What test items (projects) are included in the simplified test of insulating oil, and what methods are used for each?

   Answer: The so-called simplified test of insulating oil is relative to the full analysis test, and its test items are relatively simplified.It generally includes three items: flash point, water-soluble acid, and interfacial tension. The methods for each are as follows.

   (1) Flash point. Generally, the closed cup method is used to test the flash point. If the flash point is very low, it may be mixed with fuel oil. If the flash point of transformer oil in operation is low, it may be due to local overheating faults in electrical equipment, causing the transformer oil to crack at high temperatures and produce volatile flammable substances. Transformer oil with unqualified flash point must not be used in electrical equipment, otherwise it will be very dangerous when the equipment heats up or arcs during current interruption.

   (2) Water-soluble acid. Generally, the colorimetric method is used, expressed as pH value. New oil is required to be neutral, with a pH value of 6.0~7.0. Acidic oil can easily corrode electrical materials and precipitate sludge and other sediments that adhere to conductors, hindering heat dissipation. The pH value of insulating oil in operation can be slightly lower, but should be above 5.4.

   (3) Interfacial tension. Generally, the ring method is used. This is an indicator for checking hydrophilic polar substances and sludge products in oil. The presence of these substances will promote the oxidation of the oil itself during operation, so by measuring interfacial tension, the degree of oil aging and contamination can be judged.