Modular cable branch box

Abstract

The application is suitable for the technical field of cable branch box, and particularly relates to a modular cable branch box, which comprises a box body, a main busbar assembly and a plurality of connector modules; the connector module comprises an upper copper bar, a lower copper bar, at least one fastener and a compensation fastening assembly; the lower surface of the upper copper bar and the upper surface of the lower copper bar are mutually attached to form a lapping surface; the at least one fastener is arranged along the thickness direction of the lapping surface and penetrates the upper copper bar and the lower copper bar, and is used for clamping the upper copper bar and the lower copper bar; the compensation fastening assembly is sleeved on the screw rod of the fastener and is located between the bolt head of the fastener and the upper copper bar; the compensation fastening assembly comprises an elastic compensation part and a memory alloy compensation part in sequence from the head part to the lapping surface along the axial direction of the fastener; the elastic compensation part is abutted on one side of the head part; the memory alloy compensation part is stacked between the elastic compensation part and the upper copper bar, and can solve the problems that the positive feedback cycle cannot be interrupted and the lapping surface is overheated due to the fact that the pressing force cannot be automatically increased when the temperature of the contact interface is increased.

Description

Technical Field

[0001] This application belongs to the field of cable branch box technology, and particularly relates to a modular cable branch box. Background Technology

[0002] Cable branch boxes are devices used in power grid distribution systems to branch and transfer cables. Traditional cable branch boxes are mostly integrated fixed structures with the positions and quantities of incoming and outgoing modules predetermined, requiring the entire box to be disassembled and replaced during renovation. Modular cable branch boxes are key node devices in low-voltage distribution networks that distribute power from the main busbar to various branch feeder circuits, and are widely used in power distribution systems in commercial buildings, residential communities, industrial plants, and data centers.

[0003] In actual operation, the copper busbar lap surface of the connector module is the core weak point of the entire system. Due to the combined effects of cyclical thermal expansion and contraction caused by load fluctuations, copper creep under continuous compressive stress, and oxidation at the contact interface, the actual contact area of ​​the lap surface gradually decreases over time, and the contact resistance gradually increases. This generates additional Joule heat at the contact interface, leading to a further increase in local temperature. This temperature increase, in turn, accelerates the rate of copper creep and oxidation, forming a positive feedback loop where increased contact resistance and rising temperature mutually accelerate each other. Ultimately, this may lead to contact overheating faults, and in severe cases, insulation damage and power outages.

[0004] To address the aforementioned issues, the industry currently offers several solutions. For example, periodic manual retightening of bolts can compensate for preload loss during planned power outages by using a torque wrench to retighten the lap bolts. However, this cannot undo the material loss and oxide film thickening that have already occurred, and uniform retightening of all modules cannot address the asynchronous nature of degradation rates. Another example is surface treatment of copper busbar lap surfaces with silver, tin, or nickel plating, which can delay initial oxidation. However, the plating gradually wears away under fretting wear, and oxidation resumes once the substrate is exposed. Yet another example is connecting stainless steel disc spring washers in series in the fastening structure, which can partially compensate for thickness reduction caused by creep. However, disc springs are constant-force elastic elements, and their partial derivatives with temperature changes are zero or negative, meaning they cannot actively increase the clamping force as the temperature rises.

[0005] Therefore, it is evident that the normal clamping force provided by the fastening structure at the lap joint of existing modular cable branch boxes is not functionally related to the actual temperature state of the contact interface. Regardless of changes in the contact interface temperature, the clamping force output by the fastening structure maintains its inherent static characteristics, or only undergoes a slight passive change with the temperature coefficient of the steel's elastic modulus. When the contact interface of the connector module enters an accelerated deterioration stage due to creep relaxation and oxidation accumulation during long-term operation, the Joule heat generated by the increased contact resistance causes the lap joint temperature to gradually rise, and the fastening structure has no force response capability to this heating process. Under these conditions, the mutually accelerating relationship between increased contact resistance and temperature rise is unrestricted at the structural level, and the deterioration process continues to develop. The higher the lap joint temperature, the faster the creep rate, the more severe the oxidation, the greater the contact resistance, and the further the temperature rises, until an overheating failure occurs. Summary of the Invention

[0006] This application provides a modular cable branch box that can solve the problem of continuous overheating of the lap joint due to the inability of fasteners to increase their normal clamping force when the contact interface temperature rises, resulting in an uninterrupted positive feedback between contact resistance and temperature.

[0007] In a first aspect, embodiments of this application provide a modular cable branch box, including a box body, a main busbar assembly disposed within the box body, and a plurality of plug-in modules detachably mounted on the main busbar assembly; the plug-in modules include: Top copper busbar; The lower copper busbar is stacked on top of the upper copper busbar; the lower surface of the upper copper busbar and the upper surface of the lower copper busbar are in contact with each other to form an overlapping surface; At least one fastener, passing through the upper copper busbar and the lower copper busbar along the thickness direction of the lap surface, is used to clamp the upper copper busbar and the lower copper busbar; and A compensating fastening assembly is sleeved on the screw of the fastener and located between the bolt head of the fastener and the upper copper busbar; the compensating fastening assembly includes an elastic compensating part and a shape memory alloy compensating part in sequence from the head to the lap surface along the axial direction of the fastener; the elastic compensating part abuts against one side of the head; the shape memory alloy compensating part is stacked between the elastic compensating part and the upper copper busbar; The elastic compensation part is used to absorb the reduction in clamping thickness caused by creep relaxation by elastic deformation when the contact interface temperature of the plug module is lower than the activation temperature threshold of the shape memory alloy compensation part; the shape memory alloy compensation part is used to generate a constraint restoring force along the axial direction of the fastener when the contact interface temperature rises to exceed the activation temperature threshold, so as to increase the normal contact pressure of the lap surface.

[0008] The technical solutions described in this application embodiment have at least the following technical effects: The modular cable branch box provided in this application can maintain the stability of the initial preload by stacking an elastic compensation part and a shape memory alloy compensation part in series in the compensation fastening assembly. The elastic compensation part absorbs the reduction in clamping thickness caused by creep relaxation during normal operation. When the contact interface experiences abnormal temperature rise due to deterioration, and the temperature reaches the phase transformation activation temperature threshold of the shape memory alloy compensation part, the shape memory alloy compensation part undergoes a martensitic to austenitic phase transformation, generating a constraint restoring force of elongation deformation along the fastener axis. This can actively increase the normal clamping force of the lap surface, re-compact the contact interface, increase the actual conductive contact area, and reduce the contact resistance. This breaks the positive feedback loop between the increase in contact resistance and the temperature rise, prevents the continuous acceleration of deterioration, effectively extends the service life of the connector module, and reduces the risk of overheating failure.

[0009] Secondly, embodiments of this application provide a method for monitoring the contact surface status of a plug-in module in a modular cable branch box, applied to the modular cable branch box as described in the first aspect, the method comprising: Collect temperature data and load current data at multiple measurement points for each connector module; wherein, the temperature data at multiple measurement points includes at least the near-end temperature of the lap surface, the middle section temperature of the conductor, and the far-end temperature of the conductor; Based on the temperature difference between the near end temperature of the lap surface and the far end temperature of the conductor, and the load current data, calculate the contact thermal resistance characterization of each of the plug modules. Based on the deviation of the contact thermal resistance characterization value from the factory calibration reference value of the connector module, the degree of degradation of each connector module is classified and determined. After the grading determination, the near-end temperature of the overlapping surface is monitored. When the near-end temperature of the overlapping surface exceeds the activation temperature threshold of the shape memory alloy compensation part, an activation event and the compensation magnitude of the contact thermal resistance characterization caused by this activation event are recorded. The compensation magnitude is the decrease in the contact thermal resistance characterization caused by a single activation event. Based on the compensation magnitude, the time series of the contact thermal resistance characterization quantity is corrected for the compensation effect to obtain the net degradation sequence; wherein, the net degradation sequence is a time series reflecting the intrinsic degradation process of the contact interface after correcting the compensation effect of the shape memory alloy compensation part. Monitoring data is obtained by trend analysis based on the net deterioration sequence.

[0010] The technical solutions described in this application embodiment have at least the following technical effects: The modular cable branch box contact surface condition monitoring method provided in this application can collect temperature and load current at multiple measurement points, calculate the contact thermal resistance characterization quantity that can intuitively reflect the contact state of the lap surface based on the temperature difference and load current, and combine the automatic compensation action record of the shape memory alloy compensation unit to correct the original time series of the contact thermal resistance characterization quantity through compensation effect. After eliminating the contact thermal resistance decrease caused by automatic compensation, a net degradation sequence that can truly reflect the intrinsic degradation process of the contact interface is obtained. Finally, accurate and reliable monitoring data is obtained by trend analysis of the net degradation sequence. It can distinguish the contact thermal resistance change caused by the automatic compensation of the shape memory alloy and the intrinsic degradation of the contact interface itself, avoid the interference of automatic compensation action on the judgment of the actual degradation degree, reduce unnecessary power outage maintenance frequency, improve the accuracy of condition monitoring results and ensure power supply reliability. Attached Figure Description

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

[0012] Figure 1 This is a schematic diagram of the structure of a modular cable branch box provided in one embodiment of this application; Figure 2 This is a schematic diagram of the connector module of a modular cable branch box provided in one embodiment of this application; Figure 3 This is a flowchart illustrating a method for monitoring the contact surface status of a modular cable branch box according to an embodiment of this application. Figure 4 This is a schematic diagram of a scenario for obtaining the contact thermal resistance characterization of each connector module according to an embodiment of this application; Figure 5 This is a schematic diagram of a scenario provided by an embodiment of this application, in which the net degradation sequence is obtained by correcting the time series of contact thermal resistance characterization quantities based on the compensation amplitude. Figure 6 This is a schematic diagram of a scenario where monitoring data is obtained by trend analysis based on a net deterioration sequence, according to an embodiment of this application. Figure 7 This is a schematic diagram of a classification determination scenario provided in an embodiment of this application; Figure 8 This is a schematic diagram of the structure of the control unit provided in the embodiment of this application.

[0013] Labels for each item in the figure: 100. Modular cable branch box; 10. Box body; 20. Main busbar assembly; 30. Connector module; 31. Upper copper busbar; 32. Lower copper busbar; 33. Fastener; 34. Compensating fastening assembly; 341. Elastic compensation part; 342. Shape memory alloy compensation part; 40. Control unit; 41. Processor; 42. Memory; 43. Computer program. Detailed Implementation

[0014] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0015] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0016] In actual operation, the copper busbar lap surface of the connector module is a core weak point. Due to the combined effects of periodic thermal expansion and contraction, copper creep, and oxidation at the contact interface, the actual contact area of ​​the lap surface gradually decreases over time, leading to a gradual increase in contact resistance. This generates additional Joule heat at the contact interface, causing a localized temperature rise. The increased temperature, in turn, accelerates the rate of copper creep and oxidation, creating a positive feedback loop where increased contact resistance and temperature mutually accelerate, ultimately leading to contact overheating failure. Existing solutions to this problem include periodic manual tightening of bolts, surface treatment of the lap surface, and series connection of stainless steel disc spring washers. However, these solutions lack a functional correlation between the normal clamping force provided by the fastening structure and the temperature state of the contact interface. The clamping force output by the fastening structure remains static and cannot actively increase with rising temperatures. Once the contact interface enters the accelerated deterioration stage, the mutually accelerating relationship between contact resistance and temperature becomes unrestricted at the structural level, and the deterioration process continues until an overheating failure occurs.

[0017] To address the aforementioned issues, this application provides a modular cable branch box.

[0018] Please refer to the following: Figure 1 and Figure 2This application provides a modular cable branch box 100, including a box body 10, a main busbar assembly 20 disposed within the box body 10, and a plurality of plug-in modules 30 detachably mounted on the main busbar assembly 20; each plug-in module 30 includes an upper copper busbar 31, a lower copper busbar 32, at least one fastener 33, and a compensation fastening assembly 34, wherein: The upper copper busbar 31 is stacked on top of the lower copper busbar 32; the lower surface of the upper copper busbar 31 and the upper surface of the lower copper busbar 32 are in contact with each other to form an overlapping surface.

[0019] At least one fastener 33 is inserted through the upper copper busbar 31 and the lower copper busbar 32 along the thickness direction of the lap surface, for clamping the upper copper busbar 31 and the lower copper busbar 32.

[0020] The compensating fastening component 34 is sleeved on the screw of the fastener 33 and is located between the bolt head of the fastener 33 and the upper copper busbar 31. The compensating fastening component 34 includes an elastic compensating part 341 and a shape memory alloy compensating part 342 in sequence from the head to the lap surface along the axial direction of the fastener 33. The elastic compensating part 341 abuts against one side of the head. The shape memory alloy compensating part 342 is stacked between the elastic compensating part 341 and the upper copper busbar 31.

[0021] Under normal operating conditions of the connector module 30, the reduction in clamping thickness caused by creep relaxation is absorbed by the elastic compensation part 341; when the contact interface temperature of the lap surface rises due to deterioration to exceed the activation temperature threshold of the shape memory alloy compensation part 342, the shape memory alloy compensation part 342 generates a constraint restoring force to increase the normal contact pressure of the lap surface.

[0022] Among them, the elastic compensation part 341 is used to absorb the reduction in clamping thickness caused by creep relaxation by elastic deformation when the contact interface temperature of the plug module 30 is lower than the activation temperature threshold of the shape memory alloy compensation part 342; the shape memory alloy compensation part 342 is used to generate a constraint restoring force along the axial direction of the fastener 33 when the contact interface temperature rises to exceed the activation temperature threshold, so as to increase the normal contact pressure of the lap surface.

[0023] It is understood that the enclosure 10 is a structure used to house and protect the main busbar assembly 20 and multiple plug-in modules 30, and can be made of insulating and explosion-proof materials. The main busbar assembly 20 is a conductive busbar structure used to collect the main power and distribute the power to each plug-in module 30, providing a stable power access foundation for each pluggable plug-in module 30. The fastener 33 is a bolt and nut assembly, with the nut fastened to the side of the lower copper busbar 32 away from the upper copper busbar 31, and the compensation fastening assembly 34 is only provided on the bolt head side. The upper copper busbar 31 and the lower copper busbar 32 are a pair of conductive components in the plug-in module 30, and both can be made of T2 copper. The lap surface is the interface of interest for contact condition monitoring and degradation compensation. When the contact condition of the lap surface deteriorates due to oxidation, fretting wear, or creep relaxation, the actual conductive contact area decreases, the contact resistance increases, and the local heating of the lap surface is significantly aggravated, forming a positive feedback loop of degradation.

[0024] Fastener 33 is a mechanical connector used to clamp the upper copper busbar 31 and the lower copper busbar 32 along the thickness direction (vertical direction) of the overlapping surface. It passes through corresponding through holes on the upper copper busbar 31 and the lower copper busbar 32 along the thickness direction of the overlapping surface. Fastener 33 includes a bolt head and a threaded rod extending downward from the bolt head. After the threaded rod passes through the through holes of the upper copper busbar 31 and the lower copper busbar 32, it is locked with a nut below the lower copper busbar 32. Fastener 33 generates a normal preload force through the axial tension of the threaded rod between the bolt head and the nut. This normal preload force is transmitted to the contact interface of the overlapping surface through the elastic compensation part 341, the shape memory alloy compensation part 342 and the upper copper busbar 31, pressing the lower surface of the upper copper busbar 31 against the upper surface of the lower copper busbar 32, thereby reducing the contact resistance of the overlapping surface. The material of fastener 33 can be medium carbon alloy steel to meet the requirements of long-term preload retention and anti-relaxation under high temperature conditions.

[0025] The elastic compensation part 341 can be a preloaded disc spring assembly of elastic elements that absorbs axial displacement by elastic deformation. For example, it can be composed of multiple disc springs. Within the rated preload range, it can automatically expand and contract with the change of clamping thickness. During the normal operation of the connector module 30, it continuously absorbs the thickness reduction caused by the creep relaxation of the copper busbar, maintains the basic stability of the preload, and avoids the premature decrease of the initial clamping force due to normal creep. The shape memory alloy compensation part 342 is specifically a cylindrical washer made of nickel-titanium shape memory alloy. Its phase transformation activation temperature threshold is set to a preset value in the range of 70°C to 90°C. When the contact interface deteriorates and the temperature rises to this threshold, the shape memory alloy undergoes a phase transformation from martensite to austenite, and its axial length elongates. It generates an outward constraint restoring force in the axial direction of the fastener 33, which directly increases the normal clamping force acting on the lap surface.

[0026] As can be seen from the above, the modular cable branch box 100 provided in this application can maintain the stability of the initial preload by stacking an elastic compensation part 341 and a shape memory alloy compensation part 342 in series in the compensation fastening assembly 34. The elastic compensation part 341 absorbs the reduction in clamping thickness caused by creep relaxation during normal operation. When the contact interface experiences abnormal temperature rise due to deterioration, and the temperature reaches the phase transformation activation temperature threshold of the shape memory alloy compensation part 342, the shape memory alloy compensation part 342 undergoes a martensitic to austenitic phase transformation, generating a constraint restoring force of elongation deformation along the axial direction of the fastener 33. This can actively increase the normal clamping force of the lap surface, re-compact the contact interface, increase the actual conductive contact area, and reduce the contact resistance. This breaks the positive feedback loop between the increase in contact resistance and the temperature rise, avoids the continuous acceleration of deterioration, effectively extends the service life of the connector module 30, and reduces the risk of overheating failure.

[0027] In some embodiments, please refer to the following: Figure 1 and Figure 2 The modular cable branch box 100 includes multiple temperature sensors; the multiple temperature sensors are distributed along the conductor axis of at least one copper busbar in the connector module 30.

[0028] It can be understood that the temperature sensors distributed along the axial direction of the copper busbar conductor refers to the arrangement of multiple temperature sensing elements at intervals along the length of the copper busbar, that is, in the direction extending from the contact interface of the overlapping surface towards the far end of the conductor, forming a temperature measuring array arranged along the conductor axis. The copper busbar is at least one of the upper copper busbar 31 or the lower copper busbar 32, which is the conductive busbar in the connector module 30 that conducts the current from the overlapping surface to the branch circuit. It is typically made of T2 copper, has a rectangular cross-section, and has a wide contact area in the overlapping surface region. The middle section of the conductor is located between the two measuring points mentioned above, used to assist in determining whether the axial temperature distribution follows an approximately linear pattern. The connection method between the multiple temperature sensors and the copper busbar can be a thermally conductive adhesive connection. Each sensor achieves thermal coupling with the wide surface of the copper busbar through thermally conductive silicone grease, and is subsequently covered with a polyimide insulating film, a foamed silicone rubber thermal pad, and a stainless steel elastic pressure plate.

[0029] For example, three temperature sensors are used: a first sensor mounted near the overlap surface, a second sensor mounted in the middle of the conductor, and a third sensor mounted at the far end of the conductor. All three sensors are identical PT100 platinum resistance thermometers with Class B accuracy, allowing an error of no more than ±0.3°C plus 0.005 times the absolute temperature value. The zero point for distance measurement is taken as the edge of the copper busbar overlap surface near the main busbar. The first sensor is mounted at a distance of 3.0 mm from the zero point to detect the near-end temperature of the overlap surface; the second sensor is mounted at a distance of 18.0 mm from the zero point to detect the middle temperature of the conductor; and the third sensor is mounted at a distance of 48.0 mm from the zero point to detect the far-end temperature of the conductor. All sensors are located on the centerline along the width of the copper busbar to ensure that each measuring point acquires the temperature value of the central area of ​​the wide surface of the copper busbar, avoiding additional temperature differences introduced by the cooling effect at the edge of the copper busbar. The mounting positions of the temperature sensors avoid geometrically discontinuous areas such as curved sections and opening edges of the copper busbar to avoid interference from stress concentration or differences in local heat dissipation conditions on the temperature readings. In other embodiments of this application, the number of temperature sensors may be four or more. By increasing the density of axial measuring points, a finer temperature distribution profile can be obtained, thereby improving the detection sensitivity for early local degradation. Thermocouples may also be used instead of platinum resistance thermometers, such as K-type thermocouples (nickel-chromium-nickel-silicon), which have a faster temperature response speed and are suitable for application scenarios with high monitoring requirements for transient temperature rise.

[0030] This configuration allows for the simultaneous acquisition of spatial temperature distribution information from the near end of the contact surface to the far end of the conductor. It provides a spatial dimension independent of the load current amplitude for distinguishing between localized heating at the contact interface and uniform heating of the conductor body. This effectively reduces the probability of false alarms and missed alarms caused by load current fluctuations when relying solely on the absolute value of a single point temperature for alarm purposes.

[0031] Optionally, in some embodiments, please also refer to Figure 1 and Figure 2 The series stiffness of the elastic compensation part 341 is greater than the series stiffness of the shape memory alloy compensation part 342 in the inactive state; wherein, the inactive state is the state of the shape memory alloy compensation part 342 when it is below its phase change start temperature.

[0032] It can be understood that series stiffness refers to the ability of multiple elastic elements arranged in series in the direction of force transmission to resist elastic deformation as a whole. The elastic compensation part 341 refers to the part of the compensation fastening assembly 34 located on the head side of the fastener 33, and its material can be a stainless steel disc spring or a cylindrical helical spring. The shape memory alloy compensation part 342 refers to the part of the compensation fastening assembly 34 stacked between the elastic compensation part 341 and the upper copper busbar 31, and its material is a Ni-Ti based shape memory alloy. The inactive state refers to the state where the actual temperature of the shape memory alloy compensation part 342 has not yet reached its phase transformation initiation temperature. In this state, the internal crystal structure of the shape memory alloy compensation part 342 is mainly martensitic, and the macroscopic elastic modulus is low, resulting in a small series stiffness.

[0033] For example, the elastic compensation part 341 can be a set of eight 301 stainless steel disc springs stacked in series. Each disc spring has an outer diameter of 12.5 mm, an inner diameter of 6.2 mm, a single thickness of 0.7 mm, and a free height of 1.1 mm. The series equivalent stiffness of the stacked elastic compensation part 341 can be 8.5 kN / mm. The series equivalent stiffness of the shape memory alloy compensation part 342 in the non-activated state (at room temperature below the phase transformation start temperature As of the martensite to austenite transformation, which can be 88°C) can be 2.5 kN / mm. The stiffness ratio of the two can be 3.4:1, which meets the design target of not less than 3:1. Under this stiffness ratio, if the clamping thickness reduction is 10 μm due to the creep of the copper material, the elastic compensation part 341 will absorb a deformation displacement of 7.7 μm, while the shape memory alloy compensation part 342 will only absorb a non-activated elastic deformation of 2.3 μm, with almost no loss of its phase transformation compensation stroke.

[0034] With this configuration, by utilizing the stiffness difference between the elastic compensation unit 341 and the shape memory alloy compensation unit 342 in the series direction, the functions of creep relaxation compensation and phase change activation compensation can be decoupled and time-sequentially graded in the fastening force transmission chain. This ensures that the useful compensation stroke of the shape memory alloy compensation unit 342 will not be consumed by creep-type slow displacement during long-term normal operation, thereby guaranteeing its compensation capability and service life in deterioration temperature rise events.

[0035] Optionally, in some embodiments, please also refer to Figure 1 and Figure 2 The elastic stroke of the elastic compensation part 341 is greater than the maximum differential thermal expansion displacement between the fastener 33 and the shape memory alloy compensation part 342 within the operating temperature range, so as to reserve a compensation stroke for the phase transformation displacement of the shape memory alloy compensation part 342 when it is activated.

[0036] It can be understood that the elastic stroke of the elastic compensation part 341 refers to the maximum axial compressive displacement that the elastic compensation part 341 can generate within its fully elastic deformation range, that is, the range of axial displacement from when the elastic compensation part 341 is in a free state to when it is completely flattened or compressed. The operating temperature range refers to the entire temperature range that the connector module 30 may experience in actual service, including the minimum ambient temperature to the maximum allowable operating temperature. The maximum differential thermal expansion displacement refers to the maximum value of the relative axial displacement between the fastener 33 and the shape memory alloy compensation part 342 due to the difference in the coefficient of linear expansion and the abrupt change in the coefficient of linear expansion before and after the phase transformation of the shape memory alloy compensation part 342 within the above-mentioned operating temperature range. Since the fastener 33 and the shape memory alloy compensation part 342 are connected in series on the fastening force transmission chain, the difference in their length changes at different temperatures will introduce an axial gap component that varies with temperature. If the elastic compensation part 341 does not have enough elastic stroke to absorb this gap, the gap will directly consume the preload reserve of the fastening system. The elastic compensation section uses a set of eight 301 stainless steel disc springs stacked in series. The total free height of the disc spring assembly is 8.8 mm, the fully compressed height is 5.6 mm, and the corresponding elastic stroke is 3.2 mm. Fasteners are made of medium carbon alloy steel with a linear expansion coefficient of 11.5 × 10⁻⁻⁻⁶. 6 / K) and shape memory alloy compensation part (Ni-Ti based alloy, martensitic linear expansion coefficient is 6.6×10⁻ 6 The maximum differential thermal expansion displacement of / K in the operating temperature range (-20°C to 120°C) is 0.05mm, which is much smaller than the elastic stroke of 3.2mm, and the elastic stroke margin is sufficient.

[0037] Specifically, the design requirement that the elastic stroke of the elastic compensation part 341 is greater than the maximum differential thermal expansion displacement ensures a key function: when the shape memory alloy compensation part 342 undergoes a martensitic-to-austenitic phase transformation due to an abnormal increase in the temperature of the lap surface, generating a constraint recovery force (i.e., the axial expansion force generated by the phase transformation of the shape memory alloy under constraint), its phase transformation displacement (the shape recovery displacement in the thickness direction) can be entirely converted into an additional normal clamping force increment on the lap surface, without being partially offset by the gap caused by the differential thermal expansion effect. If the elastic stroke of the elastic compensation part 341 is insufficient, when the temperature of the lap surface rises above the activation temperature threshold, the thermal expansion of the fastener 33 due to its large coefficient of linear expansion will first consume the remaining elastic stroke of the elastic compensation part 341, making it impossible for the elastic compensation part 341 to provide sufficient axial following space when the shape memory alloy compensation part 342 undergoes a martensitic-to-austenitic phase transformation. At this time, a portion of the phase transformation displacement of the shape memory alloy compensation part 342 will be used to fill the differential thermal expansion gap instead of applying additional clamping force, and the overall compensation effect will be weakened.

[0038] Optionally, in some embodiments, please also refer to Figure 1 and Figure 2There is a heat conduction path between the shape memory alloy compensation part 342 and the lap surface; the contact interface temperature of the lap surface can be conducted to the shape memory alloy compensation part 342 through the heat conduction path, and the activation temperature threshold of the shape memory alloy compensation part 342 is higher than the steady-state temperature of the contact interface when the plug-in module 30 is running at full load.

[0039] The heat conduction path can be understood as the physical heat flow path from the contact interface of the overlapping surface, through the upper copper busbar 31 body and the thermally conductive insulating film, and finally to the bottom surface of the shape memory alloy compensation part 342. The components along this path are the upper copper busbar 31, the thermally conductive insulating film, and the bottom of the shape memory alloy pad, each sequentially undertaking the function of heat conduction. The contact interface of the overlapping surface refers to the actual conductive contact surface formed by the mutual contact of the lower surface of the upper copper busbar 31 and the upper surface of the lower copper busbar 32. When current flows through this interface, Joule heat is concentrated due to the contact resistance; therefore, the local temperature of the contact interface is the heat source temperature of the entire heat transfer path. The steady-state temperature of the contact interface refers to the relatively constant temperature value reached by the contact interface of the plug-in module 30 under normal full-load operation conditions and in a thermal equilibrium state. The activation temperature threshold refers to the minimum ambient temperature condition required for the shape memory alloy compensation part 342 to begin undergoing a martensitic-to-austenitic phase transformation and generating constraint restoring force. The activation temperature threshold of the shape memory alloy compensation part 342 is higher than the steady-state temperature of the contact interface of the plug module 30 under normal full load operation. The method to determine the range of the higher temperature is to perform multiple steady-state thermal simulation calculations or actual measurements on the cable branch box under different ambient temperatures and rated loads to obtain the maximum value of the steady-state temperature of the contact interface under all normal operating conditions. Then, the temperature increment margin that may be caused by ambient temperature fluctuations and short-term overload operation in historical operating data is statistically analyzed. The 95% confidence upper limit of the margin value is taken as the minimum value, and finally the range is determined to be between 5℃ and 15℃.

[0040] For example, the value of the higher degree can be 15°C. For the shape memory alloy compensation part 342 using a martensitic-to-austenitic phase transformation Ni-Ti based alloy, its martensitic-to-austenitic phase transformation start As temperature can be 88±3°C. Taking the steady-state temperature of the contact interface during normal full-load operation as a design benchmark of 70°C, the activation temperature threshold is set to not less than 85°C (70°C plus a 15°C safety margin), which coincides with the lower limit of the As temperature range (85 to 91°C). This ensures that the shape memory alloy compensation part 342 only starts phase transformation activation compensation after the temperature of the lap surface exceeds the upper limit of the normal operating temperature and enters the abnormal range due to contact deterioration. The specific structure of the heat conduction path includes the upper copper busbar 31 body (made of T2 copper, with a thermal conductivity of 390 W / (m·K), and the length of the heat conduction section along the bolt axis can be 5 mm), a boron nitride-filled polyimide thermally conductive insulating film (boron nitride volume fraction can be 30%, thermal conductivity can be 3 to 5 W / (m·K), thickness can be 0.2 mm, sandwiched between the bottom surface of the shape memory alloy compensation part 342 and the top surface of the upper copper busbar 31), and the Ni-Ti based alloy body of the bottom gasket of the shape memory alloy gasket (thermal conductivity can be 18 W / (m·K), single piece thickness can be 1.0 mm). The total length of the entire heat conduction path does not exceed 5 mm, and the corresponding thermal response time constant can be 3 to 5 minutes, ensuring that the response delay of the shape memory alloy compensation part 342 to the temperature change of the overlapping surface is within the acceptable range for engineering, so that it will not be sensitive to instantaneous temperature burrs due to excessively fast response, nor will it miss the effective compensation opportunity due to excessively slow response.

[0041] In addition, this application provides a method for monitoring the contact surface condition of the plug-in module of a modular cable branch box. This method can collect temperature and load current at multiple measurement points, calculate the contact thermal resistance characterization quantity that can intuitively reflect the contact state of the lap surface based on the temperature difference and load current, and combine the automatic compensation action record of the shape memory alloy compensation part to correct the original time series of the contact thermal resistance characterization quantity through compensation effect. After eliminating the contact thermal resistance decrease caused by automatic compensation, a net degradation sequence that can truly reflect the intrinsic degradation process of the contact interface is obtained. Finally, accurate and reliable monitoring data is obtained by trend analysis of the net degradation sequence. This method can distinguish the contact thermal resistance change caused by the automatic compensation of the shape memory alloy from the intrinsic degradation of the contact interface itself, avoid the interference of the automatic compensation action on the judgment of the actual degradation degree, reduce the frequency of unnecessary power outage maintenance, improve the accuracy of condition monitoring results, and ensure the reliability of power supply.

[0042] The modular cable branch box also includes a control unit, which is located inside the box. The control unit communicates with the temperature sensors of each plug-in module via an RS485 bus and collects load current data via the secondary signal line of the current transformer. The plug-in module contact surface status monitoring method of the modular cable branch box provided in this application embodiment can be applied to the control unit. In this case, the control unit is the execution body of the modular cable branch box provided in this application embodiment. This application embodiment does not impose any restrictions on the specific type of the control unit.

[0043] To better understand the method for monitoring the contact surface status of the plug-in module of the modular cable branch box provided in this application embodiment, the specific steps of the method for monitoring the contact surface status of the plug-in module of the modular cable branch box provided in this application embodiment are described below by way of example.

[0044] Figure 3 The diagram illustrates the workflow of a method for monitoring the contact surface status of a modular cable branch box's connector module according to an embodiment of this application. The specific steps of this method include: S100 collects multi-point temperature data and load current data of each connector module; among which, the multi-point temperature data includes at least the near-end temperature of the lap surface, the middle section temperature of the conductor, and the far-end temperature of the conductor.

[0045] It can be understood that multi-point temperature data refers to the set of temperature values ​​collected by multiple temperature sensors distributed along the conductor axis of the copper busbar at the same sampling time or within the same sampling period. Specifically, the near-end temperature of the overlap surface is the temperature value collected by the first sensor closest to the contact interface. This temperature directly reflects the intensity of the Joule heating generated by the contact resistance on the copper busbar body and is the core temperature signal characterizing the degree of contact degradation. The middle section temperature of the conductor is the temperature value collected by the second sensor located between the first and third sensors, used to help determine whether the axial temperature decrease follows a linear pattern. The far-end temperature of the conductor is the temperature value collected by the third sensor furthest from the overlap surface. The temperature at this location has been significantly attenuated to near the average temperature level of the conductor body due to the localized heating of the contact interface. The multi-point temperature data includes at least three temperature data points, corresponding to the near-end temperature of the overlap surface, the middle section temperature of the conductor, and the far-end temperature of the conductor, respectively.

[0046] For example, the temperature sensor converts the resistance change into a voltage signal through a bridge measurement circuit, which is then amplified by an instrumentation amplifier and acquired as a digital temperature value by the analog-to-digital converter of the control unit. The three analog channels corresponding to the three temperature sensors are sampled sequentially in a time-division multiplexing manner, and each sampling is oversampled 16 times and averaged to reduce noise; the control unit determines the temperature sensor and current transformer data of all plug-in modules at a fixed sampling period (e.g., 30 seconds).

[0047] S200 calculates the contact thermal resistance characterization of each connector module based on the temperature difference between the near end temperature of the lap surface and the far end temperature of the conductor, as well as the load current data.

[0048] For example, the contact thermal resistance characterization is a dimensionless or dimensional proxy index that is positively correlated with the contact resistance of the lap surface, calculated based on the temperature difference between the near end temperature of the lap surface and the far end temperature of the conductor and the effective value of the load current. The contact thermal resistance characterization of each plug module can be calculated by obtaining the temperature difference value between the near end temperature of the lap surface and the far end temperature of the conductor, determining the root mean square value of the load current within a preset time window, and then calculating the contact thermal resistance characterization based on the square of the temperature difference and the root mean square value of the load current.

[0049] In one possible implementation, please refer to Figure 4 , Figure 4 This diagram illustrates the step-by-step process of calculating the contact thermal resistance characterization value based on the temperature difference value, the root mean square value of the load current, and finally determining the characterization value of the contact thermal resistance; S200, based on the temperature difference between the near end temperature and the far end temperature of the conductor at the lap surface and the load current data, the contact thermal resistance characterization value of each connector module is calculated, including: S210, the temperature difference value is obtained based on the near-end temperature of the lap joint and the far-end temperature of the conductor.

[0050] It can be understood that the temperature difference is the arithmetic difference between the near end temperature of the lap surface and the far end temperature of the conductor at the same sampling time. The temperature difference is the amount of temperature drop caused by heat dissipation and thermal resistance attenuation after the Joule heat at the contact interface is conducted along the copper busbar axis to the far end of the conductor.

[0051] For example, the control unit reads the current temperature readings from three temperature sensors in each sampling cycle, verifies each reading, and if any temperature reading exceeds the sensor's operating range (e.g., below -30°C or above 150°C) or the rate of change from the previous reading exceeds a preset rate threshold (e.g., exceeding 5°C / minute, excluding instantaneous electromagnetic interference glitches), then the sampling point is marked as invalid data and replaced with the most recent valid data interpolated. After the verification passes, the control unit directly calculates the temperature difference as the near-end temperature of the lap surface minus the far-end temperature of the conductor as the temperature difference value at the current sampling time.

[0052] S220, determine the root mean square value of the load current within a preset time window; wherein, when the root mean square value of the load current is greater than or equal to a preset minimum current threshold, the calculated value of the current in the current window is used as the effective value of the current for calculation; when the root mean square value of the load current is less than the preset minimum current threshold, the effective value of the current in the previous effective window remains unchanged.

[0053] It is understandable that the preset time window is a sliding time interval used by the control unit to perform root mean square (RMS) calculations on the raw current sampling data. The length of this window (e.g., 5 minutes or 10 minutes) needs to be balanced between data noise smoothing and response speed. If the window is too short, the RMS value will be greatly affected by transient load fluctuations, resulting in high data dispersion; if the window is too long, the response speed to load changes will be slow, failing to reflect the actual operating conditions in a timely manner. The RMS value of the load current is the DC current value equivalent to the heating effect within this window time. The preset minimum current threshold is a lower current limit value determined by the design. The specific method for determining the preset time window can be through multiple experiments. Specifically, it can be set according to 10% of the rated current of the cable branch box, which can eliminate situations where current measurement noise is high and contact thermal resistance calculation results are unstable under extremely low loads.

[0054] For example, the control unit uses a preset time window of 5 minutes. Within each window, it performs analog-to-digital conversion on the secondary side signal of the current transformer at a sampling interval of 1 second, obtaining a total of 300 instantaneous current sampling points. The control unit first calculates the square value of each of these 300 sampling points, then calculates the arithmetic mean of the 300 square values, and finally takes the square root to obtain the root mean square value of the load current for that window. At the end of each window, the control unit compares the root mean square value of the load current with a preset minimum current threshold (taken as 10% of the rated current; for example, when the rated current is 100A, the minimum current threshold is 10A). If the root mean square value of the load current is greater than or equal to 10A, the control unit uses the root mean square value of the load current in the current window as the effective value of the current for the current calculation and updates the contact thermal resistance measurement; if the root mean square value of the load current is less than 10A, the control unit maintains the effective value of the current in the previous effective window unchanged.

[0055] S230 is a contact thermal resistance characterization quantity calculated based on the temperature difference and the square of the root mean square of the load current.

[0056] For example, if the root mean square value of the load current in the current window is valid, the contact thermal resistance characterization is directly calculated. The contact thermal resistance characterization is obtained by subtracting the conductor's far end temperature from the near end temperature of the lap surface. The contact thermal resistance characterization value of the current window is obtained by dividing the first result by the square of the root mean square value of the load current.

[0057] This configuration fuses temperature and current signals into a contact thermal resistance characterization quantity that is positively correlated with the magnitude of contact resistance and largely independent of the load current amplitude. This makes the characterization quantities under different load conditions directly comparable, providing a stable quantitative basis for subsequent degradation grading and trend analysis.

[0058] S300, based on the deviation of the contact thermal resistance characterization value from the factory calibration reference value of the connector module, classifies and determines the degree of deterioration of each connector module.

[0059] It is understandable that the factory calibration reference value is the initial value of the contact thermal resistance characterization obtained by calculating the contact thermal resistance characterization of the plug module under standard ambient temperature (e.g., 25°C) and rated current conditions during factory inspection. It represents the contact thermal resistance level of the plug module in a brand new state with intact contact surfaces. The deviation is the relative change of the currently calculated contact thermal resistance characterization value relative to the factory calibration reference value.

[0060] For example, the degradation level of each connector module is graded by performing linear regression fitting on the near end temperature of the lap surface, the middle section temperature of the conductor, and the far end temperature of the conductor, as well as their position coordinates in the axial direction of the copper busbar, to obtain the axial temperature gradient slope and the fitting correlation coefficient. When the axial temperature gradient slope exceeds a preset multiple of its factory calibration reference value and the fitting correlation coefficient is not less than a preset threshold, the degradation judgment is confirmed to be valid.

[0061] In one possible implementation, please refer to Figure 7 , Figure 7 A schematic diagram illustrating the specific steps of the classification determination is shown; S300, the classification determination includes: S301, based on the near-end temperature of the lap joint, the middle section temperature of the conductor, and the far-end temperature of the conductor, as well as their position coordinates along the axial direction of the copper busbar, a linear regression fitting is performed to obtain the axial temperature gradient slope and the fitting correlation coefficient; where the axial temperature gradient slope is the rate of change of temperature along the axial direction of the copper busbar.

[0062] Linear regression fitting can be understood as follows: The temperature values ​​at three axial measurement points are used as the dependent variable, and the position coordinates of these three points along the copper busbar axis (with the edge of the overlap surface as the origin, the distance from the near end of the overlap surface to zero can be 3 mm, the middle section of the conductor to zero can be 18 mm, and the far end of the conductor to zero can be 48 mm) are used as independent variables. A linear function of temperature with respect to position coordinates is fitted using the least squares method, yielding the slope of the axial temperature gradient and the correlation coefficient. The slope of the axial temperature gradient is the rate of temperature change along the copper busbar axis; a larger absolute value indicates a faster temperature decay along the axis and a more concentrated local heating at the near end of the overlap surface. The correlation coefficient is a measure of the goodness of fit, ranging from zero to one, reflecting the extent to which the temperature values ​​at the three measurement points conform to a linear distribution.

[0063] For example, in each calculation cycle, the control unit extracts three temperature values ​​(temperature at the near end of the lap joint, temperature at the middle section of the conductor, and temperature at the far end of the conductor) and their fixed axial position coordinates (the first position coordinate can be 3.0 mm, the second position coordinate can be 18.0 mm, and the third position coordinate can be 48.0 mm) from the temperature data buffer at the current sampling time, constructing three sets of position temperature data points. The control unit calls the built-in least squares linear regression subroutine to calculate the axial temperature gradient slope. Specifically, it calculates the arithmetic mean of the three position coordinates and the arithmetic mean of the three temperature values, then calculates the deviation of each position coordinate from the position mean and the deviation of each temperature value from the temperature mean, and divides the sum of the products of the two sets of deviations by the sum of the squares of the position coordinate deviations to obtain the axial temperature gradient slope. Specifically, it calculates the fitting correlation coefficient by dividing the square of the sum of the products of the above two sets of deviations by the product of the sum of the squares of the position coordinate deviations and the sum of the squares of the temperature deviations.

[0064] S302, when the slope of the axial temperature gradient exceeds a preset multiple of its factory calibration reference value and the fitting correlation coefficient is not less than a preset threshold, the grading determination is deemed valid.

[0065] It can be understood that the factory-calibrated axial temperature gradient baseline value is the initial value of the axial temperature gradient slope calculated during the factory inspection of the connector module. This represents the baseline level of the axial temperature gradient when the connector module is in a brand-new state with a uniform and intact contact interface. The preset multiplier is the upper limit of the allowable amplification factor of the current axial temperature gradient slope relative to the factory-calibrated baseline value, determined by the design. The preset threshold for the fitted correlation coefficient (such as 0.85 or 0.9) is the minimum acceptable standard for determining whether the temperature distribution conforms to a linear law.

[0066] For example, in each calculation cycle, the control unit reads the axial temperature gradient slope and the fitted correlation coefficient value at the current moment and compares them with the factory-calibrated axial temperature gradient reference value stored in non-volatile memory. The preset multiple can be 2.0 times, meaning that when the axial temperature gradient slope is greater than 2.0 times the factory-calibrated reference value, it is considered that the axial temperature gradient has significantly increased abnormally. The preset fitted correlation coefficient threshold is 0.85, meaning that when the fitted correlation coefficient is greater than or equal to 0.85, the temperature values ​​of the three measuring points are considered to have a good linear distribution along the axial direction, and the sensor data is reliable. When both conditions are met simultaneously, the control unit confirms that the current degradation judgment is valid. When the two conditions are not met simultaneously, if the axial temperature gradient slope is greater than 2.0 times the factory calibration reference value but the fitting correlation coefficient is less than 0.85, the control unit determines that the data quality is abnormal, temporarily suspends the classification judgment, and generates a sensor data verification reminder; if the axial temperature gradient slope does not exceed 2.0 times the factory calibration reference value, regardless of the value of the fitting correlation coefficient, the control unit determines that the axial temperature distribution is normal or only slightly deviates from the reference, and the degree of degradation is still within the acceptable range.

[0067] This setup, through a dual verification mechanism of axial temperature gradient slope and fitting correlation coefficient, verifies the physical rationality of the degradation judgment by utilizing the spatial distribution characteristics of temperature at multiple measurement points before performing the grading judgment. This effectively filters out false degradation signals caused by factors such as temperature sensor malfunction, loose installation, or local electromagnetic interference, significantly improving the accuracy and anti-interference capability of the grading judgment.

[0068] S400, after classification, monitor the near-end temperature of the lap surface. When the near-end temperature of the lap surface exceeds the activation temperature threshold of the shape memory alloy compensation part, record an activation event and the compensation magnitude of the contact thermal resistance characterization caused by this activation event; where the compensation magnitude is the decrease in the contact thermal resistance characterization caused by a single activation event.

[0069] An activation event can be understood as a complete martensitic-to-austenitic phase transformation activation cooling recovery process triggered by an abnormal rise in the temperature of the lap surface of the shape memory alloy compensation unit during actual operation, exceeding its activation temperature threshold. Each activation event corresponds to a constraint recovery force generated by the shape memory alloy compensation unit. This recovery force reduces the contact resistance of the lap surface, causing a step-like or ramp-like decrease in the contact thermal resistance characterization. The single compensation amplitude is the absolute value of the decrease in the contact thermal resistance characterization caused by a single activation event. Its value is equal to the difference between the most recent stable value of the contact thermal resistance characterization before the activation event and the stable value after the contact thermal resistance characterization recovers after the activation event, reflecting the degree of improvement of the contact state by this activation compensation. The activation event occurs when the near-end temperature of the lap surface first exceeds the activation temperature threshold.

[0070] For example, the control unit checks whether the near-end temperature of the lap surface is greater than or equal to the activation temperature threshold in each sampling cycle. When the near-end temperature of the lap surface rises from below the activation temperature threshold to above or equal to the activation temperature threshold, the control unit determines that an activation of the shape memory alloy compensation unit has begun and records the current timestamp as the start time of the activation event. The control unit continuously monitors the near-end temperature of the lap surface until it falls back to below the activation temperature threshold and remains stable for at least one time window, at which point the control unit determines that the activation event has ended and records the end time of activation. After the activation event ends, the control unit traces back the time series of contact thermal resistance characterization before activation. The average value of the contact thermal resistance characterization during the stable period when the fluctuation of the contact thermal resistance characterization is less than a preset fluctuation threshold before activation is used as the pre-activation baseline value; the average value of the contact thermal resistance characterization during the first stable period after activation is used as the post-activation value; the single compensation amplitude is calculated to be equal to the pre-activation baseline value minus the post-activation value. The control unit records the occurrence time of this activation event, the single compensation amplitude, the pre-activation baseline value, and the post-activation value together as one activation event data.

[0071] S500, based on the compensation amplitude, corrects the time series of contact thermal resistance characterization by compensation effect to obtain the net degradation sequence; wherein, the net degradation sequence is the time series reflecting the intrinsic degradation process of the contact interface after correcting the compensation effect of the shape memory alloy compensation part.

[0072] For example, the net degradation sequence can be obtained by correcting the time series of contact thermal resistance characterization parameters with compensation effect. This can be achieved by determining the occurrence time and compensation magnitude of each activation event to obtain activation event data, and then using the occurrence time of each activation event as a segment node to obtain the cumulative compensation value time series.

[0073] In one possible implementation, please refer to Figure 5 , Figure 5 A schematic diagram illustrating the specific process of correcting the time series of contact thermal resistance characterization parameters based on the compensation magnitude is shown; S500, based on the compensation magnitude, the time series of contact thermal resistance characterization parameters is corrected for compensation effect to obtain the net degradation sequence, including: S510, determine the occurrence time and compensation range of each activation event to obtain activation event data; wherein, the activation event data is used to indicate activation event records.

[0074] For example, the control unit reads all historical activation event data from the activation event record buffer and extracts the following fields for each record: event sequence number (incrementing from 1), event occurrence time (accurate to the minute), and single compensation magnitude (retaining three significant digits). The control unit sorts the extracted activation event data in ascending order of occurrence time to generate an ordered list of activation event data, including paired records of the occurrence time of each event from the first activation event to the Mth activation event and the corresponding single compensation magnitude, where M is the total number of historical activation events up to the current time. S520: Based on the activation event data, the cumulative compensation value time series is obtained by using the occurrence time of each activation event as the segment node.

[0075] For example, the cumulative compensation value time series is a function of the cumulative value over time, that is, the total decrease in the contact thermal resistance characterization quantity that the shape memory alloy compensation unit has cumulatively compensated for through each activation event up to any given time. The control unit may construct the cumulative compensation value time series according to the following rules: the cumulative compensation value is initialized to zero, that is, the time period before the occurrence of the first activation event; for each activation event (numbered from 1 to M), the single compensation amplitude of the activation event is added to the cumulative compensation value at the corresponding event occurrence time. Specifically, the cumulative compensation value remains zero before the occurrence of the first activation event; from the occurrence of the first activation event to the occurrence of the second activation event, it is equal to the single compensation amplitude of the first activation event; from the occurrence of the second activation event to the occurrence of the third activation event, it is equal to the sum of the single compensation amplitudes of the first and second events; and so on, after the occurrence of the Mth activation event, it is equal to the sum of the single compensation amplitudes of all M activation events. The control unit discretizes the cumulative compensation value function according to the sampling time with a time step of 30 seconds, generating a cumulative compensation value time series with the same sampling frequency as the original time series of the contact thermal resistance characterization quantity.

[0076] S530, the net degradation sequence is obtained by superimposing the original time series of the contact thermal resistance characterization quantity and the cumulative compensation value time series according to the time.

[0077] For example, the control unit aligns the contact thermal resistance characterization time series and the cumulative compensation value time series by timestamp. For each sampling moment, it determines the corresponding cumulative compensation value, calculates the net degradation value, which is equal to the original value of the contact thermal resistance characterization plus the cumulative compensation value at that moment, and stores the calculation results in the net degradation sequence data queue in chronological order. For example, suppose a certain plug-in module has experienced two activation events so far: the single compensation magnitude of the first activation event is 0.5 times 10 to the power of -4; the single compensation magnitude of the second activation event is 0.3 times 10 to the power of -4. Before the first activation event, the cumulative compensation value is zero, and the net degradation value equals the original value. From the time of the first activation event to the time of the second activation event, the cumulative compensation value is 0.5 x 10 - 4, and the net degradation value equals the original value plus 0.5 x 10 - 4. After the time of the second activation event, the cumulative compensation value is 0.8 x 10 - 4, and the net degradation value equals the original value plus 0.8 x 10 - 4. The net degradation sequence does not contain a monotonically increasing degradation trend with a step decrease in compensation.

[0078] This setup, by accumulating the compensation amplitude of each activation of the shape memory alloy compensation unit back to the original time series of the contact thermal resistance characterization, can eliminate the artificial step drop introduced by the compensation effect, restore the net degradation sequence driven only by the intrinsic degradation of the contact interface, and make the subsequent trend analysis based on data that truly reflects the degradation process, fundamentally solving the problem of interference caused by the automatic compensation of shape memory alloy to the degradation judgment.

[0079] S600, monitoring data is obtained by trend analysis based on the net deterioration sequence.

[0080] For example, trend analysis is a process of performing a time-dimensional mathematical analysis on the net degradation sequence to extract state parameters and trend parameters reflecting the intrinsic degradation process of the contact interface. Monitoring data is the output of trend analysis, including at least two types of indicators: current degradation degree and degradation rate (or degradation acceleration factor). The current degradation degree reflects the extent to which the contact interface degradation has accumulated, while the degradation rate (degradation acceleration factor) reflects whether the degradation process is accelerating, constant, or slowing down. The combination of these two indicators can provide a quantitative basis for operation and maintenance decisions (such as whether to schedule power outages for maintenance or predict remaining service life).

[0081] In one possible implementation, please refer to Figure 6 , Figure 6 This diagram illustrates how a sliding window smoothing and fitting process is applied to the net degradation sequence to extract the degradation acceleration factor and the current degree of degradation, thereby determining the monitoring data; S600, monitoring data is obtained by trend analysis based on the net degradation sequence, including: S610, the net degradation sequence is smoothed by a sliding window, and the smoothed net degradation sequence is fitted to obtain the degradation acceleration factor and the current degradation degree; wherein, the degradation acceleration factor characterizes the rate of change of the degradation process, and the current degradation degree is the percentage deviation of the current net degradation value of the contact thermal resistance characterization quantity from the factory calibration reference value.

[0082] As can be understood, sliding window smoothing refers to calculating the average or median of data within a fixed-length window by sliding it point-by-point across the net degradation sequence. The degradation acceleration factor reflects the exponential growth rate of the degradation process; a higher value indicates that the degradation process is accelerating, while a value close to zero indicates that the degradation process is developing at an approximately uniform rate. The current degree of degradation is calculated based on the net degradation fitted value corresponding to the current moment on the fitted curve and the factory calibration baseline value. It can be obtained by dividing the current net degradation fitted value by the factory calibration baseline value minus one, and then multiplying by 100%.

[0083] For example, the control unit takes the data segment of the net degradation sequence as the range covered by the sliding window. First, the original net degradation sequence data is smoothed by median sliding smoothing with a time window of 1 hour to obtain the smoothed net degradation sequence. The net degradation fitted value is equal to the factory calibration baseline value plus the degradation amplitude coefficient multiplied by the product of the natural exponential function at the degradation acceleration factor and time minus one. Nonlinear least squares fitting is performed on the smoothed sequence, where time is represented by the number of running days with the factory calibration time as zero. Then, the most recent fitting result is used as the initial value to improve the convergence speed and stability. After the fitting converges, the estimated values ​​of the degradation amplitude coefficient and the degradation acceleration factor are output. If the fitting residual is too large (e.g., the residual standard deviation exceeds 10% of the factory calibration reference value), the control department determines that the data quality is insufficient to support a reliable exponential model fitting. That is, the net degradation fitting value is equal to the factory calibration reference value plus the product of the linear degradation coefficient and time. The current degradation degree is directly obtained by taking the smoothed net degradation value at the current time, dividing the net degradation value by the factory calibration reference value minus one, and then multiplying by 100%.

[0084] S620 determines monitoring data based on the degradation acceleration factor and the current degree of degradation.

[0085] For example, the control unit inputs the degradation acceleration factor and the current degree of degradation into a preset monitoring judgment rule table. The rules are expressed as follows: If the current degree of degradation is less than 30% and the degradation acceleration factor does not exceed 1.5 times its historical baseline value, the control unit outputs a suggestion to continue regular monitoring at the standard sampling cycle; if the current degree of degradation is greater than or equal to 30% and less than 80%, or the degradation acceleration factor exceeds 1.5 times its historical baseline value, the control unit outputs a suggestion to increase the monitoring sampling frequency to twice the standard frequency (e.g., shortening 30 seconds to 15 seconds); if the current degree of degradation is greater than or equal to 80% and less than 120%, the control unit outputs a yellow warning and displays it on the host computer monitoring interface, suggesting a power outage maintenance within a preset time; if the current degree of degradation is greater than or equal to 120%, the control unit outputs a red alarm signal (which may include audible and visual alarms and remote notifications), suggesting immediate replacement. In addition, the control department extrapolates the estimated number of days remaining until the current degradation level reaches 120% based on the current degradation level and degradation acceleration factor using an exponential model. This estimated number of days is output as supplementary monitoring data, which can provide a reference time window for the formulation of operation and maintenance plans.

[0086] This setup, by fitting the net degradation sequence after compensation effect correction to an exponential trend and extracting two key degradation indicators—the degradation acceleration factor and the current degree of degradation—combined with preset grading rules to output structured monitoring data, can provide maintenance personnel with complete decision support information that combines current status assessment and future trend prediction. Under the premise of ensuring power supply reliability, it enables accurate maintenance based on the actual degradation state, avoiding maintenance delays or misjudgments of the degree of degradation caused by the memory alloy compensation effect masking the actual degradation situation.

[0087] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0088] This application also provides a control unit. Figure 8 This is a schematic diagram of the structure of a control unit provided in an embodiment of this application. Figure 8 As shown, the control unit 40 of this embodiment includes: at least one processor 41 ( Figure 8 Only one is shown in the image), at least one memory 42 ( Figure 8 (Only one is shown in the image) and a computer program 43 stored in the at least one memory 42 and executable on the at least one processor 41, wherein when the processor 41 executes the computer program 43, it causes the control unit 40 to perform the steps in any of the above-described modular cable branch box embodiments, or causes the control unit 40 to perform the functions of each module / unit in the above-described system embodiments.

[0089] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A modular cable branch box, characterized in that, The system includes a housing, a main busbar assembly disposed within the housing, and multiple plug-in modules detachably mounted on the main busbar assembly; the plug-in modules include: Top copper busbar; The lower copper busbar is stacked on top of the upper copper busbar; the lower surface of the upper copper busbar and the upper surface of the lower copper busbar are in contact with each other to form an overlapping surface; At least one fastener, passing through the upper copper busbar and the lower copper busbar along the thickness direction of the lap surface, is used to clamp the upper copper busbar and the lower copper busbar; and A compensating fastening assembly is sleeved on the screw of the fastener and located between the bolt head of the fastener and the upper copper busbar; the compensating fastening assembly includes an elastic compensating part and a shape memory alloy compensating part in sequence from the head to the lap surface along the axial direction of the fastener; the elastic compensating part abuts against one side of the head; the shape memory alloy compensating part is stacked between the elastic compensating part and the upper copper busbar; The elastic compensation part is used to absorb the reduction in clamping thickness caused by creep relaxation by elastic deformation when the contact interface temperature of the plug module is lower than the activation temperature threshold of the shape memory alloy compensation part; the shape memory alloy compensation part is used to generate a constraint restoring force along the axial direction of the fastener when the contact interface temperature rises to exceed the activation temperature threshold, so as to increase the normal contact pressure of the lap surface.

2. The modular cable branch box as described in claim 1, characterized in that, The modular cable branch box includes multiple temperature sensors; the multiple temperature sensors are distributed along the conductor axis of at least one copper busbar in the connector module.

3. The modular cable branch box as described in claim 1, characterized in that, The series stiffness of the elastic compensation part is greater than the series stiffness of the shape memory alloy compensation part in the inactive state; wherein, the inactive state is the state in which the shape memory alloy compensation part is below its phase transition start temperature.

4. The modular cable branch box as described in claim 1, characterized in that, The elastic stroke of the elastic compensation part is greater than the maximum differential thermal expansion displacement between the fastener and the shape memory alloy compensation part within the operating temperature range, so as to reserve a compensation stroke for the phase transformation displacement of the shape memory alloy compensation part when it is activated.

5. The modular cable branch box as described in claim 1, characterized in that, There is a heat conduction path between the shape memory alloy compensation part and the overlapping surface; the contact interface temperature of the overlapping surface can be conducted to the shape memory alloy compensation part through the heat conduction path, and the activation temperature threshold of the shape memory alloy compensation part is higher than the steady-state temperature of the contact interface when the plug-in module is running at full load.

6. A method for monitoring the contact surface status of a modular cable branch box, applied to the modular cable branch box as described in any one of claims 1 to 5, the method comprising: Collect temperature data and load current data at multiple measurement points for each connector module; wherein, the temperature data at multiple measurement points includes at least the near-end temperature of the lap surface, the middle section temperature of the conductor, and the far-end temperature of the conductor; Based on the temperature difference between the near end temperature of the lap surface and the far end temperature of the conductor, and the load current data, calculate the contact thermal resistance characterization of each of the plug modules. Based on the deviation of the contact thermal resistance characterization value from the factory calibration reference value of the connector module, the degree of degradation of each connector module is classified and determined. After the grading determination, the near-end temperature of the overlapping surface is monitored. When the near-end temperature of the overlapping surface exceeds the activation temperature threshold of the shape memory alloy compensation part, an activation event and the compensation magnitude of the contact thermal resistance characterization caused by this activation event are recorded. The compensation magnitude is the decrease in the contact thermal resistance characterization caused by a single activation event. Based on the compensation magnitude, the time series of the contact thermal resistance characterization quantity is corrected for the compensation effect to obtain the net degradation sequence; wherein, the net degradation sequence is a time series reflecting the intrinsic degradation process of the contact interface after correcting the compensation effect of the shape memory alloy compensation part. Monitoring data was obtained by trend analysis based on the net deterioration sequence.

7. The method for monitoring the contact surface status of the plug-in module of the modular cable branch box as described in claim 6, characterized in that, The step of calculating the contact thermal resistance characterization of each of the connector modules based on the temperature difference between the near end temperature and the far end temperature of the conductor at the lap surface and the load current data includes: The temperature difference value is obtained based on the near-end temperature of the lap surface and the far-end temperature of the conductor; Determine the root mean square value of the load current within a preset time window; wherein, when the root mean square value of the load current is greater than or equal to a preset minimum current threshold, the calculated value of the current in the current window is used as the effective value of the current in the calculation; when the root mean square value of the load current is less than the preset minimum current threshold, the effective value of the current in the previous effective window remains unchanged. The contact thermal resistance is calculated based on the temperature difference and the square of the root mean square of the load current.

8. The method for monitoring the contact surface status of the plug-in module of the modular cable branch box as described in claim 6, characterized in that, The process of correcting the time series of the contact thermal resistance characterization based on the compensation amplitude to obtain the net degradation sequence includes: Determine the occurrence time and compensation range of each activation event to obtain activation event data; wherein, the activation event data is used to indicate activation event records; Based on the activation event data, the cumulative compensation value time series is obtained by taking the occurrence time of each activation event as the segment node. The net degradation sequence is obtained by superimposing the original time series of the contact thermal resistance characterization quantity and the cumulative compensation value time series according to time.

9. The method for monitoring the contact surface status of the plug-in module of the modular cable branch box as described in claim 6, characterized in that, The monitoring data obtained by trend analysis based on the net deterioration sequence includes: The net degradation sequence is smoothed using a sliding window, and the smoothed net degradation sequence is fitted to obtain the degradation acceleration factor and the current degradation degree; wherein, the degradation acceleration factor characterizes the rate of change of the degradation process, and the current degradation degree is the percentage deviation of the current net degradation value of the contact thermal resistance characterization quantity from the factory calibration reference value. The monitoring data is determined based on the degradation acceleration factor and the current degree of degradation.

10. The method for monitoring the contact surface status of the plug-in module of the modular cable branch box as described in claim 6, characterized in that, The classification determination includes: Linear regression fitting is performed based on the near-end temperature of the lap surface, the middle section temperature of the conductor, and the far-end temperature of the conductor, as well as their position coordinates along the copper busbar axis, to obtain the axial temperature gradient slope and the fitting correlation coefficient; wherein, the axial temperature gradient slope is the rate of temperature change along the copper busbar axis. When the slope of the axial temperature gradient exceeds a preset multiple of its factory calibration reference value and the fitting correlation coefficient is not less than a preset threshold, the grading determination is deemed valid.

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