DETAILED TRANSFORMER OIL TESTING AVAILABLE
Keeping your transformer oil in excellent condition is vital to the efficient running of your equipment. In addition to our standard test, we are able to offer more detailed analysis on transformer oils.
To receive a report containing this additional analysis, order part number "TAO001" for level 2 analysis from our lab.
The tests include;
Dissolved Gas Analysis (DGA)
This is the best test to detect faults in tap selector units early in the process. Oils and silicones insulation fluids are used primarily due to their high dielectric strength, chemical stability and heat transfer properties. Normally virtually no breakdown of the dielectric fluid occurs, but when thermal or electrical faults arise, fluid and insulating material can breakdown. Breakdown gases include hydrogen, methane, ethane, acetylene, carbon monoxide and carbon dioxide, and these can all dissolve in the dielectric fluid. Quantifying and interpreting the levels of each of these enables you to identify the root cause of problems such as sparking, arcing and overheating.
High acidity increases the rate of breakdown of insulating paper which in turn can corrode the steel tanks. Oil should be changed when acidity approaches 0.3mgKOH/g, but maybe changed earlier in some applications or conditions.
A simple test designed to measure the ability of a fluid not to fail when under high voltage; the higher the dielectric strength, the better the insulator.
When fibres are present this can lead to poor electric strength as the fibres are drawn into the electrical field causing arcing. The problem becomes much more pronounced if these fibres are wet due to water in the oil as the moisture, in combination with fibre in main tanks and selectors, reduces the electric strength of the oil to very unsafe levels which can result in failure.
Polychlorinated Biphenyl Analysis
PCB's historically used in transformer applications can collect in food chains and as a result, legislation is strict to control their use. Any Liquids with 50+ ppm by weight is dangerous and must be disposed of by incineration. The current standard is for suppliers not to supply oil containing more than 10ppm. Our service quantifies the main types of PCB i.e. 1242, 1254 and 1260 and reports the total PCB ppm content.
The resistivity of oil is a measure of its electrical insulating properties. Oils of high resistivity will have a low content of free ions/particles and therefore a low concentration of conductive contaminants. This parameter is sensitive to soluble contaminants and degradation products.
The test is normally carried out at ambient temperature but useful additional information can be obtained if the test is carried out at different temperatures. Poor results at different temperatures indicate greater contamination.
Metal in Oil Analysis by ICP
ICP analysis of metal in Transformer oils is used to complement (DGA) data. When DGA results highlight a possible issue the ICP results help determine the cause of the fault type.
High energy faults can generate metal particles as well as breaking down the insulating material. Specific transformer components produce specific metal particles. These metals particles may be found alone or in differing combinations and concentrations; the type and ratio of metal particles can help identify the particular component at fault.
For example, copper (Cu) is found in windings, lead (Pb) is found in soldered joints and connectors. Iron (Fe) is in the core and tank, and aluminum (Al) can be found in windings, corona shields and bushings. Other components e.g. connectors may also contain tin (Sn), silver (Ag) and zinc (Zn).
As paper inside a transformer breaks down and weakens, furfuraldehyde is produced. There is a relationship between the furfuraldehyde present and the resulting degree of polymerization (DP) or paper strength. When DP falls, the paper becomes brittle and plans should be made for removing the transformer from use for repair or replacement. This relationship can be used to estimate the remaining service life of the transformer.
The water content of an oil sample is measured using a Karl Fischer titration and given in parts per million (ppm). For a 33kV transformer, the water content in the oil is normally considered to borderline fail when it reaches 25ppm and at fail point at 30ppm, though these limits vary depending upon oil sample type. This test should be carried out on an annual basis as an absolute minimum allowing a trend to be built and monitored and any remedial action to be taken before failure or damage arises.
Viscosity, ISO (Particle Count), Colour and Visual Appearance, S.G. (Specific Gravity) A.P.I. Gravity and a Microbiological/Bacteria check are also included in the transformer oil test.
Please contact us for more information.