Fault phase selection method based on high-frequency break variable

Abstract

A fault phase selection method based on a high-frequency break variable comprises the following steps: after a protection element starting criterion is satisfied, extracting three-phase fault component voltage data 2.5 ms before and after a protection installation position starting moment, calculating break variable voltage of each phase at the protection installation position, and then obtaining a phase selection coefficient of each phase and zero-sequence and positive-sequence break variable voltage; grounding judgment, three-phase short circuit judgment and two-phase short circuit judgment are sequentially carried out, and fault phase selection is achieved. The method can quickly and reliably act, only needs to extract data 2.5 ms after a fault to carry out fault identification, and is high in protection speed and sensitivity.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of relay protection, and particularly relates to a fault phase selection method based on a high-frequency mutation variable. BACKGROUND

[0002] As one of basic elements of relay protection, the correct action of a phase selection element is the basis for accurately calculating a distance protection measurement impedance and realizing phase division automatic reclosing. A phase selection element based on a power frequency mutation variable current has good adaptability in traditional transmission line protection. However, the fault current of an inverter type new energy station is affected by an inverter control strategy, and the equivalent positive and negative sequence impedances are quite different during a fault, showing sequence impedance characteristics quite different from those of a traditional rotating power source. In addition, the new energy station is a weakly fed power source, and the sensitivity of the side mutation variable current of the station is low, resulting in a serious performance decline of the traditional phase selection element on the station side.

[0003] A phase current difference mutation variable phase selection element is one of the most commonly used traditional phase selection elements, which compares the amplitude relationship of phase current mutation variables or two-phase current mutation variable differences to perform phase selection, and has high sensitivity and accuracy in the initial stage of a fault. However, the current mutation variable amplitude on the new energy station side is relatively small compared with that on the strong power source side, and the sensitivity is very low in a high resistance fault, and the phase selection result is easily disturbed. A phase voltage mutation variable phase selection element has high sensitivity on the weakly fed side, but its performance is still affected by the positive and negative sequence current distribution coefficients, and there is a great deficiency in principle.

[0004] A fault sequence component phase selection element compares the phase difference between the positive and negative sequence mutation variable currents and the zero negative sequence mutation variable current to perform phase selection. In theory, phase selection using the phase difference can be not affected by the small amplitude of the weakly fed side fault current, and still has high sensitivity in a high resistance fault. However, when the element is applied to an inverter type new energy station, the phase relationship between the output mutation variable sequence components is mainly affected by the control strategy and shows different characteristics, so that the traditional sequence component selection element criterion is invalid.

[0005] In summary, since the amplitude and phase of the fault current of the inverter power source are highly controlled, showing positive and negative sequence characteristics quite different from those of the conventional power source, and the new energy station usually shows weakly fed characteristics, the performance of the phase current difference mutation variable phase selection element and the fault sequence component phase selection element on the station side is deteriorated to a certain extent and there is a possibility of misoperation, no matter what type of short circuit fault occurs. In the case of a weak power grid, the performance of the system side phase selection element is also reduced to a certain extent. SUMMARY

[0006] The application aims at the defect that the equivalent positive and negative sequence impedances of the inverter power supply under power frequency always have differences when the outgoing line fails in the prior art, and provides a fault phase selection method based on high-frequency sudden variables, which can rapidly and reliably act and only needs to extract 2.5 ms of data after the fault to identify the fault, and has high protection speed and sensitivity.

[0007] The application is realized by the following technical scheme:

[0008] The application relates to a fault phase selection method based on high-frequency sudden variables.

[0009] The phase selection coefficient Among them: And The sudden variable voltage of the A phase, the B phase and the C phase at the protection installation place respectively, s=jw represents the components of the voltage, the current and the impedance under different frequencies.

[0010] The ground judgment refers to determining whether single-phase grounding is achieved according to the comparison between the phase selection coefficient and the phase selection coefficient K2, and further determining whether double-phase grounding is achieved according to the comparison between the phase selection coefficient and the phase selection coefficient K1.

[0011] The single-phase grounding refers to that when mK A >K2, it is determined that the A phase is grounded, otherwise when mK B >K2, it is determined that the B phase is grounded, and otherwise when mK C >K2, it is determined that the C phase is grounded, wherein m is a setting coefficient, and the value of m is generally m=4-8.

[0012] The double-phase grounding refers to that when the single-phase grounding condition is not met, when K A =K1, it is determined that the BC phase is grounded, otherwise when K B =K1, it is determined that the AC phase is grounded, and otherwise it is determined that the AB phase is grounded.

[0013] The phase selection coefficient is respectively: K2 takes the middle value of the three.

[0014] The three-phase short-circuit judgment refers to that the three-phase selection coefficients are all positive.

[0015] The two-phase short-circuit judgment refers to that the phase selection coefficient is compared with the phase selection coefficient K1.

[0016] When different types of faults occur, the selected phase coefficients satisfy the following relationships: Wherein: K A , K B , K C are the selected phase coefficients, Ag is A-phase grounding, BC is B-phase and C-phase short circuit, BCg is B-phase and C-phase grounding, and ABC is three-phase short circuit; when B-phase or C-phase is the special phase, the corresponding relationships are satisfied.

[0017] The grounding is determined according to the zero sequence component amplitude of the sudden change voltage at the protection installation, and specifically: Wherein: ε is a reliability coefficient, the value of which is related to the fault condition and line parameters, and is usually a small value such as 0.05 to ensure sensitivity; and are the zero sequence and positive sequence sudden change voltages at the protection installation, respectively.

[0018] When it is determined that no grounding fault has occurred, the phase high-frequency sudden change voltage amplitude is used to distinguish between three-phase fault and two-phase interphase fault of the line: when the line has a two-phase interphase fault, the fault phase high-frequency sudden change voltage is always not 0, while the three-phase fault cannot satisfy, i.e.: Technical effects

[0019] The application is based on high-frequency fault voltage and impedance component, and eliminates the influence of inverter output current in principle, so it can be applied to different inverter control strategies; the high-frequency impedance component amplitude is relatively large compared with the power frequency component amplitude, so the size of the transition resistance is relatively negligible, and the selected phase element has high anti-transition resistance performance; compared with the traditional selected phase element, the application has higher sensitivity, only needs to extract data 2.5 ms after the fault for fault identification, and has high protection speed and sensitivity. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the flowchart of the application;

[0021] Figure 2 is a weak grid sending line system of an inverter new energy station. DETAILED DESCRIPTION

[0022] This embodiment is aimed at the case that Figure 2The single feed-in inverter type new energy station of the shown model is connected to a weak power grid system, including a sending line, a main transformer, a bus and an inverter power supply unit connected in turn with the power grid, wherein: the rated capacity of the inverter type new energy station is 150 MW, the line adopts a pi equivalent circuit model, and the inverter power supply operates in a unit power factor PF=1 state before the fault. The fault starting time t is set to 1 s, the data window length for frequency spectrum analysis is 5 ms, the sampling frequency is 10 kHz, and the frequency resolution is 200 Hz. According to the frequency selection principle, the frequency should be greater than 872 Hz, so the identification criterion of high-frequency sudden change voltage and current is the average value at three frequency points of 1000 Hz, 1200 Hz and 1400 Hz to reduce the error.

[0023] In the PSCAD / EMTDC simulation software, the inverter adopts a photovoltaic low voltage ride-through strategy, different types of short circuit faults occur at different positions of the sending line through different transition resistances, the transition resistance is selected to be 0.01Ω, and the fault occurs at positions of 10%, 90% and 101% in the sending line area. The fault occurs at 1 s. After the fault, the phase selection criterion of the application is shown in Tables 1 to 4.

[0024] Table 1 The phase selection element criterion under the Ag fault condition

[0025] Table 2 The phase selection element criterion under the BC fault condition

[0026] Table 3 The phase selection element criterion under the BCg fault condition

[0027] Table 4 The phase selection element criterion under the ABC fault condition

[0028] From the phase selection results in Tables 1 to 4 under different fault conditions, it can be concluded that under different fault positions and transition resistances, the fault phase and the fault type can be correctly judged when the in-zone and out-of-zone faults occur, and the phase selection protection of the application can act quickly and reliably.

[0029] Compared with the prior art, the method can accurately judge the fault type and the fault phase within 2.5 ms after the fault, has high sensitivity and transition resistance resistance.

[0030] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the application, the protection scope of the application is subject to the claims and is not limited by the above specific embodiments, and each implementation scheme within the scope is subject to the constraints of the application.

Claims

1. A fault phase selection method based on high frequency abrupt quantity, characterized in that, After meeting the protection element starting criterion, three-phase fault component voltage data of 2.5 ms before and after the starting moment of the protection installation are extracted, and the sudden change voltage of each phase of the protection installation is calculated, then the selected phase coefficient of each phase and the zero sequence and positive sequence sudden change voltage are obtained, and in turn, the ground judgment, three-phase short circuit judgment and two-phase short circuit judgment are carried out to realize fault phase selection.

2. The faulted phase selection method based on high frequency abrupt quantity according to claim 1, characterized in that, The phase selection coefficient wherein: and are the protection installation phase A, B and C phase sudden variable voltage, s = jω represents the components of each voltage, current and impedance at different frequencies.

3. The high frequency perturbation variable based faulted phase selection method according to claim 1, characterized in that, The ground judgment refers to determining whether single-phase grounding is according to the comparison of the selected phase coefficient of each phase with the selected phase coefficient K2, and further determining whether two-phase grounding is according to the comparison of the selected phase coefficient of each phase with the selected phase coefficient K1.

4. The faulted phase selection method based on high frequency abrupt quantity according to claim 3, characterized in that, The single-phase grounding refers to: when mK A 2 is A-phase grounding, otherwise when mK B 2 is B-phase grounding, and otherwise when mK C 2 is C-phase grounding, wherein m is a setting coefficient. The whether two-phase grounding refers to: when the single-phase grounding condition is not satisfied, when K A =K1, it is determined that BC phase grounding, otherwise when K B =K1, it is determined that AC phase grounding, and otherwise it is determined that AB phase grounding.

5. The high frequency perturbation variable based faulted phase selection method according to claim 1, characterized in that, The phase selection coefficients are respectively: K2 takes an intermediate value among the three.

6. The high frequency perturbation variable based faulted phase selection method according to claim 1, characterized in that, The three-phase short circuit judgment refers to that the selected phase coefficients of three phases are all positive.

7. The high frequency perturbation variable based faulted phase selection method according to claim 1, characterized in that, The two-phase short circuit judgment refers to that the selected phase coefficient of each phase is compared with the selected phase coefficient K1. When different types of faults occur, the phase selection coefficients satisfy the following relationships: wherein: K A , K B , K C are phase selection coefficients, Ag is A-phase grounding, BC is B-phase and C-phase short circuit, BCg is B-phase and C-phase grounding, and ABC is three-phase short circuit; when B-phase or C-phase is the special phase, the corresponding relationships are satisfied.

8. The faulted phase selection method based on high frequency abrupt quantity according to claim 7, characterized in that, The ground fault is judged according to the zero sequence component amplitude of the sudden change variable voltage at the protection installation, and specifically: Wherein: epsilon is a reliability coefficient, And are the zero sequence and positive sequence sudden change variable voltage at the protection installation respectively.

9. The faulted phase selection method based on high frequency abrupt quantity according to claim 7, characterized in that, When it is judged that no ground fault occurs, the line is distinguished from three-phase fault and two-phase interphase fault by phase high-frequency mutation variable voltage amplitude: when the line occurs two-phase interphase fault, the high-frequency mutation variable voltage of fault phase is always not 0, while three-phase fault always cannot satisfy, that is:

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