Impact of the Voltage Transients After a Fast Power Abort on the Quench Detection System in the LHC Main Dipole Chain

• Published in: IEEE transactions on applied superconductivity Vol. 22; no. 3; p. 9002504
• Main Authors: Ravaioli, E., Dahlerup-Petersen, K., Formenti, F., Montabonnet, V., Pojer, M., Schmidt, R., Siemko, A., Camillocci, M. S., Steckert, J., Thiesen, H., Verweij, A.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.06.2012; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Accelerators; Applied sciences; Chains; Circuit properties; Circuits; Connection and protection apparatus; Delay; Dipoles; Electric, optical and optoelectronic circuits; Electrical engineering. Electrical power engineering; Electromagnets; Electronic circuits; Electronics; Exact sciences and technology; Large Hadron Collider; LHC; Power converters; Power electronics, power supplies; quench protection; Resistors; Signal convertors; Snubbers; Superconducting magnets; Superconductivity; superconductors; Switches; Transient analysis; Various equipment and components; Voltage transients; CERN LHC; Power converter; quench protection; Arcing fault; LHC; Parallel; Electrical model; Damage prevention; Superconducting materials; Protection system; Accelerators; Dipole; Delay time; Wave generation; Resistor; Electromechanical system; Electric arc; superconductors; Magnet; Heating element; Protective device; Power electronics; Superconducting magnet; Snubber circuit; Dipole circuit; System simulation; Capacitor; Power semiconductor switches; Comparative study
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2012.2183572

A Fast Power Abort in the LHC superconducting main dipole circuit consists in the switch-off of the power converter and the opening of the two energy-extraction switches. Each energy-extraction unit is composed of redundant electro-mechanical breakers, which are opened to force the current through an extraction resistor. When a switch is opened arcing occurs in the switch and a voltage of up to 1 kV builds up across the extraction resistor with a typical ramp rate of about 80 kV/s. The subsequent voltage transient propagates through the chain of 154 dipoles and superposes on the voltage waves caused by the switch-off of the power converter. The resulting effect caused intermittent triggering of the quench protection systems along with heater firings in the magnets when the transient occurred during a ramp of the current. A delay between power converter switch-off and opening of the energy-extraction switches was introduced to prevent this effect. Furthermore, the output filters of the power converters were modified in order to damp faster the voltage waves generated after the power-converter switch-off and to lower their amplitude. Finally, snubber capacitors were added in parallel to the extraction switches to help the commutation process by reducing the arcing effect and thus smoothing the voltage transient. A set of dedicated tests has been performed in order to understand the voltage transients and to assess the impact of the circuit modifications on the quench detection system. The results have been compared to the simulations of an electrical model of the LHC main dipole circuit developed with the Cadence suite (PSpice based).