Automatic switching circuit and automatic switching method of low-voltage single-bus reactive power compensation device

Abstract

The invention belongs to the technical field of electrical design, and particularly discloses an automatic switching circuit and an automatic switching method of a low-voltage single-bus reactive power compensation device. A bus coupler loop of the circuit is provided with current transformers 1BC2 and 2BC2, a measuring circuit I is formed by connecting output ends of the current transformers 1BC1 and 1BC2 in parallel and then connecting the output ends of the current transformers 1BC1 and 1BC2 with a power factor controller 1PFC in series to form a closed loop, and the power factor controller 1PFC is electrically connected with a reactive power compensation device on a bus section I; the measuring circuit II is formed by connecting output ends of a current transformer 2BC1 and a current transformer 2BC2 in parallel and then connecting the output ends of the current transformer 2BC1 and the current transformer 2BC2 with a power factor controller 2PFC in series to form a closed loop; and the power factor controller 2PFC is electrically connected with the reactive power compensation device on the section II bus. According to the method, two incoming lines work simultaneously, a single bus operates in a segmented mode, a first incoming line works, the single bus operates in a non-segmented mode, a second incoming line works, and the single bus operates in a non-segmented mode. The method has the characteristics of simple circuit, low investment, safety and reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical design, and in particular to an automatic switching circuit and an automatic switching method for a low-voltage single-busbar reactive compensation device with simple circuits, low investment, safety and reliability. Background Art

[0002] Typical single busbar segmented low voltage distribution system such as Figure 1 As shown in the figure, two transformers are set up to supply power to the first and second level loads. Each transformer can carry the full load. In normal operation, the two transformers are operated separately, the low voltage bus tie breaker 3QA is disconnected, and the power factor automatic compensation devices connected to their respective busbars are put into operation. When a transformer (such as Figure 1 2TA) is out of operation, the incoming circuit breaker (such as Figure 1 2QA) is disconnected, and then the busbar breaker 3QA is closed. At this time, all the loads are supplied by another transformer (such as Figure 1 Power is supplied by the circuit breaker 1TA (with incoming line circuit breaker 1QA closed). Since the second incoming line has no current and the power factor controller on bus section II is not operational, the capacitor bank on this bus section will be disconnected. If the capacitor bank connected to bus section I is insufficient to compensate for the total reactive load on both bus sections, the power factor requirement of greater than 0.92 will not be met. While configuring the compensation capacitors on each bus section to compensate for the entire reactive load would address this issue, it would also cause some reactive compensation equipment to remain idle for extended periods, increasing investment and making this an uneconomical and irrational option.

[0003] In the prior art, to address the aforementioned issues, there is patent CN112865126B, entitled "Shared Sampling Current Circuit for Reactive Compensation Devices in Low-Voltage Single-Bus Segmented Systems." This patent implements a shared sampling current for reactive compensation devices in a low-voltage single-bus segmented system by adding two intermediate relays to the low-voltage cabinet, arranging and wiring the two incoming circuit breakers and the bus tie circuit breaker, and then wiring the auxiliary contacts of the two intermediate relays to the sampling current transformers of the reactive compensation devices. This allows reactive compensation capacity to be deployed to meet the requirements in various operating modes. Although this patent allows for the deployment of reactive compensation capacity to meet the requirements, ensuring that the current transformers do not open and sharing the sampling current complicates the control circuit and reduces its reliability. Furthermore, because the sampling current is the total current and is supplied to two reactive compensation control devices simultaneously, it is impossible to ensure that the capacity deployed by each compensation device is consistent with the required compensation capacity for the bus segment, and it is impossible to accurately control the capacity deployed by each compensation device.

[0004] In the prior art, there are patents such as Patent CN215835134U, titled "A configuration device for saving reactive compensation capacity in a single-busbar segmented low-voltage power distribution system." This patent adds a relay to the control circuit, connecting the relay's auxiliary contacts to the compensation device's operation circuit, to ensure that the required reactive compensation capacity can be deployed in various operating modes. While this patent can also deploy the required reactive compensation capacity and ensure that the capacity deployed by each compensation device is consistent with the required compensation capacity of the busbar segment, its control circuit is still relatively complex, and the control process is also relatively complicated.

[0005] Therefore, the study of an automatic switching circuit for a low-voltage single-busbar reactive compensation device can not only realize reactive compensation for various operating modes of the low-voltage single-busbar segment with a relatively simple circuit, but also save reactive compensation capacity and improve safety and reliability. It is one of the key technologies that urgently need to be solved in the current single-busbar segmented low-voltage distribution system. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention provides an automatic switching circuit for a low-voltage single-busbar reactive compensation device with simple circuits, low investment, safety and reliability, and also provides an automatic switching method for a low-voltage single-busbar reactive compensation device.

[0007] The automatic switching circuit of the low-voltage single-busbar reactive power compensation device of the present invention is implemented as follows: the low-voltage single-busbar reactive power compensation device includes a bus section I and a bus section II, wherein a bus tie circuit connected via a bus tie circuit breaker 3QA is provided between the bus sections I and II, and corresponding reactive power compensation devices are respectively configured on the bus sections I and II. The primary winding of a current transformer 1BC1 is installed on the primary incoming line of the bus section I, and the primary winding of a current transformer 2BC1 is installed on the secondary incoming line of the bus section II. The primary windings of current transformers 1BC2 and 2BC2 are installed on the bus coupling circuit; The automatic switching measurement circuit includes a measurement circuit I and a measurement circuit II. The measurement circuit I is formed by connecting the secondary windings of the current transformer 1BC1 and the current transformer 1BC2 in parallel and then connecting them in series with the power factor controller 1PFC to form a closed loop. The secondary winding connection end of the current transformer 1BC1 and the connection end of the power factor controller 1PFC are grounded, and the power factor controller 1PFC is electrically connected to the reactive compensation device configured on the bus section I; the measurement circuit II is formed by connecting the secondary windings of the current transformer 2BC1 and the current transformer 2BC2 in parallel and then connecting them in series with the power factor controller 2PFC to form a closed loop. The secondary winding connection end of the current transformer 2BC1 and the connection end of the power factor controller 2PFC are grounded, and the power factor controller 2PFC is electrically connected to the reactive compensation device configured on the bus section II.

[0008] Furthermore, the primary windings of the current transformer 1BC1 and the current transformer 2BC1 are simultaneously installed on any one of the three phases A, B, and C, and the primary windings of the current transformer 1BC2 and the current transformer 2BC2 have opposite polarities.

[0009] Furthermore, the primary windings of the current transformer 1BC1 and the current transformer 1BC2 are installed in the same phase and have opposite polarities.

[0010] Furthermore, the primary windings of the current transformer 2BC1 and the current transformer 2BC2 are installed in the same phase and have opposite polarities.

[0011] Furthermore, the primary windings of the current transformer 1BC1 and the current transformer 1BC2 have the same transformation ratio, and the primary windings of the current transformer 2BC1 and the current transformer 2BC2 have the same transformation ratio.

[0012] Furthermore, the reactive compensation capacity of the reactive compensation devices configured for the bus section I and the bus section II is determined by the power factors detected by the corresponding power factor controller 1PFC and power factor controller 2PFC when each bus section is operated in sections.

[0013] Furthermore, the primary windings of the current transformer 1BC2 and the current transformer 2BC2 are installed at the same end of the bus tie circuit breaker 3QA or are connected in series at the front and rear ends of the bus tie circuit breaker 3QA.

[0014] The automatic switching method of the low-voltage single-busbar reactive power compensation device of the present invention is implemented as follows: based on the automatic switching circuit of the low-voltage single-busbar reactive power compensation device described above, it includes the following segmented operation modes: A. Two incoming lines operate simultaneously and a single busbar operates in sections: Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is closed, and bus tie breaker 3QA is opened. At this time, the corresponding power factor controllers 1PFC and 2PFC on measurement circuits I and II control the reactive power compensation device according to the current provided by the secondary windings of current transformers 1BC1 and 2BC1, respectively. B. Single-circuit incoming line operation, single busbar unsegmented operation: Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is open, and bus tie breaker 3QA is closed. At this time, the vector total current I1 input to power factor controller 1PFC in measurement circuit I is I11-I12. Power factor controller 1PFC controls the reactive power compensation device on busbar section I according to vector total current I1. Simultaneously, power factor controller 2PFC on measurement circuit II controls the reactive power compensation device on busbar section II according to the current provided by the secondary winding of current transformer 2BC2. C. Two-circuit incoming line operation and single busbar non-segmented operation: circuit breaker 2QA of busbar section II is closed, circuit breaker 1QA of busbar section I is disconnected, and bus tie breaker 3QA is closed. At this time, the vector total current I2 input to the power factor controller 2PFC in measurement circuit II is I21-I22. The power factor controller 2PFC controls the reactive power compensation device on busbar section II according to the vector total current I2. At the same time, the power factor controller 1PFC on measurement circuit I controls the reactive power compensation device on busbar section I according to the current provided by the secondary winding of current transformer 1BC2.

[0015] Furthermore, in the single busbar segmented operation mode in which the two incoming lines are working simultaneously, since the busbar circuit breaker 3QA is disconnected, the secondary winding currents of the current transformer 1BC2 and the current transformer 2BC2 in the busbar circuit are both zero.

[0016] Furthermore, in the single-circuit incoming line operation and single busbar non-segmented operation mode, the current direction in the bus tie loop is from busbar section I to busbar section II. Since the primary winding currents of current transformer 1BC2 and current transformer 1BC1 are in opposite directions, the secondary winding current I12 of current transformer 1BC2 in measurement circuit I is negative, so that the vector resultant current I1 in the input power factor controller 1PFC in measurement circuit I is I11-I12. In the two-circuit incoming line operation and single busbar non-segmented operation mode, the current direction in the bus tie circuit is from busbar section II to busbar section I. Since the primary winding currents of current transformer 2BC2 and current transformer 2BC1 are in opposite directions, the secondary winding current I22 of current transformer 2BC2 in measurement circuit II is negative, making the vector resultant current I2 in the input power factor controller 2PFC in measurement circuit II equal to I21-I22.

[0017] The beneficial effects of the present invention are: 1. In terms of circuit structure simplification, compared with the prior art that requires the addition of multiple intermediate relays (such as CN112865126B) or complex relay circuits (such as CN215835134U) to achieve reactive compensation control, the present invention achieves current vector synthesis by installing specific current transformers (1BC2, 2BC2) in the bus-bundle circuit and designing a measurement circuit consisting of the incoming current transformer and the bus-bundle current transformer in parallel. No additional relay components or complex control circuits are required. This not only greatly simplifies the structure of the control circuit, but also completely eliminates the risks of relay contact adhesion, coil burning and other failures, thereby improving the long-term stability of the automatic switching circuit.

[0018] 2. In terms of improving compensation accuracy, when two incoming lines are operating simultaneously and a single busbar is operating in sections, the power factor controllers of the two busbar sections independently control the compensation devices based on the current signals from their respective incoming current transformers, ensuring that the compensation capacity of each busbar section matches its own load demand. When a single incoming line is operating and the single busbar is operating unsegmented, the measurement circuit uses the vector sum current at the output terminals of the current transformers (1BC2, 2BC2) installed in the busbar tie circuit to provide accurate signals to the corresponding power factor controllers. Similarly, when two incoming lines are operating and the single busbar is operating unsegmented, precise control can also be achieved. This not only enables the operation of the two-section reactive power compensation device when two transformers are operating in sections, but also ensures that the compensation capacity of the two busbar sections always matches the real-time load of each busbar section when any transformer is supplying power to both busbar sections simultaneously. This saves reactive compensation capacity and effectively avoids the low power factor or device idleness caused by the mismatch between compensation capacity and demand in the prior art. It ensures that the power factor remains stable above 0.92 under various operating modes.

[0019] 3. In terms of economic optimization, the present invention does not need to configure compensation capacitors for each bus section according to the total reactive load as in the prior art. The compensation devices of each bus section can be flexibly put into use according to the actual operating mode, reducing the redundant configuration of compensation capacity, avoiding the long-term idleness of some devices, significantly reducing the initial investment cost, and improving equipment utilization.

[0020] 4. In terms of enhanced safety and reliability, the present invention reduces potential fault points and lowers the probability of failure due to complex circuits by simplifying the circuit structure; and by rationally designing the polarity and transformation ratio of the current transformer, it ensures the accuracy and stability of current signal acquisition, avoids risks such as open circuit of the current transformer, and further improves the safety and reliability of the entire reactive power compensation system, and can stably adapt to various operating conditions of the single-bus segmented low-voltage distribution system; and the power factor controller (PFC) can directly automatically control compensation according to the vector-synthesized current, thus eliminating the need for external switching signals or logical judgments, reducing the complexity of operation and maintenance, and avoiding the adverse effects of manual intervention on compensation accuracy and operational safety.

[0021] In summary, the present invention utilizes an innovative measurement circuit consisting of the output ends of the current transformers for reactive power compensation on two power supply lines connected in parallel with the current transformers on the segmented bus. This allows the power factor controller (PFC) to adaptively synthesize and match the power factor of the load on the corresponding bus based on the current vector, thereby achieving precise matching of the compensation capacity with segmented / single bus operation. This not only effectively simplifies the control circuit, thereby improving the reliability of the automatic switching circuit and significantly reducing costs, but also effectively avoids the problems of low power factor or idle equipment, fundamentally solving the problems of insufficient economy, reliability, and accuracy in reactive power compensation in single-bus segmented systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the main wiring diagram of the low-voltage power distribution system in the prior art; Figure 2 It is a control loop diagram of the automatic switching circuit of the present invention; Figure 3 This is a current flow diagram of the measuring circuit I of the automatic switching circuit in the embodiment operating in mode 2; Figure 4 This is a current flow diagram of the measuring circuit II of the automatic switching circuit in the embodiment operating in mode 2; Figure 5 This is a current flow diagram of the measuring circuit I of the automatic switching circuit in the embodiment operating in mode 3; Figure 6 This is a current flow diagram of the measuring circuit II of the automatic switching circuit in the embodiment operating in mode 3; In the figure: Ⅰ1-current flowing through power factor controller 1PFC, Ⅰ11-current flowing through the output end of current transformer 1BC1, Ⅰ12-current flowing through the output end of current transformer 1BC2, Ⅱ2-current flowing through power factor controller 2PFC, Ⅱ21-current flowing through the output end of current transformer 2BC1, Ⅱ22-current flowing through the output end of current transformer 2BC2, * is the positive pole of the current transformer. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] like Figures 2 to 6 As shown, the automatic switching circuit of the low-voltage single-bus reactive compensation device of the present invention comprises a bus section I and a bus section II. The bus sections I and II are connected with a bus tie circuit connected via a bus tie circuit breaker 3QA. The bus sections I and II are respectively provided with corresponding reactive compensation devices. The primary winding of a current transformer 1BC1 is installed on the first incoming line of the bus section I, and the primary winding of a current transformer 2BC1 is installed on the second incoming line of the bus section II. The primary windings of current transformers 1BC2 and 2BC2 are installed on the bus coupling circuit; The automatic switching measurement circuit includes a measurement circuit I and a measurement circuit II. The measurement circuit I is formed by connecting the secondary windings of the current transformer 1BC1 and the current transformer 1BC2 in parallel and then connecting them in series with the power factor controller 1PFC to form a closed loop. The secondary winding connection end of the current transformer 1BC1 and the connection end of the power factor controller 1PFC are grounded, and the power factor controller 1PFC is electrically connected to the reactive compensation device configured on the bus section I; the measurement circuit II is formed by connecting the secondary windings of the current transformer 2BC1 and the current transformer 2BC2 in parallel and then connecting them in series with the power factor controller 2PFC to form a closed loop. The secondary winding connection end of the current transformer 2BC1 and the connection end of the power factor controller 2PFC are grounded, and the power factor controller 2PFC is electrically connected to the reactive compensation device configured on the bus section II.

[0025] The primary windings of the current transformers 1BC1 and 2BC1 are simultaneously installed on any one of the three phases A, B, and C, and the primary windings of the current transformers 1BC2 and 2BC2 have opposite polarities.

[0026] The primary windings of the current transformer 1BC1 and the current transformer 1BC2 are both installed on the same phase and have opposite polarities.

[0027] The primary windings of the current transformer 2BC1 and the current transformer 2BC2 are both installed on the same phase and have opposite polarities.

[0028] The primary windings of the current transformer 1BC1 and the current transformer 1BC2 have the same transformation ratio, and the primary windings of the current transformer 2BC1 and the current transformer 2BC2 have the same transformation ratio.

[0029] The reactive compensation capacity of the reactive compensation devices configured for the bus section I and the bus section II is determined by the power factors detected by the corresponding power factor controllers 1PFC and 2PFC when the bus sections are operated in sections.

[0030] The primary windings of the current transformer 1BC2 and the current transformer 2BC2 are installed at the same end of the bus tie circuit breaker 3QA or are connected in series at the front and rear ends of the bus tie circuit breaker 3QA.

[0031] The automatic switching method of the low-voltage single-busbar reactive power compensation device of the present invention is based on the automatic switching circuit of the low-voltage single-busbar reactive power compensation device described above, and includes the following segmented operation modes: A. Two incoming lines operate simultaneously and a single busbar operates in sections: Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is closed, and bus tie breaker 3QA is opened. At this time, the corresponding power factor controllers 1PFC and 2PFC on measurement circuits I and II control the reactive power compensation device according to the current provided by the secondary windings of current transformers 1BC1 and 2BC1, respectively. B. Single-circuit incoming line operation, single busbar unsegmented operation: Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is open, and bus tie breaker 3QA is closed. At this time, the vector total current I1 input to power factor controller 1PFC in measurement circuit I is I11-I12. Power factor controller 1PFC controls the reactive power compensation device on busbar section I according to vector total current I1. Simultaneously, power factor controller 2PFC on measurement circuit II controls the reactive power compensation device on busbar section II according to the current provided by the secondary winding of current transformer 2BC2. C. Two-circuit incoming line operation and single busbar non-segmented operation: circuit breaker 2QA of busbar section II is closed, circuit breaker 1QA of busbar section I is disconnected, and bus tie breaker 3QA is closed. At this time, the vector total current I2 input to the power factor controller 2PFC in measurement circuit II is I21-I22. The power factor controller 2PFC controls the reactive power compensation device on busbar section II according to the vector total current I2. At the same time, the power factor controller 1PFC on measurement circuit I controls the reactive power compensation device on busbar section I according to the current provided by the secondary winding of current transformer 1BC2.

[0032] In the single busbar segmented operation mode with two incoming lines working simultaneously, since the busbar circuit breaker 3QA is disconnected, the secondary winding currents of the current transformers 1BC2 and 2BC2 in the busbar circuit are both zero.

[0033] In the single-circuit incoming line operation and single busbar non-segmented operation mode, the current direction in the bus tie circuit is from busbar section I to busbar section II. Since the primary winding currents of current transformer 1BC2 and current transformer 1BC1 are in opposite directions, the secondary winding current I12 of current transformer 1BC2 in measurement circuit I is negative, so that the vector resultant current I1 in the input power factor controller 1PFC in measurement circuit I is I11-I12. In the two-circuit incoming line operation and single busbar non-segmented operation mode, the current direction in the bus tie circuit is from busbar section II to busbar section I. Since the primary winding currents of current transformer 2BC2 and current transformer 2BC1 are in opposite directions, the secondary winding current I22 of current transformer 2BC2 in measurement circuit II is negative, making the vector resultant current I2 in the input power factor controller 2PFC in measurement circuit II equal to I21-I22.

[0034] Example 1

[0035] like Figures 2 to 6 As shown in FIG, the automatic switching method of the low-voltage single busbar reactive power compensation device includes the following segmented operation modes: Mode 1: Two incoming lines work simultaneously and single busbar operates in sections (the most commonly used operating mode): Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is closed, and busbar tie breaker 3QA is disconnected. At this time, the primary winding currents of current transformers 1BC2 and 2BC2 in the busbar tie circuit are both zero. The corresponding power factor controllers 1PFC and 2PFC on measurement circuit I and measurement circuit II respectively detect the load power factors of their respective busbar sections according to the currents provided by the secondary windings of current transformers 1BC1 and 2BC1, and then control the reactive power compensation devices to operate accordingly.

[0036] Mode 2: One incoming line operation, single busbar non-segmented operation: Figure 2 、 3 As shown in Figure 4, the circuit breaker 1QA of bus section I is closed, the circuit breaker 2QA of bus section II is open, and the bus tie circuit breaker 3QA is closed. At this time, the current direction in the bus tie circuit is from bus section I to bus section II. Since the primary winding currents of current transformer 1BC2 and current transformer 1BC1 are in opposite directions, the secondary winding current I12 of current transformer 1BC2 in measurement circuit I is negative, so that the vector total current I1 input to the power factor controller 1PFC in measurement circuit I is I11-I12. The vector total current I1 corresponds to the load current on bus section I. Therefore, the power factor detected by the power factor controller 1PFC is the power factor of the load on bus section I. The power factor controller 1PFC controls the automatic switching of the capacitor bank of the reactive compensation device on bus section I according to the vector total current I1, that is, according to the power factor of the load on bus section I. At the same time, the polarity of the primary winding of the current transformer 2BC2 is the same as the direction of the current, and the current I22 is positive, so that the vector total current I2 in the input power factor controller 2PFC in the measurement circuit II is I21+I22; but since the 2QA circuit breaker is disconnected, I21=0, and the current in the input power factor controller 2PFC is I22, which corresponds to the load current on the section II bus. The power factor detected by the power factor controller 2PFC is the power factor of the load on the section II bus. The power factor controller 2PFC on the measurement circuit II controls the automatic switching of the capacitor group of the reactive compensation device on the section II bus according to the current provided by the current transformer 2BC2.

[0037] Mode 3: Two-circuit incoming line operation, single busbar non-segmented operation: Figure 2 、 5As shown in Figure 6, the circuit breaker 2QA of the bus section II is closed, the circuit breaker 1QA of the bus section I is disconnected, and the bus tie circuit breaker 3QA is closed. At this time, the current direction in the bus tie circuit is from the bus section II to the bus section I. Since the primary winding current directions of the current transformer 2BC2 and the current transformer 2BC1 are opposite, the secondary winding current I22 of the current transformer 2BC2 in the measuring circuit II is negative, so that the vector current I2 in the input power factor controller 2PFC in the measuring circuit II is I21-I22, and I1 is I12. It can also ensure that the power factor controller 1PFC automatically switches the capacitor group on the bus section I according to the power factor of the load on the bus section I, and the power factor controller 2PFC automatically switches the capacitor group on the bus section II according to the power factor of the load on the bus section II.

[0038] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person 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 based on the scope of protection of the claims.

Claims

1. An automatic switching circuit for a low-voltage single-busbar reactive compensation device, comprising busbar section I and busbar section II. A busbar tie circuit connected via a busbar tie breaker 3QA is provided between busbar section I and busbar section II. Corresponding reactive compensation devices are provided on busbar section I and busbar section II, respectively. The primary winding of current transformer 1BC1 is installed on the primary incoming line of busbar section I, and the primary winding of current transformer 2BC1 is installed on the secondary incoming line of busbar section II. Its characteristics are: The primary windings of current transformers 1BC2 and 2BC2 are installed on the bus coupling circuit; The automatic switching circuit includes a measuring circuit I and a measuring circuit II. The measuring circuit I is formed by connecting the secondary windings of the current transformer 1BC1 and the current transformer 1BC2 in parallel and then connecting them in series with the power factor controller 1PFC to form a closed loop. The secondary winding connection end of the current transformer 1BC1 and the connection end of the power factor controller 1PFC are grounded, and the power factor controller 1PFC is electrically connected to the reactive compensation device configured on the bus section I; the measuring circuit II is formed by connecting the secondary windings of the current transformer 2BC1 and the current transformer 2BC2 in parallel and then connecting them in series with the power factor controller 2PFC to form a closed loop. The secondary winding connection end of the current transformer 2BC1 and the connection end of the power factor controller 2PFC are grounded, and the power factor controller 2PFC is electrically connected to the reactive compensation device configured on the bus section II.

2. The automatic switching circuit of the low-voltage single busbar reactive power compensation device according to claim 1 is characterized in that: The primary windings of the current transformers 1BC1 and 2BC1 are simultaneously installed on any one of the three phases A, B, and C, and the primary windings of the current transformers 1BC2 and 2BC2 have opposite polarities.

3. The automatic switching circuit of the low-voltage single-busbar reactive power compensation device according to claim 2 is characterized in that: The primary windings of the current transformer 1BC1 and the current transformer 1BC2 are both installed on the same phase and have opposite polarities.

4. The automatic switching circuit of the low-voltage single busbar reactive power compensation device according to claim 3 is characterized in that: The primary windings of the current transformer 2BC1 and the current transformer 2BC2 are both installed on the same phase and have opposite polarities.

5. The automatic switching circuit of the low-voltage single busbar reactive power compensation device according to claim 4 is characterized in that: The primary windings of the current transformer 1BC1 and the current transformer 1BC2 have the same transformation ratio, and the primary windings of the current transformer 2BC1 and the current transformer 2BC2 have the same transformation ratio.

6. The automatic switching circuit of the low-voltage single busbar reactive power compensation device according to any one of claims 1 to 5, characterized in that: The reactive compensation capacity of the reactive compensation devices configured for the bus section I and the bus section II is determined by the power factors detected by the corresponding power factor controllers 1PFC and 2PFC when the bus sections are operated in sections.

7. The automatic switching circuit of the low-voltage single busbar reactive power compensation device according to any one of claims 1 to 5, characterized in that: The primary windings of the current transformer 1BC2 and the current transformer 2BC2 are installed at the same end of the bus tie circuit breaker 3QA or are connected in series at the front and rear ends of the bus tie circuit breaker 3QA.

8. A method for automatically switching a low-voltage single-busbar reactive power compensation device, characterized in that: The automatic switching circuit of the low-voltage single-busbar reactive compensation device according to any one of claims 1 to 7 includes the following segmented operation modes: A. Two incoming lines operate simultaneously and a single busbar operates in sections: Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is closed, and bus tie breaker 3QA is opened. At this time, the corresponding power factor controllers 1PFC and 2PFC on measurement circuits I and II control the reactive power compensation device according to the current provided by the secondary windings of current transformers 1BC1 and 2BC1, respectively. B. Single-circuit incoming line operation, single busbar unsegmented operation: Circuit breaker 1QA of busbar section I is closed, circuit breaker 2QA of busbar section II is open, and bus tie breaker 3QA is closed. At this time, the vector total current I1 input to power factor controller 1PFC in measurement circuit I is I11-I12. Power factor controller 1PFC controls the reactive power compensation device on busbar section I according to vector total current I1. Simultaneously, power factor controller 2PFC on measurement circuit II controls the reactive power compensation device on busbar section II according to the current provided by the secondary winding of current transformer 2BC2. C. Two-circuit incoming line operation and single busbar non-segmented operation: circuit breaker 2QA of busbar section II is closed, circuit breaker 1QA of busbar section I is disconnected, and bus tie breaker 3QA is closed. At this time, the vector total current I2 input to the power factor controller 2PFC in measurement circuit II is I21-I22. The power factor controller 2PFC controls the reactive power compensation device on busbar section II according to the vector total current I2. At the same time, the power factor controller 1PFC on measurement circuit I controls the reactive power compensation device on busbar section I according to the current provided by the secondary winding of current transformer 1BC2.

9. The automatic switching method of the low-voltage single busbar reactive power compensation device according to claim 8, characterized in that: In the single busbar segmented operation mode with two incoming lines working simultaneously, since the busbar circuit breaker 3QA is disconnected, the secondary winding currents of the current transformers 1BC2 and 2BC2 in the busbar circuit are both zero.

10. The automatic switching method of the low-voltage single busbar reactive compensation device according to claim 8, characterized in that: In the single-circuit incoming line operation and single busbar non-segmented operation mode, the current direction in the bus tie circuit is from busbar section I to busbar section II. Since the primary winding currents of current transformer 1BC2 and current transformer 1BC1 are in opposite directions, the secondary winding current I12 of current transformer 1BC2 in measurement circuit I is negative, so that the vector resultant current I1 in the input power factor controller 1PFC in measurement circuit I is I11-I12. In the two-circuit incoming line operation and single busbar non-segmented operation mode, the current direction in the bus tie circuit is from busbar section II to busbar section I. Since the primary winding currents of current transformer 2BC2 and current transformer 2BC1 are in opposite directions, the secondary winding current I22 of current transformer 2BC2 in measurement circuit II is negative, making the vector resultant current I2 in the input power factor controller 2PFC in measurement circuit II equal to I21-I22.

Images