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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Out of this arose the concept of the temperature index TI as a single-point characteristic based upon accelerated ageing data.
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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.
Establish the exposure temperatures and times in accordance with the instructions of 5. The parameters are referred to as the regression coefficients. A number of recommendations and suggestions, useful in establishing times and temperatures, will be found in Annex B. You can keep in touch with standards developments and receive substantial discounts on the purchase price of standards, both in single copy and subscription format, by becoming a BSI Subscribing Member.
Consequently, a material may be assigned more than one thermal endurance characteristic derived from the measurement of properties at different thicknesses.
Instructions for calculating thermal endurance characteristics using simplified procedures. In the same way, calculate the temperature?
Since processing conditions may significantly affect the ageing characteristics of some materials, it shall be ensured that, for example, sampling, cutting sheet from the supply roll, cutting of anisotropic material in a given direction, molding, curing, pre-conditioning, are performed in the same manner for all specimens. 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.
After each removal, allow the group of specimens to cool to room temperature unless otherwise specified. It was subsequently found that the statistical confidence index included in the TEP was not widely understood or used. For undated references, the latest edition of the referenced document including any amendments applies. 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. Either a new group, possibly with a shorter cycle time, should be started, or the first cycle failure ignored and the nominal size of the group reduced by one for example, a temperature group of 21 would be treated in the mathematical process as 20; see 6.
It constitutes an editorial revision where the simplified method has been removed and now forms Part 8 of the IEC series: If such material specifications are not available, a selection of properties and methods for the evaluation of thermal endurance is given in IEC Apply the appropriate test to each specimen and then return the group to the oven from which they came, at the same temperature as before, and expose for a further cycle. Revisions Our British Standards and other publications are updated by amendment or revision.
Plot these time-temperature pairs on the thermal endurance graph and draw a smooth curve passing through these points. The reference level may for example, be a mean value one parameter or a line two parameters, slope and intercept. If this is disregarded, any reference to thermal endurance properties ceases to be meaningful since the properties of a material subjected to thermal ageing may not all deteriorate at the same rate.
The thickness of specimens is in some cases specified in the list of property measurements for the determination of thermal endurance. This will have the effect of decreasing the extrapolation, which is one of the influences in determining the size of the confidence interval, and also make the errors associated with the non-linearity less serious. The validity of the model is, therefore, not dependent on the more stringent condition of a linear relationship between the level of the diagnostic property and the degree of molecular change.
It is good practice to prepare additional specimens, or at least to provide a reserve of the original material batch from which such specimens may subsequently be prepared.
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 In addition to the above-mentioned basic assumption, some general assumptions regarding the chemical mechanisms of the thermal ageing need to be satisfied: Prepare a number of specimens following the instructions in 5.
Instructions for calculating thermal endurance characteristics using simplified procedures.
The regression analysis for slope and intercept of the thermal endurance graph and the tests for deviations from linearity shall be as in 6. In such cases, it may be possible to obtain an acceptable result by further testing at a lower temperature.
IEC () (R) | Standards Council of Canada – Conseil canadien des normes
The end-point should be selected to indicate a degree of deterioration of the insulating material which has reduced its ability to withstand a stress encountered in actual service in an insulation system.
At the same time, the calculation procedures were made more comprehensive, enabling full statistical testing of data 602216-2 using a diagnostic property of any type, including the particular case of partially incomplete data.
These further tests may be at lower or intermediate temperatures but should not generally be at higher temperatures than originally selected.