A power transmission line differential protection method, device and system

Abstract

The application discloses a power transmission line differential protection method, device and system, and the method comprises the following steps: acquiring positive sequence current, negative sequence current and zero sequence current of two differential protection devices on both sides of a power transmission line; calculating complex sequence current of each differential protection device according to the positive sequence current, the negative sequence current and the zero sequence current of each differential protection device; and performing differential protection of the power transmission line according to the complex sequence current of the two differential protection devices. The application adopts longitudinal differential protection based on the amount of complex sequence current, reduces the data transmission amount, and improves the sensitivity of the current relay during a fault.

Description

Technical Field

[0001] This invention relates to the field of power transmission line protection technology, and in particular to a method, device and system for differential protection of power transmission lines. Background Technology

[0002] The bandwidth resources of carrier channels are limited, typically below 300kB / s. Protection based on carrier channels generally employs longitudinal protection based on switch signal transmission. If phase-differential current protection is used, especially multi-terminal differential protection, data for each phase current must be transmitted, placing high demands on channel bandwidth. If multiple protection devices use the carrier channel simultaneously, channel resources become even more strained, potentially affecting the availability of differential protection. Summary of the Invention

[0003] This invention provides a method, apparatus, and system for differential protection of transmission lines, which resolves the contradiction between the high requirements for channel resources and the limited bandwidth of carrier channels in existing differential protection technologies for transmission lines, and also improves the sensitivity of protection to a certain extent.

[0004] Firstly, a differential protection method for transmission lines is provided, comprising:

[0005] Obtain the positive sequence current, negative sequence current, and zero sequence current of the two differential protection devices on both sides of the transmission line;

[0006] Calculate the complex sequence current of each differential protection device based on the positive sequence current, negative sequence current, and zero sequence current of each differential protection device;

[0007] The differential protection of the transmission line is performed based on the sequence current of the two differential protection devices.

[0008] In a second aspect, an embedded microcomputer protection device is provided, wherein an embedded microcomputer program instruction is stored on a readable storage medium of the embedded microcomputer protection device; when the embedded microcomputer program instruction is executed by a processor, it implements the transmission line differential protection method as described in the first aspect embodiment above.

[0009] Thirdly, a differential protection system for transmission lines is provided, comprising: an embedded microcomputer protection device as described in the second aspect embodiment above and a power line carrier information transmission channel, wherein the power line carrier information transmission channel comprises: a power cable, a coupler, and a communication terminal.

[0010] Thus, in this embodiment of the invention, longitudinal differential protection based on complex sequence current is adopted, which reduces the amount of data transmission and improves the sensitivity of the current relay during a fault. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a flowchart of a differential protection method for transmission lines according to an embodiment of the present invention. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] This invention discloses a differential protection method for a transmission line. The transmission line is located between two differential protection devices, which provide differential protection. Figure 1 As shown, the method includes the following steps:

[0015] Step S101: Obtain the positive sequence current, negative sequence current and zero sequence current of the two differential protection devices on both sides of the transmission line.

[0016] Positive-sequence current, negative-sequence current, and zero-sequence current can be obtained using the symmetrical component method, as follows:

[0017] Positive sequence current:

[0018] Negative sequence current:

[0019] Zero-sequence current:

[0020] in, Indicates the current of phase A. This represents the B-phase current. Represents the C-phase current, α and α 2 Both represent the turning angle, α = e j120° α 2 =e j240° .

[0021] Step S102: Calculate the complex sequence current of each differential protection device based on the positive sequence current, negative sequence current and zero sequence current of each differential protection device.

[0022] Specifically, the formula for calculating complex sequence current is:

[0023]

[0024] in, Represents complex sequence current. Indicates positive sequence current. Indicates negative sequence current. This represents the zero-sequence current.

[0025] because Substituting the aforementioned formulas for calculating positive-sequence current, negative-sequence current, and zero-sequence current into the formula for calculating complex-sequence current, and rearranging, we obtain the following formula:

[0026]

[0027] Therefore, the complex sequence current can be calculated by collecting the three-phase current.

[0028] Step S103: Perform differential protection of the transmission line based on the sequence current of the two differential protection devices.

[0029] Specifically, step S103 includes the following process:

[0030] (1) The differential protection discrimination value is calculated based on the sequence current of the two differential protection devices.

[0031] Specifically, the formula for calculating the differential protection discrimination value is:

[0032]

[0033] Among them, DI F This indicates the differential protection discrimination value. This represents the complex sequence current of the differential protection device located on one side of the transmission line. This indicates the sequence current of the differential protection device located on the other side of the transmission line. It can be considered as differential current. It can be considered as braking current.

[0034] (2) Compare the differential protection discrimination value with the preset threshold value.

[0035] The preset threshold is an empirical value; in a specific embodiment of the present invention, the preset threshold is 0.3I. N , among which, I N Indicates the rated current.

[0036] (3) Determine the location of the fault based on the size relationship obtained from the comparison.

[0037] The fault locations include: within the zones of the two differential protection devices and outside the zones of the two differential protection devices.

[0038] Specifically, this step includes the following two scenarios:

[0039] ①If the differential protection judgment value is greater than the preset threshold, the fault location is determined to be within the area of ​​the two differential protection devices.

[0040] ②If the differential protection judgment value is not greater than the preset threshold, then the fault location is determined to be outside the zone of the two differential protection devices.

[0041] Preferably, after determining the fault location, the method of this embodiment further includes:

[0042] (4) Based on the location of the fault, the two differential protection devices shall perform differential protection actions.

[0043] Specifically, this step also has the following two variations depending on the location of the fault:

[0044] ①If the fault location is within the zone of two differential protection devices, then the two differential protection devices will trip.

[0045] ②If the fault location is outside the zone of the two differential protection devices, the two differential protection devices will not perform tripping actions.

[0046] The differential protection device and the carrier communication terminal are connected via a network port for data transmission. In this embodiment of the invention, the positive-sequence current, negative-sequence current, and zero-sequence current are integrated into a complex-sequence current. During data transmission, only the complex-sequence current data needs to be transmitted, unlike phase-sequence differential protection which transmits three-phase current, thus reducing the amount of data transmitted. This embodiment of the invention can control the size of each data frame to below 20 bytes, and based on a sampling rate of 1200Hz, the data flow rate can be controlled to 24kB / s.

[0047] The sensitivity of the complex sequence current in the embodiments of the present invention will be further verified below.

[0048] I. Three-phase fault conditions

[0049] When a three-phase fault occurs, using phase A as the reference, then... α=e j120° α 2 =e j240° .

[0050] For ordinary current relays For complex sequence current, we can obtain but therefore, It can be seen that during a three-phase fault, the reverse sequence current relay has the same sensitivity as the ordinary current relay.

[0051] II. A / B phase-to-phase fault conditions

[0052] When an A-B phase-to-phase fault occurs, the fault current is usually much larger than the load current. Taking phase A as a reference, then... α=e j120° α 2 =e j240° .

[0053] For ordinary current relays, the fault current For complex sequence current, we can obtain Then it can be deduced that but therefore, It can be seen that, during an A / B phase-to-A fault, the sensitivity of the complex sequence current relay is increased by approximately 1.646 times compared to a regular current relay.

[0054] III. Phase BC Interphase Fault Conditions

[0055] When a phase-B fault occurs, the fault current is usually much larger than the load current. Taking phase A as a reference, then... α=e j120° α 2 =e j240° .

[0056] For ordinary current relays, the fault current For complex sequence current, we can obtain Then it can be deduced that but therefore, It can be seen that, during a phase-to-phase fault (BC), the sensitivity of the complex sequence current relay is increased by approximately 0.732 times compared to a regular current relay.

[0057] IV. CA Phase-to-Phase Fault Conditions

[0058] When a phase-to-phase fault (CA) occurs, the fault current is usually much larger than the load current. Taking phase A as a reference, then... α=e j120° α 2 =e j240° .

[0059] For ordinary current relays, the fault current For complex sequence current, we can obtain Then it can be deduced that but therefore, It can be seen that, during a phase-to-phase fault in CA, the sensitivity of the complex sequence current relay is increased by approximately 1.646 times compared to a regular current relay.

[0060] V. Single-phase grounding fault conditions

[0061] For ungrounded systems, the zero-sequence current is almost zero during a single-phase ground fault. For systems grounded through a small resistor, the fault current is [missing value]. U f Z represents the fault voltage at the fault point. (1) Z represents the system's equivalent positive-sequence impedance as seen from the fault point. (0) This represents the system's equivalent zero-sequence impedance as seen from the fault point, and for the faulty line, it has... but For complex sequence currents, it can be derived that... Therefore, it can be seen that during a single-phase ground fault, the sensitivity of the complex-sequence current relay is increased by approximately 1.667 times compared to a regular zero-sequence current relay.

[0062] Based on the above analysis, it can be determined that the use of complex sequence current for differential protection judgment in the embodiments of the present invention can ensure that the sensitivity will not decrease, and may even improve the sensitivity.

[0063] This invention also discloses an embedded microcomputer protection device, wherein an embedded microcomputer program instruction is stored on a readable storage medium of the embedded microcomputer protection device; when the embedded microcomputer program instruction is executed by a processor, it implements the transmission line differential protection method as described in the above embodiments.

[0064] This invention also discloses a differential protection system for transmission lines, comprising: an embedded microprocessor protection device as described in the above embodiments and a power line carrier information transmission channel. The power line carrier information transmission channel includes: a power cable, a coupler, and a communication terminal.

[0065] In summary, the embodiments of the present invention employ longitudinal differential protection based on complex sequence current, which reduces the amount of data transmission and improves the sensitivity of the current relay during a fault.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A differential protection method for transmission lines, characterized in that, include: Obtain the positive sequence current, negative sequence current, and zero sequence current of the two differential protection devices on both sides of the transmission line; Calculate the complex sequence current of each differential protection device based on the positive sequence current, negative sequence current, and zero sequence current of each differential protection device; Differential protection of the transmission line is performed based on the complex sequence current of the two differential protection devices. The formula for calculating the complex sequence current is: ； in, Represents complex sequence current. Indicates positive sequence current. Indicates negative sequence current. Represents zero-sequence current; The step of performing differential protection of the transmission line based on the complex sequence current of the two differential protection devices includes: The differential protection discrimination value is calculated based on the complex sequence current of the two differential protection devices. Compare the differential protection discrimination value with the preset threshold value; The location of the fault is determined based on the size relationship obtained from the comparison. The formula for calculating the differential protection discrimination value is: ； in, This indicates the differential protection discrimination value. This represents the complex sequence current of the differential protection device located on one side of the transmission line. This indicates the sequence current of the differential protection device located on the other side of the transmission line.

2. The differential protection method for transmission lines according to claim 1, characterized in that: The preset threshold is ,in, Indicates the rated current.

3. The differential protection method for transmission lines according to claim 1, characterized in that, The step of determining the fault location based on the magnitude relationship obtained from the comparison includes: If the differential protection discrimination value is greater than the preset threshold, then the fault location is determined to be within the area of ​​the two differential protection devices; If the differential protection discrimination value is not greater than the preset threshold, then the fault location is determined to be outside the area of ​​the two differential protection devices.

4. The differential protection method for transmission lines according to claim 3, characterized in that, After the step of determining the fault location based on the magnitude relationship obtained from the comparison, the method further includes: The two differential protection devices are instructed to perform differential protection actions based on the location of the fault.

5. The differential protection method for transmission lines according to claim 4, characterized in that, The step of causing the two differential protection devices to perform differential protection actions according to the fault location includes: If the fault location is within the zone of the two differential protection devices, then the two differential protection devices will trip. If the fault location is outside the zone of the two differential protection devices, the two differential protection devices will not perform a tripping action.

6. An embedded microcomputer protection device, characterized in that: The embedded microcomputer protection device stores embedded microcomputer program instructions on its readable storage medium; when the embedded microcomputer program instructions are executed by the processor, they implement the transmission line differential protection method as described in any one of claims 1 to 5.

7. A differential protection system for transmission lines, characterized in that, include: The embedded microcomputer protection device and power line carrier information transmission channel as described in claim 6, wherein the power line carrier information transmission channel includes: a power cable, a coupler, and a communication terminal.

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