SH/T 0206-1992 Determination of oxidation stability of transformer oil

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: SH/T 0206-92
• Chinese name: Determination of oxidation stability of transformer oil
• English name: not provided in the available source
• Replacement relationship: replaces ZB E38 003-88
• Reference adoption: International Electrotechnical Commission standard IEC 74-1963(1974) "Method for evaluating the oxidation stability of insulating oils" (the source writes "EEC 74-1963(1974)", suspected to be an error for IEC, requires confirmation against the source standard (source-text extraction))
• First issued: 1966 year
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20

2. Scope of application and non-applicability

• This standard specifies a method for determining the oxidation stability of transformer oil.
• This standard applies to transformer oil.
• Not applicable: not provided in the available source.

3. Method principle

In the presence of a copper catalyst, place a 25 g sample in an oil bath at a certain temperature, introduce oxygen, and after continuous oxidation for 164 h, determine the mass of sediment formed and the acid value, and use the sediment content and acid value to express the oxidation stability of the oil.

4. Reagents and materials (purity / preparation)

4.1 Materials

• Mineral oil: flash point (open cup) not lower than 200℃, for use in the oil bath.
• Sandpaper: grit 240.
• Quantitative filter paper: medium speed.
• Oxygen: industrial grade, purity not less than 99.2%.
• Type NaX (13X) molecular sieve or 30–60 mesh silica gel, used for dearomatization of petroleum ether.

4.2 Reagents

• Petroleum ether: 60–90℃, free of aromatics, analytical reagent.
• Benzene: analytical reagent.
• 95% ethanol: analytical reagent.
• Ethanol-benzene mixed liquid: prepared from 95% ethanol and benzene in a volume ratio of 1:4.
• Potassium hydroxide: analytical reagent, prepared as a c(KOH)=0.05 mol/L potassium hydroxide-ethanol standard titration solution.
• Formaldehyde solution: chemical reagent.
• Sulfuric acid: analytical reagent.
• Alkaline blue 6B: prepared as an approximately 20 g/L ethanol indicator solution.
• Chromic acid cleaning solution.

5. Apparatus and equipment

• Oxidation tube: its dimensions and shape are shown in the figure below (the source includes an "oxidation tube figure", with the dimension marked source-text extraction as "outer diagnosis 5 plus or minus 0.4", requires confirmation against the source standard (source-text extraction)).
• Catalyst: copper wire, conforming to the Cu1 specification in GB 466, diameter 1.00–1.02 mm, length 30.5 cm±0.1 cm.
• Oil bath: equipped with electric heating equipment and a stirring device, capable of maintaining constant temperature at 100℃±0.5℃ and 110℃±0.5℃, and automatically controlled; two-thirds of the oxidation tube should be immersed in the oil bath.
• Thermometer: 0–150℃, scale division 0.5℃.
• Oxygen flow meter: 1 L/h±0.1 L/h.
• Oxygen flow control device.
• Microburette: 2 mL, graduation 0.02 mL.
• Graduated cylinder: 50 mL.
• Stoppered conical flask: 300 mL.
• Conical flask: 100, 250 mL.
• Water bath.
• Wash bottle: 250 or 500 mL.
• Volumetric flask or stoppered graduated cylinder: 500 mL.
• Funnel: diameter 60 mm.
• Drying tower: use a gas drying tower with a capacity of 250 mL, filled inside with a solid desiccant of high hygroscopic capacity to a height of 20–25 cm.
• Oxygen cylinder: with oxygen pressure reducing device.

6. Recommended operating conditions

• Oxidation temperature: 100℃±0.5℃ when the sample contains no antioxidant additive; 110℃±0.5℃ when the sample contains antioxidant additive.
• Oxygen flow rate: 17 mL/min±0.1 mL/min.
• Oxidation time: continuous oxidation for 164 h.
• Oxygen purity: not less than 99.2%.
• After the oxygen is purified through the drying tower, it passes through the oxygen flow control system to ensure a stable oxygen flow rate.

7. Sampling and sample preparation

• In a clean, dry oxidation tube, weigh a filtered sample of 25 g±0.1 g (the source source-text extraction is "25g plus or minus . bake", requires confirmation against the source standard (source-text extraction)).
• After placing the copper spiral wire, immediately insert the oxygen delivery tube.

8. Analytical procedure

8.1 Preparation of the oxidation tube

First wash successively with ethanol-benzene mixed liquid, 95% ethanol, water, and hot chromic acid cleaning solution, then wash several times with water, finally wash with distilled water, and dry in an oven for later use.

8.2 Preparation of the copper catalyst

Polish a copper wire of 30.5 cm±0.1 cm length with 240 grit sandpaper, then wipe clean with cloth or filter paper, roll into a spiral (outer diameter 19 mm±1 mm, length 50 mm), and immediately place in a desiccator for later use. Before use, wash the copper spiral twice with benzene, then blow dry with an electric hair dryer, and immediately place in a desiccator to cool. When using, hold with tongs and immediately place into the oxidation tube with the weighed sample.

8.3 Preparation of oxygen

After the oxygen is purified through the drying tower, it passes through the oxygen flow control system to ensure a stable oxygen flow rate.

8.4 Oxidation of the sample

In a clean, dry oxidation tube, weigh a filtered sample of 25 g±0.1 g, place the copper spiral wire, and immediately insert the oxygen delivery tube. If the sample contains no antioxidant additive, place the oxidation tube into an oil bath already heated to 100℃±0.5℃. If the sample contains antioxidant additive, place the oxidation tube into an oil bath already heated to 110℃±0.5℃. Then, connect the flow meter to the oxygen delivery tube with a rubber tube, and quickly adjust the flow rate to 17 mL/min±0.1 mL/min, and record the start time. The sample is continuously oxidized for 164 h under strictly controlled conditions.

8.5 Post-oxidation handling

After oxidation is completed, cut off the oxygen, remove the oxidation tube from the oil bath, and cool in a clean, dry dark place for 1 h. Then, pour all the oxidized oil into a stoppered conical flask, draining as completely as possible. Wash the oxidation tube, oxygen delivery tube, and copper spiral with petroleum ether until no oil traces remain, and retain them for sediment determination. Combine the petroleum ether washings into the same stoppered conical flask; the petroleum ether used for washing is about 200 mL, and let stand in a dark place at room temperature for 24 h.

8.6 Determination of sediment content

8.6.1 Tube wall sediment

Dissolve the sediment on the oxidation tube, oxygen delivery tube, and copper spiral that have been washed until free of oil traces with warm ethanol-benzene mixed liquid, and place the sediment solution into a pre-weighed 100 mL conical flask. Evaporate the ethanol-benzene mixed liquid in the conical flask on a water bath, then place in a 105℃±3℃ oven and dry to constant weight, that is, the difference between two consecutive weighings does not exceed 0.0004 g.

8.6.2 Oil-soluble sediment

After standing for 24 h, filter the mixture of oxidized oil and petroleum ether through a glass funnel with filter paper into a 500 mL stoppered graduated cylinder, and wash the stoppered conical flask containing the settled mixture and the sediment on the filter paper with petroleum ether until the filter paper is free of oil traces. Combine the filtrate into the 500 mL stoppered graduated cylinder and dilute to the mark for acid value determination. Dissolve the sediment in the stoppered conical flask containing the settled mixture and on the filter paper with warm ethanol-benzene mixed liquid, and dissolve the sediment in a pre-weighed 100 mL conical flask. Evaporate the ethanol-benzene mixed liquid in the conical flask on a water bath, then place in a 105℃±3℃ oven and dry to constant weight, that is, the difference between two consecutive weighings does not exceed 0.0004 g.

8.7 Determination of acid value

After shaking uniformly the mixture of oxidized oil and petroleum ether contained in the 500 mL stoppered graduated cylinder, measure 50 mL and pour into a 250 mL conical flask, then add ethanol-benzene mixed liquid 50 mL and alkaline blue 6B indicator solution 0.5 mL, and titrate with potassium hydroxide-ethanol standard titration solution (5.5) until the color of the mixed liquid changes abruptly. Take petroleum ether 50 mL and ethanol-benzene mixed liquid 50 mL, and carry out a blank determination by the same procedure as above.

8.8 Parallel determination

When determining the post-oxidation sediment content and acid value of each sample, use the oxidation products from two oxidation tubes for parallel determination.

9. Qualitative and quantitative determination and calculation formulas

9.1 Post-oxidation sediment content X [%(m/m)] is calculated according to formula (1) and formula (2):

X = m3 / m × 100 ......(1) m3 = m1 + m2 ......(2) Where:

• m3—— mass of sediment after oxidation, g;
• m—— mass of the sample, g;
• m1—— mass of tube wall sediment, g;
• m2—— mass of oil-soluble sediment, g.

9.2 Post-oxidation acid value A(mgKOH/g) is calculated according to formula (3):

A = (V − V1) × 0.0561 × c × n / m × 10³ ......(3) Where:

• c—— actual concentration of potassium hydroxide-ethanol standard titration solution, mol/L;
• V—— volume of potassium hydroxide-ethanol standard titration solution consumed during titration, mL;
• V1—— volume of potassium hydroxide-ethanol standard titration solution consumed during blank titration, mL;
• 0.0561—— mass, expressed in grams, of acid (expressed as potassium hydroxide) equivalent to 1.00 mL potassium hydroxide-ethanol standard titration solution [c(KOH)=1.000 mol/L];
• n—— volume ratio of the entire oxidized oil and petroleum ether mixed liquid to the solution used for titration;
• m—— mass of the sample, g.

10. Precision

10.1 Repeatability

10.1.1 Post-oxidation sediment mass

The difference between two results of repeated determination by the same operator and their arithmetic mean shall not exceed the following values:

(Note: The table interval symbols are garbled in the source transcription. Their displayed interpretation is provisional; verify the interval limits and comparison signs against the original before use.)

10.1.2 Acid value after oxidation

The difference between two results obtained by repeated determination by the same operator shall not be greater than 40% of their arithmetic mean.

11. Report

The arithmetic mean of two repeated determination results shall be taken as the determination result for both the sediment content after oxidation and the acid value.

12. Referenced documents

• GB 466 Classification of copper (Editor's note: the current standard number is GB/T 466-82, and the current standard name is "Classification of copper")

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick reference for questions and answers