An online self-tuning transformer backup protection method and system

Abstract

The present invention discloses an on-line self-tuning method and system for transformer backup protection. Among them, the method includes: discriminating the fault phase of the transformer through a phase selection element; discriminating the fault direction of the transformer; adopting a calculation strategy corresponding to the fault phase to calculate the fault impedance of the transformer, and calculating the protection ranging of the transformer based on the fault impedance; calculating the operating time of the impedance protection of the transformer according to the protection ranging; and performing corresponding backup protection actions on the transformer by adopting a corresponding protection strategy according to the fault direction and the operating time of the impedance protection. The present invention can not only be used as the backup protection of the transformer body, but also be used as the ultra-long-distance backup protection of adjacent lines, realizing the on-line automatic tuning of the setting values of the protection device, reducing the workload of setting calculation, improving the efficiency of setting calculation, and achieving the purpose of intelligent tuning through the protection setting values.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical systems and their automatic relay protection, and more specifically, to an on-line self-tuning transformer backup protection method and system, as well as a storage medium and an electronic device. Background Art

[0002] Transformer backup protection can serve as a backup for the transformer's main differential protection and gas protection, and can also protect against overcurrent caused by external faults of the transformer, acting as a remote backup protection for the busbars on each side of the transformer and adjacent outgoing lines. For the overcurrent of the transformer caused by external phase-to-phase short circuits, complex-voltage overcurrent protection is generally used. For external earth fault short circuits, zero-sequence current protection or zero-sequence voltage protection, etc. are used. After the transformer adopts complex-voltage overcurrent protection, although the sensitivity of the overcurrent element is improved, if the sensitivity of the complex-voltage element is not high, the overall sensitivity of the transformer backup protection will be affected. Since the probability of line faults is relatively high, if the protection device or circuit breaker of the faulty line fails to operate, and the sensitivity of the complex-voltage overcurrent protection on the corresponding side of the main transformer is insufficient, the transformer will pass through a large fault current for a long time without being able to cut off the fault, resulting in an expansion of the accident scope and bringing serious consequences to the power system.

[0003] Line distance protection is a protection method that uses the ratio of the measured voltage and measured current at the protection installation location to identify and locate faults. It has advantages such as not requiring a channel and being less affected by the operation mode. It has always been an important type of protection and has been widely used in transmission lines with a voltage level of 110 kV and above at home and abroad. Transformer impedance protection is also usually used as a backup protection for adjacent lines and needs to be strictly coordinated with line distance protection in terms of impedance setting values and time setting values. The action setting values and action delays of traditional line distance protection and transformer impedance protection are both pre-set fixed values, so they need to be recalculated after the power grid structure or operation mode changes. The setting values of traditional distance protection are calculated offline by dispatchers according to the system wiring method and system parameters. After the setting calculation is completed, the field operation and maintenance personnel input them into the line protection device. However, the distance protection principles and action characteristics of different manufacturers are different, resulting in large differences in distance protection setting values, and there are problems such as a large amount of setting calculation work, poor adaptability of setting values, low setting calculation efficiency, and many setting links prone to errors.

[0004] In view of the technical problems in the above-mentioned prior art that traditional transformer backup protection has a large amount of setting calculation work, poor adaptability of setting values, and low setting calculation efficiency, no effective solution has been proposed yet. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, such as the large workload of setting calculation for the traditional backup protection of transformers, the poor adaptability of setting values, and the low efficiency of setting calculation, the present invention provides an online self-setting method and system for transformer backup protection to realize the online automatic setting of the setting values of the protection device, reduce the workload of setting calculation, improve the efficiency of setting calculation, and at the same time, through the intelligent setting technology of protection setting values, realize the coordinated cooperation between the transformer backup protection and the distance protection of adjacent lines.

[0006] According to one aspect of the present invention, there is provided an online self-setting method for transformer backup protection, including:

[0007] Determine the fault phase of the transformer through a phase selection element;

[0008] Determine the fault direction of the transformer;

[0009] Adopt a calculation strategy corresponding to the fault phase to calculate the fault impedance of the transformer, and calculate the protection distance measurement of the transformer based on the fault impedance;

[0010] Calculate the operating time of the impedance protection of the transformer according to the protection distance measurement;

[0011] According to the fault direction and the operating time of the impedance protection, perform corresponding backup protection actions on the transformer by adopting corresponding protection strategies.

[0012] Optionally, determining the fault phase of the transformer through a phase selection element includes:

[0013] After the phase selection element starts, obtain the amplitude of the positive sequence load current of the transformer for a certain time before the fault;

[0014] Calculate the amplitudes of the three single-phase currents after the transformer fault;

[0015] Based on the amplitude of the positive sequence load current and the amplitudes of the three single-phase currents, determine the fault phase of the transformer according to the preset discrimination conditions, where the fault phases include interphase faults, three-phase faults, and single-phase faults.

[0016] Optionally, determining the fault direction of the transformer includes:

[0017] According to the preset discrimination rules, determine whether a fault occurs in the reverse direction / forward direction of the transformer;

[0018] According to the discrimination result, determine the fault direction of the transformer.

[0019] Optionally, according to the preset discrimination rules, determining whether a fault occurs in the reverse direction of the transformer includes:

[0020] Determine whether the zero-sequence reverse direction element of the transformer operates to obtain a first result;

[0021] Determine whether the negative-sequence reverse-direction element of the transformer operates to obtain a second result;

[0022] Determine whether at least two of the three phase-to-phase reverse-direction elements of the transformer operate to obtain a third result;

[0023] According to the first result, the second result and the third result, determine whether a fault occurs in the reverse direction of the transformer.

[0024] Optionally, according to a preset determination rule, determine whether a fault occurs in the forward direction of the transformer, including:

[0025] Determine whether the zero-sequence forward-direction element of the transformer operates to obtain a fourth result;

[0026] Determine whether the negative-sequence forward-direction element of the transformer operates to obtain a fifth result;

[0027] Determine whether at least two of the three phase-to-phase forward-direction elements of the transformer operate to obtain a sixth result;

[0028] According to the fourth result, the fifth result and the sixth result, determine whether a fault occurs in the forward direction of the transformer.

[0029] Optionally, when the fault phase is a phase-to-phase short-circuit fault, the method further includes:

[0030] Calculate the fault impedance Z of the transformer using the following formula C :

[0031]

[0032] where U ΦΦ is the real-time voltage and I ΦΦ is the real-time current;

[0033] And calculate the protection ranging of the transformer using the following formula:

[0034] L C = Z C / Z 1

[0035] where Z C is the fault impedance of the transformer during a phase-to-phase short-circuit fault, and Z 1 is the positive-sequence impedance per unit length.

[0036] Optionally, when the fault phase is a single-phase ground short-circuit fault, the method further includes:

[0037] Use the following formula as the calculation formula for the iteration starting point to calculate the fault impedance Z of the transformer C(0) :

[0038]

[0039] where \(k=(Z 0 -Z 1 ) / 3Z 1 is the zero-sequence compensation coefficient, is the zero-sequence current measured at the protection installation location, \(\theta\) is the positive-sequence impedance angle of the line, and \(Z m is the measured impedance, is the measured phase voltage of phase A, is the measured phase current of phase A, and \(j\) is the imaginary symbol;

[0040] During each iterative calculation, iterative operations are performed according to whether the criterion is satisfied. The condition for the criterion to be satisfied is:

[0041]

[0042] And, the protection distance measurement \(L\) of the transformer is calculated using the following formula C :

[0043] \(L C =|Z C(n) | / Z 1

[0044] where \(Z C(n) is the fault impedance of the transformer during a single-phase ground short circuit fault after \(n\) iterative calculations, and \(Z 1 is the positive-sequence impedance per unit length.

[0045] Optionally, the operating time \(t op of the impedance protection of the transformer is calculated as follows:

[0046]

[0047] where \(t op.max is the longest operating time of the backup protection set by the user, \(L C is the protection distance measurement of the transformer, \(L\) is the total length of the line, and the meaning of \(t j is shown in the following formula:

[0048]

[0049] where \(L max is the maximum total length of the line of the transformer, and \(T max is the longest protection time of the transformer.

[0050] Optionally, according to the fault direction and the operating time of the impedance protection, the corresponding backup protection actions are performed on the transformer using the corresponding protection strategies, including:

[0051] When the interphase or ground direction element determines a reverse-direction fault and the phase current or zero-sequence current meets the user-set allowable tripping condition, the calculated fault interphase impedance is timed. When the timing is less than the preset period and an oscillation blocking is added during operation, and when the timing exceeds the preset period and the oscillation blocking is cancelled during tripping, the sectionalizer is tripped when reaching the user-set sectionalizer tripping point, or the bus coupler is tripped when reaching the bus coupler tripping time, and after the bus coupler is opened, the faulty bus section is confirmed.

[0052] Optionally, according to the fault direction and the impedance protection operation time, corresponding backup protection actions are performed on the transformer using the corresponding protection strategy, including:

[0053] When the zero-sequence direction element determines a reverse direction, it is timed according to the calculated fault impedance and protection distance measurement, and tripped according to the user-set sectionalizer or bus coupler tripping time. After the bus coupler is opened, the faulty bus section is confirmed;

[0054] It operates with a time delay according to the calculated impedance protection operation time. When the timing is less than the preset period and an oscillation blocking is added during operation, and when the timing exceeds the preset period and the oscillation blocking is cancelled during tripping.

[0055] Optionally, after the bus coupler is opened, if one of the following 5 conditions is met, it is determined as the faulty bus section:

[0056] Condition 1: The positive-sequence phase voltage U 1 ≤ 40V;

[0057] Condition 2: The negative-sequence phase voltage U 2 ≥ 3V;

[0058] Condition 3: All three positive-direction interphase impedance angles satisfy 45° ≤ arg(U ΦΦ / I ΦΦ ) ≤ 90°;

[0059] Condition 4: The zero-sequence current 3I 0 ≥ the minimum zero-sequence current setting value allowed by the user for tripping;

[0060] Condition 5: The negative-sequence current 3I 2 ≥ the minimum zero-sequence current setting value allowed by the user for tripping.

[0061] Optionally, according to the fault direction and the impedance protection operation time, corresponding backup protection actions are performed on the transformer using the corresponding protection strategy, including:

[0062] When the interphase or ground direction element determines a forward-direction fault, it is timed according to the fault phase impedance selected by the phase selector and the protection distance measurement, and operates with a time delay according to the calculated impedance protection operation time. When the forward-direction distance protection time delay expires, the three-side circuit breakers of the transformer are directly tripped.

[0063] According to another aspect of the present invention, there is provided an online self-tuning transformer backup protection system, comprising:

[0064] A fault phase discrimination module, configured to discriminate the fault phase of the transformer through a phase selection element;

[0065] A fault direction discrimination module, configured to discriminate the fault direction of the transformer;

[0066] A first calculation module, configured to calculate the fault impedance of the transformer by adopting a calculation strategy corresponding to the fault phase, and calculate the protection ranging of the transformer based on the fault impedance;

[0067] A second calculation module, configured to calculate the impedance protection operating time of the transformer according to the protection ranging;

[0068] A backup protection action module, configured to perform corresponding backup protection actions on the transformer according to the fault direction and the impedance protection operating time by adopting corresponding protection strategies.

[0069] According to yet another aspect of the present invention, there is provided a computer-readable storage medium storing a computer program for executing the method according to any one of the above aspects of the present invention.

[0070] According to yet another aspect of the present invention, there is provided an electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor for reading the executable instructions from the memory and executing the instructions to implement the method according to any one of the above aspects of the present invention.

[0071] Thus, the present invention proposes an online self-tuning transformer backup protection method with an ultra-long protection range for transformer backup protection, without the need for users to set impedance values and time values. The operating time is automatically calculated according to the fault ranging, and can be strictly coordinated with the online self-tuning distance protection of the lower-level line. Therefore, the present invention can not only be used as the backup protection of the transformer body, but also as the ultra-long-distance backup protection of adjacent lines, realizing the online automatic setting of the protection device settings, reducing the setting calculation workload, improving the setting calculation efficiency, and achieving the purpose of intelligent setting through the protection settings. Thus, the problem of seriously insufficient sensitivity when the transformer protection is used as the backup protection of adjacent long lines is solved, and compared with the traditional complex voltage overcurrent protection, it has the advantage of avoiding setting of time values and impedance values, greatly reducing the setting calculation workload of the operating personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] By referring to the following drawings, the exemplary embodiments of the present invention can be more fully understood:

[0073] Figure 1It is a schematic flowchart of an online self-tuning transformer backup protection method provided by an exemplary embodiment of the present invention;

[0074] Figure 2 It is a reverse logic diagram of transformer backup protection provided by an exemplary embodiment of the present invention;

[0075] Figure 3 It is a forward logic diagram of transformer backup protection provided by an exemplary embodiment of the present invention;

[0076] Figure 4 It is a schematic structural diagram of an online self-tuning transformer backup protection system provided by an exemplary embodiment of the present invention; and

[0077] Figure 5 It is the structure of an electronic device provided by an exemplary embodiment of the present invention. Detailed Embodiments

[0078] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments of the present invention. It should be understood that the present invention is not limited by the exemplary embodiments described herein.

[0079] It should be noted that: unless otherwise specifically stated, the relative arrangements, numerical expressions and values of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0080] Those skilled in the art can understand that the terms "first", "second", etc. in the embodiments of the present invention are only used to distinguish different steps, devices or modules, etc., and neither represent any specific technical meaning nor indicate an inevitable logical order between them.

[0081] It should also be understood that in the embodiments of the present invention, "a plurality" may refer to two or more, and "at least one" may refer to one, two or more.

[0082] It should also be understood that for any component, data or structure mentioned in the embodiments of the present invention, unless otherwise clearly defined or given a contrary indication in the context, it can generally be understood as one or more.

[0083] In addition, the term "and / or" in the present invention is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally represents an "or" relationship between the associated objects before and after.

[0084] It should also be understood that the descriptions of the various embodiments of the present invention emphasize the differences between the various embodiments, and the same or similar parts can be referred to each other. For the sake of brevity, they will not be described one by one.

[0085] Meanwhile, it should be understood that, for the sake of description convenience, the dimensions of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0086] The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention or its application or use.

[0087] Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods, and devices should be regarded as part of the specification.

[0088] It should be noted that: like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0089] Embodiments of the present invention can be applied to electronic devices such as terminal devices, computer systems, servers, etc., which can operate with many other general-purpose or special-purpose computing system environments or configurations. Examples of well-known terminal devices, computing systems, environments, and / or configurations suitable for use with terminal devices, computer systems, servers, etc. include, but are not limited to: personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, microprocessor-based systems, set-top boxes, programmable consumer electronics, network personal computers, small computer systems, large computer systems, and distributed cloud computing technology environments including any of the above systems, and so on.

[0090] Terminal devices, computer systems, servers, etc. can be described in the general context of computer system-executable instructions (such as program modules) executed by a computer system. Generally, program modules can include routines, programs, object programs, components, logics, data structures, etc., which perform specific tasks or implement specific abstract data types. The computer system / server can be implemented in a distributed cloud computing environment, where tasks are executed by remote processing devices linked through a communication network. In a distributed cloud computing environment, program modules can be located on local or remote computing system storage media including storage devices.

[0091] Exemplary method

[0092] Figure 1 is a schematic flowchart of an online self-tuning transformer backup protection method provided by an exemplary embodiment of the present invention. This embodiment can be applied to an electronic device, such asFigure 1 As shown in Figure 1 , the online self-tuning transformer backup protection method 100 includes the following steps:

[0093] Step 101, determine the fault phase of the transformer through a phase selection element.

[0094] Optionally, determining the fault phase of the transformer through a phase selection element includes: after the phase selection element starts, obtaining the amplitude of the positive sequence load current for a certain time before the transformer fault; calculating the amplitudes of the three single-phase currents after the transformer fault; and based on the amplitude of the positive sequence load current and the amplitudes of the three single-phase currents, determining the fault phase of the transformer according to preset discrimination conditions, where the fault phase includes interphase faults, three-phase faults, and single-phase faults.

[0095] Generally, when different systems have different types of faults, the current characteristics are different. In the embodiments of the present invention, for different fault characteristics, the following criteria are used for phase selection:

[0096] (1) After the phase selection element starts, recall and remember the amplitude |I fh1 | of the positive sequence load current 40 ms before the fault, and calculate the amplitudes of the three single-phase currents after the fault Then, arrange them in descending order of current amplitude and denote them as

[0097] (2) First, determine whether it is an interphase fault. If all of the following four conditions are met, it is judged as an interphase fault:

[0098]

[0099] (3) Then, determine whether it is a three-phase fault. If all of the following three conditions are met, it is a three-phase fault:

[0100]

[0101] (4) Then, determine whether it is a single-phase fault. The phases with the largest and smallest single-phase currents are both likely to be the fault phases.

[0102] However, the two non-fault phases have similar characteristics. If phase A is a clear metallic fault, the current in the fault phase will be much larger than that in the other two phases. Therefore, if simultaneously it can be directly selected as the fault phase.

[0103] Assume that a high-resistance ground fault occurs at the receiving end of this line. The current in the fault phase will be smaller than that in the other two non-fault phases. If all of the following 3 conditions are met, it can be judged as the fault phase:

[0104]

[0105] After a fault occurs, if none of the above conditions are met and the faulty phase cannot be determined, then calculate for all three-phase and three single-phase impedances, and trip using the minimum impedance among them. The minimum calculated relevant delay is 5.5 s.

[0106] Step 102: Determine the fault direction of the transformer.

[0107] Optionally, determining the fault direction of the transformer includes: determining whether a fault has occurred in the reverse direction / forward direction of the transformer according to a preset determination rule; and determining the fault direction of the transformer according to the determination result.

[0108] Optionally, determining whether a fault has occurred in the reverse direction of the transformer according to a preset determination rule includes: determining whether the zero-sequence reverse-direction element of the transformer has operated to obtain a first result; determining whether the negative-sequence reverse-direction element of the transformer has operated to obtain a second result; determining whether at least two of the three-phase reverse-direction elements of the transformer have operated to obtain a third result; and determining whether a fault has occurred in the reverse direction of the transformer according to the first result, the second result, and the third result.

[0109] In the embodiment of the present invention, the reverse-direction elements include phase-phase reverse-direction elements, zero-sequence reverse-direction elements, and negative-sequence reverse-direction elements.

[0110] Among them, the determination logic of the phase-phase reverse-direction element is as follows: First, calculate 3 phase-phase reverse-direction elements using the memory voltage and the sudden-change phase-phase current. The reverse-direction element criterion is as follows:

[0111] 45° ≤ arg(U ΦΦ-40ms / ΔI ΦΦ ) ≤ 90°

[0112] Among them, U ΦΦ-40ms is the memory voltage 40 ms before startup, ΔI ΦΦ is the phase-phase sudden-change current, ΔI ΦΦ = I ΦΦ - I ΦΦ-40ms . At the same time, use the 20 ms Fourier fundamental wave to filter out the positive-sequence voltage. If the positive-sequence voltage U Φ1 ≥ 0.1U Φn (U Φn is the rated value of the phase voltage), then after 40 ms, use the positive-sequence voltage and the real-time current to form the phase-phase direction element for the faulty phase, without holding. The phase-phase direction element criterion is:

[0113] 45° ≤ arg(U ΦΦ1 / I ΦΦ ) ≤ 90°

[0114] In the formula, U ΦΦ1 is the positive-sequence voltage, and I ΦΦ is the real-time current.

[0115] The criterion of the zero-sequence reverse-direction element is as follows:

[0116]

[0117] In the formula, Δ3U 0 , 3U 0 , 3I 0 are the sudden change of zero-sequence voltage, zero-sequence voltage and zero-sequence current respectively.

[0118] The criterion of the negative-sequence reverse-direction element is as follows:

[0119]

[0120] In the formula, Δ3U 2 , Δ3U 2 , 3I 2 are the sudden change of negative-sequence voltage, negative-sequence voltage and negative-sequence current respectively.

[0121] Moreover, the comprehensive discrimination logic for reverse-direction faults is: If any of the following conditions is met, it indicates that a reverse-direction fault has occurred:

[0122] (a) The zero-sequence reverse-direction element operates; (b) The negative-sequence reverse-direction element operates; (c) At least two of the three phase-to-phase reverse-direction elements operate.

[0123] When it is determined that there is a reverse-direction fault, in combination with the phase selection result, if it is selected as a phase-to-phase fault, then calculate the phase-to-phase impedance ranging element and other conditions.

[0124] Optionally, according to the preset discrimination rules, determine whether a positive-direction fault occurs in the transformer, including: determining whether the zero-sequence positive-direction element of the transformer operates to obtain a fourth result; determining whether the negative-sequence positive-direction element of the transformer operates to obtain a fifth result; determining whether at least two of the three phase-to-phase positive-direction elements of the transformer operate to obtain a sixth result; and determining whether a positive-direction fault occurs in the transformer according to the fourth result, the fifth result and the sixth result.

[0125] In the embodiment of the present invention, the positive-direction element includes a phase-to-phase positive-direction element, a zero-sequence positive-direction element and a negative-sequence positive-direction element.

[0126] Among them, the determination logic of the phase-to-phase positive-direction element is: First, calculate 3 phase-to-phase positive-direction elements using the memory voltage and the sudden change of phase current. The criterion of the positive-direction element is:

[0127] 225°≦arg(U ΦΦ-40ms / ΔI ΦΦ )≦270°

[0128] Among them, U ΦΦ-40ms is the memory voltage in the 40 ms before startup, is the phase - to - phase sudden - change current, At the same time, use the 20 - ms Fourier fundamental wave to filter out the positive - sequence voltage. If the positive - sequence voltage (U Φn is the rated value of the phase voltage), then after 40 ms, use the positive - sequence voltage and the real - time current to form the phase - to - phase direction element for the fault phase, without maintaining. The criterion for the phase - to - phase direction element is:

[0129] 225°≤arg(U ΦΦ1 / I ΦΦ )≤270°

[0130] In the formula, U ΦΦ1 is the positive - sequence voltage, and I ΦΦ is the real - time current.

[0131] The criterion for the zero - sequence positive - direction element is:

[0132]

[0133] In the formula, Δ3U 0 , 3U 0 , 3I 0 are the sudden - change of zero - sequence voltage, zero - sequence voltage, and zero - sequence current respectively.

[0134] The criterion for the negative - sequence positive - direction element is:

[0135]

[0136] In the formula, Δ3U 2 , 3U 2 , 3I 2 are the sudden - change of negative - sequence voltage, negative - sequence voltage, and negative - sequence current respectively.

[0137] Moreover, the comprehensive discrimination logic for positive - direction faults is: If any of the following conditions is met, it indicates that a positive - direction fault has occurred:

[0138] (a) The zero - sequence positive - direction element operates; (b) The negative - sequence positive - direction element operates; (c) At least two of the three phase - to - phase positive - direction elements operate.

[0139] Step 103: Adopt a calculation strategy corresponding to the fault phase to calculate the fault impedance of the transformer, and calculate the protection ranging of the transformer based on the fault impedance.

[0140] In the embodiment of the present invention, when the phase - selection element is selected as a phase - to - phase short - circuit fault, use the following formula to calculate the fault impedance Z C of the transformer:

[0141]

[0142] In the formula, UΦΦ is the real-time voltage, I ΦΦ is the real-time current;

[0143] Moreover, the protection distance measurement of the transformer is calculated using the following formula:

[0144] L C = Z C / Z 1

[0145] In the formula, Z C is the fault impedance of the transformer during phase-to-phase short-circuit fault, and Z 1 is the positive-sequence impedance per unit length.

[0146] In the embodiment of the present invention, when the fault phase is a single-phase ground short-circuit fault, the following formula is used as the calculation formula for the iteration starting point to calculate the fault impedance Z of the transformer C(0) :

[0147]

[0148] In the formula, k = (Z 0 - Z 1 ) / 3Z 1 is the zero-sequence compensation coefficient, k = (Z 0 - Z 1 ) / 3Z 1 is the zero-sequence current measured at the protection installation location, θ is the positive-sequence impedance angle of the line, and Z m is the measured impedance, is the measured phase voltage of phase A, is the measured phase current of phase A, and j is the imaginary symbol;

[0149] Among them, the criterion of the zero-sequence reactance relay is:

[0150]

[0151] During each iteration calculation, iterative operations are performed according to whether the criterion is satisfied. The condition for the criterion to be satisfied is:

[0152]

[0153] Moreover, the protection distance measurement L of the transformer is calculated using the following formula C :

[0154] L C = |Z C(n) | / Z 1

[0155] In the formula, Z C(n) is the fault impedance of the transformer during single-phase ground short-circuit fault after n iterations of calculation, and Z 1is the positive sequence impedance per unit length.

[0156] In the embodiment of the present invention, considering that iterative calculation occupies a large amount of protection resources and has high computing power requirements, and the convergence speed decreases exponentially after multiple iterative calculations, iterative calculation can be performed 10 times and then stop iterative calculation after 10 times.

[0157] Step 104, calculate the impedance protection operating time of the transformer according to the protection distance measurement.

[0158] Optionally, the impedance protection operating time t op of the transformer is calculated as follows:

[0159]

[0160] In the formula, t op.max is the longest operating time of the backup protection set by the user, L C is the protection distance measurement of the transformer, L is the total length of the line, and t j is defined as shown in the following formula:

[0161]

[0162] In the formula, L max is the maximum total length of the line of the transformer, and T max is the longest protection time of the transformer.

[0163] Step 105, according to the fault direction and the impedance protection operating time, adopt the corresponding protection strategy to perform the corresponding backup protection action on the transformer.

[0164] Optionally, according to the fault direction and the impedance protection operating time, adopting the corresponding protection strategy to perform the corresponding backup protection action on the transformer includes: when there is a phase or ground direction element judging a reverse-direction fault and satisfying the phase current or zero-sequence current allowed to trip set by the user, timing with the calculated fault phase impedance, adding oscillation blocking when the timing is less than the preset time period and tripping when the timing exceeds the preset time period, tripping the sectionalizer when reaching the user-specified sectionalizer trip time, or tripping the bus tie when reaching the bus tie trip time, and confirming the faulty bus section after the bus tie is opened.

[0165] Optionally, according to the fault direction and the impedance protection operating time, adopting the corresponding protection strategy to perform the corresponding backup protection action on the transformer includes: when the zero-sequence direction element judges a reverse direction, timing by itself according to the calculated fault impedance and protection distance measurement, and tripping according to the time set by the user to trip the sectionalizer or bus tie. After the bus tie is opened, confirm the faulty bus section; delay the action according to the calculated impedance protection operating time, add oscillation blocking when the timing is less than the preset time period and cancel the oscillation blocking when the timing exceeds the preset time period.

[0166] In the embodiment of the present invention, refer to Figure 2 As shown, the reverse action logic includes the reverse action logic for phase-to-phase faults and the reverse logic for ground faults. Figure 2 T1, T2, and T3 shown in it respectively correspond to the first time limit, the second time limit, and the third time limit. Among them, T1 is a fixed time limit (for example, but not limited to 1.5 s); T2 is the calculated time limit proposed by the present invention, corresponding to the impedance protection action time t calculated in the above step 104 op ; T3 is T2 + 0.5 s. Moreover, T1, T2, and T3 respectively correspond to three protection action strategies. The later the time, the larger the action range.

[0167] Among them, the reverse action logic for phase-to-phase faults is as follows: At 20 ms after startup, if a phase-to-phase or ground direction element determines a reverse fault, and the phase current or zero-sequence current that meets the user-set allowable tripping condition is present, when timing with the selected fault phase impedance and the timing is less than the preset period (for example, but not limited to 1.5 s) and an action occurs, oscillation blocking is added. When tripping after the timing exceeds the preset period (for example, but not limited to 1.5 s), oscillation blocking is cancelled. When reaching the user-set time for tripping the sectionalizer or bus coupler, trip the sectionalizer or bus coupler. After the bus coupler is tripped, it is necessary to confirm which section of the bus has a fault.

[0168] Among them, the reverse logic for ground faults is as follows: At 20 ms after startup, if the zero-sequence direction element determines a reverse direction, and the zero-sequence current 3I 0 ≧3I 0YX , (3I 0YX is the zero-sequence current that the user allows the protection to act). It is possible to perform distance measurement and automatic timing according to the selected fault phase impedance, and trip according to the user-set time for tripping the sectionalizer or bus coupler. After the bus coupler is tripped, it is necessary to confirm which section of the bus has a fault.

[0169] Then, delay the action according to the impedance protection action time calculated in step 104. When the timing is less than the preset period (for example, but not limited to 1.5 s) and an action occurs, oscillation blocking is added. When tripping after the timing exceeds the preset period (for example, but not limited to 1.5 s), oscillation blocking is cancelled.

[0170] In the embodiment of the present invention, after the sectionalizer or bus coupler is tripped, one section of the bus is the faulty bus section, and the other section of the bus is fault-free. Therefore, after the sectionalizer or bus coupler is tripped, if any of the following 5 conditions is met, it is determined that the faulty bus section is:

[0171] Condition 1: The positive-sequence phase voltage U 1 ≦40V;

[0172] Condition 2: The negative-sequence phase voltage U 2 ≥3V;

[0173] Condition 3: The impedance angles of the three positive directions are all satisfied with 45° ≤ arg(U ΦΦ / I ΦΦ ) ≤ 90°;

[0174] Condition 4: The zero-sequence current 3I 0 ≥ the minimum zero-sequence current setting value allowed for the user to trip;

[0175] Condition 5: The negative-sequence current 3I 2 ≥ the minimum zero-sequence current setting value allowed for the user to trip.

[0176] In addition, for the transformer protection device judged as the faulty busbar, continue to calculate the phase selection logic and direction element. If the phase selection logic selects a new faulty phase, the distance measurement and timing should also be based on the new faulty phase. The calculation methods of the phase-to-phase and ground impedance are the same as those calculated 20 ms after startup.

[0177] Optionally, according to the fault direction and the operating time of the impedance protection, adopt the corresponding protection strategy to perform the corresponding backup protection action on the transformer, including: when the phase-to-phase or ground direction element judges a positive-direction fault, measure the impedance of the faulty phase selected by the phase selection element and time the protection distance measurement, and delay the action according to the calculated operating time of the impedance protection. When the positive-direction distance protection delay expires, directly trip the three-side circuit breakers of the transformer.

[0178] In the embodiment of the present invention, as shown in Figure 3 , the positive-direction action logic includes the positive-direction action logic for phase-to-phase faults and the positive-direction logic for ground faults. Among them, Figure 3 T4 shown is the calculated time limit obtained by measuring the impedance of the faulty phase selected by the phase selection element and timing after the positive-direction discrimination is established. The timing formula is the calculation formula proposed in the above step 104. As Figure 3 shown, when the positive-direction distance protection delay expires, directly trip the three-side circuit breakers of the transformer. If both the positive-direction and reverse-direction fault criteria are established, then measure the distance according to the positive-direction distance protection and time it, and trip according to the relevant regulations.

[0179] In addition, the cooperation method with the adjacent line distance protection is: when the distance protection of the transformer's lower-level line also adopts the distance measurement formula and timing formula in steps 103 and 104, the transformer backup protection adds 5 km to the distance measurement result to ensure that the transformer impedance protection strictly cooperates with the lower-level line distance protection in the case of a reverse-direction fault.

[0180] Therefore, for the backup protection of transformers, the present invention proposes a method for online self-tuning backup protection of transformers with an ultra-long protection range. It does not require users to set impedance values and time values. The operating time is automatically calculated based on fault location measurement and can be strictly coordinated with the online self-tuning distance protection of the downstream line. Therefore, the present invention can not only be used as the backup protection of the transformer body but also as the ultra-long-distance backup protection of adjacent lines, realizing the online automatic tuning of the protection device settings, reducing the workload of setting calculation, improving the efficiency of setting calculation, and achieving the purpose of intelligent tuning through the protection settings. Thus, the problem of severely insufficient sensitivity when the transformer protection acts as the backup protection for adjacent long lines is solved. Moreover, compared with the traditional composite voltage overcurrent protection, it has the advantage of eliminating the need to set time values and impedance values, greatly reducing the workload of setting calculation for operating personnel.

[0181] Exemplary system

[0182] Figure 4 FIG. is a schematic structural diagram of an online self-tuning backup protection system for transformers provided by an exemplary embodiment of the present invention. As Figure 4 shown, the system 400 includes:

[0183] A fault phase discrimination module 410, configured to discriminate the fault phase of the transformer through a phase selection element;

[0184] A fault direction discrimination module 420, configured to discriminate the fault direction of the transformer;

[0185] A first calculation module 430, configured to calculate the fault impedance of the transformer by using a calculation strategy corresponding to the fault phase and calculate the protection distance measurement of the transformer based on the fault impedance;

[0186] A second calculation module 440, configured to calculate the impedance protection operating time of the transformer according to the protection distance measurement;

[0187] A backup protection action module 450, configured to perform corresponding backup protection actions on the transformer according to the fault direction and the impedance protection operating time by using a corresponding protection strategy.

[0188] Optionally, the fault phase discrimination module 410 is specifically configured to:

[0189] After the phase selection element is activated, obtain the amplitude of the load positive-sequence current for a certain time before the transformer fault;

[0190] Calculate the amplitudes of the three single-phase currents after the transformer fault;

[0191] Based on the amplitude of the load positive-sequence current and the amplitudes of the three single-phase currents, discriminate the fault phase of the transformer according to a preset discrimination condition, where the fault phase includes interphase faults, three-phase faults, and single-phase faults.

[0192] Optionally, the fault direction discrimination module 420 is specifically configured to:

[0193] Discriminate whether a fault occurs in the reverse direction / forward direction of the transformer according to a preset discrimination rule;

[0194] Determine the fault direction of the transformer according to the discrimination result.

[0195] Optionally, discriminating whether a fault occurs in the reverse direction of the transformer according to a preset discrimination rule includes:

[0196] Discriminate whether the zero-sequence reverse direction element of the transformer operates to obtain a first result;

[0197] Discriminate whether the negative-sequence reverse direction element of the transformer operates to obtain a second result;

[0198] Discriminate whether at least two of the three phase-to-phase reverse direction elements of the transformer operate to obtain a third result;

[0199] Discriminate whether a fault occurs in the reverse direction of the transformer according to the first result, the second result, and the third result.

[0200] Optionally, discriminating whether a fault occurs in the forward direction of the transformer according to a preset discrimination rule includes:

[0201] Discriminate whether the zero-sequence forward direction element of the transformer operates to obtain a fourth result;

[0202] Discriminate whether the negative-sequence forward direction element of the transformer operates to obtain a fifth result;

[0203] Discriminate whether at least two of the three phase-to-phase forward direction elements of the transformer operate to obtain a sixth result;

[0204] Discriminate whether a fault occurs in the forward direction of the transformer according to the fourth result, the fifth result, and the sixth result.

[0205] Optionally, when the fault phase is an interphase short circuit fault, the first calculation module 430 is specifically configured to:

[0206] Calculate the fault impedance Z of the transformer using the following formula C :

[0207]

[0208] In the formula, U ΦΦ is the real-time voltage, and I ΦΦ is the real-time current;

[0209] And, calculate the protection ranging of the transformer using the following formula:

[0210] L C = ZC / Z 1

[0211] Wherein, Z C is the fault impedance of the transformer during phase - to - phase short - circuit fault, and Z 1 is the positive - sequence impedance per unit length.

[0212] Optionally, when the fault phase is a single - phase - to - ground short - circuit fault, the first calculation module 430 is specifically configured to:

[0213] Use the following formula as the calculation formula for the iterative starting point to calculate the fault impedance Z of the transformer C(0) :

[0214]

[0215] Wherein, k = (Z 0 -Z 1 ) / 3Z 1 is the zero - sequence compensation coefficient, is the zero - sequence current measured at the protection installation location, θ is the positive - sequence impedance angle of the line, Z m is the measured impedance, is the measured phase voltage of phase A, is the measured phase current of phase A, and j is the imaginary symbol;

[0216] During each iterative calculation, perform iterative operations according to whether the criterion is met, where the condition for the criterion to be met is:

[0217]

[0218] And, use the following formula to calculate the protection distance measurement L of the transformer C :

[0219] L C = |Z C(n) | / Z 1

[0220] Wherein, Z C(n) is the fault impedance of the transformer during single - phase - to - ground short - circuit fault after n - th iterative calculation, and Z 1 is the positive - sequence impedance per unit length.

[0221] Optionally, the calculation formula for the operating time t op of the impedance protection of the transformer is as follows:

[0222]

[0223] Wherein, t op.max is the longest operating time of the backup protection set by the user, L C is the protection distance measurement of the transformer, L is the total length of the line, and tj The meaning is shown in the following formula:

[0224]

[0225] In the formula, L max is the maximum line full length of the transformer, and T max is the longest protection time of the transformer.

[0226] Optionally, the backup protection action module 450 is specifically configured to:

[0227] When there is a phase-to-phase or ground directional element judging a reverse-direction fault and the phase current or zero-sequence current that allows tripping set by the user is satisfied, time with the calculated fault phase impedance. Add oscillation blocking when the timing is less than 1.5 s and trip, cancel oscillation blocking when the timing exceeds 1.5 s and trip, trip the sectionalizer when reaching the user-set sectionalizer tripping time, or trip the bus coupler when reaching the bus coupler tripping time, and confirm the faulty bus section after the bus coupler is tripped.

[0228] Optionally, the backup protection action module 450 is specifically configured to:

[0229] When the zero-sequence directional element judges a reverse direction, time according to the calculated fault impedance and protection ranging, and trip according to the time set by the user for tripping the sectionalizer or bus coupler. After the bus coupler is tripped, confirm the faulty bus section;

[0230] Delay the action according to the impedance protection action time calculated. Add oscillation blocking when the timing is less than 1.5 s and trip, cancel oscillation blocking when the timing exceeds 1.5 s and trip.

[0231] Optionally, after the bus coupler is tripped, if one of the following 5 conditions is met, it is judged as the faulty bus section:

[0232] Condition 1: Positive-sequence phase voltage U 1 ≤ 40 V;

[0233] Condition 2: Negative-sequence phase voltage U 2 ≥ 3 V;

[0234] Condition 3: All three positive-direction phase impedance angles satisfy 45° ≤ arg(U ΦΦ / I ΦΦ ) ≤ 90°;

[0235] Condition 4: Zero-sequence current 3I 0 ≥ the minimum zero-sequence current setting value allowed by the user for tripping;

[0236] Condition 5: Negative-sequence current 3I 2 ≥ the minimum zero-sequence current setting value allowed by the user for tripping.

[0237] Optionally, the backup protection action module 450 is specifically configured to:

[0238] When a phase - to - phase or ground directional element determines a positive - direction fault, measure the fault - phase impedance and protection distance measurement according to the fault phase selected by the phase - selection element, and delay the action according to the impedance protection action time calculated. When the positive - direction distance protection delay expires, directly trip the three - side circuit breakers of the transformer.

[0239] The on - line self - tuning transformer backup protection system 400 according to the embodiment of the present invention corresponds to the on - line self - tuning transformer backup protection method 100 according to another embodiment of the present invention, and will not be elaborated here.

[0240] Exemplary electronic device

[0241] Figure 5 It is the structure of an electronic device provided by an exemplary embodiment of the present invention. The electronic device can be any one or both of the first device and the second device, or a stand - alone device independent of them, and the stand - alone device can communicate with the first device and the second device to receive the input signals collected from them. Figure 5 The block diagram of the electronic device according to the embodiment of the present invention is illustrated. As Figure 5 shown, the electronic device 50 includes one or more processors 51 and a memory 52.

[0242] The processor 51 can be a central processing unit (CPU) or other forms of processing units with data - processing capabilities and / or instruction - execution capabilities, and can control other components in the electronic device to perform desired functions.

[0243] The memory 52 can include one or more computer program products, and the computer program products can include various forms of computer - readable storage media, such as volatile memory and / or non - volatile memory. The volatile memory can include, for example, random access memory (RAM) and / or cache memory, etc. The non - volatile memory can include, for example, read - only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions can be stored on the computer - readable storage media, and the processor 51 can run the program instructions to implement the software programs of the various embodiments of the present invention described above for the on - line self - tuning transformer backup protection method and / or other desired functions. In one example, the electronic device may further include: an input system 53 and an output system 54, and these components are interconnected through a bus system and / or other forms of connection mechanisms (not shown).

[0244] In addition, the input system 53 may further include, for example, a keyboard, a mouse, etc.

[0245] The output system 54 can output various information externally. The output device 54 can include, for example, a display, a speaker, a printer, a communication network, and remote output devices connected thereto, etc.

[0246] Of course, for simplicity, Figure 5 only some of the components related to the present invention in the electronic device are shown, and components such as buses, input / output interfaces, etc. are omitted. In addition, according to specific application scenarios, the electronic device may further include any other appropriate components.

[0247] Exemplary computer program product and computer-readable storage medium

[0248] In addition to the above methods and devices, an embodiment of the present invention may also be a computer program product, which includes computer program instructions that, when run by a processor, cause the processor to execute the steps in the online self-tuning transformer backup protection method according to various embodiments of the present invention described in the "Exemplary Method" section above of this specification.

[0249] The computer program product can be written in any combination of one or more programming languages for programming code to perform the operations of the embodiments of the present invention. The programming languages include object-oriented programming languages such as Java, C++, etc., and also include conventional procedural programming languages such as the "C" language or similar programming languages. The programming code can be executed entirely on the user computing device, partially on the user device, executed as an independent software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0250] Furthermore, an embodiment of the present invention may also be a computer-readable storage medium, on which computer program instructions are stored, and when the computer program instructions are run by a processor, cause the processor to execute the steps in the online self-tuning transformer backup protection method according to various embodiments of the present invention described in the "Exemplary Method" section above of this specification.

[0251] The computer-readable storage medium may adopt any combination of one or more readable media. The readable media may be a readable signal medium or a readable storage medium. The readable storage medium may include, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (a non-exhaustive list) of the readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0252] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, benefits, effects, etc. mentioned in the present invention are only examples and not limitations. It cannot be considered that these advantages, benefits, effects, etc. are essential for each embodiment of the present invention. In addition, the above-disclosed specific details are only for illustrative and easy-to-understand purposes and are not limitations. The above details do not limit the present invention to necessarily adopt the above specific details for implementation.

[0253] Each embodiment in this specification is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference may be made to each other. For the system embodiment, since it basically corresponds to the method embodiment, the description is relatively simple. For the relevant parts, reference may be made to the partial description of the method embodiment.

[0254] The block diagrams of the devices, systems, equipment, and systems involved in the present invention are only illustrative examples and do not intend to require or imply that they must be connected, arranged, and configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, systems, equipment, and systems can be connected, arranged, and configured in any way. Words such as "including", "comprising", "having", etc. are open-ended words, meaning "including but not limited to", and can be used interchangeably with each other. The word "or" and "and" used herein refer to the word "and / or", and can be used interchangeably with each other, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to", and can be used interchangeably with each other.

[0255] The methods and systems of the present invention can be implemented in many ways. For example, the methods and systems of the present invention can be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above order of steps for the methods is for illustration only, and the steps of the methods of the present invention are not limited to the specific order described above, unless otherwise specifically stated. In addition, in some embodiments, the present invention can also be implemented as a program recorded in a recording medium, and these programs include machine-readable instructions for implementing the methods according to the present invention. Therefore, the present invention also covers a recording medium storing a program for executing the methods according to the present invention.

[0256] It should also be noted that in the systems, devices, and methods of the present invention, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent solutions of the present invention. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

[0257] The above description has been given for purposes of illustration and description. In addition, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. An online self-tuning backup protection method for transformers, characterized in that, it includes: Identifying the fault phase of the transformer through a phase selection element; Identifying the fault direction of the transformer; Adopting a calculation strategy corresponding to the fault phase to calculate the fault impedance of the transformer, and calculating the protection distance measurement of the transformer based on the fault impedance; Calculating the operating time of the impedance protection of the transformer according to the protection distance measurement; According to the fault direction and the operating time of the impedance protection, adopting a corresponding protection strategy to perform corresponding backup protection actions on the transformer, including: When the interphase or ground direction element determines a reverse-direction fault and the phase current or zero-sequence current that allows tripping set by the user is satisfied, time with the calculated interphase fault impedance. When the time is less than the preset period and an oscillation blocking is added when it operates, and the oscillation blocking is cancelled when the time exceeds the preset period and trips. When reaching the user's segment tripping time, trip the segment, or when reaching the bus-coupler tripping time, trip the bus-coupler, and confirm the faulty bus section after the bus-coupler is tripped; According to the fault direction and the operating time of the impedance protection, adopting a corresponding protection strategy to perform corresponding backup protection actions on the transformer, further including: When the interphase or ground direction element determines a forward-direction fault, time with the fault phase impedance selected by the phase selection element and the protection distance measurement, and delay the operation according to the calculated operating time of the impedance protection. When the forward-direction distance protection times out, directly trip the three-side circuit breakers of the transformer.

2. The method according to claim 1, characterized in that, Identifying the fault phase of the transformer through a phase selection element includes: After the phase selection element starts, obtaining the amplitude of the positive-sequence load current of the transformer for a certain time before the fault; Calculating the amplitudes of the three single-phase currents after the transformer fault; Based on the amplitude of the positive-sequence load current and the amplitudes of the three single-phase currents, identifying the fault phase of the transformer according to the preset discrimination conditions, where the fault phases include interphase faults, three-phase faults, and single-phase faults.

3. The method according to claim 1, characterized in that, Identifying the fault direction of the transformer includes: Identifying whether a reverse / forward fault occurs in the transformer according to the preset discrimination rules; Determining the fault direction of the transformer according to the discrimination result.

4. The method according to claim 3, characterized in that, Identifying whether a reverse fault occurs in the transformer according to the preset discrimination rules includes: Identifying whether the zero-sequence reverse-direction element of the transformer operates to obtain a first result; Identifying whether the negative-sequence reverse-direction element of the transformer operates to obtain a second result; Identifying whether at least two of the three interphase reverse-direction elements of the transformer operate to obtain a third result; Identifying whether a reverse fault occurs in the transformer according to the first result, the second result, and the third result.

5. The method according to claim 3, characterized in that, Identifying whether a forward fault occurs in the transformer according to the preset discrimination rules includes: Identifying whether the zero-sequence forward-direction element of the transformer operates to obtain a fourth result; Identifying whether the negative-sequence forward-direction element of the transformer operates to obtain a fifth result; Identifying whether at least two of the three interphase forward-direction elements of the transformer operate to obtain a sixth result; Based on the fourth result, the fifth result, and the sixth result, determine whether a fault occurs in the positive direction of the transformer.

6. The method according to claim 1, wherein, when the fault phase is an interphase short - circuit fault, the method further includes: Calculate the fault impedance Z of the transformer using the following formula C : Where, U ΦΦ is the real-time voltage, and I ΦΦ is the real-time current; and calculating the protection distance measurement of the transformer using the following formula: L C = Z C / Z 1 Wherein, Z C is the fault impedance of the transformer during phase-to-phase short-circuit fault, and Z 1 is the positive-sequence impedance per unit length.

7. The method according to claim 1, wherein, when the fault phase is a single - phase - to - ground short - circuit fault, the method further includes: Use the following formula as the calculation formula for the iterative starting point to calculate the fault impedance Z of the transformer C(0) :[[]]END]] where k = (Z 0 - Z 1 ) / 3Z 1 is the zero-sequence compensation coefficient, is the zero-sequence current measured at the protection installation location, θ is the positive-sequence impedance angle of the line, Z m is the measured impedance, is the measured phase voltage of phase A, is the measured phase current of phase A, and j is the imaginary symbol; during each iterative calculation, perform iterative operations according to whether the criterion is met, where the condition for the criterion to be met is: And, the protection distance measurement L of the transformer is calculated using the following formula C :[[]]END]] L C = |Z C(n) | / Z 1 Where, Z C(n) is the fault impedance of the transformer when a single-phase ground short-circuit fault occurs after n times of iterative calculation, and Z 1 is the positive-sequence impedance per unit length.

8. The method according to claim 1, wherein, The operating time t of the impedance protection of the transformer op is calculated as follows: where t op.max is the longest operating time of the backup protection set by the user, L C is the protection distance measurement of the transformer, L is the total length of the line, and t j is defined as follows: Wherein, L max is the maximum line full length of the transformer, and T max is the longest protection time of the transformer.

9. The method according to claim 1, wherein, according to the fault direction and the impedance protection operating time, adopt corresponding protection strategies to perform corresponding backup protection actions on the transformer, including: when the zero - sequence direction element determines the reverse direction, set the timing by itself according to the calculated fault impedance and protection distance measurement, and trip according to the time set by the user to trip the sectionalizer or the bus - tie breaker. After the bus - tie breaker trips, confirm the faulty bus section; delay the operation according to the calculated impedance protection operating time. Add oscillation blocking when the timing is less than the preset period, and cancel the oscillation blocking when the timing exceeds the preset period and trips.

10. The method according to claim 1 or 9, wherein, after the bus - tie breaker trips, if one of the following 5 conditions is met, it is determined that the bus section has a fault: Condition 1: Positive-sequence phase voltage U 1 ≤ 40 V; Condition 2: Negative-sequence phase voltage U 2 ≥ 3V; Condition 3: The impedance angles in three positive directions all satisfy 45° ≤ arg(U ΦΦ / I φφ ) ≤ 90°; Condition 4: Zero-sequence current 3I 0 ≥ The minimum zero-sequence current setting value at which the user allows tripping; Condition Five: Negative sequence current 3I 2 ≥ The minimum zero-sequence current setting value allowed for the user to trip the circuit breaker.

11. An on - line self - tuning backup protection system for a transformer, wherein, including: a fault phase discrimination module for discriminating the fault phase of the transformer through a phase - selection element; a fault direction discrimination module for discriminating the fault direction of the transformer; a first calculation module for calculating the fault impedance of the transformer using a calculation strategy corresponding to the fault phase and calculating the protection distance measurement of the transformer based on the fault impedance; a second calculation module for calculating the impedance protection operating time of the transformer according to the protection distance measurement; a backup protection action module for performing corresponding backup protection actions on the transformer according to the fault direction and the impedance protection operating time using corresponding protection strategies; the backup protection action module is specifically configured to, when there is an interphase or ground direction element determining a reverse - direction fault and the phase current or zero - sequence current that allows tripping set by the user is satisfied, time using the calculated inter - phase fault impedance. Add oscillation blocking when the timing is less than the preset period, cancel the oscillation blocking when the timing exceeds the preset period and trips, trip the sectionalizer when reaching the user - set sectionalizer tripping time, or trip the bus - tie breaker when reaching the bus - tie breaker tripping time, and confirm the faulty bus section after the bus - tie breaker trips; the backup protection action module is specifically configured to, when there is an interphase or ground direction element determining a positive - direction fault, time according to the fault - phase impedance selected by the phase - selection element and the protection distance measurement, delay the operation according to the calculated impedance protection operating time, and when the positive - direction distance protection delay expires, directly trip the three - side circuit breakers of the transformer.

12. A computer - readable storage medium, wherein, the storage medium stores a computer program, and the computer program is used to execute the method according to any one of claims 1 - 10 above.

13. An electronic device, wherein, the electronic device includes: a processor; A memory for storing the processor-executable instructions; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method according to any one of claims 1-10 above.

Images