CERN, the world’s largest particle physics laboratory, chose ABB FACTS technology to power its Super Proton Synchrotron (SPS) accelerator.
It’s a tough challenge, supplying electrical power for the accelerators used in particle physics research. These are the research systems used to concentrate energy and make particles collide, in order to explore the origins of the universe.
It’s the nature of the electrical load that creates the challenge. An accelerator uses 12- and 6-pulse thyristor power converters to power the magnets that control particle beams. The resulting power load can swing from zero to 230MW and 200MVAr within two seconds. Not only does the load pulse in this way, calling for rapid reactive power control to stabilise the voltage, but strong filtering is also needed, to reduce the harmonics to a very low level. CERN, the European Organisation for Nuclear Research, is the world’s largest particle physics laboratory. It provides the tools (accelerators and detectors) for physicists to explore what matter is made of, and what forces hold it together. There are several accelerators on CERN’s site on the Franco Swiss border, using static var compensators (SVC) to meet the demanding power supply needs. ABB has a long history of installing SVC systems at CERN since 1974. For the latest Super Proton Synchrotron (SPS) accelerator, after a European tender process, CERN awarded ABB the contract to design, install and commission the SVC.
The SPS accelerator measures 7km in circumference, and will serve as an injector of protons and heavy ions for CERN’s new Large Hadron Collider (LHC).
THE SOLUTION
The ABB static var compensator for the accelerator incorporates a 150MVAr thyristor-controlled reactor (TCR), with eight harmonic filters. Total power rating is 130MVAr. The system was installed in 2002. The load is divided into two independent groups, and the power is supplied directly from the 400kV European grid via two 90MVA transformers with another on standby. The compensation for the first load group is handled by an existing 120MVAr 18kV SVC, using saturated reactor technology. To meet increased power requirements and due to reliability issues, a new 150MVAr 18kV SVC was installed for the second load group. A third SVC, technically identical to the first, acts as a standby system.
TUNING OUT HARMONICS
The SVC consists of a TCR rated at 150MVAr and eight harmonic filters tuned to 100, 150, 250, 350, 550, 650 Hz and two damped high-pass filters. The filters generate a total reactive power of 130MVAr. Due to the increase in capacitive power of the new SVC, compared to the existing compensators, the natural resonance point is at a lower frequency and close to the second harmonic. This aspect required particular attention when designing the second harmonic filter in order to achieve the best compromise between a moderate filter impedance and sufficient damping. The dynamics of the SVC control, including measurement filters, was designed to take into account this low frequency resonance.
The SVC normally operates with all harmonic filters connected. To reduce SVC losses during periods of moderate network loading, the HF filter is split into two portions HF1 and HF2, allowing the disconnection of 18.2MVAr of the filter HF2.
OUTDOOR INSTALLATION
The installation is located in Prévessin in France, close to CERN’s major 400kV station. The SVC is an outdoor installation covering about 2500 square metres, with a prefabricated building for high voltage thyristor valves, cooling system and SVC control system. The SVC layout aims to minimise the time required for component maintenance and replacement. Filter reactors and filter capacitors of individual phases are arranged horizontally and not on top of each other. To reduce the likelihood of faults caused by wildlife and snow, large distances separate live parts from earth, and the general insulation level was increased to 36kV.
CERN, the European Organisation for Nuclear Research, is an international organisation with 20 Member States. Founded in 1954, the laboratory was one of Europe’s first joint ventures. A joint CERN-ABB technical paper on the new SVC installation is available on www.abb.com