IEC 62535 pdf – Insulating liquids – Test method for detection of potentially corrosive sulphur in used and unused insulating oi
This International Standard specifies a test method for detection of potentially corrosivesulphur in used and unused mineral insulating oil.
Most recent failures due to corrosive sulphur are related to the formation of copper sulphidedeposits in and on the surface of winding cellulosic paper.
The test method uses a copper conductor,wrapped with one layer of paper,immersed in theoil and heated to evaluate the capability of the oil to yield copper sulphide and transfer it topaper layers.
The growth of copper sulphide on bare copper may cause the presence of conductiveparticulates in the oil, which can act as nuclei for electrical discharge and may lead to a fault.Other test methods exist using a bare copper strip immersed in oil and heated to detect thecorrosive behaviour of oil against copper. ASTM D1275 Method B is also used for this testand a modified procedure using low oil volumes is included in Annex A.
Tests with and without paper are considered as complementary and may lead to differentresults.
The following referenced documents are indispensable for the application of this document.For dated references,only the edition cited applies.For undated references, the latest editionof the referenced document (including any amendments) applies.
lEC 60475,Method of sampling liquid dielectrics
IEC 60554-3-1，Specification for cellulosic papers for electrical purposes – Part 3:Specifications for individual materials – Sheet 1: General purpose electrical paper
ASTM D1275，Methods A and B: Standard test method for corrosive sulfur in electricalinsulating oils
ASTM D130，Standard test method for corrosiveness to copper from petroleum products bycopper strip test
DIN 51353,Testing of insulating oils; detection of corrosive sulfur; silver strip test
EN 13601，Copper and copper alloys. Copper rod, bar and wire for general electricalpurposes
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
potentially corrosive sulphur
organo-suiphur compounds present in transformer oils that may cause copper sulphideformation.
NOTE Some of these compounds may be initially corrosive，or become corrosive under certain operatingconditions
Samples shall be taken，following the procedure given in lEC 60475. Ensure that the testportion is representative by thoroughly mixing.
A piece of copper conductor wrapped with Kraft paper is immersed in the oil and subjected toheating 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 thepresence of copper sulphide deposits.
5.2Apparatus 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 instrumentmanufacturers.
– 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 transformermanufacturer or winding supplier. Dimension of the flat copper: approximately 7,5 mm x1,5 mm (or with a surface area corresponding to these dimensions). Wrapping paper width10 mm to 14 mm.The most suitable have proven to be flat conductors having four layersof wrapped paper.The paper adjacent to copper should be wound gap to gap (the gapshould be in the tolerance 100 mm, the negative value means overlapping). This is thelayer used with the copper conductor for the test itself.The rest of the paper layers haveonly a mechanical and protective function during transport and storage.