A method and device for determining busbar protection CT disconnection

Abstract

The present invention relates to a method and device for determining whether a busbar protection CT is broken, and belongs to the field of relay protection technology. When the present invention detects that both the busbar large differential current and any busbar small differential current are unbalanced, the present invention determines that a branch is a broken branch by looking at the current changes of each branch of the busbar. If only one branch current decreases and the zero-sequence current of the branch with decreasing current is in the same direction and the same size as the unbalanced differential current, the branch is considered to be a broken branch. Compared with the existing busbar protection CT broken line determination, the present invention does not require delayed processing, and can quickly determine whether the current transformer circuit is abnormal or the power grid is faulty by looking at the branch current changes and the directional relationship between the zero-sequence current and the differential current. When the current transformer circuit is abnormal, the abnormal branch can be accurately selected. Therefore, the present invention effectively avoids abnormal operation of the busbar protection and effectively reduces the occurrence of serious accidents such as large-scale power outages.

Description

Technical Field

[0001] The present invention relates to a method and a device for judging a busbar protection CT disconnection, belonging to the technical field of relay protection. Background Art

[0002] Busbars are a crucial component of power plants and substations. Busbar protection is a crucial system component for ensuring the safe and stable operation of power grids, crucial for the security of the entire regional power grid. Improper busbar protection can damage numerous power equipment, undermine system stability, cause a substation-wide power outage, and, in severe cases, disrupt the entire power system. Currently, busbar protection generally utilizes the ratio-restrained current differential principle. Its correct operation relies on the current transformers correctly transmitting the primary current. Failure to do so can lead to incorrect busbar differential protection operation. Therefore, busbar protection must be able to accurately identify CT disconnections and initiate countermeasures.

[0003] The main criterion for the existing busbar protection CT disconnection is that the differential current is greater than the CT disconnection blocking value, and an alarm signal is sent after a delay and the differential protection is locked. Figure 1 As shown, first determine whether there is unbalance based on the large difference and the small difference of each bus. When the large difference and the small difference of any bus are unbalanced, it is determined as a CT break after a delay, and the corresponding phase differential is locked. The broken branch is selected based on the maximum and minimum current values ​​of each branch current of the unbalanced bus.

[0004] First, this criterion fails to effectively distinguish between a line break and a high-resistance ground fault. In a high-resistance ground fault, the differential current may remain above the CT line break blocking threshold for a prolonged period while below the differential protection action threshold. Alternatively, the differential current may exceed the protection action threshold but fail to satisfy the braking equation. If these conditions persist for longer than the CT line break delay, the busbar protection system may mistakenly identify a CT line break and issue an alarm message, simultaneously blocking the differential protection. Even if a subsequent fault develops within the metallic zone, the busbar differential protection will remain inactive, effectively jeopardizing system safety. Second, it fails to distinguish between a fault and a CT line break. Therefore, CT line break detection is always delayed with both alarm and protection blocking to ensure that serious faults are not inadvertently blocked. However, when the CT of a heavily loaded branch is disconnected, the resulting differential current may satisfy the differential action equation. The 3 / 2 connection differential protection will not be locked by voltage, and satisfying the differential action equation will cause the branches on that section of the bus to be tripped by mistake. The double-bus double-tap connection differential protection will trip the segmented branch without being locked by voltage, and satisfying the differential action equation will cause the segmented branch to be tripped by mistake. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and device for determining busbar protection CT disconnection, so as to solve the problem that the differential protection may be malfunctioned when the current transformer circuit is abnormal under heavy load conditions, and the protection may be malfunctioned due to high resistance faults, resulting in the protection not being able to operate correctly after the fault develops into a metallic fault.

[0006] In order to solve the above technical problems, the present invention provides a method for determining whether a busbar protection CT is disconnected. The method comprises the following steps:

[0007] 1) Detect the large bus difference and the small bus difference unbalanced current;

[0008] 2) If both the busbar large differential current and any busbar small differential current are unbalanced, the current changes of each branch of the busbar are detected. If only one branch current decreases and the zero-sequence current of the branch with decreasing current is in the same direction and magnitude as the unbalanced differential current, then the branch is considered to be a broken branch;

[0009] The formula for determining whether the zero-sequence current and the unbalanced differential current are in the same direction and magnitude is:

[0010] Among them I d is the large differential flow value, is the large difference flow vector, is the zero-sequence current vector of the j-th branch, k is the quantitative relationship coefficient, and k is greater than or equal to 4 and less than or equal to 8.

[0011] When the present invention detects that both the busbar large differential current and any busbar small differential current are unbalanced, the current changes in each branch of the busbar are analyzed. If only one branch current decreases and the zero-sequence current of the branch with the decreasing current is in the same direction as the unbalanced differential current and has the same magnitude, then the branch is considered to be a broken branch. Compared with existing busbar protection CT broken line judgment, the present invention does not require delayed processing. It quickly judges whether there is a current transformer circuit abnormality or a power grid fault state based on the branch current changes and the directional relationship between the zero-sequence current and the differential current. When the current transformer circuit is abnormal, the abnormal branch can be accurately selected. Therefore, the present invention effectively avoids abnormal operation of the busbar protection and effectively reduces the occurrence of serious accidents such as large-scale power outages.

[0012] Furthermore, when it is detected that the branch is a broken branch, the differential protection is blocked.

[0013] The present invention quickly blocks the differential protection when a CT disconnection branch is detected, thereby avoiding malfunction of the differential protection caused by the CT disconnection.

[0014] Furthermore, in the step 2), the current change of each branch on the bus is calculated based on the unbalanced phase.

[0015] The present invention only detects the current changes of each branch on the busbar of the unbalanced phase, and can quickly and accurately realize the identification of CT broken wires.

[0016] Furthermore, the branch current becoming smaller refers to a current difference of a certain phase on the branch being smaller than a first set threshold.

[0017] Furthermore, the first set threshold is 0.5I set1 , where I set1 is the unbalanced current threshold.

[0018] The present invention can accurately determine whether the branch current is decreasing based on the set current threshold value.

[0019] Furthermore, the judgment basis for the imbalance of the busbar large difference and each busbar small difference is that both the large difference current and the small difference current are greater than the second set threshold, and the second set threshold is 0.5I set1 , where I set1 is the unbalanced current threshold.

[0020] The present invention also provides a device for determining whether a busbar protection CT is broken, the device comprising a memory and a processor, and a computer program stored in the memory and running on the processor. The processor is coupled to the memory, and when the processor executes the computer program, it implements the method for determining whether a busbar protection CT is broken as described in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the existing busbar protection CT disconnection judgment logic;

[0022] Figure 2 This is a schematic diagram of a double busbar wiring model in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the busbar protection CT disconnection judgment logic of the present invention;

[0024] Figure 4 It is a flow chart of the busbar protection CT disconnection determination method of the present invention. DETAILED DESCRIPTION

[0025] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0026] Example of a method for determining if a busbar protection CT is broken:

[0027] like Figure 3As shown, when the present invention detects that both the busbar large differential current and any busbar small differential current are unbalanced, the current changes of each branch of the busbar are analyzed. If only one branch current becomes smaller and the zero-sequence current of the branch with smaller current is in the same direction and magnitude as the unbalanced differential current, then the branch is considered to be a broken branch. The implementation process of this method is as follows: Figure 4 As shown, the following is a detailed description with reference to specific examples.

[0028] 1. Detect the large difference in busbar and the small difference in each section unbalanced current.

[0029] Real-time detection of busbar large difference and each section small difference unbalanced current, for this embodiment, is aimed at the double busbar connection model, such as Figure 2 As shown, the small differences to be calculated include I mother small differences and II mother small differences, and the large difference calculation formula is: Ⅰ Calculation formula for mother small difference: Ⅱ Mother small difference calculation formula:

[0030] Among them, i d is the large differential current, i dx Ⅰ Bus differential current, i dy Ⅱ bus differential current, K jd is the calculation coefficient of the large difference of the j-th branch, K jdx K is the calculation coefficient of the small difference of the j-th branch to the I mother, jdy is the calculation coefficient of the small difference between the jth branch and the II mother, and n is the number of branches.

[0031] 2. Determine whether the current is balanced based on the large difference and the small difference of each busbar.

[0032] When the large difference and any busbar small difference are greater than 0.5I set1 When , it indicates that there is current imbalance and the CT disconnection judgment needs to be quickly activated. set1 It is the unbalanced differential flow threshold for judgment.

[0033] 3. Collect statistics on the current changes in each branch on the bus.

[0034] If the large difference and any busbar small difference current are unbalanced, calculate the current change of each branch on the busbar according to the unbalanced current phase. Assuming that in this embodiment, the large difference and I bus small difference A phase current are unbalanced, the current change calculation formula, taking phase A as an example: ΔI j =k j [I ja(m) -I ja(m-t) ], find ΔI j <-0.5I set1 branch, ΔI j <-0.5I set1, indicating that the current of the branch becomes smaller, and the number of branches that meet this condition is counted. Among them, ΔI j is the j-th branch current change, k j is the j-th branch current conversion coefficient, I ja(m) is the current of the j-th branch, I ja(m-t) is the cycle-front current of the j-th branch.

[0035] 4. If there is only one branch with a decreasing current and the current decreases, the zero-sequence current and the imbalance difference are calculated. If the currents of multiple branches change (whether increasing or decreasing), it can be considered a fault or system power flow fluctuation, rather than a disconnection feature.

[0036] If the unbalanced current between the large difference and one of the small differences is greater than 0.5I set1 , and only one branch current becomes smaller, the relationship between the large and small difference unbalanced currents and the zero-sequence current of the current change branch is judged. The judgment formula used in the present invention is: Among them, I d is the large differential flow value, is the large difference flow vector, is the zero-sequence current vector of the j-th branch. K is the quantitative relationship coefficient, which can be in the range of 4-8.

[0037] In this embodiment, k=5. If the zero-sequence current and unbalanced differential current of only one current decreasing branch satisfy the above judgment formula, it means that the zero-sequence current and unbalanced differential current of the branch are in the same direction and the same magnitude, and the branch is considered to be a broken branch.

[0038] After determining that it is a broken branch, the differential protection is quickly locked, otherwise the differential protection is not locked.

[0039] The present invention can quickly determine whether it is a current transformer circuit abnormality or a power grid fault state when a system disturbance is detected. When the current transformer circuit is abnormal, the abnormal branch can be accurately selected, avoiding the high-resistance fault refusal to operate and heavy-load disconnection malfunction problems that may exist in the existing bus protection CT disconnection judgment criteria. This method and device can effectively avoid abnormal operation of bus protection, effectively reduce the occurrence of serious accidents such as large-scale power outages, effectively solve actual problems on site, and reduce operational hazards of the power grid.

[0040] Example of a device for determining if a busbar protection CT is broken:

[0041] This embodiment provides a busbar protection CT disconnection determination device, comprising a memory and a processor, and a computer program stored in the memory and running on the processor. The processor is coupled to the memory, and when the processor executes the computer program, the busbar protection CT disconnection determination method in the method embodiment is implemented.

[0042] That is, it should be understood that the methods in the above method embodiments can be implemented by computer program instructions. These computer program instructions can be provided to a processor (such as a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device, etc.), so that the processor executes these instructions to generate the functions specified in the above method flow.

[0043] Specifically, the busbar protection CT disconnection determination device may vary significantly depending on configuration or performance. It may include one or more processors (central processing units, CPUs), memory, and one or more storage media for storing applications or data. The memory and storage media may be either transient or persistent. The program stored on the storage medium may include one or more modules, each of which may include a series of instructions for operating on a data processing device. Furthermore, the processor may be configured to communicate with the storage medium, executing the series of instructions stored on the storage medium on the image processing device.

[0044] The system of this embodiment may further include one or more power supplies, one or more wired or wireless network interfaces, one or more input and output interfaces, and / or one or more operating systems, such as Windows Server™, Mac OS X™, Unix™, Linux™, FreeBSD™, etc.

[0045] The processor referred to in this embodiment is a processing device such as a microprocessor MCU or a programmable logic device FPGA.

[0046] The memory referred to in this embodiment includes physical devices used to store information, typically digitizing the information and then storing it in electrical, magnetic, or optical media. Examples include various types of memory that use electrical energy to store information, such as RAM and ROM; various types of memory that use magnetic energy to store information, such as hard disks, floppy disks, magnetic tapes, magnetic core memory, bubble memory, and USB flash drives; and various types of memory that use optical energy to store information, such as CDs and DVDs. Of course, other types of memory exist, such as quantum memory and graphene memory.

[0047] 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, 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 method for determining if a busbar protection CT is disconnected, characterized in that: The discrimination method includes the following steps: 1) Detect the large bus difference and the small bus difference unbalanced current; 2) If both the busbar large differential current and any busbar small differential current are unbalanced, the current changes of each branch of the busbar are detected. If only one branch current decreases and the zero-sequence current of the branch with decreasing current is in the same direction and magnitude as the unbalanced differential current, the branch is considered to be a broken branch and the differential protection is directly locked; The formula for determining whether the zero-sequence current and the unbalanced differential current are in the same direction and magnitude is: Among them I d is the large differential flow value, is the large difference flow vector, is the zero-sequence current vector of the j-th branch, k is the quantitative relationship coefficient, and k is greater than or equal to 4 and less than or equal to 8.

2. The method for determining a busbar protection CT disconnection according to claim 1, characterized in that: In the step 2), the current change of each branch on the bus is calculated based on the unbalanced phase.

3. The method for determining a busbar protection CT disconnection according to claim 1, characterized in that: The branch current decreases when the current difference of a phase in the branch is less than a first set threshold.

4. The method for determining a busbar protection CT disconnection according to claim 3, characterized in that: The first set threshold is 0.5I set1 , where I set1 is the unbalanced current threshold.

5. The method for determining busbar protection CT disconnection according to claim 1, characterized in that: The judgment basis of the imbalance of the busbar large difference and each busbar small difference is that the large difference current and the small difference current are both greater than the second set threshold value, and the second set threshold value is 0.5I set1 , where I set1 is the unbalanced current threshold.

6. A device for determining if a busbar protection CT is disconnected, characterized in that: The device includes a memory and a processor, and a computer program stored in the memory and running on the processor. The processor is coupled to the memory, and when the processor executes the computer program, it implements the method for determining whether a busbar protection CT is broken according to any one of claims 1 to 5.

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