A method for preventing misoperation of an electrical device and a density relay

Abstract

The application provides an electrical equipment anti-misoperation locking control method and a density relay, and belongs to the technical field of intelligent relays, and comprises the following steps: acquiring the absolute pressure and the gas body temperature of an SF6 gas chamber in real time; calculating the saturated vapor pressure based on the gas body temperature, and determining whether the gas enters a liquefied coexistence state by comparing the absolute pressure with the saturated vapor pressure; if it is determined that the gas enters the liquefied coexistence state, taking the insulation strength of the remaining gas phase as the basis for locking decision; when the insulation margin is sufficient, forcibly shielding the physical locking contact; when the insulation margin is insufficient, unshielding and outputting a locking signal. The application fills the leakage monitoring blind area during the liquefied shielding locking period, realizes the closed-loop safety monitoring of SF6 electrical equipment in the whole temperature range and the whole life cycle, and has high engineering practicability, and can be directly applied to the upgrading and modification of existing density relays without large-scale modification of primary equipment.

Description

Technical Field

[0001] This invention belongs to the field of intelligent relay technology, and particularly relates to a method for preventing misoperation and interlocking control of electrical equipment and a density relay. Background Technology

[0002] Sulfur hexafluoride (SF6) gas possesses excellent insulation and arc-quenching properties, making it widely used in high-voltage electrical equipment. Density relays are core safety components used to monitor the density of SF6 gas inside such equipment. SF6 is not an ideal gas; at room temperature, its pressure and temperature exhibit an approximately linear relationship. However, in the low-temperature, high-pressure range, its gas law demonstrates significant nonlinear characteristics. When the ambient temperature drops below its corresponding saturation temperature, SF6 undergoes a phase transition from gaseous to liquid state, causing a significant drop in pressure within the gas chamber along the saturated vapor pressure curve.

[0003] Currently, mainstream density relays are mainly divided into two categories: mechanical and electronic. Mechanical density relays rely on bimetallic strips for temperature compensation. They have a simple overall structure, but their detection accuracy is relatively low and they cannot handle gas-liquefaction conditions. Once the gas liquefies, the pressure loss caused by the phase change cannot be offset by the temperature compensation mechanism, and the equipment will directly trigger an alarm or lockout action.

[0004] Electronic density relays are currently the mainstream form used in the industry, and their typical structure is shown in the attached manual. Figure 3 As shown, it mainly consists of a metal casing, wiring terminals, a pressure acquisition interface, a status display panel, and function buttons; its internal core circuit structure is shown in the attached instruction manual. Figure 4 As shown, a typical structure includes a pressure sensor, a temperature sensor, a signal conditioning circuit, a microcontroller, a storage unit, a relay output circuit, and a power supply module. Electronic density relays calculate gas density by collecting pressure and temperature parameters and relying on the ideal gas law or simple empirical formulas.

[0005] In low-temperature operating conditions, sulfur hexafluoride (SF6) is highly susceptible to liquefaction. After liquefaction, the pressure in the gas chamber drops significantly, typically falling below the relay's preset lockout threshold. Current technologies generally employ a single pressure threshold judgment logic, identifying a low-pressure state as a media leakage fault and disconnecting the circuit breaker's operating circuit. However, in reality, some gaseous media remains inside the equipment after liquefaction. The insulation properties of this gaseous media differ significantly from those before liquefaction, but current technologies cannot accurately assess the actual insulation capacity under these conditions. This simplistic protection judgment logic in existing technologies easily leads to unnecessary equipment lockouts and unplanned shutdowns. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, this invention provides a method for preventing misoperation and interlocking control of electrical equipment, along with a density relay. This method acquires the absolute pressure of the gas chamber and the temperature of the gas itself in real time. Based on the temperature, it calculates the saturated vapor pressure and compares it with the absolute pressure to determine whether the gas has entered a liquefied coexistence state. Once a liquefied coexistence state is determined, the pressure or density criteria relied upon in existing technologies are abandoned, and only the insulation strength of the remaining gas phase is used as the basis for the interlocking decision. When the insulation margin is sufficient, the physical interlocking contacts are forcibly shielded to maintain normal equipment operation; only when the insulation margin is insufficient is the shielding released and an interlocking signal output. The liquefaction determination uses a dynamic adaptive warning temperature, which is obtained by iteratively solving the phase transition critical temperature from the parameters of the initial state of the equipment using the real gas state equation, and then superimposing a safety margin. The insulation strength is calculated by substituting the saturated gas phase density, derived from the inversion of the saturated vapor pressure and the gas body temperature, into an insulation breakdown model. This model is a modified Paschen model incorporating an electric field uniformity coefficient and a nonlinear exponent; all parameters are calibrated through a true power frequency withstand voltage test under extremely cold conditions. In the non-liquefied stage, a two-dimensional decision logic is constructed through long-cycle trend extraction and correlation analysis to distinguish between sensor temperature drift and actual minute leaks. When the ambient temperature changes drastically, a recursive least squares method with a forgetting factor is used to identify the equipment's thermal time constant online and dynamically compensate for thermal hysteresis errors. When the gas recovers from a liquefied coexistence state to a pure gas phase, the baseline equivalent pressure before liquefaction is compared with the current equivalent pressure after recovery, and a delayed leakage alarm is issued for out-of-tolerance operating conditions. This invention eliminates the problem of false lockout caused by a single pressure criterion under liquefied conditions.

[0007] The present invention specifically adopts the following technical solution:

[0008] This invention provides a method for preventing misoperation and interlocking control of SF6 electrical equipment. The core innovation of this method lies in changing the protection logic paradigm under specific operating conditions: after acquiring the absolute pressure and gas body temperature of the SF6 gas chamber in real time, the saturated vapor pressure corresponding to the current temperature is calculated based on the gas body temperature, and the gas is compared with the measured absolute pressure to determine whether the gas has entered a liquefied coexistence state; once it is determined that the gas has entered a liquefied coexistence state, the insulation strength of the remaining gas phase can be used as the (sole) basis for the interlocking decision, abandoning the traditional pressure or density criteria that have become invalid at this time: when the insulation margin is sufficient, the physical interlocking contacts are forcibly shielded to maintain the continued operation of the equipment; when the insulation margin is insufficient, the shielding is released and an interlocking signal is output to ensure safety.

[0009] The underlying basis for this criterion switching is that when SF6 liquefies, the pressure in the gas chamber drops sharply along the saturated vapor pressure curve, easily falling below the traditional low-pressure lockout threshold. However, the insulation strength of the remaining gas phase is not simultaneously lost, and the equipment still has the conditions for safe operation with liquid. The design provided by this invention breaks through the long-standing industry assumption that "pressure / density is directly equivalent to insulation strength," and makes decisions directly based on actual insulation capacity, solving the problem of false lockout under extremely cold liquefaction conditions.

[0010] In a preferred embodiment of the present invention, the determination of the liquefied coexistence state does not rely on a fixed temperature threshold, but rather employs a dynamic adaptive warning temperature. This warning temperature is obtained by iteratively solving the phase transition critical temperature corresponding to the current density using the real gas law based on the absolute pressure and temperature after the initial inflation of the equipment, and then adding an engineering safety margin. Since the initial inflation pressure of equipment in different intervals varies, their liquefaction critical temperatures also differ significantly. The dynamically calculated adaptive threshold can automatically adapt to the specific initial state of each equipment, avoiding misjudgments or omissions of phase transitions caused by fixed threshold schemes.

[0011] Regarding the quantitative standard for insulation margin, in a preferred embodiment of this invention, sufficient insulation margin means that the critical breakdown voltage of the remaining gas phase is greater than 1.15 times the rated phase voltage of the equipment. This safety factor comprehensively considers the insulation redundancy required by relevant technical standards and the operating overvoltage level that may occur during system operation, and explores the equipment's ability to operate with liquid in extremely cold environments while ensuring the insulation safety of the equipment.

[0012] Regarding the specific method for obtaining insulation strength, this invention further employs the following calculation steps: based on the saturated vapor pressure and gas volume temperature used to determine the liquefied coexistence state, the remaining saturated gas phase density is obtained by inversion; this remaining saturated gas phase density is substituted into a preset insulation breakdown model to calculate the critical breakdown voltage. This calculation process establishes a quantitative correlation between externally measurable macroscopic thermodynamic parameters and internal microscopic insulation performance. In the liquefied coexistence state, gaseous and liquid SF6 coexist in the gas chamber. The liquid portion no longer participates in the insulation process. By inverting the remaining gas phase density based on saturation parameters, the interference of liquid mass can be accurately eliminated, truly reflecting the actual state of the gaseous medium participating in insulation.

[0013] Furthermore, the aforementioned insulation breakdown model is constructed using a modified Paschen's law. The model incorporates the inherent contact gap of the circuit breaker's arc-extinguishing chamber and introduces two characteristic parameters closely related to the equipment structure: the electric field uniformity coefficient and the nonlinearity index. The electric field uniformity coefficient characterizes the degree of electric field distortion in the contact region and is calibrated based on extreme cold full-scale power frequency withstand voltage test data for multiple equipment models, with a value ranging from 0.75 to 0.95. The nonlinearity index reflects the nonlinear characteristics of SF6 gas discharge breakdown under low temperature and high density conditions, with a value ranging from 0.80 to 0.90. Both parameters are calibrated using nonlinear fitting methods in extreme cold full-scale power frequency withstand voltage tests for specific equipment models. This transforms the insulation assessment model from a general theoretical formula into a customized assessment tool adapted to the specific arc-extinguishing chamber structure of the equipment, resulting in engineering-grade reliability.

[0014] Under normal operating conditions, before the gas enters a liquefied coexistence state, this invention executes a pure gas-phase leak diagnosis logic. This logic extracts the trend of normalized pressure over time through a long-period sliding time window, and simultaneously analyzes the correlation between normalized pressure and the gas volume temperature, thereby constructing a decision space based on two dimensions: trend direction and temperature-pressure correlation. This allows for the differentiation of pressure drops caused by two different reasons: pressure changes caused by sensor temperature drift are highly correlated with ambient temperature fluctuations, while continuous pressure drops caused by actual minute gas leaks are unrelated to temperature changes. This two-dimensional decision logic eliminates long-term slow drift interference caused by sensor aging, significantly improving the accuracy of minute leak diagnosis.

[0015] To cope with special operating conditions such as cold waves and drastic changes in ambient temperature, this invention, based on the simultaneous acquisition of the gas body temperature inside the gas chamber and the ambient temperature outside the relay, incorporates a dynamic thermal hysteresis compensation function. When the rate of change in ambient temperature exceeds a preset threshold, the thermal time constant of the equipment is identified online using a recursive least squares method with a forgetting factor, dynamically compensating for the gas temperature measurement lag caused by the thermal inertia of the metal casing and the resulting pressure calculation deviation. A dual-temperature-source collaborative architecture is adopted: the gas body temperature sensor directly senses the temperature of the insulating medium, ensuring the accuracy of phase change determination and density calculation; the ambient temperature sensor acts as a feedforward signal, capturing the dynamic trend of cold waves in advance, providing a basis for thermal hysteresis compensation. The recursive least squares method with a forgetting factor can track the slow evolution of the equipment's thermal characteristics in real time, ensuring the compensation effect remains effective throughout the entire equipment lifecycle and avoiding false pressure drop signals caused by thermal hysteresis.

[0016] To further reduce monitoring blind spots, this invention also includes a leak tracing step during the liquefaction recovery period. When the system detects that the gas has completely recovered from a liquefied coexistence state to a pure gas phase state, the tracing mechanism is automatically triggered: the reference equivalent pressure frozen and stored before liquefaction is read and compared with the current equivalent pressure after the gasification recovery and stabilization. If the difference between the two exceeds the preset leak tolerance, it indicates that a real gas leak occurred during the liquefaction lockout shielding period, and the system reissues a delayed leak alarm signal. During the liquefaction lockout stage, traditional pressure monitoring methods cannot effectively identify continuous micro-leakage. This tracing mechanism, by comparing the reference states before and after liquefaction, incorporates the monitoring blind spots during liquefaction into the post-event tracing coverage, compensating for the risk of missed leaks during the state transition period.

[0017] Based on the same inventive concept, this invention also provides an intelligent SF6 density relay. This relay consists of a dual-temperature-source sensing unit, a microcontroller unit, and a signal output unit. The dual-temperature-source sensing unit synchronously collects the absolute pressure of the gas chamber, the gas body temperature, and the ambient temperature, providing raw sensing data for all subsequent calculations and decisions. The microcontroller unit is electrically connected to the dual-temperature-source sensing unit and integrates all the algorithm logic of any of the aforementioned anti-misoperation interlocking control methods, independently completing the complete calculation and decision-making process from liquefaction identification, insulation assessment, leakage diagnosis, thermal hysteresis compensation to leakage tracing. The signal output unit is electrically connected to the microcontroller unit and, based on the decision result of the microcontroller unit, implements forced shielding or normal output for the physical interlocking contacts of the circuit breaker.

[0018] This relay integrates the innovative control method described in this invention into a single device. It is compatible with the mechanical interfaces and electrical circuits of existing high-voltage switchgear, and can operate independently without relying on the substation backend system or additional communication network. It can directly replace existing mechanical or electronic density relays, has strong engineering applicability, and is easy to upgrade and modify on site.

[0019] Compared to existing technologies, this invention and its preferred embodiment introduce a residual gas phase insulation strength criterion in the liquefaction coexistence state, which can reduce the possibility of triggering a lockout based on a single pressure or density threshold due to SF6 gas liquefaction; through thermal hysteresis compensation, it can reduce false alarms due to low gas pressure caused by rapid changes in ambient temperature; through the joint discrimination of normalized pressure trend and temperature-pressure correlation, it helps to distinguish between sensor temperature drift and minor gas leaks; through leakage tracing during the liquefaction recovery period, it can supplement the judgment of leaks that may occur during liquefaction. This solution can be integrated into the density relay control unit and used for upgrading existing equipment, provided that interface conditions are met. Attached Figure Description

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0021] Figure 1This is a flowchart illustrating the overall process of an embodiment of the present invention.

[0022] Figure 2 This is a comparison chart of the SF6 saturated vapor pressure fitting curve and experimental data in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of an electronic density relay.

[0024] Figure 4 This is a typical circuit block diagram of an electronic density relay. Detailed Implementation

[0025] In the following, specific embodiments of this application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand and implement this application. Without departing from the principles of this application, features from various embodiments can be combined to obtain new implementations, or certain features from some embodiments can be substituted to obtain other preferred implementations.

[0026] To make the features and advantages of the present invention more apparent and understandable, specific embodiments are described below in conjunction with the accompanying drawings:

[0027] Existing intelligent SF6 density relay devices generally lack gas phase change recognition capabilities, relying solely on a single insulation judgment criterion for monitoring. They also suffer from issues such as thermal response lag and insufficient algorithm accuracy, making them prone to misjudgments in low-temperature environments and exhibiting dynamic calculation errors during operation. For extremely cold environments (-30℃ to -50℃) and conditions with drastic temperature fluctuations, traditional equipment exhibits three typical fault problems: First, low temperatures cause SF6 gas to liquefy, leading to a drop in gas chamber pressure. The equipment cannot distinguish between natural gas liquefaction and severe leakage, resulting in false circuit breaker blocking and affecting normal power supply. Second, when the external temperature drops sharply, the cooling rate of the gas inside the metal tank lags behind the ambient temperature change. Single-point temperature measurement methods cannot correct this deviation, ultimately causing thermal hysteresis false alarms due to distorted density calculations. Third, the equipment struggles to differentiate between zero-point drift caused by sensor aging and genuine micro-leakage, hindering effective micro-leakage monitoring.

[0028] This invention provides an intelligent density relay equipped with dual temperature source sensing, Betty-Bridgeman density calculation, and insulation critical strength criterion. It combines algorithmic prediction to eliminate false alarms caused by thermal hysteresis. When SF6 gas liquefies, it determines whether the equipment should perform a lockout operation based on the actual insulation strength, thereby ensuring continuous and safe operation of the power grid in extremely cold environments. The solution establishes a complete operational logic around phase state recognition, insulation determination, fault differentiation, dynamic compensation, and leakage tracing, forming a comprehensive global state arbitration mechanism.

[0029] This solution first relies on the Antoine equation to compare the absolute pressure of the gas with the saturated vapor pressure, completing the precise determination of the liquefaction phase change of SF6 gas. When it is detected that the gas enters the liquefied state, the pure gas-phase monitoring algorithm is actively paused to avoid false leakage alarms caused by the cold shrinkage of the gas. For the problem of mislocking under liquefaction conditions, the solution abandons the traditional single density criterion and adopts an insulation inversion idea for control: combining the gas state equation to calculate the remaining saturated gas-phase density after liquefaction, and then solving the critical breakdown voltage by modifying the Paschen's law. When the insulation margin meets the operation requirements, the locking signal is directly blocked to avoid misoperation of the equipment.

[0030] Under the normal operating state where the gas remains in the pure gas phase, the solution uses the Beattie-Bridgeman equation to calculate the equivalent pressure, extracts the slope of the pressure change and the temperature correlation coefficient with a long-period sliding window, constructs a two-dimensional decision matrix, and relies on multi-dimensional features to effectively distinguish the zero drift of the sensor from real minor leaks. For the thermal hysteresis problem caused by sudden temperature changes, the system uses the recursive least squares method with a forgetting factor to online identify the thermal time constant of the equipment, complete dynamic thermal compensation, and eliminate false low-pressure alarms caused by cold snaps; at the same time, a freezing difference method is set. After the equipment returns from the liquefied state to the gas phase state, the pressure data difference before and after liquefaction is compared to retrospectively report the leakage problems generated during the suspension stage of liquefaction monitoring and fill the monitoring blind area.

[0031] The whole set of solutions forms a full-process closed-loop monitoring and protection system for SF6 density relays under extremely cold conditions. The liquid insulation inversion technology solves the problems of mislocking and mis-tripping triggered by gas liquefaction in traditional equipment, and improves the power supply reliability of the power grid in extremely cold environments by relying on the insulation margin control mechanism. The two-dimensional decision matrix under the pure gas-phase condition can accurately distinguish sensor abnormalities from medium micro-leaks, reducing ineffective maintenance work; the dynamic thermal compensation model can effectively resist the interference caused by sudden temperature changes and suppress mis-alarms of the thermal hysteresis type. The leakage traceability mechanism supporting the liquefaction stage improves the anti-interference ability and stability of equipment operation as a whole, ensuring the safe operation of power grid facilities under extreme climate conditions.

[0032] This invention does not require any adjustment to the hardware structure and working principle of the existing electronic density relay. All functional improvements can be achieved only by rewriting and burning the control firmware inside the microcontroller. This implementation method has extremely strong compatibility. It can be directly applied to the online firmware upgrade of the already put-into-operation electronic density relay, or integrated into the factory firmware of newly produced equipment, greatly reducing the transformation cost and promotion difficulty of technology implementation.

[0033] This invention reconstructs the core control logic paradigm of existing electronic density relays, replacing the original single density threshold determination architecture with a global state arbitration architecture. The firmware integrates a phase state determination module, an insulation inversion calculation module, a two-dimensional fault diagnosis module, a dynamic thermal compensation module, and a leakage tracing module. These modules work collaboratively to achieve seamless monitoring and protection across all operating conditions, from pure gaseous phase to liquefied phase. Pressure and temperature data acquired by the original hardware are directly input into the new control logic, and after multi-dimensional calculations and state arbitration, the final alarm and interlock control signals are output.

[0034] The present invention will be further illustrated and described below with reference to the accompanying drawings and through more specific embodiments:

[0035] like Figure 1 As shown, this invention provides an intelligent anti-misoperation interlocking SF6 density relay system and method based on dual-temperature source sensing and a multi-dimensional state arbitration mechanism. This system overcomes the limitations of traditional relays that rely solely on pressure thresholds, and through state arbitration, track-specific processing, and full-cycle traceability, achieves accurate assessment and anti-misoperation protection of the insulation status of SF6 equipment under extremely cold conditions.

[0036] First, the system, based on dual-temperature source sensing and phase arbitration mechanisms, achieves accurate qualitative analysis of the equipment's operating status. The system simultaneously collects the absolute pressure of the gas chamber (…). ), gas volume temperature ( ) and ambient temperature ( Using the gas volume temperature as a reference, the saturated vapor pressure of SF6 at the current temperature is calculated in real time using the Antoine equation. By comparing the measured absolute pressure with the calculated saturated vapor pressure, the system's built-in global phase arbitration module can accurately determine whether the equipment has entered a liquefied coexistence state. Once liquefaction is determined to have occurred, the system immediately triggers a "normal monitoring suspension" mechanism, switching the operating mode from simple physical parameter monitoring to a special liquefied state processing procedure, thereby physically isolating the interference of the sudden pressure drop caused by the phase change on subsequent algorithms.

[0037] Secondly, differentiated control strategies are implemented for different phase states to achieve insulation capacity inversion from physical parameter monitoring. In the extremely cold liquefied state, the system abandons the traditional density / pressure lockout logic and instead performs insulation strength inversion assessment. The MCU uses the Beattie-Bridgeman real gas equation of state to calculate the density of the remaining undiluted gas phase based on measured pressure and temperature. Subsequently, the inverted gas phase density was substituted into the modified Paschen's law model calibrated by a full-scale experiment to calculate the actual insulation breakdown voltage of the current remaining gas phase. By comparing the breakdown voltage with a set safety margin threshold (such as 1.15 times the rated voltage), the system makes a final decision to prevent false tripping: if the insulation margin is sufficient, it actively shields the traditional physical interlocking signal and outputs a "permit liquid-cooled reduced voltage operation" command to avoid false tripping in extremely cold environments; if the margin is insufficient, it executes forced interlocking to protect the equipment.

[0038] Finally, a multi-dimensional anti-disturbance diagnosis and a recovery-period leak tracing mechanism are integrated under normal pure gas phase conditions to achieve blind-spot-free monitoring throughout the entire lifecycle. In the undiluted state, the system differentiates operating conditions by monitoring the rate of change in ambient temperature: during sudden temperature changes (such as a cold wave), the FF-RLS algorithm is used to identify the thermal time constant online and predict the hysteresis-free theoretical pressure to shield against false low-pressure alarms caused by thermal inertia; when the temperature is stable, a two-dimensional decision matrix is ​​constructed using the pressure change slope extracted by a long-period sliding window and the temperature correlation coefficient, accurately separating sensor temperature drift from actual minute leaks. More importantly, a recovery tracing mechanism is provided: when the equipment re-vaporizes from a liquefied state into a pure gas phase, the system automatically activates the freeze difference method, comparing the historical reference pressure frozen before liquefaction with the current pressure after vaporization. If the difference exceeds the tolerance, it is determined that a real physical leak has occurred in the liquefaction monitoring blind zone, and a leak alarm is immediately reissued to ensure the safe and stable operation of the equipment throughout its entire lifecycle.

[0039] The following is a detailed description of the solution implementation:

[0040] (I) System Hardware Architecture

[0041] This system adopts a hardware architecture with dual temperature sources and high computing power, providing a physical basis for complex nonlinear solutions.

[0042] 1. Dual temperature source sensing system:

[0043] T gas (Gas Body Temperature Sensor): The probe extends directly into the gas chamber or is close to the root of the gas path to directly measure the real-time thermodynamic temperature of SF6 gas, which serves as the core variable for density calculation and phase change identification.

[0044] T amb (Ambient temperature sensor): Independently installed outside the relay housing and equipped with a radiation shield (to avoid errors caused by direct sunlight and rain or snow cover), it is used to sensitively detect the cold air front and serve as a feedforward signal for the thermal hysteresis effect of the computing device.

[0045] 2. High-precision pressure acquisition: A high-precision MEMS absolute pressure sensor is used to acquire the absolute pressure P of the gas chamber. abs This eliminates atmospheric pressure fluctuations caused by high altitude or weather changes.

[0046] 3. High-performance main control unit (MCU): An ARM Cortex-M7 microcontroller with FPU (floating-point unit) is selected to support the Newton iterative solution of the Beattie-Bridgeman equation and the high-frequency matrix operation of the recursive least squares (RLS) method.

[0047] (II) Global State Arbitration Layer: Phase Change Isolation and Mode Scheduling

[0048] To resolve the logical conflict between reducing gas leakage and the pressure characterization of physical liquefaction of gas under extremely cold conditions, this system has set up a global state arbitration mechanism with the highest priority in the main loop.

[0049] 1. Dynamic adaptive calculation of liquefaction warning temperature

[0050] The liquefaction warning temperature T_ in this system liq_warn It is not a fixed preset value, but rather dynamically calculated by the MCU based on the initial physical field parameters after device initialization or re-inflation. The specific calculation mechanism is as follows:

[0051] (1) Extracting the initial state: The MCU obtains the initial absolute pressure Pabs_initial and initial temperature T_initial after the equipment is injected with SF6 gas, and uses the Beattie-Bridgeman equation to calculate the current reference constant density ρ_initial of the gas chamber. The expression of the Beattie-Bridgeman equation is as follows:

[0052]

[0053] In the above formula: P is the pressure of sulfur hexafluoride gas, MPa; ρ is the density of the gas, kg / m³. 3 T represents the temperature of SF6 gas, and A and B are temperature-related intermediate variables in the Beattie-Bridgeman equation.

[0054] During the leak-free pure gas phase operation, the total mass of the gas in the gas chamber remains constant. Therefore, the reference density ρ_initial is a constant value, providing a unique reference for subsequent theoretical liquefaction point calculations.

[0055] (2) Solving for the theoretical phase transition point: The equations of the real gas isodense cooling curve (based on Beattie-Bridgeman) and the SF6 saturated vapor pressure curve (based on Antoine equation) are combined in the MCU.

[0056] The intersection temperature T of the above equations is obtained by using numerical iterative algorithms such as Newton's descending hill method. This solution is the theoretical critical liquefaction temperature T_liq of the current equipment under leak-free conditions.

[0057] (3) Generate warning threshold: In order to ensure that the system can intervene in advance before liquefaction occurs, the liquefaction warning temperature T_liq_warn=T_liq+△T is set (where △T is the safety warning margin, which is set to 4℃ based on the maximum temperature gradient error between the sensor probe and the fluid in the center of the gas chamber during the cooling test of the covered climate chamber).

[0058] The Antoine equation expression and parameters are determined as follows:

[0059]

[0060] In the above formula: P sat Saturated vapor pressure, in MPa, T gas The value is the thermodynamic temperature of SF6 gas, in K; A, B, and C are the Antoine characteristic constants of the gas. The test results are shown in Table 1.

[0061] Table 1. Saturated vapor pressure of SF6 gas at different temperatures

[0062]

[0063] The Antoine constant was fitted using an intelligent algorithm (such as nonlinear least squares method), and the fitting parameters were: A=3.389, B=907.9, C=2.85. Figure 2 To compare the fitted curve with the experimental data, the figure shows that the two are in good agreement, with a correlation coefficient of 0.9998, which proves the accuracy and effectiveness of the obtained parameters.

[0064] Subsequently, during operation, the system will collect T data in real time. gas It is compared with the dynamically calculated T_liq_warn as one of the decision criteria.

[0065] 2. Real-time status arbitration decision

[0066] MCU collects current P in real time abs With T gas The theoretical saturation pressure P is calculated by calling the built-in SF6 saturated vapor pressure model (Antoine equation). sat And calculate the deviation between the measured pressure and the theoretical saturation pressure, ΔP = P. abs -P sat .

[0067] State I: Liquefaction Coexistence: If |ΔP| < δ (δ is the decision tolerance) and T gas ≤Liquefaction warning temperature T liq_warnAt this point, the system determines that the current pressure is decreasing along the saturated vapor pressure curve, and the gas phase mass is no longer conserved. The system automatically suspends the conventional pure gas phase calculation module, freezes the sliding time window, and directly jumps to the extreme cold liquefaction anti-maloperation interlocking mode. Here, considering the sensor measurement error of 0.001 MPa with a 1 MPa range and 0.1%FS, as well as the fluctuation margin setting for the presence of local temperature gradients in the gas, δ is set to 0.02 MPa.

[0068] State II Pure Gas Phase: If the above conditions are not met, the gas mass is determined to be conserved. The system is activated and executes the pure gas phase leakage and temperature drift discrimination mode and the cold wave thermal hysteresis anti-disturbance mode.

[0069] (III) Divide and Conquer Execution Layer Mode 1: Extreme Cold Liquefaction Prevention Interlocking Mode Based on Insulation Safety Criterion

[0070] When the system enters a liquefied coexistence state, the conventional normalized pressure (P) 20 The system completely failed due to loss of mass. The system switched from constant density monitoring to dynamic insulation capability monitoring.

[0071] In a gas-liquid coexistence state, the pressure of the gas phase is always equal to the saturated vapor pressure at the current temperature. Therefore, the measured saturated vapor pressure P can be used as a reference. sat and gas temperature T gas Substituting into the Beattie-Bridgeman equation, we can solve for the density ρ of the remaining saturated gas phase. gas .include:

[0072] Residual gas phase density ρ gas Inversion: This refers to the current P... sat ,T gas Substituting into the Beattie-Bridgeman equation, we can solve for the residual gas density ρ under extreme conditions. gas (Unit: kg / m³) 3 ).

[0073] Critical breakdown voltage U b Assessment: Applying the modified Paschen's law, the theoretical insulation strength at the current vapor density is calculated using the following expression:

[0074]

[0075] In the above formula, U b Let ρ be the theoretical critical breakdown voltage of the gas gap of the device under the current gas phase density. gasd represents the remaining saturated gas phase density under liquefied coexistence conditions, d is the inherent contact opening distance of the circuit breaker arc-extinguishing chamber, K is the electric field uniformity insulation coefficient, characterizing the degree of electric field distortion of the contact structure, with a value range of 0.75~0.95, and α is the nonlinear exponent, reflecting the nonlinear effect of discharge under extremely cold and high density conditions, with a value range of 0.80~0.90.

[0076] To achieve the above critical breakdown voltage U b Evaluation and parameter calibration: This embodiment takes a full-scale power equipment according to industry standards as an example to explain in detail the full-scale test identification method for its key characteristic parameters K and α.

[0077] True-type test calibration methods and procedures:

[0078] 1. Curing of test objects and physical parameters

[0079] In this embodiment, the LW25-126 type high-voltage AC SF6 circuit breaker (column structure) is selected as the actual calibration equipment. Its factory and structural core parameters are as follows:

[0080] Rated voltage U rated 126kV, the system's rated phase voltage is 126 / ≈72.7kV.

[0081] Rated inflation pressure (gauge pressure at 20℃): 0.50MPa (corresponding to absolute pressure P) abs =0.60MPa).

[0082] The inherent contact gap (d) of the arc-extinguishing chamber: curing parameter d = 60 mm (i.e. 0.06 m).

[0083] Circuit breaker contact electric field type: The nozzle and contact system inside the arc extinguishing chamber are optimized for flow field and belong to a quasi-uniform electric field structure.

[0084] 2. Real-world testing environment and calibration procedures

[0085] (1) Environmental preparation: The entire equipment of this model was placed in a large walk-in high and low temperature alternating climate chamber;

[0086] (2) Inflation and cooling: Inflate SF6 gas at the rated pressure (0.6MPa), start the climate chamber to cool down from 20℃ to -45℃ at a rate of 5℃ / h, so that it enters the deep liquefaction state;

[0087] (3) Power frequency withstand voltage acquisition: At four temperature anchor points of -30℃, -35℃, -40℃, and -45℃, power frequency withstand voltage was applied until breakdown occurred, and the gas phase density ρ at each anchor point was recorded. gas Compared with the actual breakdown voltage U b ;

[0088] (4) Parameter fitting: The nonlinear least squares method is used to fit multiple sets of ρ gas U b The dataset is fitted to calculate the specific coefficients for this particular model of equipment, for example, K=0.82 and α=0.86.

[0089] 3. Safety margin grading decision-making:

[0090] Safety anti-misoperation interlocking: Based on GB / T 1984-2024 "High Voltage AC Circuit Breakers" standard, and taking into account system operating overvoltage and a 15% safety insulation operating margin: If U b >1.15U rated (U) rated If the gas pressure drops below the normal blocking threshold due to liquefaction (where the voltage is the rated phase voltage of the equipment), then the insulation margin of the gas chamber is determined to be in a safe and sufficient state. At this time, even if the absolute gas pressure drops below the normal blocking threshold due to liquefaction, the microcontroller unit (MCU) will forcibly implement the soft-shielded physical blocking contact. The system only outputs a "liquefaction and voltage reduction operation" warning signal, thereby effectively preventing accidental equipment blocking and tripping under extremely cold conditions and ensuring continuous and reliable power supply to the power grid.

[0091] True insulation degradation lockout: If U b ≤1.15U rated This indicates that the remaining gas can no longer sustain the arc extinguishing requirements. The MCU immediately releases the shield and outputs a lockout trip signal to prevent the equipment from exploding.

[0092] (iv) Divide and conquer execution layer mode two: pure gas phase leakage and temperature drift discrimination mode

[0093] When the global state arbitration layer determines that the current SF6 gas is in a pure gas phase state (State II), the microcontroller unit (MCU) activates the pure gas phase leak and temperature drift discrimination mode to isolate system temperature drift interference and accurately identify minute leaks under pure gas phase conditions. The specific execution steps of the pure gas phase leak and temperature drift discrimination mode are as follows:

[0094] 1. High-precision calculation of density and equivalent pressure based on the Beattie-Bridgeman equation of state

[0095] Within each preset sampling period, the microcontroller unit uses a high-precision MEMS absolute pressure sensor to acquire the absolute pressure P of the gas chamber in real time. abs And use a gas body temperature sensor to collect real-time gas temperature T gas The actual instantaneous density ρ of the gas is calculated using the Newton-Raphson iterative method based on the Beattie-Bridgeman equation. Subsequently, the microcontroller unit keeps this actual instantaneous density ρ constant and sets the standard reference temperature T. 20Substituting 293.15K (i.e., 20℃) as the temperature variable back into the Beattie-Bridgeman equation of state, we can calculate the normalized reduced pressure P at 20℃ after eliminating the interference of the current temperature field. 20 .

[0096] 2. Trend Feature Extraction from a Long-Period Sliding Time Window: The microcontroller establishes a sliding time window with a time span of ΔT in memory. In this embodiment, the length of the sliding time window ΔT is set to 72 hours to fully cover three diurnal temperature cycles, eliminating periodic white noise in the data caused by uneven sunlight distribution or local temperature gradients in the substation. The microcontroller extracts the high-frequency accumulated P values ​​within the sliding time window. 20 Using the time series as the dependent variable and time t as the independent variable, a univariate linear regression is performed using the least squares method to construct the following trend equation:

[0097]

[0098] In the above formula, P 20 (t) represents the equivalent pressure at time t, normalized to 20°C; This represents the slope (rate of change of trend) of pressure over time. <0 indicates that the pressure is decreasing; b is the intercept of the linear regression; t is time.

[0099] By performing regression calculations, the rate of change of the trend representing the slope of pressure change over time can be determined. .like <0 and the absolute value of the slope| If the pressure exceeds the preset micro-leakage threshold (Threshold), it indicates a continuous downward trend in the equivalent pressure within the gas chamber on a macroscopic level, triggering a leak diagnosis signal. The micro-leakage threshold (Threshold) is calculated based on the legally mandated maximum annual allowable leakage rate limit in national standards, using the following formula:

[0100]

[0101] In the above formula, the range of values ​​is limited to: 6.8 × 10 -7 MPa / h ≤ Threshold ≤ 3.5 × 10 -6 MPa / h. The maximum permissible annual leakage rate F according to GB / T 11023 standard. year_max =0.5% calculation, With the equipment rated at 20°C and normalized pressure, the Threshold curing pressure is 3.5 × 10⁻⁶. -6 MPa / h.

[0102] 3. Calculation of Pearson correlation coefficient

[0103] In order to accurately identify whether the continuous drop in equivalent pressure is caused by actual gas leakage in the equipment or by aging of the semiconductor components of the pressure sensor, temperature drift of the bridge resistance, or compensation failure, the microcontroller unit simultaneously initiates decoupling mathematical calculations.

[0104] The microcontroller extracts P within the current sliding time window. 20 Sequence and real-time gas temperature T gas For each sequence, calculate the Pearson correlation coefficient r between them. The specific calculation formula is as follows:

[0105]

[0106] In the formula, n is the total number of sampling points within the window. , The normalized equivalent pressure at 20℃ for the i-th sampling point is respectively. and the gas body temperature at the i-th sampling point The corresponding arithmetic mean of the sequences. The absolute value of the Pearson correlation coefficient r, |r|, is used to quantify the degree of linear correlation between normalized pressure fluctuations and external environmental temperature fluctuations.

[0107] 4. Two-dimensional decision matrix diagnosis:

[0108] In satisfying the trend change rate Given that the slope is less than 0, the microcontroller will use the absolute value of the slope | The absolute value of the correlation coefficient |r| is mapped to the built-in two-dimensional decision matrix, and differentiated control responses are executed according to the following three diagnostic branches:

[0109] Branch A (Sensor Temperature Drift Fault Determination): If the absolute value of the correlation coefficient |r|>0.6, it indicates that the normalized pressure P 20 The slight decrease in the waveform showed a strong correlation with the fluctuations in the external temperature, exhibiting a high frequency. Based on this, the microcontroller determined that the state was not caused by physical leakage, but rather by temperature drift or temperature compensation failure in the sensor hardware. The microcontroller forcibly intercepted the output of the leakage lockout signal and issued a sensor self-test anomaly alarm command to the power grid main control room.

[0110] Branch B (True Minor Leakage Judgment): If the absolute value of the correlation coefficient |r| < 0.2 and | Threshold indicates the normalized stress P. 20 It exhibits a monotonically constant rate of decrease independent of ambient temperature fluctuations. Based on this, the microcontroller determines that a real, slow gas leak has occurred in the gas chamber, consistent with the physical characteristics of molecular diffusion, and immediately issues a "core gas micro-leakage warning" command to the power grid main control room to guide condition-based maintenance.

[0111] Branch C (Multi-factor composite interference judgment): If the absolute value of the correlation coefficient is 0.2≤|r|≤0.6, the microcontroller determines that the current data is affected by multi-factor composite noise interference from the substation, such as sudden strong winds or localized rainfall, and is in a fuzzy boundary state. The microcontroller automatically triggers the sliding window extension mechanism, temporarily and dynamically extending the sliding time window ΔT from 72 hours to 120 hours, and re-accumulates sufficient historical data for secondary convergence identification to prevent hasty false alarms.

[0112] 5. Liquefaction recovery period leakage tracing mechanism

[0113] When the external ambient temperature warms up, at the instant when the global state arbitration layer determines that the gas has completely vaporized again from the liquefied state and the relay state has switched back from state I to state II, the microcontroller unit starts the freeze difference method to trace the hysteresis leak.

[0114] The microcontroller reads the historical high-precision reference equivalent pressure P latched at the last moment before entering the liquefied state from the non-volatile memory. 20_old Simultaneously, it captures the equivalent pressure P of the first stable cycle after re-entering the pure gas phase. 20_new The microcontroller calculates the static difference ΔP between the two. wake :

[0115]

[0116] If the static difference ΔP wake If the leakage exceeds the preset leakage tolerance (set to 0.01 MPa in this embodiment), it is determined that a substantial physical leak has occurred in the gas chamber during the entire liquefaction shielding and interlocking protection period. The microcontroller then reissues a delayed leakage alarm signal during liquefaction, thereby eliminating the monitoring blind spot of the full-temperature monitoring network during the phase transition period.

[0117] (V) Divide and Conquer Execution Layer Mode 3: Cold Wave Thermal Hysteresis Anti-Disturbance Mode Based on FF-RLS

[0118] When the global state arbitration layer determines that the current SF6 gas is in a pure gas phase (state II), and the absolute value of the ambient temperature change rate |dT amb When the preset cold wave trigger threshold is reached (in this embodiment, the ambient temperature change exceeds 5°C per hour), the microcontroller unit (MCU) activates the cold wave thermal hysteresis immunity mode. This mode constructs a first-order thermal inertia model and uses recursive least squares with a forgetting factor (FF-RLS) to identify the dynamic thermal parameters of the equipment online, eliminating false low-pressure alarms caused by the hysteresis of internal gas temperature due to the thermal resistance and thermal capacity of the circuit breaker housing. Its specific implementation scheme and technical route are divided into the following five stages:

[0119] 1. Construction and Discretization of the Physical Model of First-Order Heat Transfer Dynamics in a Gas Chamber

[0120] The high-voltage circuit breaker or gas-insulated switchgear (GIS) chamber is considered as a first-order thermal inertial system. According to the principles of heat transfer, the external ambient temperature T... amb Gas T is introduced into the interior through the metal casing. gas When heat is conducted, it follows Newton's law of cooling. Its continuous-domain differential equation is defined as follows:

[0121]

[0122] In the above formula: T gas (t): The measured thermodynamic temperature of the SF6 gas inside the chamber at time t; T amb (t): The real-time thermodynamic temperature of the external environment sensor at time t; τ is the real-time thermal time constant of the gas chamber, in seconds (s). τ=R th ·C th , where R th For the thermal resistance of the casing, C th τ is the equivalent heat capacity of the gas and the shell, used to characterize how quickly the temperature of the gas chamber changes with the ambient temperature. The larger the τ is, the more significant the thermal hysteresis effect.

[0123] To perform digital discrete computation in a microcontroller unit (MCU), the above continuous differential equation is discretized using the Euler forward difference method, with the discrete sampling period set to Δt = 10 s. After substituting into the difference formula and rearranging, the following discrete model for digital domain temperature prediction is derived:

[0124]

[0125] In the above formula, k represents the discrete sampling time.

[0126] 2. Transformation of Standard Linear Regression Format for Algorithm Embedding

[0127] In order to use the recursive least squares algorithm to estimate the unknown thermal time constant τ that varies dynamically with seasons and wind speed in real time within the microcontroller unit, the above temperature prediction discrete model needs to be transformed into a standard linear regression formula.

[0128] Define the observed variable y(k) as the change in internal gas temperature between adjacent sampling periods:

[0129]

[0130] Define the driving temperature difference vector φ(k):

[0131]

[0132] Define the parameter to be identified, θ:

[0133]

[0134] At this point, the discrete model is transformed into a linear equation:

[0135] .

[0136] 3. Online parameter identification using recursive least squares with forgetting factor (FF-RLS)

[0137] In this embodiment, the microcontroller allocates a floating-point static memory space to maintain and dynamically update the system covariance matrix P (its initial value is set to a large positive matrix of 10). 5 • I, where I is the identity matrix) and the algorithm forgetting factor λ. In this embodiment, the forgetting factor λ is preferably set to 0.98 to give higher weight to the most recently collected data, so as to achieve dynamic thermal parameter tracking within about 8 minutes.

[0138] At each sampling time k, the microcontroller performs the following recursive iterative calculation steps:

[0139] (1) Calculate the gain vector K(k):

[0140]

[0141] (2) Calculate the prior prediction error (k):

[0142]

[0143] (3) Update parameter estimates (k):

[0144]

[0145] (4) Update the covariance matrix P(k):

[0146]

[0147] (5) Reverse decomposition heat time constant τ:

[0148] Based on the latest parameter estimates identified, the true thermal time constant under the current coupling between the device and the external dynamic environment is calculated in reverse. :

[0149]

[0150] 4. Obtaining the true thermal time constant with high-frequency updates Subsequently, the microcontroller unit uses this parameter to construct an ideal temperature feedforward channel under the assumption of no leakage, and calculates the theoretically expected temperature T of the internal gas response to the current cold front if the equipment is in good condition. pred (k):

[0151]

[0152] Next, combining the measured absolute pressure P at the current moment... real (k) uses the Beattie-Bridgeman equation of state as the core solution tool to deduce two equivalent pressures with independent physical meanings in both forward and reverse directions:

[0153] (1) Measured equivalent pressure P 20_real (k): Combined P 20_real (k) and the measured internal gas temperature T gas (k) Substitute into the equation of state to solve. This value includes a spurious underestimation error due to the delay in heat conduction from the outer shell.

[0154] (2) Predicting the equivalent pressure P of the thermal model 20_pred (k): Combined measured absolute pressure P abs (k) and the expected temperature T predicted by the first-order heat transfer model pred (k) Substitute into the equation of state to solve. This value represents the ideal normalized pressure value after eliminating the effect of temperature conduction hysteresis.

[0155] 5. Multidimensional dynamic residual decision-making and interlocking contact soft control

[0156] The microcontroller calculates the dynamic residual ΔP between the measured equivalent pressure and the predicted equivalent pressure. error (k):

[0157]

[0158] In the above formula, Let be the dynamic residual between the measured equivalent pressure and the predicted equivalent pressure at time k. The normalized equivalent pressure at 20°C calculated based on the measured gas temperature at time k is the pressure at time k. The normalized equivalent pressure at 20°C is calculated based on the predicted gas temperature at time k.

[0159] The dynamic residual ΔP error (k) Compare with the system's preset cold wave tolerance threshold σ (in this embodiment, σ is preferably set to 0.015MPa):

[0160] Decision branch A (thermal hysteresis false alarm interception): If ΔP error If (k) < σ, it is determined that the sharp drop in the current measured pressure is entirely caused by the thermal inertia conduction delay of the high-voltage circuit breaker's metal casing, and there is no gas leakage in the gas chamber itself. The microcontroller immediately activates the anti-maloperation protection, forcibly implements the soft-shielded physical interlocking contact command, locks the trigger level of the trip circuit, and prevents the high-voltage switchgear from being maloperated and interlocked without cause.

[0161] Decision branch B (determination of true leakage due to cold contraction): If ΔP error If (k) ≥ σ, it is determined that the current rapid pressure drop exceeds the temperature change range of pure thermodynamic thermal hysteresis, belonging to the cold contraction effect caused by the cold wave, superimposed with the actual slow gas leakage in the pipeline / gas chamber. The microcontroller immediately releases the shielding command, restores the normal interlock monitoring priority, and allows normal interlock trip level output to ensure equipment safety.

[0162] To demonstrate the liquefaction-proof interlocking capability and parameter feasibility of the present invention, the following actual extreme working condition test examples are provided.

[0163] The test object and conditions were a LW25-126 type high-voltage AC SF6 circuit breaker equipped with the intelligent density relay of this invention. The rated charging pressure was 0.40MPa (corresponding to 20℃, alarm pressure 0.35MPa, and lockout pressure 0.30MPa).

[0164] Equipment rated operating voltage U rated =126 / =72.7kV. After full-scale testing and calibration, the contact gap of this equipment is d=60mm, K=0.82, and α=0.86.

[0165] The simulation of cold waves and liquefaction processes was placed in a climate chamber, where the ambient temperature plummeted from 0°C to -45°C at a rate of 10°C / h.

[0166] Phase 1 (Thermal Hysteresis Immunity Verification): 2 hours before the temperature drops sharply, the outer shell temperature T... amb The internal temperature is -20℃, and the temperature is T. gas The measured temperature was -5℃. Due to thermal hysteresis, the system may experience false alarms due to a sudden drop in apparent pressure if there is no compensation. This system uses the FF-RLS algorithm to identify the thermal time constant τ = 3600s online and calculates the predicted equivalent pressure P. 20_pred and P20_real The residual is less than σ, which is determined to be a thermal conduction delay, thus successfully masking the false warning.

[0167] Phase Two (Verification of Liquefaction Prevention and False Lockout): When the gas temperature T gas When the temperature drops to -38°C, the absolute pressure P abs It drops to 0.28 MPa. At this point, |P abs -P sat (-38℃) | <0.02MPa. The system successfully detected the phase change and entered a "liquefied coexistence state". According to traditional relay logic, 0.28MPa is far below 0.30MPa, which would directly trigger the circuit breaker to trip and cause a power outage. The MCU of this invention calculates the current remaining gas density ρ based on the Beattie-Bridgeman equation. gas Approximately 21.5 kg / m3 Substituting the modified Paschen's law into the equation, we can assess the critical breakdown voltage:

[0168] U b =0.82×(21.5)^{0.86}×60≈105.8kV.

[0169] Safety margin comparison: 105.8kV > 1.15 × 72.7kV (83.6kV).

[0170] Test results concluded that although the pressure had fallen below the traditional blocking threshold, the system accurately determined that "the current remaining gas phase density still has the capability to completely extinguish the arc," and the MCU output a liquefaction-based pressure reduction operation signal instead of a blocking trip signal. The circuit breaker continued to operate safely online at -45℃, solving the problem of accidental blocking in extremely cold conditions.

[0171] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

[0172] This invention is not limited to the preferred embodiment described above. Anyone inspired by this invention can derive other forms of electrical equipment anti-misoperation interlocking control method and density relay. All equivalent changes and modifications made within the scope of the claims of this invention shall fall within the scope of this invention.

Claims

1. A method for preventing misoperation and interlocking control of electrical equipment, characterized in that, include: Real-time acquisition of absolute pressure and gas temperature in the SF6 gas chamber; The saturated vapor pressure is calculated based on the gas body temperature, and the absolute pressure is compared with the saturated vapor pressure to determine whether the gas has entered a liquefied coexistence state. If the state is determined to be liquefied coexistence, the insulation strength of the remaining gas phase is used as the basis for the blocking decision: when the insulation margin is sufficient, the physical blocking contacts are forcibly shielded; when the insulation margin is insufficient, the shielding is released and a blocking signal is output.

2. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: The determination of the liquefied coexistence state adopts a dynamic adaptive warning temperature. The dynamic adaptive warning temperature is obtained by iteratively solving the phase transition critical temperature corresponding to the current density using the real gas state equation based on the absolute pressure and temperature after the initial gas filling of the equipment, and then adding a safety margin.

3. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: Sufficient insulation margin means that the critical breakdown voltage of the remaining gas phase is greater than 1.15 times the rated phase voltage of the equipment.

4. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: The insulation strength of the remaining gas phase is calculated through the following steps: based on the saturated vapor pressure and the gas body temperature, the density of the remaining saturated gas phase is inverted; the density of the remaining saturated gas phase is substituted into the insulation breakdown model to calculate the critical breakdown voltage.

5. The electrical equipment anti-misoperation interlocking control method according to claim 4, characterized in that: The insulation breakdown model is a modified Paschen's law, which includes the electric field uniformity coefficient, the nonlinear exponent, and the inherent contact opening distance of the circuit breaker's arc-extinguishing chamber; the electric field uniformity coefficient is 0.75~0.95, and the nonlinear exponent is 0.80~0.90; each parameter is fitted and calibrated through a true-type power frequency withstand voltage test in an extremely cold environment.

6. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: When it is determined that the gas has not entered the liquefied coexistence state, the pure gas phase leakage diagnosis logic is executed: the time change trend of normalized pressure is extracted through a long-period sliding window, and the correlation between normalized pressure and gas temperature is combined to construct a two-dimensional decision logic to distinguish between sensor temperature drift faults and real micro gas leaks.

7. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: When the rate of change of ambient temperature exceeds the preset threshold, the cold wave thermal hysteresis compensation logic is executed: the thermal time constant of the equipment is identified online by the recursive least squares method with forgetting factor, and the gas temperature measurement error and pressure calculation error caused by the thermal inertia of the metal shell are dynamically compensated.

8. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: It also includes a liquefaction recovery period leakage tracing step: when the gas is completely restored from the liquefied coexistence state to the pure gas phase state, the reference equivalent pressure of the frozen storage before liquefaction is compared with the current equivalent pressure after recovery; if the difference between the two exceeds the preset leakage tolerance, a delayed leakage alarm signal during the liquefaction period is issued.

9. The electrical equipment anti-misoperation interlocking control method according to claim 1, characterized in that: The gas body temperature inside the gas chamber and the ambient temperature outside the relay are collected simultaneously; the gas body temperature is used for liquefaction coexistence state determination and density calculation, and the ambient temperature is used for dynamic compensation for cold wave thermal hysteresis.

10. A density relay, characterized in that, include: Dual temperature source sensing unit is used to simultaneously collect the absolute pressure of the gas chamber, the temperature of the gas body and the ambient temperature; A microcontroller unit, electrically connected to the dual-temperature-source sensing unit, is configured to perform the method according to any one of claims 1 to 9; The signal output unit is electrically connected to the microcontroller unit and is used to shield or output the circuit breaker blocking signal according to the result of the anti-misoperation blocking control method.

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