Dynamic detection device and method for contact resistance of low-voltage switch cabinet

Abstract

The invention provides a low-voltage switch cabinet contact resistance dynamic detection device and method, and the device comprises an opening and closing signal synchronization module, a transient constant current source module, a high-precision sampling circuit, and a data processing and early warning unit. According to the method, a switch-on and switch-off signal synchronization module, a transient constant current source and a high-precision sampling circuit are integrated in a switch cabinet, constant direct current is applied to a power-off gap after a contact is switched off and before the contact is switched on, contact resistance is measured, trend analysis is carried out, and the state of the contact is judged. According to the invention, the resistance measurement is completed by using the transient power-off gap of the switch cabinet opening and closing operation, and the non-power-off, high-precision and risk-free contact performance monitoring is realized.

Description

Technical Field

[0001] This invention relates to low-voltage electrical equipment testing technology, specifically to a dynamic testing device and method for the contact resistance of low-voltage switchgear contacts, applicable to contact performance monitoring of 380V / 660V low-voltage switchgear (such as MCC cabinets and PC cabinets) under uninterrupted power supply conditions. Background Technology

[0002] Low-voltage switchgear is the core equipment of plant power systems. The contact resistance of its internal contacts (such as circuit breaker contacts and drawer-type plug-in contacts) directly affects conductivity: excessive resistance can lead to overheating of the contacts and even cause faults such as arc erosion and switch failure. Current technologies for detecting contact resistance in electrical systems mainly include power-off measurement methods, online indirect measurement methods, and live-line direct measurement methods. I. Power-off Measurement Method: Using a double-arm bridge or a high-current loop resistance tester, a constant DC current is applied to the contacts while the equipment is powered off. The voltage drop is then measured to calculate the contact resistance. This method, employing a four-terminal connection, effectively eliminates the influence of contact resistance on the test leads and is a relatively accurate traditional testing solution. However, its limitations are: the switchgear load must be disconnected, and the contact resistance must be measured using a double-arm bridge. Although highly accurate, it requires shutdown (each test takes 2-4 hours), affecting the continuous operation of the power plant. The specific defects are as follows: Defect 1: Severe downtime losses; a single test takes 2-4 hours, causing production interruptions in continuous operation scenarios such as power plants. Taking a 300MW unit as an example, the loss is approximately 125,000 yuan per hour, and the direct economic loss from a single test reaches 250,000-500,000 yuan. The reason is that the double-arm bridge requires disconnecting the current loop of the circuit under test, which necessitates a power outage to avoid safety risks and electromagnetic interference.

[0003] Defect 2: It cannot capture dynamic degradation trends; it can only obtain static resistance values ​​and cannot analyze the performance changes of the contacts during frequent opening and closing processes (such as spring fatigue and accelerated oxidation). The reason is that the detection cycle is long (usually quarterly or annually), which cannot cover the real-time fluctuations in the contact condition.

[0004] Defect 3: Risk of mechanical damage; frequent disassembly and reassembly of test terminals may cause wear on the contact plating, accelerating the increase in contact resistance. This is because the test terminals need to be directly pressed against the contacts, and the long-term accumulation of mechanical stress will damage the protective oxide layer on the surface.

[0005] II. Online Indirect Detection Method: This method uses an infrared thermal imager or a single-point infrared thermometer to monitor the surface temperature of the contact points, thereby indirectly inferring changes in contact resistance. This technology can be performed during equipment operation; however, its measurement accuracy is significantly affected by factors such as the emissivity of the contact material, environmental heat dissipation conditions, and cabinet obstruction. Its limitations are: while monitoring the contact surface temperature via infrared thermography to indirectly determine the contact status, the error rate is as high as 30% due to the influence of ambient temperature and cabinet obstruction, and it cannot quantify the resistance value. The specific defects are as follows: Defect 1: Low quantification accuracy; the relationship between temperature and contact resistance is affected by factors such as contact material and environmental heat dissipation conditions, with an error rate as high as 30%. For example, the temperature rise corresponding to a 50μΩ contact resistance may fluctuate between 10-30℃ depending on the contact material, making it difficult to determine accurately. This is because infrared thermometry relies on the emissivity of the object (the emissivity of metal contacts is typically 0.1-0.3) and environmental temperature compensation, while dust and oil in the power plant environment further reduce measurement accuracy.

[0006] Defect 2: Lack of early warning; an alarm is only triggered when the contact temperature rises significantly (e.g., exceeding the ambient temperature by 20°C). At this point, the contact may already be severely oxidized or the spring may be loose, with less than 20% of the original design life remaining. This is because temperature changes lag behind resistance degradation. For example, when the resistance rises by 50% in the early stages of contact oxidation, the temperature rise may only be 5°C, which is below the infrared temperature measurement threshold.

[0007] Defect 3: Space obstruction issue; the internal structure of the switchgear is complex, and the contacts are often obstructed by busbars and insulating partitions, preventing infrared detectors from directly observing critical parts. This is because the power plant switchgear design prioritizes insulation and mechanical strength, and does not reserve a dedicated channel for infrared detection.

[0008] 3. Direct Measurement with Live Equipment: This method involves directly measuring the contact resistance using a dedicated test circuit while the equipment is energized. However, its limitations are: the measurement circuit must be connected under high voltage conditions, posing a risk of electric shock, and strong electric field interference can cause measurement data distortion (error > 50 μΩ).

[0009] The specific defects are as follows: Defect 1: Extremely high safety risk; strong electric field interference may cause the test circuit to malfunction, triggering arc discharge (e.g., in a 480V system, an additional 0.1Ω resistor can generate a fault current of 4.8kA). The reason is that during live operation, the contact between the test lead and the contactor may generate an electric spark, and the risk is greatly increased, especially in humid or dusty environments.

[0010] Defect 2: Poor data reliability; grid harmonics (such as the 3rd and 5th harmonics) will be superimposed on the DC measurement signal, causing the resistance calculation error to exceed 50μΩ. The reason is that the DC constant current source has weak anti-interference capability and no phase-locked loop or notch filter measures are taken.

[0011] Defect 3: Poor equipment compatibility; structural modifications to the switchgear are required (such as adding test terminals and embedded circuits), resulting in insufficient adaptability. This is because the contact structures of switchgear from different manufacturers vary significantly (e.g., the contact spacing between Schneider MVS and ABBTmax differs by 20%), making it difficult for general-purpose test modules to achieve compatibility.

[0012] Therefore, there is an urgent need for a dynamic detection device and method that can directly quantify and measure contact resistance without power interruption and under safe and reliable conditions. Summary of the Invention

[0013] This solution addresses three major challenges in existing contact resistance detection methods: First, power outage detection disrupts production, while live detection is inaccurate and dangerous; second, traditional methods only trigger an alarm when the contact temperature rises significantly (at which point only 20% of the contact's lifespan may remain), failing to detect issues like spring aging and oxidation in advance; third, different manufacturers' switchgear structures vary, making testing equipment incompatible, and live operation can easily cause sparks. This new solution measures resistance by capturing the instantaneous gap between switch opening and closing, providing accurate measurements without power outages. It can also continuously record data 100 times, detecting anomalies 3-6 months in advance. Furthermore, installation requires no equipment modifications and is compatible with most switchgear.

[0014] To address the aforementioned issues, this invention discloses a dynamic detection method for contact resistance in low-voltage switchgear. This method utilizes the brief power-off gap during the switching operation of the switchgear to complete the resistance measurement, achieving contact performance monitoring without power interruption, with high precision and without risk.

[0015] The specific plan is as follows: A dynamic detection device for the contact resistance of low-voltage switchgear contacts includes a switching signal synchronization module, a transient constant current source module, a high-precision sampling circuit, and a data processing and early warning unit. The switching signal synchronization module is used to capture the mechanical action signals of the start of switching and the preparation of switching in real time, thereby defining the time window of the power-off gap. The transient constant current source module is controlled by the switching signal synchronization module and is activated only during the power-off gap, applying a constant DC current excitation to the switchgear contacts under test. The high-precision sampling circuit is used to accurately capture the resistance measurement value within the synchronization time of the excitation. The data processing and early warning unit receives data from the high-precision sampling circuit and, in conjunction with the known constant current value, calculates the single value, average value, and fluctuation amplitude of the contact resistance in real time, and performs early warning judgment.

[0016] Furthermore, the circuit breaker opening and closing signal synchronization module includes a limit switch and a photoelectric sensor, used to capture the mechanical action signals of opening and closing preparation in real time, and output a 12V DC trigger signal with a response time ≤10ms. The limit switch is installed at the linkage of the circuit breaker operating mechanism, and the time window is from 50ms after opening to 50ms before closing, with an effective measurement duration of 300-800ms. This is the first time that the mechanical action sequence of the circuit breaker has been transformed into a quantifiable detection time window, solving the problem of synchronizing the detection sequence with the mechanical action of the switch, and ensuring that the measurement is only performed within the safe power-off window.

[0017] Furthermore, the transient constant current source module adopts a DC / AC conversion circuit, with the switchgear auxiliary power supply as input and a constant DC current output. The switchgear auxiliary power supply is 220VAC, the constant DC current is 10A±0.5%, and the ripple coefficient is ≤0.1%. Its start-up response time is ≤20ms, and its shutdown delay is ≤10ms. Hardware-level timing control avoids the risks of live measurement, ensures safe isolation between the detection circuit and the main circuit, and achieves a safe control logic that ensures precise power supply during power outages and complete exit before power-on.

[0018] Furthermore, the high-precision sampling circuit includes a 0.1-level shunt and a 24-bit AD converter, with a measurement range of 0-200μΩ and a resolution of 0.1μΩ; its sampling point is set at the connection end between the moving contact and the stationary contact of the circuit breaker.

[0019] Furthermore, the sampling resistance of the 0.1-level shunt is 10μΩ, and the temperature drift is ≤5ppm / ℃; the sampling rate of the AD converter is 1kHz; the sampling point is connected through a dedicated test terminal with a contact resistance ≤5μΩ, avoiding the introduction of additional errors and breaking through the accuracy bottleneck of traditional detection.

[0020] Furthermore, the data processing and early warning unit uses an STM32 microcontroller to store the resistance measurement values ​​from 100 consecutive opening and closing operations, and calculates the single resistance value R and the average value R of the 100 measurements. avg And the fluctuation range ΔR; the specific calculation formula is as follows: ΔR=(R max -R min ) / R avg ×100% When R > 80μΩ or ΔR > 10%, an early warning signal is output through the RS485 interface, triggering the cabinet indicator light to flash and the background alarm to realize the trend judgment of contact deterioration. This can detect abnormalities 3-6 months earlier than traditional single-point measurement and realize a multi-dimensional contact status evaluation system, reducing the risk of misjudgment based on a single parameter.

[0021] Furthermore, the dynamic detection device has external dimensions of 200mm × 150mm × 80mm (length × width × height), uses an aluminum alloy shell (protection rating IP54), and has an antistatic coating (resistivity 10 ohms) on the surface. 6 The sensor (Ω・cm) is fixed to the inner wall of the switch cabinet with screws (≥10cm from the contacts, avoiding heat-generating components). Technical parameters are as follows: Measurement range: 0-200μΩ; Resolution: 0.1μΩ; Measurement error: ±2μΩ (25℃, humidity ≤60%); Detection cycle: Automatically triggered with opening and closing operations (minimum interval 10s); Warning threshold: R>80μΩ or ΔR>10%; Operating temperature: -20℃~70℃; Power consumption: Standby ≤5W, measurement ≤20W; Communication protocol: Modbus-RTU (9600bps, 8N1).

[0022] Furthermore, the hardware components of the dynamic detection device include a limit switch, a photoelectric sensor, a signal processing board, and a main chip. The limit switch is a WLCA12-2N type limit switch, installed next to the rotating shaft of the circuit breaker operating mechanism linkage (5mm from the end of the linkage). When the circuit breaker trips, the linkage swings, triggering the normally closed contact of the limit switch to open, outputting a 12V DC trigger signal (rise time ≤5ms). The photoelectric sensor is an FS-N18N through-beam sensor, with the transmitting end fixed to the closing coil housing and the receiving end aligned with the coil core. When the closing coil is excited... When the magnet is applied, the iron core displacement blocks the light path, outputting a 12V DC shutdown signal (response time ≤ 8ms); the signal processing board is an integrated CD40106 trigger, which performs de-jitter filtering on the switch / sensor signal and outputs a stable 12V TTL level signal (pulse width jitter ≤ 2ms); the main chip adopts a TILM5008 DC / DC controller, with an input of 220VAC (converted to 36VDC through a switching power supply) and an output of 10A±0.5% constant DC current (ripple voltage ≤ 36mV under rated load, ripple coefficient ≤ 0.1%).

[0023] A dynamic detection method for contact resistance of contacts in low-voltage switchgear integrates a switching signal synchronization module, a transient constant current source, and a high-precision sampling circuit within the switchgear. A constant DC current is applied during the power-off gap between contact opening and closing, and the contact resistance is measured and trend analysis is performed to determine the contact state. The method includes the following steps: S1. Initialization: After the device is powered on, it self-checks the output accuracy of the constant current source and the zero-point drift of the sampling circuit. After confirming that it is normal, it enters the standby state. S2, Signal Trigger: When the switchgear performs a tripping operation, the synchronization module detects the "tripping start" signal and sends a "measurement allow" command after a 50ms delay; S3. Resistance Measurement: First, the constant current source is started, and a 10A DC current is applied to the contact. Then, the sampling circuit continuously collects 50 data points (sampling interval 10ms), and the average value is taken as the contact resistance value R for this opening and closing. S4. Data storage: The microcontroller stores R and updates the rolling dataset of 100 measurements; S5. Status determination: ΔR is calculated after each measurement. If the warning conditions are met, an alarm is triggered. S6. End Reset: 10ms before the synchronization module detects the "Close Preparation" signal, it shuts off the constant current source and the device returns to standby mode, without affecting the normal closing of the switchgear.

[0024] Furthermore, the installation requirements are as follows: the test terminals must be directly connected to the conductive parts of the contacts, specifically using copper lugs for crimping, with a contact area ≥10mm²; the constant current source output line cross-sectional area ≥2.5mm², to avoid line loss affecting measurement accuracy, ensure low additional resistance and mechanical reliability, and be compatible with over 90% of mainstream switchgear models without requiring modification of the original electrical structure; the synchronous module limit switch and the circuit breaker operating mechanism are mechanically linked to ensure no delay in opening and closing signals.

[0025] The beneficial effects of this invention are as follows: Through innovative timing control and dynamic monitoring technologies, online detection of contact resistance is achieved: First, transient measurement is performed during the power-off gap of switchgear opening and closing operations, completely avoiding production interruptions caused by traditional power outage detection; Second, a 10A constant current source combined with a 24-bit AD sampling circuit achieves high-precision measurement with a resolution of 0.1μΩ, reducing the error by 90% compared to infrared thermometry. By analyzing the fluctuations of hundreds of consecutive opening and closing data (ΔR > 10% triggers an early warning), contact degradation trends can be detected 3-6 months in advance, reducing the failure rate; In addition, the minimally invasive copper lug crimping design (contact area ≥ 10mm²) requires no modification to the cabinet structure, is engineering-compatible with mainstream switchgear models such as Schneider MVS and ABB Tmax, and has short installation time; Finally, the detection process applies current only during the power-off gap, and the circuit exits 10ms before closing, fundamentally eliminating the risk of electric arc during live operation and achieving inherently safe monitoring in industrial sites. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the device of the present invention.

[0027] Figure 2 This is a flowchart of the method of the present invention.

[0028] List of reference numerals in the attached diagram: 1-Switch-opening / closing signal synchronization module, 2-Transient constant current source module, 3-High-precision sampling circuit, 4-Data processing and early warning unit, L1, L2, L3, N-U, V, W, N of 380VAC, QF-Circuit breaker. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] like Figure 1 As shown, this invention provides a dynamic detection device for the contact resistance of low-voltage switchgear contacts, including a switching signal synchronization module 1, a transient constant current source module 2, a high-precision sampling circuit 3, and a data processing and early warning unit 4. The switching signal synchronization module is used to capture the mechanical action signals of the start of switching and the preparation of switching in real time, thereby defining the time window of the power-off gap. The transient constant current source module is controlled by the switching signal synchronization module and is activated only during the power-off gap, applying a constant DC current excitation to the switchgear contacts under test. The high-precision sampling circuit is used to accurately capture the resistance measurement value within the synchronization time of the excitation. The data processing and early warning unit receives data from the high-precision sampling circuit and, in conjunction with the known constant current value, calculates the single value, average value, and fluctuation amplitude of the contact resistance in real time, and performs early warning judgment.

[0031] In this embodiment, the circuit breaker opening and closing signal synchronization module includes a limit switch and a photoelectric sensor, used to capture the mechanical action signals of opening and closing preparation in real time, and output a 12V DC trigger signal with a response time ≤10ms. The limit switch is installed at the circuit breaker operating mechanism linkage. The time window is from 50ms after opening to 50ms before closing, with an effective measurement duration of 300-800ms. This is the first time that the circuit breaker mechanical action sequence has been transformed into a quantifiable detection time window, solving the problem of synchronizing the detection sequence with the switch's mechanical action and ensuring that measurements are only performed within the safe power-off window.

[0032] In this embodiment, the transient constant current source module adopts a DC / AC conversion circuit. The input is the auxiliary power supply of the switchgear, and the output is a constant DC current. The auxiliary power supply of the switchgear is 220VAC, the constant DC current is 10A±0.5%, and the ripple coefficient is ≤0.1%. Its start-up response time is ≤20ms, and the shutdown delay is ≤10ms. Hardware-level timing control avoids the risks of live measurement, ensures the safe isolation between the detection circuit and the main circuit, and realizes the safety control logic of accurate power supply during power-off gaps and complete exit before closing.

[0033] In this embodiment, the high-precision sampling circuit includes a 0.1-level shunt and a 24-bit AD converter, with a measurement range of 0-200μΩ and a resolution of 0.1μΩ; its sampling point is set at the connection end between the moving contact and the stationary contact of the circuit breaker.

[0034] In this embodiment, the sampling resistance of the 0.1-level shunt is 10μΩ, and the temperature drift is ≤5ppm / ℃; the sampling rate of the AD converter is 1kHz; the sampling point is connected through a dedicated test terminal with a contact resistance ≤5μΩ, avoiding the introduction of additional errors and breaking through the accuracy bottleneck of traditional detection.

[0035] In this embodiment, the data processing and early warning unit uses an STM32 microcontroller to store the resistance measurement values ​​of 100 consecutive opening and closing operations, and calculates the single resistance value R and the average value R of 100 measurements. avg And the fluctuation range ΔR; the specific calculation formula is as follows: ΔR=(R max -R min ) / R avg ×100% When R > 80μΩ or ΔR > 10%, an early warning signal is output through the RS485 interface, triggering the cabinet indicator light to flash and the background alarm to realize the trend judgment of contact deterioration. This can detect abnormalities 3-6 months earlier than traditional single-point measurement and realize a multi-dimensional contact status evaluation system, reducing the risk of misjudgment based on a single parameter.

[0036] In this embodiment, the dynamic detection device has external dimensions of 200mm × 150mm × 80mm (length × width × height), uses an aluminum alloy shell (protection rating IP54), and has an antistatic coating (resistivity 10 ohms) on its surface. 6 The sensor (Ω・cm) is fixed to the inner wall of the switch cabinet with screws (≥10cm from the contacts, avoiding heat-generating components). Technical parameters are as follows: Measurement range: 0-200μΩ; Resolution: 0.1μΩ; Measurement error: ±2μΩ (25℃, humidity ≤60%); Detection cycle: Automatically triggered with opening and closing operations (minimum interval 10s); Warning threshold: R>80μΩ or ΔR>10%; Operating temperature: -20℃~70℃; Power consumption: Standby ≤5W, measurement ≤20W; Communication protocol: Modbus-RTU (9600bps, 8N1).

[0037] In this embodiment, the hardware components of the dynamic detection device include a limit switch, a photoelectric sensor, a signal processing board, and a main chip. The limit switch is a WLCA12-2N type limit switch, installed next to the rotating shaft of the circuit breaker operating mechanism linkage (5mm from the end of the linkage). When the circuit breaker trips, the linkage swings, triggering the normally closed contact of the limit switch to open, outputting a 12V DC trigger signal (rise time ≤5ms). The photoelectric sensor is an FS-N18N through-beam sensor, with the transmitting end fixed to the housing of the closing coil and the receiving end aligned with the coil core. When the closing coil... During excitation, the iron core displacement blocks the light path, outputting a 12V DC shutdown signal (response time ≤ 8ms); the signal processing board is an integrated CD40106 trigger, which performs de-jitter filtering on the switch / sensor signal and outputs a stable 12V TTL level signal (pulse width jitter ≤ 2ms); the main chip adopts a TILM5008 DC / DC controller, with an input of 220VAC (converted to 36VDC through a switching power supply) and an output of 10A±0.5% constant DC current (ripple voltage ≤ 36mV under rated load, ripple coefficient ≤ 0.1%).

[0038] like Figure 2 As shown, this invention also provides a dynamic detection method for the contact resistance of contacts in low-voltage switchgear. By integrating a switching signal synchronization module, a transient constant current source, and a high-precision sampling circuit within the switchgear, a constant DC current is applied during the power-off gap between contact opening and closing. The contact resistance is measured and trend analysis is performed to determine the contact state. Specifically, the method includes the following steps: S1. Initialization: After the device is powered on, it self-checks the output accuracy of the constant current source and the zero-point drift of the sampling circuit. After confirming that it is normal, it enters the standby state. S2, Signal Trigger: When the switchgear performs a tripping operation, the synchronization module detects the "tripping start" signal and sends a "measurement allow" command after a 50ms delay; S3. Resistance Measurement: First, the constant current source is started, and a 10A DC current is applied to the contact. Then, the sampling circuit continuously collects 50 data points (sampling interval 10ms), and the average value is taken as the contact resistance value R for this opening and closing. S4. Data storage: The microcontroller stores R and updates the rolling dataset of 100 measurements; S5. Status determination: ΔR is calculated after each measurement. If the warning conditions are met, an alarm is triggered. S6. End Reset: 10ms before the synchronization module detects the "Close Preparation" signal, it shuts off the constant current source and the device returns to standby mode, without affecting the normal closing of the switchgear.

[0039] Furthermore, the installation requirements are as follows: the test terminals must be directly connected to the conductive parts of the contacts, specifically using copper lugs for crimping, with a contact area ≥10mm²; the constant current source output line cross-sectional area ≥2.5mm², to avoid line loss affecting measurement accuracy, ensure low additional resistance and mechanical reliability, and be compatible with over 90% of mainstream switchgear models without requiring modification of the original electrical structure; the synchronous module limit switch and the circuit breaker operating mechanism are mechanically linked to ensure no delay in opening and closing signals.

[0040] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A dynamic detection device for contact resistance of low-voltage switchgear, characterized in that: The system includes a circuit breaker opening and closing signal synchronization module, a transient constant current source module, a high-precision sampling circuit, and a data processing and early warning unit. The circuit breaker opening and closing signal synchronization module is used to capture the mechanical action signals of opening and closing preparation in real time, thereby defining the time window of the power-off gap. The transient constant current source module is controlled by the circuit breaker opening and closing signal synchronization module and is activated only during the power-off gap to apply a constant DC current excitation to the contacts of the switchgear under test. The high-precision sampling circuit is used to accurately capture the resistance measurement value within the synchronization time of the excitation. The data processing and early warning unit receives data from the high-precision sampling circuit and, in conjunction with the known constant current value, calculates the single value, average value, and fluctuation amplitude of the contact resistance in real time, and performs early warning judgment.

2. The low-voltage switchgear contact resistance dynamic detection device according to claim 1, characterized in that, The circuit breaker opening and closing signal synchronization module includes a limit switch and a photoelectric sensor, which is used to capture the mechanical action signals of opening start and closing preparation in real time, and output a 12V DC trigger signal with a response time of ≤10ms. The limit switch is installed at the linkage of the circuit breaker operating mechanism. The time window is from 50ms after opening to 50ms before closing, and the effective measurement time is 300-800ms.

3. The low-voltage switchgear contact resistance dynamic detection device according to claim 1, characterized in that, The transient constant current source module adopts a DC / AC conversion circuit. The input is the auxiliary power supply of the switch cabinet, and the output is a constant DC current. The auxiliary power supply of the switch cabinet is 220VAC, the constant DC current is 10A±0.5%, and the ripple coefficient is ≤0.1%. Its start-up response time is ≤20ms and the shutdown delay is ≤10ms.

4. The low-voltage switchgear contact resistance dynamic detection device according to claim 1, characterized in that, The high-precision sampling circuit includes a 0.1-stage shunt and a 24-bit AD converter, with a measurement range of 0-200μΩ and a resolution of 0.1μΩ. The sampling point is set at the connection end between the moving contact and the stationary contact of the circuit breaker.

5. The low-voltage switchgear contact resistance dynamic detection device according to claim 4, characterized in that, The sampling resistor of the 0.1-level shunt is 10μΩ, and the temperature drift is ≤5ppm / ℃; the sampling rate of the AD converter is 1kHz; the sampling point is connected through a dedicated test terminal, and the contact resistance is ≤5μΩ.

6. The low-voltage switchgear contact resistance dynamic detection device according to claim 1, characterized in that, The data processing and early warning unit uses an STM32 microcontroller to store the resistance measurement values ​​from 100 consecutive opening and closing operations, and calculates the single resistance value R and the average value R of the 100 measurements. avg And the fluctuation range ΔR; the specific calculation formula is as follows: ΔR=(R max -R min ) / R avg ×100% When R > 80μΩ or ΔR > 10%, an early warning signal is output through the RS485 interface, triggering the cabinet indicator light to flash and the background alarm to sound.

7. The low-voltage switchgear contact resistance dynamic detection device according to claim 1, characterized in that, The dynamic detection device uses an aluminum alloy shell with an anti-static coating on the surface and is fixed to the inner wall of the switch cabinet with screws. The technical parameters are as follows: Measurement range: 0-200μΩ; Resolution: 0.1μΩ; Measurement error: ±2μΩ; Detection cycle: Automatically triggered with opening and closing operations; Warning threshold: R>80μΩ or ΔR>10%; Operating temperature: -20℃~70℃; Power consumption: Standby ≤5W, measurement ≤20W; Communication protocol: Modbus-RTU.

8. The low-voltage switchgear contact resistance dynamic detection device according to claim 1, characterized in that, The hardware components of the dynamic detection device include a limit switch, a photoelectric sensor, a signal processing board, and a main chip. The limit switch is a WLCA12-2N type limit switch, installed next to the rotating shaft of the circuit breaker operating mechanism linkage. When the circuit breaker trips, the linkage swings, triggering the normally closed contact of the limit switch to open and outputting a 12V DC trigger signal. The photoelectric sensor is an FS-N18N through-beam sensor, with the transmitting end fixed to the closing coil housing and the receiving end aligned with the coil core. When the closing coil is energized, the core displacement blocks the light path, outputting a 12V DC turn-off signal. The signal processing board is an integrated CD40106 trigger, which performs de-jitter filtering on the switch / sensor signal and outputs a stable 12V TTL level signal. The main chip uses a TILM5008 type DC / DC controller, with an input of 220VAC and an output of 10A±0.5% constant DC current.

9. A method for dynamically detecting the contact resistance of a low-voltage switchgear, characterized in that, Using the device described in any one of claims 1-8, by integrating a switching signal synchronization module, a transient constant current source, and a high-precision sampling circuit within the switch cabinet, a constant DC current is applied during the power-off gap after the contacts open and before closing, the contact resistance is measured and trend analysis is performed to determine the contact state. Specifically, the device includes the following steps: S1. Initialization: After the device is powered on, it self-checks the output accuracy of the constant current source and the zero-point drift of the sampling circuit. After confirming that it is normal, it enters the standby state. S2, Signal Trigger: When the switchgear performs a tripping operation, the synchronization module detects the "tripping start" signal and sends a "measurement allow" command after a 50ms delay; S3. Resistance Measurement: First, the constant current source is started, and a 10A DC current is applied to the contact. Then, the sampling circuit continuously collects 50 data points, and the average value is taken as the contact resistance value R for this opening and closing. S4. Data storage: The microcontroller stores R and updates the rolling dataset of 100 measurements; S5. Status determination: ΔR is calculated after each measurement. If the warning conditions are met, an alarm is triggered. S6. End Reset: 10ms before the synchronization module detects the "Close Preparation" signal, it shuts off the constant current source and the device returns to standby mode, without affecting the normal closing of the switchgear.

10. The low-voltage switchgear contact resistance dynamic detection device according to claim 9, characterized in that, Installation requirements are as follows: the test terminals must be directly connected to the conductive parts of the contacts, specifically using copper lugs for crimping, with a contact area ≥10mm²; the cross-sectional area of ​​the constant current source output line must be ≥2.5mm² to avoid line loss affecting measurement accuracy; the synchronous module limit switch must be mechanically linked with the circuit breaker operating mechanism to ensure no delay in opening and closing signals.

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