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
General description
Oxidation induction methods are based on the detection of the oxidation exotherm that occurswhen a sample is heated in the presence of oxygen. This exotherm is sensitive to the level ofdegradation in some organic and polymeric materials and can be used as an indicator otageing. There are two oxidation induction methods available, based on the time required toreach the onset of oxidation at a constant temperature (oxidation induction time – OIT) orbased 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 OITPis often effective in those materials where OlT is difficult to determine. OIT and OITPdecrease with increasing degradation. The methods are related to the amount of antioxidantspresent 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 ascable jackets or insulation) that are polyolefin-based (e.g. polyethylene PE, cross-linkedpolyethylene XLPE) lt can also be used for some materials based on ethylene-propylenepolymers (e.g. ethylene propylene rubber EPR, ethylene propylene diene EPDM) and foisome ethylene vinyl acetate EVA materials. lt is not applicable to high temperature polymerssuch as poly ether ether ketone (PEEK).
The method is generally not suitable for chlorinated polymers (e.g. polyvinyl chloride PVCchlorosulphonated polyethylene CSPE) because of the corrosive degradation productsevolved during the measurements, which can damage the instrument. For these materialssmaller 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 takenfrom the plant, which are then measured in the laboratory. Each OlT measurement in thelaboratory can take up to 90 min to complete for unaged samples, decreasing for heavily agedsamples, whereas OlTP measurements typically take 30 min to 40 min
Measurements of OlT typically have a standard deviation of 5 % to 10 % of the mean valuewhereas measurements of OITP typically have a standard deviation of 1 % to 3 % of the meanvalue, both within the same laboratory and between different laboratories. Some of thisvariation arises from inhomogeneity of the sample materials, which becomes significant whenmaking condition measurements on samples whose mass is very low. OITP measurementsare usually more reproducible than OlT measurements but require baseline data forinterpretation of the changes.
6Measurement procedure
6.1Stabilisation of the polymeric materials
An appropriate time period shall be allowed for the polymeric materials in recentlymanufactured equipments to stabilise before any condition monitoring or accelerated ageing
IEC IEEE 62582-4-2011 pdf download
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