A direct fiber ratio differential protection method based on variable integral window

Abstract

A direct optical fiber ratio differential protection method based on variable integral window. The current on the inlet switch and the outlet switch is converted into pulses with corresponding relationship, and each pulse is directly transmitted to the comparison module point by point, and then the difference of the corresponding current is judged by the difference of the inlet and outlet pulses, so as to make a response. Based on the variable integral window, the function relationship between the pulse difference value, the starting difference threshold value, the ratio braking coefficient, the braking pulse and the inflection point pulse setting value is used to realize the direct optical fiber ratio braking differential protection.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection, specifically relating to a direct fiber optic ratio differential protection method based on a variable integral window. Background Technology

[0002] Differential protection is a line protection method, often used between main lines and branch lines. Existing differential protection systems acquire current and voltage parameters at both ends of the line via current transformers (CTs), convert them into messages, and send them to a computer. The computer interprets these messages and compares the current at the upstream and downstream points of the line. If the upstream current is equal to the downstream current, a fault is detected, and the line switch is disconnected to isolate the faulty line. However, the process of message writing, generation, transmission, reception, and interpretation involves many steps, requiring numerous devices, extensive computation, complex algorithms, and significant time consumption, making reliable device design challenging. To improve the response speed of differential protection, invention patent application CN111463758 A discloses a power line protection method that converts the current at the inlet and outlet switches into corresponding pulses and transmits each pulse directly point-to-point to a comparison module. The difference between the inlet and outlet pulses is then used to determine the difference in the corresponding current, thus triggering a response. The advantages of this approach are that it avoids message compilation and other steps, reduces the number of devices used, and greatly improves the response speed. Compared with traditional protection methods, the response time of differential protection is shortened from 26-40 milliseconds to less than 5 milliseconds. However, this method is only applicable to instantaneous protection during severe faults. When a fault occurs outside the protection zone (through-fault), the inconsistent transmission characteristics of the current transformers (CTs) at each switching node lead to the generation of differential current, and the pulse difference may exceed the set value, causing the protection to trip falsely. This necessitates setting the set value to avoid the maximum difference value when a fault occurs outside the protection zone. While this method avoids false tripping during faults outside the protection zone, it reduces the sensitivity of protection activation during faults inside the protection zone. To ensure that faults outside the protection zone do not cause false tripping while improving the sensitivity during faults inside the protection zone, the method described in the aforementioned patent application cannot be used to monitor whether a line fault has occurred. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a direct fiber optic ratio differential protection method based on a variable integral window. The current quantities at the inlet and outlet switches are converted into corresponding pulses, and each pulse is directly transmitted point-to-point to a comparison module. The difference between the inlet and outlet pulses is then used to determine the corresponding current difference, thereby triggering a response. Based on a variable integral window, direct fiber optic ratio braking differential protection is achieved by utilizing the functional relationship between the pulse difference and the starting difference threshold, the ratio braking coefficient, the braking pulse, and the inflection point pulse setpoint.

[0004] The present invention adopts the following technical solution.

[0005] A direct fiber ratio differential protection method based on a variable integral window includes:

[0006] The inlet switch and outlet switch are respectively equipped with current transformers and voltage-frequency conversion circuits to convert current into voltage. The voltage is then converted into pulses by the voltage-frequency conversion circuit. The number of pulses is directly proportional to the voltage. The pulses are transmitted to the comparison module via optical fiber.

[0007] The comparison module calculates the algebraic sum of the number of pulses corresponding to each current transformer within the time window T, and obtains the difference between the inflow and outflow currents. If the inequality relationship is satisfied:

[0008] N cd >N qd +K zd *(N r -N b )

[0009] Then it is determined that a fault has occurred in the line between each of the current transformers, and the direct optical differential protection trips.

[0010] The number of pulses corresponding to each current transformer within the time window T is denoted as N. i ;

[0011] The summation of the number of pulses corresponding to the incoming current is denoted as N. lr ,

[0012] The sum of the number of pulses corresponding to the outflowing current is denoted as N. lc ,

[0013] The algebraic sum of all pulse counts, i.e., the pulse difference corresponding to the difference between the inflow and outflow currents, is denoted as N. cd N cd =N lr -N lc ,

[0014] N qd Set the initial pulse count difference value for differential start-up.

[0015] K zd This is the ratio braking coefficient.

[0016] N r This is a braking pulse count, specifically a pulse count corresponding to the average of the inflow and outflow currents.

[0017] N r =(N lr +N lc ) / 2,

[0018] N b Set the pulse count value corresponding to the inflection point current.

[0019] Preferably, the time window T ranges from 1 to 10 ms.

[0020] Preferably, the initial pulse count difference setpoint N for differential start-up is... qd , is 0.2~2N e N e This is the pulse count corresponding to the line's rated current.

[0021] Preferably, the ratio braking coefficient K zd The value is 0.1 to 0.5.

[0022] Preferably, the pulse counting setpoint N corresponding to the inflection point current is... b , 0~5N e N e This is the pulse count corresponding to the line's rated current.

[0023] Preferably, multiple sets of ratio braking settings are set according to different ratio braking coefficients corresponding to different current inflection points. Each set of ratio braking settings includes the initial pulse count difference setting N for differential start. qd Ratio braking coefficient K zd The pulse counting setpoint N corresponding to the inflection point current b Three constant values, using a three-segment structure:

[0024] When N b1 ≤N r ≤N b2 N cd >N qd1 +K zd1 *(N r -N b1 )

[0025] When N b2 <N b ≤N b3 N cd >N qd2 +K zd2 *(Nr -N b2 )

[0026] When N b3 <N b N cd >N qd3 +K zd3 *(N r -N b3 )

[0027] N qd2 =N qd1 +K zd1 *(N b2 -N b1 )

[0028] N qd3 =N qd1 +K zd1 *(N b2 -N b1 )+K zd2 *(N b3 -N b2 )

[0029] When K zd2 Not equal to 0 and K zd1 K zd3 When K is 0, the differential protection exhibits a single-ratio braking characteristic. zd2 K zd3 Not equal to 0 and K zd1 When K is 0, the differential protection exhibits a two-stage ratio braking characteristic. zd1 K zd2 K zd3 When none of the values ​​are 0, the differential protection exhibits a three-stage ratio braking characteristic. When K... zd1 K zd2 K zd3 When both are 0, the differential protection has no ratio braking characteristic.

[0030] The beneficial effects of this invention are that, compared with the prior art,

[0031] The current quantities at the inlet and outlet switches are converted into corresponding pulses, and each pulse is directly transmitted point-to-point to the comparison module. The difference between the inlet and outlet pulses is used to determine the corresponding current difference, thus triggering a response. Based on a variable integral window, direct fiber-optic ratio-braking differential protection is implemented using the functional relationship between the pulse difference and the starting difference threshold, the ratio braking coefficient, the braking pulse, and the inflection point difference setting. When a fault occurs outside the protection zone, the differential starting threshold increases with the increase of the through current, ensuring that through-faults do not cause false trips. By selecting different pulse objects as the differential pulse and braking pulse, and changing the protection action pulse difference threshold according to the through current, false trips are avoided, solving the problem of the inapplicability of existing technologies. This allows for accurate and rapid determination of whether a fault has occurred in the distribution network line, ensuring that faults outside the protection zone do not cause false trips while improving the sensitivity to faults within the protection zone. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a direct fiber ratio differential protection method based on a variable integral window according to the present invention.

[0033] Figure 2 This is a flowchart of a direct fiber ratio differential protection method based on a variable integral window according to the present invention.

[0034] Figure 3 This is a diagram showing the three-segment ratio braking characteristics of a direct fiber optic ratio differential protection method based on a variable integral window according to the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0036] A direct fiber ratio differential protection method based on a variable integral window, such as... Figure 2 As shown, it includes:

[0037] The inlet and outlet switches are equipped with current transformers and voltage-frequency conversion circuits, respectively, to convert the current into voltage. The voltage is then converted into pulses by the voltage-frequency conversion circuit. The number of pulses is directly proportional to the voltage. The pulses are transmitted to the comparison module via optical fiber.

[0038] The comparison module calculates the algebraic sum of the number of pulses corresponding to each current transformer within the time window T, and obtains the current difference between the inflow and outflow. If the following relationship is satisfied, it is determined that a line fault has occurred between each current transformer, and the direct optical differential protection trips.

[0039] N cd >N qd +K zd *(N r -N b )

[0040] The number of pulses corresponding to each current transformer within the time window T is denoted as N1, N2, and N... i ;

[0041] The summation of the number of pulses corresponding to the incoming current is denoted as N. lr ,

[0042] The sum of the number of pulses corresponding to the outflowing current is denoted as N. lc ,

[0043] The algebraic sum of all pulse counts, i.e., the pulse difference corresponding to the difference between the inflow and outflow currents, is denoted as N. cd ,

[0044] N cd =N lr -N lc ,

[0045] N qd The initial pulse count difference is set to a value typically between 0.2 and 2N for differential start-up. e N e The pulse count corresponding to the line's rated current;

[0046] K zd This is the ratio braking coefficient; typically 0.1 to 0.5.

[0047] N r This is a braking pulse count, specifically a pulse count corresponding to the average of the inflow and outflow currents.

[0048] N r =(N lr +N lc ) / 2;

[0049] N b The pulse count setpoint corresponding to the inflection point current is typically 0–5N. e N e This is the pulse count corresponding to the line's rated current.

[0050] Multiple sets of ratio braking settings can be set based on different ratio braking coefficients corresponding to different current inflection points (each set of ratio braking settings includes the initial pulse count difference setting N for differential start). qd Ratio braking coefficient K zd The pulse counting setpoint N corresponding to the inflection point current b (Three constant values), generally using a three-segment structure. For example... Figure 3 As shown:

[0051] When N b1 ≤N r ≤N b2 N cd >N qd1 +K zd1 *(N r -N b1 )

[0052] When N b2 <N b ≤N b3 N cd >N qd2 +K zd2 *(N r -N b2 )

[0053] When N b3 <N b N cd >N qd3 +K zd3 *(N r -N b3 )

[0054] N qd2 =N qd1 +K zd1 *(N b2 -N b1 )

[0055] N qd3 =N qd1 +K zd1 *(N b2 -N b1 )+K zd2 *(N b3 -N b2 )

[0056] The shaded area above the broken line represents the operating region. The difference in operating characteristics between different differential protection systems lies only in the initial pulse count difference setting N at differential start-up. qd Ratio braking coefficient K zd The pulse counting setpoint N corresponding to the inflection point current b The values ​​of K are different. zd2 Not equal to 0 and Kzd1 K zd3 When K is 0, the differential protection exhibits a single-ratio braking characteristic. zd2 K zd3 Not equal to 0 and K zd1 When K is 0, the differential protection exhibits a two-stage ratio braking characteristic. zd1 K zd2 K zd3 When none of the values ​​are 0, the differential protection exhibits a three-stage ratio braking characteristic. When K... zd1 K zd2 K zd3 When both are 0, the differential protection has no ratio braking characteristic (differential instantaneous overcurrent protection).

[0057] The time window T is 1-10 ms;

[0058] The voltage is boosted by the reference voltage boosting circuit before being input to the voltage-frequency conversion circuit.

[0059] The pulse algebra and output of the comparison module are cleared to zero at fixed intervals, such as every 10ms.

[0060] Example 1:

[0061] like Figure 1 As shown, the power supply flows into conductor L1, passes through the main circuit breaker 1, and splits into three branches: conductor L2 and circuit breaker 2 connect to load 1, conductor L3 and circuit breaker 3 connect to load 2, and conductor L4 and circuit breaker 4 connect to load 3.

[0062] Circuit breaker 1 is equipped with a current transformer 11 and a voltage-to-frequency conversion circuit 12 at its upper end. Circuit breaker 2 is equipped with a current transformer 21 and a voltage-to-frequency conversion circuit 22 at its upper end. Circuit breaker 3 is equipped with a current transformer 31 and a voltage-to-frequency conversion circuit 32 at its upper end. Fuse 4 is equipped with a current transformer 41 and a voltage-to-frequency conversion circuit 42 at its upper end.

[0063] The comparison module 6 includes a counter, an adder, and a timer. The comparison module 6 first converts the pulses into digital quantities representing the number of pulses, and then sums the digital quantities using the adder.

[0064] A closed protection zone 5 is formed between the conductors where each current transformer 11, 21, 31, and 41 is located.

[0065] The maximum time window T is 10ms; the pulse algebra and output of the comparison module are cleared to zero every 10ms; the following calculations are performed every ms:

[0066] The number of pulses corresponding to each of the aforementioned current transformers is denoted as N1, N2, N3, and N4.

[0067] The summation of the number of pulses corresponding to the incoming current is denoted as N.lr =N1,

[0068] The sum of the number of pulses corresponding to the outflowing current is denoted as N. lc =N2 + N3 + N4,

[0069] The algebraic sum of all pulse counts, i.e., the pulse difference corresponding to the difference between the inflow and outflow currents, is denoted as N. cd N cd =N lr -N lc ,

[0070] N r This is a braking pulse count, specifically a pulse count corresponding to the average of the inflow and outflow currents.

[0071] N r =(N lr +N lc ) / 2;

[0072] N qd The initial pulse count difference for differential start is set to 0.2N. e N e The pulse count corresponding to the line's rated current;

[0073] K zd This is the ratio braking coefficient; set to 0.1.

[0074] N b The pulse count setpoint corresponding to the inflection point current is set to 0.5N. e .

[0075] N cd >N qd +K zd *(N r -N b )

[0076] If the pulse difference matches the above formula, the direct optical difference protection will activate and the fault will be cleared.

[0077] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0078] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0079] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0080] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A direct fiber optic ratio differential protection method based on a variable integral window, wherein the inlet switch and the outlet switch are respectively equipped with current transformers and voltage-to-frequency conversion circuits to convert current into voltage, and then the voltage is converted into pulses by the voltage-to-frequency conversion circuit, and the pulses are transmitted to a comparison module via optical fiber; characterized in that: The comparison module calculates the algebraic sum of the number of pulses corresponding to each current transformer within the time window T, and obtains the difference between the inflow and outflow currents. If the inequality relationship is satisfied: Then it is determined that a fault has occurred in the line between each of the current transformers, and the direct optical differential protection trips. The number of pulses corresponding to each current transformer within the time window T is denoted as N. i ; The summation of the number of pulses corresponding to the incoming current is denoted as N. lr , The sum of the number of pulses corresponding to the outflowing current is denoted as N. lc , The algebraic sum of all pulse counts, i.e., the pulse difference corresponding to the difference between the inflow and outflow currents, is denoted as N. cd N cd =N lr -N lc , N qd Set the initial pulse count difference value for differential start-up. K zd This is the ratio braking coefficient. N r The braking pulse count is the pulse count corresponding to the average of the inflow and outflow currents, wherein the braking pulse count N r Defined as: N r =(N lr +N lc ) / 2; N b Set the pulse count value corresponding to the inflection point current.

2. The direct fiber ratio differential protection method based on a variable integral window according to claim 1, characterized in that: The time window T ranges from 1 to 10 ms.

3. The direct fiber ratio differential protection method based on a variable integral window according to claim 1, characterized in that: The initial pulse count difference setpoint N for differential start-up qd The value is 0.2~2N. e N e This is the pulse count corresponding to the line's rated current.

4. The direct fiber ratio differential protection method based on a variable integral window according to claim 1, characterized in that: The ratio braking coefficient K zd The value is 0.1~0.

5.

5. The direct fiber ratio differential protection method based on a variable integral window according to claim 1, characterized in that: The pulse counting setpoint N corresponding to the inflection point current b , for 0~5N e N e This is the pulse count corresponding to the line's rated current.

6. The direct fiber ratio differential protection method based on a variable integral window according to claim 1, characterized in that: Based on different current inflection points corresponding to different ratio braking coefficients, multiple sets of ratio braking settings are set. Each set of ratio braking settings includes the initial pulse count difference setting N for differential start. qd Ratio braking coefficient K zd The pulse counting setpoint N corresponding to the inflection point current b Three constant values, using a three-segment structure: When N b1 ≤N r ≤N b2 , When N b2 <N b ≤N b3 , When N b3 <N b , When K zd2 Not equal to 0 and K zd1 K zd3 When K is 0, the differential protection exhibits a single ratio braking characteristic; when K... zd2 K zd3 Not equal to 0 and K zd1 When K is 0, the differential protection exhibits a two-stage ratio braking characteristic; when K... zd1 K zd2 K zd3 When none of the values ​​are 0, the differential protection exhibits a three-stage ratio braking characteristic; when K zd1 K zd2 K zd3 When both are 0, the differential protection has no ratio braking characteristic.

7. 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 perform the steps of the method according to any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-6.

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