DL/T 1985-2019Determination of mining ratio of SF6 gas mixture (English PDF)

4.2 Laboratory analysis and sampling

Follow the relevant regulations in DL/T 1032.

5.1 Sensor method

5.1.1 Method summary

Use thermal conductivity or infrared sensor to detect the difference in thermal conductivity or infrared absorption characteristics between SF6 and another gas the mixing ratio of the mixed gas; at the same time, an electrochemical sensor is used to detect the O2 content in the gas. The detection process is shown in Figure 1.

5.1.2 Instrument requirements

5.1.3 Environmental conditions

a) Temperature. -10°C ~ 40°C;

b) Humidity. <=85%RH.

5.1.4 Test steps

Operate as follows.

a) Turn on the power of the instrument and perform the corresponding settings according to the instructions after the instrument has been warmed up;

b) Confirm that the air inlet valve of the instrument is in the closed state, connect the air inlet of the air source and the sampling port of the instrument, and connect the exhaust gas collection device Connect to the exhaust port of the instrument;

c) During measurement, keep the oxygen sensor protection valve in a closed state, slowly open the gas flow regulating valve, and open the side Valve, flush the pipeline for 3 min~5 min, then adjust the gas flow to the setting range and open the protection valve to start After the test data is stable, record the SF6 and O2 test results;

d) After the measurement is completed, the instrument should be purged with dry nitrogen for 3 min~5 min, first close the oxygen sensor protection valve, and then Turn off the instrument;

e) Recycle the gas in the exhaust gas collection device.

5.1.5 Test results

Take the arithmetic mean of two parallel determination results as the test result, and the test result is expressed in volume fraction.

5.1.6 Precision

The absolute deviation of the two test results is SF6<=1%, O2<=0.1%.

5.2 Gas chromatography

5.2.1 Method summary

The chromatographic column is used to separate SF6, CF4, N2, O2 and other components, and the gas of each component is entered through a thermal conductivity detector (TCD).

Line testing. The test result is expressed in volume fraction.

5.2.2 Apparatus and materials

a) Gas chromatograph. It should be equipped with a TCD detector, which can detect SF6, CF4, N2, O2 and other components, and can be used Data analysis is carried out by external standard method and calibration standardization method. See Table 1 for typical gas path flow.

5.2.3 Environmental conditions

a) Temperature. -10°C ~ 40°C;

b) Humidity. <=85%RH.

5.2.4 Detection steps

Operate as follows.

a) Set the working parameters of the chromatograph according to the requirements of the instrument, and wait until the instrument is stable for use;

b) Use external standard method to quantitatively calibrate the chromatograph. The calibration working conditions of the instrument should be the same as the detection conditions.

The specified repeatability should not be greater than ±3%;

c) Connect the gas inlet of the gas source to be tested and the sampling port of the chromatograph, and control the flow of the gas to be tested according to the conditions of use of the chromatograph Flush the sampling pipeline and the loop for no less than 3 minutes, close the sampling port of the chromatograph, switch the loop valve, and quickly Sample injection

d) Record the peak area (or peak height) of each component and analyze the data;

e) After the test is completed, turn off the chromatograph according to the instrument operation procedure, and turn off the power and all gas sources.

5.2.5 Sample chromatogram

Typical chromatograms are shown in Figure 2 and Figure 3.

5.2.6.2 Calculating gas mixture ratio by external standard method

According to the peak area (or peak height) of each component, calculate the SF6, CF4, N2, O2 in the mixed gas according to formula (3) Etc. content

5.2.7 Precision

The absolute deviation of the two test results is SF6, N2, CF4<=0.5%, O2<=0.05%.