A transformer differential protection method and system based on differential current multi-dimensional information discrimination

Abstract

The present invention relates to the technical field of power system relay protection, and discloses a transformer differential protection method and system based on differential current multi-dimensional information discrimination. The method includes a processor configured to calculate the effective value of the power frequency braking current, the modulus value, and the effective value of the braking current of the fault phase when a fault occurs within the transformer zone, and compare the calculations with a first preset threshold value. When the effective value, the modulus value, and the effective value of the braking current are all greater than the first preset threshold value, the differential protection action of the power frequency differential relay is discriminated, and the differential protection is opened when the power frequency differential relay action conditions are met. Otherwise, the differential protection action of the power frequency differential relay and the modulus value and differential relay are simultaneously discriminated, and the differential protection is opened when any action condition of the power frequency differential relay or the modulus value and differential relay is met. This method improves the performance of differential protection, has a simple principle, and has a wide range of engineering applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system relay protection, and in particular relates to a transformer differential protection method and system based on differential current multi-dimensional information discrimination. Background Art

[0002] As the scale of renewable energy storage and power generation continues to expand, transformers, as key devices connecting renewable energy grids to loads, are becoming increasingly important, carrying the mission of transmitting renewable energy power. When a system fault occurs in a 100% renewable energy grid system, the fault current amplitude is small and the power frequency component is relatively low, due to factors such as the control strategy of the renewable energy generation equipment and the current limiting function of the converter. This reduces the sensitivity of the transformer differential protection, resulting in a loss of reliable operation and threatening the safety and stability of the renewable energy power system. Summary of the Invention

[0003] The present invention provides a transformer differential protection method and system based on differential current multi-dimensional information discrimination, which are used to solve the problem that the sensitivity of transformer differential protection decreases, resulting in the inability to ensure action reliability.

[0004] To solve the above technical problems, the technical solutions included in the present invention and the corresponding beneficial effects of the technical solutions are as follows:

[0005] The present invention provides a technical solution for a transformer differential protection method based on differential current multi-dimensional information discrimination. When a fault occurs in the transformer area, the effective value of the power frequency braking current and the modulus and braking current effective value of the fault phase are calculated and compared with a first preset threshold value; when the effective value, modulus and braking current effective value of the power frequency braking current are all greater than the first preset threshold value, the differential protection action of the power frequency differential relay is discriminated, and the differential protection is opened after the action conditions of the power frequency differential relay are met; otherwise, the differential protection action of the power frequency differential relay and the modulus and differential relay are discriminated at the same time, and the differential protection is opened after any action condition of the power frequency differential relay and the modulus and differential relay is met.

[0006] The beneficial effects of this technical solution include effectively resolving the issue of reduced transformer differential protection sensitivity caused by factors such as small fault current amplitude and difficulty extracting power frequency components, resulting from the control strategies of renewable energy and energy storage equipment and the current limiting effect of the converter when a fault occurs within the transformer area in 100% renewable energy generation scenarios. This improves differential protection performance. It is also applicable to differential protection of high-voltage interconnection and step-down transformers. This method is simple in principle and has a wide range of engineering applications.

[0007] When the effective value of the power frequency braking current and the modulus and effective value of the braking current are all greater than the first preset threshold value, only the power frequency differential relay is used to perform differential protection action judgment. The judgment conditions at this time are relatively strict, and the differential protection is opened after the power frequency differential relay action conditions are met; when the effective value of the power frequency braking current and any one of the modulus and effective value of the braking current is not greater than the first preset threshold value, the power frequency differential relay and the modulus and differential relay are simultaneously used to perform differential protection action judgment. After any one of the action conditions of the power frequency differential relay and the modulus and differential relay is met, the differential relay that meets the conditions opens the differential protection.

[0008] Furthermore, a method for determining whether a transformer has an internal fault is as follows: calculating the effective value of the power frequency differential current of each phase in the three phases A, B, and C of the differential current, as well as the modulus and effective value of the differential current, and determining whether the effective value of any differential current of each phase is greater than a set threshold for the starting current. When the effective value of the differential current of any phase is greater than the set threshold for the starting current, an internal fault occurs in the transformer, and the phase is a faulty phase.

[0009] Furthermore, the power frequency differential current effective value and the power frequency braking current effective value are calculated by a full-cycle Fourier algorithm;

[0010] Furthermore, the modulus value and the effective value of the differential current as well as the modulus value and the effective value of the braking current are obtained by calculating the average value of the absolute value and the average value of the current value at each cycle sampling point.

[0011] The power frequency current effective value and modulus value and the current effective value calculated by the above algorithm are used as the judgment criteria for subsequent differential protection action, which improves the sensitivity of the differential protection action and improves the performance of the differential protection.

[0012] The present invention also provides a technical solution for a transformer differential protection system based on differential current multi-dimensional information discrimination, including a processor, which is used to calculate the effective value of the power frequency braking current of the fault phase and the modulus and braking current effective value when judging that a fault occurs in the transformer area, and compare them with a first preset threshold value; when the effective value, modulus and braking current effective value of the power frequency braking current are all greater than the first preset threshold value, the differential protection action of the power frequency differential relay is discriminated, and the differential protection is opened after the action conditions of the power frequency differential relay are met; otherwise, the power frequency differential relay and the modulus and differential relay simultaneously perform differential protection action discrimination, and the differential protection is opened after any action conditions of the power frequency differential relay and the modulus and differential relay are met.

[0013] The beneficial effects of this technical solution include effectively resolving the issue of reduced transformer differential protection sensitivity caused by factors such as small fault current amplitude and difficulty extracting power frequency components, resulting from the control strategies of renewable energy and energy storage equipment and the current limiting effect of the converter when a fault occurs within the transformer area in 100% renewable energy generation scenarios. This improves differential protection performance. It is also applicable to differential protection of high-voltage interconnection and step-down transformers. This method is simple in principle and has a wide range of engineering applications.

[0014] When the effective value of the power frequency braking current and the modulus and effective value of the braking current are all greater than the first preset threshold value, only the power frequency differential relay is used to perform differential protection action judgment. The judgment conditions at this time are relatively strict, and the differential protection is opened after the power frequency differential relay action conditions are met; when the effective value of the power frequency braking current and any one of the modulus and effective value of the braking current is not greater than the first preset threshold value, the power frequency differential relay and the modulus and differential relay are simultaneously used to perform differential protection action judgment. After any one of the action conditions of the power frequency differential relay and the modulus and differential relay is met, the differential relay that meets the conditions opens the differential protection.

[0015] Furthermore, a method for determining whether a transformer has an internal fault is as follows: calculating the effective value of the power frequency differential current of each phase in the three phases A, B, and C of the differential current, as well as the modulus and effective value of the differential current, and determining whether the effective value of any differential current of each phase is greater than a set threshold for the starting current. When the effective value of the differential current of any phase is greater than the set threshold for the starting current, an internal fault occurs in the transformer, and the phase is a faulty phase.

[0016] Furthermore, the effective value of the power frequency differential current and the effective value of the power frequency braking current are calculated by a full-cycle Fourier algorithm.

[0017] Furthermore, the modulus value and the effective value of the differential current as well as the modulus value and the effective value of the braking current are obtained by calculating the average value of the absolute value and the average value of the current value at each cycle sampling point.

[0018] The power frequency current effective value and modulus value and the current effective value calculated by the above algorithm are used as the judgment criteria for subsequent differential protection action, which improves the sensitivity of the differential protection action and improves the performance of the differential protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of the transformer differential protection method based on differential current multi-dimensional information discrimination of the present invention. DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0021] The basic concept of this invention is to improve the sensitivity of differential protection when a transformer fault occurs in a 100% renewable energy power generation scenario. This invention uses a power frequency algorithm and a modulus sum algorithm to calculate the amplitudes of the transformer's differential current and braking current, respectively. The amplitude of the braking current is then divided into intervals. If both the power frequency braking current and the modulus value braking current are greater than a set threshold, only the power frequency algorithm differential relay is used to determine the result. Otherwise, the two are used to determine the result of the power frequency differential relay and the modulus value algorithm differential relay. This new differential protection method can effectively address the problem of insufficient differential protection sensitivity caused by the small amplitude of the transformer fault current and the difficulty in extracting the power frequency component in a 100% renewable energy power grid.

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0023] Method Example:

[0024] like Figure 1 As shown, the specific implementation steps of the present invention are as follows:

[0025] (1) Calculate the effective value of the power frequency differential current of each phase A, B, and C respectively The modulus and differential current RMS Determine whether the effective value of any differential current of each phase is greater than the starting current setting threshold I op ; Among them, the module value and algorithm is to calculate the average value of the absolute value and the average value of each cycle sampling point, and the power frequency algorithm is the full-cycle Fourier algorithm.

[0026] (2) When the effective value of any phase differential current is greater than the starting current setting threshold I op Calculate and compare the effective value of the power frequency braking current The modulus value and braking current effective value and the first preset threshold value I rest size.

[0027] (3) If step (2) satisfies and When the power frequency differential relay is activated, the differential protection action is judged. If the power frequency differential relay action conditions are met, the differential protection output is opened; otherwise, the differential protection output is locked.

[0028] (4) If step (2) satisfies When the power frequency differential relay and the modulus value differential relay are put into operation, the differential protection action is judged together. If any action condition of the power frequency differential relay and the modulus value differential relay is met, the differential protection output is opened; otherwise, the differential protection output is locked.

[0029] System Example:

[0030] The implementation method of the transformer differential protection system based on differential current multi-dimensional information discrimination of the present invention has been clearly introduced in the embodiment of the transformer differential protection method based on differential current multi-dimensional information discrimination, and will not be repeated here.

[0031] The above describes the specific embodiments of the present invention, but the present invention is not limited to the described embodiments. Based on the ideas provided by the present invention, the technical means in the above embodiments are transformed, replaced, and modified in a manner that is easy for a person skilled in the art to think of, and the functions they play are basically the same as those of the corresponding technical means in the present invention, and the objectives of the invention they achieve are also basically the same. The technical solutions formed in this way are formed by fine-tuning the above embodiments, and such technical solutions still fall within the scope of protection of the present invention.

Claims

1. A transformer differential protection method based on differential current multi-dimensional information discrimination, characterized in that: When a fault occurs within the transformer area, the effective value of the power frequency braking current and the modulus and braking current of the fault phase are calculated and compared with the first preset threshold value; when the effective value, modulus and braking current of the power frequency braking current are all greater than the first preset threshold value, the differential protection action of the power frequency differential relay is judged, and the differential protection is opened after the action conditions of the power frequency differential relay are met; otherwise, the differential protection action of the power frequency differential relay and the modulus and differential relay are judged at the same time, and the differential protection is opened after any action condition of the power frequency differential relay or the modulus and differential relay is met.

2. The transformer differential protection method based on differential current multi-dimensional information discrimination according to claim 1 is characterized in that: The method for determining whether a transformer has an internal fault is as follows: calculate the effective value of the power frequency differential current of each phase in the three phases A, B, and C of the differential current, as well as the modulus and effective value of the differential current, and determine whether the effective value of any differential current of each phase is greater than the set starting current threshold. When the effective value of the differential current of any phase is greater than the set starting current threshold, an internal fault occurs in the transformer, and that phase is the faulty phase.

3. The transformer differential protection method based on differential current multi-dimensional information discrimination according to claim 2 is characterized in that: The power frequency differential current effective value and the power frequency braking current effective value are calculated by using a full-cycle Fourier algorithm.

4. The transformer differential protection method based on differential current multi-dimensional information discrimination according to claim 2 is characterized in that: The modulus value and the effective value of the differential current as well as the modulus value and the effective value of the braking current are obtained by calculating the average value of the absolute value and the average value of the current value at each cycle sampling point.

5. A transformer differential protection system based on differential current multi-dimensional information discrimination, characterized in that: The invention comprises a processor, which is used to calculate the effective value of the power frequency braking current, the modulus value and the effective value of the braking current of the fault phase when judging that a fault occurs in the transformer area, and compare them with a first preset threshold value; when the effective value of the power frequency braking current, the modulus value and the effective value of the braking current are all greater than the first preset threshold value, the power frequency differential relay performs differential protection action discrimination, and the differential protection is opened after the action conditions of the power frequency differential relay are met; otherwise, the power frequency differential relay and the modulus value and the differential relay perform differential protection action discrimination at the same time, and the differential protection is opened after any action condition of the power frequency differential relay, the modulus value and the differential relay is met.

6. The transformer differential protection system based on differential current multi-dimensional information discrimination according to claim 5 is characterized in that: The method for determining whether a transformer has an internal fault is as follows: calculate the effective value of the power frequency differential current of each phase in the three phases A, B, and C of the differential current, as well as the modulus and effective value of the differential current, and determine whether the effective value of any differential current of each phase is greater than the set starting current threshold. When the effective value of the differential current of any phase is greater than the set starting current threshold, an internal fault occurs in the transformer, and that phase is the faulty phase.

7. The transformer differential protection system based on differential current multi-dimensional information discrimination according to claim 6 is characterized in that: The power frequency differential current effective value and the power frequency braking current effective value are calculated by using a full-cycle Fourier algorithm.

8. The transformer differential protection system based on differential current multi-dimensional information discrimination according to claim 7 is characterized in that: The modulus value and the effective value of the differential current as well as the modulus value and the effective value of the braking current are obtained by calculating the average value of the absolute value and the average value of the current value at each cycle sampling point.

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