SF6 density relay low-temperature correction method

Abstract

The invention discloses a low-temperature correction method for an SF6 density relay, relates to a low-temperature correction technology for a circuit breaker density relay, and aims to solve the problem of measurement misalignment caused by remarkable limitation of an existing correction method for the SF6 density relay. The method comprises the following steps: installing a density relay in a sealing test device, and filling SF6 gas to a standard pressure; placing the sealing test device in a low-temperature environment, selecting at least five temperature points, standing for 1 hour, and recording an indicating value P standard of a standard densimeter and a measured value P1 of a density relay to be corrected; calculating an error value delta P of each temperature point; performing function fitting on the error value delta P and the corresponding temperature T by adopting a quadratic polynomial function, and solving a correction error delta P1; calculating the value P correction of the corrected density relay; and low-temperature correction of the density relay is completed. The beneficial effect is that the monitoring precision in the extremely cold environment is significantly improved.

Description

Technical Field

[0001] The invention relates to a low temperature correction technology for a circuit breaker density relay. Background Art

[0002] As high-voltage power grids extend into cold regions, the reliability of SF6 electrical equipment in low-temperature environments (-40°C and below) faces significant challenges. As a critical condition monitoring component, existing calibration methods for SF6 density relays have significant limitations. First, existing calibration only covers operating conditions between -25°C and 40°C. Nonlinear errors due to sensor elastic deformation and gas adsorption in extremely cold environments can reach over 15% of the nominal value. Second, existing temperature compensation models fail to account for changes in the dielectric properties of SF6 gas caused by low-temperature phase transitions, resulting in increased deviations in density-to-pressure conversion. More critically, when temperatures fall below -30°C, relay contact sticking and bellows hysteresis can cause false alarms, directly impacting the accuracy of fault warnings for GIS equipment. Accident analysis indicates that 63% of SF6 equipment low-temperature malfunctions are related to density relay measurement inaccuracies. Therefore, a universal, high-precision calibration method is urgently needed to address measurement inaccuracies and false alarms associated with SF6 density relays in low-temperature environments, ensuring the safe and stable operation of power grids in high-altitude and cold regions. This has urgent engineering value in ensuring the safe operation of power grids in extremely cold regions. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem that the existing calibration method of SF6 density relay has significant limitations and leads to measurement inaccuracy, and proposes a low-temperature calibration method for SF6 density relay.

[0004] The low-temperature calibration method of an SF6 density relay according to the present invention comprises the following steps:

[0005] Install the density relay in the sealing test device and fill it with SF6 gas to the standard pressure;

[0006] Place the sealing test device in a low temperature environment and select at least 5 temperature points. Leave it at different temperature points for 1 hour and record the standard density meter reading P. 标准 and the measured value P1 of the density relay to be calibrated;

[0007] Calculate the error value ΔP at each temperature point;

[0008] A quadratic polynomial function is used to perform function fitting on the error value ΔP and the corresponding temperature T to solve the correction error ΔP1;

[0009] The calibration error ΔP1 and the measured value P1 of the density relay to be calibrated are used to calculate the value P of the density relay after calibration. 校正 ; Complete low temperature calibration of density relay.

[0010] Furthermore, the standard pressure is 0.6 MPa.

[0011] Furthermore, the temperature range of the low temperature environment is -40°C to 20°C; and the temperature control accuracy is ≤±1°C.

[0012] Furthermore, the sealing test device has a volume of 1L to 5L and is equipped with a standard density meter interface, a density relay interface to be calibrated, an SF6 charging valve and a safety pressure relief valve.

[0013] Furthermore, the specific formula for calculating the error value ΔP at each temperature point is:

[0014] ΔP=P 标准 -P1 (1)

[0015] Among them, P 标准 is the indication of the standard density meter; P1 is the measured value of the density relay to be calibrated.

[0016] Furthermore, the fitting formula for solving the correction error ΔP1 is:

[0017] ΔP1=(1.608*10 -5 )*T 2 -(9.863*10 -4 )*T+0.0132 (2)

[0018] Where ΔP1 is the calibration error of the density relay at different temperatures, and T is the test temperature.

[0019] Furthermore, the calculated value P of the density relay after correction is 校正 The specific formula is:

[0020] P 校正 =P1+ΔP1 (3)

[0021] Among them, P 校正 is the value of the density relay after calibration.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This paper proposes a low-temperature calibration method for SF6 density relays in low-temperature environments. This method eliminates the need for heating or low-temperature modification of the density relay. By calculating the deviation in the density reading under low-temperature conditions, a correction formula for the density relay results is derived. This method reduces the density measurement error from 18% using conventional methods to within 0.03%, significantly improving monitoring accuracy in extremely cold environments. In field measurements of SF6 tank circuit breakers in an outdoor substation in Northeast China, which operates at temperatures below -35°C for extended periods during winter, the false alarm rate was reduced from 8 per year to 0, significantly reducing operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of a low-temperature calibration method for an SF6 density relay as described in the first embodiment. DETAILED DESCRIPTION

[0025] Specific implementation method 1. Combination Figure 1 This embodiment describes a low-temperature calibration method for an SF6 density relay, which includes the following steps:

[0026] Install the density relay in the sealing test device and fill it with SF6 gas to the standard pressure;

[0027] Place the sealing test device in a low temperature environment and select at least 5 temperature points. Leave it at different temperature points for 1 hour and record the standard density meter reading P. 标准 and the measured value P1 of the density relay to be calibrated;

[0028] Calculate the error value ΔP at each temperature point;

[0029] A quadratic polynomial function is used to perform function fitting on the error value ΔP and the corresponding temperature T to solve the correction error ΔP1;

[0030] The calibration error ΔP1 and the measured value P1 of the density relay to be calibrated are used to calculate the value P of the density relay after calibration. 校正 ; Complete low temperature calibration of density relay.

[0031] In this embodiment, five temperature points are selected: -40°C, -25°C, -10°C, 0°C, and 20°C; after standing for 1 hour, the standard density meter reading P is recorded. 标准 And the measured value P1 of the density relay to be calibrated, Table 1 is obtained;

[0032] Table 1 Pressure error at different temperatures

[0033] Temperature / ℃ 20 0 -10 -25 -40 Standard value / MPa 0.6345 0.6343 0.6342 0.6342 0.4341 Measurement value / MPa 0.6344 0.6211 0.6095 0.5863 0.3557 Error value / MPa 0.0001 0.0132 0.0247 0.0479 0.0784

[0034] By analyzing the error values in the table, it can be found that as the temperature decreases, the error of the density relay to be calibrated will become larger, increasing from 0.0001 MPa at 20℃ to 0.0784 MPa at -40℃, with a deviation of more than 18%.

[0035] The corrected value of the density relay is shown in the table.

[0036] Table 2 Corrected value of density relay at different temperatures

[0037] Temperature / ℃ 20 0 -10 -25 -40 Standard value / MPa 0.6345 0.6343 0.6342 0.6342 0.4341 Correction value / MPa 0.6344 0.6343 0.6341 0.6342 0.4340

[0038] As can be seen from the table, the corrected value after error function fitting is basically the same as the standard value, with a maximum error of 0.0001 MPa and a maximum deviation of only 0.023%, meeting the correction needs of SF6 density relay under low temperature conditions.

[0039] Specific implementation method two, this implementation method is a further limitation of the SF6 density relay low temperature correction method described in specific implementation method one, in this implementation method, the standard pressure is 0.6Mpa.

[0040] In this implementation method, the standard pressure of 0.6Mpa is the rated gas supplement pressure of SF6 circuit breaker at 20℃ (corresponding to a density of about 0.6345MPa, see table 1), which is in the middle of the normal operating pressure range (0.4-0.7MPa) of the equipment. If a pressure that is too high (such as 0.8MPa) or too low (such as 0.3MPa) is selected, it may cause the fitting formula to be distorted when extrapolated outside the commonly used working condition interval, while the test data of 0.6MPa can be seamlessly mapped to the actual operating state of the equipment. At the same time, in a low temperature environment, SF6 gas at 0.6MPa reaches thermodynamic equilibrium only in 1 hour (step two), and if the pressure is too high (such as 1.0MPa), the density gradient may prolong the standing time to more than 2 hours, increasing the test cycle.

[0041] Specific implementation method three, this implementation method is a further limitation of the SF6 density relay low temperature correction method described in specific implementation method one, in this implementation method, the temperature range of the low temperature environment is -40℃-20℃; the temperature control accuracy is ≤±1℃.

[0042] In this implementation method, -40℃ is the extreme value of the lowest temperature of the actual operating environment of the equipment, ensuring that this correction method is applicable to the most severe outdoor substation scenario; and 20℃ is the standard calibration temperature of SF6 equipment, forming a complete temperature chain of "extreme cold→normal temperature", avoiding the extrapolation failure of the correction formula in the commonly used temperature zone; both the "error mutation zone" of SF6 in extreme cold and the overdesign are avoided, making the correction method a universal solution for the safety of power grids in extremely cold regions.

[0043] Specific embodiment 4. This embodiment further limits the low-temperature calibration method of an SF6 density relay described in specific embodiment 1. In this embodiment, the volume of the sealing test device is 1L~5L, and is equipped with a standard density meter interface, an interface for a density relay to be calibrated, an SF6 inflation valve and a safety pressure relief valve.

[0044] In this embodiment, through the above design, with "small volume, high precision, universal interface, and zero-risk operation" as the core, the low-temperature calibration test that originally took 2 hours is compressed to 1 hour, and the calibration error is reduced from ±0.08MPa to ±0.0001MPa, becoming a standardized tool for power grid operation and maintenance in extremely cold areas.

[0045] Specific embodiment 5: This embodiment further limits the low-temperature calibration method of the SF6 density relay described in specific embodiment 1. In this embodiment, the specific formula for calculating the error value ΔP at each temperature point is:

[0046] ΔP=P 标准 -P1 (1)

[0047] Among them, P 标准 is the indication of the standard density meter; P1 is the measured value of the density relay to be calibrated.

[0048] Specific embodiment 6: This embodiment further limits the low-temperature calibration method of the SF6 density relay described in specific embodiment 1. In this embodiment, the fitting formula for solving the calibration error ΔP1 is:

[0049] ΔP1=(1.608*10 -5 )*T 2 -(9.863*10 -4 )*T+0.0132 (2)

[0050] Where ΔP1 is the calibration error of the density relay at different temperatures, and T is the test temperature.

[0051] In this embodiment, according to the experimental data in Table 1 and Table 2, the function fitting is completed in MATLAB software using the least squares method, and the goodness of fit R 2 ≥0.99.

[0052] Specific embodiment 7: This embodiment further limits the low-temperature calibration method of the SF6 density relay described in specific embodiment 1. In this embodiment, the value P of the density relay after calculation is corrected. 校正 The specific formula is:

[0053] P 校正 =P1+ΔP1 (3).

[0054] In this embodiment, the value P of the density relay after correction is calculated. 校正 The specific formula has the advantages of no on-site modification, hundredfold improvement in accuracy, and one-time eradication of false alarms, which are specifically reflected in the following four points:

[0055] First, it's plug-and-play on-site. There's no need to replace density relays, install heaters, or install sensor compensation modules. Operations and maintenance personnel simply input the field reading of the density relay's measured value, P1, into the formula to obtain the true value, saving 100% of hardware modification costs and power outage time. Second, accuracy is improved from ±18% to ±0.03%. At -40°C, the uncorrected error can reach 0.0784 MPa (≈18%). After correction in step five, the maximum error is only 0.0001 MPa (≈0.023%), a two-order-of-magnitude improvement in accuracy. This fully meets the stringent SF6 density monitoring requirements of GIS and tank circuit breakers. Third, the false alarm rate is reduced to zero. Tests at a -35°C substation showed that applying this correction method reduced the number of false alarms from 8 to 0 throughout the year, avoiding unnecessary power outages and manual inspections, and directly reducing operation and maintenance costs by over 60%. Fourth, the algorithm is universal and can be deployed in batches. The correction formula depends only on the test temperature T and is independent of the relay brand or range. It can be embedded in SCADA, handheld terminals, or mobile phone apps to achieve unified calibration of multi-site and multi-model relays, providing a standardized and replicable solution for power grids in extremely cold regions.

[0056] At the same time, when inspecting the density relay of the SF6 circuit breaker equipment in the outdoor substation, the low-temperature correction method of the SF6 density relay in a low-temperature environment proposed in the present invention can be used to convert the displayed value into an actual value and obtain the real gas pressure state to judge whether the equipment has hidden dangers such as gas leakage and liquefaction lock, which is conducive to ensuring the safe and stable operation of the equipment.

[0057] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A low temperature calibration method for an SF6 density relay, characterized in that: The following steps are involved: Install the density relay in the sealing test device and fill it with SF6 gas to the standard pressure; Place the sealing test device in a low temperature environment and select at least 5 temperature points. Leave it at different temperature points for 1 hour and record the standard density meter reading P. 标准 and the measured value P1 of the density relay to be calibrated; Calculate the error value ΔP at each temperature point; A quadratic polynomial function is used to perform function fitting on the error value ΔP and the corresponding temperature T to solve the correction error ΔP1; The calibration error ΔP1 and the measured value P1 of the density relay to be calibrated are used to calculate the value P of the density relay after calibration. 校正 ; Complete low temperature calibration of density relay.

2. A low temperature calibration method for SF6 density relay according to claim 1, characterized in that: The standard pressure is 0.6 MPa.

3. A low temperature calibration method for SF6 density relay according to claim 1, characterized in that: The temperature range of the low temperature environment is -40°C to 20°C; the temperature control accuracy is ≤±1°C.

4. A low temperature calibration method for SF6 density relay according to claim 1, characterized in that: The sealing test device has a volume of 1L to 5L and is equipped with a standard density meter interface, a density relay interface to be calibrated, an SF6 charging valve and a safety pressure relief valve.

5. A low temperature calibration method for SF6 density relay according to claim 1, characterized in that: The specific formula for calculating the error value ΔP at each temperature point is: ΔP=P 标准 -P1 (1) Among them, P 标准 is the indication of the standard density meter; P1 is the measured value of the density relay to be calibrated.

6. A low temperature calibration method for SF6 density relay according to claim 1, characterized in that: The fitting formula for solving the correction error ΔP1 is: ΔP1=(1.608*10 -5 )*T 2 - (9.863*10 -4 )*T+ 0.0132 (2) Where ΔP1 is the calibration error of the density relay at different temperatures, and T is the test temperature.

7. A low temperature calibration method for SF6 density relay according to claim 1, characterized in that: The calculated corrected density relay value P 校正 The specific formula is: P 校正 =P1+ΔP1 (3) Among them, P 校正 is the value of the density relay after calibration.

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