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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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. Ageing data of materials with different thicknesses are not always comparable. A complicating factor is that the properties of a material subjected to thermal ageing may not all deteriorate at the same rate, and different end-points may be relevant for different applications.
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If the end-point is reached for more than one specimen during the first period, discard the group and test a further group, paying particular attention to any critical points of experimental procedure. The row in table 1 corresponding to the estimated TI shows suggested ageing times in days at oven temperatures which appear at the head of the respective columns.
These further jec may be at lower or intermediate temperatures but should not generally be at higher temperatures than originally selected. Values of the abscissa are proportional to the reciprocal of the thermodynamic absolute temperature. Instructions for calculating thermal endurance characteristics using simplified ice Guide for the statistical analysis of ageing test data Part 1: 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.
Evaluate the results, as listed in 6. The thermal endurance of an electrical insulating material is always given for a specific property and end-point.
Simultaneously with the development of the IEC series, other standards were being developed in ISO, intended to satisfy a similar requirement for plastics and rubber materials. Where the derivation is graphical or the statistical conditions are not satisfied the format is as follows: Revisions Our British Standards and other publications are updated by amendment or revision.
It may arise from inadequate experimental technique for example, oven temperature errors ; such non-linearity may be corrected by further testing.
Instructions for an adequate number of specimens are given in IEC Related publications IEC The general calculation procedures outlined here and detailed in IEC are based on the principles set out in IEC We oec improve the quality of our products and services to benefit your business. In the official version, for Bibliography, the following notes have to be added for the standards indicated: If the results show that this time to end-point is likely to be reached in about 10 periods of exposure, there is no need to alter the period of exposure originally selected.
In the case of proof tests with incomplete data usually censored at the medianit may be possible to obtain a sufficient increase in data group size by continuing iex exposure until further test specimens have failed the proof test. Where the test criterion for non-destructive or proof tests is based upon the initial value of the property, this should be determined from a group of specimens of at least twice the number of specimens in each temperature group.
If the results do not show this, the period may be changed so that the median result may be expected in at least seven cycles preferably about 10 provided this change in cycle time is made before the fourth cycle. Determination of thermal endurance properties of electrical insulating materials — Choice of test criteria IEC A simplified calculation procedure is described in IEC If, for example, 6026-2 C has reached end-point nine cyclesGroups G, H and I would have received respectively six, seven and eight cycles at testing.
Ageing procedures and evaluation of test results 1 Scope This part of IEC specifies the general ageing conditions and procedures to be used for deriving thermal endurance characteristics and gives guidance in using the detailed instructions and guidelines in the other parts of the standard. Instructions for calculating thermal endurance characteristics using simplified procedures. These are ISO and ISO respectively, which use less rigorous statistical procedures and more restricted experimental techniques.
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The following test report forms are related: NOTE 2 Attention should be given to the recommendation in 5. NOTE 1 This table is intended primarily for cyclic proof testing and non-destructive tests, but may also be used as a guide for selection of suitable time intervals for destructive tests.
If necessary, determine the initial value of the property as specified in 5. If such information is not available, preliminary screening tests may be performed to produce a forecast of the value of TI. A simplified procedure is available in IEC The analysis of TI data is based on the assumption that there is a linear relation between the logarithm of the time to end-point and the reciprocal of the thermodynamic ageing temperature. To achieve this, select the cycle length so that the mean or median time to end-point is reached in about 10 cycles but not less than seven.
If these expedients are not successful, it will be necessary to test at a temperature low enough for extrapolation not to be required. Methods based on mean values of normally distributed test results 3 3. 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 A procedure which has frequently been found very useful involves the delayed introduction of test groups following the sequence in the Table B.
Test the specimens and plot the results and the arithmetic mean of the results or a suitable transform thereof against the logarithm of exposure time as given in IEC If the data dispersion is not high through inadequate experimental technique, the effect of the high dispersion can be overcome by the use of a larger number of data values, i. The parameters are referred to as the regression coefficients. For destructive tests, see 5. For some materials, it is not possible to achieve a time to end-point of less than h while retaining satisfactory linearity.
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In cases of shorter specification times, the related times may be decreased in the same ratio if necessary. It is strongly recommended that the full evaluation procedure, as described below and in 5.
The large statistical scatter of test data which was found, together with the frequent occurrence of substantial deviations from the ideal behavior, demonstrated the need for tests to assess the validity of the basic physico-chemical model.
Consequently, a material may be assigned more than one temperature index or halving interval derived, for example, from the measurement of different properties. For the valid application of the standard, no transition, in particular no first-order transition should occur in the temperature range under study.
Early results of the ageing test may motivate an adjustment of ageing cycles or additional ageing temperatures.
Physico-chemical models postulated for the ageing processes led to the almost universal assumption of the Arrhenius equations to describe the rate of ageing. Buying standards You can buy and download PDF versions of BSI publications, including British and adopted European and international standards, through our website at bsigroup.