Ride-through investigations for a hot rolling mill process

Voltage sags can be a huge problem for many industries. Voltage sags lasting for hundred milliseconds can shutdown an industry for several hours, due to long start-up times. This will imply large costs for the company due to the subsequent loss in the production. Metal processes, especially the hot rolling mill, have been studied at the steel mill SSAB Oxelosund in Sweden. Calculations of time constants have been done for the process and these are compared to the duration times of measured voltage sags at the same industry. In the worst case, voltage sag duration time of 10 ms may shutdown the rolling mill process. Suggestions of methods to reduce the problem of the process in connection with voltage sags are presented.