Differential protection method and system for double-terminal power electronic power transmission lines

Abstract

The present invention provides a differential protection method and system suitable for a two-terminal power electronic power transmission line. By collecting the current at the protection installation points on both sides of the line, a highly sensitive line differential protection is constructed based on the amplitude and phase relationship of the current on both sides. When the amplitude and phase relationship are both within the set braking area, the differential protection is locked; when the amplitude of the current on both sides is small and the amplitude and phase relationship is not within the braking area, the differential protection can be activated. The present invention effectively solves the problem that when a fault occurs in the two-terminal power electronic power line area, the power electronic components have reduced sensitivity or even refuse to operate due to the limited amplitude and phase control of the voltage and current.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection, and more particularly to a high-sensitivity differential protection method and system suitable for a double-terminal power electronic power transmission line. Background Art

[0002] Differential protection, a fast-acting protection system that protects the entire length of a line, operates on reliable and advanced principles and is widely used in power grids of 110 kV and above. Due to the advantages of flexible DC transmission, such as independent control of active and reactive power, no commutation failures, and the ability to provide dynamic reactive power support, the direct integration of renewable energy into the grid through flexible DC transmission can effectively improve the operating conditions of the power system.

[0003] There are power electronic equipment on both sides of the new energy to flexible straight line. When a line fault occurs, the current amplitude and phase angle on both sides are affected by the control strategy of the power electronic equipment. When a phase-to-phase fault occurs in the area, the phase angle difference of the fault phase current on both sides may reach 120°~150°. Compared with the characteristic that the current on both sides of the traditional synchronous machine power supply system is basically in the same direction, it shows a more obvious through-characteristic. The differential protection faces the risk of reduced sensitivity or even refusal to operate.

[0004] To address the above issues, existing technologies generally use methods such as reducing the differential protection ratio braking coefficient or lowering the action threshold to improve sensitivity. However, such methods have the problem of reduced reliability of differential protection for out-of-zone faults.

[0005] Prior art CN202011579727.1 discloses an adaptive amplitude ratio active distribution network differential protection method, comprising the following steps: Step 1: Analyze the fault characteristics of the inverter-type distributed power source under constant power control mode to determine the phase relationship between the DG output short-circuit current and the system output short-circuit current under fault conditions; Step 2: Analyze the fault characteristics of the active distribution network containing distributed power sources from the perspective of the relative position relationship between the fault point and the fault section; Analyze the amplitude-phase relationship of the short-circuit current at both ends of the protected area based on different position relationships; Step 3: Utilize the amplitude and phase information of the current at the end of the protected section to propose a protection scheme that uses phase information to adjust the amplitude ratio constraint, set basic protection criteria and improved protection criteria, and adjust the criteria parameters. However, this patented technology does not take into account the problem that the amplitude and phase of the fault current on both sides of the currently widely used two-terminal power electronic power transmission line are controlled when a fault occurs, presenting a through-characteristic, resulting in insufficient sensitivity.

[0006] The prior art CN202211208269.X discloses a current differential protection method and system for an active distribution network, comprising: obtaining the current of the protected section of the active distribution network; judging whether the current differential protection of the protected section of the active distribution network is activated based on the error of the obtained current and the preset current phase margin; when the current differential protection is activated, selecting the differential protection criterion based on whether the current transformer is saturated to realize the differential protection of the active distribution network. The present disclosure combines the fault current characteristics and measurement errors of the active distribution network to give the braking area of ​​the current differential protection on the amplitude-phase plane, and constructs an auxiliary criterion using the harmonic content ratio and amplitude ratio of the secondary current when the CT is saturated. However, this patented technology also has the problem of reduced sensitivity due to the preset action threshold when applied to a two-terminal power electronic power transmission line.

[0007] Other new technologies, including the principle based on the similarity of current waveforms on both sides of the line and the differential protection principle based on model identification, are still in the simulation verification stage and do not meet the conditions for engineering practical application.

[0008] Therefore, it is urgent to study a high-sensitivity line differential protection method suitable for renewable energy transmission lines via flexible direct current (FDC). Summary of the Invention

[0009] In view of the above problems, the present invention proposes a high-sensitivity differential protection method and system suitable for a double-terminal power electronic power transmission line.

[0010] The present invention specifically adopts the following technical solutions.

[0011] A dynamic protection method applicable to a two-terminal power electronic power supply line, characterized in that the method comprises:

[0012] Collect currents on both sides of the line and construct the amplitude and phase relationship of the current vectors on both sides;

[0013] When the amplitude-phase relationship of the current on both sides falls into the braking area of ​​the amplitude-phase plane, the differential protection is blocked;

[0014] When the current amplitudes on both sides are less than the set threshold and the amplitude-phase relationship is not in the braking area, the differential protection is opened; when the differential current is greater than the threshold value, the differential protection is activated.

[0015] Double-terminal power electronic power supply lines include new energy sources such as wind power and photovoltaic power, which are transmitted through flexible DC systems and flexible low-frequency transmission lines.

[0016] Construct the amplitude-phase relationship of the current phasors on both sides, based on the current vector on one side of the line , and the current vector on the other side Obtain the amplitude and phase relationship of the current on both sides ,in and They are and The smaller and larger values ​​in .

[0017] The braking region of the amplitude-phase plane is the intersection of the phase braking region and the amplitude braking region.

[0018] The phase braking area is where the current phases on both sides meet ,in The value is 170°. The value is 200°.

[0019] The amplitude braking area is where the current amplitude relationship on both sides satisfies ,in The value is 0.8, The value is 1.

[0020] When the current amplitudes on both sides are less than the set threshold, the following equation is satisfied:

[0021] ,

[0022] in The value is 1.2I n .

[0023] The calculation formula for the differential current is:

[0024] ,

[0025] The threshold value is a settable differential current constant.

[0026] This application also seeks to protect a differential protection system for a two-terminal power electronic power supply line based on the aforementioned differential protection method, comprising a sampling module, a calculation module, and a signal output control module; and is characterized in that:

[0027] The sampling module is used to collect the instantaneous current values ​​of the local differential protection and the opposite differential protection of the double-terminal power electronic power supply line;

[0028] The calculation module is used to calculate the amplitude-phase relationship of the current of the double-terminal power electronic power supply circuit and determine the amplitude-phase relationship. ,in, and The current vectors at both ends of the line are and The smaller and larger values ​​in .

[0029] The signal output control module is used to determine the amplitude-phase relationship and to control the output of the differential protection action signal in combination with the differential protection action characteristics.

[0030] More preferably,

[0031] In the calculation module, the differential protection braking zone is determined by:

[0032] The current phase on both sides of the line meets , and the current amplitude relationship on both sides satisfies ;

[0033] in, The value is 170°. The value is 200°. The value is 0.8, The value is 1.

[0034] An electronic device, comprising a processor and a storage medium; characterized in that:

[0035] The storage medium is used to store instructions;

[0036] The processor is configured to operate according to the instructions to execute steps according to the differential protection method applicable to a double-terminal power electronic power line.

[0037] 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 differential protection method applicable to a two-terminal power electronic power supply line are implemented.

[0038] Compared with the prior art, the present invention has the following beneficial technical effects:

[0039] The enhanced differential protection's operating range expands beyond the traditional differential protection range. For scenarios like new energy to flexible straight lines, where two-terminal power electronic power supplies are used, the high-sensitivity differential protection prevents false trips for out-of-zone faults and significantly improves its sensitivity for in-zone faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is applicable to a logic block diagram of a dynamic protection method for a double-terminal power electronic power supply line.

[0041] Figure 2: Compared with traditional differential protection, the present invention expands the operating area;

[0042] Figure 3 is a system diagram of simulation verification;

[0043] Figure 4 shows the relationship between the phase and amplitude of the current vectors on both sides of the line when a fault occurs outside the line area;

[0044] Figure 5 shows the relationship between the phase and amplitude of the current vectors on both sides of the line during a fault.

[0045] Figure 6 shows the relationship between the phase and amplitude of the current vectors on both sides of the line when a high-resistance fault occurs. DETAILED DESCRIPTION

[0046] 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.

[0047] like Figure 1 FIG. 1 is a logic diagram of a specific implementation of the present invention, comprising the following steps:

[0048] (1) Collect the current on both sides of the transmission line and obtain the current vectors on both sides, which are recorded as , . For the high-voltage transmission system used in this patent, it also specifically refers to the corresponding A, B, and C three-phase currents.

[0049] (2) If Figure 2 , construct the amplitude-phase relationship of the current phasors on both sides, based on the current vector on one side of the line , and the current vector on the other side Obtain the amplitude and phase relationship of the current on both sides: ,in and They are and The smaller and larger values ​​in .

[0050] (3) Combination Figure 2 , determine the amplitude-phase relationship Whether the braking area phase interval is met: Specifically, the CT phase difference is generally positive. When there is an out-of-zone fault, the currents on both sides are in reverse relationship. Therefore, the phase difference of the CT phase difference relative to 180° is -10°~20°, that is, The value is 170°. The value is 200°.

[0051] (4) Combination Figure 2 , determine the amplitude-phase relationship Whether the braking area amplitude range is met: Specifically, in the amplitude discrimination formula The value of is 0.8, The reason for taking the value of 1.0 is that the fault current outside the line area has a through-characteristic, and the error that may be caused by CT transmission is taken into account.

[0052] (5) When the amplitude-phase relationship When the phase interval and amplitude interval range of the braking area are met, the differential protection is locked.

[0053] (6) When the amplitude-phase relationship When it is not in the braking area and the current on both sides of the line is less than 1.2In ( , ), combined with the differential current condition ( ) Protect protection action.

[0054] Combine Figure 2 To further illustrate, the traditional operating range in the figure represents the amplitude-phase plane representation of conventional ratio differential protection (with a ratio braking coefficient of 0.6). The enhanced sensitive differential protection operating range, introduced in this patent, expands the traditional differential protection operating range. For scenarios similar to two-terminal power electronic power supply systems, such as those from renewable energy to flexible lines, the highly sensitive differential protection maintains correct operation for out-of-range faults and significantly improves differential protection sensitivity for in-range faults.

[0055] The present application also discloses a differential protection system for a two-terminal power electronic power supply line based on the aforementioned differential protection method, comprising a sampling module, a calculation module, and a signal output control module;

[0056] The sampling module is used to collect the instantaneous current values ​​of the local differential protection and the opposite differential protection of the double-terminal power electronic power supply line;

[0057] The calculation module is used to calculate the amplitude-phase relationship of the current of the double-terminal power electronic power supply circuit and determine the amplitude-phase relationship. ,in, and The current vectors at both ends of the line are and The smaller and larger values ​​in .

[0058] In the calculation module, the differential protection braking zone is determined by:

[0059] The current phase on both sides of the line meets , and the current amplitude relationship on both sides satisfies ;

[0060] in, The value is 170°. The value is 200°. The value is 0.8, The value is 1.

[0061] The signal output control module is used to determine the amplitude-phase relationship and to control the output of the differential protection action signal in combination with the differential protection action characteristics.

[0062] Simulation verification:

[0063] Combine Figure 3The 220kV offshore wind power to flexible DC transmission line model shown is used to simulate and verify the improved sensitive differential protection.

[0064] Figure 4 This is the running trajectory of the current on both sides on the amplitude-phase plane after an out-of-zone fault. When the line is operating normally, through-load current flows on both sides of the line with opposite directions and equal magnitudes. In the amplitude-phase plane, the landing point is located in the braking zone. When a fault occurs at point AN of the busbar F1 outside the zone on the M side, through-current flows on both sides of the line. Due to the influence of the line capacitance current, the magnitudes of the currents on both sides of the line are slightly inconsistent. The amplitude-phase relationship jitters in the braking zone, but does not exceed the range of the braking zone, so the differential protection will not malfunction.

[0065] Figure 5 This is the trajectory of the amplitude and phase relationship of the current on both sides after the metallic fault on phase A at point F2 in the area. It quickly crosses the braking area before the fault to the action area, and the differential protection operates quickly.

[0066] Figure 6 For the fault of phase A at point F2 in the area through a 100-ohm transition resistor, the running trajectory of the current on both sides of the line on the amplitude-phase plane is similar to that of the metallic fault in the area. The differential protection can also operate quickly, ensuring the sensitivity of the differential protection.

[0067] 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.

[0068] 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, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), 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 punched card or 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 passing through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0069] 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.

[0070] 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" or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, 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 via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, the state information of the computer-readable program instructions is used to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), so that the electronic circuit can execute the computer-readable program instructions, thereby implementing various aspects of the present disclosure.

[0071] 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 differential protection method for a two-terminal power electronic power supply line, characterized in that: The method comprises: Collect currents on both sides of the line and construct the amplitude-phase relationship between the current vectors on both sides; When the amplitude-phase relationship of the current on both sides falls in the braking area of ​​the amplitude-phase plane, the differential protection is locked. The phase braking area is when the phase of the current on both sides meets The amplitude braking area is the current amplitude relationship on both sides that satisfies ,in, The value is 170°. The value is 200°. The value is 0.8, The value is 1. is the amplitude-phase relationship; When the current amplitudes on both sides are less than the set threshold and the amplitude-phase relationship is not in the braking area, the differential protection is opened; when the differential current is greater than the threshold value, the differential protection is activated; ， Among them, setting thresholds The value is 1.2I n .

2. The differential protection method for a two-terminal power electronic power supply line according to claim 1, characterized in that: Double-terminal power electronic power supply lines include new energy sources such as wind power and photovoltaic power, and are sent through flexible DC system transmission lines and flexible low-frequency transmission lines.

3. The differential protection method for a two-terminal power electronic power supply line according to claim 1, characterized in that: Construct the radial phase relationship of the current phasors on both sides, based on the current vector on one side of the line , and the current vector on the other side Obtain the current phase relationship on both sides ,in and They are and The smaller and larger values ​​in .

4. The differential protection method for a two-terminal power electronic power supply line according to claim 3, characterized in that: The braking region of the amplitude-phase plane is the intersection of the phase braking region and the amplitude braking region.

5. The differential protection method for a two-terminal power electronic power supply line according to claim 1, characterized in that: The calculation formula for differential current is: ， The threshold value is a settable differential current constant.

6. A differential protection system for a two-terminal power electronic power supply line based on the differential protection method according to any one of claims 1 to 5, comprising a sampling module, a calculation module, and a signal output control module; characterized in that: The sampling module is used to collect the instantaneous current values ​​of the local differential protection and the opposite differential protection of the double-terminal power electronic power supply line; The calculation module is used to calculate the amplitude-phase relationship of the current of the double-terminal power electronic power supply circuit and determine the amplitude-phase relationship. ,in, and The current vectors at both ends of the line are and The smaller and larger values ​​of ; The signal output control module is used to control the output of the differential protection action signal based on the amplitude-phase relationship judgment result and the differential protection action characteristics.

7. The differential protection system for a two-terminal power electronic power supply line according to claim 6, characterized in that: In the calculation module, the differential protection braking zone is determined by: The current phase on both sides of the line meets , and the current amplitude relationship on both sides satisfies ; in, The value is 170°. The value is 200°. The value is 0.8, The value is 1.

8. An electronic device 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 differential protection method applicable to a double-terminal power electronic power line according to any one of claims 1 to 5.

9. 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 differential protection method applicable to a two-terminal power electronic power supply line described in any one of claims 1 to 5 are implemented.

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