Power system

KTH has a high-voltage (6 kV) ring network around the campus. In the building with the PDC computers, we have two transformers that convert the high-voltage into normal 230 V.

To keep the computers running during shorter power outages, we have several large battery banks which are connected to Uninterruptable Power Supplies (UPSes). Each UPS controls the charging of its batteries and converts AC power to DC and vice versa. UPSes generally lose some energy in the process of doing these conversions during normal operation. Therefore we use the energy saving mode on the UPSes so that, if the usual power supply fails, the UPSes take over the load in 2 milliseconds thereby avoiding the conversions that usually happen during normal operation. The power in the batteries lasts 45-50 minutes which is more than enough to keep our systems running through most outages in Stockholm.

For the most sensitive equipment (like the disk servers) we also have diesel generators that can run forever (as long as they keep being refuelled). We normally have enough fuel stored to last for several days.

The graph shows that the PDC building needs much more power than other KTH buildings.