IEC 62535 Insulating liquids - Test method for detection of potentially corrosive sulphur in used and unused insulating oil
Samples shall be taken, following the procedure given in IEC 60475. Ensure that the test portion is representative by thoroughly mixing.
A piece of copper conductor wrapped with Kraft paper is immersed in the oil and subjected to heating for 72 h at 150 °C in a sealed glass headspace vial.
The copper is examined for indications of discolouration and the paper is examined for the presence of copper sulphide deposits.
5.2 Apparatus and materials
The following apparatus and materials shall be used:
- Glass headspace vial as used for chromatography, capacity approximately 20 ml, with a nominal diameter of 22,5 mm to 23 mm.
NOTE 1 Vials are commonly available from suppliers of chromatography consumables and from instrument manufacturers.
- PTFE-faced silicone septum and aluminium cap for sealing the vial.
- Crimping tool.
- Heating chamber or oven capable of being maintained at 150 °C +/- 2 °C.
- Flat, unvarnished, paper-wrapped copper conductor obtained from a transformer manufacturer or winding supplier. Dimension of the flat copper: approximately 7,5 mm x 1,5 mm (or with a surface area corresponding to these dimensions). Wrapping paper width 1 0 mm to 1 4 mm. The most suitable have proven to be flat conductors having four layers of wrapped paper. The paper adjacent to copper should be wound gap to gap (the gap should be in the tolerance +100/-0.2 mm, the negative value means overlapping). This is the layer used with the copper conductor for the test itself. The rest of the paper layers have only a mechanical and protective function during transport and storage.
NOTE 2 Possible sources of supply are:
- Asta Elektrodraht GmbH & Co. (Austria)
- Essex Nexans L+K GmbH, (Germany)
- Siemens AG, Trafowerk Nuremberg (Germany).
- Kraft paper according to IEC 60554-3-1:
- Density: 0,70 to 0,85 g/cm3
- Thickness: 0,060 mm to 0,100 mm
- Air permeability M or H
- Conductivity: < 4 mS/m
- Free nitrogen content: 0 %
- Cu-ETP according to EN 13601, (old material code: E-Cu58):
- Material code: CW 004A
- Oxygen content: < 0,04 % (w/w)
- Cu: 99,90 %
- Solvent for rinsing:
- Cyclohexane or heptane, analytical grade.
Pour 50 ml of oil into a beaker of 1 00 ml and leave in the open air for 60 min (protected from sunlight).
Transfer 15 ml of this oil into the headspace vial. The precision given by a measuring cylinder is adequate, as is use of a headspace vial pre-marked at 15 ml.
Cut the conductor in 30 mm +/- 3 mm lengths. Unwrap the outer layers of the copper conductor and leave only one layer in contact with the copper. Do not touch paper or copper with fingers during this and subsequent operations and ensure that all tools are pre-cleaned with solvent.
Place the wrapped flat conductor inside the headspace vial and close it with the septum (PTFE face towards the oil) and close the cap using a crimping tool. The crimped cap should be sufficiently tight such that hand rotating of the cap on the vial is not possible.
NOTE It is essential that, if a butyl rubber septum is used, the PTFE face seals correctly to the glass vial. The hot oil must have no access to the butyl rubber, which contains sulphur.
Place in a heating chamber for 72 h +/- 30 min at 150 °C +/- 2 °C.
After the vial has cooled, remove the cap and take out the wrapped conductor. Tweezers should always used to handle the conductor and the paper.
Unwrap the paper for evaluation of the copper surface.
Rinse the copper conductor with cyclohexane or heptane, and allow to dry for 2 min in air.
Prior to evaluation, degrease the paper by immersion in 50 ml of solvent in a beaker for 1 min. Repeat the degreasing twice in fresh solvent and allow the paper to dry for at least 5 min until all solvent is evaporated.
Carry out the test in duplicate.
Carry out a blank test, in order to ensure that all materials used are sulphur free. The blank test should be carried out with a white oil or other oil containing less than 5 mg/kg sulphur. Such a test will also assist in detecting changes to the copper.