Power system

Electricity network

The computing and storage systems at PDC use a lot of electricity. The graph below shows that the PDC building needs much more power than other KTH buildings.

These electricity requirements are normally supplied by the KTH Royal Institute of Technology high-voltage (6 kV) ring network, which goes around the main KTH campus in Stockholm. In the building that houses the PDC computers, there are two transformers that convert the high voltage into normal 230 V to supply the computers and other equipment at PDC.

Electricity backups

Batteries and UPSes

To keep the computers running during shorter power outages, PDC has several large battery banks which are connected to Uninterruptable Power Supplies (UPSes). (Photos of the UPSes and batteries can be found on the media resources infrastructure page .) 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 PDC uses 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 the PDC systems running through most electricity outages in Stockholm.

The UPSes each have what is know as a power distribution, which includes input breakers for the UPS and output breakers for each computer that has a power feed connected to that particular UPS. (There is a photo of a power distribution on the media resources infrastructure page .) The power distributions have breakers that can turn off the power if a current that is too high passes the breaker (so they acct like a fuse). The power distribution can also be used to bypass the UPS if the UPS needs maintenance, while still keeping the computers operating all the time.

Generators

For the most sensitive equipment (like the disk servers) PDC also has diesel generators that can run forever (as long as they keep being refuelled). PDC normally has enough fuel stored to last for several days. (There is a photo of the generators in the media resources infrastructure images .)