CN109142974B - Alternating current line single-end fault location method suitable for flexible direct current feed-in - Google Patents

Alternating current line single-end fault location method suitable for flexible direct current feed-in Download PDF

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CN109142974B
CN109142974B CN201811013492.2A CN201811013492A CN109142974B CN 109142974 B CN109142974 B CN 109142974B CN 201811013492 A CN201811013492 A CN 201811013492A CN 109142974 B CN109142974 B CN 109142974B
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fault
current
alternating current
voltage
phase
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CN109142974A (en
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薛士敏
陆俊弛
刘冲
范勃旸
赵杨竹雨
刘白冰
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Tianjin University
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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
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
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Abstract

The invention belongs to the field of relay protection of power systems, and particularly relates to an alternating current line single-ended fault location method suitable for flexible direct current feed-in, which comprises the following steps: and after the power transmission system detects that the single-phase earth fault occurs, acquiring the single-end electric quantity of the traditional alternating current power supply side. And carrying out discrete Fourier transform on the electrical quantity in the sampling data window to extract a fundamental frequency component, and carrying out phase-mode transformation on the fundamental frequency component by using a symmetric component method under a frequency domain to obtain sequence components of fault voltage and current. And calculating the fault voltage and negative sequence fault current distribution along the fault phase based on the distribution parameter model. And acquiring a data group consisting of fault voltage and negative sequence fault current of each distance along a group of fault phases at different moments in a time domain, and performing fault distance measurement by using unary linear regression according to the characteristic that the data group only meets the positive proportional linear relation at a fault point. The invention effectively solves the problem that the traditional fault distance measurement method is not applicable, and has higher distance measurement precision and wide applicability.

Description

Alternating current line single-end fault location method suitable for flexible direct current feed-in
Technical Field
The invention belongs to the field of relay protection of power systems, and particularly relates to a fault location method for a flexible direct-current feed-in alternating-current circuit in an alternating-current and direct-current hybrid power transmission system.
Background
The alternating current transmission line is easy to have single-pole grounding fault, and the short-circuit current of the alternating current transmission line can seriously affect the safe and stable operation of the system. Therefore, the fault point is quickly positioned and the fault is cleared, and the method has important significance for improving the economical efficiency and the reliability of system operation. Due to the fact that the problem of commutation failure does not exist, and outstanding advantages in the aspects of flexible control, electric energy quality and the like do not exist, flexible direct-current transmission plays an important role in the fields of new energy grid connection, regional power grid interconnection and the like. Under the AC-DC networking mode based on flexible DC power transmission, the fault characteristic quantity in the AC system is influenced by a converter control strategy and nonlinearity of power electronic elements, and is greatly different from the traditional AC system, so that the fault location method of the traditional AC system needs to be improved to meet new challenges.
At present, the research on fault location of an alternating current power grid transmission line under flexible direct current feed-in at home and abroad is rarely reported in documents, and the existing fault location methods can be divided into a traveling wave method, an artificial intelligence algorithm and an impedance method. The traveling wave method has many advantages in fault location, but the method has extremely high sampling frequency to equipment, and has the technical problems of difficult identification of the traveling wave head, poor anti-interference performance and the like, and the location precision is easily influenced. Artificial intelligence algorithms are suitable for processing power systems with unknown parameters, but such methods rely heavily on training processes and databases courageous with training are often difficult to obtain. The impedance method can be subdivided into two types, namely a double-end electrical quantity-based method and a single-end electrical quantity-based method, and the impedance method based on the double-end electrical quantity is limited by data synchronization and high investment cost brought by communication technology. The impedance method based on the single-end electric quantity is simple in principle and easy to realize, but the distance measurement precision is easily influenced by a fault resistor and an opposite-end system.
In order to ensure the safe operation of the converter, the flexible direct current converter station is influenced by a fault ride-through control mode. The control system adjusts the magnitude and the phase of the output current in real time according to the positive sequence voltage drop degree of the grid-connected point, so that the output fault current and the voltage at the alternating current outlet of the converter present a nonlinear relation. Once a severe short-circuit fault occurs at the near end of the converter and the voltage drop exceeds the regulation capacity of the fault ride-through control strategy, the converter is locked to isolate direct current side feed current, so that the fault distance measurement method based on the double-end electric quantity is invalid. Meanwhile, the assumption of the same phase based on the single-end electric quantity distance measurement method is further broken through. Therefore, the method for measuring the fault of the single end of the alternating current line suitable for flexible direct current feed-in has practical engineering significance, and is an urgent need for development and popularization of an alternating current-direct current hybrid power transmission system in the environment that flexible direct current power transmission and a direct current power grid are established.
Disclosure of Invention
The invention provides a method for fault location of a single end of an alternating current line containing flexible direct current feed-in aiming at an alternating current-direct current hybrid power transmission system, which realizes fault location by means of unique boundary conditions at a fault point and by means of a least square method to perform unitary linear regression. The technical scheme of the invention is as follows,
a single-end fault location method for an alternating current line suitable for flexible direct current feed-in comprises the following steps:
(1) and after the power transmission system detects that the single-phase earth fault occurs, acquiring the single-end electric quantity of the traditional alternating current power supply side. And carrying out discrete Fourier transform on the electrical quantity in the sampling data window to extract a fundamental frequency component, and carrying out phase-mode transformation on the fundamental frequency component by using a symmetric component method under a frequency domain to obtain sequence components of fault voltage and current.
(2) And calculating the fault voltage and negative sequence fault current distribution along the fault phase based on the distribution parameter model.
(3) And acquiring a data group consisting of fault voltage and negative sequence fault current of each distance along a group of fault phases at different moments in a time domain, and performing fault distance measurement by using unary linear regression according to the characteristic that the data group only meets the positive proportional linear relation at a fault point.
Preferably, the step (3) is implemented by the following steps:
the flexible direct current converter is influenced by a control strategy and provides boundary conditions for fault points:
Figure BDA0001785599110000021
in the formula (I), the compound is shown in the specification,
Figure BDA0001785599110000022
for residual voltage at the fault point, RfIs the resistance of the ground at the fault,
Figure BDA0001785599110000023
is the negative sequence current flowing through the faulted branch;
in the time domain, the residual sum function h (x) is defined:
Figure BDA0001785599110000024
in the formula, u (x, i) represents fault voltage on a fault phase line at different moments from a traditional alternating current power supply side bus x; i.e. i2(x, i) represents the negative sequence fault current on the fault phase line at different moments from the traditional alternating current power supply side bus x;
Figure BDA0001785599110000025
represents a scaling factor; i represents a set of sampled data points at different time instances; n represents the total number of sample data points, u (x, i) and i2(x, i) only satisfying the relation of formula (1) at the fault point, using least square method to carry out unary linear regression, calculating residual error sum function H (x) of each position along the line, and taking the distance x along the line corresponding to the minimum value of H (x) as the fault distance xfAnd fault location is realized.
Compared with the prior art, the invention provides a novel fault location method suitable for an alternating current-direct current hybrid system by considering the influence of a converter control strategy on a fault composite sequence network, and effectively solves the problem that the traditional fault location method is not suitable. The method has higher ranging precision and is not influenced by factors such as fault resistance, fault distance, low voltage ride through strategy of a current converter, sampling frequency, line distribution capacitance and the like. In addition, the method has wide applicability, and is suitable for all alternating current systems which are configured with flexible direct current transmission for inhibiting a negative sequence current control strategy and are accessed by an inversion type distributed power supply.
Drawings
Fig. 1 shows a flexible dc-fed ac/dc hybrid power transmission system.
Fig. 2 is a flow chart of a fault location method.
Detailed Description
The invention is described in further detail below with reference to the figures and examples. Fig. 1 shows a typical flexible dc feed ac/dc hybrid transmission system with a single phase earth fault on the ac transmission line.
The fault location method for locating the single-phase earth fault of the flexible direct-current fed-in alternating-current line mainly comprises three parts of single-end electric quantity decoupling, sequence component distribution calculation of fault voltage and fault current along the line, location criterion and the like.
1. Single ended electrical quantity decoupling
Electromagnetic induction exists among three-phase transmission lines, accuracy in calculating voltage and current distribution along the lines is affected, and therefore the traditional alternating current power supply side electric quantity must be converted into mutually independent module components through a decoupling conversion matrix. The symmetric component method is the most common transformation mode in fault analysis, the positive sequence, the negative sequence and the zero sequence obtained after decomposition are all moduli, and the symmetric component transformation matrix TSAs shown in formula (1).
Figure BDA0001785599110000031
Wherein a represents a rotational component, and a-ej120°。
2. Sequence component distribution calculation of fault voltage and fault current along line
Based on a distribution parameter model, decoupling the single-ended electrical quantity of the traditional alternating current power supply side bus by a symmetric component method, then substituting the obtained sequence component into the formula (2), and carrying out voltage and current distribution calculation along the line.
Figure BDA0001785599110000033
Wherein, p is 1, 2, 0 represents corresponding sequence component;
Figure BDA0001785599110000034
representing a fault voltage sequence component on a fault phase circuit at a position x away from a conventional alternating current power supply side bus;
Figure BDA0001785599110000035
representing a fault current sequence component on a fault phase circuit at a position x away from a conventional alternating current power supply side bus;
Figure BDA0001785599110000036
single-end electric quantity for representing traditional AC power source side busVoltage sequence components obtained after decoupling;
Figure BDA0001785599110000037
representing a current sequence component obtained after the single-end electric quantity of a traditional alternating current power supply side bus is decoupled; zcpRepresenting the characteristic impedance under the line sequence component; gamma raypRepresenting the propagation constant under the line sequence component.
3. Distance measurement criterion
Under the influence of a control strategy of the flexible direct current converter, a negative sequence network of the system after single-phase earth fault only comprises a traditional alternating current network side, and a single-ended network is formed. The negative sequence component of the fault current at the fault point is only provided by the conventional alternating current side, and the influence of the fault information of the converter side on the fault point is eliminated in principle. Based on the characteristics, the single-ended information quantity of the traditional alternating current side can be utilized to realize accurate fault location. The boundary conditions at the fault point during the single-phase earth fault are as follows:
Figure BDA0001785599110000038
in the formula (I), the compound is shown in the specification,
Figure BDA0001785599110000039
representing residual voltage at the fault point;
Figure BDA00017855991100000310
a positive sequence component representing residual voltage at a fault point;
Figure BDA00017855991100000311
a negative sequence component representing the residual voltage at the fault point;
Figure BDA00017855991100000312
a zero sequence component representing residual voltage at a fault point; rfRepresenting the ground resistance at the fault;
Figure BDA00017855991100000313
representing the negative sequence current flowing through the faulted leg.
Converting the boundary condition at the fault point of the formula (3) from a frequency domain to a time domain form to obtain a formula (4):
u(x,i)＝3Rfi2(x,i) (4)
in the formula, u (x, i) represents fault voltage on a fault phase line at different moments from a traditional alternating current power supply side bus x; i.e. i2(x, i) represents the negative sequence fault current on the fault phase line at different moments from the traditional alternating current power supply side bus x; i represents a set of sampled data points at different time instances.
The analysis shows that u (x, i) and i2(x, i) satisfies a direct proportional linear relationship only at the failure point. The direct proportional linear model is established as follows:
Figure BDA0001785599110000041
in the formula of UiRepresents a data group consisting of u (x, i); i is2iIs represented by i2(x, i).
The residual sum function h (x) is defined according to equation (5):
Figure BDA0001785599110000042
in the formula (I), the compound is shown in the specification,
Figure BDA0001785599110000043
represents a scaling factor; n represents the total number of sample data points.
Scaling factor when H (x) is minimized according to least squares
Figure BDA0001785599110000044
Comprises the following steps:
Figure BDA0001785599110000045
in the formula (I), the compound is shown in the specification,
Figure BDA0001785599110000046
representing the number of samples takenAccording to group UiAverage value of (d);
Figure BDA0001785599110000047
representing sampled data sets I2iAverage value of (d); i.e. i2(x,i)2Represents i2The square of the (x, i) value;
Figure BDA0001785599110000048
to represent
Figure BDA0001785599110000049
The square of the value.
Thus by inserting Ui、i2And (x, i) substituting (6) and (7) to perform unary linear regression, and calculating the residual sum function H (x) of each position along the line. The higher the fit of the data set to formula (5), the smaller H (x). Transient process of the converter control system for inhibiting output negative sequence current, fault voltage along the line under a frequency domain, rounding error in the current sequence component calculation process, calculation error in linear regression, mutual inductor transmission error possibly existing in practical application and the like all influence the precision of the distance measuring method. Therefore, the distance x along the line corresponding to the minimum value of H (x) is the fault distance xfAnd determining the position of the fault point through a distance measurement criterion (8):
H(xf)＝min[H(x)](8)
in summary, a flow chart of the method for fault location is shown in fig. 2.

Claims (1)

1. A single-end fault location method for an alternating current line suitable for flexible direct current feed-in comprises the following steps:
(1) after a power transmission system detects that a single-phase earth fault occurs, acquiring single-end electric quantity of a traditional alternating current power supply side, performing discrete Fourier transform on the electric quantity in a sampling data window to extract a fundamental frequency component, and performing phase-mode transformation on the fundamental frequency component by using a symmetric component method in a frequency domain to obtain sequence components of fault voltage and current;
(2) calculating the fault voltage and negative sequence fault current distribution along the fault phase based on a distribution parameter model;
(3) acquiring a data group consisting of fault voltage and negative sequence fault current of a group of fault phases at different time along each distance in a fault phase line in a time domain, and performing fault distance measurement by using unary linear regression according to the characteristic that the data group only meets a positive proportional linear relation at a fault point, wherein the implementation method comprises the following steps:
the flexible direct current converter is influenced by a control strategy and provides boundary conditions for fault points:
Figure FDA0002490588700000011
in the formula (I), the compound is shown in the specification,
Figure FDA0002490588700000012
for residual voltage at the fault point, RfIs the resistance of the ground at the fault,
Figure FDA0002490588700000013
is the negative sequence current flowing through the faulted branch;
in the time domain, the residual sum function h (x) is defined:
Figure FDA0002490588700000014
in the formula, u (x, i) represents fault voltage on a fault phase line at different moments from a traditional alternating current power supply side bus x; i.e. i2(x, i) represents the negative sequence fault current on the fault phase line at different moments from the traditional alternating current power supply side bus x;
Figure FDA0002490588700000015
represents a scaling factor; i represents a set of sampled data points at different time instances; n represents the total number of sample data points, u (x, i) and i2(x, i) only satisfying the relation of formula (1) at the fault point, using least square method to carry out unary linear regression, calculating residual error sum function H (x) of each position along the line, and taking the distance x along the line corresponding to the minimum value of H (x) as the fault distance xfAnd fault location is realized.
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CN113009275A (en) * 2021-02-22 2021-06-22 天津大学 Double-end fault location method for flexible direct-current access alternating-current hybrid line
CN112986753B (en) * 2021-02-22 2022-10-04 天津大学 Flexible direct-current power grid double-end fault location method grounded through metal return line
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