Multi-parameter acquisition and automatic temperature compensation based SF6 digital density meter and control method thereof

Abstract

The application provides a kind of SF6 digital density gauge based on multi-parameter acquisition and automatic temperature compensation and its control method, density gauge display is arranged on SF6 digital density gauge, detection interface is arranged below SF6 digital density gauge, multi-parameter acquisition module and temperature, pressure arrangement module are arranged inside digital density gauge, multi-parameter acquisition module and temperature, pressure arrangement module are electrically connected with single-chip microcomputer;The detection interface of SF6 digital density gauge is directly contacted with SF6 gas completely.The physical quantity acquisition components are highly concentrated and directly contacted with SF6 gas in the gas chamber, which ensures accurate collection of SF6 gas actual temperature, pressure, micro water and other physical quantities for temperature compensation.At the same time, the existing SF6 density algorithm model is improved, and a better convergence algorithm model is obtained.

Description

Technical Field

[0001] This invention relates to the field of SF6 digital density meters, and in particular to an SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation, and its control method. Background Technology

[0002] SF6 gas's excellent insulation and arc-extinguishing properties make it widely used in various high-voltage equipment, such as circuit breakers (SF6 switches), enclosed switchgear (GIS) or semi-enclosed switchgear (HGIS), main transformer bushings or wall bushings, current transformers (CTs), etc.

[0003] If the SF6 density decreases, it will cause a reduction in the withstand voltage and breaking capacity of circuit breakers, resulting in a significant decrease in the insulating performance of SF6 gas. To ensure the safe operation of SF6 electrical equipment, power operation departments must strictly monitor the density of SF6 gas. Currently, most domestic and international systems use mechanical density relays to monitor SF6 gas density. Mechanical density relays can only output alarm and interlocking node signals; reading and data transmission are inconvenient, making remote measurement impossible. Especially in high-voltage (500kV and above) substations / converter stations, due to their large footprint, long equipment distribution distances, and the extensive use of SF6 electrical equipment, most of these stations are equipped with mechanical density relays and have reserved gas filling interfaces for equipment replenishment or sampling testing. Currently, in the actual operation and management of these high-voltage substations / converter stations, monitoring changes in the density of SF6 gas inside each piece of equipment mainly relies on manual inspection and meter reading. Only by periodically recording the readings of each density relay and manually comparing them can the safety and health status of each piece of equipment be understood. Since these substations have hundreds or even thousands of SF6 density relays, this work brings great inconvenience to the operation and management of the stations.

[0004] On the other hand, the moisture content in SF6 gas is also an important indicator for evaluating its insulation characteristics and arc-extinguishing performance. During the manufacturing and operation of SF6 circuit breakers, moisture can accumulate in the gas chamber and valves due to: 1) the presence of moisture in fresh SF6 gas; 2) oversights in the process during installation, disassembly, maintenance, and gas replenishment; and 3) incomplete sealing leading to gas leakage and subsequent moisture seepage. Excessive moisture can cause the following hazards to equipment operation under the following conditions: 1) With the presence of some metals, water at temperatures above 200°C can cause hydrolysis of SF6, generating reactive HF and SOF2, which corrode insulating and metal components, generating heat and increasing the pressure in the gas chamber; 2) Excessive moisture may condense at lower temperatures, significantly reducing the surface insulation strength of insulating components, and even causing flashover and serious accidents. Therefore, the measurement and control of moisture in SF6 gas has become a topic of widespread concern in power systems. Summary of the Invention

[0005] The main objective of this invention is to provide a digital density meter for SF6 based on multi-parameter acquisition and automatic temperature compensation, and its control method, to solve the problems of portable dew point meters being offline, cumbersome to operate, and affecting power grid operation, and the inability of dew point meters to achieve automated power transmission and transformation management and equipment condition-based maintenance.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: an SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation, wherein the SF6 digital density meter is provided with a density meter display, and a detection interface is provided below the SF6 digital density meter. The digital density meter is provided with a multi-parameter acquisition module and a temperature and pressure processing module, and the multi-parameter acquisition module and the temperature and pressure processing module are electrically connected to a single-chip microcomputer.

[0007] The detection interface of the SF6 digital density meter is in direct and complete contact with SF6 gas.

[0008] In the preferred embodiment, the multi-parameter acquisition module includes a pressure-sensitive core, which is electrically connected to a signal conditioning board via an adapter board. The signal conditioning board is electrically connected to a power board, and both the signal conditioning board and the power board are electrically connected to an electrical connector.

[0009] In the preferred embodiment, a temperature core is also provided, which is electrically connected to a ceramic circuit board. The ceramic circuit board is electrically connected to a signal conditioning board through an adapter board.

[0010] In the preferred embodiment, the power supply employs an EMC anti-interference circuit.

[0011] In the preferred embodiment, the method includes: S1, pressure acquisition using a pressure-sensitive core, the acquisition steps being: using a measurement range of... The output is The pressure transmitter collects pressure signals;

[0012] According to the formula ,in For pressure, The pressure transmitter outputs current, converting the current signal into an actual pressure value. ;

[0013] It is also equipped with a dew point transmitter, utilizing a range of Signal output is The dew point transmitter collects the dew point signal;

[0014] Through formula ,in, For dew point, The dew point transmitter outputs current, converting the current signal into a dew point value;

[0015] The temperature is directly obtained by the temperature sensor of the temperature core (5). ,temperature The unit is ;

[0016] S2, Calculation Equivalent pressure at time :

[0017] Determine the parameters of the Beattie-Bridgman empirical formula: based on ,in, This represents the SF6 gas pressure value. This is the density value. For temperature, The molar gas constant, , For the correlation coefficient, clarify the meaning and value of each parameter;

[0018] calculate Intermediate variables at time: when At that time, calculate In the formula and The values ​​are denoted as follows: and ;

[0019] in, and ;

[0020] The density is calculated using Newton's iterative method: have to and ,Right now and ;

[0021] Choose initial values ;

[0022] Iterative calculation: by Calculate ,Right now ;

[0023] Convergence determination: If End the iteration and take For density approximation solution Otherwise, let Continue iterating;

[0024] calculate Equivalent pressure at time Approximate solution based on density and Substitution ,have to ;

[0025] S3. Calculate the saturated water vapor pressure: Using the formula for calculating saturated water vapor pressure and temperature, with temperature as the input... Calculate saturated water vapor pressure ;

[0026] Calculate the actual water vapor partial pressure: Given the relative humidity RH, according to... Calculate, where, This is the actual partial pressure of water vapor. For dew point The corresponding saturated water vapor pressure;

[0027] Converted to Trace moisture content at time: The trace moisture content is converted to the specified value according to the conversion formula. PPMv at time, denoted as ;

[0028] Assuming at the current temperature Below, the measured trace moisture content is: According to the ideal gas law and related physical principles, under equal volume conditions, the water content is directly proportional to the pressure and inversely proportional to the temperature.

[0029] The conversion formula is as follows ,in This is the equivalent pressure at 20°C calculated earlier. The current temperature The corresponding pressure, , This is the current temperature that has been collected;

[0030] Substitute the corresponding values ​​into the conversion formula to calculate... , which is the micro-water content PPMv at 20°C.

[0031] In the preferred embodiment, the method for assessing the state of SF6 gas includes:

[0032] A1. Pressure State Assessment: Calculated... With the set alarm pressure value Compare;

[0033] like This may indicate a decrease in SF6 gas density, which could pose risks such as reduced pressure resistance and decreased breaking capacity. Further investigation is needed to check for issues such as gas leakage.

[0034] A2. Micro-water status assessment: The converted... Time-related moisture content Compared with standard limits Compare;

[0035] like This indicates that the moisture content is too high, which may cause SF6 to hydrolyze at high temperatures or form condensation at low temperatures, affecting insulation performance. Corresponding measures need to be taken, such as checking equipment seals and performing gas treatment.

[0036] A3. Comprehensive assessment: Combining the pressure and micro-water status assessment results, comprehensively judge the overall state of SF6 gas;

[0037] If the pressure is normal but the moisture content is excessive, the focus should be on the source and treatment of moisture inside the equipment.

[0038] If both pressure and moisture levels are abnormal, there may be more serious equipment problems, requiring timely repair or replacement of parts to ensure the safe operation of SF6 electrical equipment.

[0039] This invention provides a digital SF6 density meter and its control method based on multi-parameter acquisition and automatic temperature compensation. By deconstructing the pressure sensing, temperature compensation mechanism, and hard-node signal triggering mechanism of traditional mechanical SF6 gas density relays, and combining the R&D experience of external partners in the field of online monitoring sensors for SF6 gas micro-moisture density, the invention highlights the following innovations and advantages:

[0040] 1. Achieve integrated multi-parameter physical quantity acquisition components, enabling SF6 gas temperature, pressure (density), and trace moisture to be fully contacted with SF6 gas through the same miniature probe, and accurately measure the real-time physical quantities of SF6 gas;

[0041] 2. Implement the function of SF6 gas density relay based on automatic temperature compensation. According to the alarm (open / close) pressure value set by the user, generate the corresponding analog electrical signal and send it to the measurement and control protection system to replace the hard node signal of the original mechanical meter.

[0042] 3. The SF6 gas density relay features a full LCD display and is resistant to high and low temperatures, strong electromagnetic interference, and lightning strikes.

[0043] This invention develops an SF6 digital remote density relay (digital meter). The meter can display the data on a local LCD panel and measure the moisture content in SF6 gas in real time with high accuracy. At the same time, it outputs parameters such as the pressure, temperature, and density of SF6 gas, which are then used by the back-end expert system to analyze and judge the internal insulation status or fault nature of the primary equipment. Attached Figure Description

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0045] Figure 1 This is a schematic diagram of the SF6 digit density representation of the present invention;

[0046] Figure 2 This is the circuit diagram of the multi-parameter acquisition chip of the present invention;

[0047] Figure 3 This is the circuit diagram of the temperature and pressure conditioning chip of the present invention;

[0048] Figure 4 This is the microcontroller processing circuit diagram of the present invention;

[0049] Figure 5 This is the EMC anti-interference circuit diagram of the present invention.

[0050] In the diagram: 1. Pressure-sensitive core; 2. Adapter board; 3. Signal conditioning board; 4. Power supply board; 5. Temperature core; 6. Ceramic circuit board; 7. Electrical connector; 8. Density meter display; 9. Detection interface. Detailed Implementation

[0051] Example 1

[0052] like Figures 1-5 As shown, an SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation is provided. The SF6 digital density meter is equipped with a density meter display 8 and a detection interface 9 at the bottom. The digital density meter is equipped with a multi-parameter acquisition module and a temperature and pressure processing module. The multi-parameter acquisition module and the temperature and pressure processing module are electrically connected to a single-chip microcomputer.

[0053] The detection interface 9 of the SF6 digital density meter is in direct and complete contact with the SF6 gas.

[0054] Figure 2Multi-parameter acquisition chip circuit diagram: The pressure-sensitive chip and temperature chip are connected to the ceramic circuit board via an adapter plate. The lower right terminal of the adapter is defined as V+, and the terminals in the counter-clockwise direction are V+, 0+, V-, and 0-, respectively. These terminals are used for signal transmission and power supply. When the ceramic circuit board is placed face up, the two smaller pads are the soldering terminals for the temperature chip. The wire length can be adjusted according to actual conditions to ensure stable and reliable electrical connections between components.

[0055] Function: The pressure-sensitive core acquires the pressure signal of SF6 gas, converting pressure changes into an electrical signal output. The temperature core acquires the temperature signal of SF6 gas, also outputting it as an electrical signal. The adapter board acts as a bridge connecting the pressure-sensitive core, temperature core, and ceramic circuit board, ensuring a smooth signal transmission path. The ceramic circuit board provides an integrated installation and connection platform for the entire multi-parameter acquisition core, enabling all components to work together to accurately acquire the physical quantities of SF6 gas temperature and pressure (density), and transmit the acquired signals to subsequent circuits for processing.

[0056] Figure 3 Medium temperature and pressure conditioning chip diagram: Connection relationship: The chip is connected to numerous pins (PA, PB, PC, PD series pins), which form complex circuit connections with other external components. The PA series pins are connected to different components to realize various functional configurations, including connections related to clock signals, data transmission (SPI interface related pins PA6 / SPI1 MISO, PA7 / SPI1 MOSI for data input and output), and connections related to chip control and power supply functions (PA13 / SWDI, PA14 / SWCLK pins).

[0057] Function: This chip primarily processes, conditions, and performs preliminary processing on the acquired temperature and pressure signals. Through circuitry with external components, it filters, amplifies, and performs analog-to-digital conversion on the raw input signals, converting the analog signals acquired by the sensors into a digital signal format suitable for microcontroller processing. Simultaneously, the chip may also possess signal calibration and compensation functions to improve signal accuracy and stability, providing a reliable data foundation for the microcontroller to accurately calculate parameters such as the density and temperature of SF6 gas, ensuring the system can accurately measure relevant physical quantities of SF6 gas.

[0058] Figure 4The circuit diagram for the single-chip microcontroller processing is as follows: The circuit is based on the STM32G030C8T6 microcontroller. Its pins are connected to the power supply (VDD_3.3V, GND ground), signal input / output pins (P_SDA, P_SCL for I2C bus communication for data transmission and data interaction with other chips or modules), and pins related to other functions (PT_DRDY, PT_FORCE+, etc., which may be related to triggering and control of specific functions). Simultaneously, it communicates with temperature and pressure regulating chips through specific pins, receiving regulated temperature and pressure data signals.

[0059] Function: The microcontroller serves as the control and data processing center of the entire system, responsible for receiving digital signals from temperature and pressure monitoring chips. Based on preset programs and algorithms, it further calculates and processes these data, such as calculating parameters like the density and water content of SF6 gas according to the gas state equation and related algorithm models. Based on user-defined alarm (on / off) pressure values, it generates corresponding analog electrical signals and sends them to the measurement and control protection system, realizing the monitoring and control functions of SF6 gas status. Simultaneously, it can control the LCD panel to display relevant measurement data, enabling human-machine interaction. Furthermore, it coordinates the work of various parts within the system, ensuring stable and accurate system operation to meet the comprehensive online monitoring needs of SF6 gas status in SF6 high-voltage equipment.

[0060] In the preferred embodiment, the multi-parameter acquisition module includes a pressure-sensitive core 1, which is electrically connected to a signal conditioning board 3 via an adapter board 2. The signal conditioning board 3 is electrically connected to a power board 4, and both the signal conditioning board 3 and the power board 4 are electrically connected to an electrical connector 7.

[0061] In the preferred embodiment, a temperature core 5 is also provided, which is electrically connected to a ceramic circuit board 6. The ceramic circuit board 6 is electrically connected to a signal conditioning board 3 through an adapter board 2.

[0062] In the preferred embodiment, the power supply employs an EMC anti-interference circuit.

[0063] like Figure 5As shown, the power input is 24V, connected to the circuit through fuse F1, and then connected to TVS1 (transient voltage suppressor diode) and GDT1 (gas discharge tube). TVS1 and GDT1 work together on the power line to suppress potential surges and fast transient bursts. The diagram also shows that during actual verification, the equipment was damaged in the third N-PE surge because the gas discharge tube at the inlet was broken down. This gas discharge tube has a pulse voltage withstand capability of 10 / 700µs 4KV +5 times. In future improvements, if space permits, a wire-wound resistor can be connected in series before the two leads of the gas discharge tube to absorb some of the surge impact.

[0064] Functions: The TVS1 (Transient Voltage Suppressor) is mainly used to quickly conduct when a transient overvoltage (such as a surge voltage) occurs in the circuit, clamping the excessively high voltage to a safe value and protecting downstream circuit components from damage. The GDT1 (Gas Discharge Tube) conducts when encountering a surge impact, discharging the surge current to ground when the voltage exceeds its breakdown voltage, thus providing shunt and protection. Adding a series wire-wound resistor (if applicable) can further buffer surge impacts, reduce the surge energy borne by the gas discharge tube, extend its service life, and also help improve the overall power supply circuit's resistance to surges and fast transient / burst interference, ensuring the stability and reliability of the product's power supply. This allows the product to operate normally in complex electromagnetic environments, improving system stability and reliability, and meeting the power supply stability requirements of SF6 digital density meters in environments with strong electromagnetic interference such as substations.

[0065] Example 2

[0066] Further explanation in conjunction with Example 1, such as Figure 1-5 The method, as shown in the diagram, includes:

[0067] S1. Pressure is collected by the pressure-sensitive core 1. The collection steps are as follows: using a measurement range of... The output is The pressure transmitter collects pressure signals;

[0068] According to the formula ,in For pressure, The pressure transmitter outputs current, converting the current signal into an actual pressure value. ;

[0069] Pressure signals are acquired using a pressure transmitter with a range of 0-1MPa and an output of 4-20mA.

[0070] According to the formula ( For pressure, (This is the output current of the pressure transmitter), which converts the current signal into the actual pressure value. .

[0071] It is also equipped with a dew point transmitter, utilizing a range of Signal output is The dew point transmitter collects the dew point signal;

[0072] Through formula ,in, For dew point, The dew point transmitter outputs current, converting the current signal into a dew point value;

[0073] Dew point signals are acquired using a dew point transmitter with a range of -80 to +20℃ and a signal output of 4 to 20mA.

[0074] Through formula ( For dew point, (This is the output current of the dew point transmitter), converting the current signal into a dew point value.

[0075] The temperature is directly obtained using a temperature sensor in temperature core 5. ,temperature The unit is ;

[0076] S2, Calculation Equivalent pressure at time :

[0077] Determine the parameters of the Beattie-Bridgman empirical formula: based on ,in, This represents the SF6 gas pressure value. This is the density value. For temperature, The molar gas constant, , For the correlation coefficient, clarify the meaning and value of each parameter;

[0078] according to ( This represents the SF6 gas pressure value (MPa). This is the density value (kg / m³). Temperature (K) molar gas constant ( ), , (For correlation coefficients), clarify the meaning and value of each parameter ( , (Determined based on gas properties).

[0079] In the above content, This represents 20°C. Throughout the calculation process, the actual collected temperature will be used. (Unit: K) and 20°C ( Converted to thermodynamic temperature Perform correlation calculations, such as calculating the equivalent pressure at 20°C. In these steps, 20°C is used as a standard temperature to analyze and evaluate the relevant parameters of SF6 gas, so as to unify the standard and accurately determine the state of SF6 gas.

[0080] calculate Intermediate variables at time: when At that time, calculate In the formula and The values ​​are denoted as follows: and ;

[0081] in, and ;

[0082] 1. The meaning of 273.15: 273.15 is the conversion constant between thermodynamic temperature and Celsius temperature. In the conversion relationship between thermodynamic temperature (unit: Kelvin, K) and Celsius temperature (unit: °C), Here the temperature is in Celsius. When converting to thermodynamic temperature, 273.15 needs to be added to obtain... This is to ensure that a consistent temperature unit is used in subsequent formula calculations based on thermodynamic temperature.

[0083] 2. The meanings of C and D: and This is to simplify subsequent calculations. The intermediate variable is defined by the formula for (equivalent pressure at 20°C).

[0084] In calculation formula In the middle, use express, use After being expressed, the formula can be simplified to This allows for the calculation of density using Newton's iteration method. And the final calculation In the process, redundant calculations can be reduced, making the calculation process more concise and clear, and facilitating improved calculation efficiency and accuracy when implemented in a program or performed manually.

[0085] The density is calculated using Newton's iterative method: have to and ,Right now and ;

[0086] Choose initial values ;

[0087] Iterative calculation: by Calculate ,Right now ;

[0088] Convergence determination: If End the iteration and take For density approximation solution Otherwise, let Continue iterating;

[0089] calculate Equivalent pressure at time Approximate solution based on density and Substitution ,have to ;

[0090] S3. Calculate the saturated water vapor pressure: Using the formula for calculating saturated water vapor pressure and temperature, with temperature as the input... Calculate saturated water vapor pressure ;

[0091] Calculate the actual water vapor partial pressure: Given the relative humidity RH, according to... Calculate, where, This is the actual partial pressure of water vapor. For dew point The corresponding saturated water vapor pressure;

[0092] Converted to Trace moisture content at time: The trace moisture content is converted to the specified value according to the conversion formula. PPMv at time, denoted as ;

[0093] Assuming at the current temperature Below, the measured trace moisture content is: According to the ideal gas law and related physical principles, under equal volume conditions, the water content is directly proportional to the pressure and inversely proportional to the temperature.

[0094] The conversion formula is as follows ,in This is the equivalent pressure at 20°C calculated earlier. The current temperature The corresponding pressure, , This is the current temperature that has been collected;

[0095] Substitute the corresponding values ​​into the conversion formula to calculate... , which is the micro-water content PPMv at 20°C.

[0096] Converted to The specific steps for measuring trace moisture content (PPMv) at 20°C are as follows:

[0097] 1. Determine the limits and basic relationships in the relevant standards:

[0098] According to DL / T 596-2005, Preventive Testing Procedures for Electrical Equipment, the limits for moisture content (PPMv, volume fraction at 20°C) in different equipment (such as circuit breaker gas chambers and other gas chambers) after overhaul and during operation are specified. For example, the limit for moisture content in circuit breaker gas chambers after overhaul should not exceed [a certain value]. (Assuming) (Not greater than) during operation (Assuming) Other air chambers, after major repairs, should not exceed [a certain size]. (Assuming) (Not greater than) during operation (Assuming) These limits will serve as the basis for subsequent judgments on whether the trace moisture content exceeds the standard.

[0099] Understanding the relationship between trace water content and parameters such as temperature and pressure is generally based on the ideal gas law. ( For pressure, For volume, For the amount of substance, The molar gas constant, The derivation is based on temperature. The calculation of trace water content involves the relationship between concepts such as partial pressure of water vapor and saturated vapor pressure, and temperature and pressure.

[0100] 2. Calculate relevant parameters at the current temperature (based on the collected temperature). (For example)

[0101] Calculate saturated water vapor pressure Based on the formula for calculating saturated water vapor pressure and temperature (which can be found in the saturated water vapor pressure table or a known empirical formula), the collected temperature data is used... (Unit is) Calculate the corresponding saturated water vapor pressure. .

[0102] Calculate the actual water vapor partial pressure Given the relative humidity $RH$, according to ( This is the actual partial pressure of water vapor. For dew point Calculate the corresponding saturated water vapor pressure. The dew point here... It is the value obtained by collecting and converting dew point data through a dew point transmitter.

[0103] 3. Derive the conversion formula and perform calculations.

[0104] Assuming at the current temperature Below, the measured trace moisture content is: (Volume fraction, related to pressure and temperature). According to the ideal gas law and related physical principles, under equal volume conditions, the water content is directly proportional to pressure and inversely proportional to temperature (this can be approximated).

[0105] Let the conversion formula be: ,in This is the equivalent pressure at 20°C calculated earlier. The current temperature The corresponding pressure (which can be obtained by acquiring and converting data through a pressure transmitter). (20°C) This is the current temperature collected (unit: ).

[0106] Substitute the corresponding values ​​into the conversion formula to calculate... That is, the micro water content (PPMv) at 20°C.

[0107] 4. Micro-water state assessment

[0108] The calculated Compared with the previously determined standard limits ( , , , (etc.) are compared.

[0109] if The value exceeds the operating limit of the corresponding equipment (such as the operating limit of the circuit breaker gas chamber). Other limits during air chamber operation If the moisture content is too high, it indicates that the SF6 may hydrolyze at high temperatures or form condensation at low temperatures, affecting insulation performance. Appropriate measures need to be taken, such as checking equipment seals and performing gas treatment. If the limit is met, the trace moisture content is within the normal range.

[0110] Example 3

[0111] Further explanation in conjunction with Example 1, such as Figure 1-5 The structure shown illustrates the SF6 gas state assessment methods, which include:

[0112] A1. Pressure State Assessment: Calculated... With the set alarm pressure value Compare;

[0113] like This may indicate a decrease in SF6 gas density, which could pose risks such as reduced pressure resistance and decreased breaking capacity. Further investigation is needed to check for issues such as gas leakage.

[0114] A2. Micro-water status assessment: The converted... Time-related moisture content Compared with standard limits Compare;

[0115] like This indicates that the moisture content is too high, which may cause SF6 to hydrolyze at high temperatures or form condensation at low temperatures, affecting insulation performance. Corresponding measures need to be taken, such as checking equipment seals and performing gas treatment.

[0116] A3. Comprehensive assessment: Combining the pressure and micro-water status assessment results, comprehensively judge the overall state of SF6 gas;

[0117] If the pressure is normal but the moisture content is excessive, the focus should be on the source and treatment of moisture inside the equipment.

[0118] If both pressure and moisture levels are abnormal, there may be more serious equipment problems, requiring timely repair or replacement of parts to ensure the safe operation of SF6 electrical equipment.

[0119] Example 4

[0120] Further explanation in conjunction with Example 1, such as Figure 1-5 The structure shown addresses the problems of mechanical density relays:

[0121] 1. Adopt digital acquisition and transmission technology

[0122] By utilizing integrated multi-parameter physical quantity acquisition components as mentioned in the text, SF6 gas temperature, pressure (density), and trace moisture content can be accurately measured in real time through complete contact between the same miniature probe and SF6 gas. The acquired analog signals are converted into digital signals using digital sensors (such as digital temperature sensors) and transmitters with good linearity (pressure transmitters, dew point transmitters) for easy subsequent processing and transmission.

[0123] Establish a reliable data communication link, such as by using RS485 or other communication interfaces, to transmit the collected multi-parameter data to the measurement and control protection system or background monitoring equipment in real time, so as to realize remote monitoring of data and overcome the problems of inconvenient reading and data transmission and inability to remotely measure mechanical density relays.

[0124] 2. Optimize density calculation and monitoring algorithms

[0125] The density of SF6 gas was calculated using precise algorithms such as the Beattie-Bridgman empirical formula combined with Newton's iterative method, and the equivalent pressure at 20°C was calculated accordingly. The SF6 gas density relay is compared with the set alarm (on / off) pressure value to achieve automatic temperature compensation. When an abnormal density is detected, a corresponding analog electrical signal is generated and sent to the monitoring and control protection system in a timely manner, replacing the hard-node signal of the original mechanical meter and improving the accuracy and reliability of monitoring.

[0126] Regarding the issue of detecting trace moisture content in SF6 gas:

[0127] 1. Improve methods and equipment for detecting trace moisture.

[0128] The micro-moisture calculation method based on multi-parameter acquisition described in this paper is adopted. By calculating the saturated water vapor pressure and the actual water vapor partial pressure, and using relevant standards (such as DL / T 596-2005) and conversion formulas, the micro-moisture content is converted to PPMv at 20°C, so as to realize the online accurate measurement of micro-moisture content and overcome the problems of non-online detection and inaccurate data of portable dew point meters.

[0129] Develop high-precision, high-stability micro-moisture sensors or detection modules and integrate them into multi-parameter acquisition systems to ensure the accuracy and reliability of micro-moisture content measurement, while reducing the impact on equipment operation (such as eliminating the need for long-term SF6 gas emissions).

[0130] 2. Achieve real-time automated monitoring and management of trace moisture content.

[0131] By integrating real-time monitoring data of trace moisture content with the entire substation's automation system, continuous monitoring of trace moisture content in the SF6 equipment's gas chambers can be achieved. When the trace moisture content exceeds a set threshold, alarm and interlock devices are automatically activated, and relevant data is transmitted remotely to the monitoring center, providing a basis for equipment condition-based maintenance and realizing automated power transmission and transformation management and equipment condition-based maintenance.

[0132] Overall system integration and optimization:

[0133] 1. Develop a comprehensive monitoring system

[0134] A digital remote density relay (digital meter) for SF6 was developed, integrating multi-parameter acquisition, automatic temperature compensation, trace moisture content calculation and monitoring, and data communication functions. This enables comprehensive online accurate measurement of SF6 gas status, automatic alarm interlocking, and real-time remote data transmission. The meter can display relevant parameters locally on an LCD panel for easy viewing by on-site maintenance personnel. Simultaneously, it transmits data to a back-end expert system for analysis and judgment, providing comprehensive support for assessing the internal insulation status or fault characteristics of primary equipment.

[0135] 2. Improve system stability and reliability

[0136] In system design, emphasis is placed on power supply EMC immunity design, such as adopting a power supply design scheme that can withstand Class IV surge and Class IV fast transient / burst interference to ensure stable and reliable operation of the system in complex electromagnetic environments such as high-voltage substations / converter stations. At the same time, hardware equipment (such as pressure-sensitive cores, temperature cores, adapter boards, signal conditioning boards, etc.) is optimized in design and selection to improve the overall system performance and service life.

[0137] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be defined as the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A control method based on multi-parameter acquisition and automatic temperature compensation SF6 digitized density meter, characterized by: The SF6 digital density gauge is provided with a density gauge display (8), and a detection interface (9) is arranged below the SF6 digital density gauge; a multi-parameter acquisition module and a temperature and pressure processing module are arranged in the digital density gauge; and the multi-parameter acquisition module and the temperature and pressure processing module are electrically connected with a single-chip microcomputer; The detection interface (9) of the SF6 digital density gauge is directly in full contact with the SF6 gas; The multi-parameter acquisition module comprises a pressure-sensitive core (1), the pressure-sensitive core (1) is electrically connected with a signal processing board (3) through an adapter plate (2), the signal processing board (3) is electrically connected with a power supply board (4), and the signal processing board (3) and the power supply board (4) are both electrically connected with an electric connector (7); A temperature core (5) is further arranged, the temperature core (5) is electrically connected with a ceramic circuit board (6), and the ceramic circuit board (6) is electrically connected with the signal processing board (3) through the adapter plate (2); The control method of the density gauge comprises: S1, the pressure sensitive core (1) collects pressure, the collection step is: using the pressure transmitter with the range of , the output is pressure signal; According to the formula where is the pressure, is the pressure transmitter output current, the current signal is converted into the actual pressure value ; A dew point transmitter is also provided, which uses a range of 0-100℃ , and a dew point transmitter with a signal output of 4-20 mA acquires the dew point signal; By the equation where, is the dew point, is the dew point transmitter output current, converting the current signal to a dew point value; The temperature sensor of the temperature core (5) directly acquires the temperature , the unit of temperature is ; S2, compute equivalent pressure at the time : Determination of Beattie-Bridgman empirical equation parameters: according to wherein, is the SF6 gas pressure value, is the density value, is the temperature, is the molar gas constant, , is the correlation coefficient, the meaning and value of each parameter are clear. Computing the intermediate variable when , the values of and in the formula are calculated, respectively denoted by and ; wherein and ; The density is calculated using Newton's iteration method: from ;​​​​ Select initial value ; Iterative calculation: according to calculated i.e. ; Convergence test: if , terminate iteration and take as the density approximation ; otherwise, let , Continue iteration; Computing the equivalent pressure at time : Substitute the approximate solution for density and into , we get ; S3, calculate saturated water vapor pressure: using the saturated water vapor pressure and temperature calculation formula, using the temperature Calculate saturated water vapor pressure ; Actual water vapor partial pressure is calculated: knowing the relative humidity RH, the actual water vapor partial pressure is calculated as where, is the actual water vapor partial pressure, is the dew point corresponding saturated water vapor pressure; converted to ppmv at 25°C: the ppmv of the micro-water content is converted to ppmv at 25°C according to the conversion formula ppmv at 25°C, denoted ； Assuming the current temperature The measured micro-water content is According to the ideal gas state equation and related physical principles, under the condition of equal volume, the micro-water content is proportional to the pressure and inversely proportional to the temperature; The conversion formula is wherein is the equivalent pressure at 20°C calculated above, is the current temperature corresponding pressure, , is the current temperature collected; Substituting the corresponding values into the conversion formula, the following is calculated i.e. the micro-water content PPMv at 20°C.

2. The control method based on multi-parameter acquisition and automatic temperature compensation SF6 digitized density meter according to claim 1, characterized in that: The power supply adopts an EMC anti-interference circuit.

3. The control method based on multi-parameter acquisition and automatic temperature compensation SF6 digitized density meter according to claim 1, characterized in that: The SF6 gas state evaluation method comprises: A1, pressure state evaluation: the calculated pressure value is compared with the set alarm pressure value and the result is output.​ If , it may indicate that the SF6 gas density is reduced, there is a risk of reducing the withstand voltage strength and breaking capacity, and further inspection is needed to check whether there is a gas leakage problem; A2, micro water state evaluation: the converted value of the micro water content at the time of the measurement is compared with the standard limit value ; If , it indicates that the moisture content is out of standard, which may make SF6 hydrolysis at high temperature or form condensation water at low temperature, affecting the insulation performance. Therefore, appropriate measures should be taken to check the equipment sealing and perform gas treatment. A3, comprehensive evaluation: combining the pressure and the micro-water state evaluation results, the overall state of the SF6 gas is comprehensively judged; If the pressure is normal but the micro-water exceeds the standard, the source of the moisture in the equipment and the treatment thereof are focused on; If both the pressure and the micro-water are abnormal, the parts need to be repaired or replaced in time to ensure the safe operation of the SF6 electrical equipment.

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