Gas density relay under-compensation fault self-diagnosis method based on daily temperature change amount

Abstract

The application discloses a gas density relay under-compensation fault self-diagnosis method based on daily temperature change amount, comprising the following steps: collecting pressure sensor data of a preset time period in the morning and a preset time period in the afternoon at regular intervals; calculating the average value of the collected pressure sensor data of the preset time period in the morning and the average value of the collected pressure sensor data of the preset time period in the afternoon respectively; obtaining the daily pressure change amount by subtracting the two average values; comparing the daily pressure change amount with the set minimum threshold value; if the daily pressure change amount is greater than or equal to the set minimum threshold value, the gas density relay continues to operate normally; if the daily pressure change amount is less than the set minimum threshold value, it is determined that the pressure sensor has a fault, and the gas density relay sends a fault alarm signal; the application has the advantages that the problem that under-compensation faults of digital density relays cannot be found during the verification interval is effectively solved, safety hazards are avoided, and the safe and stable operation of electrical equipment is ensured.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment fault diagnosis, specifically to a self-diagnosis method for undercompensated faults in gas density relays based on daily temperature variations. Background Technology

[0002] As the power grid expands, the responsibility of relay protection systems, as the first line of defense for ensuring the safe and stable operation of the power grid, is also increasing. Due to the aging of sensors in digital density relays over long periods of use, faults such as undercompensation can occur. Since the calibration cycle for density relays is typically 1-2 years, it is difficult to detect problems within this period, posing significant hidden dangers to the safe operation of SF6 electrical equipment, such as line outages or unit tripping, with serious consequences.

[0003] Chinese Patent Publication No. CN103245908A discloses a calibration device for SF6 and SF6 mixed gas density relays. This device includes: a high-low temperature constant temperature chamber and a mounting bracket for the relay under test, a temperature sensor, an adjusting cylinder, and SF6 and SF6 mixed gas storage cylinders, all housed within the chamber; and an absolute pressure sensor, a relative pressure sensor, an SF6 gas cylinder, an N2 or CF4 gas storage cylinder, a vacuum pump, and a control device located outside the chamber. The control device is connected to the temperature sensor, the gas density relay under test, the absolute pressure sensor, and the relative pressure sensor, and is used for data processing, outputting control commands, and displaying calibration results. This is intended to solve the problem of accurate testing of SF6 gas density relays across all temperatures. However, this patent application can only be used during offline calibration of the density relay. During the calibration gap, it cannot achieve self-diagnosis of undercompensation faults, posing a safety hazard to the power grid operation. Summary of the Invention

[0004] The technical problem to be solved by this invention is that existing gas density relay calibration devices are unable to achieve online self-diagnosis of undercompensation faults in gas density relays, and there are safety hazards during the calibration gap period.

[0005] This invention solves the above-mentioned technical problems through the following technical means: a self-diagnosis method for undercompensated faults of gas density relays based on daily temperature changes, comprising the following steps: Step 1: Collect pressure sensor data at preset times during the early morning and afternoon periods; Step 2: Calculate the average value of the pressure sensor data collected during the preset time period in the early morning and the average value of the pressure sensor data collected during the preset time period in the afternoon. Step 3: Subtract the two calculated average values ​​to obtain the daily pressure change; Step 4: Compare the daily pressure change with the set minimum threshold. If the daily pressure change is greater than or equal to the set minimum threshold, the gas density relay continues to operate normally. If the daily pressure change is less than the set minimum threshold, the pressure sensor is determined to be faulty, and the gas density relay issues a fault alarm signal.

[0006] Further, step one includes: Pressure sensor readings were collected every 30 minutes from 3:30 AM to 5:30 AM and from 2:00 PM to 4:00 PM, with 5 sets of data collected for each period. , , , , and , , , , .

[0007] Furthermore, step two includes: The average values ​​of the pressure sensor data collected between 3:30 AM and 5:30 AM and between 2:00 PM and 4:00 PM were calculated, i.e.: and .

[0008] Furthermore, step three includes: The daily pressure change is calculated by subtracting the average pressure sensor data collected from 3:30 AM to 5:30 AM from the average pressure sensor data collected from 2:00 PM to 4:00 PM. .

[0009] Furthermore, the relationship between the SF6 gas state parameters is as follows: (1)

[0010]

[0011]

[0012] in, For pressure; The density of the gas; For temperature; The first temperature coefficient, The second temperature coefficient, This is the deviation coefficient.

[0013] Furthermore, equation (1) is transformed into the following form: (2) Equation (2) shows that, without considering gas leakage, i.e., gas density... Under the premise of constant values, SF6 gas pressure and temperature show a linear positive correlation, with a correlation coefficient of... .

[0014] Furthermore, the set minimum threshold is obtained through a testing platform, and the method of obtaining it is as follows: 1) Use SF6 gas cylinders to fill the buffer tank inside the high and low temperature test chamber with gas. Stop filling when the preset pressure value is reached. 2) The high and low temperature test chamber is left to stand for the first preset time to allow the temperature inside the chamber and the gas temperature inside the buffer tank to stabilize at a certain level. ; 3) Set up a high and low temperature test chamber, with the temperature changing at a rate of [temperature increase per hour]. Record the corresponding high and low temperature test chamber temperatures. ; 4) Collect the temperature readings inside the high and low temperature test chamber every second preset time interval. ; 5) Obtain the SF6 gas temperature difference and multiply it by the correlation coefficient to obtain the set minimum threshold.

[0015] Furthermore, the step of obtaining the SF6 gas temperature difference and multiplying it by a correlation coefficient to obtain a set minimum threshold includes: The relationship was obtained by fitting the collected SF6 gas temperature data: (3) in, For the delay time, Let be the temperature of the SF6 gas at time t; The heat dissipation coefficient; By transforming the above equation, we can obtain: (4) make Then we have: (5) Ultimately, we can obtain: (6) The temperature difference of SF6 gas can be obtained from equation (3): Therefore, the minimum threshold is set. , This represents the minimum daily temperature range across the country, as determined by the survey.

[0016] Furthermore, the preset pressure value ranges from 0.5 MPa to 0.7 MPa.

[0017] Furthermore, the first preset time ranges from 15 min to 25 min, and the second preset time ranges from 3 min to 7 min.

[0018] The advantages of this invention are as follows: Based on a nationwide temperature survey, the invention identifies that daily maximum and minimum temperatures change seasonally, determining that the preset time period in the early morning represents the lowest temperature of the day, and the preset time period in the afternoon represents the highest temperature. Therefore, by collecting the average value of pressure sensor output data for the highest and lowest temperature time intervals throughout the day and calculating the difference, the impact of seasonal changes on detection reliability can be reduced. The minimum pressure difference caused by SF6 gas temperature changes is selected as the set threshold. By comparing the real-time change rate of the pressure sensor inside the SF6 gas digital density relay with the aforementioned set threshold, the operating status of the SF6 gas digital density relay can be self-diagnosed. This effectively solves the problem of failing to detect undercompensation faults in the digital density relay during the calibration interval, avoiding safety hazards and ensuring the safe and stable operation of electrical equipment. Attached Figure Description

[0019] Figure 1 This is a flowchart of a self-diagnosis method for undercompensated faults of a gas density relay based on daily temperature variation, as disclosed in an embodiment of the present invention. Figure 2 This is a schematic diagram of the test platform for SF6 gas temperature change in the self-diagnosis method for undercompensated faults of gas density relays based on daily temperature changes disclosed in the embodiments of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The pressure of SF6 gas at a given temperature can be used to approximate its density. In the gas chambers of electrical equipment, the pressure of SF6 gas is typically above 0.3 MPa. Within this pressure range, the ideal gas law is not applicable to SF6 gas; the Beattie-Bridgman equation is more suitable for the relationships between SF6 gas state parameters. (1)

[0022]

[0023]

[0024] in, For pressure; The density of the gas; For temperature; The first temperature coefficient, The second temperature coefficient, This is the deviation coefficient.

[0025] To facilitate the calculation of the relationship between SF6 gas temperature and pressure, equation (1) is transformed into the following form: (2) Equation (2) shows that, without considering gas leakage, i.e., gas density value Under the premise of constant values, SF6 gas pressure and temperature show a linear positive correlation, with a correlation coefficient of... .

[0026] SF6 gas temperature change It will cause changes in SF6 gas pressure This, in turn, causes a change in the output of pressure sensor 3. Therefore, the minimum change in gas pressure caused by the minimum change in SF6 gas temperature in SF6 electrical equipment within a fixed time period (daily) can be used as the set threshold. To determine whether pressure sensor 3 is malfunctioning, the pressure sensor 3 outputs a change in value. It should be greater than or equal to ,like Less than If the value is 0, it indicates that the pressure sensor 3 has an undercompensation fault.

[0027] Based on the above technical principles, such as Figure 1 As shown, this invention provides a self-diagnosis method for undercompensation faults in gas density relays based on daily temperature variations, comprising the following steps: S1. Data Acquisition. Pressure sensor 3 readings are collected periodically from 3:30 AM to 5:30 AM and from 2:00 PM to 4:00 PM. Pressure sensor 3 readings are collected every 30 minutes, resulting in 5 sets of data, which are recorded as follows: , , , , and , , , , .

[0028] S2. Calculate the average pressure. Calculate the average pressure using the data collected from 3:30 AM to 5:30 AM and from 2:00 PM to 4:00 PM, respectively. and .

[0029] S3. Calculate the pressure difference. Subtract the average pressure value collected between 3:30 AM and 5:30 AM from the average pressure value collected between 2:00 PM and 4:00 PM to calculate the daily pressure change. .

[0030] S4. The change obtained in step 3) With the set minimum threshold Comparison. If The gas density relay continues to operate normally; The pressure sensor 3 is determined to be faulty, and the gas density relay issues a fault alarm signal.

[0031] Building such Figure 2 The SF6 gas temperature test platform shown uses the high and low temperature test chamber 5 to simulate ambient temperature changes. The minimum threshold value is obtained in the following way: 1) Open solenoid valve 2 and fill buffer tank 4 with SF6 gas cylinder 1. Observe the reading of pressure sensor 3. When the reading is 0.6MPa, close solenoid valve 2. 2) Set the temperature of the high and low temperature test chamber 5 to [temperature value missing]. Start the high and low temperature test chamber 5 and let it stand for 20 minutes to allow the temperature inside the chamber and the gas temperature inside the tank to stabilize at a certain level. ; 3) Set up a high and low temperature test chamber 5, whose temperature changes by increasing per hour. Record the temperature of the high and low temperature test chamber 5. ; 4) Set the data receiver 7 to collect the temperature sensor 6's detection value every 5 minutes. ; 5) Start the high and low temperature test chamber 5 and begin data acquisition; Analyzing the data obtained from the above experiments, although the temperature of SF6 gas generally tends to be consistent with the ambient temperature, it exhibits a certain lag: according to Newton's law of cooling in heat transfer, when there is a temperature difference, SF6 gas mainly exchanges heat through natural convection. At this time, SF6 gas will not instantly reach the same temperature as the ambient temperature, which demonstrates the lag in the temperature of SF6 gas.

[0032] The relationship was obtained by fitting the collected SF6 gas temperature data: (3) in, For the delay time, Let be the temperature of the SF6 gas at time t; This is the heat dissipation coefficient.

[0033] By transforming the above equation, we can obtain: (4) make: It can be known that , Then we have: (5) Ultimately, we can obtain: (6) The heat dissipation coefficient is temperature-dependent, but when the temperature difference is small (less than 25K), it can be considered a constant value. The SF6 gas temperature difference can be obtained from equation (3): Therefore, a threshold is set. . The minimum daily temperature difference across the country (2℃) was obtained from the survey.

[0034] Through the above technical solution, this invention, based on a nationwide temperature survey, determines that daily maximum and minimum temperatures change with the seasons, establishing that the preset time period in the early morning represents the lowest temperature of the day, and the preset time period in the afternoon represents the highest temperature. Therefore, by collecting the average output data from pressure sensor 3 during the highest and lowest temperature time intervals of the day, and calculating the difference, the impact of seasonal changes on detection reliability can be reduced. The minimum pressure difference caused by SF6 gas temperature changes is selected as the set threshold. By comparing the real-time change rate of pressure sensor 3 within the SF6 gas digital density relay with the aforementioned set threshold, self-diagnosis of the SF6 gas digital density relay's operating status is achieved. This effectively solves the problem of failing to detect undercompensation faults in the digital density relay during the calibration interval, avoiding safety hazards and ensuring the safe and stable operation of electrical equipment.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-diagnosis method for undercompensation faults in gas density relays based on daily temperature variations, characterized in that: Includes the following steps: Step 1: Collect pressure sensor data at preset times during the early morning and afternoon periods; Step 2: Calculate the average value of the pressure sensor data collected during the preset time period in the early morning and the average value of the pressure sensor data collected during the preset time period in the afternoon. Step 3: Subtract the two calculated average values ​​to obtain the daily pressure change; Step 4: Compare the daily pressure change with the set minimum threshold. If the daily pressure change is greater than or equal to the set minimum threshold, the gas density relay continues to operate normally. If the daily pressure change is less than the set minimum threshold, the pressure sensor is determined to be faulty, and the gas density relay issues a fault alarm signal. The set minimum threshold is obtained through a testing platform, and the method of obtaining it is as follows: 1) Use SF6 gas cylinders to fill the buffer tank inside the high and low temperature test chamber with gas. Stop filling when the preset pressure value is reached. 2) The high and low temperature test chamber is left to stand for the first preset time to allow the temperature inside the chamber and the gas temperature inside the buffer tank to stabilize at a certain level. ; 3) Set up a high and low temperature test chamber, with the temperature changing at a rate of [temperature increase per hour]. Record the corresponding high and low temperature test chamber temperatures. ; 4) Collect the temperature readings inside the high and low temperature test chamber every second preset time interval. ; 5) The relationship was obtained by fitting the collected SF6 gas temperature data: （3） in, For the delay time, Let be the temperature of the SF6 gas at time t; The heat dissipation coefficient; The temperature difference of SF6 gas can be obtained from equation (3): Therefore, the minimum threshold is set. , This represents the minimum daily temperature range across the country obtained from the survey. The correlation coefficient.

2. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation as described in claim 1, characterized in that, Step one includes: Pressure sensor readings were collected every 30 minutes from 3:30 AM to 5:30 AM and from 2:00 PM to 4:00 PM, with 5 sets of data collected for each period. , , , , and , , , , .

3. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation according to claim 2, characterized in that, Step two includes: The average values ​​of the pressure sensor data collected between 3:30 AM and 5:30 AM and between 2:00 PM and 4:00 PM were calculated, i.e.: and .

4. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation according to claim 3, characterized in that, Step three includes: The daily pressure change is calculated by subtracting the average pressure sensor data collected from 3:30 AM to 5:30 AM from the average pressure sensor data collected from 2:00 PM to 4:00 PM. .

5. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation according to claim 1, characterized in that, The relationship between the SF6 gas state parameters is as follows: （1） in, For pressure; The density of the gas; For temperature; The first temperature coefficient, The second temperature coefficient, This is the deviation coefficient.

6. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation as described in claim 5, characterized in that, Equation (1) can be transformed into the following form: （2） Equation (2) shows that, without considering gas leakage, i.e., gas density... Under the premise of constant values, SF6 gas pressure and temperature show a linear positive correlation, with a correlation coefficient of... .

7. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation according to claim 1, characterized in that, The preset pressure value ranges from 0.5 MPa to 0.7 MPa.

8. The self-diagnosis method for undercompensated faults of gas density relays based on daily temperature variation according to claim 1, characterized in that, The first preset time ranges from 15 min to 25 min, and the second preset time ranges from 3 min to 7 min.

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