A protection method and system for identifying internal faults of a transformer based on timing relationship of equivalent excitation inductance and voltage change amount

Abstract

A protection method and system for identifying transformer internal fault based on timing relationship of equivalent excitation inductance and voltage variation amount, the method comprising: collecting transformer each side phase voltage and current when the transformer is in normal operation; calculating voltage variation amount, differential current, differential current variation amount, equivalent excitation inductance, average equivalent excitation inductance, equivalent excitation inductance variation amount, voltage variation amount short window integral value, differential current variation amount and braking current variation amount short window integral value; if the timing relationship of voltage mutation and equivalent excitation inductance mutation meets the synchronization condition, it is determined that the transformer internal fault occurs; after determining that the transformer internal fault occurs, if the variation differential protection element meets the action condition at the same time within the expansion time, the protection device acts. The application utilizes the timing synchronization characteristics of voltage mutation and equivalent excitation inductance mutation when the transformer internal fault occurs to quickly identify the transformer internal fault and perform protection trip.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology, and in particular relates to a protection method and system for identifying internal faults in transformers based on the timing relationship between equivalent excitation inductance and voltage change. Background Technology

[0002] Differential protection, as the main protection for transformers, has advantages such as high sensitivity and fast operation. However, because it cannot predict inrush current during various changes in transformer operating conditions in real time, the inrush current blocking criterion needs to be applied throughout the entire fault identification process. Therefore, the differential protection operating time is generally over 20ms. When a high proportion of new energy sources are integrated on a large scale, the fault current of the power electronic power supply exhibits obvious characteristics such as amplitude and phase control, frequency deviation, and high harmonics. This leads to insufficient sensitivity and reduced speed of transformer differential protection that relies on power frequency phasors, seriously threatening the safe operation of the system.

[0003] The equivalent model of a transformer during an internal fault is a parallel structure of the excitation branch and the fault branch. The equivalent excitation inductance during a fault decreases by more than two orders of magnitude compared to normal operation or external faults. The equivalent excitation inductance is larger during normal operation or external faults, smaller during internal faults, and fluctuates periodically between high and low values ​​when the core is saturated. Existing protection principles based on excitation inductance calculate the T-type equivalent model excitation inductance in real time using the voltage and current on each side of the transformer. Protection criteria are constructed using the differences in excitation inductance characteristics under internal and external faults and core saturation. This approach can accurately identify internal and external faults and inrush currents, and is completely unaffected by frequency deviation, harmonics, and through currents from renewable energy sources. However, due to the influence of inrush currents, the protection action time is generally greater than 20ms, indicating insufficient speed. Summary of the Invention

[0004] When an internal fault occurs in a transformer, the voltage amplitude and phase change abruptly, and the equivalent magnetizing inductance decreases. However, external faults can also cause abrupt voltage amplitude and phase changes, potentially leading to core saturation, a decrease in magnetizing inductance, and inrush current. Methods that identify internal faults solely based on the equivalent magnetizing inductance and voltage change characteristics may misdiagnose inrush current as a fault. When an external fault occurs in a normally operating transformer, the non-periodic component of the core flux linkage needs to accumulate for a period after the voltage change before the core enters magnetic saturation, causing a sharp decrease in magnetizing inductance. Therefore, this invention proposes a protection method and system for identifying transformer faults based on the equivalent magnetizing inductance, voltage change, and their timing relationship.

[0005] To achieve the above-mentioned objectives, the present invention specifically adopts the following technical solution.

[0006] A protection method for identifying internal transformer faults based on the timing relationship between equivalent magnetizing inductance and voltage change, characterized in that the protection method includes: Collect the phase voltage and current of each side of the transformer in normal operation, and calculate the change in equivalent excitation inductance, the short-window integral value of the voltage change on each side of the transformer, the change in differential current, and the short-window integral value of the braking current change; When the maximum value of the short-window integral of the voltage change on each side of the transformer meets the first sudden change condition, the first time T1 is extended. If the change of the equivalent excitation inductance meets the second sudden change condition within the first time T1, it is determined that an internal fault has occurred in the transformer, and the second time T2 is extended. Within the second time period T2, based on the short-window integral values ​​of the differential current change and the braking current change, it is determined whether the operation conditions of the differential protection element for transformer change are met. If they are met, the differential protection device operates; otherwise, the differential protection is blocked.

[0007] The present invention further includes the following preferred embodiments.

[0008] Preferably, The method for calculating the change in equivalent excitation inductance is as follows:

[0009] in, For the current sampling point Calculate the equivalent magnetizing inductance. For the current sampling point The average equivalent magnetizing inductance calculated at the previous sampling time of the previous cycle, This represents the number of sampling points per cycle.

[0010] More preferably, The method for calculating the equivalent excitation inductance is as follows:

[0011] in, For the current sampling point, For the previous sampling point, For the current sampling point Calculate the equivalent magnetizing inductance. For the current sampling point voltage sampling value, For the current sampling point Differential sampling value, This is the differential current sample value from the previous sampling point. This represents the time interval between two sampling points.

[0012] More preferably, When calculating the equivalent excitation inductance, for transformer phase differential protection, the differential current is taken as the phase differential current and the voltage is taken as the corresponding phase voltage. For longitudinal differential protection, the differential current is taken as the longitudinal differential current and the voltage is taken as the corresponding line voltage.

[0013] More preferably, The first mutation condition is: , The second mutation condition is: , in, This represents the maximum value of the short-window integral of the voltage change on each side of the transformer. δ1 is the threshold value for voltage change fluctuation, and δ2 is the threshold value for voltage sudden change. This represents the change in equivalent magnetizing inductance. δ1 is the threshold for the change in equivalent excitation inductance, and δ2 is the threshold for the sudden change in equivalent excitation inductance.

[0014] The method for calculating the voltage change floating threshold is as follows:

[0015] in, The voltage change fluctuation threshold value calculated for the current sampling point. This represents the maximum value of the short-time integral of the voltage change calculated at the current sampling point. The voltage change fluctuation threshold value calculated for the previous sampling point, when When the value is 1, ; , This is the coefficient when the voltage change increases. < ; , This is the coefficient for when the voltage change decreases. < ;satisfy , .

[0016] The method for calculating the floating threshold of the equivalent excitation inductance change is as follows:

[0017] in, The equivalent excitation inductance floating threshold value calculated for the current sampling point. This is the change in equivalent magnetizing inductance calculated at the current sampling point. The equivalent excitation inductance floating threshold value calculated for the previous sampling point, when When the value is 1, ; , This is the coefficient when the change in equivalent magnetizing inductance increases. < ; , This is the coefficient for reducing the change in equivalent magnetizing inductance. < ;satisfy , .

[0018] More preferably, The value of δ1 is (0.04~0.1). δ2 is (0.1~0.5) , This is the rated voltage on the corresponding side of the transformer. This is the average equivalent magnetizing inductance for the current cycle.

[0019] More preferably, The operating conditions for the differential protection element with varying output are:

[0020] in, This is the short-window integral value of the differential current change after differential filtering. The value is the short-window integral of the braking current change after differential filtering. δ3 is a fixed threshold, taken as (0.15~0.3)Ie, where Ie is the transformer rated current. The braking coefficient is 0.2 to 0.5.

[0021] More preferably, T1 is 1~3ms, and T2 is 3~5ms. The short-window integral value refers to the half-wave integral value before the current sampling point.

[0022] This application also claims protection for a transformer internal fault protection system based on the aforementioned protection method, characterized in that it includes: The data acquisition module is used to collect voltage and current data of each phase of the transformer; The calculation module is used to calculate voltage change, differential current, differential current change, equivalent magnetizing inductance, average equivalent magnetizing inductance, equivalent magnetizing inductance change, short-window integral value of voltage change, differential current change, and short-window integral value of braking current change. The fault identification module is used to determine the occurrence of internal transformer faults. The criteria for identification are the simultaneous occurrence of voltage surge and equivalent magnetizing inductance surge. The protection action module is used to activate the protection device to perform protection actions when the conditions for an internal fault in the transformer are met and the differential protection element for the change in quantity is satisfied.

[0023] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the computer program is loaded onto the processor, it implements a protection method for identifying transformer faults based on the aforementioned timing sequence of equivalent magnetizing inductance and voltage change.

[0024] A computer-readable storage medium storing a computer program, characterized in that, when executed by a processor, the computer program implements a protection method for identifying transformer faults based on the aforementioned timing sequence of equivalent magnetizing inductance and voltage change.

[0025] Compared with existing transformer protection technologies, this invention has the following significant advantages: 1. Unaffected by fault current limiting and through-current characteristics of new energy power sources, it has high protection sensitivity and high sensitivity to minor inter-turn faults in transformers. 2. It adopts a time-domain algorithm, which is not affected by the frequency deviation and high harmonics of the fault current of new energy sources. It has good protection speed and the protection action time is less than 5ms when a serious internal fault occurs in the transformer. 3. The protection method is simple and practical, easy to implement in engineering, and the set value does not need to be adjusted. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the protection method for identifying internal transformer faults based on the timing relationship between equivalent excitation inductance and voltage change, as per the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0028] As attached Figure 1 As shown, the protection method for identifying internal transformer faults based on the timing relationship of equivalent magnetizing inductance and voltage change disclosed in this invention includes: Step 1: Collect the phase voltage and current of each side of the normally operating transformer; Calculate the short-window integral values ​​of the changes in equivalent excitation inductance, voltage changes on each side of the transformer, differential current changes, and braking current changes; The method for calculating the change in equivalent excitation inductance is as follows:

[0029] in, For the current sampling point Calculate the equivalent magnetizing inductance. For the current sampling point The average equivalent magnetizing inductance calculated at the previous sampling time of the previous cycle, This represents the number of sampling points per cycle.

[0030] The method for calculating the equivalent excitation inductance is as follows:

[0031] in, For the current sampling point, For the previous sampling point, For the current sampling point Calculate the equivalent magnetizing inductance. For the current sampling point voltage sampling value, For the current sampling point Differential sampling value, This is the differential current sample value from the previous sampling point. This represents the time interval between two sampling points.

[0032] Step 2: When both voltage surge and equivalent magnetizing inductance surge occur simultaneously, it is determined that an internal transformer fault has occurred, and the change protection element is activated. When the maximum value of the short window integral of the voltage change on each side of the transformer satisfies the first sudden change condition, the first time T1 is extended. If the voltage changes suddenly and within the first extended time T1, if the change in the equivalent magnetizing inductance changes suddenly and satisfies the second sudden change condition, then the timing relationship between the voltage change and the equivalent magnetizing inductance change satisfies the synchronization condition, and it is determined that an internal fault has occurred in the transformer, and the second time T2 is extended. When calculating the equivalent excitation inductance, for transformer phase differential protection, the differential current is taken as the phase differential current and the voltage is taken as the corresponding phase voltage. For longitudinal differential protection, the differential current is taken as the longitudinal differential current and the voltage is taken as the corresponding line voltage.

[0033] The first mutation condition is: , The second mutation condition is: , in, This represents the maximum value of the short-window integral of the voltage change on each side of the transformer. δ1 is the threshold value for voltage change fluctuation, and δ2 is the threshold value for voltage sudden change. This represents the change in equivalent magnetizing inductance. δ1 is the threshold for the change in equivalent excitation inductance, and δ2 is the threshold for the sudden change in equivalent excitation inductance.

[0034] The method for calculating the voltage change floating threshold is as follows:

[0035] in, The voltage change fluctuation threshold value calculated for the current sampling point. This represents the maximum value of the short-time integral of the voltage change calculated at the current sampling point. The voltage change fluctuation threshold value calculated for the previous sampling point, when When the value is 1, ; , This is the coefficient when the voltage change increases. < ; , This is the coefficient for when the voltage change decreases. < ;satisfy , .

[0036] The method for calculating the floating threshold of the equivalent excitation inductance change is as follows:

[0037] in, The equivalent excitation inductance floating threshold value calculated for the current sampling point. This is the change in equivalent magnetizing inductance calculated at the current sampling point. The equivalent excitation inductance floating threshold value calculated for the previous sampling point, when When the value is 1, ; , This is the coefficient when the change in equivalent magnetizing inductance increases. < ; , This is the coefficient for reducing the change in equivalent magnetizing inductance. < ;satisfy , .

[0038] The .

[0039] Step 3: After determining that an internal transformer fault has occurred, within the second time T2, based on the short-window integral values ​​of the differential current change and the braking current change, determine whether the operation conditions of the differential protection element for transformer change are met. If they are met, the differential protection device will operate; otherwise, the differential protection will be blocked. The operating equation of the differential protection element for the change in quantity is:

[0040] in, This is the short-window integral value of the differential current change after differential filtering. The value is the short-window integral of the braking current change after differential filtering. δ3 is a fixed threshold, taken as (0.15~0.3)Ie, where Ie is the transformer rated current. The braking coefficient is 0.2 to 0.5.

[0041] T1 is 1~3ms, and T2 is 3~5ms.

[0042] This application also discloses a transformer internal fault protection system based on the aforementioned protection method, characterized in that it includes: The data acquisition module is used to collect voltage and current data of each phase of the transformer; The calculation module is used to calculate voltage change, differential current, differential current change, equivalent magnetizing inductance, average equivalent magnetizing inductance, equivalent magnetizing inductance change, short-window integral value of voltage change, differential current change, and short-window integral value of braking current change. The fault identification module is used to determine the occurrence of internal transformer faults. The criteria for identification are the simultaneous occurrence of voltage surge and equivalent magnetizing inductance surge. The protection action module is used to activate the protection device to perform protection actions when the conditions for an internal fault in the transformer are met and the differential protection element for the change in quantity is satisfied.

[0043] Example 1: A protection method for identifying transformer faults based on equivalent magnetizing inductance and voltage change timing includes the following steps: (1) Collect the phase voltage and current of each side of the transformer in normal operation; Calculate the short-window integral values ​​of the changes in equivalent excitation inductance, voltage changes on each side of the transformer, differential current changes, and braking current changes; (2) When there is an internal fault in the transformer, its physical model is equivalent to the fault branch and the excitation inductance in parallel. Therefore, the sudden changes in voltage and excitation inductance are strictly "synchronous". When there is an external fault, the voltage change will cause the magnetic flux to accumulate. The transformer core has nonlinear saturation characteristics. If the magnetic flux reaches the saturation threshold, the excitation inductance will also decrease sharply. However, the sudden change in excitation inductance is "lagging" behind the voltage change. Through the unified mathematical model of the core magnetic flux of the transformer under all working conditions, the correlation between the core initial saturation time and the voltage change was studied. It was found for the first time that after the voltage change of the phase-to-phase fault, the core enters saturation in as little as 2.6ms. Therefore, when the maximum value of the voltage change on each side of the transformer meets the first sudden change condition, it is extended by 2ms. If the change in equivalent excitation inductance is greater than (0.1~0.5) times the average equivalent excitation inductance value within the extended time, it is judged that an internal fault of the transformer has occurred, and the differential protection element of the change amount is opened for 5ms. (3) If the differential protection element meets the operating conditions within 5ms of opening the differential protection, the protection device will be started and the protection action will be performed; otherwise, the differential protection will be blocked.

[0044] The technical solution of this invention can accurately identify internal faults in transformers and quickly issue protection actions when an internal fault is detected; when an external fault occurs in the transformer, it can effectively lock out protection.

[0045] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0046] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example, but not limited to, electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination thereof. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0047] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0048] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A protection method for identifying internal transformer faults based on the timing relationship between equivalent magnetizing inductance and voltage change, characterized in that, The protection method includes: Collect the phase voltage and current of each side of the transformer in normal operation, and calculate the change in equivalent excitation inductance, the short-window integral value of the voltage change on each side of the transformer, the change in differential current, and the short-window integral value of the braking current change; When the maximum value of the short-window integral of the voltage change on each side of the transformer meets the first sudden change condition, the first time T1 is extended. If the change of the equivalent excitation inductance meets the second sudden change condition within the first time T1, it is determined that an internal fault has occurred in the transformer, and the second time T2 is extended. Within the second time period T2, based on the short-window integral values ​​of the differential current change and the braking current change, it is determined whether the operation conditions of the differential protection element for transformer change are met. If they are met, the differential protection device operates; otherwise, the differential protection is blocked.

2. The protection method for identifying internal transformer faults according to claim 1, characterized in that: The method for calculating the change in equivalent excitation inductance is as follows: in, For the current sampling point Calculate the equivalent magnetizing inductance. For the current sampling point The average equivalent magnetizing inductance calculated at the previous sampling time of the previous cycle, This represents the number of sampling points per cycle.

3. The protection method for identifying internal transformer faults according to claim 2, characterized in that: The method for calculating the equivalent excitation inductance is as follows: in, For the current sampling point, For the previous sampling point, For the current sampling point Calculate the equivalent magnetizing inductance. For the current sampling point voltage sampling value, For the current sampling point Differential sampling value, This is the differential current sample value from the previous sampling point. This represents the time interval between two sampling points.

4. The protection method for identifying internal transformer faults according to claim 3, characterized in that: When calculating the equivalent excitation inductance, for transformer phase differential protection, the differential current is taken as the phase differential current and the voltage is taken as the corresponding phase voltage. For longitudinal differential protection, the differential current is taken as the longitudinal differential current and the voltage is taken as the corresponding line voltage.

5. The protection method for identifying internal transformer faults according to claim 1, characterized in that: The first mutation condition is: , The second mutation condition is: , in, This represents the maximum value of the short-window integral of the voltage change on each side of the transformer. δ1 is the threshold value for voltage change fluctuation, and δ2 is the threshold value for voltage sudden change. This represents the change in equivalent magnetizing inductance. δ1 is the threshold for the change in equivalent excitation inductance, and δ2 is the threshold for the sudden change in equivalent excitation inductance.

6. The protection method for identifying internal transformer faults according to claim 5, characterized in that: The method for calculating the voltage change floating threshold is as follows: in, The voltage change fluctuation threshold value calculated for the current sampling point. This represents the maximum value of the short-time integral of the voltage change calculated at the current sampling point. The voltage change fluctuation threshold value calculated for the previous sampling point, when When the value is 1, ; , This is the coefficient when the voltage change increases. < ; , This is the coefficient for when the voltage change decreases. < ;satisfy , .

7. The protection method for identifying internal transformer faults according to claim 6, characterized in that: The method for calculating the floating threshold of the equivalent excitation inductance change is as follows: in, The equivalent excitation inductance floating threshold value calculated for the current sampling point. This is the change in equivalent magnetizing inductance calculated at the current sampling point. The equivalent excitation inductance floating threshold value calculated for the previous sampling point, when When the value is 1, ; , This is the coefficient when the change in equivalent magnetizing inductance increases. < ; , This is the coefficient for reducing the change in equivalent magnetizing inductance. < ;satisfy , .

8. The protection method for identifying internal faults in a transformer according to claim 7, characterized in that: δ1 is (0.04~0.1) δ2 is (0.1~0.5) , This is the rated voltage on the corresponding side of the transformer. This is the average equivalent magnetizing inductance for the current cycle.

9. The protection method for identifying internal faults in a transformer according to claim 1, characterized in that: The operating conditions for the differential protection element with varying output are: in, This is the short-window integral value of the differential current change after differential filtering. The value is the short-window integral of the braking current change after differential filtering. δ3 is a fixed threshold, taken as (0.15~0.3)Ie, where Ie is the transformer rated current. The braking coefficient is 0.2 to 0.

5.

10. The protection method for identifying internal faults in a transformer according to claim 1 or 9, characterized in that: T1 is 1~3ms, and T2 is 3~5ms. The short-window integral value refers to the half-wave integral value before the current sampling point.

11. A transformer internal fault protection system based on the protection method according to any one of claims 1-10, characterized in that, include: The data acquisition module is used to collect voltage and current data of each phase of the transformer; The calculation module is used to calculate voltage change, differential current, differential current change, equivalent magnetizing inductance, average equivalent magnetizing inductance, equivalent magnetizing inductance change, short-window integral value of voltage change, differential current change, and short-window integral value of braking current change. The fault identification module is used to determine the occurrence of internal transformer faults. The criteria for identification are the simultaneous occurrence of voltage surge and equivalent magnetizing inductance surge. The protection action module is used to activate the protection device to perform protection actions when the conditions for an internal fault in the transformer are met and the differential protection element for the change in quantity is satisfied.

12. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is loaded into the processor, it implements the protection method for identifying internal transformer faults based on the timing relationship between equivalent excitation inductance and voltage change, as described in any one of claims 1-10.

13. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the protection method for identifying internal transformer faults based on the timing relationship between equivalent excitation inductance and voltage change, as described in any one of claims 1-10.

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