Simulations of ride-through possibilities for a line operated synchronous machine

Voltage sags and interruptions are a big power quality problem for the industry. Protection equipment automatically breaks the circuit when the power quality is degraded too much. In many cases short voltage sags or interruptions that last for only a hundred milliseconds lead to stoppage for hours in the production. This is mainly due to long start-up times of the industrial process. Simulations have been done on a blast furnace blower in the steel plant SSAB Oxelosund in Sweden. A line operated synchronous machine powers this. The results show that it is possible to reconnect to the mains if the voltage interruption is no longer than 150 ms long. If the remaining voltage is higher than 55% there is no need to break at all. These results show that changing the settings in the protection equipment may reduce the number of unwanted shutdowns.