate fault position for operators, and greatly reduces manpower and material resources.
According to the preferable embodiment of the present invention, in the step (1), the distribution automation system has N feeder lines in total, the traveling wave measure of the jth feeder line is S (j), j is greater than or equal to 1 and is less than or equal to N, and the specific steps include:
A. collecting three-phase initial current traveling wave signals for each feeder line of the distribution automation system;
B. converting the three-phase initial current traveling wave signals into zero-mode initial current traveling wave signals through phase-mode conversion;
C. transforming a first wavelet modulus maximum value m (j) in the zero-modulus initial current traveling wave signal of each feeder line by using wavelet transformation;
D. calculating a travelling wave measure S (j) of each feeder line according to formula (I):
Figure BDA0001209226330000031
in the formula (I), the compound is shown in the specification,
sgn (x) is a sign function, and when x >0, sgn (x) is 1; when x is 0, sgn (x) is 0; when x is less than 0, sgn (x) ═ 1;
m (l) is the maximum value of the first wavelet mode in the zero-mode initial current traveling wave signal of the ith feeder line; l is not equal to j;
m (j) is the maximum value of the first wavelet mode in the jth feeder zero-mode initial current traveling wave signal;
m (j) represents the amplitude of the first wavelet transformation modulus maximum of the zero-modulus initial current traveling wave of the j-th feeder line, and M (j) >0, namely M (j) ═ M (j) |;
sum represents the Sum of the amplitudes of the first wavelet transform modulus maxima of all the feeder zero-modulus initial current traveling waves,
Figure BDA0001209226330000032
E. and D, selecting the feeder line corresponding to the maximum value of the traveling wave measure S (j), namely the fault feeder line, according to the traveling wave measure S (j) of each feeder line obtained in the step D.
The derivation of formula (i) is as follows, as shown in fig. 2:
in a distribution automation system, the junction of a bus and a feeder is regarded as a point of discontinuity of wave impedance. The ground fault generates an initial traveling wave, the traveling wave advances to the bus, and the refraction and reflection occur at the connection position of the bus and the feeder line. The propagation process of the initial traveling wave is shown in fig. 1. The refracted wave enters other normal feeder lines through the bus, and the reflected wave advances from the bus to the direction of the fault feeder line.
The initial traveling wave has a very high frequency and the wave impedance of the transformer is proportional to the frequency. The wave impedance of the transformer is large and the initial traveling wave does not substantially pass through the transformer. Therefore, whether the arc suppression coil is grounded at the neutral point of the transformer or not has no influence on the initial traveling wave.
Since the zero-mode component only appears under the grounding or asymmetric operation condition, the zero-mode component is sensitive to the reaction of the grounding fault. Therefore, the invention is only aimed at zero-mode initial current traveling wave analysis.
Assuming equal wave impedance of the feeders of the distribution automation system, i.e. ZL10＝ZL20＝…＝ZLN0Z. Any feeder line has single-phase earth fault, and the earth point generates fault initial travelling wave iF0. Setting wave impedance: incident wave is Z, refracted wave is ZZThe wave impedance of N-1 sound feeder lines is connected in parallel, namely:
Figure BDA0001209226330000041
refract the wave i, which can be derived from the current catadioptric coefficient formula (III)ZZAnd a reflected wave ifAs shown in formula (IV):
Figure BDA0001209226330000042
Figure BDA0001209226330000043
refracted wave i converted to each sound feederZAs shown in formula (V):
Figure BDA0001209226330000044
the wave speed of the traveling wave is close to the light speed, so that the fault feeder line has zero mode initial current traveling wave iNFor superposition of incident wave and reflected wave, the feed line is sound and the initial current traveling wave i is zero modeJRefracted waves only, iJAnd iNThe absolute value of (A) is represented by the formula (VI):
Figure BDA0001209226330000045
the positive direction of the current is defined as: from the bus bar to the feeder. Zero-mode initial current traveling wave i of fault feeder lineNAnd a sound feeder zero-mode initial current traveling wave iJAs shown in formula (VII):
Figure BDA0001209226330000051
at the instant when the current traveling wave passes through the inductor, the inductor is equivalent to an open circuit for the current traveling wave, and the current traveling wave is subjected to negative total reflection. Therefore, for analysis convenience, when the zero-mode initial traveling wave is pushed to the arc suppression coil, the current traveling wave is regarded as not refracted to the arc suppression coil, and the neutral point equivalent wave impedance ZeqTo infinity, formula (VII) is converted to formula (VIII):
Figure BDA0001209226330000052
when a single-phase earth fault occurs in a low-current earth power grid provided with a distribution automation system, the single-phase earth fault can be obtained by the formula (VII):
a. the zero-mode initial current traveling wave polarities of the sound feeder lines are the same;
b. the zero-mode initial current traveling wave amplitude of the fault feeder line is the maximum, and the ratio of the zero-mode initial current traveling wave amplitude to the healthy feeder line is equal to (N-1);
c. the zero-mode initial current traveling wave polarities of the fault feeder line and the healthy feeder line are opposite.
The zero-mode initial current traveling wave of each feeder line is described by means of the wavelet transform modulus maximum, the characteristics of the wavelet modulus maximum of the zero-mode fault initial current traveling wave are not influenced by the change of the running mode of a neutral point, the principle is reliable and clear, and the specific rule is as follows:
for a neutral point non-effective grounding system with N feeders provided with a distribution automation system, a single-phase grounding fault occurs on the feeder side, and the amplitude and polarity characteristics of the wavelet modulus maximum of the zero-modulus initial current traveling wave are as follows:
e. the polarities of the wavelet mode maximum values of the zero-mode initial current traveling waves of the sound feeder line are the same; the polarities of the wavelet mode maximum values of the zero-mode initial current traveling waves of the fault feeder line and the healthy feeder line are opposite.
f. Compared with a healthy feeder line, the amplitude of the wavelet mode maximum value of the zero-mode initial current traveling wave of the fault feeder line is the largest, and the ratio of the amplitude of the wavelet mode maximum value to the amplitude of the healthy feeder line is equal to (N-1). Namely, the wavelet mode maximum value of the fault feeder line is equal to the sum of the amplitudes of the wavelet mode maximum values of other (N-1) healthy feeder lines.
The fault measure is a positive real number which can represent the similarity degree of the characteristics of the feeder line and the fault feeder line under the reference of a certain criterion. In a plurality of feeders of the power grid with the same voltage class, if the fault measure of a certain feeder is the maximum, the possibility that the feeder is a fault feeder can be shown to be the maximum.
And constructing traveling wave measurement by using the amplitude and phase characteristics of the zero-mode current traveling wave.
And (3) assuming that a certain neutral point non-effectively grounded power grid has N feeders, and enabling S (j) to represent the traveling wave measurement of the j-th feeder.
From the conceptual requirements of the fault measures, it can be known that the traveling wave measure S (j) represents the probability of the fault occurring in the jth feeder. Therefore, the range of the traveling wave metric S (j) is limited to [0,1 ].
If the traveling wave metric S (j) of the jth feeder line is 0, it indicates that the probability of the fault occurring in the feeder line is 0%, that is, the feeder line is a sound feeder line.
If the traveling wave measure S (j) of the jth feeder line is 1, it indicates that the probability of the fault occurring in the feeder line is 100%, that is, the feeder line is a faulty feeder line.
And if the traveling wave measure of the jth feeder line is 0< S (j) <1 and is very close to 1, the probability that the fault occurs in the feeder line is very high, namely the probability that the feeder line is a fault feeder line is very high.
If the traveling wave measure of the jth feeder line is 0< S (j) <1 and is very close to 0, the probability that the fault occurs in the feeder line is very low, that is, the feeder line is a sound feeder line is very high.
The definition formula of the traveling wave measure S (j) of the j-th feeder line is formed by combining a first measurement definition formula based on the traveling wave polarity characteristic and a second measurement definition formula based on the traveling wave amplitude characteristic, and the first traveling wave measure definition formula is S1(j) To express, the travelling wave measure defines the formula dual-purpose S2(j) To indicate.
Measurement definition formula one structure based on traveling wave polarity characteristics
According to the relation of the polarity of the maximum value of the zero-mode initial current traveling wave wavelet transform mode of the sound feeder line and the fault feeder line, the polarity of the maximum value of the zero-mode initial current traveling wave wavelet transform mode of the sound feeder line and the fault feeder line is opposite, and the polarity of the maximum value of the zero-mode initial current traveling wave wavelet transform mode of the sound feeder line is the same. Constructing a traveling wave measure definition formula S related to the maximum value of the zero-mode initial current wave mode1(j) Namely:
Figure BDA0001209226330000061
sgn () is a sign function defined as:
Figure BDA0001209226330000062
as can be seen from the definition of the sign function, the sign function sgn [ m (j) × m (l) ] is used to reflect the polarity relationship between two values, and takes a value of 1 or-1. If m (j) × m (l) >0, that is, after comparing the positive and negative of both values, it is found that the polarities of both values are the same, sgn [ m (j) × m (l) ] is 1. If m (j) × m (l) <0, i.e., after comparing the positive and negative of both values, it is found that the polarities of both values are opposite, sgn [ m (j) × m (l) ] is-1. If m (j) × m (l) ═ 0, i.e., one of the two values is 0, sgn [ m (j) × m (l) ] is 0. For wavelet transforms, the case of a modulo maximum of 0 does not exist. Therefore, sgn [ m (j) × m (l) ] cannot take a value of 0.
The wavelet mode maximum m (j) of the initial traveling wave of the zero-mode current of the fault feeder line (j) is opposite to the wavelet mode maximum m (l) of all other feeder lines in polarity (l belongs to [1, N)]And l ≠ j). Thus, for normal feeder analysis, sgn [ m (j) × m (l)]Is equal to- (N-1), so that the result of formula (IX) is S1(j)＝-1。
The wavelet mode maximum m (j) of the initial traveling wave of zero-mode current of the sound feeder line (j) is the same as that of other sound feeder lines, sgn [ m (j) × m (l)]Is greater than- (N-1), so that the result of formula (IX) is S1(j)>-1。
Thus, the measure defines the formula S1(j) The requirement of a general concept of fault measure is met, and results of a fault feeder line and a sound feeder line can be distinguished obviously.
Structure of measure definition formula two based on traveling wave amplitude characteristics
Defining a measure definition formula two S based on the amplitude characteristics of the traveling wave2(j) Is composed of
Figure BDA0001209226330000071
Aiming at sound feeder analysis, the traveling wave measure is defined as two S2(j) In the range of 0<S2(j)<0.5, and S2(j) The value of (a) is small, close to 0. Amplitude coefficient S for faulty feeder2(j) 0.5. The two can be well distinguished.
In summary, the definition formula of the traveling wave measurement S (j) of the j-th feeder line is formed by combining the measurement definition formula one based on the traveling wave polarity characteristic and the measurement definition formula based on the traveling wave amplitude characteristic
Figure BDA0001209226330000072
Namely:
Figure BDA0001209226330000073
for the faulty feeder analysis, S (j) ═ 1. The traveling wave measure S (j) can obviously distinguish the feeder line where the fault is located from the sound feeder line, and meets the following requirements: and the traveling wave measure S (j) of the fault feeder line is 1, and the traveling wave measure S (j) of the sound feeder line is 0.
The line selection is realized by comparing the traveling wave measurement of the fault feeder line and the non-fault feeder line, and if the fault measurement of a certain feeder line is the largest and the difference between the fault measurement of the certain feeder line and the fault measurement of other feeder lines is the largest, the possibility that the feeder line is the fault feeder line is the largest.
Obtaining a line selection result according to the magnitude of the traveling wave measure S (j) of each feeder line, namely: a single-phase earth fault occurs on which particular feeder.
The principle of the step (2) is as follows:
at present, a power distribution automation system does not realize the functions of ground fault monitoring and positioning, but each feeder terminal FTU is provided with a three-phase CT (PT) or a zero-sequence CT (PT), and can obtain zero-mode current or voltage.
The ground fault point generates transient zero-mode current which flows to both sides along a feeder line where the ground is located.
Transient zero mode currents are mainly transient capacitive currents and possibly also transient inductive currents (provided by arc suppression coils in a resonant grounded grid). Theoretical analysis and test results prove that: the oscillation frequency of the transient capacitance current is 300 to 3000Hz, and the transient inductance current at the frequency is very small. Therefore, the arc suppression coil of the resonant grounding power grid has no influence on the monitoring of the transient zero-mode current.
Ground faults occur on the feeder, with four possibilities.
The first possibility is: the sound feeder has no ground fault, and runs symmetrically without zero-mode current. Thus, all feeder terminals FTUs of a robust feeder cannot monitor zero mode current. However, if the whole grid system has an earth fault, even if the healthy feeder line has no earth fault, the healthy feeder line will monitor zero mode current, and the transient state zero mode reactive power direction is from the bus to the line. The transient zero-mode reactive power monitored by the two FTUs has the same direction.
The second possibility is: a ground fault occurs between two section switches, i.e., two FTUs. The transient zero-mode reactive power flow direction is as follows: from the ground fault point, flows along the fault feeder to the bus side and the load side. Thus, the transient zero-mode reactive power flow direction monitored by the two feeder terminals is different, as shown in fig. 4.
The positive direction of the power flow is specified as follows: from the busbar side to the load side. In fig. 4, the transient zero-mode reactive power flow direction monitored by FTU1 of section switch 1 is negative, and is marked as "-1". The transient zero-mode reactive power flow direction monitored by FTU2 of section switch 2 is positive and is noted as "+ 1". The product of the two is negative.
A third possibility: the ground fault occurs on the load side of all the sectionalizers (i.e., the load side of all the FTUs). The transient zero-mode reactive power flow direction is as follows: from the ground fault point, flows along the fault feeder to the bus side and the load side. Thus, the transient zero-mode reactive power flow direction monitored by both feeder terminals is the same, as shown in fig. 5. The positive direction of the power flow is specified as follows: from the busbar side to the load side. In fig. 5, the transient zero-mode reactive power flow direction monitored by FTU1 of section switch 1 is negative, and is marked as "-1". The transient zero-mode reactive power flow direction monitored by the FTU2 of the section switch 2 is negative and is recorded as "-1". The product of the two is positive.
A fourth possibility: ground faults occur on the bus side of all the sectionalizers (i.e., the bus side of all the FTUs). The transient zero-mode reactive power flow direction is as follows: from the ground fault point, flows along the fault feeder to the bus side and the load side. Thus, the transient zero-mode reactive power flow direction monitored by both feeder terminals is the same, as shown in fig. 6. The positive direction of the power flow is specified as follows: from the busbar side to the load side. The transient zero-mode reactive power flow direction monitored by FTU1 of section switch 1 is positive and is noted as "+ 1". The transient zero-mode reactive power flow direction monitored by FTU2 of section switch 2 is positive and is noted as "+ 1". The product of the two is positive.
Combining the above four possible analyses yields: and monitoring the transient zero-mode reactive power flow direction of every two adjacent Feeder Terminal Units (FTUs) on the feeder line where the ground fault is positioned. If the product of the transient zero-mode reactive power flow directions of two adjacent Feeder Terminal Units (FTUs) is negative, the ground fault is indicated to occur between the two adjacent Feeder Terminal Units (FTUs). And if the product of the transient zero-mode reactive power flow directions of two adjacent Feeder Terminal Units (FTUs) is positive, indicating that no ground fault occurs between the two adjacent Feeder Terminal Units (FTUs).
When a high-resistance ground fault occurs, the amplitude of the zero-mode component is changed compared with the metallic ground, and the transient zero-mode reactive power flow direction is not influenced. Therefore, the method is also applicable to high resistance ground faults.
The invention has the beneficial effects that:
on the basis of analyzing the characteristics of the initial traveling wave of the single-phase earth fault in detail, the invention defines the concept of traveling wave measurement by means of the wavelet modulus maximum value of the zero-modulus initial current traveling wave and the comprehensive traveling wave amplitude and polarity characteristics, and provides a fault line selection method based on the traveling wave measurement. The invention analyzes the flow direction of the transient zero-mode reactive power of the ground fault in detail, summarizes and induces the difference of the flow direction of the transient zero-mode reactive power of the feeder line terminal when the ground fault occurs at different positions, and provides the method for positioning the ground fault of the power distribution automation system based on the flow direction of the transient zero-mode reactive power. The method for positioning the ground fault of the power distribution automation system based on the traveling wave measure and the transient zero-mode reactive power direction can accurately position the ground fault, and determine which two feeder line terminals (FTUs) the ground fault is positioned between, and has good sensitivity to the high-resistance ground fault.
Drawings
FIG. 1 is a schematic view of the refraction and reflection of an initial traveling wave at a bus;
FIG. 2 is a schematic diagram of the formula structure of the traveling wave measurement S (j);
FIG. 3 is a schematic diagram of a fault line selection process based on traveling wave measurements;
FIG. 4 is a schematic diagram of transient zero-mode reactive power flow when a ground fault occurs between two sectionalizers;
FIG. 5 is a schematic diagram of transient zero-mode reactive power flow when a ground fault occurs on the load side of all sectionalizers;
FIG. 6 is a schematic diagram of the transient zero mode reactive power flow when a ground fault occurs on the bus side of all sectionalizers;
FIG. 7 is a schematic diagram of an embodiment power distribution automation system;
fig. 8 is a schematic waveform diagram of a zero-mode current traveling wave of six feeder lines according to an embodiment. I is1o、I2o、I3o、I4o、I5o、I6oThe waveforms of the zero-mode current traveling waves of the feeder line 1, the feeder line 2, the feeder line 3, the feeder line 4, the feeder line 5 and the feeder line 6 are respectively;
fig. 9(a) is a schematic diagram of a zero-mode current wave of a fault feeder 1;
fig. 9(b) is a schematic diagram of a wavelet transform coefficient waveform of a fault feeder 1;
fig. 10(a) is a schematic diagram of a zero-mode current wave of the feeder 2;
FIG. 10(b) is a schematic diagram of the waveform of the wavelet transform coefficient of the feeder 2;
fig. 11(a) is a schematic diagram of a zero-mode current wave of the feeder 3;
fig. 11(b) is a schematic diagram of the waveform of the wavelet transform coefficient of the feeder 3.
Detailed Description
The invention is further defined in the following, but not limited to, the figures and examples in the description.
Examples
A power distribution automation system ground fault positioning method based on traveling wave measurement and transient zero-mode reactive power direction utilizes software MATLAB to establish a model for simulation verification, the power distribution automation system is a 110kV/10kV transformer substation and is provided with 6 feeder lines, a neutral point ungrounded system is adopted when K is opened, and a resonant grounded system is adopted when K is closed. As shown in fig. 7, the calculation step size of the simulation software is: 1 μ s, i.e. 1X 10-6And s. The fault conditions are respectively: the initial fault phase angles are simulated under the three conditions of 30 degrees, 60 degrees and 90 degrees respectively. And secondly, simulating the transition resistance by respectively taking three conditions of 10 omega, 100 omega and 500 omega. Thirdly, taking the fault point positionThe distances are 4km, 5km, 6km from the bus, the bus position and the like. The method comprises the following specific steps:
(1) the method for selecting the lines by utilizing the small current of the traveling wave measure indicates the possibility of the ground fault of each feeder line and determines which feeder line the ground fault is positioned in, and the method specifically comprises the following steps:
assuming that a single-phase earth fault with the transition resistance of 10 omega occurs in the system at the position of a feeder line 1 4km away from a bus, and initial fault phase angles are respectively set to be 30 degrees, 60 degrees and 90 degrees. And calculating to obtain a traveling wave measure according to the first wavelet modulus maximum value under the two scales of the zero-modulus initial current traveling wave of each feeder line shown in the table 1, as shown in the table 2.
TABLE 1
Figure BDA0001209226330000101
TABLE 2
Figure BDA0001209226330000102
Figure BDA0001209226330000111
As can be seen from table 2, the traveling wave measurement of the feeder 1 is the largest and is close to 1, and the fault measurements of the other feeders are much smaller, which indicates that a single-phase ground fault occurs in the feeder 1. Therefore, the simulation result verifies the effectiveness of the method.
Fig. 8 is a waveform schematic diagram of six feeder zero-mode current traveling waves.
Fig. 9(a) is a schematic diagram of a zero-mode current wave of a fault feeder 1; fig. 9(b) is a schematic diagram of a wavelet transform coefficient waveform of a fault feeder 1;
fig. 10(a) is a schematic diagram of a zero-mode current wave of the feeder 2; FIG. 10(b) is a schematic diagram of the waveform of the wavelet transform coefficient of the feeder 2;
fig. 11(a) is a schematic diagram of a zero-mode current wave of the feeder 3; fig. 11(b) is a schematic diagram of the waveform of the wavelet transform coefficient of the feeder 3;
in the step (1), as shown in fig. 3, the distribution automation system has N feeder lines, the traveling wave measure of the jth feeder line is S (j), j is greater than or equal to 1 and is less than or equal to N, and the specific steps include:
A. collecting three-phase initial current traveling wave signals for each feeder line of the distribution automation system;
B. converting the three-phase initial current traveling wave signals into zero-mode initial current traveling wave signals through phase-mode conversion;
C. transforming a first wavelet modulus maximum value m (j) in the zero-modulus initial current traveling wave signal of each feeder line by using wavelet transformation;
D. calculating a travelling wave measure S (j) of each feeder line according to formula (I):
Figure BDA0001209226330000112
in the formula (I), the compound is shown in the specification,
sgn (x) is a sign function, and when x >0, sgn (x) is 1; when x is 0, sgn (x) is 0; when x is less than 0, sgn (x) ═ 1;
m (l) is the maximum value of the first wavelet mode in the zero-mode initial current traveling wave signal of the ith feeder line; l is not equal to j;
E. and D, selecting the feeder line corresponding to the maximum value of the traveling wave measure S (j), namely the fault feeder line, according to the traveling wave measure S (j) of each feeder line obtained in the step D.
The derivation of formula (i) is as follows, as shown in fig. 2:
in a distribution automation system, the junction of a bus and a feeder is regarded as a point of discontinuity of wave impedance. The ground fault generates an initial traveling wave, the traveling wave advances to the bus, and the refraction and reflection occur at the connection position of the bus and the feeder line. The propagation process of the initial traveling wave is shown in fig. 1. The refracted wave enters other normal feeder lines through the bus, and the reflected wave advances from the bus to the direction of the fault feeder line.
The initial traveling wave has a very high frequency and the wave impedance of the transformer is proportional to the frequency. The wave impedance of the transformer is large and the initial traveling wave does not substantially pass through the transformer. Therefore, whether the arc suppression coil is grounded at the neutral point of the transformer or not has no influence on the initial traveling wave.
Since the zero-mode component only appears under the grounding or asymmetric operation condition, the zero-mode component is sensitive to the reaction of the grounding fault. Therefore, the invention is only aimed at zero-mode initial current traveling wave analysis.
Assuming equal wave impedance of the feeders of the distribution automation system, i.e. ZL10＝ZL20＝…＝ZLN0Z. Any feeder line has single-phase earth fault, and the earth point generates fault initial travelling wave iF0. Setting wave impedance: incident wave is Z, refracted wave is ZZThe wave impedance of N-1 sound feeder lines is connected in parallel, namely:
Figure BDA0001209226330000121
refract the wave i, which can be derived from the current catadioptric coefficient formula (III)ZZAnd a reflected wave ifAs shown in formula (IV):
Figure BDA0001209226330000122
Figure BDA0001209226330000123
refracted wave i converted to each sound feederZAs shown in formula (V):
Figure BDA0001209226330000124
the wave speed of the traveling wave is close to the light speed, so that the fault feeder line has zero mode initial current traveling wave iNFor superposition of incident wave and reflected wave, the feed line is sound and the initial current traveling wave i is zero modeJRefracted waves only, iJAnd iNThe absolute value of (A) is represented by the formula (VI):
Figure BDA0001209226330000125
specified electricityThe positive flow direction is as follows: from the bus bar to the feeder. Zero-mode initial current traveling wave i of fault feeder lineNAnd a sound feeder zero-mode initial current traveling wave iJAs shown in formula (VII):
Figure BDA0001209226330000131
at the instant when the current traveling wave passes through the inductor, the inductor is equivalent to an open circuit for the current traveling wave, and the current traveling wave is subjected to negative total reflection. Therefore, for analysis convenience, when the zero-mode initial traveling wave is pushed to the arc suppression coil, the current traveling wave is regarded as not refracted to the arc suppression coil, and the neutral point equivalent wave impedance ZeqTo infinity, formula (VII) is converted to formula (VIII):
Figure BDA0001209226330000132
when a single-phase earth fault occurs in a low-current earth power grid provided with a distribution automation system, the single-phase earth fault can be obtained by the formula (VII):
a. the zero-mode initial current traveling wave polarities of the sound feeder lines are the same;
b. the zero-mode initial current traveling wave amplitude of the fault feeder line is the maximum, and the ratio of the zero-mode initial current traveling wave amplitude to the healthy feeder line is equal to (N-1);
c. the zero-mode initial current traveling wave polarities of the fault feeder line and the healthy feeder line are opposite.
The zero-mode initial current traveling wave of each feeder line is described by means of the wavelet transform modulus maximum, the characteristics of the wavelet modulus maximum of the zero-mode fault initial current traveling wave are not influenced by the change of the running mode of a neutral point, the principle is reliable and clear, and the specific rule is as follows:
for a neutral point non-effective grounding system with N feeders provided with a distribution automation system, a single-phase grounding fault occurs on the feeder side, and the amplitude and polarity characteristics of the wavelet modulus maximum of the zero-modulus initial current traveling wave are as follows:
e. the polarities of the wavelet mode maximum values of the zero-mode initial current traveling waves of the sound feeder line are the same; the polarities of the wavelet mode maximum values of the zero-mode initial current traveling waves of the fault feeder line and the healthy feeder line are opposite.
f. Compared with a healthy feeder line, the amplitude of the wavelet mode maximum value of the zero-mode initial current traveling wave of the fault feeder line is the largest, and the ratio of the amplitude of the wavelet mode maximum value to the amplitude of the healthy feeder line is equal to (N-1). Namely, the wavelet mode maximum value of the fault feeder line is equal to the sum of the amplitudes of the wavelet mode maximum values of other (N-1) healthy feeder lines.
The fault measure is a positive real number which can represent the similarity degree of the characteristics of the feeder line and the fault feeder line under the reference of a certain criterion. In a plurality of feeders of the power grid with the same voltage class, if the fault measure of a certain feeder is the maximum, the possibility that the feeder is a fault feeder can be shown to be the maximum.
And constructing traveling wave measurement by using the amplitude and phase characteristics of the zero-mode current traveling wave.
And (3) assuming that a certain neutral point non-effectively grounded power grid has N feeders, and enabling S (j) to represent the traveling wave measurement of the j-th feeder.
From the conceptual requirements of the fault measures, it can be known that the traveling wave measure S (j) represents the probability of the fault occurring in the jth feeder. Therefore, the range of the traveling wave metric S (j) is limited to [0,1 ].
If the traveling wave metric S (j) of the jth feeder line is 0, it indicates that the probability of the fault occurring in the feeder line is 0%, that is, the feeder line is a sound feeder line.
If the traveling wave measure S (j) of the jth feeder line is 1, it indicates that the probability of the fault occurring in the feeder line is 100%, that is, the feeder line is a faulty feeder line.
And if the traveling wave measure of the jth feeder line is 0< S (j) <1 and is very close to 1, the probability that the fault occurs in the feeder line is very high, namely the probability that the feeder line is a fault feeder line is very high.
If the traveling wave measure of the jth feeder line is 0< S (j) <1 and is very close to 0, the probability that the fault occurs in the feeder line is very low, that is, the feeder line is a sound feeder line is very high.
The definition formula of the traveling wave measure S (j) of the j-th feeder line is formed by combining a first measurement definition formula based on the traveling wave polarity characteristic and a second measurement definition formula based on the traveling wave amplitude characteristic, and the first traveling wave measure definition formula is S1(j) To representTraveling wave measure definition type dual-purpose S2(j) To indicate.
Measurement definition formula one structure based on traveling wave polarity characteristics
According to the relation of the polarity of the maximum value of the zero-mode initial current traveling wave wavelet transform mode of the sound feeder line and the fault feeder line, the polarity of the maximum value of the zero-mode initial current traveling wave wavelet transform mode of the sound feeder line and the fault feeder line is opposite, and the polarity of the maximum value of the zero-mode initial current traveling wave wavelet transform mode of the sound feeder line is the same. Constructing a traveling wave measure definition formula S related to the maximum value of the zero-mode initial current wave mode1(j) Namely:
Figure BDA0001209226330000141
sgn () is a sign function defined as:
Figure BDA0001209226330000142
as can be seen from the definition of the sign function, the sign function sgn [ m (j) × m (l) ] is used to reflect the polarity relationship between two values, and takes a value of 1 or-1. If m (j) × m (l) >0, that is, after comparing the positive and negative of both values, it is found that the polarities of both values are the same, sgn [ m (j) × m (l) ] is 1. If m (j) × m (l) <0, i.e., after comparing the positive and negative of both values, it is found that the polarities of both values are opposite, sgn [ m (j) × m (l) ] is-1. If m (j) × m (l) ═ 0, i.e., one of the two values is 0, sgn [ m (j) × m (l) ] is 0. For wavelet transforms, the case of a modulo maximum of 0 does not exist. Therefore, sgn [ m (j) × m (l) ] cannot take a value of 0.
The wavelet mode maximum m (j) of the initial traveling wave of the zero-mode current of the fault feeder line (j) is opposite to the wavelet mode maximum m (l) of all other feeder lines in polarity (l belongs to [1, N)]And l ≠ j). Thus, for normal feeder analysis, sgn [ m (j) × m (l)]Is equal to- (N-1), so that the result of formula (IX) is S1(j)＝-1。
The maximal value m (j) of the wavelet mode of the initial traveling wave of the zero-mode current of the sound feeder line (the jth line) has the same polarity as that of the maximal values of the wavelet modes of other sound feeder lines,sgn[m(j)×m(l)]is greater than- (N-1), so that the result of formula (IX) is S1(j)>-1。
Thus, the measure defines the formula S1(j) The requirement of a general concept of fault measure is met, and results of a fault feeder line and a sound feeder line can be distinguished obviously.
Structure of measure definition formula two based on traveling wave amplitude characteristics
Defining a measure definition formula two S based on the amplitude characteristics of the traveling wave2(j) Is composed of
Figure BDA0001209226330000151
Aiming at sound feeder analysis, the traveling wave measure is defined as two S2(j) In the range of 0<S2(j)<0.5, and S2(j) The value of (a) is small, close to 0. Amplitude coefficient S for faulty feeder2(j) 0.5. The two can be well distinguished.
In summary, the definition formula of the traveling wave measurement S (j) of the j-th feeder line is formed by combining the measurement definition formula one based on the traveling wave polarity characteristic and the measurement definition formula based on the traveling wave amplitude characteristic
Figure BDA0001209226330000152
Namely:
Figure BDA0001209226330000153
for the faulty feeder analysis, S (j) ═ 1. The traveling wave measure S (j) can obviously distinguish the feeder line where the fault is located from the sound feeder line, and meets the following requirements: and the traveling wave measure S (j) of the fault feeder line is 1, and the traveling wave measure S (j) of the sound feeder line is 0.
The line selection is realized by comparing the traveling wave measurement of the fault feeder line and the non-fault feeder line, and if the fault measurement of a certain feeder line is the largest and the difference between the fault measurement of the certain feeder line and the fault measurement of other feeder lines is the largest, the possibility that the feeder line is the fault feeder line is the largest.
Obtaining a line selection result according to the magnitude of the traveling wave measure S (j) of each feeder line, namely: a single-phase earth fault occurs on which particular feeder.
(2) Based on the transient zero-mode reactive power flow direction, positioning a grounding fault point on a fault feeder line: on a feeder line where the ground fault is located, monitoring the flow direction of zero-mode reactive power of any two adjacent feeder terminal FTUs, if the product of the flow directions of the zero-mode reactive power of some two adjacent feeder terminal FTUs is negative, indicating that the ground fault occurs between the two adjacent feeder terminal FTUs, and if the product of the flow directions of the zero-mode reactive power of some two adjacent feeder terminal FTUs is positive, indicating that the ground fault does not occur between the two adjacent feeder terminal FTUs.
Assume that the feeder 1 has four FTU feeder terminals, FTU1, FTU2, FTU3, and FTU4, respectively. The feeder 2 has two feeder terminals, FTU5 and FTU6.
Assuming that a single-phase ground fault with the transition resistance of 10 omega occurs in the system at a position between the FTUs 2 and 3 of the feeder 1, the initial fault phase angles are respectively set to 30 °, 60 ° and 90 °.
Monitoring the transient zero-mode reactive power direction of each feeder terminal FTU, multiplying the transient zero-mode reactive power directions of the two phase near feeder terminals FTU, if the product is positive, marking as +1 ', if the product is negative, marking as ' -1 ', and counting the product of the transient zero-mode reactive power directions of the two phase near feeder terminals FTU, as shown in Table 3.
TABLE 3
Figure BDA0001209226330000161
The principle of the step (2) is as follows:
at present, a power distribution automation system does not realize the functions of ground fault monitoring and positioning, but each feeder terminal FTU is provided with a three-phase CT (PT) or a zero-sequence CT (PT), and can obtain zero-mode current or voltage.
The ground fault point generates transient zero-mode current which flows to both sides along a feeder line where the ground is located.
Transient zero mode currents are mainly transient capacitive currents and possibly also transient inductive currents (provided by arc suppression coils in a resonant grounded grid). Theoretical analysis and test results prove that: the oscillation frequency of the transient capacitance current is 300 to 3000Hz, and the transient inductance current at the frequency is very small. Therefore, the arc suppression coil of the resonant grounding power grid has no influence on the monitoring of the transient zero-mode current.
Ground faults occur on the feeder, with four possibilities.
The first possibility is: the sound feeder has no ground fault, and runs symmetrically without zero-mode current. Thus, all feeder terminals FTUs of a robust feeder cannot monitor zero mode current.
The second possibility is: a ground fault occurs between two section switches, i.e., two FTUs. The zero-mode reactive power flow direction is as follows: from the ground fault point, flows along the fault feeder to the bus side and the load side. Thus, the zero-mode reactive power flow direction as monitored by the two feeder terminals is different, as shown in fig. 4.
The positive direction of the power flow is specified as follows: from the busbar side to the load side. In fig. 4, the zero-mode reactive power flow direction monitored by FTU1 of section switch 1 is negative, and is marked as "-1". The zero mode reactive power flow direction monitored by FTU2 of sectionalizer 2 is positive, noted as "+ 1". The product of the two is negative.
A third possibility: the ground fault occurs on the load side of all the sectionalizers (i.e., the load side of all the FTUs). The zero-mode reactive power flow direction is as follows: from the ground fault point, flows along the fault feeder to the bus side and the load side. Thus, the zero-mode reactive power flow monitored by both feeder terminals is the same, as shown in fig. 5. The positive direction of the power flow is specified as follows: from the busbar side to the load side. In fig. 5, the zero-mode reactive power flow direction monitored by FTU1 of section switch 1 is negative, and is noted as "-1". The zero mode reactive power flow direction monitored by FTU2 of sectionalizer 2 is negative and is noted as "-1". The product of the two is positive.
A fourth possibility: ground faults occur on the bus side of all the sectionalizers (i.e., the bus side of all the FTUs). The zero-mode reactive power flow direction is as follows: from the ground fault point, flows along the fault feeder to the bus side and the load side. Thus, the zero-mode reactive power flow monitored by both feeder terminals is the same, as shown in fig. 6. The positive direction of the power flow is specified as follows: from the busbar side to the load side. The zero mode reactive power flow direction monitored by FTU1 of sectionalizer 1 is positive, noted as "+ 1". The zero mode reactive power flow direction monitored by FTU2 of sectionalizer 2 is positive, noted as "+ 1". The product of the two is positive.
Combining the above four possible analyses yields: monitoring the zero-mode reactive power flow direction of every two adjacent Feeder Terminals (FTUs) on a feeder line where the ground fault is located. If the product of the zero-mode reactive power flow directions of two adjacent Feeder Terminals (FTUs) is negative, the ground fault is indicated to occur between the two adjacent Feeder Terminals (FTUs). If the product of the flow directions of the zero-mode reactive power of two adjacent Feeder Terminals (FTUs) is positive, it is indicated that no ground fault occurs between the two adjacent Feeder Terminals (FTUs).
When a high-resistance earth fault occurs, the amplitude of only the zero-mode component is changed compared with the metallic earth, and the zero-mode reactive power flow direction is not influenced. Therefore, the method is also applicable to high resistance ground faults.

Claims (1)

1. A power distribution automation system earth fault positioning method based on traveling wave measurement and transient zero-mode reactive power direction is characterized by comprising the following specific steps:
(1) the possibility of ground fault of each feeder line is indicated by a small current line selection method of traveling wave measure, and the feeder line in which the ground fault is positioned is determined; the distribution automation system has N feeder lines, the traveling wave measure of the jth feeder line is S (j), j is more than or equal to 1 and less than or equal to N, and the method specifically comprises the following steps:
A. collecting three-phase initial current traveling wave signals for each feeder line of the distribution automation system;
B. converting the three-phase initial current traveling wave signals into zero-mode initial current traveling wave signals through phase-mode conversion;
C. transforming a first wavelet modulus maximum value m (j) in the zero-modulus initial current traveling wave signal of each feeder line by using wavelet transformation;
D. calculating a travelling wave measure S (j) of each feeder line according to formula (I):
Figure FDA0002191394820000011
in the formula (I), the compound is shown in the specification,
sgn (x) is a sign function, and when x >0, sgn (x) is 1; when x is 0, sgn (x) is 0; when x is less than 0, sgn (x) ═ 1;
m (l) is the maximum value of the first wavelet mode in the zero-mode initial current traveling wave signal of the ith feeder line; l is not equal to j;
m (j) is the maximum value of the first wavelet mode in the jth feeder zero-mode initial current traveling wave signal;
m (j) represents the amplitude of the first wavelet transformation modulus maximum of the zero-modulus initial current traveling wave of the j-th feeder line, and M (j) >0, namely M (j) ═ M (j) |;
sum represents the Sum of the amplitudes of the first wavelet transform modulus maxima of all the feeder zero-modulus initial current traveling waves,
Figure FDA0002191394820000012
E. selecting a feeder line corresponding to the maximum value of the traveling wave measure S (j), namely a fault feeder line, according to the traveling wave measure S (j) of each feeder line obtained in the step D;
(2) based on the transient zero-mode reactive power flow direction, positioning a grounding fault point on a fault feeder line: on a feeder line where the ground fault is located, monitoring the flow direction of zero-mode reactive power of any two adjacent feeder terminal FTUs, if the product of the flow directions of the zero-mode reactive power of some two adjacent feeder terminal FTUs is negative, namely the flow directions of the zero-mode reactive power of the two adjacent feeder terminal FTUs are opposite, indicating that the ground fault occurs between the two adjacent feeder terminal FTUs, and if the product of the flow directions of the zero-mode reactive power of some two adjacent feeder terminal FTUs is positive, namely the flow directions of the zero-mode reactive power of the two adjacent feeder terminal FTUs are opposite, indicating that the ground fault does not occur between the two adjacent feeder terminal FTUs.
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