IEC IEEE 62582-4-2011 pdf download.Nuclear power plants – Instrumentation and control important to safety – Electrical equipment condition monitoring methods – Part 4: Oxidation induction techniques.
4 General description Oxidation induction methods are based on the detection of the oxidation exotherm that occurs when a sample is heated in the presence of oxygen. This exotherm is sensitive to the level of degradation in some organic and polymeric materials and can be used as an indicator of ageing. There are two oxidation induction methods available, based on the time required to reach the onset of oxidation at a constant temperature (oxidation induction time – OIT) or based on the temperature at the onset of oxidation during a constant temperature ramp rate (oxidation induction temperature – OITP). The two methods are complementary, in that OITP is often effective in those materials where OIT is difficult to determine. OIT and OITP decrease with increasing degradation. The methods are related to the amount of antioxidants present in the material. As degradation proceeds, these antioxidants are depleted.
5 Applicability and reproducibility The oxidation induction method is primarily suited to samples taken from materials (such as cable jackets or insulation) that are polyolefin-based (e.g. polyethylene PE, cross-linked polyethylene XLPE). It can also be used for some materials based on ethylene-propylene polymers (e.g. ethylene propylene rubber EPR, ethylene propylene diene EPDM) and for some ethylene vinyl acetate EVA materials. It is not applicable to high temperature polymers, such as poly ether ether ketone (PEEK). The method is generally not suitable for chlorinated polymers (e.g. polyvinyl chloride PVC, chlorosulphonated polyethylene CSPE) because of the corrosive degradation products evolved during the measurements, which can damage the instrument. For these materials, smaller sample masses (1 mg to 2 mg) may enable the method to be used with care. The method is not suitable for field use in the nuclear power plant but uses samples taken from the plant, which are then measured in the laboratory. Each OIT measurement in the laboratory can take up to 90 min to complete for unaged samples, decreasing for heavily aged samples, whereas OITP measurements typically take 30 min to 40 min. Measurements of OIT typically have a standard deviation of 5 % to 1 0 % of the mean value whereas measurements of OITP typically have a standard deviation of 1 % to 3 % of the mean value, both within the same laboratory and between different laboratories. Some of this variation arises from inhomogeneity of the sample materials, which becomes significant when making condition measurements on samples whose mass is very low. OITP measurements are usually more reproducible than OIT measurements but require baseline data for interpretation of the changes.
6 Measurement procedure
6.1 Stabilisation of the polymeric materials An appropriate time period shall be allowed for the polymeric materials in recently manufactured equipments to stabilise before any condition monitoring or accelerated ageing programmes are carried out. The time period over which the polymeric materials stabilise is normally dependent on the processing additives and polymer composition. If manufacturers’ stabilisation time data are not available, a period of 6 months shall be allowed.IEC IEEE 62582-4 pdf download.