IEC · IEC · IEC · IEC · IEC · IEC ; Show all». IEC Standard | Guide for the determination of thermal endurance properties of ekectrical insulating materials – Part 2: List of. IEC , Electrical insulating materials – Thermal endurance properties – Part 2: Determination of thermal endurance properties of electrical.
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Continue the cycles of temperature exposure, cooling and application of the test until the average measured value for the specimens in the group has reached the end-point specified and provided at least one point beyond the end-point.
However, the statistical tests were considered essential, particularly after minor modifications to make them 6216-2 better to practical circumstances: These values are intended solely as illustration and may be changed as the work requires. NOTE The term Arrhenius is widely used and understood to indicate a linear relationship between the logarithm of a time and the reciprocal of the thermodynamic absolute or Kelvin temperature.
When the criterion is an absolute property level, n d is usually given the value of zero, unless reporting of the initial value is required.
However, for some materials very sensitive to the humidity in the ovens, more reliable results are obtained when the absolute humidity in the ageing oven room is controlled and equal to the absolute humidity corresponding to standard atmosphere B according to IEC This procedure is based on the assumption that the ageing rate of all specimens aged at one temperature is the same and can 60216–2 be determined from the ageing rate of the property means of the successive groups tested.
In the case of destructive tests 6.
The circulation of the air within the oven and the exchange of the air content should be adequate to ensure that the rate of thermal degradation is not influenced by accumulation of decomposition products or oxygen depletion see 5. This model is valid when the selected end-point of the diagnostic property is correlated with a particular degree of molecular change in the material which is subject to ageing.
This standard is concerned only with type 2.
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A simplified procedure, requiring a limited subset 6026-2 the following tests is reported in IEC Consequently, a material may be assigned more than one temperature index, derived, for example, from the measurement of different properties and the use of different end-point times.
The first assumption is tested by the so-called Fisher test F -test. Where the derivation is graphical or the statistical conditions are not satisfied the format is as follows: In all cases, ageing shall be continued until more than one-half of the test specimens in each group have failed to pass the proof test.
A list of organizations represented on this committee can be obtained on request to its secretary. For dated references, only the edition cited applies. Since processing conditions may significantly affect the ageing characteristics of some materials, it shall be ensured that, for example, sampling, cutting sheet from ifc supply roll, cutting of anisotropic material in a given direction, molding, curing, pre-conditioning, are performed in 602162 same manner for all specimens.
After a few cycles, the remaining specimens can be placed in the oven and the points on the ageing curve property variation curve see Figures 2, 3 and 4which are deemed necessary, determined. Establish the exposure temperatures and times in accordance with the instructions of 5. The time interval between tests of groups should be planned so that the results of at least two groups of specimens are available before the mean time to end-point, and at least one after: If such material specifications are not available, a selection of properties and methods for the evaluation of thermal endurance is given in IEC A choice of properties is given in IEC For non-destructive tests, although Table 1 suggests constant cycle lengths, test times following a geometric series may be used.
If a time different from 20 h has been used for deriving the TI, the relevant time expressed in kh shall be stated, followed by kh. To reduce the uncertainties in calculating the appropriate thermal endurance characteristic, the overall temperature range of thermal exposure needs to be carefully selected, observing the following requirements if the required thermal endurance characteristics are for a projected duration of 20 The degree of degradation indicated as the end-point of the test should be related to the allowable safe value for the material property which is desired in ice.
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It is advisable to distinguish between: However, environmental conditioning, the influence of atmospheres other than air and immersion in liquids such as oil may be important, but these are not the concern of this standard. Attention is drawn to the possibility that some of the elements of this document iecc be the subject of patent rights. The method of evaluation of TI results is by the numerical procedure detailed in IEC together with a graphical presentation as shown in Figure 1.
Very long specification times may also lead to non-linearity see also Annex A. However, it is important that a smaller range of mean times to end-point will lead to a larger confidence interval of the result for the same data dispersion.
NOTE 2 Attention should be given to the recommendation in 5.