Image: Transformer & Power Lines
Our laboratory can provide a comprehensive service for the analysis of all types of transformer oils.
MINERAL, SILICONE & MIDEL.
We supply sampling kits containing either 500ml, 250ml, 100ml or 60ml bottles depending on your test requirements.
It is recommended to perform routine tests at least once a year in order to monitor the health of your transformers. Faults can occur at any stage of your transformer’s life and evolve rapidly. Testing your transformers on a regular basis will allow you to detect any unforeseen change in the condition of your transformers.
ROUTINE Test: Colour, Appearance, Odour, Sludge, Sediment, Specific Gravity,Viscosity,Flash Point, Breakdown Voltage, Water Content & Acid Value
Insulation fluids are used primarily due to their high dielectric strength, chemical stability and heat transfer properties. When thermal or electrical faults arise, fluid and insulating material can breakdown. Breakdown gases include hydrogen, methane, ethane, 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.
A fairly straighforward and 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.
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.
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 more than 50 ppm by weight is classified as dangerous and must be disposed of by registered waste contractors normally by incineration. The current standard is for suppliers not to supply oil containing more than 10ppm. Our service quantifies the main types of PCB 1260 (most common) 1254 & 1242 and reports each of these individually in ppm.
If fibres are present this can lead to poor electric strength as the fibres are drawn into the electrical field causing arcing.Fibres can become 'free' from the insulating material around windings and from external contamination. 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.
The water content of an oil sample is measured using a Karl Fischer titrator and given in parts per million (ppm). As a guide 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.
When 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. The paper becomes brittle when the DP falls and this indicates removing the transformer from use for repair or replacement. This test can be used to estimate the remaining service life of the transformer.
High acidity increases the rate of breakdown of insulating paper which in turn can corrode the transformer steel tank. Ideally the transformer oil should be changed when acidity approaches 0.3mgKOH/g, although dependant on working conditions and application this may be changed earlier.
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