A transformer inter-turn protection method, device and system based on magnetic flux leakage characteristics

Abstract

The application discloses a transformer inter-turn protection method and system based on magnetic flux leakage characteristics, and the method determines a magnetic flux leakage change action value ΔB a1 according to the magnetic flux leakage distribution under low-voltage winding inter-turn short circuit, determines the magnetic flux leakage change action value ΔB a2 according to the magnetic flux leakage distribution under excitation inrush current and external fault, collects the magnetic flux leakage change amount of a position where a magnetic flux leakage sensor is located, and judges whether the absolute values of the magnetic flux leakage change amounts measured by three phases are greater than or less than ΔB a1 when the absolute values of any magnetic flux leakage change amount are greater than ΔB a2 and the phase magnetic flux leakage is symmetrical; if all the three phases are less than ΔB a2 or only one phase is greater than ΔB a2 , it is determined that the phase has an inter-turn short circuit fault, and protection action is performed; if two or three phases are greater than ΔB a2 , it is determined that a non-inter-turn short circuit fault occurs, and protection is locked; the application can sensitively and quickly identify the fault phase and area of slight inter-turn fault, can exclude the influence of excitation inrush current and external interference, and can realize reliable protection non-action under excitation inrush current and external short circuit.

Description

Technical Field

[0001] This invention relates to a transformer inter-turn protection method and system, and more particularly to a transformer inter-turn protection method and system based on leakage flux characteristics. Background Technology

[0002] Power transformers are complex systems with coupled circuit and magnetic fields. During fault transients, various characteristic quantities can be generated internally to sensitively reflect the operating status, such as leakage flux, pressure, and ultrasound. However, existing protection principles utilize relatively limited information and lack a comprehensive understanding of the changing patterns of the internal physical field. Under inrush current and external short-circuit interference, protection may maloperate or fail to operate, posing a serious threat to the safety and stability of the power system. Existing technologies that use axial leakage flux symmetry and radial leakage flux peak values ​​of the upper yoke to identify inrush current and high-voltage inter-turn faults require complex leakage flux sensor installation schemes and do not consider the leakage flux distribution under different winding short-circuit and external short-circuit conditions, which may lead to identification errors, protection maloperation, or failure to operate. Methods that use search coils installed in the winding gaps to detect leakage magnetic fields to identify high-voltage inter-turn faults raise the leakage flux action threshold to avoid protection maloperation during inrush current, but cannot detect short-circuit faults located in the middle of the high-voltage winding and the low-voltage winding, and raising the threshold reduces the sensitivity to identify minor inter-turn faults. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide an inter-turn protection method for identifying inrush current and external faults. The second purpose of this invention is to provide an inter-turn protection system.

[0004] Technical solution: The transformer inter-turn protection method based on leakage flux characteristics described in this invention involves installing multiple leakage flux sensors on all three phases of the transformer; the method includes:

[0005] The leakage flux values ​​collected by each leakage flux sensor in the three phases are monitored to monitor the leakage flux values ​​at each collection point in the three phases and the corresponding leakage flux changes; the maximum absolute value of the leakage flux change at each collection point is the leakage flux change of that phase at the current moment.

[0006] When the absolute value of the leakage flux change in any phase is greater than the first preset value ΔB a1 At that time, based on the position of each sampling point of any phase and its leakage magnetic field value at the current moment, it is determined whether the leakage magnetic field value of any phase at the current moment is symmetrical.

[0007] When the leakage flux value of any phase is symmetrical at the current moment, determine whether the absolute value of the leakage flux change of the three phases is greater than or less than the second preset value ΔB. a2 This is to determine the fault type of the transformer and then execute the corresponding protection action.

[0008] Furthermore, it is determined whether the absolute value of the leakage flux change at each of the three-phase sampling points at the current moment is greater than or less than the second preset value ΔB. a2 To determine the fault type of the transformer and execute the corresponding protection action, the following steps are included:

[0009] Determine whether the absolute values ​​of the leakage flux changes in all three phases are less than the second preset value ΔB. a2 Or, the absolute value of the leakage flux change in one phase is greater than the second preset value ΔB. a2 If so, it is determined that an inter-turn short circuit fault has occurred, and the corresponding protection action is executed;

[0010] Otherwise, it is determined that a non-inter-turn short-circuit fault has occurred, and the corresponding protection action is executed.

[0011] Further, determining that a non-inter-turn short-circuit fault has occurred includes the following steps:

[0012] When the absolute value of the leakage flux change in two phases is greater than the second preset ΔB a2 When this occurs, it is determined that an external phase-to-phase short-circuit fault has occurred;

[0013] When the absolute values ​​of the leakage flux changes in all three phases are greater than the second preset ΔB a2 At that time, it is determined whether there is a discontinuity angle in the leakage flux time domain waveform; if there is a discontinuity angle, it is determined that the transformer is in the excitation inrush current condition; otherwise, it is determined that the transformer is in the single-phase ground short circuit condition.

[0014] Furthermore, the change in leakage magnetic flux corresponding to each acquisition point is the difference between the leakage magnetic flux value acquired by the leakage magnetic flux sensor at that acquisition point and the reference value;

[0015] Based on the linear relationship between leakage flux value and load rate during normal operation, the leakage flux reference values ​​for each phase under the current load rate q are corrected:

[0016]

[0017] in, This is the reference value for leakage flux under the corrected load rate q. This is the reference value for leakage flux under normal operating load rate p.

[0018] Furthermore, when the leakage flux value of any phase is asymmetrical at the current moment, it is determined that an inter-turn short circuit fault has occurred in any phase, and the corresponding protection action is executed; wherein, the fault occurs near the sampling point where the absolute value of the corresponding leakage flux change is the largest.

[0019] Furthermore, the method further includes: determining the first preset value ΔB based on the leakage flux distribution of the transformer under inter-turn short circuit in the low-voltage winding. a1The second preset value ΔB is determined based on the leakage flux distribution of the transformer under inrush current and external fault conditions. a2 .

[0020] Furthermore, the first preset threshold ΔB a1 Less than the maximum change in leakage flux when there is a short circuit between turns of the low-voltage winding; the second preset threshold ΔB a2 The maximum change in leakage flux during an inter-turn short circuit exceeding a preset level is less than the maximum change in leakage flux during inrush current, single-phase-to-ground short circuit, and external phase-to-phase short circuit; and ΔB a1 <ΔB a2 .

[0021] Furthermore, the leakage flux sensor is symmetrically installed in the gap between the low-voltage winding and the medium-voltage winding of the transformer;

[0022] Based on the location of each sampling point of any phase and its leakage magnetic field value at the current moment, determine whether the leakage magnetic field value of any phase at the current moment is symmetrical, including the following steps:

[0023] Determine whether the leakage magnetic flux values ​​of each pair of acquisition points located at symmetrical positions of any phase are equal at the current moment;

[0024] When the leakage magnetic flux values ​​of each pair of sampling points set at symmetrical positions are equal at the current time, it is determined that the leakage magnetic flux value of any phase at the current time is symmetrical; otherwise, the leakage magnetic flux value of any phase at the current time is asymmetrical.

[0025] The transformer inter-turn protection system based on leakage flux characteristics described in this invention includes:

[0026] The threshold setting unit is used to determine the leakage flux change action value ΔB based on the leakage flux distribution under inter-turn short circuit of the low-voltage winding. a1 The leakage flux change action value ΔB is determined based on the leakage flux distribution under inrush current and external fault conditions. a2 The maximum absolute value of the leakage flux change at each acquisition point is the leakage flux change of that phase at the current moment.

[0027] The magnetic flux leakage detection unit is used to collect changes in magnetic flux leakage at its location, and includes multiple magnetic flux leakage sensors installed on the three phases of the transformer.

[0028] The fault protection unit is used to determine whether a fault has occurred and to perform protection based on the absolute value of the change in leakage flux.

[0029] When the absolute value of the leakage flux change at at least one sampling point of any phase at the current moment is greater than the first preset value ΔB a1 At that time, based on the position of each sampling point of any phase and its leakage magnetic field value at the current moment, it is determined whether the leakage magnetic field value of any phase at the current moment is symmetrical.

[0030] When the leakage flux value of any phase is symmetrical at the current moment, determine whether the absolute value of the leakage flux change at each sampling point of the three phases at the current moment is greater than or less than the second preset value ΔB. a2 This is to determine the fault type of the transformer and then execute the corresponding protection action.

[0031] The transformer inter-turn protection device based on leakage flux characteristics described in this invention includes:

[0032] The leakage flux monitoring unit is used to monitor the leakage flux values ​​collected by each leakage flux sensor in the three phases, so as to monitor the leakage flux values ​​at each collection point in the three phases and the corresponding leakage flux changes.

[0033] The fault protection unit is used when the absolute value of the leakage flux change at at least one sampling point of any phase at the current moment is greater than a first preset value ΔB. a1 At that time, based on the location of each sampling point of any phase and its leakage magnetic field value at the current moment, it is determined whether the leakage magnetic field value of any phase at the current moment is symmetrical; and,

[0034] When the leakage flux value of any phase is symmetrical at the current moment, determine whether the absolute value of the leakage flux change at each sampling point of the three phases at the current moment is greater than or less than the second preset value ΔB. a2 This is to determine the fault type of the transformer and then execute the corresponding protection action.

[0035] The transformer inter-turn protection system based on leakage flux characteristics according to the present invention includes: a memory, a controller, and multiple leakage flux sensors disposed on the three phases of the transformer;

[0036] The magnetic flux leakage sensor is used to collect the magnetic flux leakage value at its location in real time;

[0037] The memory stores a program that, when executed by the controller, performs the transformer inter-turn protection method based on leakage flux characteristics to determine the fault type of the transformer based on the leakage flux value collected by the leakage flux sensor, thereby performing the corresponding protection action.

[0038] Beneficial effects: Compared with the prior art, the advantages of the present invention are that it can sensitively and quickly identify the fault phase and region of minor inter-turn faults, while eliminating the influence of inrush current and external interference, and achieving reliable protection without operation in the case of inrush current and external short circuit. Attached Figure Description

[0039] Figure 1 This is a diagram showing the axial leakage flux distribution after a 1% inter-turn short circuit occurs in the low-voltage winding in an embodiment of the present invention.

[0040] Figure 2This is a diagram showing the axial leakage flux distribution after a 1% inter-turn short circuit occurs in the high-voltage or low-voltage winding in an embodiment of the present invention.

[0041] Figure 3 The diagram shows the spatial distribution and time-domain waveform of leakage flux when inrush current, external grounding of phase B, and external short circuit between phases A and B occur in the embodiments of the present invention.

[0042] Figure 4 This is a graph showing the variation of three-phase leakage flux under different operating conditions in an embodiment of the present invention.

[0043] Figure 5 This is a flowchart of the inter-turn protection method of the present invention. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0045] First, the principle of the transformer inter-turn protection method based on leakage flux characteristics described in this invention is analyzed and verified.

[0046] Figure 1 The figure shows the change in leakage flux measured along the axial path between the low-voltage and medium-voltage windings after a 1% proportional inter-turn short circuit occurs in the low-voltage winding of a 110kV three-phase transformer. The selected leakage flux change action value is ΔB. a1 Then, it can be determined that the change in leakage flux in the axial direction is greater than ΔB. a1 The interval length is R ΔB The distance from the short-circuit turn to the sensor is less than R. ΔB At / 2, the change in leakage magnetic flux at the sensor location ΔB > ΔB a1 This enables protective actions, therefore the protection range of a single sensor is R. ΔB ΔB a1 When the value is high, a larger number of leakage magnetic field sensors are required for subsequent installation, ΔB a1 A low value may cause slight fluctuations in leakage flux during normal operation to be misjudged as inter-turn short circuits. The action value ΔB is determined based on the leakage flux distribution under inrush current and external fault conditions. a2 ΔB a2 It must be less than the actual change in leakage flux under inrush current and external faults, and greater than the change in leakage flux caused by minor inter-turn faults, in order to prevent inter-turn short circuits from being misjudged as other operating conditions.

[0047] Taking the SSZ11-50000 / 110kV transformer as an example, a finite element three-dimensional simulation model was established for verification. During normal operation, the leakage flux amplitudes of the three phases are equal; during inter-turn short circuits, only the leakage flux of the fault phase changes. After a 1% proportional short circuit occurs in the high-voltage or low-voltage winding, the axial leakage flux distribution at different locations is as follows: Figure 2 As shown, Figure 2 (a) shows the gap between the iron core and the low-voltage winding. Figure 2 (b) represents the gap between the low-voltage and medium-voltage windings. Figure 2 (c) represents the gap between the medium-voltage and high-voltage windings. Figure 2 (d) represents the outer oil tank wall of the high-voltage winding. When there is no fault, the leakage flux distribution is symmetrical in the axial direction. After a fault, the leakage flux amplitude changes the most at the same height as the short-circuit turn. When the low-voltage winding is short-circuited, there is a change of about 12mT in the gap between the low-voltage and medium-voltage windings.

[0048] Since the leakage flux changes little when the distance to the faulty winding is relatively large, in order to effectively detect short circuits in the high, medium and low voltage windings, the leakage flux sensor needs to be installed in the gap between the low voltage and medium voltage windings.

[0049] Figure 3 Figures (a) to (f) show the spatial distribution and temporal waveforms of leakage flux during 0-degree no-load closing (i.e., inrush current), external grounding of phase B, and external phase-A short circuit, respectively. During inrush current and external short circuit, the leakage flux remains axially symmetrical, and the three-phase leakage flux values ​​increase significantly. During no-load closing, the phase with the largest leakage flux appears sequentially in phases A, B, and C as the closing angle changes, but their maximum values ​​are basically equal. The external short circuit patterns for the other phases are similar to those shown in the figure: during a single-phase external grounding short circuit, the leakage flux of all three phases increases, with the grounded phase being the most severely affected; during external phase-to-phase short circuits, the fault-free phase shows no significant change, while the leakage flux value of the faulty phase increases, and the spatiotemporal distribution of leakage flux in the two phases is the same.

[0050] Except for the inter-turn short circuit in the middle position, the axial leakage flux all lost its symmetry after the fault. Further analysis is needed for the fault in the middle position. Figure 4 The figure shows the variation of three-phase leakage flux under different operating conditions. It is clear that for a minor inter-turn short circuit, the change in leakage flux is much smaller than that for inrush current and external short circuit faults. In addition, at least two phases of leakage flux change during inrush current and external short circuit, while only the short-circuit phase changes during inter-turn short circuit.

[0051] In summary, minor inter-turn protection can be identified based on axial leakage flux symmetry and three-phase leakage flux values.

[0052] like Figure 5 As shown, the transformer inter-turn protection method based on leakage flux characteristics of the present invention includes the following steps: Step 1, selecting the leakage flux change action value ΔB according to the leakage flux distribution under low-voltage winding inter-turn short circuit. a1 The leakage flux change action value ΔB is determined based on the leakage flux distribution under inrush current and external fault conditions. a2 ΔB a1 Less than the maximum change in leakage flux when there is an inter-turn short circuit in the low-voltage winding; the ΔB a2 The maximum change in leakage flux is greater than that during a minor inter-turn short circuit but less than that during inrush current, single-phase-to-ground short circuit, and external phase-to-phase short circuit; ΔB a1 <ΔB a2

[0053] Step 2: Leakage flux sensors are symmetrically installed in the gap between the low-voltage winding and the medium-voltage winding. The number of leakage flux sensors installed per phase is:

[0054]

[0055] H is the winding height, R ΔB The leakage flux change after the inter-turn fault reached ΔB a1 The interval length.

[0056] Step 3: The leakage flux sensor collects the leakage flux value at its location at a certain sampling rate, calculates the deviation between the leakage flux value and the normal operating reference value to obtain the leakage flux change; based on the linear relationship between the leakage flux value and the load rate during normal operation, the leakage flux reference value of each phase under the current load rate q is corrected to eliminate the influence of load rate changes and unbalanced loads on the leakage flux amplitude of each phase.

[0057]

[0058] in, This is the reference value for leakage flux under the corrected load rate q. This is the reference value for leakage flux under normal operating load rate p.

[0059] Step 4: When the absolute value of the change in leakage magnetic field, calculated from the leakage magnetic field value measured by a certain sensor, is greater than the set action value ΔB... a1 Then, it is further determined whether the leakage magnetic field values ​​detected by each pair of leakage magnetic field sensors installed in axially symmetrical positions of the phase are equal at the same time, so as to determine whether the leakage magnetic field of the phase is symmetrical at this time.

[0060] Step 5: If the leakage flux distribution is asymmetrical, it is determined that an inter-turn short circuit fault has occurred in the phase where the leakage flux sensor is located, and the protection system operates. The fault occurs near the leakage flux sensor where the absolute value of the measured leakage flux change is the largest. If the leakage flux distribution is symmetrical, it is determined whether the absolute value of the leakage flux change in each of the three phases is greater than the set operating value ΔB. a2 If all three phases are less than ΔB a2 Or there exists only one phase greater than ΔB a2 If the circuit is short-circuited between the turns of that phase, the protection system will activate; if two or three phases have a short circuit greater than ΔB, the protection system will activate. a2 If so, it is determined that no inter-turn short circuit fault has occurred.

[0061] Step 6: Based on the absolute values ​​of the three-phase leakage flux changes, if only two phases have absolute values ​​of leakage flux changes greater than ΔB... a2 If an external phase-to-phase short circuit occurs, the protection is locked out when the absolute values ​​of the three-phase leakage flux changes are all greater than ΔB. a2 At that time, determine whether there is a discontinuity angle in the leakage flux time domain waveform.

[0062] Step 7: When there is a discontinuity angle in the leakage flux time domain waveform, it is determined that the transformer is in the inrush current condition and the protection is locked; otherwise, it is determined that the transformer has a single-phase ground fault and the protection is locked.

[0063] Based on the same inventive concept, the transformer inter-turn protection device based on leakage flux characteristics described in this invention includes:

[0064] The leakage flux monitoring unit is used to monitor the leakage flux values ​​collected by each leakage flux sensor in the three phases, so as to monitor the leakage flux values ​​at each collection point in the three phases and the corresponding leakage flux changes.

[0065] The fault protection unit is used when the absolute value of the leakage flux change at at least one sampling point of any phase at the current moment is greater than a first preset value ΔB. a1 At that time, based on the location of each sampling point of any phase and its leakage magnetic field value at the current moment, it is determined whether the leakage magnetic field value of any phase at the current moment is symmetrical; and,

[0066] When the leakage flux value of any phase is symmetrical at the current moment, determine whether the absolute value of the leakage flux change at each sampling point of the three phases at the current moment is greater than or less than the second preset value ΔB. a2 This is to determine the fault type of the transformer and then execute the corresponding protection action.

[0067] Based on the same inventive concept, the transformer inter-turn protection system based on leakage flux characteristics described in this invention includes: a memory, a controller, and multiple leakage flux sensors disposed on the three phases of the transformer.

[0068] The magnetic flux leakage sensor is used to collect the magnetic flux leakage value at its location in real time;

[0069] The memory stores a program that, when executed by the controller, performs the transformer inter-turn protection method based on leakage flux characteristics to determine the fault type of the transformer based on the leakage flux value collected by the leakage flux sensor, thereby performing the corresponding protection action.

[0070] The aforementioned storage device can be any storage device capable of storing program code, such as a USB flash drive, portable hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk.

[0071] The aforementioned processor can be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

Claims

1. A transformer inter-turn protection method based on leakage flux characteristics, characterized in that, The transformer is equipped with multiple leakage flux sensors on all three phases; the method includes: The leakage flux values ​​collected by each leakage flux sensor in the three phases are monitored to monitor the leakage flux values ​​at each collection point in the three phases and the corresponding leakage flux changes; the maximum absolute value of the leakage flux change at each collection point is the leakage flux change of that phase at the current moment. When the absolute value of the leakage flux change in any phase is greater than the first preset value ΔB a1 At that time, based on the position of each sampling point of any phase and its leakage magnetic field value at the current moment, it is determined whether the leakage magnetic field value of any phase at the current moment is symmetrical. When the leakage flux value of any phase is symmetrical at the current moment, determine whether the absolute value of the leakage flux change of the three phases is greater than or less than the second preset value ΔB. a2 In order to determine the fault type of the transformer, and thus execute the corresponding protection action; Determine whether the absolute value of the three-phase leakage flux change is greater than or less than the second preset value ΔB. a2 To determine the fault type of the transformer and execute the corresponding protection action, the following steps are included: Determine whether the absolute values ​​of the leakage flux changes in all three phases are less than the second preset value ΔB. a2 Or, the absolute value of the leakage flux change in one phase is greater than the second preset value ΔB. a2 If so, it is determined that an inter-turn short circuit fault has occurred, and the corresponding protection action is executed; Otherwise, it is determined that a non-inter-turn short-circuit fault has occurred, and the corresponding protection action is executed; The determination of a non-inter-turn short-circuit fault includes the following steps: When the absolute value of the leakage flux change in two phases is greater than the second preset value ΔB a2 When this occurs, it is determined that an external phase-to-phase short-circuit fault has occurred; When the absolute values ​​of the leakage flux changes in all three phases are greater than the second preset value ΔB a2 At that time, it is determined whether there is a discontinuity angle in the leakage flux time domain waveform; if there is a discontinuity angle, it is determined that the transformer is in the excitation inrush current condition; otherwise, it is determined that the transformer is in the single-phase ground short circuit condition.

2. The transformer inter-turn protection method based on leakage flux characteristics according to claim 1, characterized in that, The change in magnetic flux leakage at each acquisition point is the difference between the magnetic flux leakage value acquired by the magnetic flux leakage sensor at that acquisition point and the reference value. Based on the linear relationship between leakage flux value and load rate during normal operation, the leakage flux reference values ​​for each phase under the current load rate q are corrected: in, This is the reference value for leakage flux under the corrected load rate q. This is the reference value for leakage flux under normal operating load rate p.

3. The transformer inter-turn protection method based on leakage flux characteristics according to claim 1, characterized in that, When the leakage flux value of any phase is asymmetrical at the current moment, it is determined that an inter-turn short circuit fault has occurred in any phase, and the corresponding protection action is executed; wherein, the fault occurs near the sampling point where the absolute value of the corresponding leakage flux change is the largest.

4. The transformer inter-turn protection method based on leakage flux characteristics according to claim 1, characterized in that, The method further includes: The first preset value ΔB is determined based on the leakage magnetic flux distribution of the transformer under inter-turn short circuit in the low-voltage winding. a1 The second preset value ΔB is determined based on the leakage flux distribution of the transformer under inrush current and external fault conditions. a2 .

5. The transformer inter-turn protection method based on leakage flux characteristics according to claim 4, characterized in that, The first preset value ΔB a1 Less than the maximum change in leakage flux when the low-voltage winding is short-circuited between turns; the second preset value ΔB a2 The maximum change in leakage flux during an inter-turn short circuit exceeding a preset level is less than the maximum change in leakage flux during inrush current, single-phase-to-ground short circuit, and external phase-to-phase short circuit; and ΔB a1 <ΔB a2 .

6. The transformer inter-turn protection method based on leakage flux characteristics according to claim 1, characterized in that, The leakage magnetic field sensor is symmetrically installed in the gap between the low-voltage winding and the medium-voltage winding of the transformer; Based on the location of each sampling point of any phase and its leakage magnetic field value at the current moment, determine whether the leakage magnetic field value of any phase at the current moment is symmetrical, including the following steps: Determine whether the leakage magnetic flux values ​​of each pair of acquisition points located at symmetrical positions of any phase are equal at the current moment; When the leakage magnetic flux values ​​of each pair of sampling points set at symmetrical positions are equal at the current time, it is determined that the leakage magnetic flux value of any phase at the current time is symmetrical; otherwise, the leakage magnetic flux value of any phase at the current time is asymmetrical.

7. A transformer inter-turn protection device based on leakage flux characteristics, characterized in that, include: The leakage flux monitoring unit is used to monitor the leakage flux values ​​collected by each leakage flux sensor in the three phases, so as to monitor the leakage flux values ​​and corresponding leakage flux changes at each collection point in the three phases; the maximum absolute value of the leakage flux change at each collection point is the leakage flux change of that phase at the current moment. The fault protection unit is used when the absolute value of the leakage flux change in any phase exceeds a first preset value ΔB. a1 At that time, based on the location of each sampling point of any phase and its leakage magnetic field value at the current moment, it is determined whether the leakage magnetic field value of any phase at the current moment is symmetrical; and, When the leakage flux value of any phase is symmetrical at the current moment, determine whether the absolute value of the leakage flux change of the three phases is greater than or less than the second preset value ΔB. a2 In order to determine the fault type of the transformer, and thus execute the corresponding protection action; Determine whether the absolute value of the three-phase leakage flux change is greater than or less than the second preset value ΔB. a2 To determine the fault type of the transformer and execute the corresponding protection action, the following steps are included: Determine whether the absolute values ​​of the leakage flux changes in all three phases are less than the second preset value ΔB. a2 Or, the absolute value of the leakage flux change in one phase is greater than the second preset value ΔB. a2 If so, it is determined that an inter-turn short circuit fault has occurred, and the corresponding protection action is executed; Otherwise, it is determined that a non-inter-turn short-circuit fault has occurred, and the corresponding protection action is executed; The determination of a non-inter-turn short-circuit fault includes the following steps: When the absolute value of the leakage flux change in two phases is greater than the second preset value ΔB a2 When this occurs, it is determined that an external phase-to-phase short-circuit fault has occurred; When the absolute values ​​of the leakage flux changes in all three phases are greater than the second preset value ΔB a2 At that time, it is determined whether there is a discontinuity angle in the leakage flux time domain waveform; if there is a discontinuity angle, it is determined that the transformer is in the excitation inrush current condition; otherwise, it is determined that the transformer is in the single-phase ground short circuit condition.

8. A transformer inter-turn protection system based on leakage flux characteristics, characterized in that, include: The memory, controller, and multiple leakage magnetic field sensors disposed on the three phases of the transformer; The magnetic flux leakage sensor is used to collect the magnetic flux leakage value at its location in real time; The memory stores a program that, when executed by the controller, performs the transformer inter-turn protection method based on leakage flux characteristics as described in any one of claims 1 to 6, in order to determine the fault type of the transformer based on the leakage flux value collected by the leakage flux sensor, thereby performing the corresponding protection action.

Images