A technique for determining the parameters of a test loop for automated tests of electric apparatuses

Resumo

According to the standards of the International Electrotechnical Commission (IEC) and Russian national standards, test loop parameters (time constant or power factor) for testing electrical apparatuses in the three-phase short-circuit (SC) mode are determined by the graphic-analytical technique. This technique is not suitable for automated tests. In addition, the precision of measuring the loop parameters is largely determined by the instant of SC occurrence. The procedures proposed in this article to determine the test loop parameters do not possess the flaws typical of the graphic-analytical technique. These drawbacks restrict one to the algorithm of SC current analysis in the initial period, or the so-called “S function” (the curve of the sum of the squared instant values of three-phase system currents), or the curve of the total instant power in the test circuit. A common feature of the indicated functions is autonomous behavior in the transient mode, as well as the instant of SC occurrence and informativity for determining the loop parameters. The proposed procedures make it possible to find, by mathematical processing of discrete current values, the power factor and the current value of the symmetrical test current component only 16 ms after the beginning of the transient process. The new procedures can be easily used in automated tests and will make possible more precise calculations of the test loop parameters.