Powering CERN and the LHC

CERN's electricity network is denser than that of the Canton of Geneva, is powered by two different national grids and has to provide users with an availability rate as close to 100% as possible. To ensure the smooth running of the machines throughout the period of LHC physics operation, the teams from the EN Department are implementing a continuous programme of consolidation and modernisation on all the Laboratory's sites, but the biggest projects will have to wait until the long technical shutdown scheduled for 2013.


An electrical installation at CERN.

CERN's annual electricity consumption is around one terawatt hour (TWh), which roughly corresponds to a fifth of the consumption of the Canton of Geneva. However, during periods when all the machines are operating at the same time, our demand can reach the equivalent of a third of Geneva's total consumption. While the grid of the Geneva public utility company SIG (Services Industriels de Genève) covers distances of around 50 km, the CERN network is concentrated into a much smaller area. "Our network is very dense and complex," says François Duval, head of the EN/EL group, which is responsible for CERN's electrical installations. "What's more, it has evolved to meet CERN's growing energy needs over the years without any real overall plan. With 1,000 high-voltage circuit-breakers (about twice the number of the SIG network), it's not necessarily the optimum set-up you'd design and build today."

A complex network, high-power installations and thousands of users requiring a high level of availability all combine to present a significant challenge for the 75 members of the EN/EL group, who are continually busy planning and performing maintenance, consolidation and modernisation work. "We take advantage of every technical stop to replace the UPS batteries which kick in when the main power supply fails and provide emergency power for at least a few minutes," explains Duval. "Over a long period, by the end of 2011, we will have replaced all the distribution cables between the different points of the SPS."

New cables can be buried without disturbing the operation of the machines but other work will have to wait until the long technical shutdown scheduled for 2013. "We are preparing for 2013 with plans for the renovation of several interconnecting substations, including a complete overhaul of the main one on the Meyrin site, which dates back to 1965," explains Duval. "In addition, the relocation of electronic equipment to prevent radiation damage will involve significant recabling work in several sectors of the LHC." 

Modernisation of the electrical installations is needed to ensure the continued high performance of the whole network but also to improve the way the Laboratory manages energy and make it more ecological. "Various projects are currently under study at CERN, such as recovering the energy released into the air by the accelerators' cooling towers. For our part, we only install transformers with high-tech materials nowadays, in order to keep energy losses to the minimum," concludes Duval.

For those who still remember the incident of the bird that was thought to have caused a major power cut by dropping a piece of bread on a sub-station, François Duval wishes to set the record straight: "The episode with the bird and other incidents of that kind have very little effect on the network and never compromise CERN's power supply." End of story!

CERN’s electricity network

CERN is supplied by RTE, the French electricity company, via a dedicated 400 000 volt line. If needed, CERN can request SIG to provide an emergency supply of 60 MW, which is enough to run the Laboratory without its machines.

The LHC's electricity consumption represents approximately 45% of CERN's total consumption, and the experiments account for a further 15%. The rest is used to power the smaller accelerators and experiments and the various buildings.

More detailed figures are given below:

CERN's total annual electricity consumption is 1TWh -1,000,000 MWh or 1,000,000,000 kWh:
  • 40 to 45% is for the LHC (including 12 to 14% for cryogenics and 7 to 9% for cooling and ventilation)
  • 10 to 12% is for the LHC experiments (ATLAS, CMS, ALICE and LHCb)
  • 28 to 32% is for the SPS (including 6 to 7% for the North Area experiments)
  • 2 to 3% is for the PS + Booster + Linac
  • 5 to 6% is for the Computer Centre (B513)
  • 7 to 9% is for offices and restaurants, etc.

by CERN Bulletin