Method for testing low-temperature compensation amount of SF6 / CF4 density relay

Abstract

The application discloses a kind of SF6 / CF4 density relay low temperature compensation quantity test methods, belong to electrical engineering technical field.The test method is divided into seven steps such as determining temperature test allowable range, setting temperature test point, calibrating pressure reference value, configuring SF6+CF4 mixed gas, testing mixed pressure value, calculating supplementary pressure value, drawing temperature-pressure curve.The method can obtain the temperature-pressure curve of SF6 / CF4 density relay in a larger temperature range including low temperature, has technical guidance value for optimizing SF6 / CF4 density relay design, improving the measurement accuracy of SF6 / CF4 density relay, can improve the operation reliability of SF6 / CF4 circuit breaker.

Description

Technical Field

[0001] This invention belongs to the field of electrical engineering, specifically relating to a method for testing the low-temperature compensation of an SF6 / CF4 density relay. Background Technology

[0002] SF6 gas has excellent insulation and arc-extinguishing properties and is widely used in switchgear. Density relays are meters used to measure the pressure of SF6 gas in SF6 circuit breakers, GIS, and other switchgear during normal operation. When SF6 gas liquefies at low temperatures, the density relay sends a blocking signal. Therefore, density relays can be considered a "health assistant" for monitoring SF6 switchgear.

[0003] Traditional methods for calibrating SF6 gas density relays use the ambient temperature as the test temperature and 20°C as the reference temperature. The pressure value of the relay at this test temperature is then converted to 20°C and used to evaluate its performance. However, in recent years, the drawbacks of testing SF6 gas density relays at room temperature have become increasingly apparent. Because 20°C is used as the reference temperature, some SF6 switchgear operating in cold regions has experienced inaccurate SF6 density relay measurements and false latch-ups. This demonstrates that using a single temperature point to evaluate the measurement performance of SF6 density relays is not comprehensive enough. Therefore, some manufacturers have developed automatic calibration devices for SF6 gas density relays covering the entire temperature range from -40°C to 80°C, which currently show great promise for practical application.

[0004] While SF6 gas offers significant advantages, its drawbacks are also relatively prominent. Its low liquefaction temperature poses a considerable risk to SF6 switchgear operating in cold northern regions. Therefore, some switchgear manufacturers use an SF6 / CF4 mixture as the insulating medium to mitigate the liquefaction problem of SF6 gas. Compared to circuit breakers using pure SF6 gas, the temperature-pressure characteristics of the SF6 / CF4 mixture have changed. Therefore, the measurement performance of SF6 / CF4 density relays, especially their low-temperature testing performance, deserves close attention.

[0005] Inner Mongolia is located in a cold northern region, with outdoor temperatures in some areas reaching as low as -40°C in winter. A large number of SF6 / CF4 circuit breakers are also in operation there. Research and analysis revealed several issues with SF6 / CF4 circuit breakers, including variations in the mixing ratio of SF6 and CF4 gases between different manufacturers; inconsistent labeling of the gas filling ratio, using different methods such as pressure ratio, mass ratio, and volume ratio; and mismatches between the mixing ratio and density relays in the SF6 / CF4 circuit breakers.

[0006] Structurally, SF6 / CF4 density relays and SF6 density relays are identical. Their measurement accuracy depends on the accuracy of the compensation amounts provided by the gas pressure sensing element, Bourdon tube, temperature sensing element, bimetallic strip, and other temperature compensation devices at different temperatures. Since the feedback from these temperature compensation devices differs for SF6 / CF4 mixtures and SF6 gas, it is imperative to focus on the measurement performance of SF6 / CF4 density relays and propose feasible low-temperature compensation testing methods. Summary of the Invention

[0007] This invention provides a test method for the low-temperature compensation of SF6 / CF4 density relays. The purpose is to test the compensation pressure of SF6 / CF4 density relays under the operating environment temperature of SF6 switchgear, including low temperature, to provide data support for improving the measurement accuracy of SF6 / CF4 density relays and to ensure the safe and stable operation of SF6 / CF4 circuit breakers.

[0008] The objective of this invention is achieved as follows: This invention provides a method for testing the low-temperature compensation of an SF6 / CF4 density relay, comprising the following steps:

[0009] Step 1: Determine the allowable temperature range for testing.

[0010] The SF6 / CF4 density relay to be tested is denoted as the relay under test. The ratio of the rated pressure of SF6 gas to CF4 gas is denoted as the rated pressure ratio f. The rated pressure p and the rated pressure ratio f on the dial of the relay under test are read. The pressure of SF6 gas under the rated pressure p is calculated and denoted as SF6 gas pressure p1.

[0011] Consult the pressure-temperature characteristic curve of SF6 gas to obtain the liquefaction temperature of SF6 gas at pressure p1, and denote it as SF6 liquefaction temperature T. min ;

[0012] Let H be the allowable temperature test range for the relay under test, and set it as follows:

[0013] If T min -40℃, H=[-40, 40]℃;

[0014] If T min -40℃, H=[T min ,40]℃;

[0015] Step 2, determine the temperature test point

[0016] Using 40℃ as the highest temperature test point, the test step size is set according to the following rules as the temperature decreases:

[0017] In the temperature range of ≥0℃, the test step size is 10℃;

[0018] In the temperature range below 0℃, the test step size is 5℃;

[0019] Temperature test points are determined according to the following rules:

[0020] First, N ordinary temperature test points are set up within the allowable temperature test range H according to the specified test step size, and any one of them is denoted as ordinary test point t. j , compared with ordinary test point t j The corresponding temperature is denoted as the ordinary test temperature T. j j = 1, 2, ..., N;

[0021] Secondly, if 1℃ < T j -T min For temperatures below 5℃, a new special test point t0 is added, and the temperature corresponding to the special test point t0 is denoted as the special test temperature T0, where T0 = T min ;

[0022] N ordinary test points t j Combined with the special test point t0, a total of N+1 test points t are obtained within the allowable temperature test range H. i , and test point t i The corresponding temperature is denoted as the test temperature T. i , i = 0, 1, ..., N, where, when the special test point t0 does not exist, the special test temperature T0 does not exist; when the special test point t0 exists, T0 = T min ;

[0023] Step 3, calibrate the pressure reference value

[0024] Connect the outlet of the SF6 gas cylinder to the gas input terminal of an automatic calibration device for full-temperature SF6 gas density relay, and keep the gas pressure p1 of the SF6 gas input when the gas input terminal of the automatic calibration device for full-temperature SF6 gas density relay is operating at 20°C.

[0025] Using an automatic calibration device for SF6 gas density relays at all temperatures, the relay under test is tested at each test temperature T at an SF6 gas pressure p1, following a cooling process from high to low. i The corresponding pressure value is recorded as the reference pressure P. s(i) , i = 0, 1, ..., N;

[0026] After the test, the full-temperature SF6 gas density relay automatic calibration device was evacuated and then put into standby use.

[0027] Step 4, prepare the SF6+CF4 mixed gas

[0028] A gas mixing device is used to prepare an SF6+CF4 mixture, with the pressure ratio of the two gases being the rated ratio f.

[0029] After configuration, adjust the output of the gas configuration device to make the pressure of the SF6+CF4 mixed gas output at the rated pressure p.

[0030] Step 5, test the mixed pressure value

[0031] Connect the output of the gas preparation device to the gas input of the full-temperature SF6 gas density relay automatic calibration device, and keep the SF6+CF4 mixed gas pressure input when the gas input of the full-temperature SF6 gas density relay automatic calibration device is working at 20℃ at the rated pressure p;

[0032] Using an automatic calibration device for SF6 gas density relays at all temperatures, the test temperature T of the relay under test is tested at each point in time, following a cooling process from high to low. i The corresponding pressure value is recorded as the mixed pressure P. s+c(i) , i = 0, 1, ..., N;

[0033] Step 6, Calculate the compensation pressure value

[0034] Test point t i The compensation pressure value is recorded as 6. (i) For i = 0, 1, ..., N, the calculation formula is:

[0035] δ (i) =P s+c(i) -P s(i) ;

[0036] Step 7, plot the temperature-pressure curve.

[0037] Test temperature T i The horizontal axis represents the reference pressure P. s(i) Fit a T-axis to the ordinate in a planar coordinate system and plot it. i -P s(i) Curve, to test temperature T i The horizontal axis represents the mixing pressure P. s+c(i) Fit a T-axis to the ordinate in a planar coordinate system and plot it. i -P s+c(i) Curve; based on test temperature T i The horizontal axis represents the compensation pressure value δ. (i) Plot a T-axis in a plane coordinate system for the ordinate. i -δ (i) curve.

[0038] Preferably, the automatic calibration device for the full-temperature SF6 gas density relay includes an industrial control computer, a temperature control system, a detection system, a fully enclosed SF6 gas pressure regulation system, a vacuum system, and a feedback system, which can autonomously adjust and maintain the test temperature and perform pressure testing.

[0039] Preferably, during the baseline pressure test in step 3 and the mixed pressure test in step 5, the holding time for all test temperatures shall not be less than 2 hours, and the data shall be read only after the pressure value displayed by the full-temperature SF6 gas density relay automatic calibration device has stabilized.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. This invention proposes a test method for low-temperature compensation of SF6 / CF4 density relays, which can accurately obtain the temperature-pressure curves of SF6 / CF4 density relays over a large temperature range, including low temperatures. This method has direct technical guidance value for optimizing the design of SF6 / CF4 density relays and improving the measurement accuracy of SF6 / CF4 density relays.

[0042] 2. Different SF6 / CF4 circuit breaker manufacturers use different proportions of SF6+CF4 mixed gas in their circuit breakers. These different proportions result in different feedback from the compensation devices of the SF6 / CF4 density relays, leading to varying compensation amounts. Therefore, clearly defining the gas configuration ratio before measurement is a prerequisite for determining the compensation amount of SF6 / CF4 circuit breakers and is fundamental to ensuring measurement accuracy.

[0043] 3. This invention provides the lower limit temperature T for testing SF6 / CF4 density relays. min During the test, at T min Tests were conducted at near-terminal temperature points, which can be used to estimate the low-temperature blocking temperature of SF6 / CF4 circuit breakers under the test scale. The test results can provide indirect analytical criteria for judging and analyzing low-temperature blocking defects in SF6 / CF4 circuit breakers in cold regions. Simultaneously, environmental temperature selection guidance is provided for the selection of SF6 / CF4 circuit breaker equipment.

[0044] 4. In this invention, the reference pressure P of the SF6 / CF4 density relay to be tested was first tested at a pressure value of p1 for SF6 gas. s(i) This clarifies the feedback of the density relay's compensation device to SF6 gas. Secondly, the mixing pressure P of the SF6 / CF4 density relay under test was tested at various test temperatures under pressure value p. s+c(i)This clarifies the feedback of the density relay's compensation device for the SF6+CF4 mixture. The evaluation of the accuracy of the SF6 / CF4 density relay measurement is divided into two levels: namely, if the reference pressure P at each test temperature... s(i) The large deviation indicates that the density relay inherently has a significant pressure deviation for SF6 gas, suggesting a product quality and manufacturing process issue. However, if the density relay only mixes at pressure P at each test temperature... s+c(i) If the deviation is large, the design should be optimized and reasonable compensation should be provided. Attached Figure Description

[0045] Figure 1 This is a flowchart of a test method for the low-temperature compensation of an SF6 / CF4 density relay.

[0046] Figure 2 This is the wiring diagram for the SF6 / CF4 density relay test in step 5 of this embodiment of the invention. Detailed Implementation

[0047] Figure 1 This is a flowchart of a test method for the low-temperature compensation of an SF6 / CF4 density relay proposed in this invention. Figure 1 Therefore, the present invention provides a method for testing the low-temperature compensation of an SF6 / CF4 density relay, comprising the following steps:

[0048] Step 1: Determine the allowable temperature range for testing.

[0049] The SF6 / CF4 density relay to be tested is denoted as the relay under test. The ratio of the rated pressure of SF6 gas to CF4 gas is denoted as the rated pressure ratio f. The rated pressure p and the rated pressure ratio f on the dial of the relay under test are read. The pressure of SF6 gas under the rated pressure p is calculated and denoted as SF6 gas pressure p1.

[0050] Consult the pressure-temperature characteristic curve of SF6 gas to obtain the liquefaction temperature of SF6 gas at pressure p1, and denote it as SF6 liquefaction temperature T. min

[0051] Let H be the allowable temperature test range for the relay under test, and set it as follows:

[0052] If T min -40℃, H=[-40, 40]℃;

[0053] If T min -40℃, H=[T min ,40]℃.

[0054] In practice, some relays under test only show the rated mass ratio or rated volume ratio of SF6 gas and CF4 gas on their dials. The mass ratio or volume ratio needs to be converted into the rated pressure ratio.

[0055] In this embodiment, the pressure-temperature characteristic curve of SF6 gas is obtained from publicly available technical data, which can be obtained by consulting relevant regulations or standards for SF6 gas.

[0056] Step 2, determine the temperature test point

[0057] Using 40℃ as the highest temperature test point, the test step size is set according to the following rules as the temperature decreases:

[0058] In the temperature range of ≥0℃, the test step size is 10℃;

[0059] In the temperature range of <0℃, the test step size is 5℃.

[0060] Temperature test points are determined according to the following rules:

[0061] First, N ordinary temperature test points are set up within the allowable temperature test range H according to the specified test step size, and any one of them is denoted as ordinary test point t. j , compared with ordinary test point t j The corresponding temperature is denoted as the ordinary test temperature T. j j = 1, 2, ..., N;

[0062] Secondly, if 1℃ < T j -T min For temperatures below 5℃, a new special test point t0 is added, and the temperature corresponding to the special test point t0 is denoted as the special test temperature T0, where T0 = T min ;

[0063] N ordinary test points t j Combined with the special test point t0, a total of N+1 test points t are obtained within the allowable temperature test range H. i , and test point t i The corresponding temperature is denoted as the test temperature T. i , i = 0, 1, ..., N, where, when the special test point t0 does not exist, the special test temperature T0 does not exist; when the special test point t0 exists, T0 = T min .

[0064] In this embodiment, the automatic calibration device for the full-temperature SF6 gas density relay can provide a test temperature range of [-40, 80]℃, with a temperature control error of approximately 1℃. The rated pressure p of the SF6 gas density relay and the rated pressure ratio f of SF6 gas and CF4 gas vary between different manufacturers. Tests have confirmed that some SF6 / CF4 circuit breakers, under rated pressure p and rated pressure ratio f, exhibit SF6 gas liquefaction in the SF6 / CF4 gas at a certain low temperature, concentrated in the temperature range of -25℃ and below, i.e., the SF6 liquefaction temperature T. min -25.

[0065] In this embodiment, the full-temperature SF6 gas density relay automatic calibration device can provide a test temperature range of [-40, 80]℃, and some SF6 / CF4 circuit breakers may liquefy at -25℃ and below. Therefore, in step 1, the allowable temperature test range H of the relay under test is divided into two categories, namely: such as T mmin At -40℃, following the temperature test point setting method in step 2, individual temperature points can be tested within the temperature test range provided by the full-temperature SF6 gas density relay automatic calibration device. There is no possibility of liquefaction within this test temperature range; therefore, T0 = T0 does not exist. min Pressure tests in steps 3 and 5 at the specified temperature.

[0066] However, if T min >-40℃, considering the possibility that some SF6 / CF4 circuit breakers may liquefy at -25℃ and below, then -40℃... <T min ≤-25℃, near T min The temperature value indicates that SF6 gas may have already liquefied. Once SF6 gas liquefies, the test object of the SF6 / CF4 density relay changes, therefore the temperature value is less than T. min At this temperature point, no further pressure testing is required. In this embodiment, to explore the low-temperature blocking temperature of the SF6 / CF4 circuit breaker and to provide indirect analytical criteria for judging and analyzing low-temperature blocking defects of SF6 / CF4 circuit breakers in cold regions, it is necessary to perform pressure testing at T0 = T min The pressure tests in steps 3 and 5 are carried out at the specified temperature.

[0067] Step 3, calibrate the pressure reference value

[0068] Connect the outlet of the SF6 gas cylinder to the gas input terminal of an automatic calibration device for full-temperature SF6 gas density relay, and keep the gas pressure p1 of the SF6 gas input when the gas input terminal of the automatic calibration device for full-temperature SF6 gas density relay is operating at 20°C.

[0069] Using an automatic calibration device for SF6 gas density relays at all temperatures, the relay under test is tested at each test temperature T at an SF6 gas pressure p1, following a cooling process from high to low. i The corresponding pressure value is recorded as the reference pressure P. s(i) , i = 0, 1, ..., N.

[0070] After the test, the automatic calibration device for the full-temperature SF6 gas density relay was evacuated and then put into standby mode.

[0071] In this embodiment, the automatic calibration device for the full-temperature SF6 gas density relay includes an industrial control computer, a temperature control system, a detection system, a fully enclosed SF6 gas pressure regulation system, a vacuum system, and a feedback system, which can autonomously adjust and maintain the test temperature and perform pressure testing.

[0072] In this embodiment, the automatic calibration device for the full-temperature SF6 gas density relay used is the ZDT-21 multi-functional SF6 gas density relay automatic calibration device.

[0073] Step 4, prepare the SF6+CF4 mixed gas

[0074] A gas mixing device is used to prepare an SF6+CF4 mixture, with the pressure ratio of the two gases being the rated ratio f.

[0075] After configuration, adjust the output of the gas configuration device to make the pressure of the SF6+CF4 mixed gas output at the rated pressure p.

[0076] Step 5, test the mixed pressure value

[0077] Connect the output of the gas preparation device to the gas input of the full-temperature SF6 gas density relay automatic calibration device, and keep the SF6+CF4 mixed gas pressure input when the gas input of the full-temperature SF6 gas density relay automatic calibration device is working at 20℃ at the rated pressure p;

[0078] Using an automatic calibration device for SF6 gas density relays at all temperatures, the test temperature T of the relay under test is tested at each point in time, following a cooling process from high to low. i The corresponding pressure value is recorded as the mixed pressure P. s+c(i) , i = 0, 1, ..., N.

[0079] In this embodiment, during the baseline pressure test in step 3 and the mixed pressure test in step 5, the holding time for all test temperatures shall not be less than 2 hours, and the data shall be read only after the pressure value displayed by the full-temperature SF6 gas density relay automatic calibration device has stabilized.

[0080] Figure 2 The wiring diagram for the SF6 / CF4 density relay test in step 5 of this embodiment is shown below. In this diagram, 1 is the relay under test, 2 is the automatic calibration device for the full-temperature SF6 gas density relay, 3 is the gas preparation device, 4 is SF6 gas, and 5 is CF4 gas.

[0081] Step 6, Calculate the compensation pressure value

[0082] Test point t i The compensation pressure value is recorded as 6. (i) For i = 0, 1, ..., N, the calculation formula is:

[0083] δ (i) =P s+c(i) -P s(i)

[0084] The pressure compensation value δ (i) This refers to the pressure difference that the SF6 / CF4 density relay pressure controller should compensate for. This pressure difference is the data basis for ensuring the accurate metering of the SF6 / CF4 density relay.

[0085] Step 7, plot the temperature-pressure curve.

[0086] Test temperature T i The horizontal axis represents the reference pressure P. s(i) Fit a T-axis to the ordinate in a planar coordinate system and plot it. i -P s(i) Curve, to test temperature T i The horizontal axis represents the mixing pressure P. s+c(i) Fit a T-axis to the ordinate in a planar coordinate system and plot it. i -P s+c(i) Curve; based on test temperature T i The horizontal axis represents the compensation pressure value δ. (i) Plot a T-axis in a plane coordinate system for the ordinate. i -δ (i) curve.

[0087] In this embodiment, a comparative test was conducted on two SF6 / CF4 density relays, A and B, with different pressure ratios. Their rated pressures were p = 0.7 MPa, and their rated pressure ratios were f1 = 36%:64% and f2 = 53%:47%, respectively. The mixed gas pressure input to the automatic calibration device for the full-temperature SF6 gas density relay was set and maintained at 20°C with the rated pressure p and pressure ratios f1 and f2. The mixed pressure values ​​P at each test temperature were recorded. s+c(i) The table below shows the data results for SF6 / CF4 density relays with rated pressure ratios f1 = 36%:64% and f2 = 53%:47% at test temperatures of 40℃, 20℃, and -30℃:

[0088]

[0089] In this embodiment, with rated pressure ratios f1 = 36%:64% and f2 = 53%:47%, the maximum compensation pressures of the two SF6 / CF4 density relays were 4.3% and 2.1%, respectively. The test result for relay A exceeded the requirements specified in the procedure; this result will cause a measurement deviation in the density meter, which may lead to an incorrect low-pressure alarm or lockout signal at low temperatures. Meanwhile, relay B showed a smaller overall deviation, but at -38°C, the mixed pressure decreased, suggesting possible liquefaction of the SF6 gas.

Claims

1. A method for testing the low-temperature compensation of an SF6 / CF4 density relay, characterized in that, Includes the following steps: Step 1: Determine the allowable temperature range for testing. The SF6 / CF4 density relay to be tested is denoted as the relay under test. The ratio of the rated pressure of SF6 gas to CF4 gas is denoted as the rated pressure ratio f. The rated pressure p and the rated pressure ratio f on the dial of the relay under test are read. The pressure of SF6 gas under the rated pressure p is calculated and denoted as SF6 gas pressure p1. Consult the pressure-temperature characteristic curve of SF6 gas to obtain the liquefaction temperature of SF6 gas at pressure p1, and denote it as SF6 liquefaction temperature T. min ; Let H be the allowable temperature test range for the relay under test, and set it as follows: If T min ≤-40℃, H=[-40, 40]℃; If T min >-40℃, H=[T min ,40]℃; Step 2, determine the temperature test point Using 40℃ as the highest temperature test point, the test step size is set according to the following rules as the temperature decreases: In the temperature range of ≥0℃, the test step size is 10℃; In the temperature range below 0℃, the test step size is 5℃; Temperature test points are determined according to the following rules: First, N ordinary temperature test points are set up within the allowable temperature test range H according to the specified test step size, and any one of them is denoted as ordinary test point t. j , compared with ordinary test point t j The corresponding temperature is denoted as the ordinary test temperature T. j j = 1, 2, ..., N; Secondly, if 1℃ < T j -T min For temperatures below 5℃, a new special test point t0 is added, and the temperature corresponding to the special test point t0 is denoted as the special test temperature T0, where T0 = T min ; N ordinary test points t j Combined with the special test point t0, a total of N+1 test points t are obtained within the allowable temperature test range H. i , and test point t i The corresponding temperature is denoted as the test temperature T. i , i = 0, 1, ..., N, where, when the special test point t0 does not exist, the special test temperature T0 does not exist; when the special test point t0 exists, T0 = T min ; Step 3, calibrate the pressure reference value Connect the outlet of the SF6 gas cylinder to the gas input terminal of an automatic calibration device for full-temperature SF6 gas density relay, and keep the gas pressure p1 of the SF6 gas input when the gas input terminal of the automatic calibration device for full-temperature SF6 gas density relay is operating at 20°C. Using an automatic calibration device for SF6 gas density relays at all temperatures, the relay under test is tested at each test temperature T at an SF6 gas pressure p1, following a cooling process from high to low. i The corresponding pressure value is recorded as the reference pressure P. s(i) , i = 0, 1, ..., N; After the test, the full-temperature SF6 gas density relay automatic calibration device is evacuated and then put into standby mode. Step 4, prepare the SF6+CF4 mixed gas A gas mixing device is used to prepare an SF6+CF4 mixture, with the pressure ratio of the two gases being the rated pressure ratio f. After configuration, adjust the output of the gas configuration device to make the pressure of the SF6+CF4 mixed gas output at the rated pressure p; Step 5, test the mixed pressure value Connect the output of the gas preparation device to the gas input of the full-temperature SF6 gas density relay automatic calibration device, and keep the SF6+CF4 mixed gas pressure input when the gas input of the full-temperature SF6 gas density relay automatic calibration device is working at 20℃ at the rated pressure p; Using an automatic calibration device for SF6 gas density relays at all temperatures, the test temperature T of the relay under test is tested at each point in time, following a cooling process from high to low. i The corresponding pressure value is recorded as the mixed pressure P. s+c(i) , i = 0, 1, ..., N; Step 6, Calculate the compensation pressure value Test point t i The compensation pressure value is denoted as δ. (i) For i = 0, 1, ..., N, the calculation formula is: d (i) =P s+c(i) -P s(i) ; Step 7, plot the temperature-pressure curve. Test temperature T i The horizontal axis represents the reference pressure P. s(i) Fit a T-axis to the ordinate in a planar coordinate system and plot it. i -P s(i) Curve, to test temperature T i The horizontal axis represents the mixing pressure P. s+c(i) Fit a T-axis to the ordinate in a planar coordinate system and plot it. i -P s+c(i) Curve; based on test temperature T i The horizontal axis represents the compensation pressure value δ. (i) Plot a T-axis in a plane coordinate system for the ordinate. i -δ (i) curve.

2. The method for testing the low-temperature compensation of an SF6 / CF4 density relay according to claim 1, characterized in that, The automatic calibration device for the full-temperature SF6 gas density relay includes an industrial control computer, a temperature control system, a detection system, a fully enclosed SF6 gas pressure regulation system, a vacuum system, and a feedback system. It can autonomously adjust and maintain the test temperature and perform pressure testing.

3. The method for testing the low-temperature compensation of an SF6 / CF4 density relay according to claim 1, characterized in that, During the baseline pressure test described in step 3 and the mixed pressure test described in step 5, the holding time for all test temperatures shall not be less than 2 hours, and the data shall be read only after the pressure value displayed by the full-temperature SF6 gas density relay automatic calibration device has stabilized.

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