IEC 60505:2011 pdf – Evaluation and qualification of electrical insulation systems.
Test objects that include several internal conducting component parts that will have electric stress applied between them, either during the ageing or the diagnostic subcycle, shall be designed and constructed to enable verification of the ageing effect.
6.1.2 Number of test objects
Where feasible, a minimum of five lest objects shall be aged for each of the electrical, thermal, mechanical, environmental or multifactor stress combinations Included in the evaluation programme.
NOTE As a minimum number of five Is required to reach the end-point cnlerion. to obtain stallsticahly agnilicanl r•aulti. it may be necessary to include ms than five samples in each aub-t•st
6.1.3 Quality assurance tests
Before starting the rirst ageing subcycle, a visual Inspection and all normal product quality assurance tests shall be carried out on all test objects.
6.1.4 Precondltioning subcycl.
If appropriate, test objects should be preconditioned to better represent the condition of the EIS in service.
6.1.5 Initial diagnostic tests
Each test object shall be subjected to the diagnostic tests selected for the evaluation procedure before starting the first ageing subcycle.
6.1.6 Reference EIS
A reference EIS shall be tested using the same test procedure as that used for the candidate EIS. in the same laboratory, using the same type of test equipment. The performance of the reference EIS shall have been established either by service experience under typical operatIng conditions, or by approprIate functional testing In the range of the reference operating conditions.
6.2 Test conditions
6.2.1 ContInuous and cyclic testing
Functional tests may be performed as a continuous ageing test if the end.point criterion is given as time to electrical or mechanical failure or breakdown, either at ageing stress level or caused by a continuously applied diagnostic stress. Alternatively, a fixed time test followed by either a breakdown or other diagnostic test can be appropriate.
More universally applicable are cyclic life tests composed of a repeated sequence of different ageing and diagnostic subcycles This sequence of functional tests permits the application of either single or multifactor ageing tests with a minimum of unintended interference between different ageing factors and mechanisms.
The seasonal and daily variations of the outdoor environment result, to a higher or lower degree depending on the level of protection, in corresponding cyclic variations of the environmental conditions at the location of the equipment insulation.
In the absence of complete encapsulation, the risk of periodic condensation ought always to be considered. The breathing caused by periodic temperature variations may cause a unidirectional motion of particulate contamination from the outside to the inside of equipment that is not hermetically enclosed.
When these effects are simulated in functional tests, acceleration may be obtained through reduction of the cycle duratiOn. A limitation is. however, given by the thermal inertia and diffusion constants of the test object and its parts.
6.2.2 Levels of test stresses, ageing factors and diagnostic factors
Test stress conditions shall consider the most severe overall stress conditions experienced In service for which the EIS Is designed. These conditions need not occur necessarily at the maximum values of the individual stresseS. The reference operating conditions shall be clearly defined for the evaluation procedure and the levels and types of diagnostic factors shall be pertinent to these reference operating conditions.
Stress levels for the ageing subcycles shall be selected so that the mechanisms of ageing are not significantly different from those operating at the most severe stress levels in normal service. Increasing the stress level to accelerate ageing, may be permissible when It does not significantly change the ageing mechanism.
NOTE knowing the ageing mechanism is fundamental to establish weech stresses are predominant and to refer to them to design a lunctional test and choose the applopriafe models
Multifactor ageing tests are preferred as they best simulate normal service. When this procedure is not adopted, then either a sequential subcycle or a programme of single stress subcycles should be used.
Following each ageing subcycle, a conditioning subcycle and a diagnostic subcycle shall be performed where necessary. Failure of any part of the lest specimen during a diagnostic test constitutes failure at the whole system and shall be reported as such. Electric stress shall be used as the main diagnostic factor in assessing the condition of the aged test objects. On low- voltage equipment it is often necessary to include a pre—diagnostic procedure to ensure that the electric stress, used as the diagnostic factor, helps to detect weaknesses developed during the ageing cycle.