Intelligent low-voltage switch cabinet

Abstract

The application relates to the technical field of switch cabinets, in particular to an intelligent low-voltage switch cabinet, which comprises a cabinet body, an execution unit, a detection unit and a control unit; the execution unit comprises a circuit breaker trolley for disconnecting the current of a load circuit and a plurality of contactors for switching the load circuit; the detection unit is used for detecting the instantaneous reduced voltage of the load, the current harmonic phase difference of the phase current signal of a main bus, the current harmonic signal proportion and the environment temperature in the cabinet body; the control unit is used for determining the load protection level according to the instantaneous reduced voltage of the load, determining the interval duration of the start of the circuit breaker trolley and the contactor according to the duration of the instantaneous reduced voltage according to the load protection level, adjusting the asynchronous action start mode of the plurality of contactors according to the harmonic phase difference, and adjusting the access proportion of the reactive load according to the similarity of the increasing nodes in time sequence of the harmonic signal proportion and the environment temperature in the cabinet body. The application realizes the improvement of the load stability.

Description

Technical Field

[0001] This invention relates to the field of switchgear technology, and more particularly to an intelligent low-voltage switchgear. Background Technology

[0002] In existing technologies, low-voltage switchgear is equipment in low-voltage power distribution systems, mainly used for power distribution, circuit control, fault protection and monitoring. Among them, molded case circuit breaker trolleys are used to handle short-circuit faults in industrial scenarios; frame circuit breaker trolleys are used to break large currents and support the high load requirements of busbar systems; the cabinet is made of cold-rolled steel plate, aluminum alloy or composite insulation materials, and the anti-corrosion performance is improved by electrostatic powder coating to meet the requirements of harsh environments such as dust and water immersion; and fans are installed on the top or side of the cabinet.

[0003] Chinese Patent Publication No. CN114709716A discloses a low-voltage switchgear, comprising: a cabinet frame; door panels, including a front door panel and a rear door panel, respectively disposed on opposite sides of the cabinet frame; and multiple partitions disposed within the cabinet frame, dividing the cabinet frame into multiple chambers; the multiple chambers include a communication chamber, an instrument chamber, a switch chamber, a cable chamber, a main busbar chamber, and a vertical busbar chamber; the communication chamber, the instrument chamber, the switch chamber, and the cable chamber are disposed on the same side of the cabinet frame. The components are arranged sequentially from top to bottom; the main busbar compartment is located on the side of the communication compartment away from the front door panel, and the vertical busbar compartment is located on the side of the instrument compartment and the switch compartment away from the front door panel; the cable compartment includes a front cable compartment and a rear cable compartment separated from each other, with the front door panel and the rear door panel covering the front cable compartment and the rear cable compartment respectively, and each of the front cable compartment and the rear cable compartment is provided with outgoing terminals; a neutral phase and grounding busbar compartment are also separated between the front cable compartment and the rear cable compartment. Therefore, the low-voltage switchgear suffers from problems such as phase-to-phase short circuits or single-phase-to-ground short circuits caused by severe weather such as strong winds, snow, fallen trees, or external forces such as cranes, excavators touching the lines, or animals touching the lines, which lower the grid voltage; and the large voltage drop caused by the direct starting of large-capacity motors, which temporarily reduces the busbar voltage, thus reducing the operational stability of the switchgear. Summary of the Invention

[0004] To address this, the present invention provides an intelligent low-voltage switchgear to overcome the problems in the prior art where phase-to-phase short circuits or single-phase-to-ground short circuits caused by severe weather such as strong winds, snow, fallen trees, or external forces such as cranes, excavators touching the lines, or animals touching the lines cause a drop in grid voltage, and the direct starting of large-capacity motors causes a large voltage drop, resulting in a temporary decrease in bus voltage and thus reduced operational stability of the switchgear.

[0005] To achieve the above objectives, the present invention provides an intelligent low-voltage switchgear, comprising:

[0006] Cabinet;

[0007] The execution unit, which is located inside the cabinet, includes a circuit breaker trolley for disconnecting the current of the load circuit and several contactors for switching the load circuit.

[0008] The detection unit is connected to the cabinet and the execution unit respectively, and is used to detect the instantaneous voltage drop of the load, the phase difference of the current harmonics of the phase current signal of the main bus, the proportion of the current harmonic signal, and the ambient temperature inside the cabinet.

[0009] The control unit, which is connected to the execution unit and the detection unit respectively, is used to determine the load protection level based on the instantaneous voltage drop of the load, determine the interval between the sequential start of the circuit breaker trolley and the contactor in the inrush current compensation mode according to the duration of the instantaneous voltage drop based on the load protection level, adjust the asynchronous start mode of several contactors according to the harmonic phase difference, and adjust the reactive load access ratio according to the similarity of the increase node of the harmonic signal ratio and the ambient temperature inside the cabinet in the time sequence.

[0010] Furthermore, the detection unit includes:

[0011] A voltage sensor is used to detect a momentary drop in voltage at the load.

[0012] A current transformer is installed on the main bus of the load to detect the harmonic phase difference and the proportion of the harmonic signal of the phase current signal of the main bus.

[0013] A temperature sensor is installed on the inner wall of the cabinet to detect the ambient temperature of the cabinet.

[0014] Furthermore, the control unit is connected to the voltage sensor to obtain the instantaneous voltage drop. If the instantaneous voltage drop is greater than or equal to a preset first voltage and less than or equal to a preset second voltage, the load protection level is determined to be Level 1 protection.

[0015] If the instantaneous voltage drop is greater than a preset second voltage and less than or equal to a preset third voltage, then the load protection level is determined to be level two protection.

[0016] If the instantaneous voltage drop is greater than the preset third voltage, then the load protection level is determined to be level three protection.

[0017] Furthermore, the instantaneous voltage drop is the difference between the instantaneous voltage detected by the voltage sensor and the instantaneous voltage detected at the previous moment.

[0018] Furthermore, the control unit is used to determine the inrush current compensation method under the condition that the load protection level is level one protection, and to obtain the duration of the instantaneous voltage drop. If the duration is greater than or equal to a preset duration, the interval between the sequential start of the circuit breaker trolley and the contactor is increased.

[0019] Furthermore, the inrush current compensation method involves controlling the contactor to divert current after the circuit breaker trolley is engaged once, and then engaging the circuit breaker trolley a second time after the specified interval.

[0020] Furthermore, the control unit is used to acquire the harmonic phase difference under the condition that the load protection level is secondary protection, and to control the asynchronous operation start time of several of the contactors to start at the moment of harmonic phase difference before the current crosses zero.

[0021] Furthermore, the control unit is used to acquire the proportion of the harmonic signal and the ambient temperature inside the cabinet, respectively, under the condition that the load protection level is level three protection, and to calculate the similarity of the incremental nodes.

[0022] If the similarity of the incremental nodes is greater than or equal to the preset similarity, then the access ratio of the reactive load is increased.

[0023] Furthermore, the reactive load access ratio is the ratio of the reactive load power to the total power of the load circuit.

[0024] Furthermore, the harmonic signal proportion is the ratio of the effective value of the harmonic current component to the effective value of the fundamental current.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: the device of the present invention, by setting up a cabinet, execution unit, detection unit, and control unit, can cope with voltage fluctuations caused by severe weather or external damage, as well as voltage dips caused by the start-up of large-capacity motors, ensuring the operational stability of the switchgear under complex operating conditions. It uses voltage sensors to monitor instantaneous voltage changes of the load in real time, combines current transformers to obtain harmonic current information of the main busbar, and uses temperature sensors to sense the internal ambient temperature of the cabinet for operational status perception. The control unit determines the voltage dip level of the load and adjusts the starting sequence of the circuit breaker trolley and contactor to change the voltage dip at the load end from a complete drop to a shallow drop, thereby maintaining the voltage level and avoiding voltage dip protection shutdown. It adjusts the asynchronous operation mode of the contactor to generate opposite-phase harmonic current to cancel the original harmonics, thus allowing time for load voltage recovery and preventing load shutdown due to continuous low voltage. Finally, it adjusts the reactive load connection ratio to effectively suppress the impact of voltage fluctuations on the stable operation of the switchgear and improve the operational stability of the load.

[0026] Furthermore, the device described in this invention achieves graded response to voltage sag events by setting a three-level load protection mechanism. When the instantaneous voltage drops in different threshold ranges, the control unit determines the load protection level according to preset rules and adopts corresponding inrush current compensation methods, contactor asynchronous action strategies, or reactive load adjustment methods. Through graded control, frequent operation is avoided under different voltage disturbance intensities, thereby improving the continuous power supply and operational stability of critical equipment.

[0027] Furthermore, the device described in this invention introduces an inrush current compensation method. Under the first-level protection level, it dynamically adjusts the starting interval between the circuit breaker trolley and the contactor according to the duration of the voltage dip. It adopts a step-by-step control method of circuit breaker trolley primary engagement, contactor delayed shunting, and circuit breaker trolley secondary engagement. It utilizes the inductive inrush current generated at the moment of circuit breaker trolley closure to inject it back into the system, instantly raising the voltage on the busbar that is dropping, reducing the inrush current at the moment of closing, and cutting off the accompanying fault current path through the contactor. The contactor's secondary engagement utilizes the residual magnetism of the iron core to achieve rapid and low-impact power restoration, preventing secondary voltage drop and equipment damage caused by sudden current surges, thereby improving the safety and reliability of the system.

[0028] Furthermore, the device of the present invention adjusts the asynchronous start time of the contactor. Under the secondary protection level, based on the phase difference of the current harmonics, it controls the contactor to start before the current crosses zero, avoiding electromagnetic interference and mechanical stress impact caused by non-zero current switching due to harmonics. Through mechanical action, an anti-phase harmonic current is injected into the circuit to cancel the original harmonics, thereby reducing equipment losses, reducing the disturbance to the system voltage during switching, and improving the stability of load operation.

[0029] Furthermore, the device described in this invention adjusts the reactive load connection ratio by calculating the similarity between the proportion of harmonic signals and the increasing nodes of the internal temperature change of the cabinet. Under the third-level protection level, when the similarity between the harmonic content and the cabinet temperature change trend is large, it indicates that harmonic loss is the main cause of abnormal temperature rise in the cabinet. At this time, increasing the connection ratio of reactive load improves the voltage support capability of the system through reactive compensation, utilizes the inductive or capacitive characteristics of reactive load to offset the reactive component in the harmonic current, reduces the transmission loss of harmonics in the main bus, reduces Joule heat generated by the harmonic current flowing through the conductor, and delays the further rise of the internal temperature of the cabinet. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the intelligent low-voltage switchgear according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the intelligent low-voltage switchgear according to another embodiment of the present invention;

[0032] Figure 3 This is an overall structural block diagram of the intelligent low-voltage switchgear according to an embodiment of the present invention;

[0033] Figure 4 This is a block diagram of the detection unit structure of an intelligent low-voltage switchgear according to an embodiment of the present invention;

[0034] The reference numerals in the attached diagrams are as follows: 1-shell, 2-valve bracket, 3-circuit breaker trolley, 4-contact box, 5-busbar bushing, 6-instrument compartment, 7-pressure relief valve, 8-current transformer, 9-grounding switch. Detailed Implementation

[0035] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0036] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0037] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0038] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] Please see Figure 1 , Figure 2 , Figure 3 as well as Figure 4 The figures shown are, respectively, a schematic diagram of the overall structure of the intelligent low-voltage switchgear according to an embodiment of the present invention, a schematic diagram of the structure from another angle, a block diagram of the overall structure, and a block diagram of the detection unit structure. The present invention provides an intelligent low-voltage switchgear, comprising:

[0040] Cabinet;

[0041] The execution unit, which is located inside the cabinet, includes a circuit breaker trolley 3 for disconnecting the load current and several contactors for shunting the load circuit.

[0042] The detection unit is connected to the cabinet and the execution unit respectively, and is used to detect the instantaneous voltage drop of the load, the phase difference of the current harmonics of the phase current signal of the main bus, the proportion of the current harmonic signal, and the ambient temperature inside the cabinet.

[0043] The control unit, which is connected to the execution unit and the detection unit respectively, is used to determine the load protection level based on the instantaneous voltage drop of the load, determine the interval between the sequential start of the circuit breaker trolley 3 and the contactor in the inrush current compensation mode according to the duration of the instantaneous voltage drop based on the load protection level, adjust the asynchronous start mode of several contactors according to the harmonic phase difference, and adjust the reactive load access ratio according to the similarity of the increase node of the harmonic signal ratio and the ambient temperature inside the cabinet in the time sequence.

[0044] Specifically, such as Figure 1 A schematic diagram of the overall structure of the intelligent low-voltage switchgear according to an embodiment of the present invention and Figure 2 Another structural schematic diagram of the intelligent low-voltage switchgear according to an embodiment of the present invention is shown. The cabinet includes:

[0045] Casing 1;

[0046] Pressure relief valve 7 is disposed on the upper surface of housing 1 to release gas inside housing 1;

[0047] Contact box 4, which is connected to circuit breaker trolley 3, is used to insulate the contacts in circuit breaker trolley 3;

[0048] The valve bracket 2 is connected to the contact box 4 and is used to open and close the contact box 4;

[0049] Busbar bushing, which is connected to contact box 4, is used to fix the busbar of the load;

[0050] Instrument compartment 6, which is connected to housing 1, is used to install the display screens of voltage sensor, current transformer 8, and temperature sensor;

[0051] Grounding switch 9 is connected to housing 1 and is used to release the surface charge of housing 1.

[0052] Specifically, the control unit is a microprocessor or a PLC controller.

[0053] Specifically, the phase difference of the harmonics is obtained by analyzing the amplitude of the third harmonic through Fourier transform of the load bus.

[0054] In implementation, the device of this invention, by setting up a cabinet, execution unit, detection unit, and control unit, addresses voltage fluctuations caused by severe weather or external damage, as well as voltage dips caused by the start-up of large-capacity motors, ensuring the operational stability of the switchgear under complex operating conditions. It uses voltage sensors to monitor instantaneous voltage changes in the load in real time, combines current transformer 8 to obtain harmonic current information of the main busbar, and uses temperature sensors to sense the internal ambient temperature of the cabinet for operational status perception. The control unit determines the voltage dip level of the load and adjusts the starting sequence of the circuit breaker trolley 3 and the contactor to change the voltage dip at the load end from a complete drop to a shallow drop, maintaining the voltage level and avoiding voltage dip protection shutdown. It adjusts the asynchronous operation mode of the contactor to generate opposite-phase harmonic current to cancel the original harmonics, thus allowing time for load voltage recovery and preventing load shutdown due to continuous low voltage. Finally, it adjusts the reactive load connection ratio to effectively suppress the impact of voltage fluctuations on the stable operation of the switchgear and improve the operational stability of the load.

[0055] Specifically, the detection unit includes:

[0056] A voltage sensor is used to detect a momentary drop in voltage at the load.

[0057] A current transformer 8 is installed on the main bus of the load to detect the harmonic phase difference and the proportion of the harmonic signal of the phase current signal of the main bus.

[0058] A temperature sensor is installed on the inner wall of the cabinet to detect the ambient temperature of the cabinet.

[0059] Specifically, the control unit is connected to the voltage sensor to obtain the instantaneous voltage drop. If the instantaneous voltage drop is greater than or equal to a preset first voltage and less than or equal to a preset second voltage, the load protection level is determined to be Level 1 protection.

[0060] If the instantaneous voltage drop is greater than a preset second voltage and less than or equal to a preset third voltage, then the load protection level is determined to be level two protection.

[0061] If the instantaneous voltage drop is greater than the preset third voltage, then the load protection level is determined to be level three protection.

[0062] Specifically, the instantaneous voltage drop is the difference between the instantaneous voltage detected by the voltage sensor and the instantaneous voltage detected at the previous moment.

[0063] Specifically, the voltage sensor detection frequency interval is 5ms.

[0064] Specifically, under the conditions of a low-voltage switchgear for a single-phase switching power supply and a grid rated voltage of 220V, the general range of the preset first voltage is [20V, 45V], the general range of the preset second voltage is [50V, 75V], the general range of the preset third voltage is [80V, 115V], the preferred embodiment of the preset first voltage is 22V, the preferred embodiment of the preset second voltage is 55V, and the preferred embodiment of the preset third voltage is 110V.

[0065] Those skilled in the art will understand that the range of preset first voltage, preset second voltage, and preset third voltage provided in this embodiment, as well as the preferred embodiment, are the values ​​that best address the technical problem solved by the technical solution of this invention under the conditions of a low-voltage switchgear for a single-phase switching power supply and a grid rated voltage of 220V. In actual applications or experiments, those skilled in the art can make adaptive adjustments to the preset first voltage, preset second voltage, and preset third voltage according to the actual application environment and application scenario.

[0066] In practice, the device of the present invention achieves graded response to voltage sag events by setting a three-level load protection mechanism. When the instantaneous voltage drops in different threshold ranges, the control unit determines the load protection level according to preset rules and takes corresponding inrush current compensation methods, contactor asynchronous action strategies or reactive load adjustment measures. Through graded control, frequent operation is avoided under different voltage disturbance intensities, thereby improving the continuous power supply and operational stability of key equipment.

[0067] Specifically, the control unit is used to determine the inrush current compensation method under the condition that the load protection level is level one protection, and to obtain the duration of the instantaneous voltage drop. If the duration is greater than or equal to a preset duration, the interval between the sequential start of the circuit breaker trolley and the contactor is increased.

[0068] Specifically, the inrush current compensation method involves controlling the contactor to divert current after the circuit breaker trolley is engaged once, and then engaging the circuit breaker trolley a second time after the specified interval.

[0069] Specifically, under the conditions of a low-voltage switchgear for a single-phase switching power supply and a grid rated voltage of 220V, the general range of the preset duration is [5ms, 15ms], and the preferred embodiment of the preset duration is 10ms.

[0070] Those skilled in the art will understand that the range of preset durations and preferred embodiments provided in this embodiment are the values ​​that best address the technical problem solved by the present invention under the conditions of a low-voltage switchgear for a single-phase switching power supply and a grid rated voltage of 220V. In actual applications or experiments, those skilled in the art can make adaptive adjustments to the preset durations according to the actual application environment and application scenario.

[0071] In practice, the maximum interval between the sequential activation of the circuit breaker trolley 3 and the contactor is 5ms. For every 1ms increase in the difference between the duration and the preset duration, the interval between the sequential activation of the circuit breaker trolley 3 and the contactor increases by 0.2ms. The initial value of the interval is 3ms. For example, if the difference between the duration and the preset duration is 13ms, the interval is determined to be 3ms + 0.2 × 3 = 3.6ms.

[0072] In implementation, the device of the present invention introduces an inrush current compensation method. Under the first-level protection level, it dynamically adjusts the starting interval between the circuit breaker trolley 3 and the contactor according to the duration of the voltage dip. It adopts a step-by-step control method of the circuit breaker trolley 3 first closing, the contactor delaying the current shunting, and the circuit breaker trolley 3 second closing. It uses the inductive inrush current generated at the moment of the circuit breaker trolley 3 closing to inject it back into the system, instantly raising the voltage on the bus that is dropping, reducing the inrush current at the moment of closing, and cutting off the accompanying fault current path through the contactor. The contactor performs a second closing to achieve fast and low-impact power restoration by utilizing the residual magnetism of the iron core, preventing secondary voltage drop and equipment damage caused by sudden current surges, thereby improving the safety and reliability of the system.

[0073] Specifically, the control unit is used to acquire the harmonic phase difference under the condition that the load protection level is level two protection, and to control the asynchronous operation start time of several of the contactors to start at the moment of harmonic phase difference before the current crosses zero.

[0074] Specifically, the frequency interval of asynchronous operation of several contactors is an integer multiple of half a cycle of the current.

[0075] In practice, the device of the present invention adjusts the asynchronous start time of the contactor. Under the secondary protection level, based on the phase difference of the current harmonics, it controls the contactor to start before the current crosses zero, avoiding electromagnetic interference and mechanical stress impact caused by non-zero current switching due to harmonics. Through mechanical action, an anti-phase harmonic current is injected into the circuit to cancel the original harmonics, thereby reducing equipment losses, reducing the disturbance to the system voltage during switching, and improving the stability of load operation.

[0076] Specifically, the control unit is used to acquire the proportion of harmonic signals and the ambient temperature inside the cabinet, respectively, under the condition that the load protection level is level three, and to calculate the similarity of the incremental nodes.

[0077] If the similarity of the incremental nodes is greater than or equal to the preset similarity, then the access ratio of the reactive load is increased.

[0078] Specifically, the proportion of reactive loads connected is adjusted by a reactive power compensation device. The reactive load is one or more sets of power capacitor banks connected in parallel on the bus. Each power capacitor bank is connected to a switching switch, which controls the connection or disconnection of the power capacitor bank to the bus.

[0079] Specifically, the reactive load access ratio is the ratio of the power of the reactive load to the total power of the load circuit.

[0080] Specifically, the harmonic signal proportion is the ratio of the effective value of the harmonic current component to the effective value of the fundamental current.

[0081] Specifically, the calculation process for incremental node similarity involves continuously collecting data from several nodes at one-minute intervals to obtain the harmonic proportion sequence H=[H1,H2,...,H10] and the cabinet temperature sequence T=[T1,T2,...,T10]. The difference between adjacent data in each sequence is calculated to obtain the harmonic variation trend: ΔH=[H2-H1,H3-H2,...,H10-H9] and the cabinet temperature variation trend: ΔT=[T2-T1,T3-T2,...,T10-T9]. Cosine similarity is then used to calculate the directional consistency of the two trends, i.e., the similarity.

[0082] Specifically, under the conditions of a low-voltage switch cabinet for a single-phase switching power supply and a grid rated voltage of 220V, the general range of the preset similarity value is [0.65, 0.72], and the preferred embodiment of the preset similarity value is 0.7.

[0083] Those skilled in the art will understand that the range of preset similarity and the preferred embodiment provided in this embodiment are the values ​​that best represent the technical problem solved by the present invention under the conditions of a low-voltage switchgear for a single-phase switching power supply and a grid rated voltage of 220V. In actual applications or experiments, those skilled in the art can make adaptive adjustments to the preset similarity according to the actual application environment and application scenario.

[0084] In practice, for example, when the detection unit acquires the harmonic signal proportion sequence H=[0.12%, 0.15%, 0.18%, 0.21%, 0.25%, 0.28%, 0.32%, 0.35%, 0.38%, 0.41%] and the cabinet temperature sequence T=[35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃] at a period of one minute, we obtain ΔH=[0.03%, 0.03%, 0.03%, 0.04%, 0.03%, 0.04%, 0.03%, 0.03%, 0.03%]. ΔT=[1℃,1℃,1℃,1℃,1℃,1℃,1℃,1℃,1℃], and the cosine similarity calculation shows that the directional consistency between the two is approximately 0.98, which is greater than the preset similarity. The control unit determines that the proportion of harmonic signals is highly correlated with the increasing trend of cabinet temperature, indicating that the increase in harmonic current causes the cabinet to continuously heat up due to the increase in harmonic losses. The control unit sends a command to the reactive power compensation device to increase the proportion of reactive load access, controls the switching switch to close, and puts in two sets of parallel power capacitor banks, each with a capacity of 50kVar, increasing the proportion of reactive load access from the initial 15% to 25%.

[0085] In practice, the device described in this invention calculates the similarity between the proportion of harmonic signals and the increasing nodes of the internal temperature change of the cabinet, and then adjusts the proportion of reactive load connection. Under the third protection level, when the similarity between the harmonic content and the cabinet temperature change trend is large, it indicates that harmonic loss is the main cause of abnormal temperature rise in the cabinet. At this time, the proportion of reactive load connection is increased, the voltage support capability of the system is improved through reactive compensation, the inductive or capacitive characteristics of the reactive load are used to offset the reactive component in the harmonic current, reduce the transmission loss of harmonics in the main bus, reduce the Joule heat generated by the harmonic current flowing through the conductor, and delay the further rise of the internal temperature of the cabinet.

[0086] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. An intelligent low-voltage switchgear, characterized in that, include: Cabinet; The execution unit, which is located inside the cabinet, includes a circuit breaker trolley for disconnecting the current of the load circuit and several contactors for switching the load circuit. The detection unit is connected to the cabinet and the execution unit respectively, and is used to detect the instantaneous voltage drop of the load, the phase difference of the current harmonics of the phase current signal of the main bus, the proportion of the current harmonic signal, and the ambient temperature inside the cabinet. The control unit, which is connected to the execution unit and the detection unit respectively, is used to determine the load protection level based on the instantaneous voltage drop of the load, determine the interval between the sequential start of the circuit breaker trolley and the contactor in the inrush current compensation mode according to the duration of the instantaneous voltage drop based on the load protection level, adjust the asynchronous start mode of several contactors according to the harmonic phase difference, and adjust the reactive load access ratio according to the similarity of the increase node of the harmonic signal ratio and the ambient temperature inside the cabinet in the time sequence. The detection unit includes: A voltage sensor is used to detect a momentary drop in voltage at the load. A current transformer is installed on the main bus of the load to detect the harmonic phase difference and the proportion of the harmonic signal of the phase current signal of the main bus. A temperature sensor is installed on the inner wall of the cabinet to detect the ambient temperature of the cabinet. The control unit is connected to the voltage sensor to obtain the instantaneous voltage drop. If the instantaneous voltage drop is greater than or equal to a preset first voltage and less than or equal to a preset second voltage, the load protection level is determined to be Level 1 protection. If the instantaneous voltage drop is greater than a preset second voltage and less than or equal to a preset third voltage, then the load protection level is determined to be level two protection. If the instantaneous voltage drop is greater than the preset third voltage, then the load protection level is determined to be level three protection. The control unit is used to determine the inrush current compensation method under the condition that the load protection level is level one protection, and to obtain the duration of the instantaneous voltage drop. If the duration is greater than or equal to a preset duration, the interval between the sequential start of the circuit breaker trolley and the contactor is increased.

2. The intelligent low-voltage switchgear according to claim 1, characterized in that, The instantaneous voltage drop is the difference between the instantaneous voltage detected by the voltage sensor and the instantaneous voltage detected at the previous moment.

3. The intelligent low-voltage switchgear according to claim 1, characterized in that, The inrush current compensation method is that after the circuit breaker trolley is engaged once, the contactor is controlled to divert the current after the specified interval, and the circuit breaker trolley is engaged a second time.

4. The intelligent low-voltage switchgear according to claim 1, characterized in that, The control unit is used to acquire the harmonic phase difference under the condition that the load protection level is level two protection, and to control the asynchronous operation start time of several contactors to start at the moment of harmonic phase difference before the current crosses zero.

5. The intelligent low-voltage switchgear according to claim 1, characterized in that, The control unit is used to acquire the proportion of harmonic signals and the ambient temperature inside the cabinet, respectively, under the condition that the load protection level is level three, and to calculate the similarity of the incremental nodes. If the similarity of the incremental nodes is greater than or equal to the preset similarity, then the access ratio of the reactive load is increased.

6. The intelligent low-voltage switchgear according to claim 5, characterized in that, The reactive load access ratio is the ratio of the power of the reactive load to the total power of the load circuit.

7. The intelligent low-voltage switchgear according to claim 6, characterized in that, The harmonic signal proportion is the ratio of the effective value of the harmonic current component to the effective value of the fundamental current.

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