A protection method and system for identifying internal faults of transformers based on equivalent excitation inductance

Abstract

A method and system for identifying internal faults in a transformer based on equivalent excitation inductance, the method comprising: collecting phase voltage and current data on each side of the transformer; calculating differential current, differential current mutation, instantaneous equivalent excitation inductance, average equivalent excitation inductance, average equivalent excitation inductance floating threshold, instantaneous equivalent excitation inductance normalized value, and instantaneous equivalent excitation inductance normalized value change; if the instantaneous equivalent excitation inductance normalized value is less than the set threshold for one consecutive cycle after protection is activated, the protection is enabled; if the change in the equivalent instantaneous excitation inductance normalized value within one cycle is within the set threshold range, the protection device is activated to perform a protective action. The present invention utilizes the characteristic differences between the instantaneous equivalent excitation inductance normalized value and its change in the transformer during normal operation or in the event of external faults, internal faults, or inrush current to quickly identify internal faults and perform protective actions.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection, and in particular relates to a protection method and system for identifying internal faults of a transformer based on equivalent excitation inductance. Background Art

[0002] Currently, the electric quantity differential protection is the main protection for transformers. It has the advantages of high sensitivity and simple and fast operation. However, it will be affected by the frequency offset, harmonics and through current of new energy access, resulting in insufficient sensitivity and reduced speed of differential protection.

[0003] Research at home and abroad has also investigated identifying inrush currents or internal transformer faults by measuring the excitation inductance of transformers, based on the characteristic differences in excitation inductance during normal operation, external faults, internal faults, or core saturation. For example, prior art CN201210344440.X discloses a method for determining equivalent instantaneous inductance inrush current lockout for UHV voltage-regulating transformer protection. First, the operating and braking currents of phases A, B, and C of the UHV voltage-regulating transformer are calculated. By comparing the operating and braking currents, it is determined whether the phase has entered the operating region of the ratio-braking characteristic. For each phase that has entered the operating region, the equivalent port voltage of the voltage-regulating transformer is calculated using a voltage conversion method based on the medium-voltage side voltage of the UHV transformer main transformer. The variance of the equivalent instantaneous inductance, σLi, of the phase is calculated. If the variance of the equivalent instantaneous inductance exceeds a threshold value, ε (i.e., σLi > ε), it is determined to be an inrush current, and the phase protection is locked. Otherwise, it is determined to be a fault, and the judgment result is output. The above patented solution is a method for identifying magnetizing inrush current based on the equivalent instantaneous inductance of a UHV voltage-regulating transformer. The variance of the equivalent instantaneous inductance calculated by this method is relatively small both for in-zone and out-of-zone faults, and cannot distinguish between internal and external faults of the transformer. Internal faults must be identified in combination with the differential ratio braking characteristics, and the equivalent instantaneous inductance variance threshold is related to the transformer structure, wiring type, silicon steel sheet characteristics, etc., making it inconvenient for on-site adjustment.

[0004] It can be seen that although there are studies in the existing technology on measuring the transformer excitation inductance for excitation inrush current identification or transformer internal fault judgment, due to differences in transformer structure, connection type, silicon steel sheet characteristics, etc., there are problems such as difficulty in selecting the set value threshold and difficulty in engineering adjustment. Summary of the Invention

[0005] In order to solve the problem that transformer differential protection is affected by frequency offset, harmonics and through current caused by the access of new energy, resulting in insufficient sensitivity and reduced speed of differential protection, the present invention provides a protection method and system for identifying internal faults of transformer based on equivalent excitation inductance.

[0006] In order to achieve the above-mentioned purpose of the invention, the present invention specifically adopts the following technical solutions.

[0007] A protection method for identifying internal faults of a transformer based on equivalent excitation inductance, characterized in that the protection method comprises:

[0008] Collect the phase voltage and current on each side of the transformer, calculate the floating threshold value of the equivalent excitation inductance value of each phase and the average equivalent excitation inductance value, and calculate the normalized value of the instantaneous equivalent excitation inductance based on the floating threshold value;

[0009] When the differential current mutation amount is greater than the differential current mutation threshold value, the protection is activated, and the change of the normalized value of the instantaneous equivalent excitation inductance within one cycle after the protection is activated is calculated;

[0010] If the normalized value of the instantaneous equivalent excitation inductance is continuously less than the opening threshold value within one cycle after the protection is started, the protection element will be opened, otherwise the protection will be locked;

[0011] If the change in the normalized value of the instantaneous equivalent excitation inductance within one cycle after the protection is started is within the change threshold, it is determined that an internal fault has occurred in the transformer and the protection action output trips, otherwise the protection is locked.

[0012] The present invention further includes the following preferred embodiments.

[0013] Preferably,

[0014] The normalized value of the instantaneous equivalent excitation inductance is calculated as follows:

[0015]

[0016] Among them, L m is the instantaneous equivalent excitation inductance, L m_ave_th is the floating threshold value of the average equivalent excitation inductance.

[0017] More preferably,

[0018] The calculation method of the instantaneous equivalent excitation inductance value is:

[0019]

[0020] Among them, k is the kth sampling point, k-1 is the previous sampling point, L m is the current instantaneous equivalent excitation inductance value, u(k) is the kth voltage sampling value, i d (k) is the kth differential flow sampling value, i d (k-1) is the difference flow sampling value of the previous sampling point, and Δt is the time interval between two sampling points.

[0021] More preferably,

[0022] When calculating the instantaneous equivalent excitation inductance value, for the phase-difference protection of the transformer, the differential current is the phase-difference differential current, and the voltage is the corresponding phase voltage; for the longitudinal differential protection of the transformer, the differential current is the longitudinal differential current, and the voltage is the corresponding line voltage.

[0023] Further preferably,

[0024] The calculation method of the average equivalent excitation inductance value is as follows:

[0025]

[0026] where, L m_ave (k) is the average equivalent excitation inductance value within the previous cycle before the kth sampling point, L m (k-i) is the instantaneous equivalent excitation inductance value at the i sampling points before the kth sampling point, and N is the number of sampling points in one cycle;

[0027] The calculation method of the average equivalent excitation inductance floating threshold value is as follows:

[0028]

[0029] where, C1 and C′1 are coefficients when the average equivalent excitation inductance increases, C1 < C′1 and C1 + C′1 = 1; C2 and C′2 are coefficients when the average equivalent excitation inductance decreases, C2 < C′2 and C2 + C′2 = 1; L m_ave_th (k) is the average equivalent excitation inductance floating threshold value to be calculated currently, L m_ave_th (k-1) is the average equivalent excitation inductance floating threshold value calculated last time, L m_ave (k) is the average equivalent excitation inductance value calculated currently. The average equivalent excitation inductance floating threshold value in the first cycle after the protection system is powered on is calculated according to the average equivalent excitation inductance value in the first cycle.

[0030] Further preferably,

[0031] The calculation method of the change amount of the instantaneous equivalent excitation inductance normalization value within one cycle is as follows:

[0032]

[0033] where, N is the number of sampling points in one cycle, is the instantaneous equivalent excitation inductance value at the kth sampling point within one cycle.

[0034] Further preferably,

[0035] The opening threshold value is taken as 0.2.

[0036] Further preferably,

[0037] The threshold range of the change amount is 0.9-1.1.

[0038] This application also seeks to protect a transformer internal fault protection system based on the aforementioned protection method, which is characterized by comprising:

[0039] Data acquisition module, used to collect phase voltage and current data on each side of the transformer;

[0040] Calculation module, used to calculate differential current, differential current mutation, instantaneous equivalent excitation inductance value, average equivalent excitation inductance value, average equivalent excitation inductance floating threshold value, instantaneous equivalent excitation inductance normalized value, and instantaneous equivalent excitation inductance normalized value change;

[0041] A fault opening module is used to open the protection element when the protection start condition is met. The judgment condition is that the normalized value of the instantaneous equivalent excitation inductance after the protection is started is less than the set threshold for one consecutive cycle;

[0042] A fault identification module is used to determine if a transformer internal fault has occurred when the protection start condition is met. The judgment condition is that the change in the normalized value of the equivalent instantaneous excitation inductance within one cycle is within a set threshold range;

[0043] The protection action module is used to start the protection device to perform protection action when the internal fault conditions of the transformer are met.

[0044] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The computer program, when loaded into the processor, implements the aforementioned protection method for identifying internal faults of a transformer based on equivalent excitation inductance.

[0045] A computer-readable storage medium stores a computer program, wherein when the computer program is executed by a processor, the computer program implements the aforementioned protection method for identifying internal faults of a transformer based on equivalent excitation inductance.

[0046] Beneficial effects: Compared with the existing power differential protection technology, the present invention has the following significant advantages:

[0047] 1. It is not affected by the fault current penetration characteristics of new energy access, has high protection sensitivity, and is also highly sensitive to minor inter-turn faults of transformers;

[0048] 2. It adopts a time-domain algorithm, which is not affected by the frequency deviation and harmonics of renewable energy access. It has good protection speed and can cut off the faulty transformer in about 20ms when an internal fault occurs in the transformer. 3. The protection method is simple and practical, easy to implement, and the set value does not need to be adjusted. It is suitable for transformers of different structural types. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the flow of the protection method for identifying internal faults of a transformer based on equivalent excitation inductance according to the present invention;

[0050] Figure 2 This is a schematic diagram of the differential current and equivalent excitation inductance when the transformer internal fault protection is quickly activated;

[0051] Figure 3 This is a schematic diagram of the differential current and equivalent excitation inductance when the transformer does not operate reliably due to faults outside the transformer area;

[0052] Figure 4 This is a schematic diagram of the differential current and equivalent excitation inductance when the transformer no-charge protection is reliable and does not operate. DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without making creative efforts are all within the scope of protection of the present invention.

[0054] As attached Figure 1 As shown, the present invention discloses a protection method for identifying internal faults of a transformer based on equivalent excitation inductance, comprising:

[0055] Step 1: Collect phase voltage and current data on each side of the transformer;

[0056] Calculate the differential current, differential current mutation, instantaneous equivalent excitation inductance, average equivalent excitation inductance, average equivalent excitation inductance floating threshold value, and instantaneous equivalent excitation inductance normalized value;

[0057] The calculation method of the instantaneous equivalent excitation inductance value is:

[0058]

[0059] Among them, k is the kth sampling point, k-1 is the previous sampling point, L m is the current instantaneous equivalent excitation inductance value, u(k) is the kth voltage sampling value, i d (k) is the kth differential flow sampling value, i d (k-1) is the difference flow sampling value of the previous sampling point, and Δt is the time interval between two sampling points.

[0060] The calculation method of the average equivalent excitation inductance is:

[0061]

[0062] Among them, L m_ave (k) is the average equivalent excitation inductance value within one cycle before the k-th sampling point, and L m (k - i) is the instantaneous equivalent excitation inductance value at the i-th sampling point before the k-th sampling point, and N is the number of sampling points in one cycle.

[0063] The calculation method of the average equivalent excitation inductance floating threshold value is as follows:

[0064]

[0065] Among them, C1 and C′1 are coefficients when the average equivalent excitation inductance increases, C1 < C′1 and C1 + C′1 = 1; C2 and C′2 are coefficients when the average equivalent excitation inductance decreases, C2 < C′2 and C2 + C′2 = 1; L m_ave_th (k) is the average equivalent excitation inductance floating threshold value to be calculated currently, and L​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The present application also discloses a transformer internal fault protection system based on the aforementioned protection method, which is characterized by comprising:

[0075] Data acquisition module, used to collect phase voltage and current data on each side of the transformer;

[0076] Calculation module, used to calculate differential current, differential current mutation, instantaneous equivalent excitation inductance value, average equivalent excitation inductance value, average equivalent excitation inductance floating threshold value, instantaneous equivalent excitation inductance normalized value, and instantaneous equivalent excitation inductance normalized value change;

[0077] A fault opening module is used to open the protection element when the protection start condition is met. The judgment condition is that the normalized value of the instantaneous equivalent excitation inductance after the protection is started is less than the set threshold for one consecutive cycle;

[0078] A fault identification module is used to determine if a transformer internal fault has occurred when the protection start condition is met. The judgment condition is that the change in the normalized value of the equivalent instantaneous excitation inductance within one cycle is within a set threshold range;

[0079] The protection action module is used to start the protection device to perform protection action when the internal fault conditions of the transformer are met.

[0080] Example 1:

[0081] A protection method for identifying internal faults of a transformer based on equivalent excitation inductance includes the following steps:

[0082] (1) Collect phase voltage and current data on each side of the transformer;

[0083] Calculate the differential current, differential current mutation, instantaneous equivalent excitation inductance, average equivalent excitation inductance, average equivalent excitation inductance floating threshold, instantaneous equivalent excitation inductance normalized value; change in instantaneous equivalent excitation inductance normalized value;

[0084] (2) When the differential current mutation amount is greater than the differential current mutation threshold value, the protection is activated, and the change of the normalized value of the instantaneous equivalent excitation inductance within one cycle after the protection is activated is calculated;

[0085] (3) Fault opening module, which is used to open the protection element after the protection start condition is met. The judgment basis is that if the normalized value of the instantaneous equivalent excitation inductance is less than 0.2 for 20ms continuously after the protection is started, the protection element is opened; otherwise, the protection is locked;

[0086] (4) After the protection is started, if the change in the normalized value of the equivalent instantaneous excitation inductance within one cycle is between 0.9 and 1.1, it is judged that an internal fault has occurred, and the protection device is started to perform the protection action. Otherwise, it is locked to prevent false operation.

[0087] Take the B phase differential flow as an example, see the attached Figure 2-4 By using the technical solution of the present invention, it is possible to accurately identify the internal fault of the transformer and quickly initiate a protection action when it is determined that the transformer has an internal fault; see the attached Figure 3 , when the transformer has an out-of-zone fault, it can effectively lock out the protection; see the attached Figure 4 , when the transformer is empty and charged, it is effectively locked for protection.

[0088] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0089] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0090] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0091] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state 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++, and conventional procedural programming languages ​​such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of 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., utilizing an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions. The electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A protection method for identifying internal faults of a transformer based on equivalent excitation inductance, characterized in that: The protection method includes: Collect the phase voltage and current on each side of the transformer, calculate the floating threshold value of the instantaneous equivalent excitation inductance value and the average equivalent excitation inductance value of each phase, and use the ratio of the instantaneous equivalent excitation inductance to the floating threshold value as the normalized value of the instantaneous equivalent excitation inductance; When the differential current mutation is greater than the differential current mutation threshold, the protection is activated. Calculate the change in the normalized value of the instantaneous equivalent excitation inductance within one cycle after the protection is activated. Among them, N is the number of sampling points per cycle, is the instantaneous equivalent excitation inductance value at the kth sampling point within one cycle; if the normalized value of the instantaneous equivalent excitation inductance is continuously less than the opening threshold value within one cycle after the protection is activated, the protection element is opened, otherwise the protection is locked; If the change in the normalized value of the instantaneous equivalent excitation inductance within one cycle after the protection is started is within the change threshold, it is determined that an internal fault has occurred in the transformer and the protection action output trips, otherwise the protection is locked.

2. The protection method for identifying transformer internal faults based on equivalent excitation inductance according to claim 1, characterized in that: The normalized value of the instantaneous equivalent excitation inductance is calculated as follows: Among them, L m is the instantaneous equivalent excitation inductance, L m_ave_th is the floating threshold value of the average equivalent excitation inductance.

3. The protection method for identifying transformer internal faults based on equivalent excitation inductance according to claim 2, characterized in that: The calculation method of the instantaneous equivalent excitation inductance value is: Among them, k is the kth sampling point, k-1 is the previous sampling point, L m is the current instantaneous equivalent excitation inductance value, u(k) is the kth voltage sampling value, i d (k) is the kth differential flow sampling value, i d (k-1) is the difference flow sampling value of the previous sampling point, and Δt is the time interval between two sampling points.

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

5. The protection method for identifying transformer internal faults based on equivalent excitation inductance according to claim 3 or 4, characterized in that: The calculation method of the average equivalent excitation inductance is: Among them, L m_ave (k) is the average equivalent excitation inductance value in the cycle before the kth sampling point, L m (ki) is the instantaneous equivalent excitation inductance of the i sampling points before the k-th sampling point, and N is the number of sampling points per cycle; The calculation method of the floating threshold value of the average equivalent excitation inductance is: Among them, C1 and C'1 are coefficients when the average equivalent excitation inductance increases, C1 < C'1 and C1 + C'1 = 1; C2 and C'2 are coefficients when the average equivalent excitation inductance decreases, C2 < C'2 and C2 + C'2 = 1; L m_ave_th (k) is the floating threshold value of the average equivalent excitation inductance to be calculated currently, L m_ave_th (k - 1) is the floating threshold value of the average equivalent excitation inductance calculated last time. The floating threshold value of the average equivalent excitation inductance in the first cycle after the protection system is powered on is calculated according to the average equivalent excitation inductance value in the first cycle.

6. The protection method for identifying transformer internal faults based on equivalent excitation inductance according to claim 1, characterized in that: The opening threshold value is 0.

2.

7. The protection method for identifying transformer internal faults based on equivalent excitation inductance according to claim 1 or 6, characterized in that: The threshold range of the change amount is 0.9-1.

1.

8. A transformer internal fault protection system based on the protection method according to any one of claims 1 to 7, characterized in that: include: Data acquisition module, used to collect phase voltage and current data on each side of the transformer; Calculation module, used to calculate differential current, differential current mutation, instantaneous equivalent excitation inductance value, average equivalent excitation inductance value, average equivalent excitation inductance floating threshold value, instantaneous equivalent excitation inductance normalized value, and instantaneous equivalent excitation inductance normalized value change; The fault opening module is used to open the protection element when the protection start condition is met. The judgment condition is that the normalized value of the instantaneous equivalent excitation inductance after the protection is started is less than the set threshold for one consecutive cycle; The fault identification module is used to determine if a transformer internal fault has occurred when the protection start conditions are met. The judgment condition is that the change in the normalized value of the equivalent instantaneous excitation inductance within one cycle is within the set threshold range; The protection action module is used to start the protection device to perform protection action when the internal fault conditions of the transformer are met.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the computer program is loaded into a processor, the protection method for identifying internal faults of a transformer based on equivalent excitation inductance according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the protection method for identifying internal faults of a transformer based on equivalent excitation inductance according to any one of claims 1 to 7 is implemented.

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