GB/T 17623-2026Determination of the component contents of gases dissolved in insulating oil by gas chromatography (English PDF)

7.1 Oil-gas separation unit

7.1.1 Thermostatic Timer Oscillator The reciprocating oscillation frequency is 275 times/min ± 5 times/min, the amplitude is 35mm ± 3mm, the temperature control accuracy is ± 0.3°C, and the timing is precise. The temperature is ±2 min, and it is equipped with a fixing clip inside to hold a 100 mL glass syringe.

7.1.2 Vacuum Degassing Device The degassing efficiency should be no less than 90%, and the average annual change in degassing efficiency should be no more than 5%.

7.1.3 Automatic Headspace Sampler It possesses mechanical oscillation, temperature control, pressure regulation, and automatic quantitative injection functions, and should allow each dissolved gas component to react within a certain time. The two phases reach equilibrium.

Note. One of the above-mentioned oil-gas separation devices can be used during the test.

7.2 Gas Chromatograph It should include a gas path system, an injection system, a temperature control system, a chromatographic column, a detector, and recording and data processing devices. The detector should be equipped with thermal conductivity... Detectors (for measuring hydrogen, oxygen, and nitrogen), flame ionization detectors (for measuring hydrocarbons, carbon monoxide, and carbon dioxide), and nickel-catalyst conversion detectors. The device (converting carbon monoxide and carbon dioxide into methane), or equipped with a helium ionization detector. The nickel-catalyst converter in the gas path system... The optimal temperature is 350°C~360°C. The resolution of adjacent components detected by the chromatographic column should meet the requirements for quantitative analysis. Gas chromatography detection... The sensitivity should meet the minimum detection concentration requirements for each component in the oil as specified in this document. The commonly used gas path flow and chromatographic column for gas chromatographs are shown in Appendix A.

7.3 Stainless steel injection needles Dental No. 5 needle. 40mm in length. 18G No.1 needle.

7.4 Double-ended needle (for mechanical oscillation method) The double-ended needle is shown in Figure 1 and can be made using a No. 5 dental needle. Figure

8.2 Scale calibration of glass syringes At room temperature, calibrate the

40.0 mL mark on a 100 mL glass syringe by gravimetric method and mark the position.

8.3 Headspace vial calibration At room temperature, the

15.0 mL mark on the headspace vial was calibrated by gravimetric method and the position was marked, and the full-scale mark was calibrated.

8.4 Degassing device

8.4.1 Thermostatic Timer Oscillator Set the temperature and time of the constant temperature timer oscillator, and heat it to 50°C for standby.

8.4.2 Vacuum Degassing Device The degassing rate of the vacuum degassing device shall be measured monthly, and the test method is given in Appendix B.

8.4.3 Automated Headspace Sampler Set up the automatic headspace sampler according to the typical conditions in Table 2 and start it up for standby.

8.5 Gas Chromatograph Connect the gas source, turn on the chromatograph, and operate it according to the instrument manual to bring it into a stable standby state.

9.1.1 Mechanical Oscillation Method (Artificial Headspace Extraction)

9.1.1.1 Prepare the gas-storage glass syringe. Take a 5mL glass syringe A, check that the plunger is flexible and not stuck, then draw a small amount of test oil to flush the syringe. Brush the syringe barrel twice, then draw in approximately

0.5 mL of test oil. Replace the rubber cap, insert the double-ended needle with the needle pointing vertically upwards. Pour the contents of the syringe into the syringe... The air and test oil are slowly expelled, allowing the test oil to fill the gaps in the inner wall of the syringe.

9.1.1.2 Adjusting the oil sample volume. Push out a portion of the oil sample from 100mL glass syringe B, and accurately adjust the syringe plunger to the 40.0mL mark. (V1) Immediately attach the rubber cap to seal the syringe tip. When attaching the rubber cap, fill the recess with a test oil or first flatten the cap with your finger. Expel air from the concave part of the cap to prevent air bubbles from entering the oil sample syringe B.

9.1.1.3 Adding Balanced Gas. Take a 5mL glass syringe C, connect it to a dental 5-gauge needle, rinse twice with balanced gas, and then draw approximately 5.0mL of balanced gas. To balance the gas flow, slowly inject the gas from syringe C into syringe B, after adjusting the test oil volume. The gas injection rate should be such that the air bubbles at the needle tip in the oil are just barely visible. Continuous operation is recommended; see Figure 3 for operation instructions. For oil tests with low gas content, the volume of injected equilibrium gas can be appropriately increased, but the volume of the gas phase after equilibrium should be... The volume should not exceed 5 mL. Nitrogen is generally used as the balance gas in analysis; however, if nitrogen components need to be measured, argon should be used instead. Figure

9.1.2 Automatic Headspace Extraction

9.1.2.1 Headspace vial preparation. Seal the headspace vial with a perforated aluminum cap and PTFE gasket using a capping device. Insert two 18G1 needles into the headspace vial. At different points along the edge of the empty bottle septum, one is for gas inlet and the other for gas venting. The gas inlet needle should be close to the bottom of the bottle. Use nitrogen (or argon) gas at a flow rate of 2 L/min. Purge the headspace vial with carrier gas for at least 1 minute, then first pull out the vent needle, and then quickly pull out the inlet needle to obtain a well-sealed headspace filled with carrier gas. Bottle E.

9.1.2.2 Injecting the test oil. After attaching an 18G1 needle to a 100mL glass syringe B, push out a portion of the oil sample and adjust the syringe plunger to a position greater than [the specified value]. At the 20mL mark, quickly insert syringe B into headspace vial E from the edge of the headspace vial septum, bringing the needle close to the bottom of the vial. Insert a venting needle into the upper part of the syringe, and accurately inject

15.0 mL of test oil into the headspace vial using syringe B. Immediately remove the venting needle and syringe B. Place headspace vial E in the headspace sampler and process it automatically according to the conditions in Table 2.

9.1.3 Vacuum Degassing Method

9.1.3.1 Prepare syringe A according to 9.1.1.1, and connect it to the gas collection port of the vacuum gas sampling device, which has an automatic sample injection function. This step is not required.

9.1.3.2 The 100mL test oil glass syringe B is connected to the oil filling port of the vacuum gas extraction device and should be sealed to prevent air from entering.

9.1.3.3 The gas extraction process shall be carried out in accordance with the instruction manual of the device used.

9.1.3.4 After gas sampling is completed, record the volume of gas in syringe A, accurate to

0.1 mL. Vacuum gas sampling device with automatic sample introduction function. This step is omitted.

9.1.3.5 Drain all residual oil.

Note. The gas extraction procedure uses one of the methods described above. The principle of gas extraction is explained in Appendix C.

9.2 Sample Analysis

9.2.1 Instrument Calibration Open the valve of the standard mixed gas cylinder, purge the residual gas in the pressure reducing valve, take 1mL of glass syringe D, and flush with the standard mixed gas. After at least three cycles, accurately inject

0.5 mL (or 1 mL) of the standard gas mixture for calibration. If using an automated headspace sampler, follow section 9.1.2.1. The procedure is as follows: After purging with a standard mixed gas at a flow rate of 2 L/min for 1 minute, first pull out the inlet needle, then quickly pull out the vent needle. The headspace vial was placed in the headspace sampler and calibrated according to the conditions in Table 1 (the oscillation equilibration time can be shortened to 5 min). The obtained color... Calculate the peak area Ais (or peak height his) of each component on the spectrum. Instrument calibration should be performed under stable and identical operating conditions. The repeatability of two consecutive calibrations should be within their average value. Within ±1.5%. The instrument should be calibrated before each test. The operation should be repeated at least twice, and the average value Ais (or peak height his) should be recorded.

Note. Automatic headspace testing can be performed using standard oil of the same volume and known concentration for calibration.

9.2.2 Sample Analysis Use a 1mL glass syringe D to sample the gas from syringe A (mechanical oscillation method), syringe A (vacuum gas sampling method), or gas relay. Accurately extract the same volume of sample gas as the standard gas mixture used for calibration, and inject it for analysis. Automatic headspace sampling directly and automatically retrieves headspace vials. In the equilibrium gas analysis, calculate the peak area Ai (or peak height hi) of each component from the obtained chromatogram. Repeat the degassing and injection process once, and collect the results. Average value Ai (or hi). Sample analysis should use the same syringe as instrument calibration, and the same injection volume should be taken.

Note. For instrument calibration and sample analysis of vacuum sampling devices with automatic sample introduction function, please refer to Appendix D.

9.3.1 Headspace Extraction Method

9.3.1.1 Correction of gas and oil sample volumes using the mechanical vibration method The mechanical oscillation method corrects the gas sample volume Vg and test oil volume Vl at room temperature and test pressure according to equations (1) and (2), respectively. Volume at 50°C and test pressure.

9.3.1.2 Correction of Gas and Oil Sample Volumes in Automated Headspace Sampling The automatic headspace sampling method calculates the equilibrium test oil volume V'l and gas sample volume V'g at 50°C in the headspace vial according to formulas (3) and (4).