IEC 60172:2015.Test procedure for the determination of the temperature index of enamelled and tape wrapped winding wires.
IEC 60172 specifies, in accordance with the provisions of IEC 60216-1, a method for evaluating the temperature index of enamelled wire, varnished or unvarnished with an impregnating agent, and of tape wrapped round and rectangular wire, in air at atmospheric pressure by periodically monitoring changes in response to AC proof voltage tests. This procedure does not apply to fibre-insulated wire or wire covered with tapes containing inorganic fibres.
A set of specimens in accordance with Clause 5 is subjected to a testing cycle.This cycle consists of a heat-storing 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.
To avoid misleading extrapolations (see 8.4)，the correlation coefficient should be calculated as shown in Annex B,to provide a measure of linearity.
If the correlation coefficient r is equal to or greater than 0,95,the data are said to be linear and the data points will be reasonably close to a straight line.In the event that the correlation coefficient is less than 0,95,the data are said to be non-linear and an additional test should be performed at a temperature below the lowest previous temperature.
The new temperature point may be 10 C below the previous lowest temperature point.When re-calculating the temperature index and correlation coefficient,one temperature point may be deleted,starting with the highest temperature,for each new temperature point obtained.
The data will be linear if the thermal deterioration of the enamelled wire or the varnished enamelled wire appears as one chemical reaction.Non-linearity may indicate that:
a) two or more reactions which have different activation energies (slopes)are predominant at
different temperatures within the testing range;or
b)errors have been introduced through the sampling technique and/or the testing procedure.Non-linear data should not be used for extrapolation.IEC 60172 pdf.