Transformer differential protection method and system based on fault negative sequence component pointing

Abstract

The application provides a transformer differential protection method and system based on a fault negative sequence component direction. The method comprises: judging whether a fault negative sequence component direction discrimination element meets a first discrimination condition; judging whether a proportional differential element meets a second discrimination condition; and starting a transformer differential protection action in the case that the fault negative sequence component direction discrimination element meets the first discrimination condition and the proportional differential element meets the second discrimination condition. The protection method does not block through the transformer excitation inrush current, ensures that the fault is quickly removed in the case of an internal fault, the protection action time is less than three quarters of a cycle, and the protection action is not mis-operated in various external faults and abnormal operating conditions.

Description

Technical Field

[0001] This application relates to the field of power system relay protection, and more specifically, to a transformer differential protection method and system based on the pointing of fault negative sequence components. Background Technology

[0002] During the construction of new power systems, a large number of new energy sources and flexible transmission equipment are connected to the power system. When these devices are in operation, they often generate abundant harmonic components in the event of system faults. Furthermore, when system disturbances occur (such as transformer failures), the control process of flexible transmission equipment will also cause controlled changes in the fault current, resulting in a high harmonic content in the current waveform. These harmonic components cause harmonic pollution to relay protection, interfering with current transformer differential protection systems that have inrush current blocking criteria. This leads to increasingly slower main protection operating speeds, making it difficult to meet the operating speed requirements of large-capacity transformers or core main equipment transformers. Related differential protection systems face the problem of insufficient speed of operation, and may even cause protection failure to operate, resulting in decreased reliability.

[0003] 1. Due to factors such as system wiring method and power supply characteristics, when a transformer experiences an asymmetrical fault, such as a short circuit between transformer turns or a single-phase grounding, the transformer differential protection needs to eliminate the zero-sequence component during the star-delta change process. This causes electrical characteristic coupling between the faulty phase and the non-faulty phase, which may lead to an increase in the differential current harmonic content of the faulty phase and affect the start-up of the excitation inrush current criterion.

[0004] 2. In numerical analysis, integral algorithms based on Fourier decomposition are commonly used to calculate the effective values ​​of the fundamental frequency and harmonics, and then to calculate the harmonic content. More accurate Fourier algorithms require calculations using sampled data over a complete cycle, necessitating a relatively long analysis data window. Especially in applications with low fundamental frequencies and long periods (e.g., low-frequency power transmission systems), the analysis time required to calculate harmonic content and analyze waveform distortion using Fourier integration increases significantly.

[0005] The half-wave Fourier algorithm with a shorter data window requires sampling data within half a cycle for calculation, which can shorten the calculation time to some extent. However, due to the shortened calculation time window, the calculation error of the fundamental effective value and the effective value of the harmonics increases, which in turn leads to an increase in the error of the harmonic content calculation result.

[0006] 3. Although current transformer differential protection includes differential instantaneous overcurrent protection without harmonic blocking, and typical static mode tests can achieve a very fast operating speed (no more than 20ms), it needs to avoid the transformer's no-charge inrush current, and generally sets a very high setting threshold. Therefore, the differential instantaneous overcurrent protection can only reflect severe faults within the transformer zone. In addition, new energy equipment and flexible transmission equipment generally adopt current limiting strategies to ensure the safety of such equipment under system fault conditions. This results in the short-circuit current during system faults being significantly smaller than that during conventional power system faults, making it difficult for the short-circuit current to reach the differential instantaneous overcurrent setting value during transformer zone faults. At the same time, the aforementioned current limiting strategies also cause controlled changes in the fault current during the fault process. Using Fourier algorithm calculations can generate a large number of computational harmonics, causing the proportional differential protection to be continuously blocked.

[0007] 4. New energy equipment and flexible power transmission equipment are generally equipped with fast overcurrent protection to ensure equipment safety. When a fault occurs in the transformer area, if the transformer differential protection cannot act quickly, it may cause the fast overcurrent protection to trip and cut off the power supply, resulting in problems such as the expansion of the fault range and the inability to accurately locate the fault point.

[0008] 5. According to statistics, 40% of faults within the differential operating range of a transformer are internal. Taking inter-turn short circuits as an example, when an inter-turn short circuit occurs in a transformer, a circulating current tens of times the transformer's rated current will be generated within the short-circuited coil. This will generate a large amount of heat and magnetic force, further damaging the insulation and dynamic stability of the transformer's internal coils, easily leading to serious consequences such as damage to the transformer core (resulting in the transformer being completely scrapped) and ignition of the transformer oil (causing a fire disaster).

[0009] Therefore, the rapid fault clearing of transformer differential protection is of great significance for the safe and stable operation of the power grid, ensuring the safety of transformer equipment, and improving the speed and efficiency of on-site fault handling.

[0010] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0011] This application aims to provide a transformer differential protection method and system based on the fault negative sequence component pointing. This protection does not require transformer inrush current blocking, ensuring rapid fault clearing under fault conditions within the protection zone, with a protection operation time of less than three-quarters of a cycle, and does not malfunction under various fault conditions outside the protection zone and abnormal operating conditions.

[0012] According to a first aspect of this application, a transformer differential protection method based on the fault negative sequence component pointing is proposed, the method comprising:

[0013] Determine whether the fault negative sequence component pointing to the discrimination element meets the first discrimination condition;

[0014] Determine whether the proportional differential element meets the second discrimination condition;

[0015] When the fault negative sequence component points to the discrimination element and meets the first discrimination condition, and the proportional differential element meets the second discrimination condition, the transformer differential protection is activated.

[0016] According to some embodiments, determining whether the fault negative sequence component pointing to the discrimination element meets the first discrimination condition includes making a judgment based on the negative sequence high braking differential equation, wherein:

[0017] The negative-order high-braking differential equation is:

[0018]

[0019] Where k1 is a proportionality constant; I 12 ~I m2 These are the negative sequence currents on each side of the transformer, where m is a natural number; I r2 For negative sequence braking current, I d2 For negative-order differential current, I qd_set This is the minimum operating setting for the negative sequence differential current of the transformer;

[0020] If the negative sequence differential current conforms to the negative sequence high braking differential equation, it is determined that the fault negative sequence component points to the discrimination element and meets the first discrimination condition.

[0021] According to some embodiments, determining whether the fault negative sequence component pointing to the discrimination element meets the first discrimination condition includes judging based on the negative sequence current on each side of the transformer, wherein:

[0022] The phase of the negative sequence current on each side of the transformer is in the operating region of the fault negative sequence component pointing to the discrimination element, and the fault negative sequence component pointing to the discrimination element meets the first discrimination condition;

[0023] The fault negative sequence component points to the action area of ​​the discrimination element, which includes the region formed by the leading deviation boundary and the lagging deviation boundary.

[0024] With the phase of the negative sequence current vector on the high-voltage side of the transformer as a reference, the leading deviation boundary is the phase of the negative sequence current on the high-voltage side plus an angle θ, and the lagging deviation boundary is the phase of the negative sequence current on the high-voltage side minus an angle θ, where the angle θ is a constant value.

[0025] According to some embodiments, determining whether the proportional differential element meets the second discrimination condition includes:

[0026] Calculate the differential operating equation based on the phase currents on each side of the transformer;

[0027]

[0028] Where, k b1 k b2 k b3 I is a proportionality constant; h1 I h2 I1~I is the inflection point constant; m These represent the phase currents on each side of the transformer, where m is a natural number and I... d For differential current, I r For braking current, I cdqd This is the minimum operating setting for the transformer proportional differential;

[0029] When the differential current satisfies the differential action equation, the proportional differential element meets the second discrimination condition.

[0030] According to some embodiments, the transformer differential protection method further includes:

[0031] The fault negative sequence component pointing discrimination element is determined based on the voltage change of the power frequency.

[0032] The fault negative sequence component pointing to the discrimination element is determined based on the voltage drop value.

[0033] The fault negative sequence component pointing to the discrimination element is determined based on the negative sequence current on each side of the transformer.

[0034] According to some embodiments, the step of determining whether to activate the fault negative sequence component pointing discrimination element based on the power frequency change voltage includes:

[0035] Determine whether the voltage change at power frequency conforms to the voltage change at power frequency discrimination equation;

[0036] When the power frequency change voltage conforms to the power frequency change voltage discrimination equation, the fault negative sequence component is applied to the discrimination element.

[0037] According to some embodiments, the voltage discrimination equation for the power frequency change is:

[0038] ΔU d >k d ΔU dt +U dth

[0039] Wherein, ΔU dt For a floating threshold, k d ΔU is a proportionality constant. d U is the voltage change at power frequency. dth For fixed thresholds.

[0040] According to some embodiments, the step of determining whether to open the fault negative sequence component pointing discrimination element based on the voltage drop value includes:

[0041] When the positive sequence voltage drops to the first voltage threshold, or the negative sequence voltage rises to the second voltage threshold, or the zero sequence voltage rises to the third voltage threshold, the fault negative sequence component pointing to the discrimination element is enabled.

[0042] According to some embodiments, the step of determining whether to open the fault negative sequence component pointing discrimination element based on the negative sequence current on each side of the transformer includes:

[0043] When the effective value of the negative sequence current on the high-voltage side of the transformer and the effective values ​​of the negative sequence current on other sides are greater than the threshold value, the fault negative sequence component pointing to the discrimination element is opened.

[0044] According to a second aspect of this application, a transformer differential protection system based on the pointing of a fault negative sequence component is proposed, the system comprising:

[0045] The fault negative sequence component points to the discrimination element, which is used to determine whether the first discrimination condition is met based on the negative sequence high braking differential equation or the negative sequence current on other sides of the transformer.

[0046] The proportional differential element is used to calculate the differential action equation based on the phase currents on each side of the transformer and determine whether the second discrimination condition is met.

[0047] The starting element is used to receive an indication signal indicating that the fault negative sequence component points to the discrimination element meeting the first discrimination condition and the proportional differential element meeting the second discrimination condition, and to start the transformer differential protection operation in response to the indication signal.

[0048] According to some embodiments, the fault negative sequence component pointing discrimination element includes a negative sequence high braking differential element, used to determine whether the first discrimination condition is met based on the negative sequence high braking differential equation:

[0049] The negative-order high-braking differential equation is:

[0050]

[0051] Where k1 is a proportionality constant; I 12 ~I m2 These are the negative sequence currents on each side of the transformer, where m is a natural number; I r2 For negative sequence braking current, I d2 For negative-order differential current, I qd_set This is the minimum operating setting for the negative sequence differential current of the transformer;

[0052] When the negative-sequence high-braking differential element determines that the negative-sequence differential current satisfies the negative-sequence high-braking differential equation, the fault negative-sequence component pointing to the discrimination element satisfies the first discrimination condition.

[0053] According to some embodiments, the fault negative sequence component pointing to the discrimination element includes:

[0054] A directional element is used to determine whether the first discrimination condition is met based on the negative sequence current on each side of the transformer, wherein:

[0055] The phase of the negative sequence current on each side of the transformer is in the fault negative sequence component pointing to the operation area of ​​the discrimination element, which meets the first discrimination condition;

[0056] The fault negative sequence component points to the action area of ​​the discrimination element, which includes the region formed by the leading deviation boundary and the lagging deviation boundary.

[0057] With the phase of the negative sequence current vector on the high-voltage side of the transformer as a reference, the leading deviation boundary is the phase of the negative sequence current on the high-voltage side plus an angle θ, and the lagging deviation boundary is the phase of the negative sequence current on the high-voltage side minus an angle θ, where the angle θ is a constant value.

[0058] According to some embodiments, the proportional differential element is used for:

[0059] Calculate the differential operating equation based on the phase currents on each side of the transformer;

[0060]

[0061] Where, k b1 k b2 k b3 I is a proportionality constant; h1 I h2 I1~I is the inflection point constant; m These represent the phase currents on each side of the transformer, where m is a natural number and I... d For differential current, I r For braking current, I cdqd This is the minimum operating setting for the transformer proportional differential;

[0062] If the differential current satisfies the differential action equation, the proportional differential element is determined to meet the second discrimination condition.

[0063] According to some embodiments, the transformer differential protection system further includes:

[0064] A power frequency change voltage element is used to determine whether the power frequency change voltage meets the discrimination equation, and if the power frequency change voltage meets the discrimination equation, the power frequency change voltage element performs an action; wherein:

[0065] The discriminant equation is:

[0066] ΔU d >k d ΔU dt +U dth

[0067] Where, ΔU dt For a floating threshold, k d ΔU is a proportionality constant. d U is the voltage change at power frequency. dth For fixed thresholds.

[0068] According to some embodiments, the fault negative sequence component pointing to the discrimination element is used to perform an activation action when the power frequency change voltage element is activated.

[0069] According to some embodiments, the transformer differential protection system further includes:

[0070] Voltage imbalance sag element, used to determine whether to activate based on the voltage sag value;

[0071] The fault negative sequence component indicates that the discrimination element responds to the voltage imbalance drop element by performing an open operation.

[0072] According to some embodiments, the voltage imbalance sag element is used for:

[0073] The action is determined to be performed when the positive sequence voltage drops to the first voltage threshold, the negative sequence voltage rises to the second voltage threshold, or the zero sequence voltage rises to the third voltage threshold.

[0074] According to some embodiments, the fault negative sequence component pointing to the discrimination element is further used for:

[0075] If the effective value of the negative sequence current on the high-voltage side of the transformer and the effective value of the negative sequence current on other sides are greater than the threshold setting, the opening action will be performed.

[0076] This application provides a transformer differential protection method and system based on the fault negative sequence component pointing. The protection method and system do not require transformer inrush current blocking, ensuring rapid fault clearing in the case of faults within the zone, with the protection action time being less than three-quarters of a cycle, and without malfunctioning under various faults outside the zone and abnormal operating conditions.

[0077] This application adopts a transformer differential protection method and system based on the fault negative sequence component pointing principle: In the early stage of a fault within the transformer zone, the location of the asymmetrical fault source can be quickly located by judging the fault negative sequence component pointing element, thereby improving the speed of transformer differential protection, which can reach up to half the fundamental frequency. At the same time, it will not malfunction during transformer energization, fault clearing and recovery of external faults, or CT saturation of external faults, so that the transformer proportional differential protection can take into account both speed and safety.

[0078] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0079] The above and other objects, features, and advantages of this application will become more apparent from the detailed description of exemplary embodiments with reference to the accompanying drawings. The drawings described below are merely some embodiments of this application and are not intended to limit the scope of this application.

[0080] Figure 1 A schematic diagram of a transformer differential protection system based on the pointing of a fault negative sequence component is shown as an exemplary embodiment;

[0081] Figure 2 A schematic flowchart of a transformer differential protection method based on fault negative sequence component pointing is shown as an exemplary embodiment.

[0082] Figure 3 A schematic diagram of the operating region of a negative sequence current direction element in an exemplary embodiment is shown.

[0083] Figure 4 A schematic diagram of a fault negative sequence component pointing to a discrimination element is shown in an exemplary embodiment. Detailed Implementation

[0084] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0085] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0086] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0087] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0088] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments, and the modules or processes in the drawings are not necessarily essential for implementing this application, and therefore cannot be used to limit the scope of protection of this application.

[0089] Figure 1 A schematic diagram of a transformer differential protection system based on the pointing of a fault negative sequence component is shown as an exemplary embodiment.

[0090] like Figure 1 As shown, the transformer differential protection system includes a power frequency change voltage element 101, a voltage imbalance drop element 103, a fault negative sequence component pointing discrimination element 105, a proportional differential element 107, and a starting element 109.

[0091] According to the example embodiment, the power frequency change voltage element 101 is used to determine whether to operate based on a discrimination equation, wherein the discrimination equation is:

[0092] ΔU d >k d ΔU dt +U dth (1)

[0093] Where: ΔU dtThe threshold value is a floating value that gradually and automatically increases as the phase voltage surge output increases. d ΔU is a proportionality constant, ranging from 1.05 to 1.5; d U is the half-wave integral value of the phase voltage. dth For fixed thresholds.

[0094] According to the example embodiment, if the discrimination equation of the power frequency change voltage element 101 is met, the power frequency change voltage element 101 will be activated; after the power frequency change voltage element 101 is activated, the fault negative sequence component is input to the discrimination element 105.

[0095] According to the example embodiment, the voltage imbalance drop element 103 is used to determine whether to operate according to a discrimination method, wherein the discrimination method is: when the positive sequence voltage drops to below 40-45V, or the negative sequence voltage rises to above 4-10V, or the zero sequence voltage rises to above 10-20V, the voltage imbalance drop element 103 operates; after the voltage imbalance drop element 103 operates, the fault negative sequence component is opened to the discrimination element 105.

[0096] According to the example embodiment, the fault negative sequence component pointing discrimination element 105 is used to determine the negative sequence current characteristics of each side of the transformer, and the effective value of the negative sequence current on the high-voltage side of the transformer is recorded as I. h2_amp Let the negative sequence current and effective value of other sides be I. o2_amp , when I h2_amp I o2_amp All are greater than the threshold value I 2_set At that time, the open fault negative sequence component points to the discrimination element, I 2_set The value ranges from 0.2 to 1 times the rated current of the transformer.

[0097] According to the example embodiment, such as Figure 4 As shown, the fault negative sequence component pointing discrimination element 105 also includes a negative sequence high braking differential element 1051, which is used to determine based on the negative sequence high braking differential equation:

[0098]

[0099] Where k1 is a proportionality constant, with a value ranging from 0.8 to 0.95; I 12 ~I m2 These are the negative sequence currents on each side of the transformer, where m is a natural number; I r2 For negative sequence braking current, I d2 For negative-order differential current, I qd_set The minimum operating setting value for the negative sequence differential current of the transformer is set to a value ranging from 0.5 to 1 times the rated current of the transformer. When the negative sequence high braking differential element 1051 determines that the negative sequence differential current satisfies equation 5, the negative sequence component of the fault points to the action of the discrimination element 105.

[0100] According to the example embodiment, such as Figure 4 As shown, the fault negative sequence component pointing discrimination element 105 also includes a direction element 1053. The direction element 1053 is used to determine the fault based on the negative sequence current on each side of the transformer, using the phase of the negative sequence current vector on the high-voltage side of the transformer as a reference. Figure 2 As shown, the phase of the negative sequence current vector on the high-voltage side plus an angle θ is the lead deviation boundary, and the phase of the negative sequence current vector on the high-voltage side minus an angle θ is the lag deviation boundary. The shaded area formed by the lead deviation boundary and the lag deviation boundary is the fault negative sequence component pointing to the action area of ​​the discrimination element; where the angle θ is a fixed angle value, ranging from 5° to 20°.

[0101] According to the example embodiment, the directional element 1053 determines that the phase of the negative sequence current on each side of the transformer falls within the operating region, and the fault negative sequence component points to the operation of the discrimination element 105.

[0102] According to the example embodiment, the proportional differential element 107 is used to calculate the differential operating equation based on the phase currents of each side of the transformer; wherein, the differential operating equation is described as follows:

[0103]

[0104] Where, k b1 k b2 k b3 I is a proportionality constant, ranging from 0 to 1; h1 I h2 The inflection point constant is taken as 0.2 to 6 times the transformer's rated current; I1 to I m These represent the phase currents on each side of the transformer, where m is a natural number and I... d For differential current, I r For braking current, I cdqd This is the minimum operating setting for the transformer's proportional differential, with a range of 0.05 to 2 times the transformer's rated current.

[0105] According to the example embodiment, I d If equation 3 is satisfied, then the proportional differential element 107 will operate.

[0106] According to the example embodiment, the starting element 109 is used to receive an indication signal indicating that the fault negative sequence component indicates that the discrimination element 105 meets the operating conditions and the proportional differential element 107 meets the operating conditions. When the starting element 109 receives the indication signal, it starts the transformer differential protection operation.

[0107] According to an example embodiment, this application provides a transformer differential protection system based on the fault negative sequence component pointing principle. This protection system does not require transformer inrush current blocking, ensuring rapid fault clearing in the case of faults within the zone, with a protection action time of less than three-quarters of a cycle, and does not malfunction under various faults outside the zone and abnormal operating conditions.

[0108] According to the example embodiment, this application adopts a transformer differential protection system based on the fault negative sequence component pointing principle: in the early stage of a fault in the transformer zone, the location of the asymmetrical fault source can be quickly located by judging the fault negative sequence component pointing element, thereby improving the speed of transformer differential protection, which can reach half the cycle of the fundamental frequency at the fastest; at the same time, it will not malfunction during transformer energization, fault clearing and recovery of external faults, or CT saturation of external faults, so that the transformer proportional differential can take into account both speed and safety.

[0109] Figure 2 A schematic flowchart of a transformer differential protection method based on fault negative sequence component pointing is shown as an exemplary embodiment.

[0110] like Figure 2 As shown, the fault negative sequence component points to the discrimination element, which includes two discrimination characteristics:

[0111] Characteristic 1, S201, determine whether the negative-order high braking differential equation is satisfied:

[0112] The fault negative sequence component points to the discrimination element based on the negative sequence high braking differential equation:

[0113]

[0114] Where k1 is a proportionality constant, with a value ranging from 0.8 to 0.95; I 12 ~I m2 These are the negative sequence currents on each side of the transformer, where m is a natural number; I r2 For negative sequence braking current, I d2 For negative-order differential current, I qd_set The minimum operating setting value for the negative sequence differential current of the transformer is 0.5 to 1 times the rated current of the transformer; the region that satisfies Equation 4 is the area where the negative sequence component of the fault points to the operating zone of the discrimination element.

[0115] According to the example embodiment, when an asymmetrical fault occurs outside the transformer zone, the negative sequence component of the short-circuit current exhibits a through-current characteristic. When the differential circuit experiences CT saturation, the negative sequence differential will generate a negative sequence differential current. Characteristic 1 equation employs a high braking current value and a high braking coefficient. This measure ensures that the fault negative sequence component pointing to the discrimination element has good characteristics to prevent CT saturation from causing false opening. Simultaneously, if CT saturation occurs within the zone due to a fault, the current in the linear transmission zone during the initial stage of the fault does not distort, and Characteristic 1 equation can still reflect the fault within the zone.

[0116] Feature 2, S202, determines the phase of the negative sequence current on each side of the transformer.

[0117] According to the example embodiment, the fault negative sequence component pointing discrimination element includes a directional element. The directional element determines the direction based on the phase of the negative sequence current on each side of the transformer, using the phase of the negative sequence current vector on the high-voltage side of the transformer as a reference. Figure 3 As shown, the phase of the negative sequence current vector on the high-voltage side plus an angle θ is the lead deviation boundary, and the phase of the negative sequence current vector on the high-voltage side minus an angle θ is the lag deviation boundary. The shaded area formed by the lead deviation boundary and the lag deviation boundary is the fault negative sequence component pointing to the action area of ​​the discrimination element; where the angle θ is a fixed angle value, ranging from 5° to 20°.

[0118] According to the example embodiment, the directional element of characteristic 2 requires that the phase of the negative sequence current on the high voltage side be used as a reference, and the phase of the negative sequence current on other sides is only allowed to deviate slightly from that on the high voltage side. That is, from the perspective of the differential circuit, the negative sequence current on each side of the transformer is required to be injected into the transformer in almost the same phase. This characteristic itself also has a good characteristic of preventing CT saturation from causing false opening.

[0119] When characteristic 1 satisfies the equation condition, i.e. S201; or when the phase of the negative sequence current on each side of the transformer in characteristic 2 falls within the operating region, i.e. S202; then the fault negative sequence component points to the action of the discrimination element and proceeds to S203.

[0120] According to the example embodiment, the high braking current value and high braking coefficient of characteristic 1, and the high in-phase requirement of characteristic 2, also have good anti-maloperation characteristics under abnormal operating conditions such as fault recovery outside the transformer area and inrush current caused by other transformers in the system being unloaded.

[0121] According to the example embodiment, the fault negative sequence component pointing discrimination element uses the transformer voltage change element to determine the start time of the first fault in the system: whether the power frequency change voltage element conforms to the equation, the voltage imbalance drop element, and the negative sequence current characteristics on each side of the transformer are used as open criteria for the fault negative sequence component pointing discrimination element.

[0122] S204, determines the voltage change at power frequency.

[0123] According to the example embodiment, the discrimination equation for determining the voltage change at power frequency is:

[0124] ΔU d >k d ΔU dt +U dth (5)

[0125] Where: ΔU dt The threshold value is a floating value that gradually and automatically increases as the phase voltage surge output increases. d ΔU is a proportionality constant, ranging from 1.05 to 1.5; d U is the half-wave integral of the phase voltage, i.e., the voltage variation at power frequency; dth For fixed thresholds.

[0126] According to the example embodiment, if the power frequency change voltage discrimination equation is met, the power frequency change voltage element will operate; after the power frequency change voltage element operates, the fault negative sequence component will be applied to the discrimination element.

[0127] S205, determined based on voltage drop value.

[0128] According to the example embodiment, the method for determining the voltage imbalance drop element based on the voltage drop value is as follows:

[0129] When the positive sequence voltage drops below 40-45V, or the negative sequence voltage rises above 4-10V, or the zero sequence voltage rises above 10-20V, the voltage imbalance drop element will activate; after the voltage imbalance drop element activates, the fault negative sequence component will be opened to the fault discrimination element.

[0130] S206, determine the negative sequence current characteristics on each side of the transformer.

[0131] According to the example embodiment, the fault negative sequence component is used to determine the negative sequence current characteristics of each side of the transformer by the discrimination element, and the effective value of the negative sequence current on the high-voltage side of the transformer is denoted as I. h2_amp Let the negative sequence current and effective value of other sides be I. o2_amp , when I h2_amp I o2_amp All are greater than the threshold value I 2_set At that time, the open fault negative sequence component points to the discrimination element, I 2_set The value ranges from 0.2 to 1 times the rated current of the transformer.

[0132] According to the example embodiment, the fault negative sequence component pointing discrimination element determines the negative sequence current characteristics on each side of the transformer. It requires that the fault negative sequence component pointing discrimination element is opened only when there is a significant negative sequence current on both the high-voltage side and other sides of the transformer. This measure can ensure that the fault negative sequence component pointing discrimination element will not mistakenly open the differential protection when the transformer is unloaded (when the transformer is unloaded, there is only a negative sequence current on one side).

[0133] According to the example embodiment, the power frequency change voltage element is used to determine the power frequency change voltage, i.e., S204; the voltage imbalance drop element is used to determine the voltage drop value, i.e., S205; the negative sequence current characteristics of each side of the transformer are used, i.e., S206; the starting time of the first fault of the system is determined to ensure that the fault negative sequence component pointing to the discrimination element can respond quickly when the fault is in the first fault zone, and the fault negative sequence component pointing to the discrimination element will not be opened in case of conversion faults, multi-phase development faults, and complex negative sequence current flow.

[0134] S207, determine the differential operating equation based on the phase currents on each side of the transformer.

[0135] According to the example embodiment, the proportional differential element is calculated using the phase currents on each side of the transformer, and the differential operating equation is described as follows:

[0136]

[0137] Where k b1 k b2 k b3 I is a proportionality constant, ranging from 0 to 1; h1 I h2 The inflection point constant is taken as 0.2 to 6 times the transformer's rated current; I1 to I m These represent the phase currents on each side of the transformer, where m is a natural number and I... d For differential current, I r For braking current, I cdqd This is the minimum operating setting for the transformer's proportional differential, with a range of 0.05 to 2 times the transformer's rated current.

[0138] According to the example embodiment, the region that satisfies Equation 6 is the proportional differential element operation region. At this time, the proportional differential element operates and the process proceeds to S203.

[0139] S208, fast differential protection action.

[0140] According to the example embodiment, when both the fault negative sequence component pointing to the discrimination element and the proportional differential element meet the operating conditions, the fast transformer differential protection operates.

[0141] According to an example embodiment, this application provides a transformer differential protection method based on the fault negative sequence component pointing. This protection method does not require transformer inrush current blocking, ensuring rapid fault clearing in the case of faults within the zone, with a protection action time of less than three-quarters of a cycle, and does not malfunction under various faults outside the zone and abnormal operating conditions.

[0142] According to the example embodiment, this application adopts a transformer differential protection method based on the fault negative sequence component pointing: in the early stage of a fault in the transformer zone, the location of the asymmetrical fault source can be quickly located by judging the fault negative sequence component pointing element, thereby improving the speed of transformer differential protection, which can reach half the cycle of the fundamental frequency at the fastest; at the same time, it will not malfunction during transformer energization, fault clearing and recovery of external faults, or CT saturation of external faults, so that the transformer proportional differential protection can take into account both speed and safety.

[0143] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0144] Furthermore, it should be noted that the above figures are merely illustrative representations of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0145] Exemplary embodiments of this application have been specifically shown and described above. It should be understood that this application is not limited to the detailed structures, arrangements, or implementation methods described herein; rather, this application is intended to cover various modifications and equivalent arrangements contained within the spirit and scope of the appended claims.

Claims

1. A transformer differential protection method based on the pointing of the negative sequence component of a fault, characterized in that, The method includes: Determine whether the fault negative sequence component points to the discrimination element and meets the first discrimination condition, including: The judgment is made based on the negative-order high braking differential equation, where: The negative-order high-braking differential equation is: in, It is a proportionality constant, with a value range of 0.8 to 0.95; ~ These are the negative sequence currents on each side of the transformer, where m is a natural number; It is a negative sequence braking current. It is a negative-order differential current. This is the minimum operating setting for the negative sequence differential current of the transformer; If the negative-sequence differential current conforms to the negative-sequence high-braking differential equation, it is determined that the fault negative-sequence component points to the discrimination element and meets the first discrimination condition; or... The determination is based on the negative sequence current on each side of the transformer, where: The phase of the negative sequence current on each side of the transformer is in the operating region of the fault negative sequence component pointing to the discrimination element, and the fault negative sequence component pointing to the discrimination element meets the first discrimination condition; The fault negative sequence component points to the action area of ​​the discrimination element, which includes the region formed by the leading deviation boundary and the lagging deviation boundary. Using the phase of the negative sequence current vector on the high-voltage side of the transformer as a reference, the lead deviation boundary is the phase of the negative sequence current on the high-voltage side plus... The angle, the hysteresis boundary is the phase difference of the negative sequence current on the high-voltage side. horn, Angle is a constant value for angle; Determine whether the proportional differential element meets the second discrimination condition; When the fault negative sequence component points to the discrimination element and meets the first discrimination condition, and the proportional differential element meets the second discrimination condition, the transformer differential protection is activated.

2. The transformer differential protection method as described in claim 1, characterized in that, The determination of whether the proportional differential element meets the second discrimination condition includes: Calculate the differential operating equation based on the phase currents on each side of the transformer; in, , , It is a proportionality constant; , The inflection point constant; ~ These represent the phase currents on each side of the transformer, where m is a natural number. For differential flow, For braking current, This is the minimum operating setting for the transformer proportional differential; When the differential current satisfies the differential action equation, the proportional differential element meets the second discrimination condition.

3. The transformer differential protection method as described in claim 1, characterized in that, The transformer differential protection method also includes: The fault negative sequence component pointing discrimination element is determined based on the voltage change of the power frequency. The fault negative sequence component pointing to the discrimination element is determined based on the voltage drop value. The fault negative sequence component pointing to the discrimination element is determined based on the negative sequence current on each side of the transformer.

4. The transformer differential protection method as described in claim 3, characterized in that, The method for determining whether to activate the fault negative sequence component pointing discrimination element based on the power frequency voltage change includes: Determine whether the voltage change at power frequency conforms to the voltage change at power frequency discrimination equation; When the power frequency change voltage conforms to the power frequency change voltage discrimination equation, the fault negative sequence component is applied to the discrimination element.

5. The transformer differential protection method as described in claim 4, characterized in that, The voltage discrimination equation for the power frequency change is: in, For floating thresholds, It is a proportionality constant; The voltage is the change in power frequency. For fixed thresholds.

6. The transformer differential protection method as described in claim 3, characterized in that, The method for determining whether to open the fault negative sequence component based on the voltage drop value includes: When the positive sequence voltage drops to the first voltage threshold, or the negative sequence voltage rises to the second voltage threshold, or the zero sequence voltage rises to the third voltage threshold, the fault negative sequence component pointing to the discrimination element is enabled.

7. The transformer differential protection method as described in claim 3, characterized in that, The fault negative sequence component pointing discrimination element, which determines whether to open based on the negative sequence current on each side of the transformer, includes: When the effective value of the negative sequence current on the high-voltage side of the transformer and the effective values ​​of the negative sequence current on other sides are greater than the threshold value, the fault negative sequence component pointing to the discrimination element is opened.

8. A transformer differential protection system based on the pointing of the negative sequence component of a fault, characterized in that, The system includes: The fault negative sequence component points to the discrimination element, which is used to determine whether the first discrimination condition is met based on the negative sequence high braking differential equation or the negative sequence current on other sides of the transformer, wherein: The fault negative sequence component pointing discrimination element includes a negative sequence high braking differential element, used to determine whether the first discrimination condition is met based on the negative sequence high braking differential equation: The negative-order high-braking differential equation is: in, It is a proportionality constant, with a value range of 0.8 to 0.95; ~ These are the negative sequence currents on each side of the transformer, where m is a natural number; It is a negative sequence braking current. It is a negative-order differential current. This is the minimum operating setting for the negative sequence differential current of the transformer; If the negative-sequence high-braking differential element determines that the negative-sequence differential current satisfies the negative-sequence high-braking differential equation, then the fault negative-sequence component pointing to the discrimination element satisfies the first discrimination condition; or... The fault negative sequence component points to the discrimination element, which includes: A directional element is used to determine whether the first discrimination condition is met based on the negative sequence current on each side of the transformer, wherein: The phase of the negative sequence current on each side of the transformer is in the fault negative sequence component pointing to the operation area of ​​the discrimination element, which meets the first discrimination condition; The fault negative sequence component points to the action area of ​​the discrimination element, which includes the region formed by the leading deviation boundary and the lagging deviation boundary. Using the phase of the negative sequence current vector on the high-voltage side of the transformer as a reference, the lead deviation boundary is the phase of the negative sequence current on the high-voltage side plus... The angle, the hysteresis boundary is the phase difference of the negative sequence current on the high-voltage side. horn, Angle is a constant value for angle; The proportional differential element is used to calculate the differential action equation based on the phase currents on each side of the transformer and determine whether the second discrimination condition is met. The starting element is used to receive an indication signal indicating that the fault negative sequence component points to the discrimination element meeting the first discrimination condition and the proportional differential element meeting the second discrimination condition, and to start the transformer differential protection operation in response to the indication signal.

9. The transformer differential protection system as described in claim 8, characterized in that, The proportional differential element is used for: Calculate the differential operating equation based on the phase currents on each side of the transformer; in, , , It is a proportionality constant; , The inflection point constant; ~ These represent the phase currents on each side of the transformer, where m is a natural number. For differential flow, For braking current, This is the minimum operating setting for the transformer proportional differential; If the differential current satisfies the differential action equation, the proportional differential element is determined to meet the second discrimination condition.

10. The transformer differential protection system as described in claim 8, characterized in that, The transformer differential protection system also includes: A power frequency change voltage element is used to determine whether the power frequency change voltage meets the discrimination equation, and if the power frequency change voltage meets the discrimination equation, the power frequency change voltage element performs an action; wherein: The discriminant equation is: in, For floating thresholds, It is a proportionality constant; The voltage is the change in power frequency. For fixed thresholds.

11. The transformer differential protection system as described in claim 10, characterized in that: The fault negative sequence component pointing discrimination element is used to perform the activation action when the power frequency change voltage element is activated.

12. The transformer differential protection system as described in claim 8, characterized in that, The transformer differential protection system also includes: Voltage imbalance sag element, used to determine whether to activate based on the voltage sag value; The fault negative sequence component indicates that the discrimination element responds to the voltage imbalance drop element by performing an open operation.

13. The transformer differential protection system as described in claim 12, characterized in that, The voltage imbalance drop element is used for: The action is determined to be performed when the positive sequence voltage drops to the first voltage threshold, the negative sequence voltage rises to the second voltage threshold, or the zero sequence voltage rises to the third voltage threshold.

14. The transformer differential protection system as described in claim 8, characterized in that, The fault negative sequence component pointing to the discrimination element is also used for: If the effective value of the negative sequence current on the high-voltage side of the transformer and the effective value of the negative sequence current on other sides are greater than the threshold setting, the opening action will be performed.

Images