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

Abstract

The invention provides an SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation and a control method thereof, the SF6 digital density meter is provided with a density meter display, a detection docking port is arranged below the SF6 digital density meter, the digital density meter is internally provided with a multi-parameter acquisition module and a temperature and pressure arrangement module, and the multi-parameter acquisition module and the temperature and pressure arrangement module are connected with the SF6 digital density meter display. The multi-parameter acquisition module and the temperature and pressure arrangement module are electrically connected with the single-chip microcomputer. And a detection docking port of the SF6 digital density meter is directly and completely contacted with SF6 gas. High concentration of physical quantity acquisition components is realized, and the physical quantity acquisition components are directly and fully contacted with the SF6 gas in the gas chamber, so that accurate acquisition of physical quantities such as actual temperature, pressure and micro water of the SF6 gas for temperature compensation is ensured. Meanwhile, practical improvement is carried out on an existing disclosed SF6 density algorithm model, and an algorithm model with better convergence is obtained.

Description

Technical Field

[0001] The invention relates to the field of SF6 digital density meters, and in particular to a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation and a control method thereof. Background Art

[0002] The excellent insulation and arc extinguishing properties of SF6 gas 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 density of SF6 is reduced, the withstand voltage of the circuit breaker will be reduced, the breaking capacity will be reduced, and the insulation performance of SF6 gas will be greatly reduced. In order to ensure the safe operation of SF6 electrical equipment, the power operation department must strictly monitor the density of SF6 gas. At present, most domestic and foreign companies use mechanical density relays to monitor the density of SF6 gas. Mechanical density relays can only output alarm and locked node signals, and reading and data transmission are inconvenient, and telemetry cannot be achieved. Especially in high-voltage substations / converter stations (500kV and above), because they occupy a large area, the equipment is distributed over a long distance, and this type of substation / converter station uses a large number of SF6 electrical equipment. Most of these electrical equipment are equipped with mechanical density relays and corresponding gas filling interfaces are reserved to facilitate equipment gas replenishment or sampling detection. At this stage, in the actual operation and management of these high-voltage substations / converter stations, the density changes of SF6 gas inside each device are mainly measured by manual inspections, meter readings, etc., and the safety and health status of each device can be mastered by regularly recording the readings of each density relay and manually comparing them. Since these substations have hundreds or even thousands of SF6 density relays, this work brings great inconvenience to the operation and management within the station.

[0004] On the other hand, the content of micro-water in SF6 gas is also an important indicator for evaluating the insulation characteristics and arc extinguishing performance of SF6 gas. In the manufacturing and operation of SF6 circuit breakers, due to: 1) SF6 fresh gas contains a certain amount of water; 2) When the equipment is installed, disassembled, repaired and inflated, water is left in the gas chamber and pipe valve due to omissions in the process; 3) Due to poor sealing, when the gas leaks out, water will penetrate in the reverse direction. The above-mentioned excessive water content will cause the following hazards to the operation of the equipment under the following circumstances: 1) With the participation of some metal objects, water at a temperature above 200°C can cause SF6 to undergo hydrolysis reaction, generate active HF and SOF2, corrode insulating parts and metal parts, and generate heat, so that the pressure of the gas chamber increases; 2) When the temperature drops, the excessive water content may form condensation water, which significantly reduces the insulation strength of the insulating surface, and even flashes, causing serious accidents. Therefore. The measurement and control of micro-water in SF6 gas has become a topic of general concern in the power system. Summary of the invention

[0005] The main purpose of the present invention is to provide a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation and a control method thereof, so as to solve the problems that portable dew point meters are not online, the operation is cumbersome, the operation of the power grid is affected, and the dew point meter detection cannot realize the automation of power transmission and transformation management and the equipment status maintenance.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation, the SF6 digital density meter is provided with a density meter display, a detection interface is provided below the SF6 digital density meter, a multi-parameter acquisition module and a temperature and pressure sorting module are provided inside the digital density meter, and the multi-parameter acquisition module and the temperature and pressure sorting module are electrically connected to the single-chip microcomputer; The detection interface of the SF6 digital density meter is in direct and complete contact with the SF6 gas.

[0007] In the preferred embodiment, the multi-parameter acquisition module includes a pressure sensitive core, the pressure sensitive core is electrically connected to a signal conditioning board through 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; In the preferred embodiment, a temperature core is further provided, the temperature core is electrically connected to the ceramic circuit board, and the ceramic circuit board is electrically connected to the signal conditioning board via the adapter board.

[0008] In the preferred solution, the power supply adopts an EMC anti-interference circuit.

[0009] In the preferred embodiment, the method comprises: S1, the pressure sensitive core performs pressure collection, and the collection steps are: using a range of , the output is The pressure transmitter collects the pressure signal; According to the formula ,in For pressure, Output current for pressure transmitter and convert current signal into actual pressure value ; A dew point transmitter is also provided, with a measuring range of , signal output is The dew point transmitter collects the dew point signal; By formula ,in, is the dew point, Output current for the dew point transmitter and convert the current signal into a dew point value; The temperature sensor of the temperature core (5) is used to directly obtain the temperature ,temperature The unit is ; S2. Calculation The equivalent pressure : Determine the parameters of the Beattie-Bridgman empirical formula: According to ,in, is the SF6 gas pressure value, is the density value, is the temperature, is the molar gas constant, , is the correlation coefficient, clarify the meaning and value of each parameter; calculate Intermediate variables when When In the formula and The values ​​of and ; in, and ; The density is calculated using Newton's iteration method: have to and ,Right now and ; Select initial value ; Iterative calculation: Press Calculate ,Right now ; Convergence: If , end the iteration, take The density approximation solution Otherwise, let Continue to iterate; calculate The equivalent pressure : Approximate the density solution and Substitution ,have to ; S3. Calculate the saturated water vapor pressure: According to the saturated water vapor pressure and temperature calculation formula, use the temperature Calculate the saturated water vapor pressure ; Calculate the actual water vapor partial pressure: Given the relative humidity RH, press Calculate, where is the actual water vapor partial pressure, Dew point The corresponding saturated water vapor pressure; Convert to The trace water content at that time: According to the conversion formula, the trace water content is converted to The PPMv at this time is recorded as ; Assuming that the current temperature The measured 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 ,in is the equivalent pressure at 20°C calculated above, is the current temperature The corresponding pressure is , is the current temperature collected; Substituting the corresponding values ​​into the conversion formula, we get , that is, the trace water content PPMv at 20°C.

[0010] In the preferred embodiment, the method for evaluating the state of SF6 gas includes: A1. Stress state assessment: The calculated The set alarm pressure value Make comparisons; like , which may indicate that the density of SF6 gas is reduced, and there are risks such as reduced pressure resistance and reduced breaking capacity. Further inspection is required to see if there are any problems such as gas leakage. A2. Micro-water status assessment: Micro water content Compared with standard limit Compare; like , indicating that the moisture content exceeds the standard, which may cause SF6 to hydrolyze at high temperatures or form condensation at low temperatures, affecting the insulation performance. Appropriate measures need to be taken to check the equipment seal and perform gas treatment; A3. Comprehensive evaluation: Combine the pressure and water status evaluation results to comprehensively judge the overall status of SF6 gas; If the pressure is normal but the water content is excessive, you may focus on the source of moisture inside the equipment and how to deal with it; If both the pressure and trace water are abnormal, there may be more serious equipment problems and parts need to be repaired or replaced in time to ensure the safe operation of SF6 electrical equipment.

[0011] The present invention provides a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation and a control method thereof. By deconstructing the pressure sensing, temperature compensation mechanism, hard node signal triggering mechanism, etc. of the traditional mechanical SF6 gas density relay, and combining the research and development experience of the external cooperative unit in the field of SF6 gas micro-water density online monitoring sensor, the present invention highlights the following innovations and advantages: 1. Realize integrated multi-parameter physical quantity acquisition components, realize full contact between SF6 gas temperature, pressure (density), trace water, etc. in the same micro-probe and SF6 gas, and accurately measure the real-time physical quantity of SF6 gas; 2. Realize the SF6 gas density relay function based on automatic temperature compensation. According to the alarm (switch lock) pressure value set by the user, generate the corresponding analog electrical signal and send it to the measurement, control and protection system to replace the hard node signal of the original mechanical meter; 3. Realize full LCD dial display of SF6 gas density relay, which is resistant to high and low temperature and adaptable to working conditions such as strong electromagnetic interference and lightning strikes.

[0012] The present invention develops a SF6 digital remote density relay (digital meter), which can display the water content in SF6 gas in real time and accurately on a local LCD dial, and output the pressure, temperature, density and other parameters of SF6 gas for the background expert system to analyze and judge the internal insulation status or fault nature of the primary equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the digital density of SF6 of the present invention; Figure 2 This is a circuit diagram of a multi-parameter acquisition core of the present invention; Figure 3 This is the circuit diagram of the temperature and pressure arrangement chip of the present invention; Figure 4 It is a single chip microcomputer processing circuit diagram of the present invention; Figure 5 This is the EMC anti-interference circuit diagram of the present invention.

[0014] In the figure: pressure sensitive core 1; adapter board 2; signal conditioning board 3; power board 4; temperature core 5; ceramic circuit board 6; electrical connector 7; density meter display 8; detection docking interface 9. DETAILED DESCRIPTION

[0015] Example 1 like Figures 1 to 5 As shown, a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation, the SF6 digital density meter is provided with a density meter display 8, a detection interface 9 is provided below the SF6 digital density meter, a multi-parameter acquisition module and a temperature and pressure sorting module are provided inside the digital density meter, and the multi-parameter acquisition module and the temperature and pressure sorting module are electrically connected to the single-chip microcomputer; The detection interface 9 of the SF6 digital density meter is in direct and complete contact with the SF6 gas.

[0016] Figure 2 Circuit diagram of the multi-parameter acquisition core: The pressure sensitive core and the temperature core are connected to the ceramic circuit board through the adapter board. The lower right terminal in the adapter terminal is defined as V+, and the counterclockwise direction is V+, 0+, V-, 0-. These terminals are used to transmit signals and power supply, etc. When the ceramic circuit board is placed with the front side facing up, the two smaller pads are the temperature chip welding ends. The wire length can be adjusted according to the actual situation to ensure that the electrical connection between the components is stable and reliable.

[0017] Function: The pressure sensitive core is used to collect the pressure signal of SF6 gas, which converts the pressure change into an electrical signal output. The temperature core is responsible for collecting the temperature signal of SF6 gas, which is also output in the form of an electrical signal. The adapter board acts as a bridge connecting the pressure sensitive core, the temperature core and the ceramic circuit board to ensure smooth signal transmission. The ceramic circuit board provides an integrated installation and connection platform for the entire multi-parameter acquisition core, allowing each component to work together to achieve accurate acquisition of the physical quantities of SF6 gas temperature and pressure (density), and transmit the collected signals to subsequent circuits for processing.

[0018] Figure 3Figure 1: Connection relationship: The chip is connected to many 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 achieve a variety of functional configurations, including those 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).

[0019] Function: This chip mainly organizes, conditions and preliminarily processes the collected temperature and pressure signals. Through the circuit formed by external components, the input raw signal is filtered, amplified, analog-to-digital converted, and the analog signal collected by the sensor is converted into a digital signal format suitable for single-chip microcomputer processing. At the same time, the chip may also have some signal calibration and compensation functions to improve the accuracy and stability of the signal, provide a reliable data basis for the subsequent single-chip microcomputer to accurately calculate the density, temperature and other parameters of SF6 gas, and ensure that the system can accurately measure the relevant physical quantities of SF6 gas.

[0020] Figure 4 The single-chip microcomputer processing circuit diagram: Connection relationship: With the single-chip microcomputer STM32G030C8T6 as the core, its various pins are connected to the power supply (VDD_3.3V provides power, GND is grounded), signal input and output pins (P_SDA, P_SCL are used for I2C bus communication for data transmission, data interaction with other chips or modules) and pins related to other functions (PT_DRDY, PT_FORCE +, etc. may be related to the triggering and control of specific functions). At the same time, data communication is carried out with temperature and pressure sorting chips through specific pins, and the sorted temperature and pressure data signals are received.

[0021] Function: The single-chip microcomputer serves as the control and data processing center of the entire system, and is responsible for receiving digital signals from the temperature and pressure sorting chip. It further calculates and processes these data according to the preset program and algorithm, for example, it calculates the density, water content and other parameters of SF6 gas according to the gas state equation and related algorithm models. According to the alarm (switch lock) pressure value set by the user, it generates a corresponding analog electrical signal and sends it to the measurement and control protection system to realize the monitoring and control function of the SF6 gas state. At the same time, it can also control the LCD dial to display relevant measurement data, realize the human-computer interaction function, and coordinate the work of various parts in the entire system to ensure that the system operates stably and accurately to meet the comprehensive online monitoring needs of the SF6 gas state in SF6 high-voltage equipment.

[0022] In the preferred embodiment, the multi-parameter acquisition module includes a pressure sensitive core 1, the pressure sensitive core 1 is electrically connected to a signal conditioning board 3 through 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; In the preferred embodiment, a temperature core 5 is further provided, and the temperature core 5 is electrically connected to a ceramic circuit board 6 , and the ceramic circuit board 6 is electrically connected to the signal conditioning board 3 via the adapter board 2 .

[0023] In the preferred solution, the power supply adopts an EMC anti-interference circuit.

[0024] like Figure 5 As shown, the power input is 24V, which is connected to the circuit through the fuse F1, and then connected to TVS1 (transient suppression diode) and GDT1 (gas discharge tube). TVS1 and GDT1 work together on the power line to suppress possible interference such as surges and fast transient pulse groups. It can also be seen from the figure that during the actual verification process, the equipment was damaged in the third impact of N-PE because the gas discharge tube at the entrance was broken down. The gas discharge tube has a pulse voltage tolerance of 10 / 700us 4KV +5 times. In subsequent improvements, if the structural space allows, a wire-wound resistor can be connected in series before the two pins of the gas discharge tube to absorb part of the surge impact.

[0025] Function: TVS1 (transient suppression diode) is mainly used to quickly conduct when there is a momentary overvoltage (such as surge voltage) in the circuit, clamp the excessive voltage to a safe value, and protect the subsequent circuit components from damage. When encountering a surge impact, when the voltage exceeds its breakdown voltage, the GDT1 (gas discharge tube) will conduct and discharge the surge current to the ground, playing a shunting and protective role. The series wirewound resistor (if added) can further buffer the surge impact, reduce the surge energy borne by the gas discharge tube, and extend its service life. At the same time, it also helps to improve the ability of the entire power supply circuit to resist surges and fast transient pulse group interference, ensure the stability and reliability of the product power supply, enable the product to work normally in a complex electromagnetic environment, improve the stability and reliability of the system, and meet the requirements for the stability of the SF6 digital density meter power supply in strong electromagnetic interference environments such as substations.

[0026] Example 2 Further illustrate with reference to Example 1, Figure 1-5 The structure shown in FIG. 1 includes: S1, pressure sensitive core 1 performs pressure collection, the collection steps are: use the range of , the output is The pressure transmitter collects the pressure signal; According to the formula ,in For pressure, Output current for pressure transmitter and convert current signal into actual pressure value ; The pressure signal is collected using a pressure transmitter with a range of 0 - 1MPa and an output of 4 - 20mA.

[0027] According to the formula ( For pressure, The pressure transmitter outputs current), converting the current signal into the actual pressure value .

[0028] A dew point transmitter is also provided, with a measuring range of , signal output is The dew point transmitter collects the dew point signal; By formula ,in, is the dew point, Output current for the dew point transmitter and convert the current signal into a dew point value; The dew point signal is collected using a dew point transmitter with a range of -80—+20℃ and a signal output of 4-20mA.

[0029] By formula ( is the dew point, The output current of the dew point transmitter is converted into a dew point value.

[0030] The temperature sensor of the temperature core 5 directly obtains the temperature ,temperature The unit is ; S2. Calculation The equivalent pressure : Determine the parameters of the Beattie-Bridgman empirical formula: According to ,in, is the SF6 gas pressure value, is the density value, is the temperature, is the molar gas constant, , is the correlation coefficient, clarify the meaning and value of each parameter; according to ( is the SF6 gas pressure value (MPa), is the density value (kg / m³), is the temperature (K), is the molar gas constant ( ), , is the correlation coefficient), clarify the meaning and value of each parameter ( , Determined by gas characteristics).

[0031] In the above content, represents 20°C. In the entire calculation process, the actual temperature collected (in K) and 20°C ( , converted to thermodynamic temperature ) to perform related calculations, such as calculating the equivalent pressure at 20°C In the steps above, 20°C is used as a standard temperature to analyze and evaluate the relevant parameters of SF6 gas in order to unify the standards and accurately judge the state of SF6 gas.

[0032] calculate Intermediate variables when When In the formula and The values ​​of and ; in, and ; 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 is Kelvin, K) and Celsius temperature (unit is ℃), Here, the temperature is in degrees Celsius. When converted to thermodynamic temperature, we need to add 273.15 to get , so that a unified temperature unit can be used in subsequent calculations based on thermodynamic temperature formulas.

[0033] 2. The meaning of C and D: and This is to simplify subsequent calculations. (equivalent pressure at 20°C) formula.

[0034] In calculation Formula In use express, use After expressing, the formula can be simplified to In this way, when calculating the density using the Newton iteration method And the final calculation In the process, repeated calculations can be reduced, making the calculation process more concise and clear, and facilitating the improvement of calculation efficiency and accuracy during program implementation or manual calculation.

[0035] The density is calculated using Newton's iteration method: have to and ,Right now and ; Select initial value ; Iterative calculation: Press Calculate ,Right now ; Convergence: If , end the iteration, take The density approximation solution Otherwise, let Continue to iterate; calculate The equivalent pressure : Approximate the density solution and Substitution ,have to ; S3. Calculate the saturated water vapor pressure: According to the saturated water vapor pressure and temperature calculation formula, use the temperature Calculate the saturated water vapor pressure ; Calculate the actual water vapor partial pressure: Given the relative humidity RH, press Calculate, where is the actual water vapor partial pressure, Dew point The corresponding saturated water vapor pressure; Convert to The trace water content at that time: According to the conversion formula, the trace water content is converted to The PPMv at this time is recorded as ; Assuming that the current temperature The measured 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 ,in is the equivalent pressure at 20°C calculated above, is the current temperature The corresponding pressure is , is the current temperature collected; Substituting the corresponding values ​​into the conversion formula, we get , that is, the trace water content PPMv at 20°C.

[0036] Convert to Specific steps for measuring the moisture content (PPMv) at (20°C): 1. Determine the limits and basic relationships in relevant standards: According to DL / T 596 - 2005 Preventive Test Procedures for Power Equipment, the PPMv (volume fraction at 20°C) limit of micro-water content in different equipment (such as circuit breaker air chambers and other air chambers) after overhaul and during operation is clearly defined. For example, the PPMv (volume fraction at 20°C) limit of micro-water content in the circuit breaker air chamber after overhaul is not more than (Assumption ), no more than (Assumption ); other air chambers after overhaul shall not exceed (Assumption ), no more than (Assumption ). These limits will serve as the basis for subsequent judgment on whether the trace water content exceeds the standard.

[0037] Understand the relationship between trace water content and parameters such as temperature and pressure, generally based on the ideal gas state equation ( For pressure, is the volume, is the amount of substance, is the molar gas constant, The calculation of trace water content involves the relationship between the partial pressure of water vapor, saturated vapor pressure and other concepts and temperature and pressure.

[0038] 2. Calculate the relevant parameters at the current temperature (based on the collected temperature For example): Calculate the saturated water vapor pressure :According to the saturated water vapor pressure and temperature calculation formula (which can be obtained by looking up the saturated water vapor pressure table or known empirical formula), use the collected temperature (Unit: ) Calculate the corresponding saturated water vapor pressure .

[0039] Calculate the actual water vapor partial pressure :Given the relative humidity $RH$, press ( is the actual water vapor partial pressure, Dew point The corresponding saturated water vapor pressure is calculated. The dew point here is It is the value collected and converted by the dew point transmitter.

[0040] 3. Derive the conversion formula and calculate

[0041] Assuming that the current temperature The measured water content is (Volume fraction, related to pressure and temperature). According to the ideal gas state equation and related physical principles, under the condition of equal volume, the water content is proportional to the pressure and inversely proportional to the temperature (can be approximately considered).

[0042] Assume the conversion formula is ,in is the equivalent pressure at 20°C calculated above, is the current temperature The corresponding pressure (can be obtained by collecting and converting through the pressure transmitter), (20°C), is the current temperature collected (in units of ).

[0043] Substituting the corresponding values ​​into the conversion formula, we get , that is, the trace water content (PPMv) at 20°C.

[0044] 4. Micro-water status assessment The calculated Compared with the standard limit value determined previously ( , , , etc.) for comparison.

[0045] if Greater than the operating limit of the corresponding equipment (such as the operating limit of the circuit breaker gas chamber Or other air chamber operating limit ), it means that the water content exceeds the standard, which may cause SF6 to hydrolyze at high temperatures or form condensation at low temperatures, affecting the insulation performance. Appropriate measures need to be taken, such as checking the equipment seal and performing gas treatment. If it is within the limit, the trace water content is normal.

[0046] Example 3 Further illustrate with reference to Example 1, Figure 1-5 The structure shown in the figure, the method for evaluating the state of SF6 gas includes: A1. Stress state assessment: The calculated The set alarm pressure value Make comparisons; like , which may indicate that the density of SF6 gas is reduced, and there are risks such as reduced pressure resistance and reduced breaking capacity. Further inspection is required to see if there are any problems such as gas leakage. A2. Micro-water status assessment: Micro water content Compared with standard limit Compare; like , indicating that the moisture content exceeds the standard, which may cause SF6 to hydrolyze at high temperatures or form condensation at low temperatures, affecting the insulation performance. Appropriate measures need to be taken to check the equipment seal and perform gas treatment; A3. Comprehensive evaluation: Combine the pressure and water status evaluation results to comprehensively judge the overall status of SF6 gas; If the pressure is normal but the water content is excessive, you may focus on the source of moisture inside the equipment and how to deal with it; If both the pressure and trace water are abnormal, there may be more serious equipment problems and parts need to be repaired or replaced in time to ensure the safe operation of SF6 electrical equipment.

[0047] Example 4 Further illustrate with reference to Example 1, Figure 1-5 The structure shown here is aimed at the problem of mechanical density relay: 1. Adopt digital acquisition and transmission technology By using the integrated multi-parameter physical quantity acquisition components mentioned in the article, the SF6 gas temperature, pressure (density), trace water, etc. can be fully contacted with the SF6 gas in the same microprobe to accurately measure the real-time physical quantity. The collected analog signals are converted into digital signals through digital sensors (such as digital temperature sensors) and transmitters with good linearity (pressure transmitters, dew point transmitters) for subsequent processing and transmission.

[0048] Establish a reliable data communication link, such as using RS485 and other communication interfaces, to transmit the collected multi-parameter data in real time to the measurement and control protection system or background monitoring equipment, realize remote monitoring of data, and overcome the problems of inconvenient reading and data transmission of mechanical density relays and the inability to remotely measure.

[0049] 2. Optimize density calculation and monitoring algorithms The density of SF6 gas is calculated using the Beattie-Bridgman empirical formula combined with the Newton iteration method and other accurate algorithms, and the equivalent pressure at 20°C is calculated based on the The pressure is compared with the set alarm (switch lock) pressure value to realize the SF6 gas density relay function based on automatic temperature compensation. When abnormal density is detected, the corresponding analog electrical signal is generated in time and sent to the measurement, control and protection system to replace the hard node signal of the original mechanical meter, thus improving the accuracy and reliability of monitoring.

[0050] Regarding the problem of detecting trace water content in SF6 gas: 1. Improve the method and equipment for detecting trace water The micro-water calculation method based on multi-parameter acquisition described in the article is adopted to calculate the saturated water vapor pressure and the actual water vapor partial pressure, and use the relevant standards (such as DL / T 596-2005) and conversion formulas to convert the micro-water content to PPMv at 20°C, so as to achieve online and accurate measurement of the micro-water content, thus overcoming the problems of non-online detection and inaccurate data of portable dew point meters.

[0051] Develop high-precision and high-stability micro-water sensors or detection modules and integrate them into multi-parameter acquisition systems to ensure the accuracy and reliability of micro-water content measurement while reducing the impact on equipment operation (such as no need to discharge SF6 gas for a long time).

[0052] 2. Realize real-time monitoring and automated management of trace water content The real-time monitoring data of micro-water content is integrated with the automation system of the entire substation to realize continuous monitoring of the micro-water content in the gas chamber of the SF6 equipment. When the micro-water content exceeds the set threshold, the alarm and locking device are automatically activated, and the relevant data is transmitted to the monitoring center, providing a basis for equipment status maintenance, realizing the automation of power transmission and transformation management and equipment status maintenance.

[0053] Overall system integration and optimization: 1. Develop an integrated monitoring system Develop SF6 digital remote density relay (digital meter), which integrates multi-parameter acquisition, automatic temperature compensation, micro-water content calculation and monitoring, data communication and other functions, and realizes comprehensive online accurate measurement of SF6 gas state, automatic alarm interlocking and real-time data remote transmission. The meter can display relevant parameters on the local LCD dial, which is convenient for on-site operation and maintenance personnel to view, and transmit data to the background expert system for analysis and judgment, providing comprehensive support for the evaluation of the internal insulation state or fault nature of primary equipment.

[0054] 2. Improve system stability and reliability In the system design, we pay attention to the EMC anti-interference design of the power supply, such as adopting a power supply design that can resist level IV surge and level IV fast transient pulse group interference to ensure that the system operates stably and reliably in complex electromagnetic environments such as high-voltage substations / converter stations. At the same time, we optimize the design and selection of hardware equipment (such as pressure-sensitive cores, temperature cores, adapter boards, signal conditioning boards, etc.) to improve the overall performance and service life of the system.

[0055] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation, characterized by: The SF6 digital density meter is provided with a density meter display (8), a detection interface (9) is provided below the SF6 digital density meter, a multi-parameter acquisition module and a temperature and pressure sorting module are provided inside the digital density meter, and the multi-parameter acquisition module and the temperature and pressure sorting module are electrically connected to the single-chip computer; The detection interface (9) of the SF6 digital density meter is in direct and complete contact with the SF6 gas.

2. According to claim 1, a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation is characterized by: The multi-parameter acquisition module comprises a pressure sensitive core (1), the pressure sensitive core (1) 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 supply board (4), and both the signal conditioning board (3) and the power supply board (4) are electrically connected to an electrical connector (7).

3. According to claim 2, a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation is characterized by: A temperature core (5) is also provided, the temperature core (5) is electrically connected to a ceramic circuit board (6), and the ceramic circuit board (6) is electrically connected to a signal conditioning board (3) via an adapter board (2).

4. The SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation according to claim 1 is characterized in that: The power supply adopts EMC anti-interference circuit.

5. According to claim 3, a control method of a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation is characterized by: The method includes: S1, pressure sensitive core (1) to collect pressure, the collection steps are: use the range of , the output is The pressure transmitter collects the pressure signal; According to the formula ,in For pressure, Output current for pressure transmitter and convert current signal into actual pressure value ; A dew point transmitter is also provided, with a measuring range of , signal output is The dew point transmitter collects the dew point signal; By formula ,in, is the dew point, Output current for the dew point transmitter and convert the current signal into a dew point value; The temperature sensor of the temperature core (5) directly obtains the temperature ,temperature The unit is ; S2. Calculation The equivalent pressure : Determine the parameters of the Beattie-Bridgman empirical formula: According to ,in, is the SF6 gas pressure value, is the density value, is the temperature, is the molar gas constant, , is the correlation coefficient, clarify the meaning and value of each parameter; calculate Intermediate variables when When In the formula and The values ​​of and ; in, and ; The density is calculated using Newton's iteration method: have to and ,Right now and ; Select initial value ; Iterative calculation: Press Calculate ,Right now ; Convergence: If , end the iteration, take The density approximation solution Otherwise, let Continue to iterate; calculate The equivalent pressure : Approximate the density solution and Substitution ,have to ; S3. Calculate the saturated water vapor pressure: According to the saturated water vapor pressure and temperature calculation formula, use the temperature Calculate the saturated water vapor pressure ; Calculate the actual water vapor partial pressure: Given the relative humidity RH, press Calculate, where is the actual water vapor partial pressure, Dew point The corresponding saturated water vapor pressure; Convert to The trace water content at that time: According to the conversion formula, the trace water content is converted to The PPMv at this time is recorded as ; Assuming that the current temperature The measured 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 ,in is the equivalent pressure at 20°C calculated above, is the current temperature The corresponding pressure is , is the current temperature collected; Substituting the corresponding values ​​into the conversion formula, we get , that is, the trace water content PPMv at 20°C.

6. According to claim 4, a control method of a SF6 digital density meter based on multi-parameter acquisition and automatic temperature compensation is characterized by: The methods for evaluating the status of SF6 gas include: A1. Stress state assessment: The calculated The set alarm pressure value Make comparisons; like , which may indicate that the density of SF6 gas is reduced, and there are risks such as reduced pressure resistance and reduced breaking capacity. Further inspection is required to see if there are any problems such as gas leakage. A2. Micro-water status assessment: Micro water content Compared with standard limit Compare; like , indicating that the moisture content exceeds the standard, which may cause SF6 to hydrolyze at high temperatures or form condensation at low temperatures, affecting the insulation performance. Appropriate measures need to be taken to check the equipment seal and perform gas treatment; A3. Comprehensive evaluation: Combine the pressure and water status evaluation results to comprehensively judge the overall status of SF6 gas; If the pressure is normal but the water content is excessive, you may focus on the source of moisture inside the equipment and how to deal with it; If both the pressure and trace water are abnormal, there may be more serious equipment problems and parts need to be repaired or replaced in time to ensure the safe operation of SF6 electrical equipment.

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