CN-122026283-A - Longitudinal impedance differential protection method

CN122026283ACN 122026283 ACN122026283 ACN 122026283ACN-122026283-A

Abstract

The invention relates to the technical field of relay protection of direct-current transmission systems, in particular to a longitudinal impedance differential protection method. Firstly, establishing a Berhelone equivalent circuit model considering line distribution parameters, selecting T joints as a common reference point, constructing a deduction matrix from each end to the reference point, secondly, after faults occur, carrying out phase-mode transformation on fault wave recording information, then deducting the fault wave recording information to the common reference point through the deduction matrix, thirdly, carrying out frequency spectrum analysis on fault signals, adaptively selecting optimal analysis frequency by establishing a quality evaluation model to eliminate transient component interference and improve calculation accuracy, calculating equivalent deduction impedance of a transmitting end and a receiving end under the analysis frequency, constructing a braking quantity based on action quantity and impedance amplitude sum of impedance vector sum, forming reliable differential protection criterion, and realizing rapid and accurate discrimination of faults in a region. The method can effectively detect faults and reliably act in the area, so that the protection has higher sensitivity, reliability and anti-interference capability.

Inventors

HUANG ZIHENG
DING ZHIHAO
LIN XIANGNING
LI ZHENGTIAN
WU HONGLIANG
JIANG JINYU

Assignees

华中科技大学

Dates

Publication Date: 20260512
Application Date: 20251231

Claims (10)

1. A method of differential protection of a pilot impedance comprising: monitoring voltage and current data of a three-terminal direct current system in real time, and judging whether the three-terminal direct current system fails according to the voltage and current data; When faults are judged to occur, acquiring voltage and current recording data of each end of the three-terminal direct current system, wherein the voltage and current recording data of each end comprises voltage data and current data of the end acquired in a preset time period before and after the faults occur; Respectively deducting the voltage and current recording data of each end to a common reference point of the three-terminal direct current system based on a Berhelson model to obtain voltage and current deduction data of each end; Calculating the transmitting end deduction impedance and the receiving end deduction impedance aiming at the protected circuit in the three-terminal direct current system according to the voltage and current deduction data of each end; Judging whether the protected circuit has an intra-area fault or not according to the transmitting end deduction impedance and the receiving end deduction impedance; and generating a protection action instruction when the fault in the protected line occurrence area is judged.
2. The method of claim 1, wherein determining whether the three-terminal dc system has a fault according to the voltage-current data comprises: respectively calculating the positive current change rate of each end of the three-end direct current system according to the voltage and current data; respectively judging whether the absolute value of the positive current change rate of each end is larger than a preset threshold value; and when the absolute value of the positive current change rate of each end is larger than a preset threshold value, judging that the fault occurs.
3. The method of claim 1, wherein the step of deriving voltage-current recording data of each terminal to a common reference point of the three-terminal dc system based on the berzuron model to obtain voltage-current derived data of each terminal includes: Performing Karenbauer transformation on the voltage and current recording data of each end to obtain voltage and current modulus data of each end; based on the Berlong model, respectively deducting the voltage and current modulus data of each end to the common reference point to obtain voltage and current deduction modulus data of each end; And respectively carrying out inverse transformation on the voltage and current deduction modulus data of each end to obtain the voltage and current deduction data of each end.
4. The method according to claim 1, wherein calculating the transmit-side derived impedance and the receive-side derived impedance for the protected line in the three-terminal dc system according to the voltage-current derived data of each terminal comprises: carrying out frequency domain analysis on the voltage and current recording data of any end so as to determine target analysis frequency; Based on the target analysis frequency, performing single-frequency point DFT calculation on the voltage and current deduction data of each end to obtain amplitude-frequency information of each end; and calculating the derived impedance of the transmitting end and the derived impedance of the receiving end according to the amplitude-frequency information of each end.
5. The method of claim 4, wherein the voltage-current recording data of each terminal includes positive fault current of each terminal, and the performing frequency domain analysis on the voltage-current recording data of any terminal to determine the target analysis frequency comprises: Performing fast Fourier transform on the positive fault current at any end to generate a frequency domain complex sequence; according to the frequency domain complex sequence, calculating an energy spectrum by a Parseval theorem; normalizing the energy spectrum to obtain a normalized energy spectrum; screening the normalized energy spectrum based on a preset energy threshold to obtain a candidate frequency set, wherein the candidate frequency set comprises all frequency points with corresponding normalized energy larger than the preset energy threshold; respectively carrying out comprehensive quality evaluation on each frequency point in the candidate frequency set to obtain a quality score of each frequency point in the candidate frequency set; and selecting a frequency point with the highest corresponding quality score to obtain the target analysis frequency.
6. The method of claim 5, wherein the performing the comprehensive quality evaluation on each frequency point in the candidate frequency set to obtain a quality score of each frequency point in the candidate frequency set includes: for each frequency point in the candidate frequency set, calculating an energy concentration factor and a signal to noise ratio factor of the frequency point; The energy concentration factor is defined as the ratio of the peak energy at the frequency point to the total energy within the 3dB bandwidth of the frequency point, and the signal-to-noise ratio factor is defined as the ratio of the signal energy at the frequency point to the average energy of the background noise plateau far away from the fault characteristic frequency band; and for each frequency point in the candidate frequency set, calculating the weighted sum of the energy concentration factor and the signal-to-noise ratio factor of the frequency point to obtain the quality score of the frequency point.
7. The method of claim 1, wherein determining whether the protected line has an intra-zone fault according to the transmit-side derived impedance and the receive-side derived impedance comprises: Calculating the action quantity according to the transmitting end deduction impedance and the receiving end deduction impedance through a first formula, and calculating the braking quantity through a second formula; the first formula is: ; Wherein, the In order to be the action quantity, For the purpose of the transmit-side derived impedance, Deducing impedance for the receiving end; The second formula is: ; Wherein, the Is the braking amount; Judging whether a protection criterion is met or not according to the action quantity and the braking quantity; the protection criteria are as follows: And is also provided with ; Wherein, the Is a coefficient of proportional braking and is used for controlling the speed of the vehicle, In order for the coefficient of reliability to be a good factor, Is a fixed value; and when the protection criterion is met, judging that the protected line has an intra-area fault.
8. A differential impedance device for longitudinal impedance, comprising: the fault monitoring module is used for monitoring voltage and current data of the three-terminal direct current system in real time and judging whether the three-terminal direct current system has faults or not according to the voltage and current data; The data acquisition module is used for acquiring voltage and current recording data of each end of the three-end direct current system when faults are judged to occur, wherein the voltage and current recording data of each end comprise voltage data and current data of the end acquired in a preset time period before and after the faults occur; The deduction module is used for deducting the voltage and current recording data of each end to a common reference point of the three-terminal direct current system based on the Berlong model to obtain voltage and current deduction data of each end; The impedance calculation module is used for calculating the transmitting end deduction impedance and the receiving end deduction impedance of the protected circuit in the three-terminal direct current system according to the voltage and current deduction data of each end; the fault judging module is used for judging whether the protected circuit has an intra-area fault or not according to the transmitting end deduction impedance and the receiving end deduction impedance; And the protection action module is used for generating a protection action instruction when judging that the protected circuit generates the fault in the area.
9. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing a longitudinal impedance differential protection method as claimed in any one of claims 1 to 7 when the computer program is executed by the processor.
10. A non-transitory computer readable storage medium storing computer instructions for causing a computer to perform a method of differential impedance longitudinal protection as claimed in any one of claims 1 to 7.

Description

Longitudinal impedance differential protection method Technical Field The invention relates to the technical field of relay protection of direct-current transmission systems, in particular to a longitudinal impedance differential protection method. Background Three-terminal direct current transmission system is widely applied in the construction of novel power system due to the flexibility and economy of the three-terminal direct current transmission system in the aspects of new energy collection and consumption. But its T-topology results in a more complex fault transient than a conventional two-terminal system. When the system fails, the electrical differences of all ends are obvious, so that the problems of dead zone protection, insufficient sensitivity and the like are generated, the reliability of differential protection is seriously threatened, and further protection refusal or misoperation is caused, and serious threat is formed to the safety of the system. Therefore, the research on a novel protection scheme which can adapt to three-terminal direct current topology has important engineering significance for guaranteeing the safe and stable operation of a new energy source delivery channel. The fault protection problem of the three-terminal direct current circuit belongs to the complex multivariable nonlinear electric quantity coupling problem. The traditional longitudinal differential protection principle is clear, but the protection criterion (differential current) is extremely easy to be interfered by factors such as distributed capacitance current, transient current distribution inequality under a complex fault path and the like, and high sensitivity is difficult to realize on the premise of ensuring no misoperation. In recent years, although researches are attempted to introduce transient or traveling wave information to improve the protection performance, the methods often highly depend on accurate wave head identification and high sampling rate, and the reliability is difficult to ensure under the complex refraction and reflection interference of a T joint. This makes it difficult for conventional protection methods to cope with the varying operating conditions and fault types of three-terminal direct current systems. Therefore, research on a novel protection scheme which can adapt to three-terminal direct current network topology, is not influenced by the grid-connected characteristic of new energy and has low requirements on communication and sampling rate is needed to ensure safe and stable operation of a new energy direct current delivery system. Disclosure of Invention The invention aims to provide a longitudinal impedance differential protection method for solving the technical problems. The technical scheme includes that the longitudinal impedance differential protection method comprises the steps of monitoring voltage and current data of a three-terminal direct current system in real time, judging whether the three-terminal direct current system breaks down according to the voltage and current data, obtaining voltage and current recording data of each terminal of the three-terminal direct current system when the three-terminal direct current system breaks down, judging whether the protected circuit breaks down in a region according to the voltage and current recording data of each terminal, wherein the voltage and current recording data of each terminal are collected in a preset time period before and after the occurrence of the faults, respectively deducting the voltage and current recording data of each terminal to a common reference point of the three-terminal direct current system based on a Berlong model to obtain the voltage and current deducting data of each terminal, calculating the sending terminal deducting impedance and the receiving terminal deducting impedance for the protected circuit in the three-terminal direct current system according to the sending terminal deducting impedance and the receiving terminal deducting impedance, and generating a protection action command when the internal faults of the protected circuit occur in the region are judged. The invention has the beneficial effects that the measured values of all sides of the three-terminal system are uniformly converted to the common reference point for comparison through the electric quantity deduction based on the Berlong model, thereby fundamentally overcoming the technical problems of uneven fault current distribution, protection dead zone and the like when the traditional current differential protection is applied to complex topology. The method can accurately identify the fault area and reliably act, reduces the influence of the distributed capacitive current of the circuit and the dependence on data synchronization, can effectively avoid the influence of transient direct current components and high-frequency oscillation, and ensures that the protection has higher sensitivity, reliability and anti-interfer