Protection circuit of medium-voltage bus

Abstract

The utility model relates to the technical field of bus protection, discloses a protection circuit of a medium-voltage bus, and aims to solve the problems of delay and high cost in the prior art. According to the scheme, the system mainly comprises a bus protection device, a voltage transformer, a first current transformer, a first circuit breaker, feeder protection devices, a second current transformer and a second circuit breaker, the number of the feeder protection devices is the same as that of feeder lines, the voltage transformer is arranged on a medium-voltage bus, and the first circuit breaker and the first current transformer are arranged on an incoming line of the medium-voltage bus. The voltage transformer and the first current transformer are respectively connected with the bus protection device, the bus protection device is connected with a control end of the first circuit breaker, each second circuit breaker and each second current transformer are correspondingly arranged on a feeder line of a medium-voltage bus, each second current transformer is connected with the corresponding feeder line protection device, and each second current transformer is connected with the corresponding feeder line protection device. And each feeder protection device is connected with the control end of the corresponding second circuit breaker and the bus protection device. According to the utility model, the protection cost and delay of the medium-voltage bus are reduced.

Description

Technical Field

[0001] This utility model relates to the field of busbar protection technology, specifically to a protection circuit for a medium-voltage busbar. Background Technology

[0002] The core principle of busbar protection is to identify faults by monitoring current changes and then disconnect the corresponding circuit breakers. This is primarily achieved by configuring current transformers and busbar differential protection devices. The current transformers collect the current in each branch of the busbar, and the busbar differential protection devices calculate the current in each branch to perform corresponding protection actions.

[0003] Generally, 110kV and above busbars require one set of protection devices, while 220kV and above require two sets. Each branch of the busbar (including incoming lines, outgoing lines, and bus couplers) is equipped with one or two dedicated current transformers for busbar protection. For medium-voltage busbars (usually 35kV or 10kV), due to cost considerations, dedicated busbar differential protection is generally not installed. Instead, backup protection based on adjacent components is used, such as backup protection on the 33kV side of the transformer and line protection.

[0004] Because current medium-voltage busbars lack instantaneous overcurrent protection, they rely on backup protection from adjacent components to protect against busbar faults. The inventors discovered several drawbacks: First, this method typically involves a delay (usually 0.3–0.5 seconds), failing to provide instantaneous protection against busbar faults. If a fault actually occurs, the adjacent protection will not activate before the busbar overheats, burns out, or even the switchgear explodes, severely impacting system operation and power restoration. Since medium-voltage system faults have a relatively smaller impact on the power grid compared to high-voltage systems, they receive little attention. Second, medium-voltage busbars at the end of distribution systems generally use single-busbar connections with only one power source, while feeder circuits are all load terminals and may be numerous. Using conventional busbar protection devices requires adding a dedicated current transformer to each circuit, configuring a busbar protection cabinet, and designing secondary control circuits from the busbar protection cabinet to each branch. When there are many feeder circuits, multiple busbar protection devices may be needed to achieve protection. This approach significantly impacts the overall system design and increases costs considerably. Utility Model Content

[0005] This invention aims to solve the problems of delay and high cost in existing medium-voltage bus protection methods, and proposes a protection circuit for medium-voltage bus.

[0006] The technical solution adopted by this utility model to solve the above-mentioned technical problems is:

[0007] A protection circuit for a medium-voltage busbar, wherein the medium-voltage busbar is connected in parallel with multiple feeders, the protection circuit includes: a busbar protection device, a voltage transformer, a first current transformer, a first circuit breaker, feeder protection devices (the same number as the feeders), a second current transformer, and a second circuit breaker. The voltage transformer is installed on the medium-voltage busbar. The first circuit breaker is connected in series on the incoming line of the medium-voltage busbar. The first current transformer is located at the end of the first circuit breaker furthest from the medium-voltage busbar. The voltage transformer and the first current transformer are respectively connected to the first signal input terminal of the busbar protection device. The signal output terminal of the busbar protection device is connected to the control terminal of the first circuit breaker. Each second circuit breaker is connected in series on its corresponding feeder of the medium-voltage busbar. Two current transformers are installed at the end of the second circuit breaker of the corresponding feeder that is furthest from the medium-voltage busbar. Each second current transformer is connected to the signal input terminal of the corresponding feeder protection device. The signal output terminal of each feeder protection device is connected to the control terminal of the corresponding second circuit breaker and the second signal input terminal of the busbar protection device. The feeder protection device is configured to control the opening of the corresponding second circuit breaker based on the signal detected by the corresponding second current transformer. The busbar protection device is configured to block the busbar protection after receiving the action signal of any feeder protection device, and to open the busbar protection when no action signal of the feeder protection device is received. The first circuit breaker is controlled to open based on the signals detected by the voltage transformer and the first current transformer.

[0008] Furthermore, the voltage of the medium-voltage bus is 35kV or 10kV.

[0009] The beneficial effects of this utility model are as follows: The protection circuit for the medium-voltage busbar provided by this utility model, by setting a busbar protection device on the incoming line and a feeder protection device on each feeder, and connecting each feeder protection device to the busbar protection device, allows the busbar protection device to lock or unlock the busbar protection according to the action signal of the feeder protection device. It eliminates the need to add a dedicated current transformer to each circuit, thereby reducing costs. Furthermore, this utility model achieves instantaneous overcurrent protection for the medium-voltage busbar, avoiding the delay caused by backup protection and improving safety. Attached Figure Description

[0010] Figure 1 A schematic diagram of a protection circuit for a medium-voltage busbar is provided for an embodiment.

[0011] Explanation of reference numerals in the attached figures:

[0012] 30B - Busbar protection device; 501, 502, ..., 50n - Feeder protection device; PT - Voltage transformer; CT1 - First current transformer; CT21, CT22, ..., CT2n - Second current transformer; D1 - First circuit breaker; D21, D22, ..., D2n - Second circuit breaker; d0 - First location; d1 - Second location. Detailed Implementation

[0013] To enable those skilled in the art to better understand the present invention, the technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0014] Figure 1 A schematic diagram of a protection circuit for a medium-voltage busbar is shown. Please refer to [link / reference]. Figure 1 In this embodiment, the medium-voltage bus is a single bus of 35kV or 10kV, and the medium-voltage bus is powered by only one power source, which supplies power to the medium-voltage bus through the incoming line; the medium-voltage bus is connected in parallel with multiple feeders, namely feeder 1, feeder 2, ..., feeder n, each feeder is a load end, that is, the medium-voltage bus is connected to the corresponding load through n feeders respectively.

[0015] The protection circuit includes: a bus protection device 30B, a voltage transformer PT, a first current transformer CT1, a first circuit breaker D1, a feeder protection device with the same number of feeders, a second current transformer, and a second circuit breaker. The voltage transformer PT is installed on the medium-voltage bus. The first circuit breaker D1 is connected in series on the incoming line of the medium-voltage bus. The first current transformer CT1 is installed at the end of the first circuit breaker D1 away from the medium-voltage bus. The voltage transformer PT and the first current transformer CT1 are respectively connected to the first signal input terminal of the bus protection device 30B. The signal output terminal of the bus protection device 30B is connected to the control terminal of the first circuit breaker D1.

[0016] Please see Figure 1In this embodiment, the second circuit breakers corresponding to the feeders include D21, D22, ..., D2n. Each second circuit breaker is connected in series with the corresponding feeder, that is, D21 is connected in series with feeder 1, D22 is connected in series with feeder 2, and so on, with D2n connected in series with feeder n. The second AC current transformers corresponding to the feeders include CT21, CT22, ..., CT2n. Each second current transformer is located at the end of the second circuit breaker of the corresponding feeder that is far away from the medium-voltage busbar, that is, CT21 is located at the end of D21 that is far away from the medium-voltage busbar, CT22 is located at the end of D22 that is far away from the medium-voltage busbar, and so on, with CT2n located at the end of D2n that is far away from the medium-voltage busbar. Each feeder has corresponding feeder protection devices 501, 502, ..., 50n. That is, feeder 1's protection device is 501, feeder 2's is 502, and so on, with feeder n's protection device being 50n. Each second current transformer is connected to the signal input terminal of its corresponding feeder protection device; for example, CT21 is connected to the signal input terminal of 501, CT22 to 502, and so on, with CT2n to 50n. The signal output terminal of each feeder protection device is connected to the control terminal of its corresponding second circuit breaker and the second signal input terminal of the bus protection device 30B. That is, 501's signal output terminal is connected to the control terminal of D21 and the second signal input terminal of bus protection device 30B, 502's is connected to the control terminal of D22 and the second signal input terminal of bus protection device 30B, and so on, with 50n's signal output terminal connected to the control terminal of D2n and the second signal input terminal of bus protection device 30B.

[0017] In this embodiment, the feeder protection device is configured to control the opening of the corresponding second circuit breaker according to the signal detected by the corresponding second current transformer, and the bus protection device 30B is configured to block the bus protection after receiving the operation signal of any feeder protection device, and to open the bus protection when no operation signal of the feeder protection device is received, and to control the opening of the first circuit breaker D1 according to the signal detected by the voltage transformer PT and the first current transformer CT1.

[0018] In this embodiment, the voltage transformer PT is used to collect the voltage signal of the medium-voltage bus in real time and send it to the bus protection device 30B. The first current transformer CT1 is used to collect the current signal of the incoming line in real time and send it to the bus protection device 30B. The second current transformer is used to collect the current signal of the corresponding feeder in real time and send it to the corresponding feeder protection device. When the received current signal is abnormal, the feeder protection device disconnects the corresponding second circuit breaker to achieve circuit protection. At the same time, it also sends an action signal to the bus protection device 30B. When the bus protection device 30B receives any feeder signal... When the protection device sends an action signal, the bus protection is blocked to prevent false operation of the bus protection during feeder branch faults. When the bus protection device 30B does not receive an action signal from the feeder protection device, the bus protection is opened. At this time, it is judged whether the voltage signal collected by the voltage transformer PT and the current signal collected by the first current transformer CT1 are abnormal. If abnormal, the first circuit breaker D1 is disconnected. The voltage transformer PT is used to assist in the judgment. When there is a medium voltage bus fault, the voltage of the medium voltage bus will be significantly reduced, thereby avoiding misjudgment caused by using a single current and further improving the accuracy of bus fault judgment.

[0019] Please see Figure 1 When a fault occurs at the first point d0, it will cause an abnormal current. At this time, 501 determines that the current is abnormal based on the current detected by CT21, and controls the disconnection of D21. At the same time, the action signal is sent to the bus protection device 30B. After receiving the action signal, the bus protection device 30B locks the bus protection to avoid false operation of the bus protection when the feeder branch is faulty. When a fault occurs at the second point d1, it will cause both abnormal current and abnormal voltage. At this time, the bus protection device 30B determines that both the current and voltage are abnormal based on the voltage detected by the voltage transformer PT and the current detected by the first current transformer CT1. All second circuit breakers will not operate, the bus protection will be opened, and the first circuit breaker D1 will be disconnected.

[0020] Based on the aforementioned protection circuit, the busbar protection device 30B and feeder protection device in this embodiment function to compare voltage and current, and control the circuit breaker's disconnection. Therefore, the busbar protection device 30B and feeder protection device can be implemented using simple digital circuits combining comparators and AND gates, without the need for a computer program. Alternatively, the busbar protection device 30B and feeder protection device can be controllers loaded with a computer program. This computer program is used to compare voltage and current, and control the circuit breaker's disconnection; it is a conventional computer program in the art and not an improvement on this embodiment, so it will not be elaborated upon here.

[0021] In summary, the medium-voltage bus protection circuit provided in this embodiment, by setting a bus protection device 30B on the incoming line and a feeder protection device on each feeder, and connecting each feeder protection device to the bus protection device 30B, allows the bus protection device 30B to lock or unlock the bus protection according to the action signal of the feeder protection device. This eliminates the need to add a dedicated current transformer to each circuit, thereby reducing costs. Furthermore, this embodiment achieves instantaneous overcurrent protection for the medium-voltage bus, avoiding the delay caused by backup protection and improving safety.

[0022] It should be noted that the present invention provides only a specific structure of a protection circuit for a medium-voltage busbar. The relevant modules involved are all hardware system modules or functional modules that combine computer software programs or protocols with hardware in the prior art. The computer software programs or protocols involved in these functional modules are technologies known to those skilled in the art and are not improvements to this system, so they will not be described in detail here. The improvement of this system lies in the interaction or connection relationship between the modules, that is, in improving the overall structure of the system to solve the corresponding technical problems that this system aims to address.

Claims

1. A protection circuit for a medium-voltage busbar, wherein the medium-voltage busbar is connected in parallel with multiple feeders, characterized in that, The protection circuit includes: a busbar protection device, a voltage transformer, a first current transformer, a first circuit breaker, a feeder protection device (the same number as the feeders), a second current transformer, and a second circuit breaker. The voltage transformers are installed on the medium-voltage busbar. The first circuit breaker is connected in series on the incoming line of the medium-voltage busbar. The first current transformer is located at the end of the first circuit breaker furthest from the medium-voltage busbar. The voltage transformer and the first current transformer are respectively connected to the first signal input terminal of the busbar protection device. The signal output terminal of the busbar protection device is connected to the control terminal of the first circuit breaker. Each second circuit breaker is connected in series on the corresponding feeder of the medium-voltage busbar, and each second current transformer is located on the corresponding feeder. The second circuit breaker is located at the end furthest from the medium-voltage busbar. Each second current transformer is connected to the signal input terminal of the corresponding feeder protection device. The signal output terminal of each feeder protection device is connected to the control terminal of the corresponding second circuit breaker and the second signal input terminal of the busbar protection device. The feeder protection device is configured to control the opening of the corresponding second circuit breaker based on the signal detected by the corresponding second current transformer. The busbar protection device is configured to block the busbar protection after receiving the operation signal of any feeder protection device, and to open the busbar protection when no operation signal of the feeder protection device is received. The first circuit breaker is controlled to open based on the signals detected by the voltage transformer and the first current transformer.

2. The protection circuit for the medium-voltage busbar according to claim 1, characterized in that, The voltage of the medium-voltage bus is 35kV or 10kV.

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