IEC 60172-2020 Test procedure for the determination of the temperature index of enamelled and tape wrapped winding wires.
4 Summary of procedure A set of specimens in accordance with Clause 5 is subjected to a testing cycle. This cycle consists of a heat-exposure period at a temperature given in Clause 6, followed by a proof voltage test at room temperature in accordance with Clause 7. This cycle is repeated until a sufficient number of specimens has failed. The time to failure is calculated in accordance with Clause 8. The test is carried out at three or more temperatures. A regression line is calculated in accordance with 8.4 and the time to failure values plotted on thermal endurance graph paper as a function of the exposure temperature. The temperature in degrees Celsius, corresponding to the point of intersection of the regression line with the ordinate of 20 000 h endurance represents the temperature index of the winding wire under test.
5 Test specimens
5.1.1 Enamelled non-tape wrapped round wire This procedure applies to enamelled round wires that are not tape wrapped. The thermal index can be determined by evaluating enamelled non-tape wrapped round wire with a nominal conductor diameter of 0,224 mm up to and including 2,65 mm. NOTE For round enamelled winding wires, experience has shown that nominal conductor diameters of 0,800 mm up to and including 1 ,60 mm are generally found convenient to handle and test. Wires with a nominal conductor diameter between 0,280 mm and 0,500 mm are permitted for use when the specification range of diameters is limited to 0,500 mm and finer. The grade of insulation used for determining the thermal index shall be grade 2 or grade 2B for self-bonding winding wires. Specimens shall be prepared as follows:
a) A wire specimen approximately 400 mm in length shall be twisted together over a distance of 1 25 mm with a device as shown in Figure 1 . The force (weight) applied to the wire pair while being twisted and the number of twists are specified in Table 1 .IEC 60172 pdf download.