CN113514700B - System impedance checking method based on actual fault information - Google Patents
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Abstract
The invention provides a system impedance checking method based on actual fault information, which comprises the following steps: calculating the resistance value and the reactance value of the actual fault position from the bus; obtaining an initial impedance value of the system; calculating the rough value of the no-load voltage of the bus; calculating a preliminary impedance value of a fault loop according to the rough value of the no-load voltage of the bus and the short-circuit current value during fault; calculating a correction value of the system impedance according to the type of the actual fault; calculating the no-load voltage of the bus by taking the impedance correction value as an initial value; utilizing and calculating a theoretical current value of the fault short circuit; an optimum function with respect to the system impedance value is constructed with the minimum value of the difference between the actual current values sought to be shorted to the fault as an objective function. The invention carries out iterative computation after each fault occurrence to obtain a more accurate system impedance value, has good timeliness and accuracy, and provides basic support for the subsequent concrete application of short-circuit current computation, protection setting, fault positioning and the like.
Description
Technical Field
The invention relates to the technical field of relay protection of power systems, in particular to a system impedance checking method based on actual fault information.
Background
In a distribution line, the impedance presented from a power supply access point to a power supply side is called the system impedance of a power system, mainly an inductive impedance component, which is formed by superposing generator impedance, line impedance and transformer impedance, and is commonly used in the fields of short-circuit capacity calculation, breaker interruption capacity verification, relay protection setting calculation and the like. For a long time, the system impedance in the prior art is generally calculated and provided to adjacent grid management institutions by each level of grid management institutions, or provided to lower level grid management institutions and other demanding parties such as design houses, users and the like step by step from top to bottom. During calculation, system impedance calculation in a full-scale mode is generally performed according to parameters of equipment at all levels, such as parameters of a generator, a transformer and a power transmission and distribution line, and according to changes of a power grid operation mode. Because of the numerous parameters involved in calculation, the coordination between departments and units is unusual and complicated, the ideal accuracy is difficult to achieve, and the parameters cannot be updated in time. Some documents in the field also provide that the system impedance is roughly estimated according to the circuit principle by using the electric parameters actually operated by the system, but the calculation mode is greatly influenced by electric transient data, so that the calculation accuracy is not high, and the calculation mode can not be updated in time according to the actual condition of the circuit.
The system impedance obtaining method is difficult to ensure the accuracy and timeliness, and a large impression is brought to the use (such as calculation of a short circuit point and the like) of a subsequent unit or a user.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a system impedance checking method, which is based on actual fault information of a system, and obtains a more accurate system impedance value by performing iterative calculation after each fault occurrence, has good timeliness, and provides basic support for the following concrete applications such as short-circuit current calculation, protection setting, fault positioning and the like.
In order to achieve the technical effects, the invention provides a system impedance checking method based on actual fault information, which comprises the following steps:
s1, calculating a resistance value Rdt and a reactance value Xdt of an actual fault position from a bus;
S2, obtaining an initial impedance value of the system, wherein the initial impedance value comprises an initial resistance value Rs_raw and an initial reactance value xs_raw;
s3, calculating a rough value of no-load voltage of the bus according to the bus voltage Ubus and the load current If before the fault and combining an initial impedance value of the system Wherein/>J is an imaginary number;
s4, calculating a primary impedance value Zd_raw of a fault loop according to the no-load voltage rough value Us0 of the bus and a short circuit current value during fault;
s5, calculating a correction value Zs0 of the system impedance according to the type of the actual fault;
s6, taking the impedance correction value Zs0 as an initial value, and calculating the no-load voltage U0 of the bus; calculating a theoretical current value Id_ theory of fault short circuit by using the U0 and the Zs 0;
And S7, constructing an optimal function related to the system impedance value by taking the minimum value of the difference between the Id_ theory and the actual current value Id_face of the fault short circuit as an objective function.
In some preferred embodiments, the method further comprises the step of:
S8, after each bus fails, repeating the steps S6-S7 when the system impedance value checked in the previous failure is Zs 0;
and S9, taking the minimum value of the difference between the Id_ theory and the actual current value Id_face of the fault short circuit as a first objective function, taking the minimum value of the difference between the theoretical current value and the actual current value of the historical fault short circuit under the condition of seeking the system impedance value as a second objective function, and constructing an optimal function related to the system impedance value.
In some preferred embodiments, before said step S1, the method further comprises the steps of:
And collecting bus information of faults, wherein the bus information comprises an accurate topological structure, a wire model and length, an actual fault position and an actual fault type of the distribution line.
In some preferred embodiments, the preliminary impedance value zd_raw in step S4 is calculated as follows:
according to the short circuit type of the system, calculating the primary impedance value Zd_raw of the system respectively;
for a two-phase short circuit,
For a three-phase short circuit,
Wherein max (ida, ibb, idc) is a function seeking the maximum value in the three-phase current;
In some preferred embodiments, the method for calculating the correction value Zs0 of the system impedance in step S5 includes:
If the actual fault class is a metal fault, the rough value Zs0 of the system impedance is calculated as follows:
wherein Φ=270- (90- δ) - θ, δ being the line impedance angle at the actual fault point, θ being the phase angle of the initial value of the system impedance;
if the actual fault type is arc fault, calculating an arc impedance value RF according to the actual current value Id_face of fault short circuit: rf=1443.57×larc/id_face, wherein Larc is arc length;
The rough value Zs0 of the system impedance is calculated as follows:
Where Φ=270- (90- δ ') - θ, δ' is the impedance angle of the line resistance at the actual fault point after the arc resistance is superimposed with the line reactance at the actual fault point.
In some preferred embodiments, the method for obtaining the initial impedance value of the system in step S2 includes: provided by the power system management department; or calculated based on system architecture and parameters.
The invention has the beneficial effects that:
Based on the actual fault information of the system, the relatively accurate system impedance value is obtained by carrying out iterative calculation after each fault occurs, so that the system has good timeliness and accuracy, and basic support is provided for the subsequent concrete applications such as short-circuit current calculation, protection setting and fault positioning; the distribution network operation unit can obtain the accurate system impedance value in a certain operation mode without depending on the support of a front-end power grid management department.
Drawings
FIG. 1 is a schematic flow chart of a system impedance checking method based on actual fault information according to an embodiment of the invention;
FIG. 2 is a schematic diagram showing a method for calculating the impedance correction value Zs0 according to an embodiment of the present invention;
Fig. 3 is a flowchart of an iterative checking method for the impedance correction value Zs0 after each bus failure according to an embodiment of the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent. In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.
As shown in fig. 1, the present invention provides a system impedance checking method based on actual fault information, which includes the steps of:
S1, calculating a resistance value Rdt and a reactance value Xdt of the actual fault position from the bus.
The actual fault position is obtained by a line inspection result of the distribution network line operation maintenance team on faults. The calculation of the resistance value Rdt and the reactance value Xdt is common general knowledge in the art, and will not be described in detail herein. In some preferred embodiments, before this step S1, the method further includes the treatment and collection of bus and fault information, specifically including: and collecting bus information of faults, wherein the bus information comprises an accurate topological structure, a wire model and length, an actual fault position and an actual fault type of the distribution line. Because in actual distribution lines, the corresponding outgoing lines of the bus are more than one, the specific outgoing lines with faults can be accurately treated and collected at the moment, and all outgoing lines contained in the bus can be accurately treated and collected in advance, and after a data set is established, the data of the corresponding outgoing lines can be searched in the data set after the faults occur.
S2, obtaining an initial impedance value of the system, wherein the initial impedance value comprises an initial resistance value Rs_raw and an initial reactance value xs_raw.
In some preferred embodiments, the system impedance is generally formed by overlapping the generator impedance, the line impedance and the transformer impedance, and in the existing management work of the distribution network in China, the system resistance is generally provided by a superior power grid management mechanism, and the system resistance calculation in a full-scale mode is performed according to the change of the power grid operation mode by matching a plurality of departments and units during calculation. However, because of poor timeliness and accuracy, only the system impedance obtained for the first time is used as an initial impedance value in the invention, so that the subsequent further iterative calibration is convenient.
In other preferred embodiments, the calculation may be further performed according to the system structure and parameters, and the specific method may include:
wherein/> The delta If is the current phasor difference value at the corresponding moment.
It should be understood that whatever method of obtaining the system impedance is used is not an important aspect of the present application, so long as a rough value of the system impedance can be obtained as an initial value for the overall scheme. The application does not further require the method and accuracy for obtaining the initial value of the system impedance.
S3, calculating a rough value of no-load voltage of the bus according to the bus voltage Ubus and the load current If before the fault and combining an initial impedance value of the systemWherein/>J is an imaginary number; since the initial impedance value of the system at this time is not accurate, only a rough value with respect to the no-load voltage of the bus is obtained.
And S4, calculating a primary impedance value Zd_raw of a fault loop according to the no-load voltage rough value Us0 of the bus and the short circuit current value during fault. The impedance value can be calculated by the voltage and the current as a conventional technical means in the art, but the impedance calculation modes under each short circuit condition are not very same because of a plurality of short circuit types of the distribution line, and a person skilled in the art needs to select a corresponding calculation method according to actual conditions. In some preferred embodiments, a specific method for calculating the preliminary impedance value zd_raw according to the phase short type is given:
For the two-phase short circuit type, the preliminary impedance value
For three-phase short circuit type, preliminary impedance value
Where max (ida, ibb, idc) is the function of the maximum value of the current sought in the three-phase circuit.
And S5, calculating a correction value Zs0 of the system impedance according to the type of the actual fault.
Wherein the categories of actual faults mainly comprise metal faults and arc faults. The system impedance calculation modes under the two fault types are different, and a specific calculation method needs to be determined by a person skilled in the art in combination with actual conditions and theoretical knowledge of the field.
In some preferred embodiments, as shown in fig. 2, another method for calculating the correction value Zs0 of the impedance is provided, including:
If the actual fault class is a metal fault, the rough value Zs0 of the system impedance is calculated as follows:
wherein Φ=270- (90- δ) - θ, δ being the line impedance angle at the actual fault point, θ being the phase angle of the initial value of the system impedance;
if the actual fault type is arc fault, calculating an arc impedance value RF according to the actual current value Id_face of fault short circuit: rf=1443.57×larc/id_face, wherein Larc is arc length;
The rough value Zs0 of the system impedance is calculated as follows:
Where Φ=270- (90- δ ') - θ, δ' is the impedance angle of the line resistance at the actual fault point after the arc resistance is superimposed with the line reactance at the actual fault point.
In some preferred embodiments, the step of calculating the correction value Zs0 of the system impedance further comprises: judging whether the impedance value is out of limit, if so, ending the flow.
S6, taking the impedance correction value Zs0 as an initial value, and calculating the no-load voltage U0 of the bus; and calculating a theoretical current value Id_ theory of fault short circuit by using the U0 and the Zs 0. It should be understood that the impedance correction value Zs0 at this time is an independent variable with respect to the theoretical current value id_ theory, and thus an error between the impedance correction value Zs0 and the actual impedance value can be obtained by examining an error of the theoretical current value id_ theory.
And S7, constructing an optimal function related to the system impedance value by taking the minimum value of the difference between the Id_ theory and the actual current value Id_face of the fault short circuit as an objective function. The optimal function may be a gradient descent method, a newton method, a quasi-newton method, a conjugate gradient method, or other commonly used optimal function solving algorithms, and a person skilled in the art may select a specific solving algorithm according to the actual situation, which is not limited in the present invention. It should be noted that, as described above, since the impedance correction value Zs0 is an independent variable with respect to the theoretical current value id_ theory, and the actual current value id_face of the fault short circuit is exact, by analyzing the error values of id_ theory and id_face, a more accurate impedance correction value Zs0 can be obtained. In some preferred embodiments, an error determination step may be set, an error threshold is set, and a threshold within the threshold range is considered normal, and the checking of the system impedance is continued; if the threshold is exceeded, indicating that there is an error in the previous step, reporting the error to the system or technician.
In other preferred embodiments, as shown in fig. 3, in order to perform optimal checking on the impedance correction value Zs0 and ensure timeliness of the checking result, the system impedance checking method further includes the step of performing iterative checking on the impedance correction value Zs0 according to each time the bus fails, including:
and S8, after each bus fails, repeating the steps S6-S7 when the system impedance value checked in the previous failure is Zs 0.
And S9, taking the minimum value of the difference between the Id_ theory and the actual current value Id_face of the fault short circuit as a first objective function, taking the minimum value of the difference between the theoretical current value and the actual current value of the historical fault short circuit under the condition of seeking the system impedance value as a second objective function, and constructing an optimal function related to the system impedance value. It should be noted that the purpose of this step S9 is to: and (3) accurately calibrating the system impedance again after the bus fails in a certain set operation mode and an accurate failure position is found, until an optimal system impedance value is obtained, and checking that all the historical system impedance total errors calculated after the short-circuit failure occurs before the calibration are minimum.
Furthermore, the operations of the processes described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The processes (or variations and/or combinations thereof) described herein may be performed under control of one or more computer systems configured with executable instructions, and may be implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications), by hardware, or combinations thereof, collectively executing on one or more processors. The computer program includes a plurality of instructions executable by one or more processors.
Further, the method may be implemented in any type of computing platform operatively connected to a suitable computing platform, including, but not limited to, a personal computer, mini-computer, mainframe, workstation, network or distributed computing environment, separate or integrated computer platform, or in communication with a charged particle tool or other imaging device, and so forth. Aspects of the invention may be implemented in machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, optical read and/or write storage medium, RAM, ROM, etc., such that it is readable by a programmable computer, which when read by a computer, is operable to configure and operate the computer to perform the processes described herein. Further, the machine readable code, or portions thereof, may be transmitted over a wired or wireless network. When such media includes instructions or programs that, in conjunction with a microprocessor or other data processor, implement the steps described above, the invention described herein includes these and other different types of non-transitory computer-readable storage media. The invention also includes the computer itself when programmed according to the methods and techniques of the present invention.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (5)
1. The system impedance checking method based on the actual fault information is characterized by comprising the following steps:
s1, calculating a resistance value Rdt and a reactance value Xdt of an actual fault position from a bus;
S2, obtaining an initial impedance value of the system, wherein the initial impedance value comprises an initial resistance value Rs_raw and an initial reactance value xs_raw;
s3, calculating a rough value of no-load voltage of the bus according to the bus voltage Ubus and the load current If before the fault and combining an initial impedance value of the system Wherein/>J is an imaginary number;
s4, calculating a primary impedance value Zd_raw of a fault loop according to the no-load voltage rough value Us0 of the bus and a short circuit current value during fault;
s5, calculating a correction value Zs0 of the system impedance according to the type of the actual fault;
s6, taking the impedance correction value Zs0 as an initial value, and calculating the no-load voltage U0 of the bus; calculating a theoretical current value Id_ theory of fault short circuit by using the U0 and the Zs 0;
S7, constructing an optimal function related to the system impedance by taking the minimum value of the difference between the Id_ theory and the actual current value Id_face of the fault short circuit as an objective function;
the method for calculating the correction value Zs0 of the system impedance in step S5 includes:
if the actual fault type is a metal fault, the system impedance correction value Zs0 is calculated as follows:
wherein Φ=270- (90- δ) - θ, δ being the line impedance angle at the actual fault point, θ being the phase angle of the initial value of the system impedance;
if the actual fault type is arc fault, calculating an arc impedance value RF according to the actual current value Id_face of fault short circuit: rf=1443.57×larc/id_face, wherein Larc is arc length;
The correction value Zs0 of the system impedance is calculated as follows:
Where Φ=270- (90- δ ') - θ, δ' is the impedance angle of the line resistance at the actual fault point after the arc resistance is superimposed with the line reactance at the actual fault point.
2. The system impedance checking method according to claim 1, further comprising the step of:
S8, after each bus fails, repeating the steps S6-S7 when the system impedance value checked in the previous failure is Zs 0;
and S9, taking the minimum value of the difference between the Id_ theory and the actual current value Id_face of the fault short circuit as a first objective function, taking the minimum value of the difference between the theoretical current value and the actual current value of the historical fault short circuit under the condition of seeking the system impedance value as a second objective function, and constructing an optimal function related to the system impedance value.
3. The system impedance checking method according to claim 1, further comprising, before said step S1, the step of:
And collecting bus information of faults, wherein the bus information comprises an accurate topological structure, a wire model and length, an actual fault position and an actual fault type of a distribution line to which the bus belongs.
4. The system impedance checking method according to claim 1, wherein the preliminary impedance value zd_raw in step S4 is calculated as follows:
according to the short circuit type of the system, calculating the primary impedance value Zd_raw of the system respectively;
for a two-phase short circuit,
For a three-phase short circuit,
Where max (ida, ibb, idc) is a function that seeks the maximum value in the three-phase current.
5. The system impedance checking method according to claim 1, wherein the method of obtaining the initial impedance value of the system in step S2 comprises: provided by the power system management department; or calculated based on system architecture and parameters.
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