CN-119921275-B - Circuit longitudinal differential protection method containing mixed flow controller

CN119921275BCN 119921275 BCN119921275 BCN 119921275BCN-119921275-B

Abstract

The invention provides a line longitudinal differential protection method comprising a mixed current controller, which comprises the steps of collecting power frequency currents at two ends of each phase line, calculating to obtain differential currents of each phase and braking currents of each phase, obtaining negative sequence current starting auxiliary criteria according to the differential currents of each phase and the braking currents of each phase, obtaining ratio braking action criteria according to the differential currents of each phase and the braking currents of each phase, combining the negative sequence current starting auxiliary criteria and the ratio braking action criteria to judge asymmetric faults in a line area, obtaining symmetric three-phase fault criteria according to the differential currents and judging symmetric three-phase faults in the line area, obtaining excitation surge current criteria according to the differential currents of each phase, judging excitation surge current according to the excitation surge current criteria, and carrying out line longitudinal differential protection according to the asymmetric fault judgment results, the symmetric three-phase fault judgment results and the excitation surge current judgment results. The invention can effectively solve the situation of line longitudinal differential protection misoperation and refusal operation caused by the access of the hybrid power flow controller and improve the reliability of line protection.

Inventors

FAN DENGBO
LI MAOYING
GAO XU
MA YINGXIN
WANG XIAOFEI
ZHANG QIANWEI
HAO ZHIGUO
DU JUAN
ZHUANG BO
NIU XUEFEI

Assignees

国网冀北电力有限公司
国网冀北电力有限公司电力科学研究院
西安交通大学
国家电网有限公司

Dates

Publication Date: 20260512
Application Date: 20250121

Claims (8)

1. The method for protecting the longitudinal differential of the circuit containing the mixed flow controller is characterized by comprising the following steps of: S1, collecting power frequency currents at two ends of each phase line and calculating to obtain differential currents of each phase and braking currents of each phase; S2, acquiring a negative sequence current starting auxiliary criterion according to each phase difference current, acquiring a ratio braking action criterion according to each phase difference current and each phase braking current, and judging asymmetric faults in a line area by combining the negative sequence current starting auxiliary criterion and the ratio braking action criterion; s3, acquiring a symmetrical three-phase fault criterion according to each phase difference current and judging a symmetrical three-phase fault in a line area; s4, obtaining excitation surge current criteria according to the phase difference currents, and judging the excitation surge current according to the excitation surge current criteria; s5, performing line longitudinal differential protection according to the asymmetric fault judgment result, the symmetric three-phase fault judgment result and the excitation surge judgment result; the method for acquiring the negative sequence current starting auxiliary criterion in the step S2 comprises the following steps of utilizing A-phase differential current Phase difference current And C phase difference current Calculating the negative sequence component of the phasor of a three-phase differential current Defining a negative sequence current starting auxiliary criterion as follows: ; Wherein, the Rated current of primary windings of the series transformers is set, and n is a threshold coefficient; The method for acquiring the excitation surge current criterion according to each phase difference current in the step S4 comprises the steps of extracting a second harmonic component in each phase of differential current vector by utilizing FFT (fast Fourier transform), and comparing the second harmonic component with a power frequency component of the differential current vector to obtain the excitation surge current criterion: ; Wherein, the 、 And The second harmonic components of A, B and C-phase differential currents respectively, 、、 The power frequency components of A, B and C phase differential current vectors respectively, Is the second harmonic braking coefficient.
2. The method for protecting a line differential with a hybrid current controller according to claim 1, wherein the power frequency current in step S1 comprises a primary side-feed power frequency current of an a-phase series transformer Primary side supply end power frequency current of B-phase series transformer Primary side feeding end power frequency current of transformer connected in series with C phase Primary side receiving end power frequency current of A-phase series transformer Primary side receiving end power frequency current of B-phase series transformer Primary side receiving end power frequency current of transformer connected in series with C phase 。
3. The method for protecting a line longitudinal differential including a hybrid current controller according to claim 2, wherein the method for calculating differential currents of each phase is as follows: ; Wherein, the Is a phase A differential current; Is a B-phase differential current; Is a C-phase differential current; the calculation method of each phase of braking current comprises the following steps: ; Wherein, the A is phase braking current; braking current for B phase; and is C-phase braking current.
4. The method for protecting a line longitudinal differential including a hybrid flow controller according to claim 3, wherein the ratio brake action criterion in step S2 is: ; Wherein, the Is the minimum action current; is inflection point current; is the ratio brake coefficient.
5. The method for protecting a line differential with a hybrid flow controller according to claim 4, wherein the method for determining an asymmetrical fault in the line area is characterized in that the asymmetrical fault in the line area is determined to occur if any one of the three phases satisfies a ratio braking action criterion while also satisfying a negative sequence current start auxiliary criterion.
6. The method for protecting a line differential between hybrid tidal current controllers according to any one of claims 3 to 5, wherein the symmetrical three-phase fault criteria in step S3 are: ; wherein m is a threshold value.
7. The method for protecting a line longitudinal differential including a hybrid current controller according to claim 6, wherein the method for judging a symmetric three-phase fault in a line area is that a symmetric three-phase fault in the line area is judged to occur if any one of three phases satisfies a symmetric three-phase fault criterion, and the method for judging a magnetizing inrush current is that a magnetizing inrush current exists in three phases if any one of the three phases satisfies a magnetizing inrush current criterion.
8. The method for protecting a line longitudinal differential including a hybrid tidal current controller according to claim 7, wherein the method for protecting a line longitudinal differential in step S5 is characterized in that an excitation surge current exists in three phases, an excitation surge current is determined, a line longitudinal differential protection action signal is blocked, the excitation surge current does not exist in the three phases, an asymmetric fault determination result and a symmetric three-phase fault determination result are detected, if an asymmetric fault or a symmetric three-phase fault exists, a line longitudinal differential protection action is performed, and otherwise, the line longitudinal differential protection action is not performed.

Description

Circuit longitudinal differential protection method containing mixed flow controller Technical Field The invention relates to the technical field of relay protection of power systems, in particular to a circuit longitudinal differential protection method. Background With the large-scale development and utilization of renewable energy sources, such as new energy sources of wind energy, solar energy and the like, the structure and operation mode of an electric power system have changed significantly. These new energy generation are intermittent and unpredictable, making the power flow distribution in the grid more complex and dynamic. In this case, the conventional power network may suffer from unbalanced distribution of power flow, that is, some power transmission lines may become bottlenecks due to overload, and other lines may have underutilized capacity. To address this challenge, hybrid power flow controllers (Hybrid Power Flow Controller, HPFCs) are introduced into the power grid as an advanced power electronics device. The hybrid power flow controller is composed of a series transformer, a parallel transformer, a cascade H bridge and other components, and can realize rapid, continuous and flexible control of the power flow of the line by adjusting the voltage and current amplitude and phase at two ends of the line. Such regulation capability helps balance the load in the grid, alleviates bottleneck problems, and improves the stability and efficiency of the overall power system. However, the access of the hybrid power flow controller also brings new problems to the existing line longitudinal differential protection. The conventional longitudinal differential protection relies on differential current on a detection line to perform fault judgment, and under the action of a hybrid power flow controller, non-zero differential current can appear on the line even in a normal operation state. This situation may cause malfunction or refusal of the longitudinal differential protection, thereby affecting the safe operation of the power grid. According to the characteristics of the hybrid power flow controller, the hybrid power flow controller can generate phase shifting effect on current at two sidesWhen the system operates normally, if the longitudinal differential protection is still constructed by using the current transformers 1 and 2 under ideal conditions, the differential current is not 0, and meanwhile, the magnitude of the braking current is reduced to a certain extent, so that misoperation of protection is caused, and the differential current and the braking current are shown in the following formula. Make the braking proportionIt can be seen that when the phase is shiftedWhen the phase shift angle is smaller, k is smaller and the risk of misoperation is avoidedWhen the braking ratio k is larger, the braking ratio k is increased, and the vehicle may enter a longitudinal differential protection action area to cause misoperation. The application patent number CN112271707B discloses that the protection starting criterion constructed according to the change of the voltage gradient value of the direct current line is adopted, after the protection starting criterion is met, the time domain energy value of the fault voltage counter wave at two ends of the fault point is calculated, the intra-area fault or the extra-area fault of the high voltage direct current power line can be determined according to the intra-area fault identification criterion and the fault pole selection criterion, and when the intra-area fault is judged, the intra-area fault of the negative electrode or the intra-area fault of the double electrode can be calculated by combining the fault pole selection criterion, so that the malfunction caused by the extra-area fault is avoided through 500ms delay in the engineering is not needed, and the quick action performance and the reliability of the protection of the direct current power line are improved. But this application is less flexible for the special protection requirements of the access of the extra equipment. Therefore, a new differential protection method needs to be proposed for a line including a hybrid power flow controller. The method can accurately identify the fault condition by improving a protection algorithm and logic under the condition of keeping the original current transformer position unchanged, and avoid the protection misoperation or refusal phenomenon caused by the existence of the hybrid power flow controller. Disclosure of Invention Aiming at the technical problem that the prior art is easy to cause protection misoperation or refusal operation when equipment such as a hybrid current controller is accessed, the invention provides a line longitudinal differential protection method containing the hybrid current controller, which can improve a protection algorithm and logic on the basis that the position of an original line longitudinal differential protection current tra