CN201166563Y - Apparatus for on-line monitoring SF6 gas status of high tension SF6 electrical equipment - Google Patents

Abstract

The utility model is an on-line monitoring device for SF ₆ gas state of high-voltage SF ₆ electrical equipment, which is composed of a pressure sensor, a temperature sensor, a humidity sensor, a signal conditioning module, a main control module and an output display module, wherein the pressure, temperature and humidity sensors are The signal output terminals are respectively connected to the corresponding input terminals of the signal conditioning module, the output terminals of the signal conditioning module are connected to the input terminals of the main control module, and the I/O expansion output terminals of the main control module are respectively connected to the isolation conversion and digital-to-analog conversion of the signal conditioning module Inputs and Outputs shows the module inputs. During work, the monitoring device amplifies the signals obtained by the sensors installed in the SF ₆ gas chamber of the equipment, performs modulus conversion, data calculation and online analysis, and obtains indoor gas pressure, temperature rise, humidity and other information, which can comprehensively monitor SF ₆ The state parameters of the gas have the advantages of simple and reliable structure, small interference, high application value, etc., and meet the actual needs of the power system and the requirements of modern industrial development.

Description

High-voltage SF6 electrical equipment SF6 gas state online monitoring device

technical field

The utility model belongs to the technical field of electric power equipment, and relates to a device for fault monitoring of high-voltage electrical equipment, in particular to a device for monitoring the fault of high-voltage sulfur hexafluoride (SF 6 ) electrical equipment by using sulfur hexafluoride (SF ₆ ) gas pressure fluctuations.

Background technique

Sulfur hexafluoride (SF ₆ ) has excellent electrical insulation and arc extinguishing properties, and is considered to be the most ideal gas insulation and arc extinguishing medium so far. The unique properties of SF ₆ gas make the electrical equipment using it as an insulating arc extinguishing medium have high dielectric strength, strong arc extinguishing ability, large breaking capacity, fire and explosion protection, small size, small footprint and space, light weight, and low noise. Small size, low operating temperature, easy installation, safe and reliable fully sealed electrical appliances, no oxidation problems, long maintenance cycle and many other advantages. With the rapid development of today's electric power industry, SF ₆ electrical equipment has been more and more widely used, and its various levels of equipment, especially high-voltage and ultra-high-voltage equipment, have more and more application types, including fully enclosed combined electrical appliances (GIS), circuit breaker (GCB), transformer, current transformer (GICT), voltage transformer (GIPT), power cable (GIC), bushing, lightning arrester, etc., have played a good role in the safe and economical operation of the power system .

Although SF ₆ gas has great advantages as an electrical insulation and arc extinguishing medium, the change of the state of SF ₆ gas has a great impact on the electrical performance of equipment and the living environment of human beings, which is embodied in pressure, temperature, humidity, density, air , arc decomposition products, etc. affect the electrical performance of the equipment. The electrical properties of SF ₆ gas are closely related to the state of the gas. The electrical properties of SF ₆ vary greatly in different states. Therefore, it is necessary to keep the gas in the best state during the operation of the equipment to ensure the stability of SF ₆ electrical equipment. At the same time, since the switch mechanism, primary circuit and contact parts of SF ₆ electrical equipment are all enclosed in the sealed air chamber with SF ₆ as insulating gas, circuit-related faults will more or less cause SF ₆ gas-related state parameters Severe cases may cause accidents in various situations. Therefore, through online detection and analysis of changes in the state parameters of SF ₆ gas, it is largely helpful to the discovery, diagnosis, and location of equipment failures.

Before the technical solution of this utility model was proposed, the methods for detecting the gas state of SF ₆ equipment mainly included off-line moisture measurement, gas leakage detection, arc decomposition product detection, mechanical density relay and pressure gauge detection, and digital density relay detection They are basically offline tests, and each of them has some defects in specific applications. The summary and analysis are as follows.

Off-line moisture measurement: At present, the trace moisture content of SF ₆ gas is tested by an off-line moisture meter. According to the "Preventive Test Regulations for Electric Power Equipment", the equipment is tested every 1 to 3 years. Its advantage is that the test accuracy is high, and the disadvantage is that the test is greatly affected by the environmental conditions, it needs to discharge SF ₆ gas to the atmosphere, it cannot reflect the real-time situation of moisture changes, and it consumes manpower and material resources.

Gas leakage detection: According to the national standard GB8905-1997 "Guidelines for Gas Management and Monitoring in SF ₆ Electrical Equipment", the annual gas leakage rate of SF ₆ equipment should be ≤1%. When leakage occurs in the operating SF ₆ equipment, the annual air leakage rate of the equipment can be detected and calculated by local bandage method or pressure conversion method. When using the local wrapping method to detect, the equipment must first be shut down, and then the suspected leakage point is wrapped with plastic film for detection, which will cause less power transmission loss, consume manpower and material resources, and cannot fully and instantly reflect the sealing status of the equipment; the pressure conversion method is through The change of the pressure gauge within a certain period is used to calculate the annual air leakage rate. The gas density in the equipment is obtained by manually _observing the pressure indication value and checking the SF ₆ density curve. It is difficult to obtain an accurate value due to the coarse scale of the density curve and the large deviation of manual calculation. It is necessary to have sufficient cycle time and a large leak to find the leak, so it is difficult to find the leak in the early stage of the fault.

Detection of arc decomposition products: The detection results of arc decomposition products can reflect the condition of the equipment gas and serve as a reference criterion for judging the internal faults of the equipment. At present, there are two commonly used detection methods in the world: laboratory advanced analytical instrument analysis and on-site chemical detection tube test. The analysis of advanced analytical instruments in the laboratory requires the combined testing of chromatograph-mass spectrometer-infrared spectrophotometer. The equipment is expensive and requires on-site sampling and then analysis in the laboratory. Therefore, it is generally only used for research purposes; although the on-site detection tube test method is convenient, its accuracy is low, and it is a semi-quantitative test method.

Mechanical density relay and pressure gauge detection: Traditional pressure and density monitoring is realized through SF ₆ gas density relay and pressure gauge. If SF ₆ gas leaks or liquefies, the density relay will send an alarm signal through the protection circuit until the action of the lock switch to protect the equipment and prevent accidents. The mechanical density relay is a pressure comparison device. During the test, the air pressure of the small sealed air chamber filled with pure SF ₆ gas and the main air chamber of the equipment will change with the ambient temperature. If the two air chambers are not leaking, When the ambient temperature changes, the air pressure change is always synchronous, and the pressure inside and outside the bellows (that is, the main air chamber) is always balanced, that is, the gas density in the main air chamber does not change, the density relay will not operate, and the density relay will not be affected. The influence of ambient temperature changes; if the main air chamber leaks, the mass of SF ₆ gas in the main air chamber decreases, and its volume is constant, then the gas density in the main air chamber decreases, and the corresponding gas pressure in the main air chamber decreases , The bellows deforms and stretches in order to balance the air pressure in the pipe and the air pressure in the main air chamber, and drives the pointer or contact to move. Due to the long-term operation of the mechanical pressure gauge on the job site, it is very common to cause misalignment due to metal fatigue. The vibration of the switchgear causes the pointer to loosen, and there are also cases where the equipment is over-inflated due to mechanical jamming . The mechanical density relay has been used as a traditional gas density detection device. In principle, it is a pressure comparator that cannot directly reflect the density of the gas, and often has its own failures. Some of them cause false alarms due to air leakage in the standard small gas chamber. There are also cases where the equipment leaks due to mechanical jamming and does not call the police, and there are cases where the air pressure increases due to equipment failure due to lack of overvoltage protection and does not call the police. In addition to outputting alarms and lockouts, continuous monitoring values cannot be output. The relay can only read data manually on site (non-pointer density relays cannot even read any data), and cannot perform telemetry and remote control.

Digital density relay detection: In recent years, many mainstream electric companies in the world have successively developed and launched a variety of digital gas state monitoring units for online detection of the density and pressure parameters of sulfur hexafluoride gas. The function of the relay, that is, temperature and pressure sensors are used to calculate the SF ₆ gas density through the Beattie-Bridgman actual gas state equation, and it contains a density alarm and a blocking relay, which can transmit data remotely, and some products contain a humidity detection function. The sensors are generally high-cost, large-volume dew point resistance-capacitance humidity sensors. Except for Mitsubishi's Hybrid Sensor, the above products do not have fault diagnosis function, but Mitsubishi's Hybrid Sensor uses the content of decomposed gas to judge whether there is a fault in the equipment, and the detection of decomposed gas is more difficult , and its diffusion is affected by the installation position of the sensor. According to the installation position of the current density relay, it is difficult to detect the decomposition products, and the transmission of pressure is almost independent of the installation position. The time of detecting pressure fluctuations is almost synchronized with the time of failure .

At present, the maintenance method of power equipment is gradually changing from planned maintenance to condition-based maintenance. The basic condition for implementing condition-based maintenance is to have enough operating state parameters to determine the best time for condition-based maintenance. On-line monitoring of SF ₆ gas status meets the requirements of this advanced maintenance method, and is of great significance for ensuring the normal operation of equipment, discovering and judging potential equipment failures, locating existing failures, and mastering the overall operating conditions of equipment.

Utility model content

The purpose of this utility model is to solve the problems existing in the prior art. On the basis of synthesizing the functions and advantages of other related products in the world, through a comprehensive analysis of the state of SF ₆ gas, combined with the actual situation of the power system, a The utility model relates to an on-line monitoring device for SF _{6 gas state of high-voltage SF 6 electrical} equipment with simple and reliable structure, little interference and good economy.

The technical solution for realizing the purpose of the above invention is as follows: the provided high-voltage SF ₆ electrical equipment SF ₆ gas state on-line monitoring device is composed of a pressure sensor, a temperature sensor, a humidity sensor, and a signal containing an isolation conversion and a digital-to-analog conversion circuit. It consists of a conditioning module, a main control module containing an I/O expansion circuit, and an output display module. The signal output terminals of the pressure sensor, temperature sensor and humidity sensor are respectively connected to the pressure, temperature and humidity signal input terminals of the signal conditioning module. The output terminal of the conditioning module is connected to the input terminal of the main control module, and the I/O expansion output terminal of the main control module is respectively connected to the isolation conversion and digital-to-analog conversion input terminals of the signal conditioning module and the input terminal of the output display module. In the work, the pressure, temperature and humidity fluctuation signals obtained by the sensors pre-installed on the SF ₆ gas chamber of the equipment and the monitoring and detection device composed of the later circuit are amplified, modulo-to-digital conversion, data calculation and online analysis, and the indoor Indoor gas information such as gas pressure, temperature rise, humidity, etc. Once a gas failure occurs inside the equipment, causing one or more state parameters to rise to a certain limit, the online monitoring device will send back an alarm signal, prompting possible equipment failure. , and judge and locate whether there is gas leakage, overheating and moisture exceeding the standard in the gas chamber of the SF ₆ equipment, as well as the location of the fault, so as to detect the fault at an early stage, prevent the fault from further developing into an equipment accident, and reduce losses.

On the basis of synthesizing the advantages of other related products at home and abroad, the utility model proposes the overall design scheme of the SF ₆ gas state online monitoring unit through a comprehensive analysis of the SF ₆ gas state and combined with the actual situation of the power system. In this design, in addition to _the detection of conventional state parameters (pressure, temperature, etc.) The gas pressure signal that is less disturbed and has a different nature from other interference signals is analyzed, so as to carry out the design idea of electrical equipment fault judgment. During the development process of the utility model, the designer fully selected the hardware components of the component units through extensive research and testing, taking into account both usability and economy, so that the design of the utility model has a relatively High practical value. Through theoretical analysis and experiments, we found a method to test the humidity of SF ₆ gas with relatively low-priced sensors, solved the existing problems, realized the idea of judging electrical faults through pressure, temperature, and humidity signals, and achieved ideal results. In addition, in software design, assembly language programming is adopted to realize the method of real-time calculation of gas density through single-chip microcomputer, which improves the test accuracy and overall operation speed.

Description of drawings

Fig. 1 is a hardware block diagram of an embodiment of the SF ₆ gas state online monitoring device for high-voltage SF ₆ electrical equipment described in the present invention.

Figure 2 is a schematic diagram of the conditioning circuit for the pressure signal.

Figure 3 is a schematic diagram of the temperature signal conditioning circuit.

Figure 4 is a schematic diagram of the conditioning circuit for the humidity signal.

Detailed ways

The structural design of the present utility model and the content of functional design are as follows.

1. Selection of sensors: The reliability of the sensor is directly related to the accuracy and reliability of the unit test. The utility model design uses three sensors to complete the overall test task, namely pressure, temperature and humidity sensors.

1.1 Selection of pressure sensor

The pressure sensor is the most important sensor in this device, and its accuracy and sensitivity are directly related to the pressure test, the accuracy of density calculation and the stability and reliability of fault judgment. According to the design requirement of the present invention, the pressure mutation detection requires the output stability of the sensor to be good, the response is fast, and the sensitivity is as high as possible, so as to facilitate the detection of small pressure mutation signals. Because the sensor is directly in contact with the SF ₆ gas, and the SF ₆ gas will produce some corrosive products after the action of the arc, so the sensor is required to have good corrosion resistance. The sensor also requires the volume to be as small as possible and has a sealing method suitable for gas sealing, so as to reduce the volume of the unit and increase the reliability of gas sealing. It also requires the sensor to have a wide temperature compensation range and the temperature coefficient as small as possible. According to the functional design requirements of the present utility model, the pressure sensor selected by the designer is the M86 miniature stainless steel piezoresistive pressure sensor produced by the IC company of the United States through comprehensive balance considerations. This sensor has two types: gauge pressure type and absolute pressure type. In line with the general practice of pressure display, choose a gauge pressure sensor. The pressure sensor has the characteristics of high sensitivity, good dynamic performance, small size, firm structure, compatibility with harsh media, and simple and reliable sealing method. Its output is linear, the temperature compensation range is -20°C to +85°C, and the pressure hysteresis is small. , the output is linear to facilitate calibration and software programming.

1.2 Selection of temperature sensor

The temperature sensor uses Honeywell (Pt1000) platinum resistance sensor which is widely used in industrial temperature measurement, temperature control and detection. Platinum resistors have many advantages, such as high precision, good stability, reliable performance, high mechanical strength, high resistivity, and large temperature measurement range. The most important point is that SF ₆ will produce strong corrosion after arcing. Selecting a platinum resistor with very stable chemical properties can prevent the sensor from being corroded and causing misalignment.

1.3 Selection of Humidity Sensor

The selection of the humidity sensor in the utility model considers the humidity range of the measured medium, test accuracy requirements, sampling methods, medium compatibility, working environment requirements, shape and structure requirements, replaceability requirements, and cost requirements. Under normal conditions, the humidity range of SF ₆ gas used for power equipment is tens to hundreds of μL/L (equivalent to the range below 5% RH, the operating equipment requires a maximum humidity of no more than 500 μL/L, and the gas chamber that generates arcs requires No more than 300μL/L, expressed as 2%RH and 1.2%RH by relative humidity at 20°C), which belongs to the low humidity range in the humidity test. Because of the large difference with the humidity in the environment and the small absolute value of humidity, it belongs to the trace test , so there are many influencing factors. Compared with the relative humidity range test (5%RH~90%RH range), the humidity range test is recognized as a more difficult test. The measurement of low humidity in the gas medium generally uses a dew point resistance-capacitance sensor. The principle is to use the characteristics of the electrical characteristics of some hygroscopic materials to change with the amount of absorbed water molecules. Generally, the capacitance or impedance of the sensitive element is used to test the humidity. Its advantage is that it adopts pure weak electricity measurement, no other physical or chemical process, low power consumption, wide measurement range, fast response, good low humidity response, no need for constant gas flow, moderate measurement accuracy, etc., many Off-line hygrometers all use this sensor as a humidity measuring element. However, they have their own disadvantages. For example, due to the corrosion of the moisture-absorbing layer or the decay of the chemical structure, the characteristics of the sensor change. The hygrometer made of it needs to be checked every six months to ensure the accuracy of the humidity measurement; some humidity sensor signal processing methods Complicated and relatively large. The price of these sensors is very high, and the functional relationship between the output response and the gas humidity is generally non-linear, and it needs to be converted into other humidity units, and it needs to be calculated with the test data of the temperature and pressure sensors. Due to the different compensation methods of different sensors, the difference in the post-processing circuit is relatively large. This kind of sensor is generally sold in the form of a humidity transmitter, which is not suitable for the development and production of independent products. After extensive research and experiments, the designer of this utility model has adopted the HM1520 quartz crystal oscillator sensor product of the French Humriel company. This is a low-cost humidity sensor based on the quartz crystal oscillator principle. There are two quartz crystal oscillators in the sensor. Crystal oscillator, one is a reference oscillator, which is in a sealed state, and the other is a humidity measuring oscillator. When the gas containing moisture passes through the measuring crystal oscillator, the measuring crystal oscillator absorbs the moisture in the gas, causing its quality to change, resulting in the vibration frequency of the crystal oscillator. At this time, the frequency of the reference crystal oscillator has not changed, and the frequency of the wet measuring crystal oscillator is compared with the reference crystal oscillator. After detection, low-pass filtering, and amplification, it becomes a voltage signal output. The advantage of this kind of humidity sensor is that it is small in size, the design of the post-processing circuit is relatively simple, the interchangeability is good, and the cost is much lower. Its accuracy is the best in the low-humidity section. The temperature basically has no effect on its output, and no temperature compensation is required. At the same time, because it adopts a solid polymer structure, its media compatibility is also very good, and it is basically suitable for the humidity test of SF ₆ media.

2. Digital SF ₆ gas state online monitoring device

Referring to Fig. 1, the hardware circuit part of the high-voltage SF ₆ electrical equipment SF ₆ gas state online monitoring device described in the utility model includes three parts: a signal conditioning module, a main control module and an output display module. The signal conditioning module is composed of drive amplifier circuit 1, channel selection circuit 2, analog-to-digital conversion circuit 4 and isolation conversion circuit 3, the main control module is composed of data processor 7 and I/O expansion circuit 8, and the output display module is controlled by the output The circuit 12, the output isolation circuit 11, the output display lamp 14, the alarm relay group 13 and the status lamp 15 are composed, and the signal output terminals of the pressure sensor P, the temperature sensor T and the humidity sensor H are respectively connected to the pressure, temperature and pressure of the driving amplifier circuit 1. Humidity signal input terminal, the output terminal of the driving amplifier circuit 1 is connected to the input terminal of the data processor 7 after passing through the channel selection circuit 2 and the analog-to-digital conversion circuit 4 in sequence, and the output signal of the data processor 7 is connected to the input terminal of the data processor 7 after passing through the I/O expansion circuit 8 Divided into two routes, one route is connected to the input terminals of the analog-to-digital conversion circuit 4 and the isolation conversion circuit 3 at the same time, and the other route is respectively connected to the input terminals of the output isolation circuit 11, the output display lamp 14 and the status lamp 15 after passing through the output control circuit 12 , the output terminals of the isolation conversion circuit 3 and the output isolation circuit 12 are connected to the input terminals of the channel selection circuit 2 and the alarm relay group 13 respectively. In a specific embodiment of the present invention, the drive amplifier circuit 1 is composed of a current source chip LM124, the channel selection circuit 2 adopts an integrated chip model CD4051, and the analog-to-digital conversion circuit 4 adopts a 12-bit digital-to-analog conversion model of AD574 The data processor 7 is composed of an AT89C51 single-chip microcomputer configured with a real-time clock circuit 5, a RAM expansion circuit 6, a power monitoring circuit 9 and a keyboard expansion circuit 10. The isolation conversion circuit 3 is composed of a TLP521 optocoupler isolation module. I/O The expansion circuit 8 is composed of an INTEL8255 chip, and the output control circuit 12 and the output isolation circuit 11 are respectively composed of an integrated digital tube ZCL002 and a TLP521 optocoupler isolation module.

2.1 Signal conditioning module

The function of the signal conditioning module is to convert the millivolt and resistance signals from pressure, temperature and humidity sensors into voltage signals from 0V to 10V. These three voltage signals are connected to the analog-to-digital conversion chip through the channel selection chip CD4051, and converted into digital quantities for the central processing unit to display, calculate and control. Each part is introduced as follows:

2.1.1 Pressure signal conditioning

Figure 2 is a schematic diagram of the conditioning circuit for the pressure signal. Among them, the sensor P adopts a piezoresistive pressure sensor, which has low temperature drift and good linearity. The pressure sensor is powered by a constant current source provided by the current source chip LM124. The output of the pressure sensor is a millivolt level signal, which is filtered and differentially amplified into a 0-10V voltage signal and then enters the CD4051. After the analog signal is gated, it enters the AD574 for digital-to-analog conversion.

2.1.2 Temperature Signal Conditioning

Figure 3 is a schematic diagram of the temperature signal conditioning circuit. The temperature conditioning circuit is realized by two LM124s. One of the LM124s provides a 1V reference voltage. With the Honeywell high-precision platinum resistance temperature sensor, the accurate temperature value can be measured, and then the signal is amplified by the post-stage op amp to a voltage signal of 0-10V. Enter AD conversion after being gated by CD4051.

2.1.3 Humidity Signal Conditioning

See Figure 4 for the humidity signal conditioning circuit. The output signal of the humidity sensor adopted in the present invention is a voltage signal, and its typical output is about 1000mV, which is relatively easy to measure. In the actual performance experiment of the sensor, the output of the sensor can be measured by a multimeter. The actual output range is about a few hundred millivolts to more than a thousand millivolts. The output signal of the sensor is checked with an oscilloscope, and it is found that some of the output signals High-frequency signal, therefore, the ordinary RC low-pass filter is used in the conditioning circuit to process the signal, which can achieve a certain effect, but in addition to the high-frequency signal, there are many periodic low-frequency components, which cannot be removed by this circuit , after being processed by software filtering, a better effect is achieved.

2.1.4 Digital-to-analog conversion module

The device adopts 12-bit digital-to-analog converter, which is determined by the precision and operation speed required by the equipment operation. AD574 is a high-precision and low-price successive approximation AD converter launched by the American Analog Devices Company. It is the most widely used and moderately priced A/D converter in my country in recent years. Connect with 8-bit or 16-bit microprocessor bus interface. AD574 has precision reference voltage and clock circuit inside, and can complete AD conversion independently without any external components, which provides great convenience for the application.

2.2 Main control module

The main control module is constructed with the AT89C51 single-chip microcomputer as the core. This chip is fully compatible with the C51 series single-chip microcomputer. The speed can reach 30MHz, and 32K flash memory is integrated inside it. In order to record the data in normal state and fault state, the system expands 8K static memory (SRAM) 6264. Due to the limited ports of the AT89C51 single-chip microcomputer, in order to realize channel selection, output display and indicator light control, two 8255 chips are used to expand the I/O function. Using the MAX813L chip to realize the monitoring of the power supply and the hardware watchdog function can further improve the reliability of the system. In view of the fact that the utility model is designed to operate on-site in a substation and there are many interferences, the higher integration of AT89C51 can increase the stability of the system; the monitoring device is designed for long-term online, and its low-power idle mode can effectively reduce the power consumption of electrical units And CPU loss, and because of the possibility of temporary loss of on-site power supply, its power-down mode can also prevent the data stored in the system from being lost, and the comprehensive utilization of its internal resources can reduce the system cost. The real-time clock circuit 5, the RAM expansion circuit 6, the power monitoring circuit 9 and the keyboard expansion circuit 10 in the main control module II are all conventional configuration circuits, and will not be repeated here.

2.3 Output display module

The output display module is composed of a status light (LED indicator light), a digital tube (output display light) and its corresponding control chip, and an alarm relay. In order to improve the efficiency of the single-chip microcomputer, the high-brightness integrated digital tube ZCL002, which integrates latching, driving, and amplification, is used to realize the output display function, which can facilitate the CPU to perform centralized calculations; since the digital tube can only display numbers, the LED indicator light is expanded to match the digital display. When the LED indicator marked with the parameter name is on, the digital tube displays the value of the current parameter or the corresponding fault parameter value.

3. Functional design of digital SF ₆ gas state online monitoring device

3.1 Alarm and lock function

While the device measures and converts the basic parameters of SF ₆ gas, it uses them for real-time analysis and judgment in the device. When the equipment is abnormal or faulty, an alarm signal will be given, and if there is a serious gas leakage, the action of the switch will be blocked to protect the electrical equipment and prevent serious equipment accidents. At the same time, the designer believes that SF ₆ gas is the carrier of SF ₆ electrical equipment fault information, and based on this principle, the overheat fault and discharge fault alarm functions are designed.

3.1.1 Low SF ₆ gas density alarm and blocking function (large leakage alarm and blocking)

In a well-sealed SF ₆ equipment, the amount of SF ₆ gas filled is constant, and the volume of the equipment is constant. According to the BB gas state equation, the density of the gas should also be constant, and the gas pressure varies with the environment. Vary with changes in temperature. As the ambient temperature increases, the gas pressure increases, and as the ambient temperature decreases, the gas pressure decreases. The design of the utility model adopts the comparison of the SF ₆ gas density calculated by the direct test and calculation of the BB gas state equation with the preset alarm density and blocking density value. When the gas density of the equipment reaches the alarm preset value, the circuit system will make the alarm relay act. The main control room generates an alarm signal to remind the equipment of gas leakage; when the gas pressure is further reduced and reaches the preset value of the lockout, the insulation and arc extinguishing ability of the gas cannot meet the design requirements at this time, and an arc may be caused if the switch operates at this time Difficulty in extinguishing leads to burning of switch contacts or even equipment explosion accidents, so the circuit system of the device activates the blocking relay, and cuts off the operating power of the equipment through the electrical circuit, thereby preventing the equipment from operating when the arc extinguishing and insulation capabilities are reduced, and preventing accidents; When the gas density rises to the alarm and lockout preset value after emergency treatment (such as inflating the equipment), the device will disconnect the alarm or lockout circuit and return to the normal state.

3.1.2 High pressure alarm and its principle (overheat fault location or alarm)

The device described in the utility model is designed with a high-pressure alarm relay, and the pressure parameter is selected to detect the pressure of the equipment. Once an overheating fault occurs inside the equipment, causing the pressure to rise to a certain limit, the device will act as a high-pressure alarm relay, which will be generated in the main control room of the substation. The alarm signal indicates the occurrence of possible equipment accidents, so that equipment failures can be found in the early stage, preventing further development of failures into equipment accidents and reducing losses.

3.1.3 Pressure fluctuation analysis and judgment or fault location (discharge fault location or alarm)

Among the state parameters of SF ₆ gas, gas temperature, density, humidity and decomposition product content should all be slow variables. Once a sudden discharge fault occurs, the parameter that changes the fastest is the pressure parameter. Any sudden failure will produce the release of energy. According to the physical and chemical principles, the released energy will cause a sudden rise in the local temperature and pressure of the gas. Since the pressure wave is a longitudinal wave, the transmission of pressure changes in the gas is isotropic At the same time, the transfer process of temperature change in SF ₆ gas is generally very slow, and it must be carried out through the convection and radiation of the gas, and the sudden rise of pressure due to its isotropic nature, is far away from the location where the fault occurs. That is, it can be easily detected almost synchronously. Therefore, the sudden change of pressure brings the most direct and almost synchronous information of equipment failure, which is very suitable for equipment failure judgment. During a day, as the ambient temperature changes, the gas pressure will also fluctuate to a certain extent, but this fluctuation is slow and the amplitude is small. When a fault occurs in the equipment, the pressure will suddenly rise in a short period of time (about 1 second), and will slowly decline within tens of seconds. According to these two criteria, the software can be used to judge the change to know the equipment If a fault occurs in the SF 6 equipment, since each gas chamber of the SF ₆ equipment is equipped with this unit, the fault can be located to the faulty gas chamber. Utilizing the characteristics that the interference signal is generally a spike pulse, rising and falling quickly, it can prevent the influence of the incoming circuit interference signal; the slow pressure change can also be excluded by the time criterion, that is, the interference signal will not be recognized as a fault signal . The utility model can achieve some functions of these complex detection equipment by using a simple pressure sensor and software interpretation. As long as the sensitivity of the pressure sensor is large enough, since the interference factors of the pressure in the electrical environment are few and easy to eliminate, it can be detected. Small discharge faults, even partial discharge faults.

3.1.4 Gas leak detection (trace leak location and alarm)

The design of the utility model considers the on-line leakage detection, and its principle is to use the pressure conversion method to calculate the gas leakage rate of the equipment. Its calculation formula is as follows:

In the formula: ρ ₀ -initial gas density; ρ _t -gas density at the end of the cycle; T _r -cycle time; T ₀ -year time, which is the total time of 8760 hours per year.

When designing the unit, the density value after power-on or reset is stored as the initial gas density ρ ₀ , the test cycle is variable, and the density value ρ ₁ at the same time the next day is taken as the first test cycle for calculation, and the cycle The time T ₁ is 24 hours, and the annual air leakage rate M ₁ calculated in 24 hours is obtained. After 24 hours, the density value ρ ₂ of the third day is taken. The cycle time T ₂ is 48 hours, and the annual air leakage rate calculated in 48 hours is obtained. Gas rate M ₂ , and so on, calculated according to the frequency of once a day to get M _r . As the time increases, the accuracy of leak rate calculation will gradually increase. When the leak rate exceeds the preset value, the leak light will light up, indicating that the equipment has leaks.

This function mainly monitors relatively small leaks, and its function is to remind the equipment that there is a leak. The alarm level is relatively low compared to the design, and the action relay function is not designed. More serious leaks can be detected through the density alarm, and the combination of these two functions can provide a more comprehensive monitoring of various leaks. When it is found that there is leakage in the equipment, the leakage calculation parameters stored in the unit can be taken out by the host computer for analysis, and the date when the leakage occurs can be judged, which is convenient for comprehensive analysis to determine the cause of the leakage.

Through the above functional design, the utility model basically realizes the detection of various fault information reflected by the state of SF ₆ gas, such as discharge faults, overheating faults, and gas leakage faults, with small interference, sensitive response, and comprehensive and other advantages; it records more comprehensive historical parameter information of equipment gas, which is convenient for all-round analysis of equipment operating conditions, and meets the requirements for condition-based maintenance of electrical equipment.

3.2 Information storage function

The device of the utility model is designed with the function of storing historical data, so as to carry out comprehensive monitoring and analysis on the condition of the equipment.

3.2.1 General information stored

The general information stored includes: temperature, pressure, humidity, and density information of the gas. The sampling and storage cycle is one day. After one year's data is full, the data at the beginning of the cycle is automatically covered, that is, one year's historical data is retained, which is convenient for comprehensive analysis of the equipment.

Theoretically, the humidity of the gas in the SF ₆ equipment in good condition does not change with the change of the ambient temperature, but in fact, due to the existence of the metal materials and insulating materials in the equipment to absorb and decompose moisture, the actual humidity in the equipment changes with the ambient temperature. However, when the ambient temperature rises, the humidity increases, and vice versa, it decreases, and its effect is quite obvious. According to the actual measurement with an offline moisture meter, the humidity test value of a certain device at noon within a day is 190μL/L, and the ambient temperature is 38°C. Using the same instrument at night, the test value is 120 μL/L, and the ambient temperature is 31-38°C. If If the data stored is not designed to be stored on a daily cycle, the data will fluctuate irregularly, and the data will be useless. The small cycle of environmental temperature change is one day. Collect data at the same time every day, and the difference in environmental conditions will be minimized. The historical data of humidity and density will be better comparable, and the data value will be relatively high. Similarly, the calculation of the leakage rate is also calculated on a daily basis to reduce calculation errors. Therefore, the utility model device takes one day as a cycle to store and calculate values, which can minimize the impact of environmental conditions on the test, and then obtain comparable and valuable historical data.

3.2.2 Stored fault information

The stored fault information includes: pressure surge fault information (including pressure surge start time, pressure surge peak time, pressure surge start pressure, peak pressure, recovery time) and leakage rate. The total data storage capacity is 365 days of four general information (temperature, pressure, density, humidity), one leak rate information and a small amount of fault information, generally less than 2000 data, but the reflected equipment information is more comprehensive .

4. Communication function

With the advancement of technology, field intelligent devices that are required to comply with the fieldbus protocol must have a complete and reliable communication interface. The device of the utility model reserves two data communication interfaces, one is RS232 interface and the other is RS485 interface. When faced with a specific communication mode during on-site operation, a corresponding interface conversion module can be configured to meet the requirements. The RS232 interface is mainly used to communicate with the configuration host computer to obtain the data stored in the unit and perform parameter setting, etc.; the RS485 interface is mainly used to communicate with the host computer in the main control room. During normal operation, the host computer is in the master working mode, and the utility model device is a slave working mode. In order to improve the reliability of communication, the communication protocol adopts the transmission protocol in "Electric Power Industry Standard".

Claims (3)

1, a kind of high pressure SF ₆ electrical equipment SF ₆ gas state on-line monitoring device, it is characterized in that it is made of pressure sensor (P), temperature sensor (T), humidity sensor (H), contains isolation transformation and digital-to-analog conversion circuit ( 3, 4) The signal conditioning module, the main control module containing the I/O expansion circuit (8), and the output display module are composed of the signal output of the pressure sensor (P), temperature sensor (T) and humidity sensor (H) The terminals are respectively connected to the pressure, temperature and humidity signal input terminals of the signal conditioning module, the output terminals of the signal conditioning module are connected to the input terminals of the main control module, and the I/O expansion output terminals of the main control module are respectively connected to the isolation terminals of the signal conditioning module. Transformation and digital-to-analog conversion input terminals and output display module input terminals. 2. The on-line monitoring device for SF ₆ gas state of high-voltage SF ₆ electrical equipment according to claim 1, characterized in that the signal conditioning module consists of a drive amplifier circuit (1), a channel selection circuit (2), and an analog-to-digital conversion circuit (4) and an isolation conversion circuit (3), the main control module is composed of a data processor (7) and an I/O expansion circuit (8), and the output display module is composed of an output control circuit (12), an output isolation circuit (11), an output display Light (14), alarm relay group (13) and status light (15), the signal output terminals of pressure sensor (P), temperature sensor (T) and humidity sensor (H) are respectively connected to the drive amplifier circuit (1) The input terminals of pressure, temperature and humidity signals, the output terminals of the driving amplifier circuit (1) are connected to the input terminals of the data processor (7) after sequentially passing through the channel selection circuit (2) and the analog-to-digital conversion circuit (4), and the data processor The output signal of (7) is divided into two paths after the I/O expansion circuit (8), one path is connected with the input end of the analog-to-digital conversion circuit (4) and the isolation conversion circuit (3) at the same time, and the other path is passed through the output control circuit ( 12) are respectively connected to the input terminals of the output isolation circuit (11), the output display lamp (14) and the status lamp (15), and the output terminals of the isolation conversion circuit (3) and the output isolation circuit (12) are respectively connected to the channel selection The input terminal of circuit (2) and alarm relay group (13). 3. The high-voltage SF ₆ electrical equipment SF ₆ gas state online monitoring device according to claim 1, characterized in that the pressure sensor used is a stainless steel surface piezoresistive pressure sensor, the temperature sensor is a platinum resistance temperature sensor, and the humidity sensor It is a quartz crystal oscillator type humidity sensor.

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