Temperature rises of windings are determined by the resistance method
standard give us a formula as below:
the key requirement in note: The resistance of windings at the end of the test can be determined by taking resistance measurements as soon as possible after switching off and then at short intervals so that a curve of resistance against time can be plotted for ascertaining the resistance at the instant of switching off.
To make the calculation easier, I made a program file for the calculation using an excel sheet plus VBA. The form can automatically draw a fitted curve according to the input resistance value and the corresponding time point (time interval), the default equation of the fitted curve is a quadratic equation, double-click on the curve to replace the fitted equation. The interface of the form is shown below:
The table header and the cells with the yellow background are the cells whose contents can be changed. After entering the resistance value, the program automatically calculates and fills in the time value according to the previously given time interval value. There are also a lot of menu cells in the table, which makes it easier to fill in and print.