RS-485 bus passive protection device for on-line monitoring equipment of transformer substation

Abstract

The invention provides an RS-485 bus passive protection device for on-line monitoring equipment of a transformer substation. The RS-485 bus passive protection device comprises a primary protection module, a primary filtering module, a residual voltage release module and a residual interference elimination module which are sequentially connected in series along an RS-485 bus signal path, all the modules are matched in sequence to provide graded protection for the RS-485 bus, the primary protection module is used for discharging high-voltage impact current generated by lightning stroke and surge, the primary filtering module is used for attenuating pulse group interference signals in the bus, the residual voltage release module is used for carrying out secondary clamping on residual high voltage and slowly releasing residual charges, and the secondary filtering module is used for carrying out secondary filtering on the residual high voltage. And the residual interference elimination module is used for filtering residual interference signals so as to ensure normal communication. The problem that high-voltage pulses such as field surges and lightning strokes break down an RS485 interface of online monitoring equipment is solved, meanwhile, interference of interference signals such as pulse groups and conducted disturbance on a bus is effectively solved, and the equipment can safely and reliably work in a complex electromagnetic environment.

Description

Technical Field

[0001] This invention belongs to the field of substation technology, specifically relating to an RS-485 bus passive protection device for online monitoring equipment in substations. Background Technology

[0002] The RS-485 bus is widely used as the data communication interface for online monitoring equipment in substations due to its advantages such as long communication distance, high speed, simple networking, strong openness, and ease of implementation. However, the electromagnetic environment at substation sites is extremely complex. High-voltage transient impacts such as lightning strikes or surges often enter the equipment interface along the RS-485 communication line, causing damage to the interface circuit components and preventing the equipment from working properly. At the same time, pulse group interference, conducted disturbances, and other electromagnetic interference signals in the substation can also couple to the RS-485 line, seriously interfering with data communication and causing equipment malfunctions or even communication interruptions.

[0003] Traditional RS-485 interface protection measures typically employ single-stage protection, such as using only gas discharge tubes or TVS diodes for simple surge discharge, or connecting a single filter in series on the signal line for initial interference suppression. However, in the actual operating environment of substations, surge energy is high, the interference spectrum is broad, and interference signals are diverse. Single-stage protection schemes are insufficient to effectively cope with complex interference, resulting in existing RS-485 bus protection devices being unable to operate reliably for extended periods under harsh environments of strong lightning strikes, high surges, and multiple interferences. How to reliably solve the various electromagnetic interference and surge impact problems of RS-485 communication interfaces without affecting communication speed and signal integrity is a pressing technical challenge in the field of substation online monitoring. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the aforementioned background technology and provide an RS-485 bus passive protection device for substation online monitoring equipment. This device effectively solves the problem of high-voltage pulses such as surges and lightning strikes damaging the RS485 interface of the online monitoring equipment. It also effectively solves the interference of pulse groups, conducted disturbances, and other interference signals on the bus, enabling the equipment to operate safely and reliably in complex electromagnetic environments.

[0005] The technical solution adopted in this invention is: an RS-485 bus passive protection device for online monitoring equipment in substations, comprising a primary protection module, a primary filtering module, a residual voltage release module, and a residual interference cancellation module connected in series along the RS-485 bus signal path; each module cooperates in sequence to provide hierarchical protection for the RS-485 bus, wherein the primary protection module is used to discharge high-voltage inrush current generated by lightning strikes and surges, the primary filtering module is used to attenuate pulse group interference signals in the bus, the residual voltage release module is used to perform secondary clamping on residual high voltage and slowly release residual charge, and the residual interference cancellation module is used to filter out residual interference signals, thereby ensuring normal communication.

[0006] In the above technical solution, the primary protection module includes a gas discharge tube and a first TVS thyristor; The two terminals of the gas discharge tube are directly connected to signal line A and signal line B at the RS-485 differential interface, respectively, so as to conduct the surge current into the protective ground when a high voltage surge occurs on either signal line. The first TVS thyristor is connected across signal line A and signal line B at the interface, with its positive and negative terminals directly connected to signal line A and signal line B, respectively, to provide transient clamping overvoltage when the differential mode voltage exceeds its clamping voltage. The output terminals of signal lines A and B of the primary protection module are respectively connected to the input terminals of signal lines A and B of the primary filter module, ensuring that the differential signal processed by the primary protection module can be correctly sent to the primary filter module for subsequent processing.

[0007] In the above technical solution, the primary filtering module includes a first common-mode choke and a resistor network; The first common-mode choke has a first winding and a second winding wound on the same magnetic core. The first winding is connected in series to signal line A after the primary protection module, and the second winding is connected in series to signal line B after the primary protection module. The two windings have the same number of turns and the same winding direction, so as to maintain a low impedance path for differential-mode signals while suppressing common-mode interference. The resistor network consists of a first resistor and a second resistor. One end of the first resistor is connected to the signal line A at the rear end of the first common mode choke, and the other end serves as the output terminal of the signal line A of the primary filter module and is connected to the input terminal of the signal line A of the residual voltage release module. One end of the second resistor is connected to the signal line B at the rear end of the first common mode choke, and the other end serves as the output terminal of the signal line B of this module and is connected to the input terminal of the signal line B of the residual voltage release module. The resistor network is used to dampen and attenuate the residual differential mode pulse group interference signal.

[0008] In the above technical solution, the residual voltage release module includes a second TVS thyristor and a current-limiting resistor; the current-limiting resistor includes a third resistor and a fourth resistor; The second TVS thyristor is connected between RS-485 differential signal line A and signal line B after passing through the primary filter module. It is used to conduct and transiently clamp the high voltage when the differential mode voltage between signal line A and signal line B exceeds its clamping voltage. One end of the third resistor is connected to the connection node between the second TVS thyristor and signal line A, and the other end serves as the output terminal of signal line A of the residual voltage release module and is connected to the input terminal of signal line A of the residual interference cancellation module. One end of the fourth resistor is connected to the connection node between the second TVS thyristor and signal line B, and the other end serves as the output terminal of signal line B of the residual voltage release module and is connected to the input terminal of signal line B of the residual interference cancellation module. After the second TVS thyristor is released from clamping, the third and fourth resistors limit and dampen the residual inrush current on the two signal lines, respectively, gradually releasing the remaining energy and thus protecting the subsequent circuits.

[0009] In the above technical solution, the residual interference cancellation module includes the following components arranged in sequence at the output terminal of the residual voltage release module: a first high-voltage capacitor network, a bidirectional TVS diode, a second common-mode choke, and a second high-voltage capacitor network; The first high-voltage capacitor network consists of at least two capacitors, which are connected across signal line A and signal line B after processing by the residual voltage release module, and are used to filter out differential-mode high-frequency interference generated after secondary clamping. The bidirectional TVS diode is connected in parallel between signal line A and signal line B to achieve transient clamping when transient voltage spikes of positive and negative polarities occur. The second common-mode choke includes a third winding and a fourth winding wound on the same magnetic core. The third winding is connected in series to signal line A after passing through the first high-voltage capacitor network and the bidirectional TVS tube, and the fourth winding is connected in series to signal line B after passing through the first high-voltage capacitor network and the bidirectional TVS tube. The two windings have the same number of turns and the same winding direction, so as to further suppress common-mode noise and maintain the differential-mode signal channel. The second high-voltage capacitor network consists of several capacitors and is connected across signal line A and signal line B at the output of the second common-mode choke. It is used to perform secondary filtering on the differential-mode high-frequency interference remaining after common-mode suppression. The input terminals of the first high-voltage capacitor network and the bidirectional TVS tube are respectively connected to the output terminals of signal line A and signal line B of the residual voltage release module. The output terminal of the second common-mode choke is respectively connected to the input terminals of signal line A and signal line B of the RS-485 transceiver interface of the online monitoring equipment, ensuring that the differential signal after filtering and clamping by the module can be correctly sent to the subsequent RS-485 transceiver.

[0010] The above technical solution also includes an intelligent monitoring module, which is connected to the RS-485 bus signal line for real-time surge detection. The intelligent monitoring module includes a sampling circuit and a low-power detection unit. The sampling circuit samples abnormal surge voltage or current on the RS-485 bus line, and the low-power detection unit determines the occurrence of a surge based on the sampling signal and outputs a maintenance signal to prompt equipment maintenance or condition maintenance.

[0011] In the above technical solution, the primary protection module, primary filtering module, residual voltage release module and residual interference elimination module all adopt a modular structure design. Adjacent modules are connected in series through detachable electrical connectors or terminals, so that each functional module can be independently disassembled, replaced and maintained, improving the convenience of device maintenance.

[0012] The above technical solution has a self-recovery protection function, including: A thermistor is connected in series to at least one of the RS-485 differential signal lines A and B. When overvoltage or overcurrent surge occurs, its resistance increases due to heat to temporarily cut off or limit the current path. It automatically resumes conduction after the temperature drops. The redundant transient suppression protection element is connected in parallel between signal line A and signal line B. It consists of at least two TVS devices. When one TVS device fails due to overload, the other TVS device can still continue to clamp the surge voltage to ensure the continuity and reliability of the protection function.

[0013] In the above technical solution, the thermistor is a positive temperature coefficient thermistor or a self-resetting fuse; The redundant transient suppression protection element consists of at least two TVS diodes connected in parallel, with different rated clamping voltages for the two TVS diodes to share surge energy and maintain clamping function by the other when one fails.

[0014] The above technical solution also includes a metal shielding cavity and a multi-layer printed circuit board structure. The multi-layer printed circuit board is fixed inside the metal shielding cavity by insulating pillars, and the metal shielding cavity is electrically connected to the grounding layer of the circuit board by screws or press-fit springs to form a complete Faraday cage structure, ensuring that the compartments of each functional module can work safely under electromagnetic shielding. The metal shielding cavity is a conductive shell, and the internal space is divided into four electromagnetic compartments by partitions, which respectively house the primary protection module, the primary filtering module, the residual voltage release module, and the residual interference elimination module. The multilayer printed circuit board has a five-layer structure, including: The top signal layer is used to install the gas discharge tube and the first TVS thyristor of the primary protection module; The second grounding isolation layer is electrically connected to the metal shielded cavity shell and is used to isolate the top layer from the third layer. The third signal layer is used to install the first common-mode choke and resistor network of the primary filter module, as well as the second TVS thyristor and current-limiting resistor of the residual voltage release module; The fourth grounding isolation layer is used to isolate the third layer from the bottom layer, and forms a shielded isolation area at the boundary of each module through a via ground grid; The bottom signal / power layer is used to install the first high-voltage capacitor network, bidirectional TVS diode, second common-mode choke, and second high-voltage capacitor network of the residual interference cancellation module, and is led out to the RS-485 transceiver interface. The layers of the multilayer printed circuit board are electrically connected to the input / output terminals of the corresponding modules through blind or buried vias. The first and second common-mode chokes are covered with high-permeability material shielding sleeves to prevent magnetic saturation and suppress stray coupling. The wiring of the first and second high-voltage capacitor networks and the ground layer minimizes the loop area, thereby isolating each module in terms of physical structure and electromagnetic shielding and synergistically improving the overall immunity and reliability of the device.

[0015] The beneficial effects of this invention are as follows: By connecting the primary protection module, primary filtering module, residual voltage release module, and residual interference elimination module in series according to the signal flow sequence, this device forms a "four-level hierarchical protection" system, which can effectively intercept lightning surges, pulse groups, and high-frequency interference at different energy and frequency levels, avoid single-level protection overload or failure, and improve the overall reliability and communication stability of RS-485 bus in the strong interference environment of substations.

[0016] Furthermore, the present invention connects a gas discharge tube and a TVS thyristor in parallel at the differential interface. On the one hand, the gas discharge tube is used to withstand large current pulses and quickly discharge surge energy; on the other hand, the TVS thyristor is used for transient clamping during differential mode overvoltage. The two complement each other to ensure dual protection against high-speed, high-energy surges, significantly reducing the risk of damage to interface devices.

[0017] Furthermore, this invention employs a common-mode choke with dual windings on the same magnetic core, providing high impedance to common-mode interference while maintaining low impedance to differential-mode signals. Simultaneously, a limiting resistor is connected in series after the windings to dampen and attenuate differential-mode pulse bursts. This combined common-mode and differential-mode filtering method can efficiently attenuate various transient and narrow-pulse interferences without affecting communication speed, thereby improving data transmission quality.

[0018] Furthermore, in the secondary clamping structure of this invention, the TVS thyristor is connected across the differential pair for transient clamping of residual overvoltage, and the subsequent series resistor further limits the current and mitigates residual energy after the TVS unclamps. This structure effectively extends the service life of the protection device and ensures a smooth transition even under continuous impacts, preventing high-frequency noise or voltage spikes from propagating to the next stage circuit.

[0019] Furthermore, the residual interference cancellation module of this invention is sequentially configured with a differential-mode capacitor, a bidirectional TVS, a common-mode choke, and a secondary differential-mode capacitor, forming a multi-stage, cross-mode filtering and clamping combination. This not only filters out the differential-mode high-frequency components remaining after clamping but also finely suppresses common-mode residual noise, ultimately ensuring that the signal entering the transceiver has excellent clarity and stability.

[0020] Furthermore, this invention adds an intelligent monitoring module with a sampling circuit and a low-power detection unit, which can record surge events in real time and issue maintenance reminders, enabling the device to have self-diagnostic capabilities. Maintenance personnel can then promptly replace or repair protective components, avoiding communication interruptions due to long-term unknown wear and tear, thus improving equipment availability and maintenance efficiency.

[0021] Furthermore, the modular design of this invention separates the four functional units, allowing for replacement as needed via detachable connectors, facilitating on-site maintenance and upgrades. Users can quickly add, remove, or replace corresponding modules according to different operating conditions, reducing downtime and maintenance costs, and enhancing the product's applicability and flexibility.

[0022] Furthermore, this invention connects a thermistor in series on the signal line to automatically limit or cut off current in case of overvoltage / overcurrent, eliminating short-term pulse damage without manual intervention; parallel redundant TVS diodes ensure continuous clamping even if one fails. This self-recovering architecture combines fast response and continuous protection, significantly improving the reliability and maintainability of surge protection.

[0023] Furthermore, this invention utilizes multiple parallel TVS diodes with different rated clamping voltages to share energy, and combines this with the self-recovery characteristics of the thermistor, enabling the protection device to operate stably even under high-frequency, high-energy impacts. Even if a component ages and fails, the system can still maintain its clamping capability, ensuring uninterrupted communication links.

[0024] Furthermore, this invention combines a metal shielding cavity with a multi-layer PCB to form a complete Faraday cage isolated from the plane. This physically isolates each module electromagnetically and strictly layers the wiring, minimizing electromagnetic coupling between modules and to the outside. The magnetic shielding sleeve and minimum loop design further prevent random magnetic interference and radiation interference, providing a solid hardware barrier for the long-term stable operation of the device in environments with strong power interference. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the module connection of the present invention.

[0026] Among them, 1-primary protection module, 2-primary filtering module, 3-residual voltage release module, 4-residual interference cancellation module, 11-gas discharge tube, 12-first TVS thyristor, 21-first common mode choke, 22-first resistor, 23-second resistor, 31-second TVS thyristor, 32-third resistor, 33-fourth resistor, 41-first high voltage capacitor network, 42-bidirectional TVS tube, 43-second common mode choke, 44-second high voltage capacitor network. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but these descriptions do not constitute a limitation on the present invention.

[0028] like Figure 1 As shown, this invention provides a passive protection device specifically for the RS-485 bus interface of online monitoring equipment in substations. The device sequentially includes: a primary protection module 1, a primary filtering module 2, a residual voltage release module 3, and a residual interference cancellation module 4. The A and B signal lines of the RS-485 communication pass through each of the above modules, forming a multi-level protection and filtering circuit structure to cope with the impact of complex electromagnetic environments such as high-energy lightning surges, fast pulse groups, and strong common-mode interference on the communication interface.

[0029] The primary protection module 1 is mainly responsible for withstanding and dissipating the huge transient surge energy from the line. This module includes devices such as a gas discharge tube 11 and a transient suppression diode (first TVS thyristor 12).

[0030] The two terminals of the gas discharge tube 11 are directly connected to signal line A and signal line B at the RS-485 differential interface, respectively, so as to conduct the impact current into the protective ground when a high voltage impact occurs on either signal line. The first TVS thyristor 12 is connected across signal line A and signal line B at the interface, with its positive and negative terminals directly connected to signal line A and signal line B, respectively, for transient clamping overvoltage when the differential mode voltage exceeds its clamping voltage; The output terminals of signal lines A and B of the primary protection module 1 are respectively connected to the input terminals of signal lines A and B of the primary filter module, ensuring that the differential signal processed by the primary protection module 1 can be correctly sent to the primary filter module 2 for subsequent processing.

[0031] like Figure 1 As shown, the gas discharge tube 11 preferably adopts a three-electrode discharge tube structure, with one end connected to the A line of the RS-485 and the other end connected to the B line. The common lead of the discharge tube is grounded (connected to the frame ground FG of the device). During normal communication, the gas discharge tube 11 is in a high-impedance state and does not affect the signal. When a high-voltage surge such as a lightning strike occurs on the line and reaches its trigger voltage (e.g., about 600V to 800V), the gas discharge tube 11 quickly breaks down and conducts, directly discharging the high-energy surge current between the A and B lines to the ground grid. The gas discharge tube 11 has a very large current-carrying capacity (e.g., it can withstand a current of more than 5kA under an 8 / 20µs waveform), which can absorb most of the surge energy and play the role of the first coarse protection.

[0032] The first TVS thyristor 12 is used to quickly clamp surges, further reducing the surge voltage amplitude. Preferably, the first TVS thyristor 12 is composed of multiple transient suppression diodes, for example, a bridge rectifier diode network to rectify overvoltages of any polarity on lines A and B to the grounded TVS element, achieving comprehensive clamping of common-mode and differential-mode surges. Under normal operating voltage, the first TVS thyristor 12 exhibits high resistance, and its response speed is on the nanosecond level when a surge occurs, acting before the gas discharge tube to limit the transient voltage. When the gas discharge tube 11 is turned on, the first TVS thyristor 12 works in conjunction to further clamp the discharge tube holding voltage (tens of volts) to an even lower level, thereby rapidly reducing the residual voltage on lines A and B. By combining the gas discharge tube and TVS, the primary protection module 1 can handle high-energy surges while ensuring rapid response: the first TVS thyristor 12 quickly suppresses voltage spikes, while the gas discharge tube 11 diverts the main energy. The two work together to effectively protect the subsequent circuits from damage caused by thousands of volts of impact.

[0033] The primary filter module 2 includes a first common-mode choke 21 and a resistor network; The first common-mode choke 21 has a first winding and a second winding wound on the same magnetic core. The first winding is connected in series to the signal line A after the primary protection module, and the second winding is connected in series to the signal line B after the primary protection module. The two windings have the same number of turns and the same winding direction, so as to maintain a low impedance path for differential-mode signals while suppressing common-mode interference. The resistor network consists of a first resistor 22 and a second resistor 23. One end of the first resistor 22 is connected to the signal line A at the rear end of the first common mode choke 21, and the other end serves as the output terminal of the signal line A of the primary filter module and is connected to the input terminal of the signal line A of the residual voltage release module. One end of the second resistor 23 is connected to the signal line B at the rear end of the first common mode choke 21, and the other end serves as the output terminal of the signal line B of this module and is connected to the input terminal of the signal line B of the residual voltage release module. The resistor network is used to dampen and attenuate the residual differential mode pulse group interference signal.

[0034] The primary filtering module 2 follows immediately after the primary protection module. Its function is to perform preliminary filtering of interference after the surge primary discharge and to limit the transmission of surge current to subsequent stages. This module includes a first common-mode choke 21 and components such as first and second resistors 22 and 23 connected in series. Figure 1 As shown, the first common-mode choke 21 is a common-mode choke with a pair of windings connected in series on lines A and B, respectively, and having magnetic coupling. When a common-mode transient current appears on lines A and B (the currents in the two lines are in the same direction, such as from a common-mode lightning strike or a sudden change in ground potential), the common-mode inductor exhibits a high impedance, suppressing the propagation of the transient common-mode current. However, for differential-mode signals (normal RS-485 data current) in opposite directions on lines A and B, since the magnetic fluxes of the two windings cancel each other out, the first common-mode choke 21 exhibits a very small impedance to the differential-mode signal, thus not significantly weakening the communication waveform. The first common-mode choke 21 also has a certain energy storage and buffering function, which can reduce the surge front steepness (di / dt) and provide a buffer for subsequent stages.

[0035] Preferably, the first common-mode choke 21 is a high-permeability ferrite choke specifically for communication interfaces, which has an impedance of several hundred ohms or more under high-frequency noise above 10MHz, and the rated current is sufficient to pass the RS-485 signal current without saturation (e.g., rated current ≥100mA).

[0036] Following the first common-mode choke 21, a first resistor 22 and a second resistor 23 are connected in series on lines A and B, respectively. The first and second resistors 22 and 23 are primarily used for surge damping and noise filtering: on the one hand, they form an RC network together with the parasitic capacitance / filter capacitors of subsequent stages to attenuate high-frequency interference; on the other hand, they limit the amplitude of the surge current and share some of the transient energy, thereby protecting subsequent delicate protection devices from excessive stress. The resistance values ​​of the first and second resistors 22 and 23 should provide damping as much as possible without excessively affecting the RS-485 bus impedance and signal quality.

[0037] Preferably, each resistor is a metal film resistor of approximately 5Ω to 10Ω (capable of withstanding surge instantaneous power consumption), such as a 10Ω, 1 / 2W resistor. This resistance value introduces only a small amount of impedance in a typical 120Ω differential-mode impedance bus, ensuring that high-speed communication remains essentially distortion-free. At the same time, the RC time constant formed by the subsequent filter capacitor (in the order of a few nanofarads) is approximately in the order of tens of nanoseconds, which can effectively absorb pulse interference energy above tens of MHz.

[0038] The residual voltage release module 3 is used to further clamp and release the remaining overvoltage after the surge has been clipped by the first two stages, ensuring that the output port voltage drops to a safe level. This module includes a second TVS thyristor 31 and a current-limiting resistor; the current-limiting resistor includes a third resistor 32 and a fourth resistor 33. The second TVS thyristor 31 is connected between RS-485 differential signal line A and signal line B after passing through the primary filter module. It is used to conduct and transiently clamp the high voltage when the differential mode voltage between signal line A and signal line B exceeds its clamping voltage. One end of the third resistor 32 is connected to the connection node between the second TVS thyristor 31 and signal line A, and the other end serves as the output terminal of signal line A of the residual voltage release module and is connected to the input terminal of signal line A of the residual interference cancellation module. One end of the fourth resistor 33 is connected to the connection node between the second TVS thyristor 31 and the signal line B, and the other end serves as the output terminal of the signal line B of the residual voltage release module and is connected to the input terminal of the signal line B of the residual interference cancellation module. After the second TVS thyristor 31 is released from clamping, the third resistor 32 and the fourth resistor 33 limit and dampen the residual inrush current on the two signal lines respectively, gradually releasing the remaining energy and thus protecting the subsequent circuits.

[0039] like Figure 1 As shown, the second TVS thyristor 31 is connected between lines A and B, forming the differential mode clamping device for the second interval. Compared to the first TVS thyristor 12 in the primary protection, the clamping threshold of the second TVS thyristor 31 can be designed to be lower, allowing for fine clamping of secondary surges. For example, a bidirectional TVS diode with a reverse turn-off voltage of approximately 30V (connected to lines A and B respectively) can be used. It conducts when the surge overvoltage is around 40V, quickly clamping the residual differential mode voltage between lines A and B to within tens of volts. This protects the transceiver interface of the subsequent stage from excessive differential mode voltage impact. The third and fourth resistors 32 and 33 are connected in series in lines A and B respectively (located after the second TVS thyristor 31), and their function is similar to that of the first and second resistors 22 and 23 mentioned above: limiting the current when the second TVS thyristor 31 is turned on, avoiding excessive loss of the second TVS thyristor 31, and simultaneously working with the subsequent filter network to improve the attenuation capability of pulse groups.

[0040] Preferably, the values ​​of the third and fourth resistors 32 and 33 are similar to or slightly higher than those of the preceding stages, for example, each approximately 10Ω and 1 / 4W. The distribution of multiple series resistors helps to spread the voltage drop and power consumption of surges, improving the overall reliability of the circuit.

[0041] It should be noted that the second TVS thyristor 31 of the residual voltage release module 3 and the first TVS thyristor 12 of the primary protection module 1 can work together: during a large surge, the first TVS thyristor 12 activates first and works with the discharge tube to discharge current, while the second TVS thyristor 31 conducts at a lower voltage to absorb the remaining energy, thus completely reducing the surge residual voltage to a safe range. For example, when the gas discharge tube 11 activates, the voltage across its terminals is maintained at approximately tens of volts. At this time, the second TVS thyristor 31 further clamps this differential mode voltage to approximately 30V, ensuring that the subsequent circuitry hardly experiences stress exceeding the rated withstand voltage of the communication interface. Simultaneously, due to the presence of the third and fourth resistors 32 and 33, the current conducted by the second TVS thyristor 31 rapidly decays after the surge ends, avoiding device heating caused by continuous current, thereby achieving rapid release and dissipation of surge energy.

[0042] The residual interference cancellation module includes the following components arranged in sequence at the output terminal of the residual voltage release module: a first high-voltage capacitor network 41, a bidirectional TVS diode 42, a second common-mode choke 43, and a second high-voltage capacitor network 44. The first high-voltage capacitor network 41 consists of at least two capacitors, which are connected across the signal line A and signal line B after the residual voltage release module is processed, and are used to filter out differential-mode high-frequency interference generated after secondary clamping. The bidirectional TVS diode 42 is connected in parallel between signal line A and signal line B to achieve transient clamping when transient voltage spikes of positive and negative polarities occur. The second common-mode choke 43 includes a third winding and a fourth winding wound on the same magnetic core. The third winding is connected in series to the signal line A after passing through the first high-voltage capacitor network and the bidirectional TVS tube, and the fourth winding is connected in series to the signal line B after passing through the first high-voltage capacitor network and the bidirectional TVS tube. The two windings have the same number of turns and the same winding direction, so as to further suppress common-mode noise and maintain the differential-mode signal channel. The second high-voltage capacitor network 44 consists of several capacitors and is connected across signal line A and signal line B at the output end of the second common-mode choke. It is used to perform secondary filtering on the differential-mode high-frequency interference remaining after common-mode suppression. The input terminals of the first high-voltage capacitor network 41 and the bidirectional TVS tube 42 are respectively connected to the signal line A and signal line B output terminals of the residual voltage release module. The output terminal of the second common-mode choke 43 is respectively connected to the signal line A and signal line B input terminals of the RS-485 transceiver interface of the online monitoring equipment, ensuring that the differential signal after filtering and clamping by the module can be correctly sent to the subsequent RS-485 transceiver.

[0043] The residual interference cancellation module 4 is located at the very end of the circuit, immediately connected to the protected RS-485 transceiver interface. It is used to filter out residual high-frequency interference signals, electrostatic transients, and micro-amplitude surge pulses, providing final purification and protection for the communication line.

[0044] like Figure 1 As shown. The first high-voltage capacitor network 41 consists of two high-voltage capacitors, which bypass lines A and B to ground (FG) respectively; similarly, the second high-voltage capacitor network 44 also consists of two capacitors connected to lines A and B to ground respectively. The two capacitor networks are placed on both sides of the second common-mode choke 43, forming a π-type filter topology: that is, a capacitor-inductor-capacitor structure.

[0045] This multi-stage filter can more effectively attenuate wideband interference signals: the first high-voltage capacitor network 41 is located on the input side, which can bypass some common-mode noise directly before it enters the common-mode inductor; the second high-voltage capacitor network 44 is located on the output side, forming a closed filter loop with the previous stage to filter out residual interference after passing through the inductor. Since high common-mode voltage may occur in substation environments, high-voltage withstand devices are specifically used in the first and second high-voltage capacitor networks 41 and 44. Preferably, each capacitor has a value in the order of nanofarads and a withstand voltage of not less than 2kV to balance low impedance to high-frequency disturbances and resistance to lightning strikes. For example, each capacitor can be a 6.8nF / 2000V ceramic capacitor, which presents low impedance in the several MHz frequency band, effectively introducing high-frequency noise to the ground and being able to withstand the high voltage of a lightning strike without breakdown. It should be noted that these capacitors have relatively small capacitance, sufficient to filter interference above MHz, but have only a slight impact on RS-485 signals (typically differential signals from several hundred kHz to 1MHz), ensuring that the communication waveform is not distorted.

[0046] A bidirectional TVS diode 42 is connected between lines A and B as a final-stage transient voltage suppression device. Its function is to quickly clamp any residual differential-mode transients (such as transient spikes caused by electrostatic discharge or fast pulse groups) to a level acceptable to the transceiver. Because the line voltage is already limited to a low level after the preceding protection stage, a device with a lower operating voltage can be selected for the bidirectional TVS diode 42 to further improve clamping accuracy. It is preferable to use a low-voltage bidirectional TVS diode specifically designed for communication lines (e.g., a device with a reverse turn-off voltage of around 7V and a clamping voltage not exceeding 15V, such as the commercially available SM712). This TVS diode does not conduct under normal RS-485 differential-mode signal voltage (generally ≤5V peak value), thus not affecting communication; when a spike of tens of volts occurs on the line, it will momentarily conduct, clamping the potential difference between lines A and B within ten volts, ensuring that the differential-mode voltage of the downstream transceiver chip is always within a safe range.

[0047] In addition, since common-mode interference is mainly filtered to ground through the first and second high-voltage capacitor networks 41 and 44 and the second common-mode choke 43 in this stage, and the bidirectional TVS transistor 42 mainly handles differential-mode interference, it together with the previous second TVS thyristor 31 constitutes a two-stage differential-mode protection to share transient power and further improve the ability to resist fast transient (EFT) and electrostatic discharge (ESD).

[0048] The second common-mode choke 43 functions similarly to the first common-mode choke 21, but is positioned at the final output, focusing on filtering high-frequency common-mode noise and protecting signal integrity. The second common-mode choke 43 is connected in series on lines A and B near the interface. Its selection prioritizes high-frequency impedance and low leakage inductance, making it highly impedance to common-mode interference in the several MHz to hundreds of MHz frequency range, while being almost transparent to differential-mode signals. Thus, when electromagnetic radiation or common-mode pulses generated by switching operations are present around the equipment, the second common-mode choke 43, in conjunction with the first and second high-voltage capacitor networks 41 and 44, isolates and guides residual common-mode interference to ground, preventing coupling into the differential signal. The second common-mode choke 43 can be a choke coil similar to inductor 21, requiring sufficient impedance at high frequencies (e.g., several hundred ohms at 100MHz), a rated current sufficient for RS-485 bus drive current, and consideration of the symmetry of twisted-pair transmission to minimize the impact on differential-mode signals. Through the multi-stage filtering of the residual interference cancellation module 4, the noise and spikes of the RS-485 signal before entering the transceiver are basically eliminated, ensuring stable and reliable communication.

[0049] The present invention also includes a metal shielding cavity and a multi-layer printed circuit board structure. The multi-layer printed circuit board is fixed inside the metal shielding cavity by insulating pillars, and the metal shielding cavity is electrically connected to the grounding layer of the circuit board by screws or press-fit springs to form a complete Faraday cage structure, ensuring that the compartments of each functional module can work safely under electromagnetic shielding. The metal shielding cavity is a conductive shell, and the internal space is divided into four electromagnetic compartments by partitions, which respectively house the primary protection module, the primary filtering module, the residual voltage release module, and the residual interference elimination module. The multilayer printed circuit board has a five-layer structure, including: The top signal layer is used to install the gas discharge tube 11 and the first TVS thyristor 12 of the primary protection module; The second grounding isolation layer is electrically connected to the metal shielded cavity shell and is used to isolate the top layer from the third layer. The third signal layer is used to install the first common-mode choke 21 and resistor network of the primary filter module, as well as the second TVS thyristor 31 and current-limiting resistor of the residual voltage release module. The fourth grounding isolation layer is used to isolate the third layer from the bottom layer, and forms a shielded isolation area at the boundary of each module through a via ground grid; The bottom signal / power layer is used to install the first high-voltage capacitor network 41, bidirectional TVS tube 42, second common-mode choke 43 and second high-voltage capacitor network 44 of the residual interference cancellation module, and leads to the RS-485 transceiver interface. The layers of the multilayer printed circuit board are electrically connected to the input / output terminals of the corresponding modules through blind or buried vias. The first common-mode choke 21 and the second common-mode choke 43 are covered with a high-permeability material shielding sleeve to prevent magnetic saturation and suppress stray coupling. The wiring of the first high-voltage capacitor network 41 and the second high-voltage capacitor network 44 to the ground layer minimizes the loop area, thereby isolating each module in terms of physical structure and electromagnetic shielding and synergistically improving the overall immunity and reliability of the device.

[0050] To adapt to the harsh electromagnetic environment of substations, this invention employs isolation and shielding measures in device layout and printed circuit board design. A multi-layer PCB (e.g., a 5-layer board) is preferred, with the ground plane partitioned: the protective ground (FG, i.e., the metal casing or shielding ground) for surge discharge is separated from the signal ground. In the input area where the primary protection module 1 and primary filter module 2 are located, a large area of ​​metal grounding is arranged as a surge current return path (connected to the frame ground FG). After these high-energy surges are discharged to the FG through the gas discharge tube 11, the first TVS thyristor 12, etc., the current will dissipate to the ground along the nearest ground plane. Multiple grounding vias are provided on the PCB near the input terminals to tightly connect the grounding areas of the discharge tube and TVS tube to the metal casing or ground, ensuring the shortest path for surge current to reach the ground and reducing its distribution on the board. Simultaneously, by isolating the protective ground from the signal layer between PCB layers and surrounding sensitive lines with shielded copper foil / ground plane, inductive coupling of the surge electromagnetic field to subsequent circuits is prevented.

[0051] The components of each functional module are arranged on the circuit board according to their functional zones: primary protection devices (gas discharge tubes, primary TVS, etc.) are installed close to the line input and ground terminals, with the distance between them and the lead length minimized to reduce parasitic inductance and resistance; the inductors and resistors of the filtering module are arranged in the intermediate transition area; fine protection and filtering devices (secondary TVS, capacitor network, final stage common-mode inductor, etc.) are installed close to the line output terminal (i.e., RS-485 transceiver interface). This zoned arrangement isolates high-energy areas from sensitive areas: on the one hand, large surges are mainly closed at the front-end devices and the front-end ground plane, and will not pass through the sensitive device area; on the other hand, the small signal area of ​​the later stage is surrounded by multiple ground planes to form a shielded cavity, which provides good shielding against external electromagnetic fields. The grounding design of the printed circuit board is particularly critical: the frame ground (FG) is used for surge discharge and shielding, and is reliably connected to the equipment chassis and the earth; while the signal ground of the RS-485 transceiver serves as a logic reference ground, and is connected to the FG at only one point through a common-mode inductor, etc. This grounding method ensures that surge current flows through its own ground loop and not through the signal ground, thus avoiding ground potential back interference. Simultaneously, a metal casing or shield encapsulates the entire protection circuit, forming a Faraday cage that provides shielding protection against power frequency high-voltage electric fields and radio frequency interference. One or more layers in a multilayer PCB can be configured as a solid ground layer (FG ground), serving not only as an electromagnetic shielding layer but also as a heat sink to rapidly conduct heat generated by surge energy, improving overall system reliability.

[0052] In summary, through the above layout and shielding design, this device achieves electromagnetic isolation and grounding separation of different functional areas in its structure, which limits strong surges and noise to specific areas and ensures the cleanliness and safety of RS-485 signal lines.

[0053] This protection device further includes an intelligent monitoring module for real-time detection of abnormal surge events on the RS-485 bus. This module acquires transient voltage / current changes on the line via a signal line connected to the RS-485 bus, and the data is sampled and processed by a sampling circuit. A low-power detection unit continuously monitors the sampled signal and immediately generates a maintenance alert signal when an overvoltage or overcurrent surge is detected. For example, the intelligent monitoring module can illuminate an alarm indicator light or send an alarm message via the communication interface after detecting a surge, reminding maintenance personnel to check the operating status of the protection device and perform timely repairs. The purpose of this design is to record and report events when surges that are difficult to detect with the naked eye occur, allowing users to take preventative measures and rationally schedule equipment maintenance. Since RS-485 differential buses are commonly used in industrial environments and exposed to harsh electromagnetic conditions, transient interference such as lightning strikes and power surges can damage the communication ports. The addition of the intelligent monitoring module enables the protection device not only to passively protect against surges but also to actively monitor the frequency and severity of surges, thereby improving the reliability and maintainability of the system.

[0054] Preferably, the sampling circuit uses a high-impedance voltage divider network connected in parallel between RS-485 differential signal lines A and B to form a 10:1 voltage divider, reducing the maximum surge (≤400V differential mode) to ≤40V. A TVS protection element (30V level) is connected in series to prevent overvoltage damage to subsequent circuits; and an RC filter is connected at the voltage divider output to filter out high-speed spike noise and retain the surge envelope. The low-power detection unit uses a low-power comparator (such as TLV7031) or an on-chip MCU (such as TIMSP430FR2xxx series) with a built-in comparator. Its open-drain output drives a general-purpose LED, which is connected to +3.3V through a 330Ω current-limiting resistor. The detection signal drives a small-power relay (5V / 10mA coil), and the normally open contact can be connected in parallel with the monitoring system, closing the contact in a surge event. After sampling, the MCU sends a "surge alarm" frame to the host computer via RS-485 or serial port (UART), with the format referring to Modbus or a custom protocol. Its workflow includes: The sampling circuit samples the voltage divider signal at a low frequency. When the comparator outputs high (no surge), the LED turns off, the relay opens, and the MCU remains in sleep mode. When the voltage divider signal exceeds the threshold, the comparator outputs low, waking up the MCU, lighting up the red LED, activating the relay, and sending an alarm code through the communication port. After a 1-second delay, the comparator determines the surge has ended, the output returns to high level, the MCU resets the relay and turns off the LED, and returns to sleep mode.

[0055] The primary protection module, primary filtering module, residual voltage release module, and residual interference cancellation module of this protection device all adopt a modular design. Each functional module is connected in series to form a complete protection circuit via detachable electrical connectors or terminals. This design allows each functional module to be independently disassembled, replaced, and maintained without disassembling or altering the entire device. For example, when the performance of a certain protection module degrades after multiple surge impacts, maintenance personnel can directly unplug the faulty module and insert a new one without disconnecting the entire device or removing other parts. The modular design greatly improves the ease of maintenance and flexibility of use. On the one hand, users can upgrade or replace a module as needed (e.g., selecting a higher-specification surge suppression module) without affecting other parts; on the other hand, if a module fails, on-site maintenance can complete the replacement in a very short time, minimizing communication system downtime. This plug-and-play modular approach not only reduces maintenance difficulty and cost but also improves the reliability and lifespan of the device during long-term operation. It is worth mentioning that the modular connector design also ensures the reliability of the module connections and low contact resistance, guaranteeing the integrity of high-speed differential signal transmission.

[0056] Preferably, a 5-layer backplane PCB is installed inside the metal shielded cavity, with slots on both sides or top of the backplane. The four functional modules are each made into an independent daughter card / board. The daughter card edges have gold fingers or crimp pins, which, when engaged with the backplane slots, complete the A / B signal, grounding, and shielding connections. Internal partitions physically divide each daughter card into four EMI compartments; the backplane ground layer is connected to the partitions and cavity shell at multiple points via spring clips, forming continuous shielding. During operation, if a stage (such as the residual voltage release module) fails, simply open the cavity cover, remove the corresponding daughter card, and insert a replacement card. The entire operation is completed within minutes without disassembling other stages. The backplane has pre-installed positioning pins and connector guides for each daughter card to ensure accurate positioning during repeated insertion and removal, avoiding misinsertion.

[0057] The backplane slots must meet surge current carrying capacity (≥5kA / 20µs) and differential impedance control (≈120Ω). A hierarchical pinout structure, with signal pins contacting first and ground pins contacting later, prevents signals from being suspended during insertion and removal. The cavity partition and the metal surface of the daughter card are pressed together by springs / finger springs, maintaining 360° shielding continuity. Inter-module serial logic is hardwired on the backplane copper layer according to the aforementioned "four-level sequence," ensuring that daughter card replacement does not affect signal flow.

[0058] This protection device is also equipped with a main surge protection module, which has a self-recovery protection function. In the event of overvoltage or overcurrent surge, it can temporarily cut off or limit the current path and automatically restore normal operation after the fault is cleared. This self-recovery function consists of the following two parts: Thermistor: Thermistors (such as positive temperature coefficient thermistors (PTC) or resettable fuses) are connected in series in RS-485 differential signal lines A and / or B. When an abnormal overvoltage or overcurrent surge occurs on the bus line, the thermistor's resistance rises rapidly upon heating, temporarily interrupting or significantly limiting the current flowing through the line. This process is equivalent to adding a dynamic current limiter to the circuit, preventing excessive surge current from directly entering subsequent circuits and causing damage. After the surge, once the thermistor cools down, its resistance automatically returns to a low-resistance state, thus re-conducting the signal line and restoring normal communication. In this way, the thermistor momentarily trips to protect the circuit during a surge and automatically resets afterwards, without requiring manual replacement of the fuse, demonstrating excellent self-resetting characteristics.

[0059] It should be noted that the selection of the thermal element should take into account the normal operating current and voltage of the RS-485 bus to ensure that its impedance is very small during normal communication and does not affect signal transmission.

[0060] When an abnormal surge occurs, the overheating failure state of the thermistor can effectively limit the duration of the fault current, protecting downstream precision components from overcurrent impact. Without such a self-resetting current-limiting component, the large current caused by the surge may continue to flow through the transient suppression component and quickly burn it out. Therefore, the thermistor is crucial for ensuring the durability of the entire protection circuit.

[0061] Redundant transient suppression protection element: This part consists of at least two transient suppression diodes (TVS diodes) connected in parallel across signal line A and signal line B, used to clamp and limit transient surge voltages between bus differential lines.

[0062] Compared to traditional protection using a single TVS device, parallel TVS diodes offer a redundant design: when one TVS fails due to a severe surge overload (such as short circuit breakdown or performance degradation), the other parallel TVS continues to operate normally, thus providing clamping protection for subsequent surges and ensuring the continuity and reliability of the protection function. Using multiple protection devices in parallel also distributes surge energy, reducing the stress on individual devices.

[0063] For example, in this embodiment, two TVS diodes with slightly different rated clamping voltages are connected in parallel: when a surge occurs on the bus, the TVS with the lower clamping voltage will conduct first to clamp the voltage; in extreme cases, if it fails due to overload, the other TVS with a slightly higher clamping voltage can continue to provide protection and limit the surge voltage. This differentiated parallel design allows both devices to share the current and reduce residual voltage under normal surge conditions, while also ensuring that if one device fails, the other can still independently perform the protection task. By increasing the redundancy of surge protection, the device can maintain effective protection of the communication line even in multiple lightning surge events, avoiding the risk of protection failure due to the failure of a single protective component.

[0064] It is important to note that to achieve the above effects, well-matched TVS diodes should be selected, and their rated breakdown / clamping voltages should be within the safe range of the RS-485 bus. Furthermore, the layout of parallel devices should be as symmetrical as possible to reduce parasitic differences, thereby improving the uniformity of current distribution.

[0065] In summary, this specific embodiment introduces a self-recovering protection circuit composed of a thermistor and redundant TVS, enabling the RS-485 bus protection device to possess overcurrent protection capabilities of "rapid disconnection and automatic recovery" and surge voltage suppression capabilities of "dual clamping." The thermistor provides short-term fault isolation, preventing continuous fault current from damaging the protection components and communication equipment; the redundant TVS network provides stronger surge absorption capacity and fault tolerance. The combination of these two features allows the device to maintain its protection performance even after withstanding multiple surge impacts, greatly improving the stability and safety of the RS-485 bus in complex electromagnetic environments. Through the organic combination of the above modules and components, the RS-485 bus passive protection device of this invention can effectively protect communication lines and monitoring equipment when surge interference such as lightning strikes and electrical fast transients occurs, while also providing timely maintenance reminders and facilitating rapid recovery afterward, better meeting the requirements of substation online monitoring equipment for communication reliability and maintainability. In this embodiment, the intelligent monitoring module and the main surge protection module are separated by ≥20mm on the PCB, and a ground isolation groove is used to separate them from the ground plane to ensure that high-voltage surges do not leak into the low-voltage sampling circuit. The sampling circuit and comparator circuit should be placed on the signal ground layer of the PCB, and the signal ground and the protective ground should be connected at only one point (the casing grounding point) to avoid ground loop interference.

[0066] This invention is specifically designed for the communication interface of industrial control equipment such as substation online monitoring systems. These devices are frequently deployed in high-voltage substations, and the RS-485 communication lines may be routed long distances outdoors, making them highly susceptible to interference from lightning strikes, power operation overvoltages, and electromagnetic pulses. Without adequate protection, surge impacts can damage the interface chip, and strong interference can lead to communication interruptions and bit errors, severely impacting the reliability of online monitoring.

[0067] This invention utilizes a multi-stage series network of passive devices to achieve graded interception and absorption of various overvoltages and electromagnetic interferences. The primary protection module withstands and discharges surges of several thousand volts, the intermediate module gradually dissipates residual energy and filters out mid-frequency pulse interference, and the final module further refines the filtering and clamps minute transients to ensure stable output port voltage. The entire protection process requires no power supply, and all devices are passive components, resulting in high reliability and rapid response, capable of responding to transient events in the nanosecond range. RS-485 interfaces protected by this device show significantly improved surge withstand levels (e.g., meeting the IEC61000-4-5 common-mode and differential-mode 4kV surge test requirements), fast burst immunity (±2kV level with no communication interruption under IEC61000-4-4 standard), and electrostatic discharge protection level (IEC61000-4-2 contact discharge above 8kV).

[0068] Compared with existing technologies, this invention solves the technical problem of simultaneously addressing surge protection and interference resistance in existing RS-485 interfaces through a multi-module collaborative passive protection architecture. It significantly improves the interface's anti-interference capability without affecting normal communication performance. Practical applications show that in substation environments with frequent thunderstorms and strong interference, the device of this invention effectively protects the communication interfaces of monitoring equipment from damage, maintaining stable and continuous data transmission. This provides crucial support for the long-term reliable operation of online monitoring systems, demonstrating significant technological advancements and beneficial effects.

[0069] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A passive protection device for RS-485 bus used in online monitoring equipment of substations, characterized in that: It includes a primary protection module, a primary filtering module, a residual voltage release module, and a residual interference cancellation module, which are connected in series along the RS-485 bus signal path. Each module works in sequence to provide hierarchical protection for the RS-485 bus. The primary protection module is used to discharge the high-voltage inrush current generated by lightning strikes and surges. The primary filtering module is used to attenuate the pulse group interference signal in the bus. The residual voltage release module is used to perform secondary clamping on the residual high voltage and slowly release the residual charge. The residual interference cancellation module is used to filter out the remaining interference signal, thereby ensuring normal communication.

2. The protection device according to claim 1, characterized in that: The primary protection module includes a gas discharge tube and a first TVS thyristor; The two terminals of the gas discharge tube are directly connected to signal line A and signal line B at the RS-485 differential interface, respectively, so as to conduct the surge current into the protective ground when a high voltage surge occurs on either signal line. The first TVS thyristor is connected across signal line A and signal line B at the interface, with its positive and negative terminals directly connected to signal line A and signal line B, respectively, to provide transient clamping overvoltage when the differential mode voltage exceeds its clamping voltage. The output terminals of signal lines A and B of the primary protection module are respectively connected to the input terminals of signal lines A and B of the primary filter module, ensuring that the differential signal processed by the primary protection module can be correctly sent to the primary filter module for subsequent processing.

3. The protection device according to claim 1, characterized in that: The primary filter module includes a first common-mode choke and a resistor network; The first common-mode choke has a first winding and a second winding wound on the same magnetic core. The first winding is connected in series to signal line A after the primary protection module, and the second winding is connected in series to signal line B after the primary protection module. The two windings have the same number of turns and the same winding direction, so as to maintain a low impedance path for differential-mode signals while suppressing common-mode interference. The resistor network consists of a first resistor and a second resistor. One end of the first resistor is connected to the signal line A at the rear end of the first common mode choke, and the other end serves as the output terminal of the signal line A of the primary filter module and is connected to the input terminal of the signal line A of the residual voltage release module. One end of the second resistor is connected to the signal line B at the rear end of the first common mode choke, and the other end serves as the output terminal of the signal line B of this module and is connected to the input terminal of the signal line B of the residual voltage release module. The resistor network is used to dampen and attenuate the residual differential mode pulse group interference signal.

4. The protection device according to claim 1, characterized in that: The residual voltage release module includes a second TVS thyristor and a current-limiting resistor; the current-limiting resistor includes a third resistor and a fourth resistor; The second TVS thyristor is connected between RS-485 differential signal line A and signal line B after passing through the primary filter module. It is used to conduct and transiently clamp the high voltage when the differential mode voltage between signal line A and signal line B exceeds its clamping voltage. One end of the third resistor is connected to the connection node between the second TVS thyristor and signal line A, and the other end serves as the output terminal of signal line A of the residual voltage release module and is connected to the input terminal of signal line A of the residual interference cancellation module. One end of the fourth resistor is connected to the connection node between the second TVS thyristor and signal line B, and the other end serves as the output terminal of signal line B of the residual voltage release module and is connected to the input terminal of signal line B of the residual interference cancellation module. After the second TVS thyristor is released from clamping, the third and fourth resistors limit and dampen the residual inrush current on the two signal lines, respectively, gradually releasing the remaining energy and thus protecting the subsequent circuits.

5. The protection device according to claim 1, characterized in that: The residual interference cancellation module includes the following components arranged in sequence at the output terminal of the residual voltage release module: a first high-voltage capacitor network, a bidirectional TVS diode, a second common-mode choke, and a second high-voltage capacitor network. The first high-voltage capacitor network consists of at least two capacitors, which are connected across signal line A and signal line B after processing by the residual voltage release module, and are used to filter out differential-mode high-frequency interference generated after secondary clamping. The bidirectional TVS diode is connected in parallel between signal line A and signal line B to achieve transient clamping when transient voltage spikes of positive and negative polarities occur. The second common-mode choke includes a third winding and a fourth winding wound on the same magnetic core. The third winding is connected in series to signal line A after passing through the first high-voltage capacitor network and the bidirectional TVS tube, and the fourth winding is connected in series to signal line B after passing through the first high-voltage capacitor network and the bidirectional TVS tube. The two windings have the same number of turns and the same winding direction, so as to further suppress common-mode noise and maintain the differential-mode signal channel. The second high-voltage capacitor network consists of several capacitors and is connected across signal line A and signal line B at the output of the second common-mode choke. It is used to perform secondary filtering on the differential-mode high-frequency interference remaining after common-mode suppression. The input terminals of the first high-voltage capacitor network and the bidirectional TVS tube are respectively connected to the output terminals of signal line A and signal line B of the residual voltage release module. The output terminal of the second common-mode choke is respectively connected to the input terminals of signal line A and signal line B of the RS-485 transceiver interface of the online monitoring equipment, ensuring that the differential signal after filtering and clamping by the module can be correctly sent to the subsequent RS-485 transceiver.

6. The protection device according to claim 1, characterized in that: It also includes an intelligent monitoring module, which is connected to the RS-485 bus signal line for real-time surge detection. The intelligent monitoring module includes a sampling circuit and a low-power detection unit. The sampling circuit samples abnormal surge voltage or current on the RS-485 bus line, and the low-power detection unit determines the occurrence of a surge based on the sampling signal and outputs a maintenance signal to prompt equipment maintenance or condition maintenance.

7. The protection device according to claim 1, characterized in that: The primary protection module, primary filtering module, residual voltage release module, and residual interference elimination module all adopt a modular structure design. Adjacent modules are connected in series through detachable electrical connectors or terminals, thereby enabling each functional module to be independently disassembled, replaced, and maintained, improving the ease of device maintenance.

8. The protection device according to claim 1, characterized in that: It has self-recovery protection features, including: A thermistor is connected in series to at least one of the RS-485 differential signal lines A and B. When overvoltage or overcurrent surge occurs, its resistance increases due to heat to temporarily cut off or limit the current path. It automatically resumes conduction after the temperature drops. The redundant transient suppression protection element is connected in parallel between signal line A and signal line B. It consists of at least two TVS devices. When one TVS device fails due to overload, the other TVS device can still continue to clamp the surge voltage to ensure the continuity and reliability of the protection function.

9. The protection device according to claim 8, characterized in that: The thermal element is a positive temperature coefficient thermistor or a self-resetting fuse; The redundant transient suppression protection element consists of at least two TVS diodes connected in parallel, with different rated clamping voltages for the two TVS diodes to share surge energy and maintain clamping function by the other when one fails.

10. The protection device according to claim 1, characterized in that: It also includes a metal shielding cavity and a multi-layer printed circuit board structure. The multi-layer printed circuit board is fixed inside the metal shielding cavity by insulating pillars, and the metal shielding cavity is electrically connected to the grounding layer of the circuit board by screws or press-fit springs to form a complete Faraday cage structure, ensuring that the compartments of each functional module can work safely under electromagnetic shielding. The metal shielding cavity is a conductive shell, and the internal space is divided into four electromagnetic compartments by partitions, which respectively house the primary protection module, the primary filtering module, the residual voltage release module, and the residual interference elimination module. The multilayer printed circuit board has a five-layer structure, including: The top signal layer is used to install the gas discharge tube and the first TVS thyristor of the primary protection module; The second grounding isolation layer is electrically connected to the outer shell of the metal shielding cavity and is used to isolate the top layer from the third layer. The third signal layer is used to install the common-mode choke and resistor network of the primary filter module, as well as the second TVS thyristor and current-limiting resistor of the residual voltage release module. The fourth grounding isolation layer is used to isolate the third layer from the bottom layer, and forms a shielded isolation area at the boundary of each module through a via ground grid; The bottom signal / power layer is used to install the first high-voltage capacitor network, bidirectional TVS diode, second common-mode choke, and second high-voltage capacitor network of the residual interference cancellation module, and is led out to the RS-485 transceiver interface. The layers of the multilayer printed circuit board are electrically connected to the input / output terminals of the corresponding modules through blind or buried vias. The first and second common-mode chokes are covered with high-permeability material shielding sleeves to prevent magnetic saturation and suppress stray coupling. The wiring of the first and second high-voltage capacitor networks and the ground layer minimizes the loop area, thereby isolating each module in terms of physical structure and electromagnetic shielding and synergistically improving the overall immunity and reliability of the device.

Images