Branch current fundamental wave content-based current transformer disconnection discrimination method and system

Abstract

The invention discloses a current transformer disconnection judgment method and system based on branch current fundamental wave content. The method comprises the following steps: acquiring a three-phase current effective value and a three-phase fundamental wave current effective value of each branch; when the power system does not have a fault, judging whether the current transformer is disconnected, determining the three-phase current fundamental wave content by using the three-phase fundamental wave current effective value and the three-phase current effective value, determining the maximum value of the inter-phase fundamental wave content difference by using the three-phase current fundamental wave content, and when the maximum value of the inter-phase fundamental wave content difference is greater than a set threshold value, judging whether the current transformer is disconnected. Current transformer disconnection is determined; taking a phase corresponding to the maximum value in the three-phase current fundamental wave content as a reference phase, and when the current fundamental wave content of the reference phase is not less than 0.8 and is not less than two times of the current fundamental wave content of other phases (to-be-identified phases), if the maximum value in the three-phase current effective values is greater than the precision minimum value of the current acquired by the relay protection device, determining that the current is acquired by the relay protection device; and if yes, determining that the to-be-identified phase of the current transformer is broken. The low-current sampling precision of a relay protection device is met, and the broken line identification sensitivity is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of relay protection of power systems, and more specifically relates to a method and system for identifying current transformer (CT) disconnection based on the fundamental wave content ratio of branch currents. Background Art

[0002] The power system uses relay protection equipment to cut off faults to ensure the safety of equipment and the power grid. Relay protection identifies faults by converting the large current in the primary system into a small current measurable by the protection through a current transformer (CT), and then identifies grid faults through various protection functions such as differential protection, distance protection, and power direction protection. Once the current transformer has an abnormality, including disconnection, phase sequence abnormality, reverse polarity connection, etc., it will cause misoperation and refusal to operate of the protection function, and in severe cases, it will cause large-scale power outages and equipment damage.

[0003] In the prior art, there are many methods for identifying CT disconnection in relay protection, but it is necessary to set a current threshold to avoid grid unbalanced current or collect error current. The relatively high setting value makes the sensitivity of CT disconnection identification not high, and it cannot be identified under light load and small current conditions, and will be misidentified under high-resistance fault conditions, thus causing misoperation and refusal to operate of the relay protection device. Summary of the Invention

[0004] To solve the deficiencies in the prior art, the present invention provides a method and system for identifying current transformer disconnection based on the fundamental wave content of branch currents, which uses the difference in the fundamental wave content ratio between the healthy phase and the disconnected phase to identify CT disconnection. When the small current sampling accuracy of the relay protection device meets the requirements, the setting value is independent of the load current of the power grid system, so the sensitivity of disconnection identification is significantly improved.

[0005] The present invention adopts the following technical solutions.

[0006] The present invention proposes a method for identifying current transformer disconnection based on the fundamental wave content of branch currents, including:

[0007] Collect the three-phase currents and voltages of each branch in the power transmission and transformation system to determine the effective values of the three-phase currents and the effective values of the three-phase fundamental wave currents of each branch;

[0008] When the power system does not have a fault, determine whether the current transformer is disconnected;

[0009] When determining whether the current transformer is disconnected, use the effective values of the three-phase fundamental wave currents and the effective values of the three-phase currents to determine the fundamental wave content of the three-phase currents, use the fundamental wave content of the three-phase currents to determine the maximum value of the fundamental wave content difference between phases. When the maximum value of the fundamental wave content difference between phases is greater than the set threshold, it is determined that there is a current transformer disconnection;

[0010] Taking the phase corresponding to the maximum value of the fundamental wave content of the three-phase current as the reference phase, when the fundamental wave content of the reference phase is not less than 0.8 and not less than 2 times the fundamental wave content of the phase to be identified, if the maximum value of the three-phase current effective values is greater than the minimum value of the current acquisition accuracy of the relay protection device, then it is determined that the phase to be identified of the current transformer is disconnected.

[0011] Preferably, the effective values of the three-phase fundamental wave currents are IArms1, IBrms1, and ICrms1 respectively, the effective values of the three-phase currents are IArms, IBrms, and ICrms respectively, and the fundamental wave contents of the three-phase currents satisfy the following relational expressions:

[0012] KA = IArms1 / IArms

[0013] KB = IBrms1 / IBrms

[0014] KC = 1Crms1 / ICrms

[0015] In the formula, KA, KB, and KC are the fundamental wave contents of the three-phase currents.

[0016] Preferably, taking the absolute value of the difference between the fundamental wave contents of any two phases and dividing it by the maximum value of the fundamental wave contents of the two phases as the fundamental wave content difference between phases, and taking the maximum value of the three fundamental wave content differences between phases, the following relational expression represents it:

[0017]

[0018] In the formula, K is the maximum value of the fundamental wave content differences between phases.

[0019] Preferably, when the maximum value of the fundamental wave content differences between phases is greater than 20%, it is determined that there is a disconnection in the current transformer.

[0020] Preferably, taking the phase corresponding to the maximum value of the fundamental wave content of the three-phase current as the reference phase, the following relational expression is satisfied:

[0021] K1 = max{KA, KB, KC}

[0022] When the fundamental wave content of the reference phase is not less than 0.8 and not less than 2 times the fundamental wave content of the phase to be identified, if the maximum value of the three-phase current effective values is greater than the minimum value of the current acquisition accuracy of the relay protection device, then it is determined that the phase to be identified of the CT is disconnected, including:

[0023] When K1 ≠ KA and K1 ≥ 0.8 and K1 ≠ 2KA, if max{IA, IB, IC} > Iminset, then it is determined that the A phase of the CT is disconnected;

[0024] When K1≠KB, K1≥0.8 and K1≥2KB, if max{IA, IB, IC}>Iminset, it is determined that the B-phase of the CT is broken.

[0025] When K1≠KC, K1≥0.8 and K1≥2KC, if max{IA, IB, IC}>Iminset, it is determined that the C-phase of the CT is broken.

[0026] Among them, IA, IB, and IC are the effective values of the three-phase currents, Iminset is the minimum value of the current acquisition accuracy of the relay protection device, taking 0.01In, In is the secondary rated current of the current transformer, and the value is 5A or 1A.

[0027] Preferably, the method further includes: disconnection alarm and locking the corresponding protection function.

[0028] Preferably, the method further includes: in the one-and-a-half breaker connection mode, each breaker in a string is used as an independent branch, and based on the fundamental wave content of the branch current, the disconnection of a group of current transformers corresponding to each breaker is discriminated;

[0029] Alternatively, two adjacent breakers in a string are used as an independent branch, and based on the fundamental wave content of the branch current, the disconnection of two groups of current transformers corresponding to the two adjacent breakers is discriminated.

[0030] The present invention also proposes a current transformer disconnection discrimination system based on the fundamental wave content of the branch current, including:

[0031] An acquisition module, configured to acquire the three-phase currents and voltages of each branch in the power transmission and transformation system to determine the effective values of the three-phase currents and the effective values of the three-phase fundamental wave currents of each branch;

[0032] A disconnection discrimination module, configured to, when the power system does not have a fault and discriminates whether the current transformer is disconnected, determine the three-phase fundamental wave current content by using the effective values of the three-phase fundamental wave currents and the effective values of the three-phase currents, determine the maximum value of the difference in the fundamental wave content between phases by using the three-phase fundamental wave current content, and when the maximum value of the difference in the fundamental wave content between phases is greater than the set threshold, determine that there is a disconnection of the current transformer; taking the phase corresponding to the maximum value of the three-phase fundamental wave current content as the reference phase, when the fundamental wave current content of the reference phase is not less than 0.8 and not less than 2 times the fundamental wave current content of the phase to be identified, if the maximum value of the three-phase current effective values is greater than the minimum value of the current acquisition accuracy of the relay protection device, it is determined that the phase to be identified of the current transformer is disconnected.

[0033] A terminal includes a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0034] A computer-readable storage medium stores a computer program thereon, and when the program is executed by a processor, the steps of the method are implemented.

[0035] The beneficial effects of the present invention are as follows. Compared with the prior art, it at least includes that the method proposed by the present invention uses the minimum sampling accuracy value of the relay protection device as the current threshold, which has nothing to do with the magnitude of the system load current, improves the sensitivity of CT disconnection recognition, and can be widely applied to small power sources and light load systems with a high proportion of new energy connected to the grid, improving the power generation efficiency of new energy such as photovoltaic and wind power. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flowchart of a current transformer disconnection discrimination method based on the fundamental wave content of branch current proposed by the present invention;

[0037] Figure 2 is a wiring diagram of a 500 kV relay protection device in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, 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 a part of the embodiments of the present invention, rather than all the embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0039] The present invention proposes a current transformer disconnection discrimination method based on the fundamental wave content of branch current, as Figure 1 shown, the method includes:

[0040] Step 1, collect the three-phase currents and voltages of each branch in the power transmission and transformation system to determine the effective values of the three-phase currents and the effective values of the three-phase fundamental wave currents of each branch.

[0041] Specifically, the A, B, and C phase currents and voltages of branches such as transformers, reactors, busbars, or transmission lines are collected through current transformers, voltage transformers, and AD conversion branches, and the collected data is stored in the relay protection device for subsequent calculations.

[0042] In the embodiment, the root mean square method of sampling values is used to calculate the effective values of the three-phase currents or voltages of each branch, and the Fourier method is used to calculate the effective values of the three-phase fundamental wave currents of each branch. Among them, the current or voltage frequency is 50 Hz or 60 Hz, which is a non-restrictive and preferable choice.

[0043] Specifically, the calculation formula for the effective value of the three-phase current or voltage is:

[0044]

[0045] where \(K_{Arms}\), \(K_{Brms}\), and \(K_{Crms}\) are the effective values of the currents or voltages of phases A, B, and C respectively, and \(X\) A (k), \(X\) B (k), \(X\) C (k) are the sampled values of the currents or voltages of phases A, B, and C at the k-th point within the current current or voltage cycle, and N is the number of sampling points within one current or voltage cycle;

[0046] The effective values of the three-phase fundamental currents are \(I_{Arms1}\), \(I_{Brms1}\), and \(I_{Crms1}\) respectively, and the effective values of the three-phase currents are \(I_{Arms}\), \(I_{Brms}\), and \(I_{Crms}\) respectively;

[0047] The effective values of the three-phase fundamental voltages are \(U_{Arms1}\), \(U_{Brms1}\), and \(U_{Crms1}\) respectively, and the effective values of the three-phase voltages are \(U_{Arms}\), \(U_{Brms}\), and \(U_{Crms}\) respectively;

[0048] In the embodiment, when the current or voltage frequency is 50 Hz, sampling is performed at 20 ms intervals within one current or voltage cycle, so 48 samples are taken for the current or voltage, and N = 48.

[0049] Specifically, the formulas for the real and imaginary parts of the three-phase fundamental current or fundamental voltage of the branch are:

[0050]

[0051] where \(a\) 1 and \(b\) 1 are the real and imaginary parts of the three-phase fundamental current or fundamental voltage of the branch respectively, \(x\) k is the sampled value of the current or voltage at the k-th point, \(x\) 0 is the last sampled value of the current or voltage in the previous current or voltage cycle, and \(x\) N is the last sampled value of the current or voltage in the current current or voltage cycle.

[0052] Specifically, the effective values of the three-phase fundamental current or three-phase fundamental voltage satisfy the following relationship:

[0053]

[0054] where \(K_{rms1}\) is the effective value of the three-phase fundamental current or three-phase fundamental voltage;

[0055] The effective values of the three-phase voltages, negative-sequence voltages, and zero-sequence voltages are also calculated;

[0056] The negative-sequence voltage \(U\) 2 satisfies the following relationship:

[0057]

[0058] Wherein, U a , U b , U c respectively represent the instantaneous values of the three-phase voltages, and a = e j2π / 3 is the positive-sequence rotation operator.

[0059] The zero-sequence voltage U 0 satisfies the following relational expression:

[0060]

[0061] Wherein, U a , U b , U c respectively represent the instantaneous values of the three-phase voltages.

[0062] Step 2: When the power system does not have a fault, determine whether the CT is disconnected; otherwise, return to Step 1.

[0063] In the embodiment, the methods for determining whether the power system has a fault include but are not limited to: the determination method based on the composite voltage criterion, the determination method based on the differential current, the determination method based on the externally connected zero-sequence current, and the determination method based on the identification of the sudden change in current; those skilled in the art can select different fault determination methods according to the actual engineering requirements.

[0064] When the power system has a fault, return to Step 1, and currently, it is not possible to determine whether the CT is disconnected; when the power system does not have a fault, determine whether the CT is disconnected.

[0065] Relying solely on the voltage measurement method cannot identify all faults. Therefore, the current measurement method is required to handle the situations that cannot be identified by the voltage measurement method;

[0066] When the voltage of a branch cannot be collected to identify the system fault, the branch current method can be used to identify the system fault. The methods for identifying faults by the branch current method include: the differential current identification method, the energy ratio method, the sudden change in current identification method, or the zero-sequence current identification method.

[0067] Wavelet analysis can be used to calculate the high-frequency and low-frequency energy ratio to form a fault discrimination scheme. Its main principle utilizes the attenuation effect of the substation bus boundary on the high-frequency energy. For the line branch of the bus, when the fault occurs outside the forward zone, the protection device measures less high-frequency energy, while when the fault occurs inside the forward zone, the protection device measures more high-frequency energy. By using the energy ratio of the high-frequency and low-frequency bands, an energy ratio fault discrimination can be formed.

[0068] By selecting an appropriate threshold value for the high-frequency and low-frequency energy proportion coefficient, the in-zone or out-of-zone faults of the line can be distinguished, and the line fault and normal operation can be distinguished.

[0069] Step 3: Determine the fundamental wave content of the three-phase current using the effective values of the three-phase fundamental waves and the effective values of the three-phase currents. Determine the maximum value of the difference in fundamental wave content between phases using the fundamental wave content of the three-phase current. When the maximum value of the difference in fundamental wave content between phases is greater than the set threshold, it is determined that a CT disconnection exists, and proceed to Step 4; otherwise, return to Step 1.

[0070] In the embodiment, the effective values of the three-phase fundamental waves are IArms1, IBrms1, and ICrms1 respectively, the effective values of the three-phase currents are IArms, IBrms, and ICrms respectively, and the fundamental wave content of the three-phase current satisfies the following relational expressions:

[0071] KA = IArms1 / IArms (9)

[0072] KB = IBrms1 / IBrms (10)

[0073] KC = ICrms1 / ICrms (11)

[0074] In the formula, KA, KB, and KC are the fundamental wave content of the three-phase current;

[0075] The absolute value of the difference between the fundamental wave content of any two-phase currents and the ratio of the maximum value of the fundamental wave content of the two phases is used as the difference in fundamental wave content between phases; take the maximum value of the differences in fundamental wave content between three phases, as shown in the following relational expression:

[0076]

[0077] In the formula, K is the maximum value of the difference in fundamental wave content between phases;

[0078] When the maximum value of the difference in fundamental wave content between phases is greater than 20%, it is determined that a CT disconnection exists.

[0079] Step 4: Using the phase corresponding to the maximum value of the fundamental wave content of the three-phase current as the reference phase, when the fundamental wave content of the reference phase is not less than 0.8 and not less than twice the fundamental wave content of the phase to be identified, if the maximum value of the effective values of the three-phase currents is greater than the minimum value of the accuracy of the current collected by the relay protection device, then it is determined that the phase to be identified of the CT is disconnected.

[0080] Under normal operation of the power system, the fundamental wave content is the main current content, approaching 100%, the current is close to an ideal sine wave, and the values of KA, KB, and KC are close to being equal to 1. When a phase current is interrupted, the current waveform is an abnormal waveform containing high-order harmonics or DC components. Using the abnormal characteristics of graphical similarity and combining the inherent characteristics that the three-phase currents in the circuit are equal in magnitude and have a phase difference of 120°, it can identify CT disconnection more sensitively than the usual differential current or zero-sequence current methods. The standard sine wave can be described by the fundamental wave. By using the difference in fundamental wave content, the similarity of the images can be distinguished, thereby distinguishing whether the CT branch is disconnected.

[0081] Specifically, it includes:

[0082] 1), Taking the phase corresponding to the maximum value of the fundamental wave content of the three-phase currents as the reference phase, satisfying the following relational expression:

[0083] K1 = max{KA, KB, KC} (13)

[0084] 2), When the fundamental wave content of the reference phase current is not less than 0.8 and not less than 2 times the fundamental wave content of the other phases (i.e., the phases to be identified), if the maximum value of the three-phase current effective values is greater than the minimum accuracy of the current collected by the relay protection device, it is determined that the phase to be identified of the CT is disconnected;

[0085] In the embodiment, when K1 ≠ KA and K1 ≥ 0.8 and K1 ≥ 2KA, if max{IA, IB, IC} > Iminset, it is determined that the A phase of the CT is disconnected; when K1 ≠ KB and K1 ≥ 0.8 and K1 ≥ 2KB, if max{IA, IB, IC} > Iminset, it is determined that the B phase of the CT is disconnected; when K1 ≠ KC and K1 ≥ 0.8 and K1 ≥ 2KC, if max{IA, IB, IC} > Iminset, it is determined that the C phase of the CT is disconnected; where IA, IB, and IC are the effective values of the three-phase currents, Iminset is the minimum accuracy of the current collected by the relay protection device, and in the embodiment, it is taken as 0.01In, In is the secondary rated current of the current transformer, and the value is 5A or 1A.

[0086] IA, IB, and IC can be the effective values of the three-phase currents or the fundamental wave effective values of the three-phase currents.

[0087] Step 5, issue a disconnection alarm, block the corresponding protection function, and return to step 1.

[0088] The method further includes: in a one-and-a-half breaker connection mode, each breaker in a string is used as an independent branch, and based on the fundamental wave content of the branch current, the disconnection of a group of current transformers corresponding to each breaker is discriminated;

[0089] Alternatively, two adjacent circuit breakers in a string are regarded as an independent branch, and the disconnection of two groups of current transformers corresponding to the two adjacent circuit breakers is discriminated based on the fundamental wave content of the branch current.

[0090] Figure 2 Figure 500kV relay protection device wiring diagram, a total of 4 string circuit breaker units, circuit breakers 5011, 5012, 5013 are the first string, 5021, 5022, 5023 are the second string, 5031, 5032, 5033 are the third string, 5041, 5042, 5043 are the fourth string. Each string of circuit breaker units contains three groups of current transformers (CTs), configured according to 6-7-6, that is, the two side circuit breaker current transformers have 6 secondary windings, and the middle circuit breaker has 7 secondary windings. The secondary windings are respectively connected to line protection, circuit breaker protection, transformer protection and bus protection according to functional requirements, and the action range of the protection is bounded by the secondary windings of the connected current transformers. The line protection is connected to the A, B, and C phase currents of the middle circuit breaker current transformer and the A, B, and C phase currents of the side circuit breaker current transformer, and is connected to the A, B, and C phase voltages through the potential transformer PT. The access quantities of the line protection on both sides are the same. The 500kV line is relatively special. The three-phase current of each circuit breaker can be regarded as an independent branch current for discrimination, or the currents of two circuit breakers can be combined as a branch for discrimination. First, the composite voltage is calculated through the three-phase voltages of the potential transformer. According to the composite voltage, it is discriminated whether a fault occurs in the system. In the case of no fault, for the three-phase current of each circuit breaker, the method of fundamental wave content ratio proposed by the present invention can quickly identify whether CT disconnection occurs, and select the disconnection phase to give an alarm and block the protection. The CT disconnection is identified by the difference in the fundamental wave content ratio of the A, B, and C phase currents. Under normal operating conditions, the fundamental wave current content ratios of the A, B, and C phase currents are basically the same. Once a certain phase current is disconnected, its remaining current is the zero drift current and interference current, and the fundamental wave content ratio decreases rapidly, even approaching 0. The present invention calculates the effective values of the three-phase currents of each phase of the branch based on the root mean square algorithm, extracts the fundamental wave (50Hz or 60Hz) of each phase based on the Fourier algorithm, calculates the effective values of the fundamental wave content of each phase current, and selects the disconnection phase to give an alarm and block the protection function through the difference in the fundamental wave content ratio between the disconnection phase and the healthy phase.

[0091] The present invention also proposes a current transformer disconnection discrimination system based on the fundamental wave content of the branch current, including:

[0092] An acquisition module, configured to acquire the three-phase currents and voltages of each branch in the power transmission and transformation system to determine the effective values of the three-phase currents and the effective values of the three-phase fundamental wave currents of each branch;

[0093] The open - circuit discrimination module is used to discriminate whether the current transformer is open - circuited when the power system has no fault. When determining the fundamental wave content of the three - phase current, it uses the effective values of the three - phase fundamental wave currents and the effective values of the three - phase currents. It determines the maximum value of the difference in fundamental wave content between phases using the fundamental wave content of the three - phase current. When the maximum value of the difference in fundamental wave content between phases is greater than the set threshold, it is determined that there is an open - circuit in the current transformer. Taking the phase corresponding to the maximum value in the fundamental wave content of the three - phase current as the reference phase, when the fundamental wave content of the reference phase is not less than 0.8 and not less than 2 times the fundamental wave content of the phase to be identified, if the maximum value in the effective values of the three - phase currents is greater than the minimum accuracy of the current collected by the relay protection device, then it is determined that the phase to be identified of the current transformer is open - circuited.

[0094] The present disclosure may be a system, a method, and / or a computer program product. The computer program product may include a computer - readable storage medium having thereon computer - readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0095] The computer - readable storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. The computer - readable storage medium may be, for example, but is 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 of the foregoing. More specific examples (a non - exhaustive list) of the computer - readable storage medium 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 disc (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punched card or raised structures in grooves storing instructions thereon, and any suitable combination of the foregoing. The computer - readable storage medium used herein is not construed as an instantaneous signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated through a waveguide or other transmission medium (e.g., an optical pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0096] The computer - readable program instructions described herein can be downloaded from the computer - readable storage medium to various computing / processing devices, or downloaded to an external computer or external storage device through a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include a copper transmission cable, an optical fiber transmission, a wireless transmission, a router, a firewall, a switch, a gateway computer, and / or an edge server. The network adapter or network interface in each computing / processing device receives the computer - readable program instructions from the network and forwards the computer - readable program instructions for storage in the computer - readable storage medium in each computing / processing device.

[0097] Computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related 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++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand-alone software package, partially on the user's computer and 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 through 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., through the Internet using an Internet service provider). In some embodiments, by using the state information of the computer-readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field-programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer-readable program instructions to implement various aspects of the present disclosure.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or make equivalent substitutions, and any modification or equivalent substitution that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for determining a current transformer disconnection based on branch current fundamental content, characterized in that: include: Collect the three-phase current and voltage of each branch in the power transmission and transformation system to determine the effective value of the three-phase current and the effective value of the three-phase fundamental current of each branch; When there is no fault in the power system, determine whether the current transformer is disconnected; When determining whether the current transformer is disconnected, the three-phase fundamental current effective value and the three-phase current effective value are used to determine the three-phase current fundamental content, and the three-phase current fundamental content is used to determine the maximum value of the phase-to-phase fundamental content difference. When the maximum value of the phase-to-phase fundamental content difference is greater than the set threshold, it is determined that the current transformer is disconnected. Take the phase corresponding to the maximum value of the three-phase current fundamental content as the reference phase, and the current fundamental content of the reference phase is not less than 0.8 and not less than 2 times the current fundamental content of the phase to be identified. If the maximum value of the three-phase current effective value is greater than the minimum accuracy of the current collected by the relay protection device, it is determined that the phase to be identified of the current transformer is broken.

2. The current transformer disconnection determination method based on branch current fundamental content according to claim 1 is characterized in that: The three-phase fundamental current effective values ​​are IArms1, IBrms1, and ICrms1 respectively. The three-phase current effective values ​​are IArms, IBrms, and ICrms respectively. The fundamental content of the three-phase current satisfies the following relationship: KA=IArms1 / IArms KB=IBrms1 / IBrms KC=ICrms1 / ICrms Where KA, KB, and KC are the fundamental wave contents of the three-phase current.

3. The current transformer disconnection determination method based on branch current fundamental content according to claim 2 is characterized in that: The ratio of the absolute value of the difference between the fundamental wave content of any two phase currents to the maximum value of the fundamental wave content of the two phases is taken as the phase-to-phase fundamental wave content difference. The maximum value of the three phase-to-phase fundamental wave content differences is taken, which is expressed by the following relationship: Where K is the maximum value of the fundamental content difference between phases.

4. The current transformer disconnection determination method based on branch current fundamental content according to claim 3 is characterized in that: When the maximum value of the phase-to-phase fundamental wave content difference is greater than 20%, it is determined that the current transformer is broken.

5. The current transformer disconnection determination method based on branch current fundamental content according to claim 3 is characterized in that: The phase corresponding to the maximum value of the fundamental wave content of the three-phase current is taken as the reference phase, satisfying the following relationship: K1=max{KA、KB、KC} When the current fundamental content of the reference phase is not less than 0.8 and not less than 2 times the current fundamental content of the phase to be identified, if the maximum value of the three-phase current effective value is greater than the minimum value of the accuracy of the current collected by the relay protection device, the phase to be identified of the current transformer is judged to be broken, including: When K1≠KA and K1≥0.8 and K1≥2KB, if max{IA, IB, IC}>Iminset, it is determined that the A phase of the current transformer is broken; When K1≤KB and K1≥0.8 and K1≥2KB, if max{IA, IB, IC}>Iminset, it is determined that the B phase of the current transformer is broken; When K1≠KC and K1≥0.8 and K1≥2KC, if max{IA, IB, IC}>Iminset, it is determined that the C phase of the current transformer is broken; Among them, IA, IB, and IC are the effective values ​​of the three-phase currents, Iminset is the minimum accuracy of the current collected by the relay protection device, which is 0.01In, and In is the secondary rated current of the current transformer, which is 5A or 1A.

6. The current transformer disconnection determination method based on branch current fundamental content according to claim 1 is characterized in that: Also includes: Disconnection alarm and lockout corresponding protection function.

7. The current transformer disconnection determination method based on branch current fundamental content according to claim 1, characterized in that: Also includes: In a half-circuit breaker wiring mode, each circuit breaker in a string is regarded as an independent branch, and the broken wire of a group of current transformers corresponding to each circuit breaker is judged based on the fundamental wave content of the branch current; Alternatively, two adjacent circuit breakers in a string are used as an independent branch, and the disconnection of two groups of current transformers corresponding to the two adjacent circuit breakers is determined based on the fundamental wave content of the branch current.

8. A current transformer disconnection determination system based on branch current fundamental wave content, characterized in that: include: The acquisition module is used to collect the three-phase current and voltage of each branch in the power transmission and transformation system to determine the effective value of the three-phase current and the effective value of the three-phase fundamental current of each branch; The disconnection determination module is used to determine whether the current transformer is disconnected when there is no fault in the power system. The three-phase fundamental current effective value and the three-phase current effective value are used to determine the three-phase current fundamental content, and the three-phase current fundamental content is used to determine the maximum value of the phase-to-phase fundamental content difference. When the maximum value of the phase-to-phase fundamental content difference is greater than a set threshold, it is determined that the current transformer is disconnected; the phase corresponding to the maximum value of the three-phase current fundamental content is taken as the reference phase, and the current fundamental content of the reference phase is not less than 0.8 and not less than 2 times the current fundamental content of the phase to be identified. If the maximum value of the three-phase current effective value is greater than the minimum accuracy of the current acquisition of the relay protection device, it is determined that the phase to be identified of the current transformer is disconnected.

9. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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