Copyrighted material licensed to BR Demo by Thomson Reuters ( TS 60034-18-33 @IEC:2010(E) -11- Where it is required to apply a power-frequency voltage between the turns,the coil is to be woundpreferablywithtwoparallelconductors(bifilar)orthecoilhastobecutinthe 4.2 Numberof test specimens An adequate number of test specimens shall be aged at each of the combinations of ageing temperatures and voltages that are being used in orderto obtain statistical confidence.This number shall not be less than five.The details given in IEC 62539 shall be observed. NOTE If bars or half-coils are used, the minimum number is five bars or half-coils. If full coils are used, the minimum number is five full coils. (Scientific), I 4.3 Initial qualitycontrol tests Each insulating material intended for the preparation of test specimens shall be tested to Inc., determine that it meets specifications. The quality tests chosen shall ensure that each subscr ageing, but the choice of which tests to perform will be left to the discretion of the tions.techstreet.com, manufacturer. 4.4 Initial diagnostic tests Each completed test object shall be subjected to all the conditioning and diagnostic tests Ageing sub-cycle 5.1 Ageing stress levels In the selection of the electrical and thermal stress levels for the ageing sub-cycles, it is important that the mechanism of ageing during these sub-cycles be not significantly different from that in normal service. 5.2 Accelerationfactors The test stresses shall be related to the following reference ageing factor levels: a) Un - the maximum rated voltage of the insulation system; b) Tc -the thermal class temperature as defined in IEC 60085. Table 1gives guidelines for the selection of stress levels. Table1-Guidelines for the selection of stress levels Test Electrical Thermal level stress stress 1,7 UN 1 Tc - 10 K 2 1,9 UN Tc 3 2,1 Un Tc + 10 K 4 2,3 Un Tc + 20 K 2,5 UN 5 Tc + 30 K Uncontrolled when p The test levels for converter fed machines depend upon how the rated voltage has been defined.It may be appropriate to increase the test levels by a factor to allow for the maximum overshoot which is likely to arise on the voltage at the machine terminals, as described in print material -12- TS60034-18-33IEC:2010(E) IEc 60034-18-42. This may be as high as 1,7 for a 3 level converter but lower if there are more levels. In the selection of the ageing temperatures in this table, it has been assumed that the thermal ageing mechanism is the same within the entire test temperature range and that it follows Arrhenius's law with reasonable accuracy. As with single-factor thermal ageing tests, there is by the possibilitythat radical changes inthe ageing mechanism will occur at thehighest ageing temperatures due, for example, to the proximity of the glass transition temperature or a large and they shall be reported. It is not essential to combine the electrical and thermal stresses in the way shown in Table 1 if a known or expected interaction between electrical and thermal ageing makes them Sc inappropriate.For example,it may be considered more appropriate to combine electrical stresses 2,3 and 4 with thermal stresses 3,4 and 5 respectively. The important principle is to choose test conditions that produce failures within the required timescale. nc 5.3 Durationand numberofageingsub-cycles Eachstresscombinationshallbechosensothatthemeantimetofailureisnotlessthan 20 days.The lowest stress combination shall produce a mean time to failure greater than 250 days. The duration of each sub-cycle shall be selected so that about 1o sub-cycles will pass beforethemeanfailureinthegroupofspecimens.Consequently,thisdurationshallnotbe period for each ageing cycle. 5.4 Full multifactortesting procedure The ageing factors are applied simultaneously and at least three ageing conditions shall be other combinations of test levels are chosen, they shall be justified. For example, comparison may be preferred with previous combined thermal and electrical te