IEC TR 62039-2021 pdf free download – Selection guidelines for polymeric materials for outdoor use under HV stress.
The minimum requirements are given in Table 1.
4.6volume resistivity
Volume resistivity measurements can show the presence of conductive contaminants ininsulation materials. This property can have some importance in the assessment of additivesthat are often used (e.g. fillers containing different levels of ionic impurities). The volumeresistivity parameter is also sensitive to incorrect curing processes of some resin systems.
The test method is in accordance with IEC 62631-3-1.The test method is applicable to core,housing and structural materials.
The minimum requirements are given in Table 1.
NOTE The applicability for coating materials is also under consideration by CIGRE.
4.7Breakdown field strength
The electrical breakdown strength is an important property of insulation materials and shouldbe verified for housing and structural materials. The breakdown strength of the core materialdoes not need to be measured separately because it is evaluated during the test that measuresthe resistance to chemical and physical degradation by water(see 3.4).
Sheet test samples are given in lEC 60243-1 for alternating current and lEC 60243-2 for directcurrent.
Insulating materials usually have high intrinsic electrical strength. In order to evaluate that, adifferent test arrangement is necessary.Such an arrangement is presented in lEC 60455-2 forrigid insulation materials (e.g. epoxy resin) and flexible insulation materials (e.g. siliconerubber). The different test arrangements in lEC 60243-1,IEC 60243-2 and lEC 60455-2 resultin different levels of the breakdown strength.
The minimum requirements are given in Table 1.
NOTE The applicability for coating materials is also under consideration by GIGRE.4.8Stress corrosion test (resistance to chemical attack)
4.8.1 General
Core materials can be susceptible to acid attack that can be associated with water penetration.When significant tensile mechanical loads are applied to the core simultaneously，stresscorrosion can occur.As a result, brittle fracture can occur.
lf a core material is to be evaluated regarding its acid resistance, for example a core materialused for outdoor insulators that are predominantly subjected to tensile stress, an acid resistancetest can apply.
The test is performed under ambient temperature to confirm the mechanical resistance of thecore material to stress corrosion.
4.8.2Test specimens
Three specimens prepared in accordance with the normal production process are selected.Thespecimens have a length of insulation between end fittings of at least 10 times the core diameter,and not less than 800 mm.Suitable end fittings are used.To avoid any latent damage to thecore by the difficult removal of the housing it is permissible to prepare bare rod samples for thistest.
4.8.3Procedure
The visible core surface should be smoothed by means of a fine abrasive cloth (grain size 180).Anon-transparent acid container should be placed to surround the visible core surface and besealed at the base to prevent any leaking acid.The size of the acid container should ensurethat the core material is surrounded by the liquid radius of not less than 1 cm and along a lengthof not less than 4 cm.Following the filling of the container with the acid, it should be coveredand/or sealed to prevent evaporation of the acid by more than 5 % of its volume during the testperiod.
The specimen is subjected to a tensile load applied between the metal fittings. The tensile loadis increased rapidly but smoothly from zero to the full load.The full load for unidirectional glassfibre composites should be 340 MPa (for other materials different mechanical loads can be used)and maintained for 96 h. Immediately after applying the load, nitric acid of a concentration of1N (N = normal) is poured into the acid container(1 N = 63 g HNO3 plus 937 g H,0).Bothhorizontal and vertical set-up positions of the specimen are acceptable.
Figure 4 shows an example of a vertical test set-up.IEC TR 62039 pdf download.