A method for interpolation compensation of temperature-pressure characteristic curve of C4F7N / CO2 / O2 ternary gas mixture

Abstract

The present invention relates to a C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method, belonging to the field of insulating gas compensation. It includes: measuring the temperature value and pressure value of the ternary mixed gas in the device to be tested, and then obtaining the pressure value at 20°C corresponding to the measured pressure value under the built-in rated mixing ratio as the first pressure value; obtaining the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio as the second pressure value according to the actual mixing ratio of the ternary mixed gas in the device to be tested, the measured pressure value and the temperature value; calculating the deviation between the second pressure value and the first pressure value, and outputting the first pressure value if the deviation is less than the threshold; otherwise, interpolating the mixing ratio through gas virtual compensation to obtain the pressure value corresponding to the interpolated mixing ratio and output it. This method solves the problem of large errors in the gas density obtained by the density relay when the actual mixing ratio of the ternary mixed gas is inconsistent with the built-in mixing ratio by performing mixing ratio interpolation.

Description

Technical Field

[0001] The invention relates to the field of insulating gas compensation, and in particular to an interpolation compensation method for a temperature-pressure characteristic curve of a C4F7N / CO2 / O2 ternary mixed gas. Background Art

[0002] The C4F7N / CO2 / O2 ternary gas mixture is increasingly widely used in the power industry as an insulating medium for high-voltage electrical equipment due to its environmental friendliness and good insulation properties. The density of the ternary gas mixture directly affects its insulation properties. Therefore, it is necessary to focus on monitoring its density changes during the operation of electrical equipment. The current existing method for monitoring the density of the C4F7N / CO2 / O2 ternary gas mixture mainly measures the temperature and pressure values ​​of the ternary gas mixture through a density relay installed on the electrical equipment, and converts the measured pressure value into its corresponding pressure value at 20°C through the temperature-pressure characteristic curve built into the density relay, thereby obtaining the density of the ternary gas mixture.

[0003] The existing C4F7N / CO2 / O2 ternary gas mixture density relay usually has a built-in temperature-pressure characteristic curve of the ternary gas mixture at a certain set rated mixing ratio, and relies on the built-in temperature-pressure characteristic curve to obtain the density of the ternary gas mixture. However, the temperature-pressure characteristic curve at a single rated mixing ratio must be obtained by continuous testing in the laboratory for more than 3 months for 24 hours, which is very time-consuming and labor-intensive.

[0004] Moreover, in actual use, due to irregularities in the gas charging and distribution of electrical equipment, leakage, etc., there is a certain deviation between the actual mixing ratio of the C4F7N / CO2 / O2 ternary mixed gas in the electrical equipment and the rated mixing ratio built into the density relay. It is understandable that when the mixing ratio of the ternary mixed gas changes, its temperature-pressure characteristic curve will also change accordingly. At this time, if the temperature-pressure characteristic curve built into the density relay, that is, the temperature-pressure characteristic curve at the rated mixing ratio, is used, the corresponding pressure value at 20°C will be converted with a large error, resulting in a large error in the density of the ternary mixed gas obtained, causing the density relay to misjudge.

[0005] Therefore, it is an urgent problem to provide an interpolation compensation method for the temperature-pressure characteristic curve of the C4F7N / CO2 / O2 ternary mixed gas, so that the density relay can still obtain a more accurate corresponding pressure value at 20°C when the actual mixing ratio of the ternary mixed gas is inconsistent with the mixing ratio built into the density relay, thereby obtaining a more prepared density value. Summary of the invention

[0006] In view of the above analysis, the present invention aims to provide a method for interpolation compensation of the temperature-pressure characteristic curve of a C4F7N / CO2 / O2 ternary mixed gas, so as to solve the problem that when the actual mixing ratio of the ternary mixed gas is inconsistent with the mixing ratio built into the density relay, there is a large error in the gas density obtained by the density relay.

[0007] The present invention provides a C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method, the method comprising the following steps:

[0008] Measuring the temperature and pressure of the C4F7N / CO2 / O2 ternary mixed gas in the device under test by a density relay, and obtaining the pressure value at 20° C. corresponding to each built-in rated mixing ratio of the measured pressure value based on the measured temperature and pressure values ​​and the rated mixing ratio and temperature-pressure characteristic curve built into the density relay as the first pressure value;

[0009] According to the actual mixing ratio of the ternary mixed gas in the device to be tested and the measured pressure value, the partial pressure values ​​of the three gases C4F7N, CO2, and O2 are obtained; based on the partial pressure values ​​of the three gases C4F7N, CO2, and O2 and the measured temperature values, the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio is obtained as the second pressure value; the deviation between the second pressure value and the first pressure value is calculated, and if the deviation is less than the threshold value, the density relay outputs the first pressure value; otherwise, the mixing ratio is interpolated through gas virtual compensation to make the actual mixing ratio become the target mixing ratio, and the pressure value corresponding to the interpolated mixing ratio is obtained based on the target mixing ratio.

[0010] Further, the pressure value at 20° C. corresponding to each rated mixing ratio is obtained as the first pressure value through the following steps:

[0011] Based on the measured temperature and pressure values, two temperature and pressure characteristic curves closest to them are found through density interpolation;

[0012] Calculate the temperature proportionality coefficient based on the measured temperature value and the temperature values ​​corresponding to the two temperature-pressure characteristic curves closest thereto;

[0013] Based on the temperature proportionality coefficient and the pressure values ​​at 20° C. corresponding to the two temperature-pressure characteristic curves closest thereto, the pressure value at 20° C. corresponding to the pressure value of the ternary mixed gas measured at the built-in rated mixing ratio is obtained.

[0014] Furthermore, the temperature proportionality coefficient is calculated by the following formula:

[0015] , (1)

[0016] in, Indicates the temperature proportionality coefficient of the rated mixing ratio ki, Indicates the measured temperature value, , It indicates the temperature value corresponding to the two temperature-pressure characteristic curves closest to it under the rated mixing ratio ki.

[0017] Further, the pressure value of the ternary mixed gas measured at 20° C. corresponding to the built-in rated mixing ratio is obtained by the following formula as the first pressure value:

[0018] , (2)

[0019] in, Indicates the measured pressure value at 20°C corresponding to the rated mixing ratio ki. , It indicates the pressure value corresponding to the two temperature-pressure characteristic curves closest to the rated mixing ratio ki at 20°C.

[0020] Further, the pressure value of the ternary mixed gas at 20° C. at the actual mixing ratio obtained based on the partial pressure values ​​of the three gases C4F7N, CO2, and O2 and the measured temperature value includes:

[0021] The molar volume of the C4F7N gas is obtained based on the partial pressure value of the C4F7N gas and the measured temperature value, and the pressure value of the C4F7N gas of equal molar volume at 20° C. is obtained based on the molar volume of the C4F7N gas;

[0022] Based on the partial pressure values ​​of CO2 and O2 gases, the ideal gas state equation is used to obtain the density of CO2 and O2 gases, and based on the density of CO2 and O2 gases, the pressure values ​​of CO2 and O2 gases with equal density at 20°C are obtained;

[0023] The pressure value of the ternary mixed gas at 20°C at an actual mixing ratio is obtained based on the pressure value of equimolar volume of C4F7N gas at 20°C and the pressure values ​​of CO2 and O2 gases at 20°C with equal density.

[0024] Furthermore, the molar volume of C4F7N gas is obtained by the following equation:

[0025] , (4)

[0026] in, is the pressure value, R is the gas constant, is the Kelvin temperature value, is the molar volume of the gas, , , To correct the parameters, is the critical temperature value, To compare the temperature values, is the critical pressure, is the eccentricity factor.

[0027] Furthermore, the density of CO2 and O2 gases is obtained by the following ideal gas state equation:

[0028] , (5)

[0029] in, is the pressure value, is the density of the gas, is the gas constant, is the Kelvin temperature value, is the relative molecular mass.

[0030] Furthermore, the deviation between the second pressure value and the first pressure value is calculated by the following formula:

[0031] , (7)

[0032] in, Indicates the pressure value at 20°C corresponding to the measured pressure value at the rated mixing ratio ki, P 20 represents the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio, i∈[1,n], n is the total number of rated mixing ratios built into the density relay.

[0033] Furthermore, the interpolation of the mixture ratio by gas virtual compensation so that the actual mixture ratio becomes the target mixture ratio includes:

[0034] When the density relay has multiple rated mixing ratios of the ternary mixed gas built in, a minimum deviation is selected from the deviations between the second pressure value and all the first pressure values, and the built-in rated mixing ratio corresponding to the minimum deviation is the built-in rated mixing ratio closest to the actual mixing ratio, that is, the target mixing ratio;

[0035] The mixture ratio is interpolated by gas virtual compensation so that the actual mixture ratio becomes the target mixture ratio.

[0036] Furthermore, the pressure value corresponding to the interpolated mixing ratio obtained based on the target mixing ratio includes:

[0037] Obtaining a pressure value of the ternary mixed gas at 20° C. corresponding to the target mixing ratio based on the measured temperature value, the measured pressure value and the compensated total pressure value;

[0038] Obtaining the pressure value of each gas compensated at 20° C. corresponding to the target mixing ratio based on the measured temperature value and the compensated pressure value of each gas;

[0039] Based on the pressure value of the ternary mixed gas at 20° C. corresponding to the target mixing ratio and the compensated pressure values ​​of each gas at 20° C. corresponding to the target mixing ratio, the pressure value corresponding to the mixing ratio after interpolation is obtained.

[0040] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0041] 1. The present invention performs density interpolation on the temperature-pressure characteristic curve built into the density relay to obtain the pressure value of the C4F7N / CO2 / O2 ternary mixed gas at the built-in rated mixing ratio, thereby improving the accuracy of the output result of the density relay.

[0042] 2. The present invention further improves the accuracy of the output result of the density relay by comparing the deviation between the second pressure value and the first pressure value and interpolating the mixing ratio when the deviation is greater than a threshold value. This solves the problem that when the actual mixing ratio of the C4F7N / CO2 / O2 ternary mixed gas is inconsistent with the mixing ratio built into the density relay, there is a large error in the gas density obtained by the density relay, which is of great significance for ensuring the safe and stable operation of electrical equipment.

[0043] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0045] Figure 1 Flow chart of the interpolation compensation method for the temperature-pressure characteristic curve of the C4F7N / CO2 / O2 ternary mixed gas according to an embodiment of the present invention;

[0046] Figure 2 Schematic diagram of the temperature-pressure characteristic curve of the C4F7N / CO2 / O2 ternary mixed gas at a certain rated mixing ratio in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0048] A specific embodiment of the present invention discloses a method for interpolating and compensating the temperature-pressure characteristic curve of a C4F7N / CO2 / O2 ternary mixed gas. Figure 1 As shown, the method comprises the following steps:

[0049] Step S1, measuring the temperature value and pressure value of the C4F7N / CO2 / O2 ternary mixed gas in the device to be tested by a density relay, and obtaining the pressure value at 20° C. corresponding to each built-in rated mixing ratio of the measured pressure value based on the measured temperature value and pressure value and the rated mixing ratio and temperature-pressure characteristic curve built into the density relay as a first pressure value;

[0050] Step S2, according to the actual mixing ratio of the ternary mixed gas in the device to be tested and the measured pressure value, obtain the partial pressure values ​​of the three gases C4F7N, CO2, and O2; based on the partial pressure values ​​of the three gases C4F7N, CO2, and O2 and the measured temperature values, obtain the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio as the second pressure value; calculate the deviation between the second pressure value and the first pressure value, if the deviation is less than the threshold value, the density relay outputs the first pressure value; otherwise, the mixing ratio is interpolated through gas virtual compensation to make the actual mixing ratio become the target mixing ratio, and the pressure value corresponding to the interpolated mixing ratio is obtained based on the target mixing ratio.

[0051] Specifically, in step S1, the density relay includes a temperature sensor and a pressure sensor, and the temperature value and the pressure value of the ternary mixed gas are measured respectively by the temperature sensor and the pressure sensor.

[0052] It should be noted that in order to compensate for the gas pressure changes caused by changes in ambient temperature, the measured pressure values ​​of the ternary mixed gas need to be converted to the corresponding pressure values ​​at 20°C to ensure that when only the ambient temperature changes, the pressure values ​​and gas density at 20°C remain unchanged.

[0053] Specifically, the temperature-pressure characteristic curve of the C4F7N / CO2 / O2 ternary mixed gas at a certain rated mixing ratio is as follows: Figure 2 As shown by Figure 2 It can be seen that the temperature-pressure characteristic curve is a cluster of temperature-pressure characteristic curves with temperature as the X-axis and pressure as the Y-axis, representing the temperature-pressure curves corresponding to different gas densities under the rated mixing ratio. Each temperature-pressure characteristic curve corresponds to a gas density, which is obtained through experiments.

[0054] Furthermore, one or more rated mixing ratios of the ternary mixed gas and temperature-pressure characteristic curves at the one or more rated mixing ratios are built into the density relay.

[0055] It should be noted that when using C4F7N / CO2 / O2 ternary mixed gas as the insulating medium of high-voltage electrical equipment, the ternary mixed gas usually uses the rated mixing ratio. At present, the rated mixing ratios of C4F7N, CO2, and O2 in the ternary mixed gas put into operation in high-voltage electrical equipment are mainly the following four: k1=8.5%:86%:5.5%, k2=6%:88.5%:5.5%, k3=3.5%:91%:5.5%, k4=3.5%:86.5%:10%. Since the rated mixing ratios of the ternary mixed gas in high-voltage electrical equipment are different, the temperature-pressure characteristic curves of the ternary mixed gas at multiple rated mixing ratios are built into the density relay to improve the accuracy of the measurement.

[0056] Further, the pressure value at 20° C. corresponding to each rated mixing ratio is obtained as the first pressure value through the following steps:

[0057] Based on the measured temperature and pressure values, two temperature and pressure characteristic curves closest to them are found through density interpolation;

[0058] Calculate the temperature proportionality coefficient based on the measured temperature value and the temperature values ​​corresponding to the two temperature-pressure characteristic curves closest thereto;

[0059] Based on the temperature proportionality coefficient and the pressure values ​​at 20° C. corresponding to the two temperature-pressure characteristic curves closest thereto, the pressure value at 20° C. corresponding to the pressure value of the ternary mixed gas measured at the built-in rated mixing ratio is obtained.

[0060] Specifically, the step of finding two temperature-pressure characteristic curves closest to the measured temperature value and pressure value includes:

[0061] Substitute the measured pressure value into all temperature-pressure characteristic curves under the built-in rated mixing ratio to obtain the corresponding temperature values;

[0062] The difference between the measured temperature value and the temperature values ​​corresponding to all temperature-pressure characteristic curves is calculated, and the temperature-pressure characteristic curve corresponding to when the difference is less than 0 and is the maximum and the temperature-pressure characteristic curve corresponding to when the difference is greater than 0 and is the minimum are selected as the two temperature-pressure characteristic curves closest to it.

[0063] Furthermore, the temperature proportionality coefficient is calculated by the following formula:

[0064] , (1)

[0065] in, Indicates the temperature proportionality coefficient of the rated mixing ratio ki, Indicates the measured temperature value, , It indicates the temperature value corresponding to the two temperature-pressure characteristic curves closest to it under the rated mixing ratio ki.

[0066] Further, the pressure value of the ternary mixed gas measured at 20° C. corresponding to the built-in rated mixing ratio is obtained by the following formula as the first pressure value:

[0067] , (2)

[0068] in, Indicates the measured pressure value at 20°C corresponding to the rated mixing ratio ki. , It indicates the pressure value corresponding to the two temperature-pressure characteristic curves closest to the rated mixing ratio ki at 20°C.

[0069] It should be noted that since each built-in temperature-pressure characteristic curve is obtained through experiments, and the temperature-pressure characteristic curves corresponding to the ternary mixed gas at different densities are different, in order to balance the time and manpower and material resources consumed in the actual experiment, the experiment is carried out at equal density intervals. Therefore, the built-in temperature-pressure characteristic curve cannot cover all densities, resulting in the actual measured temperature and pressure values ​​may not fall on the built-in temperature-pressure characteristic curve, and the corresponding pressure value at 20°C cannot be directly read according to the characteristic curve, so density interpolation is required.

[0070] For example, assume that the density relay has built-in temperature and pressure characteristic curves of the ternary mixed gas at the above four rated mixing ratios, represented as k1, k2, k3, and k4, and the temperature and pressure characteristic curves at each rated mixing ratio are a cluster of temperature and pressure characteristic curves arranged from small to large according to gas density. Assume that the current temperature value of the ternary mixed gas measured by the temperature sensor is T, and the pressure value of the ternary mixed gas measured by the pressure sensor is P. For the rated mixing ratio k1: Substitute P into all temperature and pressure characteristic curves under k1 to obtain the corresponding temperature values, recorded as T k1,1 ,......,T k1,n , where n represents the number of all temperature-pressure characteristic curves under k1, 1 represents the temperature-pressure characteristic curve with the smallest density, and n represents the temperature-pressure characteristic curve with the largest density. Calculate △T k1,t =TT k1,t (t∈n), if △T k1,2 <0 and maximum, then select T k1,2 The corresponding temperature-pressure characteristic curve 2 and T k1,3 The corresponding temperature-pressure characteristic curve 3 is the two temperature-pressure characteristic curves closest to the measured T and P. The temperature proportionality coefficient of k1 is calculated by formula (1): In T k1,2 and T k1,3 Find the pressure value P at 20°C corresponding to P on the two corresponding temperature-pressure characteristic curves k1,2,20 , P k1,3,20 , the pressure value P of the ternary mixed gas measured at 20°C corresponding to k1 is obtained by formula (2): Similarly, the pressure values ​​at 20°C corresponding to the pressure values ​​P of the ternary mixed gas measured at k2, k3, and k4 are obtained by the above method respectively. , , . , , , are both the first pressure values.

[0071] It should be noted that, since the temperature-pressure characteristic curves for each rated mixing ratio in the above example are arranged from small to large in terms of gas density, when △T k1,2 <0 and the maximum corresponding temperature-pressure characteristic curve 2, the adjacent temperature-pressure characteristic curve 3 is △T k1,3 >0 and the corresponding temperature-pressure characteristic curve when it is minimum.

[0072] It can be understood that the present invention obtains the pressure value of the C4F7N / CO2 / O2 ternary mixed gas at the built-in rated mixing ratio by performing density interpolation on the temperature-pressure characteristic curve built into the density relay, thereby improving the accuracy of the output result of the density relay.

[0073] Specifically, in step S2, the partial pressure values ​​of the three gases C4F7N, CO2, and O2 are obtained by the following formula according to Dalton's law of partial pressure:

[0074] P C4F7N =PC C4F7N

[0075] P CO2 =PC CO2

[0076] P O2 =PC O2 , (3)

[0077] Among them, P C4F7N , P CO2 , P O2 Respectively represent the partial pressure values ​​of C4F7N, CO2, and O2 gases, P represents the measured pressure value, C C4F7N , C CO2 , C O2They respectively represent the proportion of C4F7N, CO2 and O2 gases in the actual mixing ratio.

[0078] It should be noted that the actual mixing ratio of the C4F7N / CO2 / O2 ternary mixed gas can be obtained by a mixing ratio detector or by other existing technologies, which will not be described in detail in this application.

[0079] Further, the pressure value of the ternary mixed gas at 20° C. at the actual mixing ratio obtained based on the partial pressure values ​​of the three gases C4F7N, CO2, and O2 and the measured temperature value includes:

[0080] The molar volume of the C4F7N gas is obtained based on the partial pressure value of the C4F7N gas and the measured temperature value, and the pressure value of the C4F7N gas of equal molar volume at 20° C. is obtained based on the molar volume of the C4F7N gas;

[0081] Based on the partial pressure values ​​of CO2 and O2 gases, the ideal gas state equation is used to obtain the density of CO2 and O2 gases, and based on the density of CO2 and O2 gases, the pressure values ​​of CO2 and O2 gases with equal density at 20°C are obtained;

[0082] The pressure value of the ternary mixed gas at 20°C at an actual mixing ratio is obtained based on the pressure value of equimolar volume of C4F7N gas at 20°C and the pressure values ​​of CO2 and O2 gases at 20°C with equal density.

[0083] Furthermore, the molar volume of C4F7N gas is obtained by the following equation:

[0084] , (4)

[0085] in, is the pressure value, R is the gas constant, is the Kelvin temperature value, is the molar volume of the gas, , , To correct the parameters, is the critical temperature value, To compare the temperature values, is the critical pressure, is the eccentricity factor.

[0086] Preferably, R is 8.314 J / (mol·K), Take 385.928K, Take 2.5028MPa, Take 0.47340.

[0087] It should be noted that the partial pressure value of C4F7N gas and the measured temperature value are substituted into the above equation (4) , , calculate the molar volume of C4F7N gas.

[0088] Further, the molar volume of C4F7N gas and 20℃ are substituted into the above equation (4) , , calculated , which is the pressure value P of the equimolar volume of C4F7N gas at 20°C C4F7N,20 .

[0089] Furthermore, the density of CO2 and O2 gases is obtained by the following ideal gas state equation:

[0090] , (5)

[0091] in, is the pressure value, is the density of the gas, is the gas constant, is the Kelvin temperature value, is the relative molecular mass.

[0092] It should be noted that CO2 and O2 gases are small molecules, and their densities are calculated using the ideal gas state equation. The relative molecular masses of CO2 and O2 gases are 44 and 32, respectively. Substitute the partial pressure value of CO2 gas and the measured temperature value into the above equation (5) , , calculate the density of CO2 gas ; Substitute the partial pressure of O2 gas and the measured temperature into the above equation (5) , , calculate the density of O2 gas .

[0093] Further, the density of CO2 gas and 20℃ are substituted into the above equation (5) , , calculated , which is the pressure value P of CO2 gas with equal density at 20℃ CO2,20 ; Substitute the density of O2 gas and 20℃ into the above equation (5) , , calculated , which is the pressure value P of the O2 gas with equal density at 20℃ O2,20 .

[0094] Furthermore, the pressure value of the ternary mixed gas at 20° C. under the actual mixing ratio is obtained by the following formula as the second pressure value:

[0095] P 20 =P C4F7N,20 +P CO2,20 +P O2,20 , (6)

[0096] Among them, P 20 is the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio.

[0097] Furthermore, the deviation between the second pressure value and the first pressure value is calculated by the following formula:

[0098] , (7)

[0099] Wherein, i∈[1,n], n is the total number of rated mixing ratios built into the density relay.

[0100] Furthermore, when multiple rated mixing ratios of the ternary mixed gas are built into the density relay, the deviation between the second pressure value and all the first pressure values ​​is calculated, and the minimum deviation is selected. If the minimum deviation is less than a threshold value, the density relay outputs the first pressure value corresponding to the minimum deviation.

[0101] It should be noted that when the mixing ratio of the ternary mixed gas changes, its temperature-pressure characteristic curve also changes because the temperature-pressure curves of the three gases C4F7N, CO2, and O2 are different. According to practical experience, if the ternary mixed gas in the device under test does not have irregular gas filling or gas leakage, the deviation generally does not exceed 0.2%; set an appropriate threshold, for example, set the threshold to 0.3%; when When the temperature-pressure characteristic curve under the built-in rated mixing ratio is used, the density relay directly outputs the first pressure value corresponding to the deviation. When the deviation is greater than the threshold, it means that all built-in rated mixing ratios are greatly different from the actual mixing ratio, so the temperature-pressure characteristic curve under the built-in rated mixing ratio cannot be directly used.

[0102] Furthermore, the interpolation of the mixture ratio by gas virtual compensation so that the actual mixture ratio becomes the target mixture ratio includes:

[0103] When the density relay has multiple rated mixing ratios of the ternary mixed gas built in, a minimum deviation is selected from the deviations between the second pressure value and all the first pressure values, and the built-in rated mixing ratio corresponding to the minimum deviation is the built-in rated mixing ratio closest to the actual mixing ratio, that is, the target mixing ratio;

[0104] The mixture ratio is interpolated by gas virtual compensation so that the actual mixture ratio becomes the target mixture ratio.

[0105] Furthermore, the mixing ratio is interpolated by formulas (8)-(11):

[0106] , (8)

[0107] in, Represents the proportion of C4F7N gas in the actual mixing ratio, Represents the measured pressure value, Represents the pressure value of the compensated C4F7N gas, Represents the total pressure value of the compensation, Represents the proportion of C4F7N gas in the target mixing ratio.

[0108] , (9)

[0109] in, Represents the proportion of CO2 gas in the actual mixing ratio, Represents the pressure value of the compensated CO2 gas, Represents the proportion of CO2 gas in the target mixing ratio.

[0110] , (10)

[0111] in, Represents the proportion of O2 gas in the actual mixing ratio, Represents the pressure value of compensated O2 gas, Represents the proportion of O2 gas in the target mixing ratio.

[0112] . (11)

[0113] It can be understood that since the target mixture ratio is a fixed value, the total pressure value of the compensation It is also a fixed value and can be preset in advance.

[0114] Furthermore, the pressure value corresponding to the interpolated mixing ratio obtained based on the target mixing ratio includes:

[0115] Obtaining a pressure value of the ternary mixed gas at 20° C. corresponding to the target mixing ratio based on the measured temperature value, the measured pressure value and the compensated total pressure value;

[0116] Obtaining the pressure value of each gas compensated at 20° C. corresponding to the target mixing ratio based on the measured temperature value and the compensated pressure value of each gas;

[0117] Based on the pressure value of the ternary mixed gas at 20°C corresponding to the target mixing ratio and the compensated pressure values ​​of each gas at 20°C corresponding to the target mixing ratio, the pressure value corresponding to the mixing ratio after interpolation is obtained and output by the density relay.

[0118] Specifically, according to the method in step S1, Instead of the measured pressure value P, the density relay temperature pressure characteristic curve cluster at the target mixing ratio is interpolated to obtain the pressure value of the ternary mixed gas at 20°C corresponding to the target mixing ratio. Similarly, according to the method in step S1, , , Instead of the measured pressure value P, the compensated pressure values ​​of C4F7N, CO2, and O2 gases at 20°C corresponding to the target mixing ratio are obtained. , , .

[0119] Furthermore, the pressure value corresponding to the interpolated mixing ratio is obtained by the following formula:

[0120] , (12)

[0121] in, Represents the pressure value corresponding to the interpolated mixing ratio, represents the pressure value of the ternary mixed gas at 20°C corresponding to the target mixing ratio, Represents the pressure value of the compensated C4F7N gas at 20°C corresponding to the target mixing ratio, Represents the pressure value of the compensated CO2 gas at 20°C corresponding to the target mixing ratio. Represents the pressure value of compensated O2 gas at 20°C corresponding to the target mixing ratio; is the coefficient, which can be 1 or -1.

[0122] It should be noted that when the pressure value of the gas compensation is a positive number, the corresponding coefficient is -1, otherwise, the corresponding coefficient is 1. For example, when When it is a positive number, it means that C4F7N gas is virtually supplemented. When outputting the corresponding pressure value, the supplemented part needs to be subtracted. Take -1; when When it is a negative number, it means that the C4F7N gas is virtually reduced. When outputting the corresponding pressure value, the reduced part needs to be added. Take 1.

[0123] It can be understood that the present invention further improves the accuracy of the output result of the density relay by comparing the deviation between the second pressure value and the first pressure value, and interpolating the mixing ratio when the deviation is greater than the threshold value. This solves the problem that when the actual mixing ratio of the C4F7N / CO2 / O2 ternary mixed gas is inconsistent with the mixing ratio built into the density relay, there is a large error in the gas density obtained by the density relay, which is of great significance to ensuring the safe and stable operation of electrical equipment.

[0124] Compared with the prior art, the C4F7N / CO2 / O2 ternary mixed gas temperature and pressure characteristic curve interpolation compensation method provided by the present invention has the following beneficial effects:

[0125] The present invention performs density interpolation on the temperature-pressure characteristic curve built into the density relay to obtain the pressure value of the C4F7N / CO2 / O2 ternary mixed gas at the built-in rated mixing ratio, thereby improving the accuracy of the output result of the density relay.

[0126] The present invention further improves the accuracy of the output result of the density relay by comparing the deviation between the second pressure value and the first pressure value and performing mixing ratio interpolation when the deviation is greater than a threshold value. This solves the problem that when the actual mixing ratio of the C4F7N / CO2 / O2 ternary mixed gas is inconsistent with the mixing ratio built into the density relay, there is a large error in the gas density obtained by the density relay, which is of great significance for ensuring the safe and stable operation of electrical equipment.

[0127] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.

[0128] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for interpolation compensation of temperature-pressure characteristic curve of C4F7N / CO2 / O2 ternary mixed gas, characterized in that: The method comprises the following steps: Measuring the temperature and pressure of the C4F7N / CO2 / O2 ternary mixed gas in the device under test by a density relay, and obtaining the pressure value at 20° C. corresponding to each built-in rated mixing ratio of the measured pressure value based on the measured temperature and pressure values ​​and the rated mixing ratio and temperature-pressure characteristic curve built into the density relay as the first pressure value; According to the actual mixing ratio of the ternary mixed gas in the device to be tested and the measured pressure value, the partial pressure values ​​of the three gases C4F7N, CO2, and O2 are obtained; based on the partial pressure values ​​of the three gases C4F7N, CO2, and O2 and the measured temperature value, the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio is obtained as the second pressure value; the deviation between the second pressure value and the first pressure value is calculated, and if the deviation is less than the threshold value, the density relay outputs the first pressure value; otherwise, the mixing ratio is interpolated through gas virtual compensation to make the actual mixing ratio become the target mixing ratio, and the pressure value corresponding to the interpolated mixing ratio is obtained based on the target mixing ratio; The mixing ratio is interpolated by formulas (8)-(11): ， （8） in, Represents the proportion of C4F7N gas in the actual mixing ratio, Represents the measured pressure value, Represents the pressure value of the compensated C4F7N gas, Represents the total pressure value of the compensation, Represents the proportion of C4F7N gas in the target mixing ratio; ， （9） in, Represents the proportion of CO2 gas in the actual mixing ratio, Represents the pressure value of the compensated CO2 gas, Represents the proportion of CO2 gas in the target mixing ratio; ， （10） in, Represents the proportion of O2 gas in the actual mixing ratio, Represents the pressure value of compensated O2 gas, Represents the proportion of O2 gas in the target mixing ratio; （11）。 2. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 1, characterized in that: The pressure value at 20°C corresponding to each rated mixing ratio is obtained as the first pressure value by the following steps: Based on the measured temperature and pressure values, two temperature and pressure characteristic curves closest to them are found through density interpolation; Calculate the temperature proportionality coefficient based on the measured temperature value and the temperature values ​​corresponding to the two temperature-pressure characteristic curves closest thereto; Based on the temperature proportionality coefficient and the pressure values ​​at 20° C. corresponding to the two temperature-pressure characteristic curves closest thereto, the pressure value at 20° C. corresponding to the pressure value of the ternary mixed gas measured at the built-in rated mixing ratio is obtained.

3. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 2, characterized in that: The temperature proportionality coefficient is calculated by the following formula: ， （1） in, Indicates the temperature proportionality coefficient of the rated mixing ratio ki, Indicates the measured temperature value, , It indicates the temperature value corresponding to the two temperature-pressure characteristic curves closest to it under the rated mixing ratio ki.

4. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 3, characterized in that: The pressure value of the ternary mixed gas measured at 20° C. corresponding to the built-in rated mixing ratio is obtained by the following formula as the first pressure value: ， （2） in, Indicates the measured pressure value at 20°C corresponding to the rated mixing ratio ki. , It indicates the pressure value corresponding to the two temperature-pressure characteristic curves closest to the rated mixing ratio ki at 20°C.

5. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 1, characterized in that: The pressure value of the ternary mixed gas at 20° C. at the actual mixing ratio obtained based on the partial pressure values ​​of C4F7N, CO2, and O2 and the measured temperature value includes: The molar volume of the C4F7N gas is obtained based on the partial pressure value of the C4F7N gas and the measured temperature value, and the pressure value of the C4F7N gas of equal molar volume at 20° C. is obtained based on the molar volume of the C4F7N gas; Based on the partial pressure values ​​of CO2 and O2 gases, the ideal gas state equation is used to obtain the density of CO2 and O2 gases, and based on the density of CO2 and O2 gases, the pressure values ​​of CO2 and O2 gases with equal density at 20°C are obtained; The pressure value of the ternary mixed gas at 20°C at an actual mixing ratio is obtained based on the pressure value of equimolar volume of C4F7N gas at 20°C and the pressure values ​​of CO2 and O2 gases at 20°C with equal density.

6. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 5, characterized in that: The molar volume of C4F7N gas is obtained by the following equation: ， （4） in, is the pressure value, R is the gas constant, is the Kelvin temperature value, is the molar volume of the gas, , , To correct the parameters, is the critical temperature value, To compare the temperature values, is the critical pressure, is the eccentricity factor.

7. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 5, characterized in that: The density of CO2 and O2 gases is obtained by the following ideal gas state equation: ， （5） in, is the pressure value, is the density of the gas, is the gas constant, is the Kelvin temperature value, is the relative molecular mass.

8. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 5, characterized in that: The deviation between the second pressure value and the first pressure value is calculated by the following formula: ， （7） in, Indicates the pressure value at 20°C corresponding to the measured pressure value at the rated mixing ratio ki, P 20 represents the pressure value of the ternary mixed gas at 20°C under the actual mixing ratio, i∈[1,n], n is the total number of rated mixing ratios built into the density relay.

9. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 1, characterized in that: The interpolation of the mixture ratio by gas virtual compensation so that the actual mixture ratio becomes the target mixture ratio comprises: When the density relay has multiple rated mixing ratios of the ternary mixed gas built in, a minimum deviation is selected from the deviations between the second pressure value and all the first pressure values, and the built-in rated mixing ratio corresponding to the minimum deviation is the built-in rated mixing ratio closest to the actual mixing ratio, that is, the target mixing ratio; The mixture ratio is interpolated by gas virtual compensation so that the actual mixture ratio becomes the target mixture ratio.

10. The C4F7N / CO2 / O2 ternary mixed gas temperature-pressure characteristic curve interpolation compensation method according to claim 9, characterized in that: The pressure value corresponding to the interpolated mixing ratio obtained based on the target mixing ratio includes: Obtaining a pressure value of the ternary mixed gas at 20° C. corresponding to the target mixing ratio based on the measured temperature value, the measured pressure value and the compensated total pressure value; Obtaining the pressure value of each gas compensated at 20° C. corresponding to the target mixing ratio based on the measured temperature value and the compensated pressure value of each gas; Based on the pressure value of the ternary mixed gas at 20° C. corresponding to the target mixing ratio and the compensated pressure values ​​of each gas at 20° C. corresponding to the target mixing ratio, the pressure value corresponding to the mixing ratio after interpolation is obtained.

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