Applying process immunity time to assess annual industrial process trips

The effect of voltage sag to customer´s process has been studied by different authors. They propose methods in order to assess annual indices related to process trip due to sags and long duration interruptions (LDI). However, these methods don´t consider the process immunity time (PIT) during the estimation of these indices. This paper introduces a procedure where PIT is included in order to increase the accuracy of annual indices. The procedure is applied to a representative distribution network. The results show that (i) the difference, between the values obtained considering PIT or not, is approx. on average 50% and (ii) only 6% the total of event between sag and LDI affects the customer´s process.